CN117337406A

CN117337406A - Multispectral four-mirror based imaging system with small form factor

Info

Publication number: CN117337406A
Application number: CN202280027698.9A
Authority: CN
Inventors: 崔荣完
Original assignee: Cso Ltd
Current assignee: Cso Ltd
Priority date: 2021-02-10
Filing date: 2022-02-03
Publication date: 2024-01-02
Also published as: KR20230136669A; WO2022173642A1; EP4291936A1; IL304975A

Abstract

A total reflection optical system or a reflection and refraction optical system is described, comprising: a concave primary mirror having a central aperture and a radius, having one of a parabolic, non-parabolic conical, and aspherical surface; a convex secondary mirror facing the primary mirror, having an aspherical surface, wherein an optical axis extends from an apex of the primary mirror to an apex of the secondary mirror; a concave tertiary mirror disposed behind the primary mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a concave quaternary mirror disposed in the central aperture of the primary mirror or behind the primary mirror having one of a spherical surface, a parabolic surface, a non-parabolic surface conical shape, and a non-spherical surface; and/or at least one image plane having one or more aggregated sensors. Additional multispectral imaging may utilize one or more beam splitters, one or more fold mirrors, one or more focal length optimizers, and/or additional image planes.

Description

Multispectral four-mirror based imaging system with small form factor

Cross Reference to Related Applications

This application is a continuation of U.S. patent application Ser. No. 16/989635, filed 8/10/2020, which claims priority from U.S. provisional application Ser. No. 62885296, filed 8/11/2019, the entire contents of each of which are incorporated herein by reference in their entirety and form a part of this specification.

Technical Field

The present disclosure relates generally to optical imaging systems, and more particularly to four mirror-based optical imaging systems for small form factors in satellites or aircraft.

Background

Optical imaging systems are useful in many applications, such as imaging planets or stars. Known optical system designs for satellite imaging include conventional three mirror non-aberration lens (TMA) designs and Korsch designs. Existing optical imaging solutions suffer from drawbacks in terms of size and corresponding resolution capabilities. Thus, there is a need for improved optical imaging.

Disclosure of Invention

In one aspect, a total reflection optical system is disclosed. The total reflection optical system includes a concave main mirror having a central aperture and a radius, the main mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a convex secondary mirror facing the primary mirror, the secondary mirror having an aspheric surface, wherein the optical axis extends from an apex of the primary mirror to an apex of the secondary mirror; a concave tertiary mirror disposed behind the primary mirror, the tertiary mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a concave quaternary mirror disposed in or behind the central aperture of the primary mirror, the quaternary mirror having one of a spherical, parabolic, non-parabolic conical, and non-spherical surface; and at least one image plane having one or more aggregated sensors. The image plane is positioned at a distance from the optical axis that is no greater than the radius of the primary mirror.

In some embodiments, the optical system may additionally include: an entrance pupil positioned near the primary or secondary mirror; and an exit pupil or Lyot stop positioned at one of 1) near the tertiary mirror, 2) between the tertiary mirror and the quaternary mirror, and 3) between the quaternary mirror and the image plane.

In some embodiments, the optical system may additionally include one or more folding mirrors arranged to deflect light rays from the quaternary mirror to the image plane, wherein the one or more folding mirrors may be configured to fold the light ray path. The exit pupil may be positioned between the tertiary and quaternary mirrors, or between the quaternary and first fold mirrors, based on the use of the first fold mirror. One of the fold mirrors may be tilted at a particular angle with respect to the optical axis of the system. One of the fold mirrors located in front of the image plane may widen the field of view with reflective and transmissive portions in the same spectral range, where each portion may correspond to a particular sensor of the one or more sensors. One of the fold mirrors located in front of the image plane may enable simultaneous polychromatic imaging, wherein one of the fold mirrors may reflect over a first spectral range and transmit over other spectral ranges and may reflect over a second spectral range and transmit over other spectral ranges, wherein one of the aggregated sensors may be dedicated to the first spectral range and a different one of the aggregated sensors may be dedicated to the second spectral range.

In some embodiments, a shape factor defined as the ratio of the distance between the secondary mirror and the tertiary mirror to the effective focal length of the optical system may be less than 0.09. The apexes of the primary and secondary mirrors may form an optical axis, which may be a geometric reference line extending from the apex of the primary mirror to the apex of the secondary mirror. The primary and secondary mirrors may be symmetrical about the optical axis or periodic. The diagonal of the periodic mirror may be at an angle of 0 degrees or 45 degrees to the diagonal of the image plane. The optical axis of the tertiary mirror may not coincide with the mechanical axis.

In some embodiments, the radius of the secondary mirror may be in the range of 1% to 3% of the effective focal length, while the radius of the tertiary mirror may be in the range of 2% to 3% of the effective focal length. The radius of the quaternary mirror may be in the range of 6% to 22% of the effective focal length.

In some embodiments, fold mirrors may enable simultaneous polychromatic imaging, wherein each fold mirror may reflect over a particular spectral range and transmit over other spectral ranges, and wherein a corresponding one of each added fold mirror and aggregated sensor may be associated with a different spectral range.

In some embodiments, the distance along the optical axis from the tertiary mirror to the image plane may be in the range of 3% to 9% of the effective focal length, and the distance along the optical axis from the secondary mirror to the tertiary mirror may be in the range of 4% to 9% of the effective focal length. At a height of 500 km, the imaging resolution of the system may be better than 1m.

In some embodiments, the system may be adapted to support simultaneous polychromatic imaging, comprising: 1) Panchromatic and RGB and near infrared; 2) Visible and infrared (near infrared, short wave infrared, medium wave infrared or long wave infrared); 3) Visible light and visible light; 4) Infrared and infrared; 5) UV and visible light; and 6) UV and IR imaging.

In some embodiments, the diameter of the primary mirror may be in the range of 3% to 8% of the effective focal length. The focal distance from the primary mirror may be in the range of 1% to 6% of the effective focal length. The effective focal length may be in the range of 300 mm to 20000 mm. The optical system may further comprise a support structure for one or more mirrors. The support structure may be additively manufactured.

In some implementations, the image plane may include a Charge Coupled Device (CCD) -in-CMOS Time Delay Integration (TDI) sensor. The CCD-in-CMOS TDI sensor may be a multispectral TDI, backside illuminated imager. The CCD-in-CMOS TDI sensor may include seven CCD arrays of 4096×256 pixels each. The CCD-in-CMOS TDI sensor may include four full-color CCD arrays of 16384×96 pixels each and eight multispectral CCD arrays of 8192×48 pixels.

In some embodiments, the primary mirror may have a circular or non-circular shape, the tertiary mirror may have a segmented non-circular shape, and the quaternary mirror has a circular or non-circular shape. The non-circular shape of the primary mirror may enhance the Modulation Transfer Function (MTF) and signal-to-noise ratio (SNR).

In some embodiments, the four-stage mirror may face the three-stage mirror and may be positioned to avoid interference of light rays from the second mirror to the three-stage mirror. The optical system may further comprise a support structure for the mirror, the support structure comprising a cylindrical tube or conical baffle of the primary mirror. The four mirrors may be constructed of zero CTE material, low CTE material, or mild CTE material, wherein the four mirrors and the support structure may be made of one material. The system may be adapted to provide imaging in star (driving), scanning or push-broom, video, stereo, BRDF (bi-directional reflectance distribution function), HDR (high dynamic range), polarized and low light modes.

In some embodiments, the system may be adapted to be mounted on an onboard satellite for non-imaging tasks including communication satellites, or on an imaging satellite, quasi-imaging satellite, or scientific task satellite. The system may be adapted to be mounted on an on-board aircraft, unmanned aerial vehicle, and balloon. The back focal length between the four-stage mirror and the at least one image plane may be in the range of 2% to 5% of the effective focal length.

In another aspect, a total reflection optical system is disclosed, comprising: a concave primary mirror having a central aperture and a radius, the primary mirror having one of a parabolic, non-parabolic, conical and aspherical surface; a convex secondary mirror facing the primary mirror, the secondary mirror having a hyperbolic surface with an optical axis extending from an apex of the primary mirror to an apex of the secondary mirror; a concave tertiary mirror disposed behind the primary mirror, the tertiary mirror having one of a parabolic, non-parabolic, conical, and aspherical surface; a concave quaternary mirror disposed in front of the central aperture of the primary mirror, the quaternary mirror having one of a spherical, parabolic, non-parabolic, conical, and non-spherical surface; and at least one image plane having one or more aggregated sensors, wherein the image plane is positioned at a radial distance from the optical axis that is no greater than a radius of the primary mirror.

In another aspect, a total reflection optical system is disclosed, comprising: a concave primary mirror having a central aperture and a radius, the primary mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a convex secondary mirror facing the primary mirror, the secondary mirror having an aspheric surface, wherein the optical axis extends from an apex of the primary mirror to an apex of the secondary mirror; a concave tertiary mirror disposed behind the primary mirror, the tertiary mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a concave quaternary mirror disposed in or behind the central aperture of the primary mirror, the quaternary mirror having one of a spherical surface, a parabolic surface, a non-parabolic surface conical shape, and a non-spherical surface; at least one image plane having one or more aggregated sensors, wherein the image plane is positioned at a radial distance from the optical axis that is no greater than a radius of the primary mirror; a first beam splitter and a second beam splitter configured to split light of a particular spectral range, wherein the first beam splitter and the second beam splitter have a relative tilt angle with respect to each other, and wherein the first beam splitter and the second beam splitter each receive light reflected by the secondary mirror; a first folding mirror that receives light from the first beam splitter and a second folding mirror that receives light from the second beam splitter; a second tertiary mirror receiving light from the first folding mirror and a third tertiary mirror receiving light from the second folding mirror; a second fourth stage mirror that receives light from the second third stage mirror and a third fourth stage mirror that receives light from the third stage mirror; and a second image plane receiving the focused light from the second quaternary mirror and a third image plane receiving the focused light from the third quaternary mirror, each of the second image plane and the third image plane having one or more concentrated sensors converting light into electrical signals.

In some embodiments, the second image plane and the third image plane may each be positioned proximate the primary mirror at a radial distance from the optical axis that is greater than a radius of the primary mirror. The first beam splitter and the second beam splitter may each be positioned between the primary mirror and the secondary mirror. The first beam splitter and the second beam splitter may each have an inclination angle of 65 degrees to 115 degrees with respect to the optical axis.

In some embodiments, the optical system may additionally include an exit pupil or Lyot stop located at one of the following positions: 1) near the second and third fourth stage mirrors, 2) between the second and third stage mirrors and the second and third fourth stage mirrors, and 3) between the second and third fourth stage mirrors and the second and third image planes, and wherein an intermediate focus may be formed near the first and second fold mirrors.

In another aspect, a reflective and catadioptric optical system is disclosed, comprising: a concave primary mirror having a central aperture and a radius, the primary mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a convex secondary mirror facing the primary mirror, the secondary mirror having an aspheric surface, wherein the optical axis extends from an apex of the primary mirror to an apex of the secondary mirror; a concave tertiary mirror disposed behind the primary mirror, the tertiary mirror having one of a parabolic, non-parabolic conical, and aspherical surface; a concave quaternary mirror disposed in or behind the central aperture of the primary mirror, the quaternary mirror having one of a spherical surface, a parabolic surface, a non-parabolic surface conical shape, and a non-spherical surface; a primary folding mirror or beam splitter configured to receive light from the quaternary mirror; a first primary image plane receiving a first portion of the light rays from the primary folding mirror or beam splitter and a second primary image plane receiving a second portion of the light rays from the primary folding mirror or beam splitter, each of the first and second primary image planes having one or more concentrated sensors, wherein each of the first and second primary image planes is positioned at a radial distance from the optical axis that is no greater than a radius of the primary mirror.

In some embodiments, the catadioptric optical system may further comprise a first beam splitter and a second beam splitter configured to split light of a particular spectral range, wherein the first beam splitter and the second beam splitter may have relative tilt angles with respect to each other, and wherein the first beam splitter and the second beam splitter may each receive light reflected by the secondary mirror; a first folding mirror that receives light from the first beam splitter and a second folding mirror that receives light from the second beam splitter; a first group of lenses receiving light from the first folding mirror and a second group of lenses receiving light from the second folding mirror; and a third image plane receiving light from the first set of lenses and a fourth image plane receiving light from the second set of lenses, each of the third and fourth image planes may have one or more concentrated sensors converting light into electrical signals.

In some embodiments, the third image plane and the fourth image plane may each include a commercially available sensor, and wherein the focal lengths of the first set of lenses and the second set of lenses may each be independently adjusted to match the optical resolution of each of the first set of lenses and the second set of lenses to the pixel size of each of the commercially available sensors.

In some embodiments, the first and second sets of lenses may each comprise lenses having spherical or non-spherical surfaces. The first beam splitter and the second beam splitter may each be positioned between the primary mirror and the secondary mirror. The first beam splitter and the second beam splitter may each have an inclination angle of 65 degrees to 115 degrees with respect to the optical axis.

In some embodiments, the reflective and catadioptric optical system may additionally include an exit pupil or Lyot stop, the image plane being located in the first and second sets of lenses and before the third and fourth image planes, and wherein an intermediate focus may be formed near the first and second folding mirrors.

In some embodiments, the lenses of the first and second sets of lenses may be radiation-hardened lenses or radiation-resistant lenses. The fold mirror may perform a scan to cover the field of view of the optical system with fewer sensors than when the fold mirror does not perform a scan.

In some embodiments, the reflective and catadioptric optical system may further comprise an inertial measurement unit connected to the first and second folding mirrors to compensate for unwanted movement of the system by stabilizing a line of sight of the system or an instantaneous field of view of an image sensor positioned at the third and fourth image planes.

In some embodiments, the catadioptric optical system may further comprise: a first beam splitter, a second beam splitter, and a third beam splitter, the first beam splitter, the second beam splitter, and the third beam splitter configured to split light rays of a particular spectral range, and wherein the first beam splitter, the second beam splitter, and the third beam splitter can each receive light rays reflected by the secondary mirror; a first folding mirror that receives light from the first beam splitter, a second folding mirror that receives light from the second beam splitter, and a third folding mirror that receives light from the third beam splitter; a first group of lenses receiving light from the first folding mirror, a second group of lenses receiving light from the second folding mirror, and a third group of lenses receiving light from the third folding mirror; and a third image plane receiving light from the first set of lenses, a fourth image plane receiving light from the second set of lenses, and a fifth image plane receiving light from the third set of lenses, each of the third, fourth, and fifth image planes may have one or more concentrated sensors converting light into electrical signals.

In some embodiments, the catadioptric optical system may further comprise: a first beam splitter configured to split light rays of a particular spectral range, wherein the first beam splitter is receptive of light rays reflected by the secondary mirror; a first folding mirror that receives light from the first beam splitter; a first set of lenses receiving light from the first folding mirror, wherein the first set of lenses may include a second beam splitter or a reflective polarizer; and a third image plane receiving light from the first path in the first set of lenses and a fourth image plane receiving light from the second path in the first set of lenses, the first path and the second path based on a second beam splitter or a reflective polarizer, the third image plane and the fourth image plane each having one or more concentrated sensors converting light into electrical signals.

In some embodiments, the catadioptric optical system may further comprise: a first beam splitter configured to split light rays of a particular spectral range, wherein the first beam splitter is receptive of light rays reflected by the secondary mirror; a first folding mirror that receives light from the first beam splitter; a first set of lenses receiving light from the first folding mirror, wherein the first set of lenses may include a filter wheel or slider including a narrow band spectral filter within a spectral range defined by the first beam splitter; and a third image plane receiving light from the first set of lenses, the third image plane may have one or more concentrated sensors converting light into electrical signals.

In some embodiments, the catadioptric optical system may further comprise: a first beam splitter configured to split light rays of a particular spectral range, wherein the first beam splitter is receptive of light rays reflected by the secondary mirror; a first fold mirror receiving light from a first beam splitter or a first filter wheel or slider disposed between the first beam splitter and the fold mirror; a first set of lenses receiving light from the first folding mirror, wherein the first set of lenses may include a second filter wheel or slider when the first filter wheel or slider may not be utilized, the first filter wheel or slider and the second filter wheel or slider may include zero, 45, 90, and 135 degree polarizers for polarized imaging; and a third image plane receiving light from the first set of lenses, the third image plane may have one or more concentrated sensors converting light into electrical signals.

In some embodiments, the catadioptric optical system may further comprise: eight beam splitters configured to split light of a particular spectral range, and wherein each of the eight beam splitters is operable to receive light reflected by the secondary mirror, respectively; eight fold mirrors that receive light from respective beam splitters; eight sets of lenses that receive light from respective folding mirrors; and eight additional image planes receiving light rays from the respective lens groups, each of the eight additional image planes may have one or more concentrated sensors converting light into electrical signals, wherein each of the eight additional image planes may be positioned proximate the primary mirror at a radial distance from the optical axis that is greater than a radius of the primary mirror.

Drawings

Elements in the drawings are not necessarily drawn to scale to enhance the clarity of the elements and to improve the understanding of the various elements and embodiments described herein. Additionally, to provide a clear view of the various embodiments described herein, elements that are well known and well understood to those skilled in the art are not depicted and, thus, the drawings are summarized in a clear and concise form.

Fig. 1A and 1B are schematic diagrams of embodiments of an optical system that may be used for imaging.

Fig. 1C and 1D are schematic diagrams of another embodiment of an optical system that may be used for imaging.

Fig. 1E and 1F are schematic diagrams showing diagonal lines for the periodic mirror and the image plane, respectively.

Fig. 1G and 1H illustrate example embodiments of an optical system with a periodic primary mirror.

Fig. 2A is a schematic diagram illustrating an embodiment of a payload system for a satellite, which may include various optical systems described herein.

Fig. 2B is a schematic diagram illustrating an embodiment of an image plane circuit that may be used with the various optical systems described herein.

Fig. 3-5 are schematic diagrams illustrating various embodiments of configuration layouts of mirrors and imaging planes that may be used with the various optical systems described herein.

Fig. 6-9 are schematic diagrams illustrating various embodiments of a configuration layout of mirrors, including one or more fold mirrors and an imaging plane, that may be used with the various optical systems described herein.

Fig. 10-13 are schematic diagrams illustrating various embodiments of a configuration layout of mirrors, including one or more fold mirrors and two imaging planes, that may be used with the various optical systems described herein.

Fig. 14A to 14D are various views of an embodiment of an image pickup system including the optical system of fig. 1.

Fig. 15A to 17B are graphs showing various embodiments of performance characteristics of the optical system of fig. 1A.

Fig. 18A to 20B are graphs showing various embodiments of performance characteristics of the optical system of fig. 1C.

Fig. 21A and 21B are graphs showing distortion performance of the optical systems of fig. 1A and 1C, respectively.

FIG. 22 is a schematic diagram illustrating an embodiment of a configuration layout of mirrors that may be used with the various optical systems described herein, including two beam splitters, two folding mirrors, and three imaging planes.

Fig. 23-28A are schematic diagrams illustrating various embodiments of a configuration layout of mirrors and lenses that may be used with the various optical systems described herein, including one or more beam splitters, one or more folding mirrors, and two or more imaging planes.

Fig. 28B is a diagram illustrating a projection of an embodiment of an image plane circuit that may be used with the configuration layout of fig. 28A.

Fig. 29A and 29B are schematic views of another embodiment of an optical system that can be used for imaging.

Detailed Description

In the following discussion relating to various embodiments and applications, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the embodiments described herein may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure.

Various inventive features are described below, each of which may be used independently of the other or in combination with another feature or features. However, any single inventive feature may not address all or only one of the problems discussed above. In addition, one or more of the problems discussed above may not be fully solved by the features of each of the embodiments described below.

Described herein are embodiments of low volume, high resolution optical imaging systems and methods that may be used in satellite and other aviation systems. The optical system 100, as shown in fig. 1A, is one embodiment that may be used to provide high resolution imaging performance in a "micro" or small form factor (volume envelope (volumetric envelope)). The optical system may be "piggyback" on other tasks with existing high bandwidth capabilities.

The satellite constellations in orbit can operate in cooperation with each other to coordinate ground coverage. The orbits of the satellites in the constellation may be synchronized. For example, the orbit may be geostationary, wherein the orbit period of the satellites may be equal to the average rotation period of the earth and the same direction as the rotation of the earth. Alternatively, the orbit may be sun-synchronized, such as a near-polar orbit around the earth, where the satellite passes through any given point on the earth's surface at the same local average sun time, or orbit precession passes through one complete revolution each year, so the satellite always maintains the same relationship with the sun. The synchronization system introduces complexity by requiring dedicated platforms and sensors, reflectors and operator stations. For telemetry, typical examples of such synchronization constellations include the programs of PLANETSCOPE (also known as DOVE), skySat, BLACKSKY, and CARBONITE.

The systems described herein may be used in systems of synchronous and asynchronous tracks. Thus, in some embodiments, the imaging system may be used with an asynchronous constellation of earth-looking camera systems (ACEC, asynchronous Constellation of Earth observation Camera system). This is especially true for constellations of many small satellites such as CUBESAT, and low earth orbit broadband data relay satellite constellations such as the space NGSO satellite system, oneWeb, and amazon KUIPER systems. Any of the optical systems described herein or features thereof may include any of the features of the micro-optical and imaging systems as well as other aspects described in "research on the feasibility of micro-imaging systems for asynchronous, large satellite constellations" (Study on the feasibility of micro camera systems for asynchronous, gigantic satellite constellation, youngwan Choi, proc. Spie 11127,Earth Observing Systems XXIV,111270Z (9September 2019,available at https:// doi. Org/10.1117/12.2529090)), the entire contents of which are incorporated herein by reference.

An asynchronous constellation may include a camera system on any available platform that has planned tasks but may carry additional payloads. An asynchronous constellation may differ from a nominal constellation in that it will not be operated synchronously and not provide coordinated floor coverage for the sole purpose of providing an image stream only. The most important benefits of asynchronous constellations are the cost, time and effort to avoid or minimize the development of platforms, the need for specific reflection systems, and the operation of a dedicated surface control system, which can be a significant fixed cost. An advantage of using LEO broadband data relay satellites for asynchronous constellation imaging is their wide data bandwidth. CUBESAT or other platforms with dedicated imaging or other tasks may suffer from reduced data bandwidth. In the absence of data bandwidth problems, an asynchronous constellation with LEO data relay satellites may stream image data in dedicated channels as a satellite streaming movie or other content so that a user may selectively receive, record, and process the image data.

To do this, a much smaller or miniature camera system is needed that has size advantages and can accommodate any available space. Recent developments in smaller cameras have focused on size advantages, and thus such developments have relied on optical designs that are easier to design, simpler to develop, or cheaper to construct. However, this approach appears reasonable, but may limit or restrict the use of such cameras for critical tasks due to performance degradation such as optical resolution.

Other embodiments of the optical system 100 and imaging system described herein may be used for constellation operation, and are miniature in physical dimensions and advanced in performance. Systems and methods for a small form factor four mirror telescope are described.

The embodiments described herein may be a planned on-board satellite platform, as an auxiliary payload or as an add-on system. In some embodiments, the imaging system may have dimensions on the star sensor or tracker scale. The imaging system may be lightweight. The imaging system may minimize power consumption. The imaging system and its interface with the platform may be simple to install and operate. The imaging system may be capable of proper imaging, which may be described by its specifications. The imaging system may have an appropriate MTF value. The imaging system may be designed to operate over a wide spectral range and be equipped with multiple channels over the spectral range with full color, red, green, blue, and near infrared as baseline sets. The imaging system may be capable of having a large field of view.

An important requirement for such an imaging system is distortion characteristics. A camera system with a small f-number, a small aperture with a longer effective focal length with higher resolution may require a Time Delay Integration (TDI) sensor to achieve an appropriate signal-to-noise ratio (SNR), and for further ground processing. Distortion caused by the optical design can lead to blurring of the imaging system. To avoid significant degradation of the image quality of TDI imaging, system-induced distortion should be minimized over the entire field of view (FOV).

The optical imaging systems described herein are based on a reflective or mirror system, which may be unusual for small, affordable systems. The usual cameras for CAN-or NANO-SAT are based on cata-dioptric design to simplify the design and reduce the cost. Examples include PLANETSCOPE (also known as DOVE), SKYSAT, BLACKSKY, and CARBONITE.

The design of SKYSAT cameras is based on a rayleigh-Cassegrain (Ritchey-Cassegrain) telescope with two mirrors (primary and secondary) and a small number of lenses. It is distinguished by easy manufacturing, low cost and simple alignment/assembly logic. In addition, it also utilizes COTS frame CMOS sensors. The carbolite camera is an example of a commercial off-the-shelf astronomical telescope modified to accommodate the spatial environment and equipped with commercial CMOS sensors for color video imaging. In a sense, the use of commercial telescopes seems to be a sensible measure, reducing development or manufacturing effort, greatly reducing costs, and improving the efficiency of operational management. The entire process has been developed for implementing earth-observing satellite constellations.

Unlike those methods, the optical system embodiments described herein for imaging are based on a reflective design, which is a four mirror system. The optical systems described herein may not have limitations on the spectral range to be covered. The system may be free of chromatic aberration, which may be critical for multispectral imaging. The multi-mirror system may have high design flexibility due to its freedom. The system may be light weighted by mirrors to reduce quality. The system may have a small form factor.

Fig. 1A is a perspective schematic diagram showing an optical layout of the first optical system 100 of the optical route. Fig. 1B is a perspective schematic view of the optical system 100 without showing the light path for clarity. The optical line may indicate a plurality of spectral bands. Referring to fig. 1C, a perspective view showing the optical layout of the second optical system 150 of light rays is shown. For clarity, fig. 1D shows optical system 150 without optical lines.

The first two mirrors of the optical system 100, 150, namely the primary mirror 104 and the secondary mirror 105 in fig. 1A and 1B, and the primary mirror 154 and the secondary mirror 155 in fig. 1C and 1D, are responsible for the magnification of the system so that it can determine its effective focal length or resolution. As used herein, the "effective focal length" has its usual and customary meaning and includes, but is not limited to, the distance from the principal plane of the optical mirror to the imaging plane 118, 168. The entrance pupil 124 of the optical system 100 (shown in fig. 1A and 1B) and the entrance pupil 174 of the optical system 150 (shown in fig. 1C and 1D) control the amount of light passing through the respective systems and may be located at the respective primary mirrors. The entrance pupil may be an optical image of a physical aperture stop, as seen through the front (object side) of the optical system. The corresponding image of the aperture seen through the back side of the optical system is referred to as the exit pupil.

The primary mirrors 104, 154 may be supported by a structural support 102 having radially extending beams 103 to support the mirror structure. The structure 102 and beams 103 may minimize deformations on the primary mirror surface that may be caused by bonding and thermal environmental changes. In addition, it protects the primary mirror from random vibrations and shocks that the camera may experience during transmission.

In some embodiments, the various mirrors and support structures for any of the optical systems described herein may be formed from aluminum, ceramic, engineered composites, other suitable materials, or combinations thereof. In some embodiments, the one or more structures and/or the one or more mirrors may be fabricated by a 3D printing technique, also known as an additive manufacturing technique. For example, both the mirror and the support structure may be additively manufactured as one integral piece.

The tertiary mirror 113 in fig. 1A and 1B and the tertiary mirror 163 in fig. 1C and 1D help widen the field of view and correct the corresponding residual optical aberration. The tertiary mirrors 113, 163 may not include an optical axis, for example, for easier manufacturability, and two or more tertiary mirrors may be manufactured from one base member. The four-stage mirror 114 in fig. 1A and 1B and the four-stage mirror 164 in fig. 1C and 1D can minimize distortion and control back focal length. As used herein, "back focal length" has a usual and customary meaning and includes, but is not limited to, the distance between the last surface of an optical mirror and its image plane. The fields of view of the optical systems 100, 150 are designed such that the light rays do not interfere with the central aperture of the respective quaternary and primary mirrors. The four-stage mirrors 114, 164 reflect the respective light along an optical path to the imaging planes 118, 168.

Fig. 1D shows the second optical system 150, but the optical path is not shown for clarity. The diameter of the aperture or central aperture 110 in fig. 1B and the diameter of the central aperture 160 in fig. 1D are minimized to maximize the area of use of the primary mirror, and in some embodiments are no larger than the corresponding secondary mirrors 105, 155. The diameters of the central aperture 110 in fig. 1B and the aperture 160 in fig. 1D may be designed to be large enough not to interfere with light passing through the central apertures 110 and 160.

The primary mirror 104, 154 and/or the secondary mirror 105, 155 may be symmetrical or periodic about the respective optical axis. Fig. 1E and 1F are schematic diagrams showing the periodic mirror and the diagonal of the image plane, respectively. The diagonal of the periodic mirror may be at an angle of 0 degrees or 45 degrees to the diagonal of the image plane. The optical axis of the tertiary mirror may not coincide with the mechanical axis.

Fig. 1G and 1H illustrate example embodiments of optical systems 170, 190 with periodic primary mirrors 174, 194, respectively. The optical systems 170, 190 also include secondary mirrors 175, 195, tertiary mirrors 173, 193, quaternary mirrors 184, 198, and imaging planes 189, 199, respectively. The optical systems 170, 190 may have the same or similar features and/or functions as the optical systems 100 or 150.

The optical system 100, 150 may include any of the same or similar features and/or functions as other embodiments of the optical system described herein, and vice versa. For example, the optical systems 100, 150 may include any of the same or similar features and/or functions as the optical systems 210, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1430, 1460, whereas the optical systems 210, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1430, 1460 may include any of the same or similar features and/or functions as the optical systems 100, 150. For example, for any of the optical systems described herein, the primary mirror may be concave and have a central aperture.

The primary mirror may have a parabolic, non-parabolic conical surface or an aspherical surface. As used herein, "parabolic" has its usual and customary meaning and includes, but is not limited to, a reflective surface for collecting light energy, and may have a shape that is part of a circular paraboloid, i.e., a surface resulting from a parabola that rotates about its axis. As used herein, a "non-parabolic conical surface" has its usual and customary meaning and includes, but is not limited to, a curve rotated about its axis, wherein the curve is obtained as the intersection of the conical surface with a plane other than parabolic. For example, the "non-parabolic tapered surface" may be hyperbolic, elliptical, or circular. As used herein, "aspheric surface" has its usual and customary meaning and includes, but is not limited to, an aspheric surface. In some embodiments, the spherical surface may be slightly altered to reduce spherical aberration.

The secondary mirror may be convex and face the primary mirror. The secondary mirror may have an aspherical surface. The tertiary mirror may be concave and disposed behind the primary mirror. "behind … …" refers to the side of the primary mirror that is opposite the side of the primary mirror that reflects incident light to the secondary mirror. The tertiary mirror may have a parabolic, non-parabolic conical surface or an aspheric surface. The four-stage mirror may be concave and disposed in the central aperture of the primary mirror, either before the primary mirror or after the primary mirror, for example as shown in fig. 3. The four-stage mirror may have one of a spherical surface, a parabolic surface, a non-parabolic conical surface, or a non-spherical surface.

There may be at least one image plane with one or more aggregated sensors, wherein the image plane is positioned at a specific distance from the optical axis. The optical axis may be defined as a geometric reference line extending between the vertices of the primary and secondary mirrors. The vertex of a given mirror may be the point on the mirror surface where the principal axis intersects the mirror.

The optical system 100 may have a larger primary mirror 104 and thus a higher resolution relative to the primary mirror 154 of the optical system 150. The resolution of the optical system 100 may be better than 1m at a 500 km height. The optical system 150 may have a resolution of better than 2m at a 500 km height. The optical system 150 may have a larger field of view than the optical system 100. The optical system 100 may have a narrower field of view relative to the optical system 150. The optical system 100 may have a volumetric size of 200 millimeters (width) by 200 millimeters (height) by 250 millimeters (length). The optical system 150 may have a volume size of 100 millimeters (width) by 100 millimeters (height) by 150 millimeters (length). The optical system 150 may be lighter in weight than the optical system 100. Both optical systems 100, 150 may have an appropriate MTF for higher resolution imaging.

Both optical systems 100, 150 may have similar mirror types and optical paths. Their respective purposes and tasks may be different. The purpose of the optical system 100 may be to map the earth's surface and obtain geospatial data. The purpose of the optical system 150 may be for remote sensing and environmental monitoring.

In some embodiments, the optical system 100, 150 may implement various parameters for the track system and/or the imaging system. Example parameters that may be implemented using the optical systems 100, 150 are described in table 1. For example, the design orbit may be set to 500 km and the spectral band may be designed to be compatible with large satellite and scientific satellite imaging other than full-color bands. The full color spectral band (PAN spectral band) can be designed to include up to the red edge, improving the Modulation Transfer Function (MTF) in the spectral band, which may be unavoidable due to its small aperture size.

TABLE 1

Fig. 2A is a block diagram of an example payload system 200 configuration of an optical system 210 in a satellite. The optical system 210 is shown in schematic form. The optical system 210 includes a concave primary mirror 204 having a central aperture 212. The primary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. The smaller convex secondary mirror 205 faces the primary mirror 204 and has an aspherical surface. The secondary mirror may have an aspherical surface. A concave tertiary mirror 213 is arranged behind the primary mirror 204. The tertiary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. A concave quaternary mirror 214 is disposed slightly behind the central aperture 212 of the primary mirror 204, wherein the quaternary mirror may have one of a spherical, parabolic, non-parabolic conical or non-spherical surface. The primary mirror 204, tertiary mirror 213, and quaternary mirror 214 each have a positive magnification or focal length, and the secondary mirror 205 has a negative magnification. "after … …" may be defined as described above. After … … "may also refer to a direction toward the right in fig. 2A, such that" after the primary mirror 204 "may refer to a direction toward the right in the figure of the primary mirror 204.

An image sensor 216 having up to 'n' collection sensors that convert light into electrical signals is located behind the primary mirror 204. In some embodiments, the image sensor 216 may transmit the output format of the 32 sub-LVDS (low voltage differential signaling) channels of digital data to the control and processing electronics portion 220 of the satellite via the interface 218. In other embodiments, other output formats are used. The sensor 216 includes read-out integrated circuits (ROIC) for infrared, visible light and other array sensors. The ROIC supported functions include processing and shaping of image signals, and may include unit cell (unit cell) preamplifiers. Interface 218 also includes control signals from control and processing electronics 220, where in some embodiments the control signals may include a Serial Peripheral Interface (SPI) and a clock signal.

In some implementations, the data formatting and distribution subsystem 224 receives data through the interface 218 and then further sends the data to the data processing and machine learning subsystem 226 and the data storage and archiving subsystem 230 for storage. Stored data from data storage and archiving subsystem 230 may be sent directly to data processing subsystem 226 for various types of processing. The output of the processed data from data processing subsystem 226 may be sent directly to data storage and archiving subsystem 230 for storage. The processed data from the data processing subsystem 226 and the output of the data from the data storage and archiving subsystem 230 may be sent to the data formatting, encryption and transmission subsystem 228. The output of the data formatting, encryption and transmission subsystem 228, such as image data, is then sent to a satellite bus for further distribution, which may include sending to earth stations, relay satellites, or other entities receiving the data. The data processing subsystem 226 may include one or more processors and one or more memories, such as a memory for program instructions and a memory and/or cache for data.

The payload control electronics subsystem 222 receives remote commands from the satellite bus and provides housekeeping data to the satellite bus. Payload control electronics subsystem 222 provides commands to portions of payload system 200, including to image sensor 216 and/or to thermal control, temperature data, and optical focus subsystem 234. Thermal control, temperature data, and optical focus subsystem 234 provides control signals, such as thermal control and optical focus signals, to optical system 210 via interface 232 and receives temperature data from optical system 210.

The power conversion, distribution and telemetry subsystem 236 receives remote control commands from the satellite bus and provides telemetry data to the satellite bus. The power conversion, distribution and telemetry subsystem 236 may also receive power such as solar panels or batteries from satellites.

An important issue with imaging systems for small satellites such as CUBESAT is calibration, including absolute calibration and inter-sensor calibration. For example, most images of commercial CUBESAT are not calibrated in a standard manner on standard radiance or reflectance scales. Thus, comparing image data to large commercial or scientific satellite imaging, such as MODIS or LANDSAT, can be challenging. Even inter-sensor calibration is uncertain, which may be due primarily to temporary instability or inconsistency in commercial sensor performance.

Instead, sensors of the optical systems described herein, such as the aggregate sensor of sensors 216 in optical system 210, may be developed and customized for space applications and their consistency and stability may be verified. Importantly, the optical system 210 and all of the optical systems described herein can be processed according to standards and calibrated relative to one another such that all image data from the system is compatible with one another and also with the reference system.

Referring to fig. 2B, an example embodiment of a sensor circuit for image sensor 216 is shown. The image sensor 216 may include a Read Out Integrated Circuit (ROIC) 272 and a Charge Coupled Device (CCD) array 270. Photons incident on the surface of the CCD array 270 (as oriented in the figure, the top surface) create a charge that can be read by the electronic device and converted into a digital copy of the light pattern that falls on the device. In certain embodiments, charge coupled devices in a complementary metal oxide semiconductor (CCD-in-CMOS) Time Delay Integration (TDI) sensor from IMEC International may be used for optical system 210, even if a pixel size of 5 (μm) is preferred. In some embodiments, the backside illuminated sensor combines a TDI CCD array with CMOS drivers and readout pixels at a pitch of 5.4 μm using a format of 270 4096 columns and 256 stages per multi-band CCD array. On-chip control and sequencer circuits may be included. In some embodiments, 130 megahertz clock 262 may be used as an input to the image sensor along with a Serial Peripheral Interface (SPI) for control. The imager may interface through the SPI and may integrate an on-chip PLL to transmit the output format of the 32sub-LVDS (low voltage differential signaling) channel as part of the ROIC 272. A seven-band version of the circuit may include seven CCD arrays, each 4096×256 pixels.

In other implementations, other sensor circuits may be used for the image sensor 216, which may have different sized arrays 270 and different ROICs 272 for output of data. For example, the image sensor 216 may include four full color CCD arrays of 16384×96 pixels each and eight multispectral CCD arrays of 8192×48 pixels.

To maximize the area exposed to light, backside illumination techniques may be used. This includes bonding the sensor wafer to the carrier wafer and thinning it from the backside. This directly exposes the CCD gate to light without interfering with the metal lines. Thus, the effective fill factor reaches 100%. Backside illuminated CMOS imagers have a very high intrinsic light sensitivity and are very efficient in detecting (near) uv and blue light. Several anti-reflective coatings (ARCs) can be used to achieve high quantum efficiencies in selected regions of the spectrum, such as over 70% in the UV range or over 90% in the visible range.

With a TDI sensor, image quality is sensitive to platform motion, which can be expressed in terms of image light leak (MTF). The image light leak MTF of optical system 210 may be 0.974, where the light leak is 0.2 pixels, the number of TDI steps at 128, and the clock phase is 4. This may place demands on the attitude stability of the platform, which may be 22 micro-arcness per second (μrad/sec) or 4.54 arcseconds per second (arcsec/sec). When the attitude stability requirement relaxes to the light leakage of one pixel, the light leakage MTF becomes 0.75, and the stability may be 23arcsec/sec.

Referring to fig. 3, a schematic diagram of an embodiment of a total reflection optical system 300 is shown. The optical design of the optical system 300 may be different from the conventional three-mirror anti-mat TMA or three-mirror Korsch designs. The Korsch design may have an ellipsoidal surface for the primary mirror, a hyperbolic surface for the secondary mirror, and an ellipsoidal surface for the tertiary mirror.

The optical system 300 includes a concave primary mirror 304 having a central aperture 310, wherein the primary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. The smaller convex secondary mirror 305 faces the primary mirror 304 and has an aspherical surface. A concave tertiary mirror 313 is arranged behind the primary mirror 304, wherein the tertiary mirror may have one of a parabolic, non-parabolic conical and aspherical surface. A concave quaternary mirror 314 is disposed in front of the central aperture 310 of the primary mirror 304, wherein the quaternary mirror may have one of a spherical, parabolic, non-parabolic conical or non-spherical surface. Primary mirror 304, tertiary mirror 313, and quaternary mirror 314 each have a positive magnification or focal length, and secondary mirror 305 has a negative magnification.

An image plane 316 with one or more collection sensors that convert light into electrical signals is positioned behind the primary mirror 304. In some embodiments, the image plane 316 is positioned at a particular distance from the optical axis defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, which may define an "optical axis". The specific distance is within the physical radius (from the optical axis) of the primary mirror. Thus, the image plane does not exceed the cylindrical envelope defined by the radius of the optical axis of the primary mirror. The radius of the primary mirror may extend perpendicularly from the major axis of the mirror to the outermost edge of the mirror. The principal axis may be a geometric reference line through the center of the mirror, which is precisely perpendicular to the surface of the mirror.

The optical system 300 uses secondary mirrors 305 that are symmetrical about the optical axis. The tertiary mirror 313 can have a segmented non-circular shape. The four-stage mirror 314 may have a circular or non-circular shape. The primary mirror 304 may have a circular or non-circular shape, with the latter serving to enhance the Modulation Transfer Function (MTF) and signal-to-noise ratio (SNR). The circular shape is inscribed in a non-circular shape, which may be periodic about the optical axis.

For the example of a square and its inner circle, the inner circle may be the shape of the primary mirror for conventional optical system designs. If the radius of the inner circle is "r", the area of the square will be 4/pi larger. For large cameras with large capacity allocated, this is generally not a problem. However, for a small satellite, typically rectangular, square primary mirror may have a larger area of 4/pi and increase MTF and SNR.

None of Korsch and other four-mirror optical designs use paraboloids for the primary and/or tertiary mirrors. Because the primary and/or tertiary mirrors of the optical system 300 have parabolic surfaces, the optical system 300 may provide a unique, affordable solution to the task with budget constraints. For paraboloids, a general test setup may be used for manufacturing, or stitching measurements are possible. In addition, commercial product lines may be used for parabolic reflector fabrication, particularly when the reflector is less than 300 millimeters. In contrast, non-parabolic conical or aspheric surfaces may require special test tools, including Computer Generated Holograms (CGH) or nulling optics.

For paraboloids, a general test setup may be used for manufacturing, or stitching measurements are possible. In addition, commercial product lines may be used for parabolic reflector fabrication, particularly when the reflector is less than 300 millimeters.

The primary mirror 304 and the secondary mirror 305 forming the optical axis are symmetrical or periodic around the axis. The primary and secondary mirror images face each other. The tertiary mirror 313 faces the back side of the primary mirror 304 and may be a segmented mirror. As used herein, "segmented mirror" includes its ordinary and customary meaning and includes, but is not limited to, an array of segmented smaller mirrors designed to act as a single larger curved mirror. The optical axis of tertiary mirror 313 may not coincide with the mechanical axis. As used herein, a "mechanical axis" has its usual and customary meaning and may include, but is not limited to, a normal vector at the center or edge of the mirror. In some embodiments, tertiary mirror 313 is a segment of a larger mirror. In such embodiments, the optical axis of tertiary mirror 313 may refer to the optical axis of the larger mirror, while the mechanical axis may refer to the optical axis of the segmented mirror. The fourth stage mirror 314 faces the third stage mirror 313 and is positioned to avoid interference with light rays from the second mirror 305 to the third stage mirror 313.

The metering and support structure for the mirrors may be a cylindrical tube or conical baffle for the primary mirror 304, such as those shown and described with reference to fig. 14A-14D. The cylindrical envelope may be coextensive with the cylindrical structure to limit the specific distance that the imaging plane is positioned relative to the optical axis between the primary and secondary mirrors. For example, the position of the imaging plane may be radially constrained by the radius of the cylindrical structure.

The light rays first impinge on the primary mirror 304 and are reflected by the primary mirror 304, then impinge on the secondary mirror 305 and are reflected by the secondary mirror 305, then impinge on the tertiary mirror 313 and are reflected by the tertiary mirror 313, and finally impinge on the quaternary mirror 314 and are reflected by the quaternary mirror 314, so that the light rays reach the image plane 316. The image plane 316 includes one or more sensors that may be clustered in order. The entrance pupil of the optical system 300 may be positioned near the primary mirror 304 or the secondary mirror 305. The intermediate focus is formed around the vertex of the primary mirror 304, between the primary mirror 304 and the secondary mirror 305, or between the primary mirror 304 and the tertiary mirror 313. An exit pupil or Lyot (Lyot) stop may be located near the quaternary mirror 314, between the tertiary mirror 313 and the quaternary mirror 314, or between the quaternary mirror 314 and the image plane 316. As used herein, "Lyot stop" has its usual and customary meaning and includes, but is not limited to, an optical stop that reduces the amount of splay that may be caused by diffraction of other stops and baffles in an optical system. The Lyot diaphragm may be located at the image of the entrance pupil of the system and have a slightly smaller diameter than the image of the pupil.

The optical system 300 has a small form factor. The shape factor is defined as the ratio of the distance 1) between the secondary mirror 305 and the tertiary mirror 313 to the effective focal length 2) of the optical system 300. In some embodiments, the optical system 300 has a form factor of less than 0.2 and 0.09. The form factor may be about 0.09 to 0.2, about 0.04 to less than 0.25. The form factor may be less than 0.25. The form factor may have the following values or about the following values: 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09. 010. 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, or 0.25. The form factor may be less than 0.04, less than 0.05, less than 0.06, less than 0.07, less than 0.08, less than 0.09, less than 0.10, less than 0.11, less than 0.12, less than 0.13, less than 0.14, less than 0.15, less than 0.16, less than 0.17, less than 0.18, less than 0.19, less than 0.20, less than 0.21, less than 0.22, less than 0.23, less than 0.24, or less than 0.25.

In addition to the small form factor, the optical system 300 also has a shorter physical distance from the tertiary mirror 313 to the image plane 316 than in the prior art. The prior art has a considerable distance between the tertiary mirror and the image plane and requires that one or more folding mirrors be adapted to a limited size. Such a configuration may lead to optical alignment difficulties, thermal instability during operation, which may end up with performance degradation. Due to the small form factor and short distance between the tertiary mirror 313 and the image plane 316, the optical system 300 eliminates unnecessary folding mirrors and simplifies alignment and assembly and operational stability.

The optical system may be designed as a mirror with zero Coefficient of Thermal Expansion (CTE) materials (such as Zerodur, fused silica, suprasil, astrostiall, etc.), low CTE materials (such as borosilicate glass, e.g., BOROFLOAT, pyrex, etc.), and mild CTE materials (such as crown glass, e.g., NBK 7).

For CTE matching, the optical system uses a specific combination of mirrors and structural materials. Superinvar, invar, or engineered composites may be used for zero CTE mirror materials. Because of the use of a composite of valance, kovalance, ceramic or design, low CTE mirror materials may be used. Titanium, ceramic, or engineered composites may be used for mild CTE mirror materials.

The monolithic structure can be used as the final solution for the optical system. The mirrors and structures may be made of a material including aluminum, ceramic, engineered composites, and are not limited to this list.

Referring to fig. 4, a schematic diagram of another embodiment of a total reflection optical system 400 is shown. Optical system 400 includes a primary mirror 404, a secondary mirror 405, a tertiary mirror 413, a quaternary mirror 414, and an image plane 416. The primary mirror 404, secondary mirror 405, tertiary mirror 413, quaternary mirror 414, and image plane 416 may have the same or similar features and/or functions as the primary mirror 304, secondary mirror 305, tertiary mirror 313, quaternary mirror 314, and image plane 316, respectively, of the optical system 300, and the primary mirror 304, secondary mirror 305, tertiary mirror 313, quaternary mirror 314, and image plane 316 of the optical system 300 may have the same or similar features and/or functions as the primary mirror 404, secondary mirror 405, tertiary mirror 413, quaternary mirror 414, and image plane 416, respectively.

However, in optical system 400, a four-stage mirror 414 is positioned behind primary mirror 404 but near aperture 410 in primary mirror 404. The tertiary mirror 413 is positioned further behind the primary mirror 404 in the optical system 400 than in the optical system 300. In some embodiments, tertiary mirror 413 may be positioned a distance behind primary mirror 404 in the range of 20% to 60%, 30% to 50%, or 35% to 45% of the diameter of primary mirror 404. The primary mirror 404 of the optical system 300 in fig. 3 may be fabricated in one body with the tertiary mirror 313 such that the centroid is closer to the primary mirror 304 and the crosstalk moment of inertia (MOI) of the system may be reduced. The optical system 400 of fig. 4 differs from the optical system 300 in terms of effective focal length and field of view. The configuration of the optical system 400 has the advantage that placing the quaternary mirror 414 closer to the primary mirror 404 may make it easier to place the lyot stop on the quaternary mirror 414 and may minimize the central aperture size or aperture 410 of the primary mirror.

Referring to fig. 5, a schematic diagram of another embodiment of a total reflection optical system 500 is shown. The optical system 500 includes a primary mirror 504, a secondary mirror 505, a tertiary mirror 513, a quaternary mirror 514, and an image plane 516. The primary mirror 504, secondary mirror 505, tertiary mirror 513, quaternary mirror 514, and image plane 516 may have the same or similar features and/or functions as the primary mirror 304, secondary mirror 305, tertiary mirror 313, quaternary mirror 314, and image plane 316, respectively, of the optical system 300, and the primary mirror 304, secondary mirror 305, tertiary mirror 313, quaternary mirror 314, and image plane 316 of the optical system 300 may have the same or similar features and/or functions as the primary mirror 504, secondary mirror 505, tertiary mirror 513, quaternary mirror 514, and image plane 516, respectively.

However, in optical system 500, the distance that the fourth mirror 514 is located behind the primary mirror 504 is greater than the distance between the fourth mirror 414 and the primary mirror 404 of optical system 400. In addition, in the optical system 500, the tertiary mirror 513 is positioned behind the primary mirror 504 by a distance greater than the distance of the corresponding mirror of the optical system 400. In some embodiments, tertiary mirror 513 can be positioned at a distance behind primary mirror 504 that is in the range of 45% to 55% of the diameter of primary mirror 504. The optical system 500 may be designed for a much smaller pixel sensor, such as a pixel sensor having a pixel size of less than 4 μm in some embodiments. The optical system 500 may differ from the optical system 300 in terms of effective focal length and field of view. In some embodiments, the optical system 500 may have a shorter effective focal length and a wider field of view relative to the optical system 300, which may allow the system 500 to include sensors having smaller pixel sizes. Tertiary mirror 613 is positioned behind primary mirror 604 similar to in optical system 400. An additional fold mirror 615 receives light from the four-stage mirror 614 and reflects it to an image plane 616 that is located above the fold mirror 615. In some embodiments, the image plane 616 is positioned above and parallel to the optical axis.

Some embodiments of the optical system may have a longer system optical path length between the four-stage mirror 614 and the image plane 616 using the fold mirror 615. If the image plane 616 is behind the tertiary mirror 613, the system optical path length is the distance between the secondary mirror 605 and the image plane 616. By using folding mirror 615, the system optical path length is the distance between secondary mirror 605 and tertiary mirror 613. The image plane 616 may be positioned to meet the focal length and field of view requirements. The configuration of the optical system 600 may provide a compact design. Another advantage is that the system 600 may allow for easier installation of the sensor cooler and a heat sink for the cooler. In addition, in the optical system 600, the sensor for the image plane may be positioned closer to the primary mirror support structure, and the sensor may be held in a more stable manner.

Referring to fig. 7, another embodiment of a total reflection optical system 700 with a fold mirror 715 is shown. The optical system 700 may have the same or similar features and/or functions as the optical system 600, and the optical system 600 may have the same or similar features and/or functions as the optical system 700. Optical system 600 includes primary mirror 704, secondary mirror 705, tertiary mirror 713, quaternary mirror 714, and imaging plane 716, which may have the same or similar features and/or functions as primary mirror 604, secondary mirror 605, tertiary mirror 613, quaternary mirror 614, and imaging plane 616, respectively, of optical system 600, and primary mirror 604, secondary mirror 605, tertiary mirror 613, quaternary mirror 614, and imaging plane 616 of optical system 600 may have the same or similar features and/or functions as primary mirror 704, secondary mirror 705, tertiary mirror 713, quaternary mirror 714, and imaging plane 716, respectively. As in optical system 600, a four-stage mirror 714 is positioned behind primary mirror 704 but near aperture 710 in primary mirror 704. Tertiary mirror 713 is positioned behind primary mirror 704 similar to in optical system 600. The fold mirror 715 receives light from the four-stage mirror 714 and reflects the light to an image plane 716 located below the fold mirror 715. In some embodiments, the image plane 716 is positioned below and parallel to the optical axis. An advantage of the configuration of the optical system 700 is that the configuration of the mirrors, including the fold mirror 715, results in a more compact design. Another advantage is that the optical system 700 may use sensors in a larger package for the image plane. CMOS sensors or sensors with ROIC tend to have larger packages so that they can include more circuits or components that help minimize readout noise, cross-talk, and blooming.

Referring to fig. 8, another embodiment of a total reflection optical system 800 having a fold mirror 815 is shown. The optical system 800 may have the same or similar features and/or functions as the optical system 700, and the optical system 700 may have the same or similar features and/or functions as the optical system 800. Optical system 800 includes a primary mirror 804, a secondary mirror 805, a tertiary mirror 813, a quaternary mirror 814, and an imaging plane 816, which may have the same or similar features and/or functions as primary mirror 704, secondary mirror 705, tertiary mirror 713, quaternary mirror 714, and imaging plane 716, respectively, of optical system 700, and primary mirror 704, secondary mirror 705, tertiary mirror 713, quaternary mirror 714, and imaging plane 716 of optical system 700 may have the same or similar features and/or functions as primary mirror 804, secondary mirror 805, tertiary mirror 813, quaternary mirror 814, and imaging plane 816, respectively. However, image plane 816 is closer to its respective optical axis than image plane 716. The four-stage mirror 814 is located behind the primary mirror 804, but further back than the four-stage mirror 814 in the corresponding components of the optical system 700. Tertiary mirror 813 is positioned further behind primary mirror 804 than in optical system 700. Folding mirror 815 receives light from the four-stage mirror 814 and reflects it to an image plane 816 that is below the folding mirror 815. In some embodiments, the image plane 816 is positioned below and parallel to the optical axis. The optical system 800 is designed for smaller pixel sensors, typically commercial pixel sensors or MILs-STD pixel sensors. An advantage of the optical system 800 is that it can utilize up-to-date sensors, including commercial pixel sensors or MILs-STD pixel sensors.

Referring to fig. 9, another embodiment of a total reflection optical system 900 with a fold mirror 915 is shown. The optical system 900 may have the same or similar features and/or functions as the optical system 800. The optical system 900 includes a primary mirror 904, a secondary mirror 905, a tertiary mirror 913, a quaternary mirror 914, and an image plane 916, which may have the same or similar features and/or functions as the primary mirror 804, the secondary mirror 805, the tertiary mirror 813, the quaternary mirror 814, and the image plane 816, respectively, of the optical system 800, and the primary mirror 804, the secondary mirror 805, the tertiary mirror 813, the quaternary mirror 814, and the image plane 816 of the optical system 800 may have the same or similar features and/or functions as the primary mirror 904, the secondary mirror 905, the tertiary mirror 913, the quaternary mirror 914, and the image plane 916, respectively.

However, in optical system 900, image plane 916 is closer to its respective optical axis than image plane 816. The fourth order mirror 914 is positioned behind the primary mirror 904 at a similar distance as the optical system 800. The tertiary mirror 913 is located behind the primary mirror 904, a distance similar to that of the optical system 800. The fold mirror 915 receives light from the quaternary mirror 914 and reflects it to an image plane 916 located above the fold mirror 915. In some embodiments, the image plane 916 is positioned above and parallel to the optical axis. The optical system 900 has the advantage that the sensor of the image plane can be more stable against vibrations and that the cooler with the radiator can be more easily installed than other optical system configurations.

Referring to fig. 10, an embodiment of a total reflection optical system 1000 having multiple image planes and a folding mirror 1015 is shown. The optical system 1000 may have the same or similar features and/or functions as the optical system 600. Optical system 1000 includes primary mirror 1004, secondary mirror 1005, tertiary mirror 1013, quaternary mirror 1014, and first image plane 1016, which may have the same or similar features and/or functions as primary mirror 604, secondary mirror 605, tertiary mirror 613, quaternary mirror 614, and image plane 616, respectively, of optical system 600, and primary mirror 604, secondary mirror 605, tertiary mirror 613, quaternary mirror 614, and image plane 616 of optical system 600 may have the same or similar features and/or functions as primary mirror 1004, secondary mirror 1005, tertiary mirror 1013, quaternary mirror 1014, and first image plane 1016, respectively. The distance from the first image plane 1016 to the optical axis is the same as the distance from the image plane 616 to each optical axis. However, the optical system 1000 has a second image plane 1016' similar to the first image plane 1016. The first image plane 1016 may be dedicated to a first spectral range and the second image plane 1016' may be dedicated to a second spectral range.

The four-stage mirror 1014 is located behind the primary mirror 1004 and near the aperture 1010 in the primary mirror 1004 at a similar distance as in the corresponding components of the optical system 600. The tertiary mirror 1013 is located behind the primary mirror 1004 at a distance similar to that in the corresponding components of the optical system 600. The folding mirror 1015 receives light from the quaternary mirror 1014 and reflects some light in a particular spectral range to a first image plane 1016 located above the folding mirror 1015. The folding mirror 1015 may transmit light rays within a second range different from the reflected light rays. The optical system 1000 achieves simultaneous polychromatic imaging by having the fold mirror 1015 reflect over a first spectral range and transmit over a second spectral range. In some embodiments, the first image plane 1016 is positioned above and parallel to the optical axis, while the second image plane 1016' is positioned below and perpendicular to the optical axis on a side of the optical axis opposite the first image plane 1016. An advantage of the optical system 1000 is that the optical system 1000 can perform multicolor imaging due to the nature of the fold mirror and the multiple imaging planes.

Referring to fig. 11, another embodiment of a total reflection optical system 1100 having multiple image planes and a fold mirror 1115 is shown. The optical system 1100 may have the same or similar features and/or functions as the optical system 1000. The optical system 1100 includes a primary mirror 1104, a secondary mirror 1105, a tertiary mirror 1113, a quaternary mirror 1114, a fold mirror 1115, and a first image plane 1116, which may have the same or similar features and/or functions as the primary mirror 1004, the secondary mirror 1005, the tertiary mirror 1013, the quaternary mirror 1014, the fold mirror 1015, and the first image plane 1016, respectively, of the optical system 1000, and the primary mirror 1004, the secondary mirror 1005, the tertiary mirror 1013, the quaternary mirror 1014, the fold mirror 1015, and the first image plane 1016 of the optical system 1000 may have the same or similar features and/or functions as the primary mirror 1104, the secondary mirror 1105, the tertiary mirror 1113, the quaternary mirror 1114, the fold mirror 1115, and the first image plane 1116, respectively. However, in the optical system 1100, the first image plane 1116 is farther from the optical axis than the first image plane 1016 is from its corresponding optical axis. The optical system 1100 has a second image plane 1116' similar to the first image plane 1116. The first image plane 1116 may be dedicated to a first spectral range and the second image plane 1116' may be dedicated to a second spectral range.

The quaternary mirror 1114 is positioned behind the primary mirror 1104 and near the aperture 1110 in the primary mirror 1104 at a distance similar to the distance in the corresponding components of the optical system 1000. The tertiary mirror 1113 is positioned behind the primary mirror 1104 at a distance similar to that in the corresponding components of the optical system 1000. Folding mirror 1115 receives light from four-stage mirror 1114 and reflects some of the light to a first image plane 1116 located below folding mirror 1115. The optical system 1100 achieves simultaneous polychromatic imaging by having the fold mirror 1115 reflect over a first spectral range and transmit over a second spectral range. In some embodiments, the first image plane 1116 is positioned below and parallel to the optical axis, while the second image plane 1116' is positioned below and perpendicular to the optical axis. One advantage is that the optical system 1100 can use sensors in a larger package for the image plane. CMOS sensors or sensors with ROIC tend to have larger packages so that they can include more circuits or components that help minimize readout noise, cross-talk, and halo.

Referring to fig. 12, another embodiment of a total reflection optical system 1200 having multiple image planes and a fold mirror 1215 is shown. The optical system 1200 may have the same or similar features and/or functions as the optical system 1100. The optical system 1200 includes a primary mirror 1204, a secondary mirror 1205, a tertiary mirror 1213, a quaternary mirror 1214, a fold mirror 1215, and a first image plane 1216, which may have the same or similar features and/or functions as the primary mirror 1104, the secondary mirror 1105, the tertiary mirror 1113, the quaternary mirror 1114, the fold mirror 1115, and the first image plane 1116, respectively, of the optical system 1100, and the primary mirror 1104, the secondary mirror 1105, the tertiary mirror 1113, the quaternary mirror 1114, the fold mirror 1115, and the first image plane 1116 of the optical system 1100 may have the same or similar features and/or functions as the primary mirror 1204, the secondary mirror 1205, the tertiary mirror 1213, the quaternary mirror 1214, the fold mirror 1215, and the first image plane 1216, respectively. However, in the optical system 1200, the first image plane 1216 is a shorter distance from the optical axis than the first image plane 1116 is from its corresponding optical axis. The optical system 1200 has a second image plane 1216' similar to the first image plane 1216. The first image plane 1216 may be dedicated to a first spectral range and the second image plane 1216' may be dedicated to a second spectral range.

The distance of the four-stage mirror 1214 behind the primary mirror 1204 is greater than in the corresponding components of the optical system 1100. The tertiary mirror 1213 is positioned behind the primary mirror 1204 a distance greater than in the corresponding components of the optical system 1100. The fold mirror 1215 receives light from the quaternary mirror 1214 and reflects it to a first image plane 1216 below the fold mirror 1215. The optical system 1200 achieves simultaneous polychromatic imaging by reflecting a fold mirror 1215 over a first spectral range and transmitting it over a second spectral range. In some embodiments, the first image plane 1216 is positioned below and parallel to the optical axis, while the second image plane 1216' is positioned below and perpendicular to the optical axis. The second image plane 1216 'is positioned closer to the optical axis than the second image plane 1116' is to its corresponding optical axis. The optical system 1200 is designed as a smaller pixel sensor that utilizes an image plane. An advantage of the optical system 1200 is that it can utilize up-to-date sensors, including commercial sensors or MILs-STD sensors.

Referring to fig. 13, another embodiment of a total reflection optical system 1300 having multiple image planes and a fold mirror 1315 is shown. The optical system 1300 may have the same or similar features and/or functions as the optical system 1000. The optical system 1300 includes a primary mirror 1304, a secondary mirror 1305, a tertiary mirror 1313, a quaternary mirror 1314, a fold mirror 1315, and a first image plane 1316, which may have the same or similar features and/or functions as the primary mirror 1004, the secondary mirror 1005, the tertiary mirror 1013, the quaternary mirror 1014, the fold mirror 1015, and the first image plane 1016, respectively, of the optical system 1000, and the primary mirror 1004, the secondary mirror 1005, the tertiary mirror 1013, the quaternary mirror 1014, the fold mirror 1015, and the first image plane 1016 of the optical system 1000 may have the same or similar features and/or functions as the primary mirror 1304, the secondary mirror 1314, the tertiary mirror 1313, the quaternary mirror 1314, the fold mirror 1315, and the first image plane 1316, respectively. However, in the optical system 1300, the first image plane 1316 is a shorter distance from the optical axis than the first image plane 1016 is from its corresponding optical axis. The optical system 1300 has a second image plane 1316' similar to the first image plane 1316. The first image plane 1316 may be dedicated to a first spectral range and the second image plane 1316' may be dedicated to a second spectral range.

The distance of the four-stage mirror 1314 behind the primary mirror 1304 is greater than the distance in the corresponding component of the optical system 1000. The tertiary mirror 1313 is located behind the primary mirror 1304 a distance greater than in the corresponding components of the optical system 1000. Fold mirror 1315 receives light from four-stage mirror 1314 and reflects it to a first image plane 1316 located above fold mirror 1315. The optical system 1300 achieves simultaneous polychromatic imaging by reflecting the fold mirror 1315 over a first spectral range and transmitting it over a second spectral range. In some embodiments, the first image plane 1316 is positioned above and parallel to the optical axis, while the second image plane 1316' is positioned below and perpendicular to the optical axis. The second image plane 1316 'is positioned closer to the optical axis than the second image plane 1016' is to its corresponding optical axis. The optical system 1300 has the advantage that a cooler with a radiator for the sensor can be installed more easily than other optical system configurations.

Referring to fig. 14A, a cutaway perspective view of an imaging system 1400 having an optical system is shown. Case 1410 shows the housing of the camera and may be a mechanical interface to the satellite bus. A metering structure 1418, shown as a tapered structure, maintains the distance between the primary mirror 1404 and the secondary mirror 1405. The metering structure 1418 may maintain this distance to within 1 micron when the temperature is varied by 1 ℃. The support structure 1408, best shown in fig. 14D as a cylindrical tube, supports the primary mirror 1404. In some embodiments, the radius of the cylindrical structure 1408 may be defined by a radius from the portion of the optical axis extending between the primary mirror 1404 and the secondary mirror 1405. The inner surface of the curved sidewall of the cylindrical structure 1408 may be limited to a particular distance from the optical axis of the image plane 316 described above.

In certain embodiments, the dimensions of the camera are 200 millimeters by 250 millimeters. Depending on the focal length of the optical system, the size range is 75mm×75mm, and the design resolution is 5m at 500 km, and the size range is 750mm×10mm×1000mm, and the design resolution is 0.25m at 500 km. The overall volume envelope of the camera system may be less than 0.01m ³ Less than 0.008m ³ Less than 0.006m ³ Less than 0.004m ³ Less than 0.003m ³ Less than 0.001m ³ Or from 0.0005m ³ To 0.01m ³ 。

The shape factor is defined as the ratio of the distance between the secondary mirror and the tertiary mirror to the focal length of the optical system. The distance between the second mirror and the tertiary mirror may be measured along the optical path. In certain embodiments, the optical system may be implemented with a form factor having the above-described values, e.g., less than 0.2, less than 0.15, or less than 0.1. For the prior art, a form factor of greater than 0.25 is known. With the relatively small form factor of the optical system described herein, the optical system can provide imaging resolution better than 1m, 0.5m, or 0.25m at 500 km heights. The optical system can also achieve imaging resolution better than 0.1m on elliptical orbit. In other embodiments, the form factor may be in a range between 0.04 and 0.09. Examples of focal lengths, distances between secondary and tertiary mirrors for each focal length, and corresponding form factors for the system are provided in table 2.

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TABLE 2

Referring to fig. 14B, an embodiment of an optical system 1430 for a video camera is shown. Metering structure 1448, shown as a tapered structure, maintains the distance between primary and secondary mirrors 1434, 1435 and the design to within ±1 micron when the temperature changes by one degree celsius.

For thermal control of the metering structure, a temperature sensor and heater (wire or patch type) may be mounted on the metering structure. The payload control electronics read the data from the temperature sensor and control the heater to maintain the metrology structure 1448 within a specified range so that the focus of the imaging system is on the focused sensor.

The annular structure 1440 is a support structure for the primary mirror 1434 and supports the primary mirror in a kinematic manner to minimize structural distortion that may occur during assembly. In addition, the ring structure 1440 may be an interface to a satellite bus, which may eliminate the need for a box-type housing, such as the housing 1410 shown in fig. 14A.

Referring to fig. 14C, a partial cutaway perspective view of an optical system 1460 for the camera is shown. The illustrated tapered metering structure 1478 maintains the distance between the primary mirror 1464 and the secondary mirror 1465, which in some embodiments may be maintained within ±1 micron when the temperature of the metering structure 1478 changes by one degree celsius. The support structure 1470 for the primary mirror 1464, shown as a ring structure, supports the primary mirror kinematic mount structure 1472 to minimize structural distortion that may occur during assembly. In addition, the support structure 1470 may be an interface to a satellite bus. In some embodiments, the radius of the support structure 1470 may be defined by the physical radius from the optical axis of the primary mirror 1464. The inner surface of the annular structure 1470 may be a limitation of a specific distance from the optical axis of the image plane 316 described above. The diameter of the primary mirror 1464 is about 7% of the focal length of the optical system, which determines the width and height of the camera system. The length of the imaging system is determined by the distance between the secondary mirror 1465 and the tertiary mirror, which is about 4% to 9% of the focal length of the optical system.

Fig. 14D is a partial cutaway perspective view of optical system 1480 showing cylindrical housing 1408, the radius of cylindrical housing 1408 being equal to the radius of primary mirror 1404. The imaging plane may be located at a radial distance from the optical axis that is no longer the radius 1486. Thus, the housing 1408 may also have the same or nearly the same radius as the primary mirror to save space. The optical axis extends between the vertices of the primary and secondary mirrors.

Performance of

The performance of optical system 100 and optical system 150 is analyzed to evaluate its design modulation transfer function, tolerance modulation transfer function, and distortion thereof. Although MTF and distortion are one method of evaluating the optical performance of a system, they also indicate the quality of the resulting image. The MTF of the full-color band is lower than that of other large-scale image pickup systems because of its small aperture. Although the MTF value is low, the image quality can be enhanced by post-processing on the ground, and can also benefit by having a smaller anti-aliasing effect.

Referring to fig. 15A and 15B, the optical design MTF and the margin MTF of the full color band of the optical system 100 are shown, respectively. The nyquist frequency of the MTF value is estimated to be 100 mm/period for the full-color band and 25 mm/period for the multispectral band. For tolerances, the sensitivity of each component was studied taking into account assembly and alignment logic.

Referring to fig. 16A and 16B, these figures represent the optical design MTF and the margin MTF, respectively, of the near infrared band of the optical system 100. Referring to fig. 17A and 17B, these figures represent the optical design MTF and the margin MTF, respectively, of the blue band of the optical system 100.

The MTF estimates for the optical system 100 are summarized in table 3. For the full color band, the design MTF is higher than 11% and the tolerance value is slightly higher than 10%. For the multispectral band, the design value is more than 57%, and the tolerance value is better than 51%. By tolerance, the MTF drop is higher for the multispectral bands, as these bands are far from the optical axis and the reflected sampling frequency is lower.

TABLE 3 Table 3

Referring to fig. 18A and 18B, the figures show the analysis results of the full band optical design MTF and the margin MTF of the optical system 150, respectively. In a similar manner to optical system 100, the nyquist frequency is 100 mm/period for full color bands and 25 mm/period for multi-spectral bands. The sensitivity of the components was studied taking into account the assembly and alignment logic.

Referring to fig. 19A and 19B, these figures represent the optical design MTF and the margin MTF, respectively, of the near infrared band of the optical system 150. Referring to fig. 20A and 20B, these figures represent the optical design MTF and the margin MTF, respectively, of the blue band of the optical system 150.

The estimated MTF values for the optical system 150 are summarized in table 4. The design MTF for the full-color band is greater than 15% and the margin is greater than 14%. For the multispectral bands, the result is different from the optical system 100. Due to the wide field of view (FOV) and its position in the field of view, MTF drop is not common and is more severe than the optical system 100. The lowest multispectral MTF value is slightly above 40% in the external field, surprisingly in the near infrared band, which band is closer to the optical axis. The tolerance value is controlled to be more than 35%.

Spectral band	Design of MTF	Tolerance MTF
			PAN (450-720 nm)	≥15	≥14
NIP (770-890 nm)	≥40	≥35
			Red (630-690 nm)	≥46	≥41
Green (520-590 nanometer)	≥49	≥44
			Blue (450-520 nm)	≥53	≥46

TABLE 4 Table 4

Referring to fig. 21A and 21B, distortion performance of the optical system 100 and the optical system 150 are shown, respectively. The distortion magnitude of the optical system 150 is 0.08 microns, higher than that of the optical system 100, and the distortion magnitude at the edge is 0.02 microns due to its larger field of view. It should be noted that the distortion magnitude of the two camera systems is still well below 1/50 pixel, which results in having sufficient margin for TDI imaging and indicating a much smaller probability of image quality degradation.

Despite having a small form factor, the optical system 100 has better performance than other imaging systems in constellation operation, as shown in table 5. The optical system 100 is designed to have a ground sampling distance of 0.9 meters and a swath width of 10.8 kilometers at 500 kilometers height, which is comparable to or better than SKYSAT. It should also be emphasized that the optical system 100 may operate in both the panchromatic and near infrared bands, which is optimally compatible with other telemetry tasks, as well as the lack of other cameras identified in table 5.

TABLE 5

The advantages of the optical system 150 over the DOVE camera are better resolution, different spectral bands and axially shorter, as shown in table 6. At 500 km height, the optical system 150 has a ground sampling distance of 1.85 meters, which is the half resolution of DOVE or PLANETSCOPE. The optical system 150 may be equipped with custom spectral bands that are necessary to extract meaningful spectral information.

TABLE 6

Advantages and advantages

The optical system is based on four-reflector total reflection optical design, and has no chromatic aberration and distortion. The lack of chromatic aberration helps the optical system to go beyond the visible spectrum, supporting imaging in the infrared and ultraviolet spectrum. The undistorted helps the optical system support accurate metrology in TDI imaging and post-processing in the orbit.

Some prior art, particularly cheaper solutions, still rely heavily on combinations of lenses and mirrors in refractive-reflective designs, limiting their application, or their optical design needs to be modified from the beginning to accommodate different spectral ranges. In addition, refractive-reflective designs do not readily involve TDI imaging, particularly for wider field-of-view imaging, because of inherent or residual aberrations.

The form factor is smaller than in larger, bulkier systems of the prior art. The optical system described herein has a much smaller form factor than the prior art. The optical system described herein is small and thus can be mounted on small flying objects, including CUBESAT, microsatellites, airplanes, UAVs, drones, or balloons. The optical systems described herein may also be provided on board the aircraft as a secondary or tertiary payload, which helps to provide a diversity of missions or more opportunities for flight missions. The optical system is small and light, thus contributing to reduced reflection costs and increased reflection opportunities compared to the prior art. In constellation operation, reflection cost is a driving factor. The optical system can be developed at a lower cost, making the optical system cheaper than the prior art. In developing the optical system, smaller test equipment and facilities may be used due to the smaller aperture. In addition, the optical system is lightweight and can be transported at a low logistic cost.

The development process of the optical system can be more effectively automated than in the prior art. Developing larger prior art technologies always requires labor resources, resulting in increased budgets. For such optical systems, which have smaller aperture sizes and are lightweight, iterative or repeated processes or steps can be automated even with economical equipment. These processes may include optical alignment, optical measurements (such as wavefront error, modulation transfer function, focal length, field of view, instantaneous field of view, distortion, signal-to-noise ratio), and these processes under various conditions. In addition to the economic efficiency, the optical system can maintain the stability of operation due to the short physical distance between the mirrors.

The optical system is based on a four-mirror optical design and provides design flexibility supported by the degrees of freedom of the optical design. The optical system can provide imaging in star, scan or push broom, video, stereo, BRDF (bi-directional reflectance distribution function), HDR (high dynamic range), polarization or low light modes with minimal modifications to the optical design. Optical systems based on four-mirror optical designs can support full color, multispectral, hyperspectral, infrared and UV imaging with minimal design modifications, mainly due to pixel size differences. The optical system has a certain degree of freedom of optical design, and can support remote sensing or scientific imaging with super resolution, high dynamic range, polarization and the like.

The optical system may support planetary or deep space tasks, which require small size factors for payload selection. The optical system may be subject to a variety of different tasks because the price and reflection opportunities of the optical system may include imaging based on artificial intelligence. The optical system can be used for a precise star sensor and a star sensor.

The optical system based on a four mirror optical design can support polychromatic simultaneous imaging. The optical system may include, but is not limited to, full color +rgb +near infrared, visible light +infrared (near infrared, short wave infrared, medium wave infrared, or long wave infrared), visible light +visible light, infrared +infrared, UV +visible light, or UV +infrared imaging.

The optical system is small in size and can be loaded on satellites that are not imaging tasks, such as communication satellites (e.g., spaceX Starlink). The optical system may also be mounted on other imaging satellites, quasi-imaging satellites (such as SAR mission satellites or scientific mission satellites). This function may result in synchronous or asynchronous constellation operation of the optical system, which enhances the time resolution of the imaging or increases the imaging opportunity. The prior art constellation operations often require significant fixed costs of expensive satellite and camera systems, all-weather operation of dedicated control stations, and non-automatic image receiving centers. The optical system is capable of synchronous or asynchronous constellation operation, whereby resources for control and data reception can be allocated, thereby significantly reducing fixed costs.

Additional embodiments

Referring to fig. 22, a schematic diagram of an embodiment of a total reflection optical system 1500 is shown. The optical system 1500 may include any or all of the features of the various four mirror designs described herein with respect to systems 100-1300 (e.g., fig. 1A, 1C, and 3-13). The optical system 1500 may also be configured for additional multispectral imaging with additional auxiliary mirrors.

In certain embodiments, the systems 100-1300 are designed for higher resolution imaging in a broad spectrum band (including the visible spectrum band and the near infrared spectrum band). Concurrently with visible and near infrared imaging, the systems 100-1300 are capable of medium resolution imaging in the short, medium and long wave infrared when equipped with custom sensors of pixel size custom made with respect to the focal length ratio for visible band imaging. From this perspective, the system numbered 100 through 1300 is capable of two spectral range imaging simultaneously: for example, visible-near infrared and short wave infrared, visible-near infrared and medium wave infrared, short wave infrared and medium wave infrared, medium wave infrared and long wave infrared, and the like.

As shown in fig. 22, system 1500 may use additional tertiary and quaternary mirrors including a beam splitter auxiliary and quaternary mirror system to add more spectral ranges than systems 100 through 1300. The optical system 1500 includes a concave primary mirror 1504 having a central aperture 1510, wherein the primary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. The smaller convex secondary mirror 1505 faces the primary mirror 1504 and has an aspherical surface. A concave tertiary mirror 1513 is disposed behind the primary mirror 1504 (rearward with respect to the direction of incidence of the light), wherein the tertiary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. A concave quaternary reflector 1514 is disposed adjacent the central aperture 1510 of the primary reflector 1504, wherein the quaternary reflector may have one of a spherical, parabolic, non-parabolic conical, and non-spherical surface. The four-stage mirror 1514 is positioned near the central aperture 1510 facing the three-stage mirror 1513 to accommodate folding mirrors 1522 and 1532 (described below) outside the incident beam radius defined by the radius of the primary mirror 1504. The primary mirror 1504, tertiary mirror 1513, and quaternary mirror 1514 each have a positive focal length, and the secondary mirror 1505 has a negative focal length.

An image plane 1516 with one or more concentrated sensors that convert light into electrical signals is positioned behind the primary mirror 1504. In some embodiments, the image plane 1516 is positioned at a particular distance from the optical axis defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and the line may define an "optical axis".

The optical system 1500 uses beam splitters 1521 and 1531 to split a particular spectral range of light directed to the tertiary mirror 1513. Beam splitters 1521 and 1531 are located between primary mirror 1504 and secondary mirror 1505 and have opposite inclinations relative to each other. Each beam splitter may have an inclination angle in the range of 65 degrees to 115 degrees with respect to the optical axis.

After beam splitters 1521 and 1531, tertiary mirrors 1523 and 1533, and quaternary mirrors 1524 and 1534, the light rays are focused to imaging planes 1526 and 1536. Image planes 1526 and 1536 with one or more concentrated sensors that convert light into electrical signals are positioned near the primary mirror 1504. In certain embodiments, a set of auxiliary mirrors including fold mirrors 1522 and 1532, tertiary mirrors 1523 and 1533, quaternary mirrors 1524 and 1534, and image planes 1526 and 1536 are positioned circumferentially at a specific distance from the optical axis and are positioned about the optical axis.

Light rays first enter the primary mirror 1504 and are reflected by the primary mirror 1504, then enter the secondary mirror 1505 and are reflected by the secondary mirror 1505, then enter the tertiary mirror 1513 and are reflected after passing through the beam splitters 1521 and 1531, and finally enter the quaternary mirror 1514 and are reflected by the quaternary mirror 1514 so that the light rays reach the image plane 1516. The image plane 1516 includes one or more sensors that may be clustered in order. The entrance pupil of the optical system 1500 may be positioned near the primary or secondary mirrors 1504, 1505. An intermediate focus is formed around the apex of the primary mirror 1504, positioned between the primary and secondary mirrors 1504, 1505, or between the primary mirror 1504 and the tertiary mirror 1513. The exit pupil or Lyot stop may be located near the quaternary mirror 1514, between the tertiary mirror 1513 and the quaternary mirror 1514, or between the quaternary mirror 1514 and the image plane 1516.

For additional multispectral imaging, light reflected by secondary mirror 1505 is incident on beam splitters 1521 and 1531, which beam splitters 1521 and 1531 redirect light to fold mirrors 1522 and 1532. The light rays are then reflected by the tertiary mirrors 1523 and 1533 and finally by the quaternary mirrors 1524 and 1534 so that the light rays reach the image planes 1526 and 1536.

Intermediate focusing is formed near fold mirrors 1522 and 1532 using beam splitters 1521 and 1531. The exit pupil or Lyot (Lyot) stop may be located near the quaternary mirrors 1524 and 1534, between the tertiary mirror 1523/1533 and the quaternary mirror 1524/1534, or between the quaternary mirror 1524/1534 and the image plane 1526/1536.

Referring to FIG. 23, a schematic diagram of an embodiment of a catadioptric and reflection system 1600 is shown. The optical system 1600 is based on a four mirror design, such as system number 100 to 1300 and system 1500. Thus, the baseline design of system 1600 has primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, fold or beam splitter 1615, and image planes 1616/1616'. The optical system 1600 differs from the systems 100-1300 and 1500 in that the optical system 1600 is capable of additional multispectral imaging with focal length reducers or optimizers 1623 and 1633 comprised of spherical or aspherical surface lenses.

While systems 100 through 1300 and 1500 are capable of highest resolution imaging in the visible and near infrared spectral ranges, the systems utilize custom or custom sensors to capture images in the short, medium, and long wave infrared simultaneously.

In contrast, optical system 1600 is capable of multispectral imaging with off-the-shelf or off-the-shelf sensors, rather than custom-made or custom-made pixel sensors. To achieve this, system 1600 has a series of split mirrors that split light rays of a particular spectral range and then transmit or reflect the light rays.

The optical system 1600 includes a concave primary mirror 1604 having a central aperture 1610, where the primary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. The smaller convex secondary mirror 1605 faces the primary mirror 1604 and has an aspherical surface. A concave tertiary mirror 1613 is disposed behind the primary mirror 1604 (behind with respect to the direction of incidence of the light), wherein the tertiary mirror may have one of a parabolic, non-parabolic conical, and aspherical surface. A concave quaternary reflector 1614 is disposed adjacent the central aperture 1610 of the primary reflector 1604, wherein the quaternary reflector may have one of a spherical, parabolic, non-parabolic conical, and non-spherical surface. The four-stage mirror 1614 is positioned near the central aperture 1610 facing the three-stage mirror 1613 to accommodate folding mirrors 1622 and 1632 (described below) outside of the incident beam radius defined by the radius of the primary mirror 1604. The primary mirror 1604, tertiary mirror 1613, and quaternary mirror 1614 each have a positive magnification or focal length, and the secondary mirror 1605 has a negative magnification.

An image plane 1616 with one or more concentrated sensors that convert light into electrical signals is located behind the primary mirror 1604. In some embodiments, the image plane 1616 is positioned at a particular distance from the optical axis defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and the line may define an "optical axis".

Optical system 1600 uses beam splitters 1621 and 1631 to split a particular spectral range of light directed to tertiary mirror 1513. Beam splitters 1621 and 1631 are located between primary mirror 1604 and secondary mirror 1605 and have opposite inclinations relative to each other. Each of the splitters may have an inclination angle of 65 to 115 degrees with respect to the optical axis.

After beam splitters 1621 and 1631, lens groups 1623 and 1633 focus the light onto image planes 1626 and 1636. In certain embodiments, lens groups 1623 and 1633, having image planes 1626 and 1636, are located at a particular distance in the circumferential direction from the optical axis and are positioned about the optical axis.

The lens groups 1623 and 1633 act as focal length optimizers to adjust and optimize the focal length to match its optical resolution to the pixel size of the off-the-shelf or off-the-shelf sensor. In some embodiments, the focal length of the first lens group 1623 may be different than the focal length of the second lens group 1633. For space applications, the lenses in lens groups 1623 and 1633 are radiation hardening lenses or radiation resistant lenses; for aerospace applications, commercial lenses are used in combination with radiation protective lenses to obtain optimal performance. For CTE matching with the lens material, titanium, ceramic, aluminum, And the combination of the designed composite structure is fabricated by additive manufacturing techniques.

In some embodiments, light rays first enter primary mirror 1604 and are reflected by primary mirror 1604, then enter secondary mirror 1605 and are reflected by secondary mirror 1605, then enter tertiary mirror 1613 and are reflected after passing through beam splitters 1621 and 1631, and finally enter quaternary mirror 1614 and are reflected by quaternary mirror 1614 such that the light rays reach image plane 1616. The image plane 1616 includes one or more sensors that may be sequentially aggregated. The entrance pupil of the optical system 1600 may be positioned near the primary or secondary mirror 1604, 1605. The intermediate focus is formed around the vertex of the primary mirror 1604, between the primary mirror 1604 and the secondary mirror 1605, or between the primary mirror 1604 and the tertiary mirror 1613. The exit pupil or lyot stop may be located near the quaternary mirror 1614, between the tertiary mirror 1613 and the quaternary mirror 1614, or between the quaternary mirror 1614 and the image plane 1616.

For additional multispectral imaging, light reflected by secondary mirror 1605 is incident on beam splitters 1621 and 1631, and beam splitters 1621 and 1631 redirect the light to folding mirrors 1622 and 1632. The light then passes through focal length optimizers 1623 and 1633 and reaches image planes 1626 and 1636.

Intermediate focusing is formed near fold mirrors 1622 and 1632 using beam splitters 1621 and 1631. An exit pupil or an lyot stop may be positioned in the lens groups 1623 and 1633 before the image plane 1626/1636.

Referring to fig. 24, a schematic diagram of another embodiment of a catadioptric and reflective system 1700 is shown. The optical system 1700 includes a primary mirror 1704, a secondary mirror 1705, a tertiary mirror 1713 (not shown for simplicity), a quaternary mirror 1714 (not shown for simplicity), and an image plane 1716 (not shown for simplicity). The primary mirror 1704, secondary mirror 1705, tertiary mirror 1713, quaternary mirror 1714, and image plane 1716 may have the same or similar features and/or functions as the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616, respectively, of the optical system 1600, and the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616 of the optical system 1600 may have the same or similar features and/or functions as the primary mirror 1704, secondary mirror 1705, tertiary mirror 1713, quaternary mirror 1714, and image plane 1716, respectively.

For additional multispectral imaging, optical system 1700 includes focal length optimizers 1733, 1733', or 1733 "to match its optical resolution to the pixel size of an off-the-shelf or off-the-shelf sensor. Focal length optimizers 1733, 1733 'and fig. 1733 "may have the same or similar features and/or functions as focal length optimizers 1623 and 1633 of optical system 1600, and focal length optimizers 1623 and 1633 of optical system 1600 may have the same or similar features and/or functions as focal length optimizers 1733, 1733' and fig. 1733".

The focal length optimizer may be positioned with an inclination angle with respect to the "optical axis", which inclination angle may be defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and which line may define the "optical axis". If the position and tilt angle of beam splitters 1731, 1731' or 1731 "are adjusted, a series of beam splitters may be placed along the optical axis so that additional multispectral imaging may be performed. The beam splitter may be positioned to have an inclination angle inclined from 65 degrees to 115 degrees with respect to the optical axis. After the beam splitters, fold mirrors 1732, 1732' and fig. 1732 "direct light through focal length optimizers 1733, 1733' and fig. 1733" and to image planes 1736, 1736' and 1736".

Referring to fig. 25, a schematic diagram of another embodiment of a catadioptric and reflective system 1800 is shown. The optical system 1800 includes a primary mirror 1804, a secondary mirror 1805, a tertiary mirror (not shown for clarity), a quaternary mirror (not shown for clarity), and an image plane (not shown for clarity). The primary mirror 1804, secondary mirror 1805, tertiary mirror, quaternary mirror, and image plane may have the same or similar features and/or functions as the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616, respectively, of the optical system 1600, and the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616 of the optical system 1600 may have the same or similar features and/or functions as the primary mirror 1804, secondary mirror 1805, tertiary mirror, quaternary mirror, and image plane, respectively.

For additional multispectral imaging, the optical system 1800 includes a focal length optimizer 1833 to match its optical resolution to the pixel size of an off-the-shelf or off-the-shelf sensor. The focal length optimizers 1833 may have the same or similar features and/or functions as the focal length optimizers 1623 and 1633 of the optical system 1600, and the focal length optimizers 1623 and 1633 of the optical system 1600 may have the same or similar features and/or functions as the focal length optimizers 1833.

The focal length optimizer may be positioned with an inclination angle with respect to the "optical axis", which inclination angle may be defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and which line may define the "optical axis". The positions and tilt angles of the beam splitter 1831 and fold mirror 1832 are adjusted to place one or more beam splitters along the optical axis so that additional multispectral imaging may be performed. The beam splitter may be positioned to have an inclination angle of 65 to 115 degrees with respect to the optical axis.

However, focal length optimizer 1833 differs from focal length optimizers 1623 and 1633 of optical system 1600 in that focal length optimizer 1833 has an additional lens branching to further separate the spectral range from the light rays passing through focal length optimizer 1833. In one embodiment, another beam splitter 1835 is placed in the focal length optimizer 1833 and enables additional multispectral imaging simultaneously. Such separation may be applied to visible light 1 to visible light 2, visible light to near infrared, short wave infrared 1 to 2, medium wave infrared 1 to 2, long wave infrared 1 to 2, etc., but the application is not limited to the specific examples herein. At the end of each lens branch of the focal length optimizer 1833, there is an image plane 1826 and fig. 1836'.

In another embodiment, focal length optimizer 1833 may differ from focal length optimizers 1623 and 1633 of optical system 1600 in that instead of a beam splitter, focal length optimizer 1833 may utilize reflective polarizer 1835 to separate s-polarized light and p-polarized light. Polarization imaging can be performed for each spectral band by reflective polarizer 1835.

Referring to fig. 26A and 26B, schematic diagrams of other embodiments of catadioptric and reflective systems 1900 and 2000, respectively, are shown. Optical systems 1900 and 2000 include primary mirrors 1904/2004, secondary mirrors 1905/2005, tertiary mirrors (not shown for clarity), quaternary mirrors (not shown for clarity), and image planes (not shown for clarity), respectively. The primary mirror 1904/2004, secondary mirror 1905/2005, tertiary mirror, quaternary mirror, and image plane may have the same or similar features and/or functions as the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616, respectively, of the optical system 1600, and the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616 of the optical system 1600 may have the same or similar features and/or functions as the primary mirror 1904/2004, secondary mirror 1905/2005, tertiary mirror, quaternary mirror, and image plane, respectively.

For additional multispectral imaging, the optical systems 1900/2000 include focal length optimizers 1933/2033, respectively, to match their optical resolution to the pixel size of an off-the-shelf or off-the-shelf sensor. Focal length optimizers 1933/2033 may have the same or similar features and/or functions as focal length optimizers 1623 and 1633 of optical system 1600, and focal length optimizers 1623 and 1633 of optical system 1600 may have the same or similar features and/or functions as focal length optimizers 1933/2033.

The focal length optimizer may be positioned with an inclination angle of 65 to 115 degrees with respect to an "optical axis", which may be defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and which may define the "optical axis". By adjusting the position and tilt angle of the beam splitters 1931/2031 and fold mirrors 1932/2032, respectively, a series of beam splitters can be placed along the optical axis, allowing additional multispectral imaging. The beam splitters 1931/2031 may be positioned to have an inclination angle of 65 degrees to 115 degrees with respect to the optical axis. After beam splitters 1931/2031, folding mirrors 1932/2032 direct light through focal length optimizers 1933/2033 to image planes 1936/2036.

However, focal length optimizers 1933/2033 differ from focal length optimizers 1623 and 1633 in that focal length optimizers 1933/2033 have filter wheels or sliders that use spectral filters or calibration targets.

The filter wheel or slider 1934 may have a narrow band spectral filter within the spectral range defined by the beam splitter 1931.

The filter wheel or slider 2034 may have calibration targets that may include transmissive or diffusive targets at different levels of transmission or reflectivity, respectively. For a diffuse target, a set of spectral diodes may be reference light sources and mounted circumferentially on a lens barrel.

Referring to fig. 27A and 27B, schematic diagrams of other embodiments of catadioptric and reflective systems 2100 and 2200, respectively, are shown. The optical systems 2100 and 2200 include a primary mirror 2104/2204, a secondary mirror 2105/2205, a tertiary mirror (not shown for clarity), a quaternary mirror (not shown for clarity), and an image plane (not shown for clarity), respectively. The primary mirror 2104/2204, secondary mirror 2105/2205, tertiary mirror, quaternary mirror, and image plane may have the same or similar features and/or functions as the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616, respectively, of the optical system 1600, and the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616 of the optical system 1600 may have the same or similar features and/or functions as the primary mirror 2104/2204, secondary mirror 2105/2205, tertiary mirror, quaternary mirror, and image plane, respectively.

For additional multispectral imaging, optical systems 2100/2200 include focal length optimizers 2133/2233, respectively, to match their optical resolution to the pixel size of an off-the-shelf or off-the-shelf sensor. The focal length optimizers 2133/2233 may have the same or similar features and/or functions as the focal length optimizers 1623 and 1633 of the optical system 1600, and the focal length optimizers 1623 and 1633 of the optical system 1600 may have the same or similar features and/or functions as the focal length optimizers 2133/2233.

The focal length optimizer may be positioned with an inclination angle of 65 to 115 degrees with respect to an "optical axis", which may be defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and which may define the "optical axis". By adjusting the position and tilt angle of beam splitter 2131/2231 and fold mirror 2132/2232, respectively, a series of beam splitters can be placed along the optical axis so that additional multispectral imaging can be performed. Beam splitter 2131/2231 may be positioned to have an oblique angle in the range of 65 degrees to 115 degrees relative to the optical axis. After beam splitter 2131/2231, folding mirror 2132/2232 directs the light through focal length optimizer 2133/2233 to image plane 2136/2236.

However, the focal length optimizers 2133/2233 differ from the focal length optimizers 1623 and 1633 in that the focal length optimizers 2133/2233 have filter wheels or sliders 2134/2234 that use polarizers or hyperspectral filters.

The filter wheel or slide 2134 or 2134' may include polarizers at 0, 45, 90, 135 degrees or at other polarization angles for polarized imaging. In certain embodiments, a filter wheel or slide 2134' may be positioned between beam splitter 2131 and folding mirror 2132.

The filter wheel or slider 2234 may include a fabry-perot interferometer for hyperspectral imaging, or the filter wheel or slider 2234' may include a linearly variable filter for hyperspectral imaging. In some embodiments, a filter wheel or slider 2234' may be positioned between the beam splitter 2231 and the fold mirror 2232.

Referring to fig. 28A, a schematic diagram of another embodiment of a catadioptric and reflective system 2300 is shown. The optical system 2300 includes a primary mirror 2304, a secondary mirror 2305, a tertiary mirror 2313, a quaternary mirror 2314, a fold mirror or beam splitter 2315, and an image plane 2316/2316'. The primary mirror 2304, secondary mirror 2305, tertiary mirror 2313, quaternary mirror 2314, fold mirror/beam splitter 2315, and image plane 2316/2316' may have the same or similar features and/or functions as the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, fold mirror/beam splitter 1615, and image plane 1616/1616' of the optical system 1600, respectively, and the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, fold mirror/beam splitter 1615 may have the same or similar features and/or functions as the primary mirror 2304, secondary mirror 2305, tertiary mirror 2313, quaternary mirror 2314, fold mirror/beam splitter 2315, and image plane 2316/2316', respectively.

For additional multispectral imaging, optical system 2300 includes a focal length optimizer 2323/2333, respectively, to match its optical resolution to the pixel size of an off-the-shelf or off-the-shelf sensor. Focal length optimizers 2323/2333 may have the same or similar features and/or functions as focal length optimizers 1623 and 1633 of optical system 1600, and focal length optimizers 1623 and 1633 of optical system 1600 may have the same or similar features and/or functions as focal length optimizers 2323/2333.

The focal length optimizer may be positioned at an oblique angle of 65 degrees to 115 degrees with respect to the "optical axis". The "optical axis" may be defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and the line may define the "optical axis". The positions and tilt angles of beam splitters 2321/2331 and folding mirrors 2322/2332, respectively, may be adjusted to place a series of beam splitters along the optical axis so that additional multispectral imaging may be performed. Beam splitters 2321/2331 may be positioned with an oblique angle between 65-15 degrees with respect to the optical axis. After beam splitters 2321/2331, folding mirrors 2322/2332 direct light through focal optimizers 2323/2333 to image planes 2326/2336.

However, the optical system 2300 differs from the system 1600 in that the folding mirrors 2315, 2322, and 2332 may be used as scanning mirrors or forward motion compensators.

The scan mirror is used to cover the field of view of the optical system 2300 with fewer sensors than the system is designed to have. Conventionally, when the imaging sensor has a small number of pixels, such as those used in systems 100-1300 described above, this approach is referred to as a swipe (whiskbroom) scan. For the optical system 2300, the method is similar to stamping (stamping) on the earth's surface, scanning in the field of view of the system. For example, the projection of the sensor may be as shown in fig. 28B.

The forward motion compensator may stabilize the line of sight of the optical system 2300 or the instantaneous field of view of the image sensor positioned at the image planes 2316, 2316', 2326 and 2336. Folding mirrors 2315, 2322 and 2332 are connected to the inertial measurement unit and controlled to compensate for unwanted movements, which can help reduce image blur caused by unstable movements of the platform, such as spacecraft, fighter aircraft, drones, unmanned aircraft or balloons.

Unlike conventional forward motion compensators, folding mirrors 2315, 2322 and 2332 can be used for low light level imaging, discarding time delay integrating sensors that have been used for such tasks. Folding mirrors 2315, 2322 and 2332 are connected to the IMU and controlled to compensate for unwanted movement, which can help maintain the line of sight of optical system 2300 or the instantaneous field of view (IFOV) of the image sensor so that the sensor can collect more light over a given period of time. The method can replace pitching maneuver of a platform, such as a spacecraft, an unmanned aerial vehicle or an unmanned aerial vehicle and a universal joint.

In addition, unlike conventional forward motion compensators, folding mirrors 2315, 2322 and 2332 may be used to generate pixel shifted images. Folding mirrors 2315, 2322 and 2332 are connected to the IMU and controlled to compensate for unwanted movement, the line of sight of the movable system 2300 or IFOV of the image sensor, such that the projection of the sensor is offset by 1/n pixel. The resulting image data may be used for super resolution to enhance the image resolution by post-processing.

Referring to fig. 29A and 29B, a schematic diagram of another embodiment of a catadioptric and reflective system 2400 is shown. Fig. 29A shows a perspective view of the optical system 2400, and fig. 29B shows a front view facing the main mirror 2404 and a set of focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483 and 2493 described below. Optical system 2400 includes a primary mirror 2404, a secondary mirror 2405, a tertiary mirror (not shown for clarity), a quaternary mirror (not shown for clarity), and an image plane (not shown for clarity). The primary mirror 2404, secondary mirror 2405, tertiary mirror, quaternary mirror, and image plane may have the same or similar features and/or functions as the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616, respectively, of the optical system 1600, and the primary mirror 1604, secondary mirror 1605, tertiary mirror 1613, quaternary mirror 1614, and image plane 1616 of the optical system 1600 may have the same or similar features and/or functions as the primary mirror 2404, secondary mirror 2405, tertiary mirror, quaternary mirror, and image plane, respectively.

For additional multispectral imaging, optical system 2400 includes focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493 to match its optical resolution to the pixel size of an off-the-shelf or off-the-shelf sensor, respectively. The focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493 may have the same or similar features and/or functions as the focal length optimizers 1623 and 1633 of the optical system 1600, and the focal length optimizers 1623 and 1633 of the optical system 1600 may have the same or similar features and/or functions as the focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493.

The focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483 and 2493 may be positioned with inclination angles in the range of 65 degrees to 115 degrees with respect to the circumferential direction of the optical axis, the inclination angles being defined by mechanical symmetry about a line passing through the vertices of the primary and secondary mirrors, and the line may define an "optical axis". The positions and tilt angles of the beam splitters (not specifically mentioned for simplicity) 2421, 2493, 2441, 2453, 2483, 2471, 2481 and 2491 and the fold mirrors (not all mentioned for simplicity) 2422, 2432, 2442, 2404, 2473, 2472, 2482 and 2492 are adjusted and the focal length optimizers 2423, 2463, 2443, 2453, 2463, 24732483 and 2493 can find their proper positions along a circumference having a diameter larger than that of the main mirror 2404. The beam splitters 2421, 2431, 2441, 2451, 2461, 2471, 2481 and 2491 may be positioned to have an inclination angle between 65 degrees and 115 degrees with respect to the circumferential direction of the optical axis. After the beam splitters 2421, 2463, 2426, 2453, 2486, 2436, 2456 and 2473, the fold mirrors 2422, 2432, 2496, 2452, 2483, 2472, 2482 and 2493 direct light through the focal length optimizers 2476, 2466, 2446, 2453, 2463, 2473, 2483 and 2493 to the image planes 2426, 2436, 2446, 2456, 2466, 2476, 2486 and 2496 (not all image planes are mentioned for simplicity).

The focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493 may have the same or similar features and/or functions as the focal length optimizers 1833 of the optical system, and the focal length optimizers 1833 of the optical system may have the same or similar features and/or functions as the focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493.

The focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493 may have the same or similar features and/or functions as the focal length optimizers 1933/2033 of the optical system 1900 (fig. 26A)/2000 (fig. 26B), and the focal length optimizers 1933/2033 of the optical system 1900 (fig. 26A)/2000 (fig. 26B) may have the same or similar features and/or functions as the focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493.

The focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493 may have the same or similar features and/or functions as the focal length optimizers 2133/2233 of the optical system 2100 (fig. 27A)/2200 (fig. 27B), and the focal length optimizers 2133/2233 of the optical system 2100 (fig. 27A)/2200 (fig. 27B) may have the same or similar features and/or functions as the focal length optimizers 2423, 2433, 2443, 2453, 2463, 2473, 2483, and 2493.

The fold mirrors 2415, 2422, 2432, 2442, 2452, 2462, 2472, 2482, and 2492 can have the same or similar features and/or functions as the fold mirrors 2315, 2322, and 2332 of the optical system 2300 (fig. 28A), and the fold mirrors 2315, 2322, and 2332 of the optical system 2300 (fig. 28A) can have the same or similar features and/or functions as the fold mirrors 2415, 2422, 2432, 2442, 2452, 2462, 2472, 2482, and 2492.

While there has been illustrated and described what are presently considered to be example embodiments, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from claimed subject matter. In addition, many modifications may be made to adapt a particular situation to the teachings of the claimed subject matter without departing from the central concept described herein. Therefore, it is intended that the claimed subject matter not be limited to the particular embodiments disclosed, but that such claimed subject matter may also include all embodiments falling within the scope of the appended claims, and equivalents thereof.

It is contemplated that various combinations or sub-combinations of the specific features and aspects of the above-disclosed embodiments may be made and still fall within one or more of the inventions. Additionally, the disclosure of any particular feature, aspect, method, property, characteristic, quality, attribute, element, etc. herein in connection with an embodiment may be used in all other embodiments set forth herein. Thus, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, the scope of the invention in this disclosure should not be limited by the specific disclosed embodiments described above. In addition, while the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the various embodiments described and the appended claims. Any of the methods disclosed herein need not be performed in the order described.

The scope of the disclosure herein also includes any and all overlaps, sub-ranges, and combinations thereof. Language such as "at most", "at least", "greater than", "less than", "between", etc., includes the recited numbers. As used herein, a number beginning with a term such as "approximately," "about," "up to about," and "substantially" includes the number and also refers to an amount or feature that is near the amount or feature that still performs the desired function or achieves the desired result. For example, the terms "approximately," "about," and "substantially" may refer to an amount that is less than 10% of the amount or feature, less than 5%, less than 1%, less than 0.1%, and less than 0.01%. Features of the embodiments disclosed herein are preceded by terms such as approximately "," about "and" substantially "as used herein to represent features having some variability that still perform the desired function or achieve the desired result of the feature.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural depending upon the context and/or application. For clarity, various single/plural permutations may be explicitly set forth herein.

It will be understood by those skilled in the art that the terms used herein are generally intended to be "open" terms (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "comprising" should be interpreted as "including but not limited to," etc.). Those of skill in the art will further appreciate that if an intent is a particular number of introduced embodiment references, such intent will be explicitly recited in the embodiment, and in the absence of such references, such intent is absent. For example, as an aid to understanding, the present disclosure may include the use of the introductory phrases "at least one" and "one or more" to introduce embodiment notes. However, the use of such phrases should not be construed to imply that the introduction of an embodiment by the indefinite articles "a" or "an" limits any particular embodiment referred to by such introduced embodiment to embodiments containing only one such reference, even though the same embodiment includes the introduced phrases "at least one" or "one or more" and indefinite articles such as the indefinite articles "a" or "an" (e.g., "a" and/or "an") should typically be interpreted to mean "at least one" or "one or more"); the same is true for the use of explicit articles for introducing embodiment references. In addition, even if a specific number of an introduced embodiment reference is explicitly recited, those skilled in the art will recognize that such reference should generally be interpreted to mean at least the recited number (e.g., a bare reference to "two references" without other modifiers, generally meaning at least two references, or two or more references). In addition, in the case of a convention analogous to "at least one of A, B and C, etc." in the general case such a construction is intended in the sense one skilled in the art would understand the convention (e.g., "a system having at least one of A, B and C" would include but not be limited to systems having A, B, C, A and B, A and C, B and C, and/or A, B, C alone, etc.). In the case of conventions like "at least one of A, B or C, etc." in general such a construction is intended to be an understanding of the convention by those skilled in the art (e.g. "a system having at least one of A, B or C" would include but not be limited to systems having A, B, C, A and B, A and C, B and C, and/or A, B and B, etc. alone). Those skilled in the art will further appreciate that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, embodiment, or drawings, should be understood to contemplate the possibilities of including one term, either term, or both. For example, the term "A or B" will be understood to include the possibilities of "A" or "B" or "A and B

Although the subject matter has been described herein in terms of certain embodiments and certain exemplary methods, it should be understood that the scope of the subject matter is not limited in this respect. Rather, the applicant expects variations of the methods and materials disclosed herein that would be apparent to one skilled in the art to fall within the scope of the disclosed subject matter.

Claims

1. A total reflection optical system comprising:

a concave primary mirror having a central aperture and a radius, the primary mirror having one of a parabolic, non-parabolic conical, and aspherical surface;

a convex secondary mirror facing the primary mirror, the secondary mirror having an aspheric surface, wherein an optical axis extends from an apex of the primary mirror to an apex of the secondary mirror;

a concave tertiary mirror disposed behind the primary mirror, the tertiary mirror having one of a parabolic, non-parabolic conical, and aspherical surface;

a concave quaternary mirror disposed in or behind the central aperture of the primary mirror, the quaternary mirror having one of a spherical surface, a parabolic surface, a non-parabolic surface conical shape, and a non-spherical surface;

At least one image plane having one or more aggregated sensors, wherein the image plane is positioned at a radial distance from the optical axis that is no greater than a radius of the primary mirror;

a first beam splitter and a second beam splitter configured to split light of a particular spectral range, wherein the first beam splitter and the second beam splitter have a relative tilt angle with respect to each other, and wherein the first beam splitter and the second beam splitter each receive light reflected by the secondary mirror;

a first folding mirror that receives light from the first beam splitter and a second folding mirror that receives light from the second beam splitter;

a second tertiary mirror receiving light from the first folding mirror and a third tertiary mirror receiving light from the second folding mirror;

a second fourth stage mirror that receives light from the second third stage mirror and a third fourth stage mirror that receives light from the third stage mirror; and

a second image plane receiving focused light from the second quaternary mirror and a third image plane receiving focused light from the third quaternary mirror, each of the second and third image planes having one or more concentrated sensors converting light into electrical signals.

2. The optical system of claim 1, wherein the second image plane and the third image plane are each positioned proximate to the primary mirror at a radial distance from the optical axis that is greater than a radius of the primary mirror.

3. The optical system of claim 1 or 2, wherein the first and second beam splitters are each positioned between the primary mirror and the secondary mirror.

4. The optical system of any preceding claim, wherein the first and second beam splitters each have an inclination angle in the range of 65 degrees to 115 degrees with respect to the optical axis.

5. The optical system of any of the preceding claims, further comprising an exit pupil or a Lyot stop, the exit pupil or Lyot stop being located in one of the following positions: 1) Near the second and third fourth stage mirrors; 2) Between the second and third tertiary mirrors and the second and third quaternary mirrors; and 3) between the second and third fourth stage mirrors and the second and third image planes, and wherein an intermediate focus is formed near the first and second fold mirrors.

6. A reflective and catadioptric optical system comprising:

a primary folding mirror or beam splitter configured to receive light from the quaternary mirror;

a first primary image plane receiving a first portion of light rays from the primary folding mirror or the beam splitter and a second primary image plane receiving a second portion of light rays from the primary folding mirror or the beam splitter, each of the first and second primary image planes having one or more aggregated sensors, wherein each of the first and second primary image planes is positioned at a radial distance from the optical axis that is no greater than a radius of the primary mirror.

7. The catadioptric optical system of claim 6, further comprising:

a first group of lenses receiving light from the first folding mirror and a second group of lenses receiving light from the second folding mirror; and

a third image plane receiving light from the first set of lenses and a fourth image plane receiving light from the second set of lenses, the third and fourth image planes each having one or more concentrated sensors converting light into electrical signals.

8. The catadioptric optical system of claim 7, wherein the third and fourth image planes each comprise a commercially available sensor, and wherein the focal lengths of the first and second sets of lenses are each independently adjusted to match the optical resolution of each of the first and second sets of lenses to the pixel size of each of the commercially available sensors.

9. The catadioptric optical system of claim 7 or 8, wherein the first and second sets of lenses each comprise a lens having a spherical or aspherical surface.

10. The catadioptric optical system of any one of claims 7 to 9, wherein the first and second beam splitters are each positioned between the primary and secondary mirrors.

11. The catadioptric optical system of any one of claims 7 to 10, wherein the first and second beam splitters each have an inclination angle in a range of 65 degrees to 115 degrees with respect to the optical axis.

12. The catadioptric optical system of any one of claims 7 to 11, further comprising an exit pupil or a Lyot stop positioned in the first and second sets of lenses and before the third and fourth image planes, and wherein an intermediate focus is formed near the first and second fold mirrors.

13. The reflective and catadioptric optical system of any one of claims 7 to 12, wherein the lenses of the first and second sets of lenses are radiation hardening lenses or radiation resistant lenses.

14. The catadioptric optical system of any one of claims 7 to 13, wherein a fold mirror performs scanning to cover a field of view of the optical system with fewer sensors than when the fold mirror does not perform scanning.

15. The catadioptric optical system of any one of claims 7 to 14, further comprising an inertial measurement unit connected to the first and second folding mirrors to compensate for unwanted movement of the system by stabilizing a line of sight of the system or an instantaneous field of view of an image sensor positioned at the third and fourth image planes.

16. The catadioptric optical system of claim 6, further comprising:

a first beam splitter, a second beam splitter, and a third beam splitter configured to split light rays of a particular spectral range, and wherein the first beam splitter, the second beam splitter, and the third beam splitter each receive light rays reflected by the secondary mirror;

a first folding mirror that receives light from the first beam splitter, a second folding mirror that receives light from the second beam splitter, and a third folding mirror that receives light from the third beam splitter;

A first group of lenses receiving light from the first folding mirror, a second group of lenses receiving light from the second folding mirror, and a third group of lenses receiving light from the third folding mirror; and

a third image plane receiving light from the first set of lenses, a fourth image plane receiving light from the second set of lenses, and a fifth image plane receiving light from the third set of lenses, the third, fourth, and fifth image planes each having one or more concentrated sensors converting light into electrical signals.

17. The catadioptric optical system of claim 6, further comprising:

a first beam splitter configured to split light rays of a specific spectral range, wherein the first beam splitter receives light rays reflected by the secondary mirror;

a first folding mirror receiving light from the first beam splitter;

a first set of lenses receiving light from the first folding mirror, wherein the first set of lenses includes a second beam splitter or a reflective polarizer; and

a third image plane receiving light from a first path in the first set of lenses; and a fourth image plane receiving light from a second path in the first set of lenses, the first path and the second path based on the second beam splitter or the reflective polarizer, the third image plane and the fourth image plane each having one or more concentrated sensors converting light into electrical signals.

18. The catadioptric optical system of claim 6, further comprising:

a first folding mirror receiving light from the first beam splitter;

a first set of lenses receiving light from the first folding mirror, wherein the first set of lenses includes a filter wheel or slider that includes a narrow band spectral filter within a spectral range defined by the first beam splitter; and

a third image plane receiving light from the first set of lenses, the third image plane having one or more concentrated sensors converting light into electrical signals.

19. The catadioptric optical system of claim 6, further comprising:

a first fold mirror receiving light from the first beam splitter or a first filter wheel or slider disposed between the first beam splitter and the fold mirror;

A first set of lenses receiving light from the first folding mirror, wherein when the first filter wheel or slider is not in use, the first set of lenses includes a second filter wheel or slider, the first filter wheel or slider and the second filter wheel or slider including zero, 45, 90, and 135 degree polarizers for polarized imaging; and

20. The catadioptric optical system of claim 6, further comprising:

eight beam splitters configured to split light of a particular spectral range, and wherein each of the eight beam splitters receives light reflected by the secondary mirror, respectively;

eight folding mirrors that receive light from the respective beam splitters;

eight sets of lenses receiving light rays from the corresponding folding mirrors; and

eight further image planes receiving light rays from the respective lens groups, each of the eight further image planes having one or more concentrated sensors converting light into electrical signals, wherein each of the eight further image planes is positioned close to the primary mirror and at a radial distance from the optical axis that is greater than a radius of the primary mirror.