JP2001099677A - Star sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a star sensor which is provided with both functions as a star tracker function and a star scanner function. SOLUTION: An imaging element 2 such as an area CCD or the like is attached to a spacecraft in such a way that the direction of its vertical transfer and the spin direction of the spacecraft become identical. At the time, by taking into consideration the focal position or the like of an optical system, the direction of the spin of the spacecraft and the direction of the vertical transfer of the imaging element 2 are made opposite to each other. Then, when the spacecraft is in a spin-stable-posture control mode, the vertical transfer rate FV of the imaging element 2 is set at FV=ω/(θV/NV) according to the spin rate ω of the spacecraft (where θV represents the width in the vertical direction of the visual field of the imaging element 2 and NV represents the number of pixels in the vertical direction of the imaging element 2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a star sensor mounted on a space vehicle such as an artificial satellite.

[0002]

2. Description of the Related Art Generally, three-axis stable attitude control or spin stable attitude control is used for attitude control of a space vehicle such as an artificial satellite in space. Regardless of the attitude control method, it is necessary to know the current attitude of the spacecraft in the celestial sphere (inertial space). Therefore, the star tracker is used in the three-axis stable attitude control method, and the star scanner is used in the spin stable attitude control method. Generally used. Each of them grasps its own attitude based on the apparent position of a star (fixed star) on the celestial sphere, and is collectively called a star sensor.

In recent years, deep space exploration satellites and the like are provided with attitude control functions of both three-axis stable attitude control and spin stable attitude control. As in the case of spin stable attitude control, there is an apparatus in which the attitude control method is switched and operated as needed.

However, in this type of spacecraft, it was necessary to separately mount a star tracker and a star scanner. Conventionally, it is impossible to realize the function performed by the star tracker with the star scanner, and vice versa. For this reason, there have been various problems such as an increase in the weight of the spacecraft, difficulty in securing a mounting location for the star sensor, and difficulty in securing the field of view.

[0005]

As described above, only the conventional star sensors are specialized in the function as a star tracker or a star scanner. Therefore, a space navigation system of a type in which the attitude control method can be switched. The body had to be equipped with both a star tracker and a star scanner, causing various adverse effects such as an increase in the weight of the spacecraft.

[0006] The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a star sensor having both functions of a star tracker and a star scanner.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a star sensor used in a spacecraft having an attitude control mode including a three-axis stable attitude control mode and a spin stable attitude control mode, An optical system that captures light from a star on a celestial sphere, and an image that captures light captured by the optical system and converts the captured light into a video signal. The vertical charge transfer direction is the same as the spin direction of the universe. A storage device having a charge storage type image sensor mounted in a direction, an area for storing a star tracker function program, and an area for storing a star scanner function program; and When in the attitude control mode, the start tracker function program is read from the storage means, and when the space body is in the spin stable attitude control mode, A posture identification unit that reads the star scanner function program from a storage unit, and that identifies the posture of the space body based on the video signal that is sent from the charge storage type imaging device, based on the read function program. The charge accumulation type imaging is performed to cancel a flow of an image caused by a spin motion of the space object in a video signal supplied to the attitude identification means when the space object is in the spin stable attitude control mode. Vertical transfer speed control means for changing the vertical transfer speed of the element according to the spin rate of the space body.

[0008] By taking such measures, the star sensor according to the present invention can serve as a start tracker when the space body is in the three-axis stable attitude control mode.
When the spacecraft is in the spin stable attitude control mode, it functions as a star scanner. In particular, when functioning as a star scanner, it is necessary to cancel the flow of an image caused by the spin motion of the cosmic body, and this is realized by the vertical transfer speed control means.

That is, the charge storage type image pickup device is set so that its vertical charge transfer direction is the same as the spin direction of the space body.
In addition, the vertical transfer direction is set to be opposite to the spin direction, and the vertical transfer speed is changed according to the spin rate of the cosmic body, whereby the flow of the image in the field of view of the image sensor can be canceled. Therefore, it is possible to obtain a captured image of a star with no flow, thereby enabling the star tracker function and the star scanner function to coexist.

It is necessary that the spin direction of the space body and the vertical transfer direction of the image sensor are opposite to each other. This is because of the balance with the focal position of the optical system. You only have to decide the mounting direction.

Further, in the present invention, an area for storing a star catalog in which position information of stars on a celestial sphere is made into a database is provided in the storage means, and the attitude of the space object is identified by the attitude identification with reference to the star catalog. Means may be identified, and the database may be shared between the start tracker function and the star scanner function.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a star sensor according to an embodiment of the present invention. This star sensor is used by being mounted on a spacecraft (not numbered) having a three-axis stable attitude control function and a spin stable attitude control function. The star sensor includes an optical system 1 including a lens, a filter, a mirror, and the like, an image sensor 2 that converts light captured from the optical system 1 into an electric signal, and a circuit unit 3. In the present embodiment, an area CCD (Charge Coupled Device) is used as the image sensor 2.

Here, the imaging device 2 is installed, for example, on the side surface of the spacecraft, and is mounted so that the vertical transfer direction and the spin direction of the spacecraft are parallel. In addition, the direction of the vertical transfer direction is determined in consideration of the focal position of the optical system 1 and the like.
The directions of the spins are opposite to each other.

That is, an analog CCD pixel signal sent from the image pickup device 2 is supplied to an A / D (analog / digital) converter 33 via a signal processing circuit 31 of the circuit section 3 and is converted into a digital signal. Is stored. At this time, the image sensor 2 operates in synchronization with the vertical and horizontal transfer clocks supplied from the CCD drive circuit 32. The signal processing circuit 31, the A / D converter 33, and the memory 34 are provided with timing signals from a CCD driving circuit.

The CCD drive circuit 32 generates a vertical transfer clock, a horizontal transfer clock, and a timing signal based on a clock frequency signal and a CCD drive trigger provided from the control unit 35.

The control unit 35 includes memories 36, 37, 39,
Various functions are executed based on various function programs stored in 310 and 311 and commands and telemetry given from the external interface unit 38. At that time, the image data stored in the memory 34 is used.

The memory 36 has an OS in the control unit 35.
(Operating System) is stored. The memory 37 stores a star catalog in which the position information of the stars on the celestial sphere is stored in a database. This star catalog is shared by a start tracker function and a star scanner function described later.

The memory 39 stores a start tracker function program required when the star sensor functions as a start tracker. The memory 310 stores a star scanner function program required when the star sensor functions as a star scanner. Memory 3
11 stores a function program common to the start tracker function and the star scanner function.

The control section 35 has a vertical transfer clock control means 35a. The vertical transfer clock control means 35a changes the clock rate of the vertical transfer clock in the image sensor 2 according to the spin rate when the spacecraft is in the spin stable attitude control mode.

The star sensor having the above configuration can be regarded as a conventional start tracker with a star scanner function added. That is, by switching the driving method and the data processing method of the image pickup device 2 by a program, a start tracker function and a star scanner function are provided. At this time, the basic idea of the present invention lies in how the driving method of the image sensor 2 and the data processing method are devised so that the star tracker function can be added to the start tracker. explain.

In general, a star tracker is designed on the assumption that an image is taken in a substantially stationary state, so that when a spacecraft is spinning, an image flows, so to speak.
The original function cannot be obtained. However, since this image flow is caused by the position of the star in the visual field moving at a constant speed in a certain direction, it can be canceled by moving the image sensor 2 in the same direction according to this speed. It is possible. By the way, this type of image flow is called "smear" by those skilled in the art.

For this reason, in the present embodiment, the vertical transfer direction of the image sensor 2 is adjusted to the direction in which the stars flow, and the vertical transfer speed is set to the opposite direction to the star flow, instead of physically moving the image sensor 2. The movement of the image sensor 2 is virtually realized by the adjustment, so that the flow of the image is canceled. At this time, since the speed at which the stars flow in the field of view depends on the spin rate of the spacecraft, the vertical transfer speed is varied accordingly. This variable control of the vertical transfer speed is executed by the vertical transfer clock control means 35a.

Here, the following parameters are defined. Spin rate of spacecraft: ω [deg / sec] Vertical width of visual field of image sensor 2: θV [deg] Horizontal width of visual field of image sensor 2: θH [deg] Pixels of image sensor 2 in vertical direction Number (pixels on the image plane portion): NV Number of pixels in the horizontal direction of the image sensor 2 (including dummy pixels): NH Frequency of vertical transfer clock of the image sensor 2: FV [Hz] Frequency of horizontal transfer clock of the image sensor 2 : FH [Hz] When the conditions of the equations (1) and (2) are satisfied between the above parameters, an image with almost no flow can be obtained in the image sensor 2. FV = ω / (θV / NV) (1) FH ≧ FV × NH (2) In the equation (1), since the viewing angle changes by ω per second, the field of view per pixel is obtained. This is derived from the fact that this should be divided by (θV / NV). Equation (2) shows the conditions that must generally hold for a CCD image sensor.

By applying general values to the above parameters, ω = 60 [deg / sec], θV = 18 [deg], θH = 2
4 [deg], NV = 300, NH = 420, FV =
1000 [Hz] and FH = 420000 [Hz]. The values of FV and FH obtained here are in a range that can be sufficiently realized even with a conventional start tracker.

Once a starless image is obtained as described above, the star position can be calculated and the attitude of the spacecraft can be identified by the same processing as a conventional star tracker. it can. That is, from the horizontal position of the star image (corresponding to the position of the pixel) and the time information at which the position was read, the position of the star in the belt region surrounding the spacecraft shown in FIG. Can be known as
By comparing this with the star catalog, the attitude of the spacecraft can be known as a function of time. Even if a slight image flow occurs, the effect can be dealt with by a centroid calculation generally used in a star tracker.

In FIG. 2, the optical system 1 of the star sensor is shown.
It is shown that the belt region is formed along the horizontal field of view. It is also shown that the vertical transfer direction of the image sensor 2 and the spin direction of the spacecraft are parallel.

As described above, in this embodiment, the area CCD
The imaging device 2 is mounted on the spacecraft such that the vertical transfer direction is the same as the spin direction of the spacecraft. When the space body is in the spin stable attitude control mode, the vertical transfer speed FV of the image sensor 2 is changed according to the spin rate ω of the space body, FV = ω / (θV / NV) (where θV = imaging The vertical width of the field of view of the element 2, NV = the number of pixels in the vertical direction of the imaging element 2).

From the above, a star scanner function can be added to the start tracker, and a single star sensor can have both the start tracker function and the star scanner function. As a result, the weight of the sensor portion in the spacecraft can be reduced, and more mission equipment can be mounted accordingly. Further, it becomes easy to examine the mounting position of the sensor portion and to secure the visual field. Further, the total manufacturing cost of the sensor part can be reduced.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, a CCD is used as the image pickup device 2.
(Photodiode) may be used as the image sensor 2.

If the spin rate of the spacecraft is very low, the charge accumulation time of the image sensor 2 becomes too long. Therefore, the FV may be temporarily switched at a high speed. Such a process is generally known in the field of an imaging device such as a CCD.

In the above embodiment, the frequency of the CCD vertical transfer clock is changed according to the spin rate of the spacecraft. Conversely, the image flow is minimized while changing the CCD vertical transfer clock frequency. An application such as measuring an unknown spin rate by searching for a frequency is also conceivable. This can be used particularly when an abnormality occurs in the spacecraft and it becomes impossible to measure the spin rate by a normal method. In addition, various modifications can be made without departing from the spirit of the present invention.

[0032]

As described above in detail, according to the present invention, it is possible to provide a star sensor having both functions of a star tracker and a star scanner.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a star sensor according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a belt region surrounding a spacecraft.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical system 2 ... Imaging element 3 ... Circuit part 31 ... Signal processing circuit 32 ... CCD drive circuit 33 ... A / D converter 34 ... Image memory 35 ... Control part 35a ... Vertical transfer clock control means 36 ... Data processing memory 37: Star catalog storage memory 38: External interface unit 39: Star tracker function program storage memory 310: Star scanner function program storage memory 311: Common function program storage memory

Claims (2)

[Claims] 1. A star sensor for use in a space object provided with an attitude control mode including a three-axis stable attitude control mode and a spin stable attitude control mode, comprising: an optical system that captures light from a star on a celestial sphere; A charge accumulation type imaging device for imaging light taken by the system and converting it into a video signal, the charge storage type imaging device having a vertical charge transfer direction set in the same direction as the spin direction of the space object, A storage unit having an area for storing a function program and an area for storing a star scanner function program; and a start tracker function program from the storage unit when the space object is in the three-axis stable attitude control mode. When the space object is in the spin stable attitude control mode, the star scanner function program is read from the storage means. Attitude determining means for identifying the attitude of the space object based on the video signal sent from the charge storage type image sensor by the read function program; and When in the attitude control mode, the vertical transfer speed of the charge storage type imaging device is set to the space level in order to cancel the flow of the image caused by the spin motion of the cosmic body in the video signal given to the attitude identification means. A vertical transfer speed control means that varies according to the spin rate of the body. 2. The storage means includes an area for storing a star catalog in which positional information of stars on a celestial sphere is stored in a database, and the attitude identification means refers to the star catalog to determine the attitude of the space object. 2. The method of claim 1, wherein
2. The star sensor according to 1.