WO2019140159A1 - Liaison descendante de données de radiofréquence pour un système de satellite en orbite proche de la terre à taux de revisite élevé - Google Patents

Liaison descendante de données de radiofréquence pour un système de satellite en orbite proche de la terre à taux de revisite élevé Download PDF

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Publication number
WO2019140159A1
WO2019140159A1 PCT/US2019/013153 US2019013153W WO2019140159A1 WO 2019140159 A1 WO2019140159 A1 WO 2019140159A1 US 2019013153 W US2019013153 W US 2019013153W WO 2019140159 A1 WO2019140159 A1 WO 2019140159A1
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WIPO (PCT)
Prior art keywords
satellite
ground station
data
location
processor
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PCT/US2019/013153
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English (en)
Inventor
Dan Nobbe
Ronald E. Reedy
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Skeyeon, Inc.
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Priority claimed from US15/868,812 external-priority patent/US10715245B2/en
Application filed by Skeyeon, Inc. filed Critical Skeyeon, Inc.
Publication of WO2019140159A1 publication Critical patent/WO2019140159A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
    • B64G1/1021—Earth observation satellites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
    • B64G1/1021—Earth observation satellites
    • B64G1/1028—Earth observation satellites using optical means for mapping, surveying or detection, e.g. of intelligence
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/10—Artificial satellites; Systems of such satellites; Interplanetary vehicles
    • B64G1/1085—Swarms and constellations
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/24—Guiding or controlling apparatus, e.g. for attitude control
    • B64G1/242—Orbits and trajectories
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/24—Guiding or controlling apparatus, e.g. for attitude control
    • B64G1/26—Guiding or controlling apparatus, e.g. for attitude control using jets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/40—Arrangements or adaptations of propulsion systems
    • B64G1/405—Ion or plasma engines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/42—Arrangements or adaptations of power supply systems
    • B64G1/44—Arrangements or adaptations of power supply systems using radiation, e.g. deployable solar arrays
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/62—Systems for re-entry into the earth's atmosphere; Retarding or landing devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/66—Arrangements or adaptations of apparatus or instruments, not otherwise provided for
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18515—Transmission equipment in satellites or space-based relays
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/24—Guiding or controlling apparatus, e.g. for attitude control
    • B64G1/28—Guiding or controlling apparatus, e.g. for attitude control using inertia or gyro effect
    • B64G1/286—Guiding or controlling apparatus, e.g. for attitude control using inertia or gyro effect using control momentum gyroscopes (CMGs)
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/24—Guiding or controlling apparatus, e.g. for attitude control
    • B64G1/36—Guiding or controlling apparatus, e.g. for attitude control using sensors, e.g. sun-sensors, horizon sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/42—Arrangements or adaptations of power supply systems
    • B64G1/425—Power storage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
    • B64G1/00—Cosmonautic vehicles
    • B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
    • B64G1/46—Arrangements or adaptations of devices for control of environment or living conditions
    • B64G1/50—Arrangements or adaptations of devices for control of environment or living conditions for temperature control

Definitions

  • Satellites are used in many aspects of modern life, including earth observation and reconnaissance, telecommunications, navigation (e.g., global positions systems, or“GPS”), environmental measurements and monitoring and many other functions.
  • GPS global positions systems
  • a key advantage of satellites is that they remain in orbit due to their high velocity that creates an outward centripetal force equal to gravity’s inward force.
  • Figure 8 graphically illustrates a best and worst case curve for expected lifetime of orbiting vehicles as a function of altitude.
  • a satellite will be able to observe a large fraction of the earth’s surface at some point in time.
  • a key parameter for satellites used for earth observation is the relationship between altitude, orbital angle, and constellation size. At higher altitudes, the satellite will be able to observe a larger percentage of the earth’s surface, however the orbital time will be longer and the instrument package required to effectively cover a larger area at a longer range will be larger and more complex, on the other hand, a longer orbital time means that the satellite will appear to be in view of a given point on the earth for a longer period and the number of satellites required to keep all of the earth in view all of the time decreases. In order for one satellite to cover the entire surface of the earth, sun synchronous polar orbits are frequently used.
  • Satellite orbital heights are typically categorized in three broad segments: low earth orbit (LEO), medium earth orbit (MEO) and geostationary earth orbit (GEO).
  • LEO low earth orbit
  • MEO medium earth orbit
  • GEO geostationary earth orbit
  • Table I The general uses and characteristics of these orbits are shown in Table I and represent generally accepted usage of the terms LEO, MEO and GEO. Satellites can orbit at any altitude above the atmosphere, and the gaps in altitude shown in Table 1 , such as between LEO and MEO, are also used, if less regularly. It is also common that satellites may orbit in eccentric, non-circular orbits, thereby passing through a range of altitudes in a given orbit.
  • the satellite will only be in view of a given section of the earth’s surface for a few minutes, and at lower altitudes, line of sight communication may only be possible for a minute or less. This requires a large constellation satellites or accepting a lower“revisit” rate for a given point on the Earth’s surface.
  • the orbital window for a downlink to a given station is too small to tolerate a small number of earth stations with the power available in a small satellite.
  • the downlink must be sufficiently robust to allow for near real time download of data, with latency on the order of seconds or at most, a few minutes.
  • the processor can buffer the captured data for later transmission when a receiving station is within range. Consequently, the ground station network must in some respects mirror the satellite network, with a large number of ground stations to ensure that a given satellite can be continuously pushing its image data down. Achieving low power consumption for a given bandwidth is also essential, since the small satellite profile required to achieve a low per satellite cost has a correspondingly small surface area available for solar panels to generate power for the downlink and antennas to provide the antenna gain.
  • a downlink is described that operates in the Ku band and works with a satellite network of imaging devices with a roughly 1 meter resolution imaging 240 square km per second.
  • a downlink is described that operates with an earth network that uses approximately 70 earth stations to cover the continental United States and to provide continuous downlink coverage within that area.
  • Figure 1 shows an example overall design of a low profile satellite used with the present invention.
  • Figure 2 shows a perspective view of an example low profile satellite used with the present invention.
  • Figure 3 shows a cross-section of an example low profile satellite illustrating various components for use with the present invention.
  • Figure 4 shows an example antenna design for a low cost earth station for use with the present invention.
  • Figure 5 shows an example earth station spacing plan for use with the present invention.
  • Figure 6 shows an example of satellites interacting with plural ground stations for use with the present invention.
  • Figure 7 shows an example of satellite necklaces for use with the present invention.
  • Figure 8 graphically illustrates a best and worst case curve for expected lifetime of orbiting vehicles as a function of altitude.
  • the presented embodiments provide digital, optical imaging systems as well as other imaging schemes, such as synthetic aperture radar (SAR) and/or thermal imagers.
  • SAR synthetic aperture radar
  • thermal imagers Each system is equally suitable, as long as associated imaging equipment acquires and generates data at an acquisition and transmission rate comparable with the contemplated invention to and from a comparable altitude.
  • a constellation of NEO imaging orbiters is placed in orbits at an altitude of about 260km.
  • the vehicles are equipped with digital imaging optics that will resolve features down to 1 meter in size across a 30km wide imaged swath, with an orbital velocity of roughly 8km/second.
  • the useful amount of time that a given satellite is overhead is about one minute, and if there is no overlap, a single swath will scan across the equator in about 1350 orbits.
  • the circumference of the earth is
  • a large satellite at 260km will experience considerable drag, which requires a large amount of propellant to keep in orbit, further increasing the size of the vehicle. Accordingly, a 260km satellite must be small and present a low drag profile, such as that disclosed in the related application entitled“System For Producing Remote Sensing Data From Near Earth Orbit.” Flowever, the small size means limited surface area for solar panels, which results in lower available power for the radio downlink, which in the present embodiment must operate in near real time. Accordingly, the present invention is designed for a power budget of 30 watts.
  • FIG. 1 illustrates an exemplary version of a NEO vehicle 100.
  • the vehicle is a low drag,“pizza box” design with a wedged leading edge and solar panels deployed perpendicular to the axis of flight, to minimize the cross sectional area exposed to forward collisions from atomic oxygen and other particles.
  • The“flat” form factor limits the area available for parabolic or large antenna arrays. Accordingly, the antenna for the downlink radio is constructed in the present invention as a flat, phased array antenna.
  • the NEO vehicle 100 can include an electric propulsion engine 106 to generate thrust by, for example, consuming an ionized fuel to maintain the desired orbit.
  • the engine 106 can be integrated within the bus 102, shielded by one or more panels of the bus 100, and/or dimensioned to extend beyond a surface of the bus 102, in accordance with the present disclosure.
  • One or more stabilization surfaces or panels 108 can be employed, designed to enhance the stability of the NEO vehicle 100, as well as support solar paneling to collect power.
  • the NEO vehicle 100 is defined by a narrow cross section, as exemplified in vehicle bus 102.
  • the bus 102 includes a first or top panel 1 10, a second or bottom panel 1 12, and lateral sides 1 14 and 1 16.
  • a leading edge 104 At the nose of the NEO vehicle 100 is a leading edge 104, which is configured with a bevel to slope toward one or both the first or second panel 1 10, 112.
  • the example NEO vehicle 100 of Figure 2 is shown in perspective view, illustrating a bevel 1 18 sloping from the leading edge 104 to the panel 1 10.
  • the bevel 118 is angled at 20 degrees, and another bevel opposite bevel 1 18 slopes toward panel 112. In some examples, the angle is greater than or less than 20 degrees.
  • the bevel 1 18 slopes at a first angle, whereas the opposite bevel slopes at a second angle different from the first angle.
  • the bevel can slope at a constant angle on a flat surface, or can progress at a varying gradient toward the panels 1 10, 1 12. Other variations on the surface of the bevel can also be
  • the small cross section of the NEO vehicle 100 reduces drag on the vehicle 100 from atmospheric particles and aids in maintaining stable orientation in orbit.
  • FIG. 3 shows a cross-section of an example NEO vehicle 100 illustrating various components, including a radio frequency antenna 150 (e.g., a phased array).
  • a computing platform 152 can include a processor, memory storage, and/or various sensor types, such as attitude control gyroscopes.
  • a battery 154 or other storage system e.g., capacitor, etc. can be used to store power collected by solar panels in order to, for example, power the various components and the electronic engine 106 of the NEO vehicle 100.
  • One or more optical imaging systems/lenses 156,158 are also included (e.g., variable field of view, multispectral imaging, etc.).
  • the lenses 156, 158 are configured to have a thickness sufficient to provide detailed imaging (e.g., a 1 m resolution at NEO altitudes) yet thin enough to fit within the vehicle bus 102, along with the various other components.
  • a folded light path contributes to reduced thickness of an optical assembly, while a radar assembly can be made from an array similar to the radio phased array antenna.
  • the system can include a mechanical device to control the orientation of the lenses 156, 158 and or the antenna 150 to adjust the focus of the respective system.
  • a baffle 162 can be used to provide stability as well as filtering stray light effects from non-imaged sources, supported by one or more posts 164.
  • Each spacecraft is configured with sufficient area/volume to house one or more imaging systems, such as two camera lenses 156, 158, and one or more baffles 162.
  • a camera lens can be a 10cm thick optical lens system, and a baffle external to the vehicle bus is used.
  • the spacecraft have equal applicability for systems configured for image capture (e.g., optical data collection) and radar capable spacecraft.
  • considerations related to size of the vehicle, weight, drag, power demands, as well as propellant needs, may change based on these and other factors.
  • the cross- sectional area for an imaging satellite is greater than that for a radar capable satellite (e.g., about 5 cm thick vehicle bus for radar satellite, compared with about 10cm thick to house the camera optics).
  • Additional and alternative components may be included in the NEO vehicle 100, such as radar or radio components, sensors, electronics bays for electronics and control circuitry, cooling, navigation, attitude control, and other componentry, depending on the conditions of the orbiting environment (e.g., air particle density), the particular application of the satellite (e.g., optical imaging, thermal imaging, radar imaging, other types of remote earth sensor data collection, telecommunications transceiver, scientific research etc.), for instance.
  • the system can include one or more passive and/or active systems to manage thermal changes, due to operation of the components themselves, in response to environmental conditions, etc.
  • the computing platform 152 can be configured to adjust the duty cycle of one or more components, transfer power storage and/or use from a given set of batteries to another, or another suitable measure designed to limit overheating within the NEO vehicle 100.
  • a fuel storage tank 160 is coupled with the engine 106 to generate thrust to counter the forces on the NEO vehicle 100 from drag, or to position the vehicle in the proper orbit.
  • the present and desired orbit can be compared and any adjustments can be implemented by the computing platform 152.
  • the computing platform 152 can determine spatial information indicative of a current altitude of the satellite, an
  • orientation of the satellite relative to a terrestrial surface and a position of the satellite relative to other satellites. This data can be compared against a desired altitude, orientation or position. If the computing platform 152 determines an adjustment is needed, the ion engine 106 is controlled to generate thrust sufficient to achieve the desired altitude, orientation or position.
  • the ground stations must be numerous in order to achieve near continuous download of data.
  • a vehicle can“see” a ground station within a circle on the earth of about 490km and for about 60 seconds.
  • the downlink must transmit at a data rate of 400 Mbps after error coding is factored in.
  • the inventors have determined that the most favorable link parameters to achieve low power consumption while preserving adequate link margins is to use the“Ku” band (e.g., about 1 1.7-12.7 GHz) with a Quadrature Phase-Shift Keying (QPSK) modulation scheme has a symbol rate of 2 bits/symbol.
  • QPSK Quadrature Phase-Shift Keying
  • BPSK Binary Phase Shift Keying
  • FSK Frequency-Shift Keying
  • an 870 Mbps data rate can be achieved using 543.75 MHz of bandwidth, consuming approximately 22.5 W of power.
  • a suitable NEO vehicle antenna size is approximately 17.2x17.2 cm, as described with respect to Figure 4. In such a
  • a 875 Mbps data rate can be achieved using 1094 MHz of bandwidth, consuming approximately 3401 W of power with an antenna size of approximately 17.2x17.2 cm.
  • Satellite constellations Due to extremely high satellite costs plus high launch costs, satellite constellations are typically limited to a few to a few dozen satellites. Some proposed systems include up to about 100 satellites, promising revisit times down to a day or so.
  • the average time to a useable image may not be as important as the worst case time, which we define as the time between images that meet a certain set of characteristics (e.g., a specific location plus morning or evening, plus no cloud cover, etc.).
  • a certain set of characteristics e.g., a specific location plus morning or evening, plus no cloud cover, etc.
  • getting images of a specific area (e.g., a battlefield or a river flood plain) with a long revisit time constellation can make a worst case scenario push from days into weeks.
  • a system with a 3-day average revisit time could be overhead at night for several sequential passes, and then encounter cloud cover or dust storms when it is finally overhead with correct lighting. So an average revisit time of 3 days can become a one or two-week worst case scenario, a delay that reduces or even eliminates the value of the images.
  • the NEO vehicle 100 includes a widespread array of receiving stations rather than the normally low number of centralized receiving stations found in use with traditional satellite systems. For example, with three receiving stations (e.g., US, Australia and Europe), a traditional LEO satellite will be within transmission range approximately every 30 minutes (90/3), at best. If the imagery data is available with an inherent delay of a week due to the long revisit time described above, a further 30 minute delay is relatively small. In the event that a satellite is not in communication with a ground based station at the time of imaging, the satellite imaging and processing components can buffer the image data, and transmit to the next available ground station (e.g., when imaging an ocean or uninhabitable area).
  • the satellite imaging and processing components can buffer the image data, and transmit to the next available ground station (e.g., when imaging an ocean or uninhabitable area).
  • receiving stations may be mounted atop commercial cellular base stations, of which there are about 300,000 in the US alone. Most such base stations are designed to support cellular communications radially outward. Therefore, an upwardly pointed radiation pattern can use the open area at the top of the base station tower or on top of a suitable structure (e.g., a building, etc.), directing and receiving all energy to/from an orbiting NEO satellite and away from any interference with the cellular signals.
  • a suitable structure e.g., a building, etc.
  • a simple antenna with a relatively wide beam will enable a relatively large footprint on earth’s surface.
  • a beam with full width half max (FWHM) beam angle of 45° from 100 km altitude would have a circular footprint about 200 km in diameter.
  • FWHM full width half max
  • a useable receive time of about 26 seconds would result.
  • a narrower beam would reduce this time while a wider beam would increase it.
  • a phased array antenna is provided on both the NEO satellite and the ground based station.
  • the beamwidths for the antennas are small (e.g., 6.4 and 3.2 degrees). This narrow beamwidth allows the antennas to achieve a high gain (e.g., 28.9 and 34.9 dB), which serves to reduce power
  • Phased array technology has historically been used in military and space applications, but recent advances in silicon technology are enabling highly integrated, cost effective solutions to be developed for next generation cell phone communications systems in commercial markets.
  • downloads may occur when a vehicle is passing over long stretches of ocean or other“dead zones”, of which the oceans are the largest.
  • receivers may also be placed on ships or buoys to receive the images, which can then be transmitted to processing centers via traditional high capacity satellites or fiber links.
  • NEO vehicles may include a vehicle-to-vehicle communication system, such as with point-to-point laser systems.
  • a vehicle-to-vehicle communication system such as with point-to-point laser systems.
  • Using such an inter-vehicle link would enable very high-speed data rate transfer between vehicles, enabling downloads to be handled by a vehicle other than the one collecting an image.
  • Adding this flexibility to the system has several benefits, including filling dead-zone gaps, backup capability if receivers are unavailable, and backup capability if a downlink transmitter on a NEO vehicle becomes disabled.
  • an altitude of 260km allows for about 1 meter resolution of the earth’s surface by optical imagers with a power requirement for the imager and radio combination that can be satisfied in a small, low drag profile vehicle that can be kept in orbit for several years, as disclosed in the related application entitled“System For Producing Remote Sensing Data From Near Earth Orbit.”
  • the communications scheme only requires one ground station every 420km or so for a total of about 60 to 100 ground stations to cover the United States. Additionally or alternatively, up to about 850 ground stations can cover the Earth’s land mass, and up to about 1 ,100 ground stations can cover the Earth’s surface (e.g., including water borne or airborne antennas, etc.).
  • the satellite will be able to“see” a ground station for about 63 seconds before it must establish a new link with the next ground station on its orbital path.
  • One component of the communications system is a planar antenna.
  • the phased array antenna 150 includes a plurality of elements 151 designed to communicate with a ground based transponder.
  • the elements 151 are arranged in a grid, with M number of elements 151 along they horizontal axis times N number of elements 151 along the vertical axis to define the phased antenna array.
  • MxN elements 151 can be used to facilitate communications.
  • a 16x16 element phase array antenna can be used to facilitate communications.
  • This configuration has the advantage of a low profile integration into the satellite, as well as being steerable to“point” the downlink at the earth station improving link
  • the beamwidth is set for 6.4 degrees, and the array size is 17.1 cm x 17.1 cm, small enough to fit within the“Cubesat” unit form factor of 2U (20cm) width on a vehicle having a 10cm maximum vertical thickness (1 U) while still carrying the image package, engine, electronics, and solar panels.
  • the ground station utilizes a larger antenna that is also a phased array, in the present invention the array is 28x28 elements with an overall size of 34.5 x 34.5cm.
  • This larger size has a higher gain than the antenna on the vehicle, which allows the satellite to transmit at a lower power.
  • the antenna on the satellite it is also steerable so that the maximum antenna gain can be“pointed” at the satellite.
  • the satellite will be“in view” of a ground station for about 60 seconds. During this window, the ground station must establish a link with the satellite, download the image data for at least a 60 second period of images, download telemetry from the satellite regarding operational status, and upload any commands to the satellite. The ground station also forwards the downloaded data and telemetry to a terrestrial wide area network for collection and processing at the satellite constellation control facility.
  • One feature of the present system is a design plan for locating ground based stations in such a manner as to ensure continuous coverage.
  • plural ground based stations 240-240N can be separated by a distance 124 to ensure the range 120-120N of adjacent station antennas overlap 122.
  • each ground based station 240-240N has an approximate range 126, beyond which the associated antenna is unable to receive data from a passing NEO vehicle 100.
  • the range 120N from the antenna array associated with adjacent ground based station 240N is configured to“hand off” the information from the NEO vehicle 100.
  • Such signal transfer is described with respect to Figure 6.
  • FIG. 6 shows an example of satellites interacting with plural ground stations in accordance with aspects of this disclosure.
  • a plurality of satellites 100A-100C are in a near earth orbit, as described herein.
  • a vehicle-to-vehicle laser communication system may be included to improve data download rates, flexibility and reliability.
  • Each satellite 100A-100C is equipped with communications systems to communicate with other satellites (e.g., laser communications, radio communications, etc.).
  • communications systems e.g., laser communications, radio communications, etc.
  • distance between satellites will be approximately 450 km.
  • the horizon from 160 km altitude is more than 1 ,000 km away
  • a laser communications system is capable of providing a direct link to multiple satellites in the same orbital plane. Since the vehicles will be oriented along the orbital plane in order to minimize drag, the control system for the inter-vehicle laser communications may be simple, for example, including possibly a fixed orientation.
  • satellite 100B can send and receive information to satellite 100A via link 244 and with satellite 100C via link 246.
  • line of sight laser communications to neighbor vehicles will be effective.
  • distance between satellites will be approximately 450 km.
  • a laser communications system is capable of providing a direct link to multiple satellites in the same orbital plane with minimal atmospheric diffusion effects at low power. Since the vehicles will be oriented along the orbital plane in order to minimize drag and their relative positions change very slowly, the pointing system for the inter-vehicle laser communications may be relatively simple.
  • inter-vehicle link would enable very high-speed data rate transfer between vehicles, enabling downloads to be handled by a vehicle other than the one collecting an image. Adding this flexibility to the system has several benefits, including filling dead-zone gaps, backup capability if receivers are unavailable, and backup capability if a downlink transmitter on a NEO vehicle becomes disabled.
  • each satellite 100A-100C is configured to send and receive information to and from ground based systems 240A-240C.
  • Each ground based system 240A-240C is configured to communicate with another ground based system via communication links 248, 250.
  • communication links 248 and 250 can be laser based, radio frequency transmissions, wired connections, or a combination thereof.
  • the communication links may utilize dynamic beam shapes to maximize data download during each pass of satellites.
  • the system further includes a distributed earth receiver system relying on a large number of receivers each downloading data during a satellite overpass.
  • ground based systems 240A-240C are configured to communicate with satellites 100A-100C to send and receive information via communication links 242A- 242C.
  • a ground based system can communicate with more than one satellite, or vice versa.
  • ground based system 240A is communicating with satellite 100A via communications link 242A, and is also configured to communicate with satellite 100B via link 252.
  • ground based station 240A can anticipate the arrival of satellite 100B and adjust one or more antennas to facilitate data transfer.
  • the position of satellites within the orbit can be determined based on information stored in a database and available to each ground station and/or satellite.
  • the database can be updated in response to data received through earlier ground based station communications to improve estimates of a given satellite’s location, speed and/or other operational parameters.
  • communication between the ground based station 240A and satellites 100A and 100B can occur simultaneously or in succession.
  • each ground station is connected to a satellite ephemeris server that contains data on when, where on the horizon, and on what trajectory the next satellite will appear in view of any given ground station.
  • Each ground station then, aims its antenna beam at the location in the sky where the satellite is next expected to appear.
  • each satellite stores its own corresponding table of ground stations in order of appearance, with instructions for where on the surface of the earth to aim its antenna to track the next ground station.
  • the information regarding location of the ground station is transmitted to each satellite during a communication event. Additionally or alternatively, the location data includes information regarding the frequency, power, Doppler shift, etc., associated with a particular satellite. Access to such transmission characteristics further enhances the ability to track satellite movement, and allows a ground satellite to anticipate the arrival of a satellite and prepare the antenna for a particular transmission.
  • both the ground station and the spacecraft can estimate the Doppler shift and compensate for it.
  • Such anticipation and compensation facilitates initial signal acquisition. For instance, if the receiving system knows to shift up by 100 kFIz during signal acquisition, the signal is acquired more efficiently and effectively.
  • the Doppler shift will change continuously as the spacecraft moves through the ground station coverage area, and the frequency shift will be continuously tracked and corrected based on the spacecraft movement, speed, location, distance from the ground station, etc.
  • the electrically steerable nature of the antennas coupled with the fact that the location of both the ground station and satellite are known allows for fast and efficient link establishment as the satellite moves over the earth.
  • the ground station table on the satellite is updated periodically by the reverse link from the earth station. It is noted that the uplink requirements are substantially less demanding than the downlink since a very low data rate uplink, on the order of a few thousand bits per second, is sufficient to keep the satellites onboard ground station table up to date. In the event that the table fails, the satellite reverts to an acquisition mode where the earth under the flight path is scanned for an acquisition signal from a ground station; when a signal is acquired, the satellite’s tables are refreshed by the ground station.
  • a single ground station communicates with multiple satellites.
  • the satellites can transmit information in a unique frequency and/or with varying modulation schemes.
  • the ground station may have multiple antennas (e.g., steerable antenna) configured to track the movement of a satellite and/or the transmission characteristics of the satellite.
  • the ground station is portable.
  • the ground station can be mounted on a vehicle (e.g., a wheeled vehicle, an airborne vehicle, a watercraft, etc.) such that a communications link can be provided in an area that does not maintain a permanent receiver.
  • a ground station can be deployed in disaster areas, conflict areas, and/or areas were imaging may be available for short periods.
  • Portable ground stations can communicate with other ground based stations via cellular data links and/or temporary communications cabling, as the environment and/or situation allows.
  • one or more NEO vehicles 100 can maintain an orbit 256 around the Earth 258, in accordance with the present disclosure.
  • 90 satellites per necklace can be used, however more or fewer satellites per necklace may be appropriate for a given application.
  • 45 satellites per necklace would space the vehicles at 2-minute intervals, while 180 would space vehicles at 30-second intervals.
  • the earth will rotate during the interval between arrivals of two sequential NEOs, with that distance determined by the time separation between the satellites. Different spacing distances may impact other subsystem designs such as optical imaging and radio links, but the concept remains that a NEO satellite system can provide relatively high rates of coverage.
  • Figure 6 shows three satellites in succession, any number of satellites into the tens of thousands can be employed in a satellite constellation, and can be aligned in a single direction of travel in a single orbit, or may be traveling at angles with respect to each other, and occupy multiple orbits (see, e.g., Figure 7).
  • the system includes a large number of the low-cost, low-mass, low altitude NEO vehicles, thereby enabling revisit times substantially faster than any previous satellite system.
  • the NEO vehicles spend virtually all of their orbit at the low altitude, high atmospheric density conditions that have heretofore been virtually impossible to consider. Short revisit times at low altitudes enable near-real time imaging at high resolution and low cost.
  • the system further includes a distributed earth receiver system relying on a large number of receivers each downloading data during a satellite overpass.
  • the communication link may utilize optimized beam shapes to maximize data download during each pass.
  • a vehicle-to-vehicle laser communication system may be included to improve data download rates, flexibility and reliability.

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  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Plasma & Fusion (AREA)
  • Evolutionary Computation (AREA)
  • Radio Relay Systems (AREA)

Abstract

L'invention concerne un système de satellite qui fonctionne à des altitudes comprises entre 100 et 350 km reposant sur des véhicules comprenant un moteur à ions autonome pour contrer la traînée atmosphérique afin de maintenir une dynamique d'orbite quasi constante. Le système fonctionne à des altitudes qui sont sensiblement inférieures aux satellites classiques, réduisant la taille, le poids et le coût des véhicules et de leurs sous-systèmes constitutifs tels que des imageurs optiques, des radars et des liaisons radio. Le système peut comprendre un grand nombre de véhicules de faible coût, de masse et d'altitude, permettant des temps de revisite sensiblement plus courts que les systèmes de satellites précédents. Les véhicules passent leur orbite à basse altitude, des conditions de densité atmosphérique élevée qui n'étaient jusqu'ici pratiquement impossibles à considérer pour des orbites stables. Des temps de revisite courts à basses altitudes permettent une imagerie en temps quasi-réel à haute résolution et à faible coût. À de telles altitudes, le système n'a pas d'impact sur les problèmes de débris spatiaux des orbites LEO classiques, et est auto-nettoyant en ce que des débris spatiaux ou une embarcation désemparés se désorbiteront.
PCT/US2019/013153 2018-01-11 2019-01-11 Liaison descendante de données de radiofréquence pour un système de satellite en orbite proche de la terre à taux de revisite élevé WO2019140159A1 (fr)

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