CA-3131519-C - DETERMINING SPACE OBJECT ATTITUDE STABILITIES FROM RADAR CROSS-SECTION STATISTICS

CA3131519CCA 3131519 CCA3131519 CCA 3131519CCA-3131519-C

Abstract

A technique for determining space object attitude stabilities from radar cross-section statistics. In particular, such determinations can be made via employing various phased-array radars (106) with various fields of views, which can monitor various space objects (108), e.g. satellites, space debris, rocket bodies, space stations, over various periods of time as the space objects (108) come into the fields of views. For example, a technique for estimating attitude stability of low-Earth RSOs (108) using RCS statistics from various radars (106), e.g. group of radars, phased-array radar network. Assuming a non- isotropic shape, an Earth-oriented RSO (108) can have an elevation- angle dependent RCS when viewed from a ground-based radar (106) Therefore, an RSO attitude stability can be tested by looking for a difference in a median or mean RCS when the RSO (108) is viewed at different elevation angles.

Inventors

Matthew A. Stevenson
MICHAEL NICOLLS
Chris Rosner

Assignees

LEOLABS, INC.

Dates

Publication Date: 20260505
Application Date: 20200224
Priority Date: 20190918

Claims (1)

CLAIMS Claim 1. A method comprising: receiving, via a processor, a plurality of radar cross-section (RCS) measurements of a space object from a radar having a field of view, wherein the RCS measurements are obtained from a plurality of passes of the space object into the field of view; estimating, via the processor, a first expected RCS value based on the RCS measurements when the space object is within the field of view at a first elevation angle relative to the radar, and a second expected RCS value based on the RCS measurements when the space object is within the field of view at a second elevation angle relative to the radar, wherein the first elevation angle is greater than the second elevation angle; determining, via the processor, a stability index (SI) based on the first expected RCS value and the second expected RCS value; receiving, via the processor, an RCS measurement from the radar when the space object is within the field of view at the first elevation angle or the second elevation angle, wherein the RCS measurement is received after the SI has been determined; inputting, via the processor, the SI updated based on the RCS measurement being slidably windowed into a finite state machine (FSM), wherein the FSM tracks the space object between a plurality of states; and taking, via the processor, an action based on a change detected in one of the states. Claim 2. The method of claim 1, wherein the radar is a phased-array radar. Claim 3. The method of claim 1, wherein the states include an attitude-stabilized state and an indeterminant state. Claim 4. The method of claim 1, wherein the FSM transitions between the states via a comparison between the SI after the SI has been updated and at least one of an amplitude threshold or a time-based threshold. Page 30 Date Re1rue/Date Received 2024-02-15 Claim 5. The method of claim 4, wherein the comparison is between the SI after the SI has been updated and the amplitude threshold. Claim 6. The method of claim 4, wherein the comparison is between the SI after the SI has been updated and the time-based threshold. Claim 7. The method of claim 4, wherein the comparison is between the SI after the SI has been updated and both the amplitude threshold and the time-based threshold. Claim 8. The method of claim 1, wherein the FSM transitions between the states via a comparison between the SI before the SI has been updated and at least one of an amplitude threshold or a time-based threshold. Claim 9. The method of claim 8, wherein the comparison is between the SI before the SI has been updated and the amplitude threshold. Claim 10. The method of claim 8, wherein the comparison is between the SI before the SI has been updated and the time-based threshold. Claim 11. The method of claim 8, wherein the comparison is between the SI before the SI has been updated and both the amplitude threshold and the time-based threshold. Claim 12. The method of claim 1 , wherein the FSM transitions between the states via a comparison between the SI after the SI has been updated, the SI before the SI has been updated, an amplitude threshold, and a time-based threshold. Claim 13. The method of claim 1, wherein the FSM includes a plurality of thresholds that are tuned via a random sampling simulation algorithm. Claim 14. The method of claim 13, wherein the random sampling simulation algorithm includes a Monte Carlo simulation. Page 31 Date Re1rue/Date Received 2024-02-15 Claim 15. The method of claim 1, wherein one of the states is an attitude-stabilized state, wherein the change is detected in the attitude-stabilized state. Claim 16. The method of claim 15, wherein the action includes triggering a software event associated with the change. Claim 17. The method of claim 16, wherein the software event is accessible via a frontend application programming interface (API) associated with the processor. Claim 18. The method of claim 1, wherein the space object includes a plurality of photovoltaic panels that are deployed. Claim 19. The method of claim 1, wherein the space object is non-spherical. Claim 20. The method of claim 1, wherein the RCS measurement is measured via the radar when the space object is within the field of view at the first elevation angle. Claim 21. The method of claim 1, wherein the RCS measurement is measured via the radar when the space object is within the field of view at the second elevation angle. Claim 22. The method of claim 1, wherein the action includes participating, via the processor, in an identification of an attitude-steerable space object. Claim 23. The method of claim 22, wherein the space object is the attitude-steerable space object. Claim 24. The method of claim 1, wherein the radar is of a radar network including a plurality of radar sites. Claim 25. The method of claim 24, wherein at least two of the sites are ground-based and are in different locations. Page 32 Date Re1rue/Date Received 2024-02-15 Claim 26. The method of claim 24, wherein each of the radar sites includes a phasedarray radar. Claim 27. The method of claim 1, wherein the SI is a first SI, wherein the action includes associating, via the processor, the space object with a constellation of space objects based on the first SI being sufficiently similar to a second SI based on a criterion, wherein at least one member of the constellation of space objects is associated with the second SI. Claim 28. The method of claim 1, wherein the first expected RCS value is a median value. Claim 29. The method of claim 1, wherein the first expected RCS value is an mean value. Claim 30. The method of claim 1, wherein the second expected RCS value is a median value. Claim 31. The method of claim 1, wherein the second expected RCS value is an mean value. Claim 32. The method of claim 1, wherein the SI is based on a ratio of the first expected RCS and the second expected RCS value. Claim 33. The method of claim 32, wherein the SI is based on a logarithm of the ratio. Claim 34. A system comprising: a server programmed to: receive a plurality of radar cross-section (RCS) measurements of a space object from a radar having a field of view, wherein the RCS measurements are obtained from a plurality of passes of the space object into the field of view; Page 33 Date Re1rue/Date Received 2024-02-15 estimate a first expected RCS value based on the RCS measurements when the space object is within the field of view at a first elevation angle relative to the radar, and a second expected RCS value based on the RCS measurements when the space object is within the field of view at a second elevation angle relative to the radar, wherein the first elevation angle is greater than the second elevation angle; determine a stability index (SI) based on the first expected RCS value and the second expected RCS value; receive an RCS measurement from the radar when the space object is within the field of view at the first elevation angle or the second elevation angle, wherein the RCS measurement is received after the SI has been determined; input the SI updated based on the RCS measurement being slidably windowed into a finite state machine (FSM) , wherein the FSM tracks the space object between a plurality of states; and take an action based on a change detected in one of the states. Page 34 Date Re1rue/Date Received 2024-02-15

Description

TITLE OF APPLICATION DETERMINING SPACE OBJECT ATTITUDE STABILITIES FROM RADAR CROSSSECTION STATISTICS TECHNICAL FIELD [0001] This disclosure relates to determining space object attitude stabilities. BACKGROUND [0002] There is a desire for a user (e.g., satellite operator, regulatory agency) to know whether or not a satellite has a stabilized attitude (e.g., rotational orientation with respect to Earth). In order to obtain this knowledge, a contiguous radar track (e.g., steerable radar dish) or an optical instrument (e.g., telescope) can be used. However, these technologies are laborious to manufacture, expensive to maintain, lacking in sufficient directivity, difficult to scale, complicated by weather, or limited due to physical size or altitude of the satellite. SUMMARY [0003] Broadly, this disclosure enables various technologies for determining space object attitude stabilities from radar cross-section statistics. In particular, such determinations can be made via employing various phased-array radars with various fields of views, which can monitor various space objects (e.g., satellites, space debris, rocket bodies, space stations) over various periods of time (e.g., minutes, hours, days, weeks, months) as the space objects come into the fields of views. For example, a technique can estimate attitude stability of low-Earth resident space objects (RSOs) using radar cross-section (RCS) statistics from various radars (e.g., group of radars, phasedarray radar network). Assuming a non-isotropic shape, an Earth-oriented RSO can have an elevation-angle dependent RCS when viewed from a ground-based radar. [0004] Therefore, an RSO attitude stability can be tested by looking for a difference in a median or mean RCS when the RSO is viewed at different elevation angles. For example, the technique can be performed using data from a radar (e.g., phased array) Page 1 Date Re1rue/Date Received 2024-02-15 positioned in Earth's Northern Hemisphere, Southern Hemisphere, Eastern Hemisphere, Western Hemisphere (e.g., land-platform-based, land-vehicle-based, marine-vehiclebased, aerial-vehicle-based, marine-platform-based). [0005] In an embodiment, a method comprises: receiving, via a processor, a plurality of RCS measurements of a space object from a radar having a field of view, wherein the RCS measurements are obtained from a plurality of passes of the space object into the field of view; estimating, via the processor, a first expected RCS value based on the RCS measurements when the space object is within the field of view at a first elevation angle relative to the radar, and a second expected RCS value based on the RCS measurements when the space object is within the field of view at a second elevation angle relative to the radar, wherein the first elevation angle is greater than the second elevation angle; determining, via the processor, a stability index (SI) based on the first expected RCS value and the second expected RCS value; receiving, via the processor, an RCS measurement from the radar when the space object is within the field of view at the first elevation angle or the second elevation angle, wherein the RCS measurement is received after the SI has been determined; inputting, via the processor, the SI into a finite state machine (FSM) after the SI is updated based on the RCS measurement being slidably windowed, wherein the FSM tracks the space object between a plurality of states; and taking, via the processor, an action based on a change detected in one of the states. [0006] In an embodiment, a system comprises: a server programmed to: receive a plurality of RCS measurements of a space object from a radar having a field of view, wherein the RCS measurements are obtained from a plurality of passes of the space object into the field of view; estimate a first expected RCS value based on the RCS measurements when the space object is within the field of view at a first elevation angle relative to the radar, and a second expected RCS value based on the RCS measurements when the space object is within the field of view at a second elevation angle relative to the radar, wherein the first elevation angle is greater than the second elevation angle; determine an SI based on the first expected RCS value and the second expected RCS value; receive an RCS measurement from the radar when the space object is within the field of view at the first elevation angle or the second elevation angle, wherein the RCS measurement is received after the SI has been determined; input the SI into a FSM after Page2 Date Re1rue/Date Received 2024-02-15 the SI is updated based on the RCS measurement being slidably windowed, wherein the FSM tracks the space object between a plurality of states; and take an action based on a change detected in one of the states. DESCRIPTION OF DRAWINGS [0007] FIG. 1 shows a diagram of an embodiment of a network according to this disclosure. [0008] FIG. 2 shows a flowchart of an embodiment of a method for determi