US-12620116-B2 - Systems and methods for the accurate tracking of orbital objects

Abstract

The present disclosure achieves accurate tracking of sunlit orbital objects, including small, dim orbital debris, using a ground-based telescope and detector which tracks the orbital object. The angular position of the orbital object relative to background celestial objects is accurately determined over a trajectory, allowing accurate determination of the orbit parameters.

Inventors

• Brett Alverson Spivey
• Christopher SEXTON

Assignees

• JASR Systems, LLC

Dates

Publication Date

20260505

Application Date

20221221

Claims (20)

1. 1 . A system for tracking an orbital object, the system comprising: a ground-based telescope coupled to a tracking gimbal; a camera coupled to the telescope; wherein the telescope and the camera are collectively operable for acquiring image frames of a solar illuminated orbital object tracked by the telescope and the camera; and a memory and a processor coupled to the camera storing instructions executed to determine a location of the orbital object within the camera field vs. time; wherein the memory and the processor further store instructions executed to compare an observed orientation of celestial background objects in the camera field while the solar illuminated orbital object is tracked by the telescope and the camera with an accurately registered database of true celestial background data; wherein the memory and the processor further store instructions executed to use the comparison of the observed orientation of the celestial background objects with the true celestial background data to correct the orbital object's determined location vs. time; and wherein the solar illuminated orbital object moves with respect to the celestial background objects in the camera field and the tracking gimbal of the telescope is locked onto the solar illuminated orbital object and moves with the solar illuminated orbital object in real time.
2. 2 . The system of claim 1 , wherein the camera operates at high enough frame rate to ameliorate streaking of celestial background images.
3. 3 . The system of claim 1 , wherein optical input to the camera is intensity modulated to break up celestial background streaks into a spatial pattern on the camera.
4. 4 . The system of claim 1 , wherein the memory and the processor further store instructions executed to control the tracking gimbal to keep the solar illuminated orbital object in a field of view of the camera.
5. 5 . The system of claim 1 , wherein the memory and the processor further store instructions executed to perform data reduction of orbital object track data by accumulation in time of the image frames, first shifting the image frames a predetermined amount for the orbital object motion and then summing in time.
6. 6 . The system of claim 1 , wherein the memory and the processor further store instructions executed to perform data reduction of celestial background track data by accumulation in time of celestial background objects, first shifting the image frames a predetermined amount for background motion and then summing in time.
7. 7 . The system of claim 1 , wherein the memory and the processor further store instructions executed to perform either or both of: spatial correlation of the celestial background images with accurately registered database celestial image data via 2-D image correlation; and extracting center locations of celestial objects, then correlating extracted celestial background object locations with accurately registered database celestial object locations via point cloud image correlation.
8. 8 . The system of claim 1 , wherein the memory and the processor further store instructions executed to determine both offset and image rotation of the celestial objects with respect to an accurately registered celestial object database.
9. 9 . The system of claim 1 , wherein the memory and the processor further store instructions executed to use geometrical inversion to convert the orbital object celestial locations vs. time into orbital parameters of the orbital object.
10. 10 . The system of claim 1 , wherein the system further comprises a laser and detector to measure round-trip time-of-flight of a laser pulse to the orbital object, to determine range vs. time.
11. 11 . The system of claim 10 , wherein the memory and the processor further store instructions executed to use geometrical inversion to convert the orbital object celestial locations and range vs. time into orbital parameters of the orbital object.
12. 12 . A method for tracking an orbital object, the method comprising: providing a ground-based telescope coupled to a tracking gimbal; providing a camera coupled to the telescope; wherein the telescope and the camera are collectively operable for acquiring image frames of a solar illuminated orbital object tracked by the telescope and the camera; determining a location of the orbital object within a camera field vs. time; comparing an observed orientation of celestial background objects in the camera field while the solar illuminated orbital object is tracked by the telescope and the camera with an accurately registered database of true celestial background data; and using the comparison of the observed orientation of the celestial background objects with the true celestial background data to correct the orbital object's determined location vs. time; wherein the solar illuminated orbital object moves with respect to the celestial background objects in the camera field and the tracking gimbal of the telescope is locked onto the solar illuminated orbital object and moves with the solar illuminated orbital object in real time.
13. 13 . The method of claim 12 , wherein the camera operates at high enough frame rate to ameliorate streaking of the celestial background images.
14. 14 . The method of claim 12 , wherein optical input to the camera is intensity modulated to break up celestial background streaks into a spatial pattern on the camera.
15. 15 . The method of claim 12 , wherein camera data is used to control the tracking gimbal to keep the solar illuminated orbital object in a field of view of the camera.
16. 16 . The method of claim 12 , further comprising performing data reduction of orbital object track data by accumulation in time of the image frames, first shifting the image frames a predetermined amount for the orbital object motion and then summing in time.
17. 17 . The method of claim 12 , further comprising performing data reduction of celestial background track data by accumulation in time of celestial background objects, first shifting the image frames a predetermined amount for background motion and then summing in time.
18. 18 . The method of claim 12 , further comprising performing either or both of: spatial correlation of the celestial background images with accurately registered database celestial image data via 2-D image correlation; and extracting center locations of celestial objects, then correlating extracted celestial background object locations with accurately registered database celestial object locations via point cloud image correlation.
19. 19 . The method of claim 12 , further comprising determining both offset and image rotation of the celestial objects with respect to an accurately registered celestial object database.
20. 20 . The method of claim 12 , further comprising using geometrical inversion to convert the orbital object celestial locations vs. time into orbital parameters of the orbital object.

Description

BACKGROUND The present disclosure relates to accurate tracking of orbital objects. The primary motivation for accurate tracking is to predict more accurate conjunctions of orbital objects which may lead to a collision. In particular, accurate prediction of potential collisions between orbital debris and satellites may allow the satellite to divert and avoid the collision. The present disclosure achieves accurate tracking of sunlit orbital objects, including small, dim orbital debris, using a ground-based telescope and detector which tracks the orbital object. The orbital object is sunlit, yet the sun is below the horizon. Objects in LEO have a short time window before the orbital object is eclipsed by the earth and no longer sunlit. At sunrise/sunset, the sky is still relatively bright, and the sky background creates noise in the detector. As the sun position becomes lower with respect to the horizon, the sky darkens, and the sky background creates less detector noise. The orbital object eventually becomes eclipsed by the earth and no longer sunlit. Lower altitude objects eclipse soonest after sunset and leave eclipse latest before sunrise, and so observing lower altitude objects is often accompanied by substantial sky background, requiring longer integration from the tracker to obtain adequate SNR. Optical tracking of satellites or large orbital objects (>10 cm) is straightforward as the intensity of the object in the telescope image is relatively strong compared to the noise of the camera and background. Tracking smaller orbital objects (<10 cm) is more challenging as the object must be extracted from the noisy background. SUMMARY The present disclosure achieves accurate tracking of sunlit orbital objects, including small, dim orbital debris, using a ground-based telescope and detector which tracks the orbital object. The angular position of the orbital object relative to background celestial objects is accurately determined over a trajectory, allowing accurate determination of the orbit parameters. Because the orbital object and the background celestial objects are detected simultaneously, the jitter due to the telescope tracking system can be removed. The motion of the orbital object relative to the stars and other celestial objects is used to compute the orbital parameters of the object. The system may also include range measurements, using the same telescope with a laser or a separate ranging system. The orbital object is sunlit, yet the sun is below the horizon. To track small orbital debris, which has a low signal return, the telescope is slewed to track the dim orbital object, allowing integration of the signal to obtain adequate signal-to-noise ratio (SNR). Prior art discusses telescopes which track the celestial background and observe the orbital object moving across the detector. The present disclosure instead tracks the orbital object and lets the celestial background move across the detector, so that one can integrate the orbital object signal to improve SNR, and thereby track the dimmest orbital objects. The encoders on the telescope mount, combined with the position of the orbital object image on the detector, allows determination of the angular position vs. time of the orbital object. However, this determination of the angular position has some degree of angular error which we wish to improve. For example, thermal changes, wind loading, calibration errors, etc. can all lead to inaccuracies. The atmosphere also causes a prism effect which deflects the apparent angular position of the orbital object, this deflection angle depending on parameters such as atmospheric temperature profile, and thus creates additional angular errors. Angular errors can be improved by observing celestial objects within the field of the camera as well as the tracked orbital object. The angular locations of these celestial objects are known with a high degree of accuracy. In addition, the prism effect of the atmosphere is cancelled by registering the orbital object position to the celestial background. By observing many of these celestial objects across the tracked trajectory, the present disclosure is also able to take advantage of fitting the orbital parameters to many independent measurements, thus reducing errors by ensemble averaging. Particularly for low altitude orbital objects, the angular rate to track the object can be relatively high, resulting in a streaking of the background celestial objects due to the slewing of the telescope to track the orbital object. This streaking degrades the accuracy of the determination of the angular location of the celestial object in the direction of the streak. The present disclosure mitigates this streaking. The present method ameliorates the streaking by using a high frame rate on the detector. The streak length is proportional to frame integration time. Higher frame rates thus lead to smaller streaks. The drawback to higher frame rates is that camera noise is accumulated