Detecting orbital debris

1. A method performed by a network device, the method comprising:

determining an exposure time associated with an image sensor coupled to a spacecraft for capturing an image of a target object orbiting the Earth, the image sensor including a matrix of photo-sensitive pixels;

computing a maximum relative angular velocity associated with the target object based on the exposure time and a dimension of a pixel in the matrix of pixels;

identifying a first pointing direction of the image sensor for initiating a search for the target object;

accessing target object orbital data;

generating, based on the first pointing direction and the target object orbital data, a first angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the first pointing direction;

dividing the first angular velocity probability distribution map into a first set of angular velocity regions (AVRs), each AVR having a central angular velocity and having a size corresponding to the computed maximum relative angular velocity, wherein the first set of AVRs includes AVRs of varying sizes, the size of an AVR further based on a magnitude of an angular velocity of the target object at the center of the AVR;

selecting a first AVR from the first set of AVRs for scanning by the image sensor; and

generating a search schedule that includes a first entry for informing the spacecraft to scan the first AVR, where scanning the first AVR comprises positioning the image sensor at the first pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the first AVR.

2. The method of claim 1 , wherein computing the maximum relative angular velocity comprises dividing the pixel dimension by the exposure time.

3. The method of claim 1 , further comprising:

determining, for the first entry added to the search schedule, whether an additional scan of the first AVR is to be performed; and

responsive to determining that an additional scan of the first AVR is to be performed, updating the search schedule with a second entry for informing the spacecraft to scan the first AVR.

4. The method of claim 1 , further comprising:

determining whether the search schedule is complete;

based on determining that the search schedule is not complete, identifying a second pointing direction of the image sensor at the end of scanning the first AVR;

generating, based on the second pointing direction and the target object orbital data, a second angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the second pointing direction;

dividing the second angular velocity probability distribution map into a second set of AVRs;

selecting a second AVR from the second set of AVRs for scanning by the image sensor; and

updating the search schedule for the image sensor with a second entry for informing the spacecraft to scan the second AVR, where scanning the second AVR comprises positioning the image sensor at the second pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the second AVR.

5. The method of claim 4 , wherein the size of the second set of AVRs is smaller than a size of the first set of AVRs.

6. The method of claim 5 , further comprising:

identifying a third pointing direction of the image sensor at the end of scanning the second AVR;

generating, based on the third pointing direction and the target object orbital data, a third angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the third pointing direction; and

dividing the third angular velocity probability distribution map into a third set of AVRs, the size of the third set of AVRs being smaller than the size of the second set of AVRs.

7. The method of claim 1 , further comprising:

determining whether the search schedule is complete; and

based on determining that the search schedule is complete, transmitting the search schedule to the spacecraft.

8. The method of claim 7 , further comprising:

receiving, at the spacecraft and from the network device, the search schedule;

reading, by the spacecraft, the first entry in the search schedule;

based on reading the first entry, slewing, by the spacecraft, the image sensor starting from the first pointing direction for scanning the first AVR; and

enabling, by the spacecraft, the image sensor for recording sensor readings as the image sensor scans the first AVR.

9. The method of claim 8 , further comprising:

determining, by the spacecraft, whether there are additional entries in the search schedule;

based on determining that there are additional entries in the search schedule, reading, by the spacecraft, the next entry in the search schedule, the next entry including information for the spacecraft to scan a next AVR, where scanning the next AVR comprises positioning the image sensor at the next pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the next AVR;

responsive to reading the next entry, slewing, by the spacecraft, the image sensor starting from the next pointing direction for scanning the next AVR; and

enabling, by the spacecraft, the image sensor for recording sensor readings as the image sensor scans the next AVR.

10. The method of claim 1 , wherein the target object includes orbital debris.

11. The method of claim 1 , wherein the exposure time includes a time used by the image sensor for recording sensor readings, the exposure time based on at least one of a noise floor and threshold signal-to-noise ratio (threshold SNR) associated with the image sensor.

12. The method of claim 11 , wherein the exposure time is based on at least one of size and distance of the target object.

13. The method of claim 1 , wherein the size of each AVR is at most as large as the maximum relative angular velocity.

14. The method of claim 1 , wherein the size of an AVR is proportional to the magnitude of the angular velocity at the center of the AVR, the size being smaller for a smaller angular velocity at the center of the AVR in comparison to a larger angular velocity at the center of the AVR.

15. The method of claim 1 , wherein first set of AVRs includes AVRs with a shape that is one of a circular shape and a hexagonal shape.

16. The method of claim 1 , wherein selecting a first AVR from the first set of AVRs comprises selecting the first AVR based on one of a random selection strategy and a probability of detection of the target object that is associated with each AVR in the first set of AVRs.

17. The method of claim 1 , wherein the network device includes a ground-based computing device.

18. A computer program product, embodied in a non-transitory computer-readable medium and including instructions executable by a processor, the instructions when executed configured to cause the processor to perform operations comprising:

determining an exposure time associated with an image sensor coupled to a spacecraft for capturing an image of a target object orbiting the Earth, the image sensor including a matrix of photo-sensitive pixels;

computing a maximum relative angular velocity associated with the target object based on the exposure time and a dimension of a pixel in the matrix of pixels;

identifying a first pointing direction of the image sensor for initiating a search for the target object;

accessing target object orbital data;

generating, based on the first pointing direction and the target object orbital data, a first angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the first pointing direction;

dividing the first angular velocity probability distribution map into a first set of angular velocity regions (AVRs), each AVR having a central angular velocity and having a size corresponding to the computed maximum relative angular velocity, wherein the first set of AVRs includes AVRs of varying sizes, the size of an AVR further based on a magnitude of an angular velocity of the target object at the center of the AVR;

selecting a first AVR from the first set of AVRs for scanning by the image sensor; and

generating a search schedule that includes a first entry for informing the spacecraft to scan the first AVR, where scanning the first AVR comprises positioning the image sensor at the first pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the first AVR.

19. The computer program product of claim 18 , wherein computing the maximum relative angular velocity comprises dividing the pixel dimension by the exposure time.

20. The computer program product of claim 18 , further including instructions that are configured to cause the processor to perform operations comprising:

determining, for the first entry added to the search schedule, whether an additional scan of the first AVR is to be performed; and

responsive to determining that an additional scan of the first AVR is to be performed, updating the search schedule with a second entry for informing the spacecraft to scan the first AVR.

21. The computer program product of claim 18 , further including instructions that are configured to cause the processor to perform operations comprising:

determining whether the search schedule is complete;

based on determining that the search schedule is not complete, identifying a second pointing direction of the image sensor at the end of scanning the first AVR;

generating, based on the second pointing direction and the target object orbital data, a second angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the second pointing direction;

dividing the second angular velocity probability distribution map into a second set of AVRs;

selecting a second AVR from the second set of AVRs for scanning by the image sensor; and

updating the search schedule for the image sensor with a second entry for informing the spacecraft to scan the second AVR, where scanning the second AVR comprises positioning the image sensor at the second pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the second AVR.

22. The computer program product of claim 21 , wherein the size of the second set of AVRs is smaller than a size of the first set of AVRs.

23. The computer program product of claim 22 , further including instructions that are configured to cause the processor to perform operations comprising:

identifying a third pointing direction of the image sensor at the end of scanning the second AVR;

generating, based on the third pointing direction and the target object orbital data, a third angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the third pointing direction; and

dividing the third angular velocity probability distribution map into a third set of AVRs, the size of the third set of AVRs being smaller than the size of the second set of AVRs.

24. The computer program product of claim 18 , further including instructions that are configured to cause the processor to perform operations comprising:

determining whether the search schedule is complete; and

based on determining that the search schedule is complete, transmitting the search schedule to the spacecraft.

25. The computer program product of claim 24 , further including instructions that are configured to cause the processor to perform operations comprising:

receiving, at the spacecraft and from a network device, the search schedule;

reading, by the spacecraft, the first entry in the search schedule;

based on reading the first entry, slewing, by the spacecraft, the image sensor starting from the first pointing direction for scanning the first AVR; and

enabling, by the spacecraft, the image sensor for recording sensor readings as the image sensor scans the first AVR.

26. The computer program product of claim 25 , further including instructions that are configured to cause the processor to perform operations comprising:

determining, by the spacecraft, whether there are additional entries in the search schedule;

based on determining that there are additional entries in the search schedule, reading, by the spacecraft, the next entry in the search schedule, the next entry including information for the spacecraft to scan a next AVR, where scanning the next AVR comprises positioning the image sensor at the next pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the next AVR;

responsive to reading the next entry, slewing, by the spacecraft, the image sensor starting from the next pointing direction for scanning the next AVR; and

enabling, by the spacecraft, the image sensor for recording sensor readings as the image sensor scans the next AVR.

27. The computer program product of claim 18 , wherein the target object includes orbital debris.

28. The computer program product of claim 18 , wherein the exposure time includes a time used by the image sensor for recording sensor readings, the exposure time based on at least one of a noise floor and threshold signal-to-noise ratio (threshold SNR) associated with the image sensor.

29. The computer program product of claim 28 , wherein the exposure time is based on at least one of size and distance of the target object.

30. The computer program product of claim 18 , wherein the size of each AVR is at most as large as the maximum relative angular velocity.

31. The computer program product of claim 18 , wherein the size of an AVR is proportional to the magnitude of the angular velocity at the center of the AVR, the size being smaller for a smaller angular velocity at the center of the AVR in comparison to a larger angular velocity at the center of the AVR.

32. The computer program product of claim 18 , wherein first set of AVRs includes AVRs with a shape that is one of a circular shape and a hexagonal shape.

33. The computer program product of claim 18 , wherein selecting a first AVR from the first set of AVRs comprises selecting the first AVR based on one of a random selection strategy and a probability of detection of the target object that is associated with each AVR in the first set of AVRs.

34. The computer program product of claim 18 , comprising a ground-based computing device.

35. A method performed by a network device, the method comprising:

determining an exposure time associated with an image sensor coupled to a spacecraft for capturing an image of a target object orbiting the Earth, the image sensor including a matrix of photo-sensitive pixels;

computing a maximum relative angular velocity associated with the target object based on the exposure time and a dimension of a pixel in the matrix of pixels;

identifying a first pointing direction of the image sensor for initiating a search for the target object;

accessing target object orbital data;

generating, based on the first pointing direction and the target object orbital data, a first angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the first pointing direction;

dividing the first angular velocity probability distribution map into a first set of angular velocity regions (AVRs), each AVR having a central angular velocity and having a size corresponding to the computed maximum relative angular velocity, wherein the size of each AVR is at most as large as the maximum relative angular velocity;

selecting a first AVR from the first set of AVRs for scanning by the image sensor; and

generating a search schedule that includes a first entry for informing the spacecraft to scan the first AVR, where scanning the first AVR comprises positioning the image sensor at the first pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the first AVR.

36. A computer program product, embodied in a non-transitory computer-readable medium and including instructions executable by a processor, the instructions when executed configured to cause the processor to perform operations comprising:

determining an exposure time associated with an image sensor coupled to a spacecraft for capturing an image of a target object orbiting the Earth, the image sensor including a matrix of photo-sensitive pixels;

computing a maximum relative angular velocity associated with the target object based on the exposure time and a dimension of a pixel in the matrix of pixels;

identifying a first pointing direction of the image sensor for initiating a search for the target object;

accessing target object orbital data;

generating, based on the first pointing direction and the target object orbital data, a first angular velocity probability distribution map that indicates probabilities of the target object having different angular velocities as viewed by the image sensor when the image sensor is pointing in the first pointing direction;

dividing the first angular velocity probability distribution map into a first set of angular velocity regions (AVRs), each AVR having a central angular velocity and having a size corresponding to the computed maximum relative angular velocity, wherein the size of each AVR is at most as large as the maximum relative angular velocity;

selecting a first AVR from the first set of AVRs for scanning by the image sensor; and

generating a search schedule that includes a first entry for informing the spacecraft to scan the first AVR, where scanning the first AVR comprises positioning the image sensor at the first pointing direction and rotating the image sensor at an angular speed and direction corresponding to the central angular velocity of the first AVR.