Autonomous Vision Based Detection of Non-stellar Objects Flying in formation with Camera Point of View SFFMT 213 München May 31 st 213 Mathias Benn, As.Prof, PhD John L. Jørgensen, Prof. DTU Space
Overview Introduction The PRISMA Mission The µ-advanced Stellar Compass (µasc) The Vision Based Sensor (VBS) System Far Range Object Tracking VBS Data Analysis Tracked Non-Stellar Objects (NSOs) Objects Characteristics Detection Frequency Pointing Accuracy towards Known Target. Future Implementations Conclusion 2 DTU Space, Technical University of Denmark
The PRISMA Mission A technical demonstration satellite mission Attitude Control Systems: Magnetourqers (Main + Target) Hydrazine HPGP Microprop Reaction wheels Navigation Sensors: GPS Formation Flying RF Vision Based Sensor Navigation Modes: Autonomous Formation Flying Homing and Rendezvous Proximity Operations Final Approach and Recede Target Two standard STR CHUs on backside Short Range CHU Far Range CHU Main Image: SSC 3 DTU Space, Technical University of Denmark
The μasc Instrument Instrument performance: High precision attitude determination (<2 for XY, <2 for Z) Low light instrument (Dynamic range: +7-4 in magnitude) Down to 4Hz attitude update frequency 4 DTU Space, Technical University of Denmark
VBS Modes Far Range: Stars can be detected in coordination with detection of the Target spacecraft, enabling attitude determination of the Far Range CHU. Intermediate Range: Stars are undetectable due to the brightness of the Target spacecraft, and no features of the Target can be detected. Short Range: Features of the Target spacecraft are detectable. Non-cooperative: Target spacecraft is passive, only illuminated by the ambient scene radiance. Cooperative: Target provides detectable feature points in specific geometric patterns. 5 DTU Space, Technical University of Denmark
Far Range Method Determine Target spacecraft from all objects seen by the CHU. Determine inertial pointing towards Target spacecraft in reference to Main spacecraft. 6 DTU Space, Technical University of Denmark
What Do We See 7 DTU Space, Technical University of Denmark
Rerun of VBS Algorithms on Recorded Centroids Recorded NSO Objects 2.5 x 16 2 1.5 1.5 Number of Recorded NSO Objects for the µasc on PRISMA CHU A CHU B CHU C CHU A 2898486 CHU B 15754 CHU C 217739 Total 6126549 Number of detected NSO s Q2-1 Q3-1 Q4-1 Q1-11 Q2-11 Q3-11 Q4-11 Q1-12 Time UTC Rerun of the VBS algorithms is performed on recorded centroid data from the three startracker CHUs. Namely: CHU A, B and C. More than 3hours of centroids recorded at 2Hz has been processed. From all the centroids, ~6millions are marked as Non-Stellar Objects (NSOs). VBS algorithms are similar to the inflight algorithms with the extension of outputting all tracked objects. 8 DTU Space, Technical University of Denmark
Tracked Objects Detected Centroids of Tracked Objects for CHU B with Tracking History > 2 Detected Centroids of Tracked Objects for CHU C with Tracking History > 2 1 1 1 2 2 2 3 CCD Y [pxl] CCD Y [pxl] CCD Y [pxl] Detected Centroids of Tracked Objects for CHU A with Tracking History > 2 3 3 4 4 4 5 5 5 1 2 3 4 CCD X [pxl] 5 6 7 1 CHU A 2 3 4 CCD X [pxl] CHU B 5 6 7 1 2 3 4 CCD X [pxl] 5 6 CHU C Different inflight scenarios experienced by the CHUs. CHU A: Inertial pointing stability test, pointing perpendicular to the orbit plane. CHU B: Normal operation while pointing ~45º off the orbit plane. CHU C: Mainly with the Target spacecraft in FoV while pointing along the orbit flight path. 9 DTU Space, Technical University of Denmark 7
Tracked Objects Detected Centroids of Tracked Objects for CHU A with Tracking History > 2 Detected Centroids of Tracked Objects for CHU B with Tracking History > 2 Detected Centroids of Tracked Objects for CHU C with Tracking History > 2 1 1 1 2 2 2 CCD Y [pxl] 3 CCD Y [pxl] 3 CCD Y [pxl] 3 4 4 4 5 5 5 1 2 3 4 5 6 7 CCD X [pxl] CHU A 1 2 3 4 5 6 7 CCD X [pxl] CHU B 1 2 3 4 5 6 7 CCD X [pxl] CHU C Different inflight scenarios experienced by the CHUs. CHU A: Inertial pointing stability test, pointing perpendicular to the orbit plane. CHU B: Normal operation while pointing ~45º off the orbit plane. CHU C: Mainly with the Target spacecraft in FoV while pointing along the orbit flight path. 1 DTU Space, Technical University of Denmark
Object Characteristics 1 5 Representation of the Sequential Tracked Objects 1 4 CHU A CHU B CHU C 1 4 1 3 Number of Tracked Objects based on Angular Velocities CHU A CHU B CHU C Sequential tracking history 1 3 1 2 1 1 Number of tracked objects 1 2 1 1 1 1 1 1 1 2 1 3 1 4 Number of tracked outputs 1 1 2 3 4 5 6 7 Bins of mean angular velocity ["/s] CHU A have with the long durations of steady inertial pointings resulted in accomplishing great tracking history of detected objects. CHU B reflect tracking of objects that are similar to each other. CHU C is very likely to have the Target spacecraft available for tracking, illustrated by the peak in angular velocities. 11 DTU Space, Technical University of Denmark
Frequency of Tracked Objects 5 45 Time Difference Between Detection of NSOs with a Tracking History of 1 Detections PRISMA Orbit Period 16 14 Time Difference Between Detection of NSOs with a Tracking History of 1 Detections PRISMA Orbit Period Number of detected objects in bin 4 35 3 25 2 15 1 Number of detected objects in bin 12 1 8 6 4 5 2 1-1 1 1 1 1 2 1 3 1 4 1 5 Bins of time difference between detections [s] 1-1 1 1 1 1 2 1 3 1 4 1 5 Bins of time difference between detections [s] Objects with short tracking history provides frequencies at the update rate of the CHU system. Objects with long duration tracking synchronizes up with the orbital rate of PRISMA. 12 DTU Space, Technical University of Denmark
Pointing Accuracy towards Known Target 12 1 Deviation Between Predicted VBS Pointings and Detected Pointings Over Distance from Main to Target VBS Output Theoretical Max Mean prediction deviation ["] 8 6 4 2.5 1 1.5 2 2.5 3 3.5 Distance between Main and Target [m] x 1 4 The theoretical expected maximum is based on the angular size of the Target spacecraft from where reflections can occur, together with the centroiding accuracy of the µasc system. For distances below 1km the deviation is within the expected maximum The few samples at ~3km is just on the boundary due to acceleration of the Target spacecraft during approach and recede maneuvers. 13 DTU Space, Technical University of Denmark
Future Implementations Several missions are including the VBS algorithms for both formation flying, spacecraft tracking, landmark tracking and asteroid detection. The full autonomy of the system has enabled the usage of the VBS system on Sample-Return missions. The VBS system is planned to be combined with several subsystems: µ-inertial Reference Unit (MIRU): 6DOF strapdown inertial sensor package integrated with the µasc standard CHU or VBS CHU, increasing attitude update rate from 4Hz to 2Hz. Infrared Camera: Detects wavelengths of 14-16um with a resolution of 64x48 pixels. LTCC Microthruster: A micromachined nozzle system with the dimensions of 17x17x3mm. In vacuum the predicted power efficiency is.5 mun/mw with a specific impulse of 12s. 14 DTU Space, Technical University of Denmark
Conclusion By post-processing of inflight recorded centroid data, it has been shown that the VBS system is very much capable of detecting and tracking several Non-stellar Objects simultaneously. From a satellite orbiting the Earth, all satellites detectable by the star tracker CHUs can be tracked as soon as their inertial angular movement, with respect to the Main spacecraft, fits within the bandpass values provided to the VBS system. The VBS system is capable of providing high accuracy inertial pointings of all tracked objects in combination with key tracking information, that can be used for determine the confidence and precision of the detected object. Different boresight pointings relative to flight path have shown a wide covering range for tracking of fast and slow moving NSOs. The full autonomy of the VBS system is especially useful for missions with limited commandability, such as e.g. Sample-Return missions. 15 DTU Space, Technical University of Denmark
Thank you for your attention AD ASTRA PER ASPERA Surmounting adversity reaching for the stars 16 DTU Space, Technical University of Denmark
Slide appendices 17 DTU Space, Technical University of Denmark
FR CHU Running Hot 18 DTU Space, Technical University of Denmark
FR CHU Running Hot 19 DTU Space, Technical University of Denmark