Satellite Orbit and Ephemeris Determination using Inter Satellite Links
Satellite Orbit and Ephemeris Determination using Inter Satellite Links Satellite Orbit and Ephemeris Determination using Inter Satellite Links
Autonomous Onboard ProcessingInter Satellite LinksAs can be seen from the figure above, the state is not estimated very well, due to the highprocess noise required to keep the filter adaptable to fast changes. The error estimate of such aKalman filter is far too noisy to be used as a correction value, but it is sufficient to detect orbiterrors. To evaluate the reaction of the onboard processor to the injected fault, the error log ofall satellites is shown below. It has the following format < Day> SV 1998 07 01 12:02:59.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:00.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:00.000 SV 26 Non Detected Position Error = 0.351 m1998 07 01 12:03:01.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:01.000 SV 26 Non Detected Position Error = 0.652 m1998 07 01 12:03:02.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:02.000 SV 26 Non Detected Position Error = 0.827 m1998 07 01 12:03:03.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:03.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:03.000 SV 26 Check Result: NO GO1998 07 01 12:03:03.000 SV 27 Removed Unhealthy SV ID 261998 07 01 12:03:03.000 SV 28 Removed Unhealthy SV ID 261998 07 01 12:03:03.000 SV 29 Removed Unhealthy SV ID 261998 07 01 12:03:03.000 SV 30 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 00 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 01 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 02 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 03 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 04 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 05 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 06 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 08 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 09 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 10 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 11 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 12 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 13 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 14 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 15 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 16 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 17 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 18 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 19 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 20 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 21 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 22 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 23 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 24 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 25 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 26 Chi Square Test Failed1998 07 01 12:03:04.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:04.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:04.000 SV 26 Check Result: NO GO1998 07 01 12:03:05.000 SV 26 Chi Square Test Failed1998 07 01 12:03:05.000 SV 26 Ramp Detected [Position]Page 176R. Wolf
Inter Satellite LinksAutonomous Onboard Processing1998 07 01 12:03:05.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:05.000 SV 26 Check Result: NO GO1998 07 01 12:03:06.000 SV 26 Chi Square Test Failed1998 07 01 12:03:06.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:06.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:06.000 SV 26 Check Result: NO GO1998 07 01 12:03:07.000 SV 26 Chi Square Test Failed1998 07 01 12:03:07.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:07.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:07.000 SV 26 Check Result: NO GO1998 07 01 12:03:08.000 SV 26 Chi Square Test Failed1998 07 01 12:03:08.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:08.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:08.000 SV 26 Check Result: NO GO1998 07 01 12:03:09.000 SV 26 Chi Square Test Failed1998 07 01 12:03:09.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:09.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:09.000 SV 26 Check Result: NO GO1998 07 01 12:03:10.000 SV 26 Chi Square Test Failed1998 07 01 12:03:10.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:10.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:10.000 SV 26 Check Result: NO GO1998 07 01 12:03:11.000 SV 26 Chi Square Test Failed1998 07 01 12:03:11.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:11.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:11.000 SV 26 Check Result: NO GO1998 07 01 12:03:12.000 SV 26 Chi Square Test Failed1998 07 01 12:03:12.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:12.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:12.000 SV 26 Check Result: NO GO1998 07 01 12:03:13.000 SV 26 Chi Square Test Failed1998 07 01 12:03:13.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:13.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:13.000 SV 26 Check Result: NO GO1998 07 01 12:03:13.000 SV 26 Switched OffThe event takes place at 12:02:55. Four seconds later, a position drift is detected (the rampdetector has a threshold of 2 cm/s). At this time, the satellites position is still within the 1x1x1meter cube and therefore still considered to be integer. Another second later, the integritylimit of one meter is exceeded by 0.3 meters, but the estimated error is still within the limit.This is the first time a real non-integrity case exists, because the user has a hazardousmisleading information. He still used SV 26 although the orbit parameters are not correctanymore. The position error remains undetected for another two seconds and grows to nearly1 meter, before the estimated position error is large enough to trigger a NO GO. From nowon, the user is alarmed and will discontinue to use SV 26.In the next epoch, all other satellites will exclude SV 26 from their integrity processing. Onesecond after the state limit check has detected the error, the Chi Square test also raises analarm.As a result of the simulation, the user has been alarmed 3 seconds after occurrence of the nonintegritysituation, which is an acceptable time to alarm event for a CAT I landing (6 secondsR. Wolf Page 177
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Autonomous Onboard Processing<strong>Inter</strong> <strong>Satellite</strong> <strong>Links</strong>As can be seen from the figure above, the state is not estimated very well, due to the highprocess noise required to keep the filter adaptable to fast changes. The error estimate of such aKalman filter is far too noisy to be used as a correction value, but it is sufficient to detect orbiterrors. To evaluate the reaction of the onboard processor to the injected fault, the error log ofall satellites is shown below. It has the following format < Day> SV 1998 07 01 12:02:59.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:00.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:00.000 SV 26 Non Detected Position Error = 0.351 m1998 07 01 12:03:01.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:01.000 SV 26 Non Detected Position Error = 0.652 m1998 07 01 12:03:02.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:02.000 SV 26 Non Detected Position Error = 0.827 m1998 07 01 12:03:03.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:03.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:03.000 SV 26 Check Result: NO GO1998 07 01 12:03:03.000 SV 27 Removed Unhealthy SV ID 261998 07 01 12:03:03.000 SV 28 Removed Unhealthy SV ID 261998 07 01 12:03:03.000 SV 29 Removed Unhealthy SV ID 261998 07 01 12:03:03.000 SV 30 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 00 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 01 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 02 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 03 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 04 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 05 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 06 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 08 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 09 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 10 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 11 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 12 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 13 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 14 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 15 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 16 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 17 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 18 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 19 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 20 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 21 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 22 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 23 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 24 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 25 Removed Unhealthy SV ID 261998 07 01 12:03:04.000 SV 26 Chi Square Test Failed1998 07 01 12:03:04.000 SV 26 Ramp Detected [Position]1998 07 01 12:03:04.000 SV 26 Limit Exceeded [Position]1998 07 01 12:03:04.000 SV 26 Check Result: NO GO1998 07 01 12:03:05.000 SV 26 Chi Square Test Failed1998 07 01 12:03:05.000 SV 26 Ramp Detected [Position]Page 176R. Wolf
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