Geodätische Woche Congress Center Essen, 8.- 10. Oktober 2013 SLR-based orbit determination and orbit prediction of space debris objects Harald Wirnsberger, Oliver Baur, Georg Kirchner Space Research Institute Austrian Academy of Sciences
Space Debris a few facts 16805 tracked objects in Earth orbit (NORAD satellite catalogue) NORAD TLE from https://www.space-track.org on 23.08.2013 2
Space Debris a few facts payload in orbit: 3752 (22%) debris objects: 13053 (78%) NORAD TLE from https://www.space-track.org on 23.08.2013 3
Space Debris a few facts only 7% corresponds to active satellites NORAD TLE from https://www.space-track.org on 23.08.2013 4
Space Surveillance Network part of the United States Strategic Command detects, tracks and catalogs objects > 10 cm active/inactive satellites spent rocket bodies fragmentation debris illustration from http://www.stratcom.mil/ distribution in NORAD Two Line Elements (TLE) format using ground-based radar and passive optical tracking low accuracy of predicted orbits (several hundreds of meters to kilometers) 5
Presentation: USA Space Debris Environment, Operations, and Policy Updates 49. Session of Committee on the Peaceful Uses of Outer Space - United Nations, February 2012 6
Presentation: USA Space Debris Environment, Operations, and Policy Updates 49. Session of Committee on the Peaceful Uses of Outer Space United Nations, February 2012 Presentation: Active Debris Removal:current status of activities in CNESIAF Workshop on Space Debris Removal United Nations, February 2013 7
SLR comes into play Graz observatory demonstrated laser ranging to Space Debris objects in January 2012 Laser capable to measure Space Debris objects pulse energy of 25 mj at 532 nm on loan from German Aerospace Center Stuttgart (DLR) standard Laser in Graz 1 khz repetition rate with pulse width of 10 ns 2 khz repetition rate with pulse width of 0.01 ns and pulse energy of 0.4 mj at 532 nm challenging measurements relatively few return rates, technological challenges, single photon detection,... 8
case study: ENVISAT Why ENVISAT? one of the highest priorities debris since 08.04.2012 LEO: 780 820 km altitude at 98 inclination mass: 8 tons / size: 10 m x 4 m x 4 m equipped with Laser Retro Reflectors (LRR) idealised Space Debris object (tracked by ~ 15 SLR stations) orbit determination and prediction (software GEODYN2) estimated parameters in orbit determination process 6 elements of state vector empirical accelerations (along track) atmospheric drag coefficient ( cd ), solar radiation coefficient ( cr ) measurement bias per station 6 day orbit prediction using estimated parameters 9
quality of TLE predicted orbits 6 day orbit prediction of ENVISAT based on TLE compared to SLR determined reference orbit: several hundreds of meters to kilometers accuracy depends on age of prediction along track component is critical 10
benefit of SLR SLR based orbit prediction compared to SLR determined reference orbit: number of observations: 208 normal points uncertainty of about 100 m after 3 days of prediction along track error dominating 11
an absolute measure SLR residuals of ENVISAT observed predicted (in SLRF05) considering displacement due to solid earth tides, ocean tides, pole tides and ocean loading (IERS 2010) tropospheric delay according to Mendes- Pavlis model no center of mass correction applied one order of magnitude smaller uncertainty of AAS prediction based on SLR observations 12
comparison of SLR residuals Austrian Academy of Sciences (AAS) Range Bias: -0.32 m Time Bias: -23 ms German Aerospace Center (DLR) Range Bias: -5.59 m Time Bias: -25 ms Space Geodesy Facility, UK (SGF) Range Bias: 11.21 m Time Bias: +41 ms but TB and RB are station dependent! 13
challenges estimation of ~20 parameters from a subset of a few SLR observations to ENVISAT: temporal distribution spatial distribution critical task for LEO objects is atmospheric modelling atmospheric density model ballistic coefficient, solar activity, geomagnetic indices,... 14
Conclusion SLR can NOT provide a complete Space Debris catalogue, but: TLE predictions serve as early warning system SLR provide precise orbit information of hazardous objects accurate laser-determined orbits help to improve predictions of Space Debris objects avoid unnecessary anti-collision manoeuvres allow active debris removal save fuel and extend life times of active satellites AAS ENVISAT predictions are available on ILRS homepage: ftp://cddis.gsfc.nasa.gov/pub/slr/cpf_predicts/2013/envisat/ 15
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Danke für die Au f m k am ks er eit 17
quality of reference orbit SLR residuals of reference orbit: no center of mass correction applied (attitude?) X [m] Y [m] Z [m] SLR array offset -4.920 +1.350-1.180 CoM correction -3.862-0.009 +0.003 713 normal points RMS: 5.2 m mean: 0.002 m Source: ILRS homepage, http://ilrs.gsfc.nasa.gov/missions/ 18