The Need for Comparative SSA T.S. Kelso & Dan Oltrogge Center for Space Standards & Innovation 2018 Oct 5

Overview Introduction Background Case Studies Conclusions IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Introduction Segal’s Law: A man with a watch knows what time it is. A man with two watches is never sure. Reality is quite a bit different Example: Timekeeping at USNO, BIPM, GPS Comparing data against similar independent data: Minimizes uncertainty and associated risk Identifies outliers to help eliminate problems affecting safety of flight IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Background Satellite operators are developing independent SSA for their systems Motivated by perceived lack of quality & others’ unwillingness to share Many believe they only need good data for their satellites Reluctant to exchange orbital data Motivated by national security or commercial competitiveness Implicitly assumes independent systems are immune to unexpected errors Space Data Center (SDC) Ingests data from 30 operators & JSpOC for conjunction assessment ~270 GEO & ~440 LEO/MEO satellites with ephemerides Gets full TLEs & SP ephemerides for full public catalog from JSpOC Routinely performs comparative assessments in daily operations Shares data & results with affected parties to ensure better overall SSA IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Case Study #1 Initial validation of new user found problems with 2 satellites’ data Comparison of ephemerides & TLEs differed by over 10,000 km 3D analysis ultimately showed problem was due to incorrect reference frame used in operator’s JSpOC-formatted data (ITRF vs. J2000) Problem had gone undetected for over six months in data exchange with JSpOC Proper comparative analysis should have caught this problem immediately, as it did in the SDC IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Case Study #2 Problem detected comparing ephemerides used by JSpOC in CA screening using operator ephemerides provided by SDC Using the same ephemeris, difference should be less than 10 m (due to EOP) Situation arose where difference was > 100 km Subsequent analysis showed an anomaly in the operator data, as the mismodeling of a maneuver Resulting JSpOC conversion of data for CDM produced GEO orbit with perigee altitude below the Earth’s surface (-2,132 km) Operator advised of anomalous data; JSpOC advised, as well All SDA members advised of how to detect this type of situation IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Case Study #3 Problem detected in comparing SDC & JSpOC ephemerides (provided by operator) at TCA Difference of ~12,000 km detected Separate weekly comparative analysis showed no discrepancy Comparison of piecewise ephemerides pointed to a problem with operator ephemerides Five of eleven ephemerides were bad over 15 days Time tag in JSpOC format incorrectly calculated the day of the year on some dates Adjusting bad ephemerides by one full day corrected the problem Weekly comparisons happened to use good data Operator advised of results and took corrective action IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Case Study #4 Problem detected in weekly comparative analyses for GEO Only occurred for SES and when TLE had epoch of 0000 UTC Showed as TLE jumping away from SDC ephemeris and drifting Occurred for more than a dozen satellites with differences of 50-100 km IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Case Study #4 Problem detected in weekly comparative analyses for GEO Only occurred for SES and when TLE had epoch of 0000 UTC Showed as TLE jumping away from SDC ephemeris and drifting Occurred for more than a dozen satellites with differences of 50-100 km Ultimately determined the problem was caused by Millstone using SES data to generate TLEs, which were then added to the public catalog Data was simply reformatted as TLE, even though it used osculating elements and True of Date reference system, instead of Brouwer mean elements and TEME JSpOC was advised of the problem SDC (via CelesTrak) created supplemental TLEs to address JSpOC need IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Other Cases Missed maneuvers Cross-tagging Natural consequence of not incorporating planned maneuvers Supplemental TLEs provided by SDC to JSpOC to resolve issues Cross-tagging Can occur often in GEO clusters Complicated by maneuvers and time of day, daylight, weather Problems are immediately reported to JSpOC to ensure best-possible SSA is available to the entire community for safety of flight IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Conclusions These are just a few of the problems detected and reported All systems fail at some point Bad input data Incorrectly formatted data or an unanticipated change in format Faulty algorithms or the application of algorithms in situations outside of their expected use Problems converting data from one format to another Misunderstanding of coordinate systems or other metrics being used Unnoticed failures in data transfer that may lead to data latency Regular comparative analyses help identify issues for resolution IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5

Questions? IAC-18-A6.7.8 69th International Astronautical Congress (IAC), Bremen, Germany, 2018 October 1-5