Siding Spring Fixed Incoming Direction SPK File ========================================================================= Version 0.1 -- November 10, 2014 -- BVS/NAIF Abstract ======================================================= This SPK contains fixed positions of two bogus objects -- IDs 1003228001 and 1003228002 -- that are intended to represent direction opposite of Mars-relative velocity of the comet Siding Spring tail degree. The position of the first object -- 1003228001 -- represents this direction computed as the geometric position of Siding Spring as seen from the center of Mars in the MARSIAU frame at 2014-10-15 00:00:00 UTC (slightly less than 5 days before closest approach) and scaling this position to 1 AU to make this object a distant observer. The position of the second object -- 1003228002 -- represents this direction computed as the inertial geometric anti-velocity of Siding Spring as seen from the center of Mars in the MARSIAU frame at 2014-10-19 18:27:31.351224 UTC, which is the time of closest approach of the comet to Mars based on this SPK (provided on the NAIF Web site, http://naif.jpl.nasa.gov/) pub/naif/M01/misc/ss/css_horizons_141110.bsp and scaling this position to 1 AU to make this object a distant observer. The actual vectors relative to Mars in MARSIAU frame are provided below in the _XYZ keywords. The angular separation between these two directions is ~0.339 degrees. Appendix: PINPOINT Inputs ======================================================= \begindata SITES += 'SIDING_SPRING_A' SIDING_SPRING_A_CENTER = 499 SIDING_SPRING_A_FRAME = 'MARSIAU' SIDING_SPRING_A_IDCODE = 1003228001 SIDING_SPRING_A_XYZ = ( 143399212.46186602 -36933584.22182135 -21262622.78864780 ) SIDING_SPRING_A_BOUNDS = ( @2013-AUG-01, @2014-DEC-01 ) SITES += 'SIDING_SPRING_V' SIDING_SPRING_V_CENTER = 499 SIDING_SPRING_V_FRAME = 'MARSIAU' SIDING_SPRING_V_IDCODE = 1003228002 SIDING_SPRING_V_XYZ = ( 143166886.47198248 -37406026.54046664 -21989877.27065506 ) SIDING_SPRING_V_BOUNDS = ( @2013-AUG-01, @2014-DEC-01 ) \begintext End of PINPOINT inputs.