[Spice_announce] New JPL Martian Satellite Ephemeris: MAR063

[Charles H. Acton]

A new ephemeris for the Martian satellites, named MAR063, has been 
released by JPL's Solar System Dynamics Group. This replaces the 
MAR033 ephemeris produced many years ago.

The time span of the file is approximately:

   START:  1962 DEC 04
   STOP:   2024 DEC 30

A SPICE SPK version of this ephemeris is available from the NAIF server at:

  ftp://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/satellites/


A description of this ephemeris is also available from the NAIF server at:

   ftp://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/satellites/mar063.pdf


A comparison was made of the mar063 and maro33 ephemerides for Phobos 
during the short, current time span of 2005 JAN 01 to 2007 JAN 01, 
using one hour as the step size for sampling both files. The 
statistical results of that comparison are shown below.

    Components of the position difference vector (in view frame coordinates)
    for the states with the MAXIMUM ABSOLUTE difference in position:

    5a) Down track (km):                        11.581808003063

    5b) In orbit plane (km):                    0.0060556985163999

    5c) Normal to orbit plane (km):            -0.41535988013494

    5d) Delta time down track (sec):            5.5001968830593

    5e) Epoch (TDB, seconds past J2000):        219549664.18393

    5f) Epoch (TDB, calendar format):           2006-DEC-16-14:01:04.183

This shows the primary difference being in the down track component 
(~11.5 km), which is equivalent to about 5.5 seconds. The epoch of 
this maximum difference is 2006 DEC 16.


An identical comparison, except now covering the somewhat longer 
period of 2003 JAN 01 to 2010 JAN 01 yields the following statistical 
differences.

    Components of the position difference vector (in view frame coordinates)
    for the states with the MAXIMUM ABSOLUTE difference in position:

    5a) Down track (km):                        12.969271330750

    5b) In orbit plane (km):                    0.076607193804452

    5c) Normal to orbit plane (km):            -0.61847498050010

    5d) Delta time down track (sec):            6.1580222336082

    5e) Epoch (TDB, seconds past J2000):        314564464.18392

    5f) Epoch (TDB, calendar format):           2009-DEC-20-07:01:04.183

These numbers are consistent with the memo documenting the ephemeris 
(mar063.pdf) showing the difference in the down track component 
growing constantly over the span of the ephemeris, starting from 
around 1980.


A comparison done for Deimos during the 2005 to 2007 period yields 
these statistical differences.

    Components of the position difference vector (in view frame coordinates)
    for the states with the MAXIMUM ABSOLUTE difference in position:

    5a) Down track (km):                        54.504575054250

    5b) In orbit plane (km):                    1.9026579897473

    5c) Normal to orbit plane (km):             18.431650434469

    5d) Delta time down track (sec):            40.331102204122

    5e) Epoch (TDB, seconds past J2000):        220683664.18393

    5f) Epoch (TDB, calendar format):           2006-DEC-29-17:01:04.183

The difference in the down track component for Deimos also grows 
constantly over the span of the ephemeris, starting from around 1980.