File:     mex_cruise.bsp    
Created:  20 June 2001 by NAIF/NJB
Bodies:   MEX (NAIF ID -41)
Coverage:

   Start of Interval (ET)              End of Interval (ET)
   --------------------------------    --------------------------------
   2003 JUN 01 19:23:40.071            2004 JAN 07 01:13:10.817


This SPK file contains a Mars Express predict cruise ephemeris.
This ephemeris is an approximation to that provided by an
ESOC orbit file named Mars_Express_orbit (obtained from Chuck Acton).  

This SPK file was made by sampling states from the ESOC source
ephemeris using the ESOC reader routines 

   ROFOP
   ROFRR
   RBINFO

and writing one SPK segment per "block" in the input ephemeris.
Within each block, states were sampled at equally spaced intervals,
with the spacing dependent on the time span covered by the block.

The fit of the ephemeris provided in this SPK file to the source 
ephemeris was tested by comparing states sampled from each input block 
and from each corresponding output SPK segment.  The sampling was
done at a density of 10000 states/block.  The worst-case position 
errors over all samples were < 2cm.  The worst-case velocity errors 
were < 3 micron/sec.

This file uses type 9 SPK segments (variable-spacing sliding window 
Lagrange interpolation for each state component).  

Note concerning SPK data type selection:  because the velocity data from 
the source ephemeris were presumed not to exactly match the time 
derivatives of the position data, independent interpolation of 
position and velocity was considered desirable.  An experiment was 
done using Hermite interpolation; that method yielded a very inferior 
velocity fit.


 -Nat Bachman