MEX Orbit Number Files
======================
This "aareadme.txt" file describes the contents of the kernels/orbnum
directory of the MEX SPICE data server. It also provides the file naming
conventions used for the MEX Orbit Number files, and it provides
identification of the most current version of each kind of ORBNUM file.
These are created from the SPK files converted from the ESOC's DDID Orbit
Files.
Orbit Number files (*.ORB) contained in this directory are unix text files.
These may be used in a non-compatible text environment by using the ASCII
mode of FTP to port the files.
Contact
ESA SPICE Team spice@sciops.esa.int
, or
Alfredo Escalante Lopez aescalante@sciops.esa.int
if you have any questions.
References
==========
1. Data Delivery Interface Document (DDID) Appendix H - FD
products Issue 3.0 (MEX-ESC-IF-5003)
Important Note Regarding Orbit Number Files
===========================================
In the Mars Express orbit number files produced by NAIF's ORBNUM utility
program each of the records contains the time of THAT orbit's pericenter and
the time of the NEXT orbit's apocenter. For example, the line for orbit '3'
provide UTC and SCLK of orbit '3' pericenter and UTC of orbit '4' apocenter.
Since the project accepted orbit numbering scheme dictates the orbit number
change to occur at apocenter, the time boundaries for a given orbit can be
determined by taking the apocenter time from the PREVIOUS orbit record and
the apocenter time from THIS orbit record.
Orbit number 1 corresponds to the first mapping orbit, 2004 JAN 4.
All derived quantities provided on each record -- sub-solar lon/lat,
sub-spacecraft lon/lat/alt, and orbital elements -- are computed for the
time of pericenter.
Example
-------
This is an example of MEX orbit number file (spacing was altered to fit the
page):
No Event UTC PERI Event SCLK PERI OP-Event UTC APO ...
== ==================== ================ ==================== ...
1 2003 DEC 30 14:31:08 1/031415532.6386 2003 DEC 30 18:18:32 ...
2 2003 DEC 30 22:05:53 1/031442817.0170 2003 DEC 31 01:53:20 ...
3 2003 DEC 31 05:40:46 1/031470110.0775 2003 DEC 31 09:28:11 ...
4 2003 DEC 31 13:15:33 1/031497397.5425 2003 DEC 31 17:03:01 ...
...
Given this example one can determine that:
-- orbit 3 pericenter time is ''2003 DEC 31 05:40:46''
-- orbit 3 time boundaries are from ''2003 DEC 31 01:53:20'' to
''2003 DEC 31 09:28:11''
Mars Express Orbit Number Directory Structure
=============================================
aareadme.txt This file.
former_versions Subdirectory that contains obsolete
versions of the ORBNUM files that have been
updated in the Current ORBNUM File Set.
ORMF_______________xxxxx.ORB Contains Mars Express orbit pericenter and
apocenter times, orbital elements, and
additional geometry parameters computed
from the SPK long term file named:
ORMF_______________xxxxx.BSP
where xxxxx designates the version number.
This is the predicted file that should be
used for planning.
ORMM_MERGED_xxxxx.ORB Contains Mars Express orbit pericenter and
apocenter times, orbital elements, and
additional geometry parameters computed
from the latest set of ORMM SPK files
available in the FTP server. xxxxx
designates the version number. This file
corresponds to the reconstructed orbit of
the spacecraft, and therefore should be
used for data analysis, but not for
planning.
ORMC_FD_xxxxxxxxxxxxxxxx.BSP Contains MEX spacecraft long term orbit
pericenter and apocenter times, orbital
elements, and additional geometry
parameters computed from the corresponding
ORMC spk kernel. This files are used in
order to analyse different options before
implementing the long term operational
orbit (ORMF).
-------------------
This file was last modified on March 22th, 2021. (R. Valles)
End of aareadme file.