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MEX Orbit Number Files
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Last update: 22 MAR 2004
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. [Ref 2a]
Contact Jorge Diaz del Rio (jdiaz@rssd.esa.int) or Joe Zender
(Joe.Zender@esa.int) if you have any questions regarding this file.
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References
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1. Data Delivery Interface Document (DDID) Appendix H - FD
products Issue 1.3 (MEX-ESC-IF-5003)
2. Selected SPICE Tutorials from the NAIF server:
ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/office/individual_docs/
a) Porting Kernels Tutorial 09_porting_kernels.ppt
b) Derived Quantities Tutorial 21_derived_quant.ppt
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Important Note Regarding Orbit Number Files
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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 13
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.
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Example
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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''
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Mars Express Orbit Number Directory Structure
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aareadme.txt Text file describing the directory structure, the naming
conventions for the ORBNUMs, and the current version(s)
of each file.
former_versions Subdirectory that contains obsolete versions of the
ORBNUM files that have been updated in the Current
ORBNUM File Set.
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MEX Orbit Number Naming Covention ffff_______________vvvvv.ORB
ffff_MERGED_vvvvv.ORB
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token description
------------ --------------------------------------------------
ffff Source Product Type Identifier:
ORMF -- S/C Orbit, Mars centric. Long
Term Planning
ORMM -- S/C Orbit, operational, Mars
centric.
vvvvv version number
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Current Orbit Number File Set
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Name Comments
------------------------------ -----------------------------------------------
ORMF_______________xxxxx.ORB Contains Mars Express orbit pericenter and
apocenter times, orbital elements, and
additional geometry parameters computed from
the SPK file named:
ORMF_______________xxxxx.BSP
where xxxxx designates the version number.
the biggest number, the latest version.
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.