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XMM-Newton Science Analysis System Page: 1
orbit
January 10, 2003
Abstract
Create a FITS timeseries \HK-like" le from the ODF Spacecraft Reconstructed
Orbit File.
1 Instruments/Modes
Instrument Mode
EPIC ALL
RGS ALL
OM ALL
2 Use
pipeline processing yes
interactive analysis yes
3 Description
This task makes position information from the XMM ODF available as a FITS format product le. It has
been determined that this product would have value both for constructing Good Time Intervals (using
tabgtigen) based on orbit information, and for possibly creating barycentric correction tables. It is felt
that a FITS format le conforming as much as possible to established Orbit le conventions would be
more useful than the ascii Orbit le provided in the ODF.
This task will utilise the OAL getPosition routine to return the x-y-z components of the position vector
in km as well as the x-y-z components of the corresponding velocity vector in km/s, both with respect
to the reference Kepler orbit. Both sets of values will be written into a standard OGIP-compliant FITS
binary extension table with a TIME column value, derived from a start, stop and sampling interval time,
each specied by the user. This task will default to sampling the entire input le with a timestep interval
of 60.0 seconds.
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3.1 Detailed Description
The ODF Orbit le iis described in [1]. The Periodic Housekeeping data is described in [2].
4 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
outle yes string none valid le name
Output orbit lename in FITS.
selecttimes no boolean no yes|no
Input starttime and endtimes or use default whole le.
starttime no real|stringnone >0.0 s
Start time for interval in any param \TIME" format.
endtime no real|stringnone >0.0 s
End time for interval in any param \TIME" format.
timestep no real 60.0 >0.0 s
Bin size (in sec) of step through Orbit information.
Note: The only param TIME format supported currently is
the \seconds since XMM reference time" mode.
5 Errors
This section documents warnings and errors generated by this task (if any). Note that warnings and
errors can also be generated in the SAS infrastructure libraries, in which case they would not be docu-
mented here. Refer to the index of all errors and warnings available in the HTML version of the SAS
documentation.
StartANDEndNotInODFRange (error)
Start AND End times
selected not congruent with input ODF obs times.
StarttimeGTEndtime (error)
Starttime entered greater
than Endtime entered.
StartDefault (warning)
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corrective action: Start time entered less than ODF obs start time Default to obs start
time from ODF
EndDefault (warning)
corrective action: End time entered greater than ODF obs end time Default to obs end
time from ODF
StartANDEndAreDefault (warning)
corrective action: Start time AND End time are 0 Default to obs start time, obs end time
from ODF
badTimestep (warning)
Default to 60 seconds
corrective action: Timestep parameter entered less than 0 or
greater than time in le
6 Input Files
1. None. SAS ODF must be properly set.
7 Output Files
1. FITS le with single binary extension containing seven columns; TIME in seconds since
TSTART, x-y-z position vectors in km, and x-y-z velocity vectors in km/s.
8 Algorithm
subroutine orbit
read_parameters # get parameters from param file
OAL_odfInfo # get StartTime, EndTime of file
open_outfile # open FITS output file
addTable # create new table
foreach column # create 7 new columns: time, x, y, z, Vx, Vy, Vz
addColumn
next
for start_time to stop_time, step sampling_interval
OAL_getPosition # return position and velocity vectors from ODF
foreach column # time, x, y, z, Vx, Vy, Vz
fill_column_temp_pointer
if (column_temp_pointer(i) not defined)
column_temp_pointer(i) = HUGE
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end if
next
next
OAL_proposalInfo # get basic info to write as keywords
write_attributes_to_outfile # add proposal info as keywords
release Table # close FITS extension
release Set # close FITS file
OAL_releaseMemory # close ODF files
close_outfile
end subroutine orbit
9 Comments
 This task simply converts some of the available Orbit parameters from their current ODF
ascii format (as a Spacecraft Reconstructed Orbit File). It is assumed these positional and
velocity parameters can be better accessed in FITS for constructing possible GTI's.
 It is not clear the usefulness of the orbit le for barycentric correction but it is clear this
le should be presented in a format that maximizes using preexisting software to calculate
such values FROM this le.
10 Future developments
Currently, the OAL only returns the x-y-z positional coordinates from the orbit le. It is important for
this to be expanded to also include the velocity vectors. The ESOC ICD XSCS Orbit Access Software
document [3] describes other parameters users might eventually nd useful to access in FITS format and
may be included in later versions of this task as keywords.
It might be useful to arrange the output les to conform to a known standard, such as the XTE Orbit File,
which are not only already OGIP- compliant, but would allow these les to take advantage of FTOOLS
designed to read such formats. This can be accomplished with a slight expansion of the OAL getPosition
routine.
The OAL rst attempts to extract the RECONSTRUCTED orbit le to ll the output le, and failing
that, will extract the PREDICTED orbit le. It may be useful in the future to have a switch allowing
the extraction of EITHER, chosen by the user.
References
[1] ESA. XMM Interface Control Document: Observation and Slew Data Files (XSCS to SSC) (SciSIM
to SOCSIM). Technical Report XMM-SOC-ICD-0004-SSD Issue 2.5, ESA/SSD, June 2000. Found
at the URL: ftp://astro.estec.esa.nl/pub/XMM/documents/odf icd.ps.gz.
[2] K. Galloway. XMM technical note: Periodic housekeeping telemetry denition. Technical Report
XMM-SOC-TN-0040-SSD 0.2, ESA/SSD, August 5 1999.
[3] S.Pallaschke. XMM ICD - XSCS Orbit Access Software. Technical Report XMM-SOC-ICD-0019-OAD
Issue 1.0, ESA/ESOC/FCSD/OAD, October 1997.
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