prefilter - Derive attitude and orbit related quantities.




prefilter derives attitude and orbit related quantities based on pointing and position information.

NORAD two line elements (TLEs) are propagated to determine the satellite position and quaternions are interpolated from an attitude file at fixed time intervals. The time, position and attitude are then employed to derive and output some subset of the following quantities (based on the columns parameter): TIME, POSITION, VELOCITY, QUATERNION, PNTUNIT, POLAR, BORESIGHT, SAT_ALT, SAT_LAT, SAT_LON, RA, DEC, ROLL, ELV, BR_EARTH, FOV_FLAG, SUNSHINE, SUN_ANGLE, MOON_ANGLE, RAM_ANGLE, ANG_DIST, COR_ASCA, COR_SAX, MCILWAIN_L, SAA, SAA_TIME

prefilter was originally developed for the Swift mission, but it can be used for other missions provided a coordfits style attitude file and two line elements are available.

prefilter provides options for comparing its computations to functionally similar tools developed for ASCA (mkfilter2) and XTE (xtefilt).

Note that while the mission epoch is in UTC, the start and end parameters are expressed in the time system of the attitude file. The time system and related keywords (TIMESYS, TIMEUNIT, MJDREF*, ...) are copied from the input attitude file to the output.


outname [filename]
Name of the output file. To overwrite a preexisting file with the same name, prefix the name with an exclamation point '!', or set the 'clobber' parameter = YES.
columns ALL|[space-separated-values]|@[filename]
Specifies which derived quantities to output.
orbmode TLE|atSetElement|atSetElement2|XTE
Specifies the orbit mode which controls how orbname will be processed.
orbname [filename]
Name of the orbit file.
attname [filename]
Name of the attitude file.
alignfile [string]
Name of the coordfits alignment file or NONE.
leapname [filename]
Name of the leap second file.
rigname [filename]
Name of the atFunctions rigidity file.
start [real]
Output start time in seconds since mission epoch expressed in TIMESYS.
end [real]
Output end time in seconds since mission epoch expressed in TIMESYS.
interval [real]
Output interval [seconds].
ranom [real]
Nominal right ascension of spacecraft boresight [degrees].
decnom [real]
Nominal declination of spacecraft boresight [degrees].
attextrap [real]
Limit on attitude extrapolation [seconds].
missepoch [string]
Mission epoch in UTC specified as yyyy-dd-mmThh:mm:ss.sss.
origin [string]
Value for FITS ORIGIN keyword.
(clobber = NO) [boolean]
If outname already exists, then "clobber = yes" will overwrite it.
(history = yes) [boolean]
If set, HISTORY keywords are written to output.
(chatter = 1) [integer, 0 - 5]
Controls the amount of informative text written to standard output. Setting chatter = 5 will produce detailed diagnostic output, otherwise this task normally does not write any output.


1. Execute prefilter prompting the user for parameter values.


2. Execute prefilter providing the attitude file name and indicating the TLE file to process on the command line.

	prefilter attname=./ATTITUDE.fits orbmode=TLE orbname=./TLE.fits


prefilter implementation notes


January 2004