Spacecraft Observation File

The SpacecraftObservationFile object provides functionalities for reading and writing SpacecraftObservation data (azimuth, elevation, range, range-rate, right ascension, and declination) to or from FreeFlyer's ASCII file format. The time system for data contained in the SpacecraftObservationFile is TAI in Modified Julian format and range and range-rate data are given in km and km/s, respectively. Azimuth, elevation, right ascension, and declination data are given in radians in the reference frame of the observing Sensor. Lastly, the spacecraft observer position is given in km, in the ICRF inertial reference frame.

•For information on how to simulate Spacecraft Observation data, see Simulating Tracking Data.

•For information on how to generate Spacecraft Observation files, see Generating Tracking Data Files.

•For information on viewing and editing data in an Spacecraft Observation file, see Using the Tracking Data Editor.

•For information on including an Spacecraft Observation file in a Kalman Filter, Unscented Kalman Filter, or Batch Least Squares OD process, see Including Tracking Data in an Estimation Process.

The Spacecraft Observation file format holds the observation epoch to the millisecond level.

An example of the format of a Spacecraft Observation file is given below. The columns from left to right include measurement data as follows:

Label	Units	Required	Description
Range	km	Yes	Range measurement.
Range Rate	km/s	Yes	Range rate measurement.
Azimuth/Right Ascension	rad	Yes	Azimuth or Right Ascension measurement (measurement type dictated by 'Angle Type').
Elevation/Declination	rad	Yes	Elevation or Declination measurement (measurement type dictated by 'Angle Type').
Epoch	days	Yes	Epoch of measurement, in the MJD TAI GSFC frame.
Observing Sensor ID	-	Yes	ID number of the observing sensor.
Observing Spacecraft ID	-	Yes	ID number of the observing spacecraft.
Observed Spacecraft ID	-	Yes	ID number of the observed spacecraft.
Angle Type	-	Yes	The type of angles measured (possible values: AzEl or RADEC).
Spacecraft Observer Position	km	No	The position of the observing spacecraft at time of observation, in the ICRF inertial frame.
Range validity flag	-	No	Flag indicating whether the Range measurement is valid.
Range Rate validity flag	-	No	Flag indicating whether the Range Rate measurement is valid.
Azimuth/Right Ascension validity flag	-	No	Flag indicating whether the Azimuth/Right Ascension measurement is valid.
Elevation/Declination validity flag	-	No	Flag indicating whether the Elevation/Declination measurement is valid.

Some example of observation file data:

Sample Observation File 1 (AzEl measurements)

12297.238457499 2.135224033 4.335511756 -0.616492305 25197.976087963 29 5 3 AzEl 1 1 1 1

13708.128070804 6.152020826 3.908099797 -0.326413058 25197.979560185 29 5 3 AzEl 1 1 1 1

15937.570221369 7.997769207 3.710554700 0.032234892 25197.983032407 29 5 3 AzEl 1 1 1 1

Sample Observation File 2 (RADEC measurements)

16905.226378790 -8.977009946 2.331375443 0.225204531 25198.014282407 29 5 3 RADEC 1 1 1 1

14158.547455177 -9.063519169 2.358530067 -0.039845580 25198.017754630 29 5 3 RADEC 1 1 1 1

11735.331555999 -7.072311621 2.226702991 -0.218066599 25198.021226852 29 5 3 RADEC 1 1 1 1

Sample Observation File 3 (AzEl measurements with Observer Position)

12297.238457499 2.135224033 4.335511756 -0.616492305 25197.976087963 29 5 3 AzEl -3410.6730 5950.9570 -1788.6270 1 1 1 1

13708.128070804 6.152020826 3.908099797 -0.326413058 25197.979560185 29 5 3 AzEl -2681.8432 5337.3893 -3815.8650 1 1 1 1

15937.570221369 7.997769207 3.710554700 0.032234892 25197.983032407 29 5 3 AzEl -1685.2488 4190.9361 -5461.2015 1 1 1 1

Spacecraft Observation File

See Also