STK Ephemeris File

The STK® Ephemeris File is an ephemeris-file format for use with Analytical Graphics Inc.’s Satellite Tool Kit®. This format can be used for both input and output of Spacecraft orbital data. The STK Ephemeris allows you to store the state of the Spacecraft at each time step during the mission to a file. When the data is stored in a file, FreeFlyer or Analytical Graphics' Satellite Tool Kit can import the data and perform calculations on the trajectory information.

See the Working with Ephemerides guide for more information about creating and importing an Ephemeris file.

Format

The STK Ephemeris is an ASCII file with the format defined by the STK Users Manual. FreeFlyer writes a STK v3.0 formatted file. STK is a registered trademark of Analytical Graphics, Incorporated.

When FreeFlyer ingests a STK formatted ephemeris, it assumes the "ScenarioEpoch" is defined using the UTC time system with a MJD GSFC reference date. The STK Ephemeris "ScenarioEpoch" is written using the Gregorian UTC time system (dd mmm yyyy hh:mm:ss.s).

Note: Once a STK formatted ephemeris is parsed, the "ScenarioEpoch" is automatically converted from the UTC to the TAI time system by FreeFlyer. This results in the Spacecraft.Epoch property reporting the equivalent TAI Julian date of the UTC epoch in the STK ephemeris. This process also applies when writing a STK ephemeris; where the Spacecraft.Epoch is converted to the UTC time system before being written to a STK ephemeris file as the "ScenarioEpoch".

See Also