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External Propagator

The StkExternal propagator enables you to import the ephemeris for a vehicle directly from a file. This is useful when the ephemeris has been obtained from a source other than STK, but you want to do further analysis within STK. The file contains ephemeris information such as position and velocity and may appear in a variety of formats and coordinate types. For more details about formats, see the formats section in the ephemeris files (*.e) topic or the CCSDS orbit ephemeris message format (*.oem or *.xml ) topic. You can create external ephemeris files within STK using the Create Data File tool. You can also create an ephemeris file COM plugin to utilize ephemeris files in formats not normally supported by STK.

To use an external ephemeris file to propagate a vehicle:

  1. Select the StkExternal Propagator.
  2. From the Ephemeris Type drop-down menu, select STK Ephemeris, STK Binary Ephemeris, CCSDS Ephemeris, ITC Ephemeris or an ephemeris plugin (if you have one registered).
  3. Note: The CCSDS ephemeris file format can be either XML or Keyword-Value.

  4. Type the file path and name of the external ephemeris file in the text box, or use the button to browse for a file.
  5. STK Ephemeris files must end in a .e extension, STK Binary Ephemeris files must end in a .be extension, CCSDS format files must end in a .oem or .xml extension and ITC format files must end in an itc extension.

  6. The start and stop times contained in the external file are displayed in the time interval control and are read only. A limited number of options are available from the drop-down menu. For more information on the options available for start and stop times see Time Options.
  7. (Optional) Override the times contained in the loaded file by selecting the appropriately named option and specifying the time of the first ephemeris point. For more information on the options available for time instances see Time Options.
  8. Select Limit ephemeris for analysis to the Scenario Interval. This option constrains the ephemeris to be no larger than the scenario interval when used in Access, Chains, STK's Coverage capability, and STK's Analysis Workbench capability. Reporting continues to report the entire ephemeris without regard to this limit being set.
  9. Within your external ephemeris file, you can designate the level of message feedback provided by STK concerning its reading of the file. See "MessageLevel" in the Keyword table of the topic Ephemeris File Format.

When you use an external propagator, STK reads the ephemeris from the external file only once, and then it stores the information internally. If you change the ephemeris file outside of STK and want to use the new information, save the ephemeris file and click the Reload Ephemeris button.