Ephemeris Generation

Specify the following parameters for ephemeris generation for a satellite:

Ephemeris Generation Controls
Parameter Description
StartTime Specify the date and time at which the ephemeris period is to begin. This field defaults to the scenario start time (or satellite epoch). This field is ignored if ephemeris is generated automatically.
Span The duration of the ephemeris period, counted from the ephemeris start in the case of manual generation, and from the end of the filtering process in the case of automatic generation. It is calculated as the difference between the scenario start time (or satellite epoch) and the the scenario stop time.
TimeStep The time step for the generated ephemeris (see below).
AlignTimeGrid Controls the alignment of ephemeris prediction output nodes to a preferred evenly spaced grid which is defined based on the requested time step. The nodes on the preferred evenly spaced grid have the property that represent an integer number of time steps from 00:00Z. Set to true to align to the preferred grid or to false to enforce prediction at purely even time steps from the initial prediction time. In both cases, the specified initial and final prediction times are contained in the resulting ephemeris. In the case where AlignTimeGrid is true, the first and last time steps in the resulting ephemeris may differ from the requested time step.
CoordFrame For spacecraft with initial conditions referenced to the Earth, choose between ICRF, J2000, TEMEofDate or Fixed. For spacecraft with initial conditions referenced to the Sun, choose between ICRF, J2000, or Fixed. For satellites with initial conditions referenced to the Moon, choose between ICRF, J2000, Fixed, Mean Earth, and Inertial.
Acceleration

A boolean flag that causes the acceleration to be written to the STK ephemeris (*.e) file. The information is used during interpolation.

This control is hidden if the file extension is *.oem since acceleration output is not currently supported for CCSDS 502 files.
Covariance

Set to true to output covariance data.
The CovarianceCoordSystem may specify the reference frame used for covariance representation in the ephemeris file. Choose between the same coordinate system used for the ephemeris representation and the "Gaussian (RIC)" frame. The RIC frame designation is synonymous with the UVW frame designation. This option is only available when the CCSDS Ephemeris file format is selected.

This control is hidden if the file extension is *.oem since covariance output is not currently supported for CCSDS 502 files.
CovarianceType Choose between "Position3x3Covariance" or "Position Velocity 6x6 Covariance". This property is hidden if the Covariance control is not enabled.
StateErrorTransition Set to true to include the state-error transition function in the output ephemeris. The state error transition will use the time of the first ephemeris point in the file as its reference epoch and will be defined to transition deviations at the reference epoch in the coordinate frame of the ephemeris output to the time associated with the state-error transition matrix. The state-error transition matrix can only be output to ephemeris files in the STK *.e format.
CovarianceCoordFrame Specifies the reference frame used for covariance representation in the ephemeris file. Choose between the same coordinate system used for the ephemeris representation and the "Gaussian (RIC)" frame. The RIC frame designation is synonymous with the UVW frame designation. This option is only available when the CCSDS Ephemeris file format is selected.
CreateFile Set to true to have an ephemeris file created; otherwise set to false.
FileFormat

The file format of the output ephemeris file(s) is as follows:

  • STK Ephemeris is in the STK *.e format.
  • STK Binary Ephemeris is in the STK *.be binary format.
  • CCSDS Ephemeris is in the CCSDS 502 format. Files will have a .oem extension.
  • SPICE BSP is the SPICE ephemeris format. Files will have a .bsp extension.
  • SPICE IDs for satellite objects are specified using the SPICE.ID property on the satellites.
Filename Click the current value to display a file selection window, where you can specify the path and filename of the output ephemeris file. Use extension *.e for STK Ephemeris format, *.oem for CCSDS 502 format.
SendToScript Set to true to have the ephemeris sent to a script; otherwise set to false.
ScriptFilename If the ephemeris is to be sent to a script, enter the path and filename of the script here.

Time Step and Ephemeris Points

The location of points on the ephemeris interval (defined by the StartTime and Span) is determined by the TimeStep as follows:

Given an ephemeris start time of ts and an end time of tf, where tf > ts, and a time step of dt, then the ephemeris is the set of points {t0, t1, t2,... tn-1, tn} where t0 = ts, tn = tf, and points t1 .... tn-1 are integral multiples of dt, referenced to 00:00:00.00 UTCG.

For example, suppose that StartTime is set to 12:51.40, Span is set to 6 minutes, and TimeStep is set to 2 minutes. Contrary to what one might expect, the output ephemeris is not {12:51:40, 12:53:40, 12:55:40, 12:57:40}. Instead, we get {12:51:40, 12:52:00, 12:54:00, 12:56:00, 12:57:40}. Similarly, if TimeStep is set to 3 minutes, the output is {12:51:40, 12:54:00, 12:57:00, 12:57:40}.