Initial State Tool

Use the Initial State tool to set the current vehicle's initial state (i.e. epoch, position, and velocity) from either the vehicle's own currently propagated ephemeris or from data in a file.

Ephemeris data loaded from a file is used to generate the state when the source type is set to STK file. Ephemeris data includes a table of time, position, and velocity values appropriate for interpolation. Other source types are files containing initial states whose data is not dense enough in time to provide accurate interpolation. Typically just one state per file, though a list of states is allowed for certain formats. AGI recommends you avoid Interpolation to generate the initial state for such files. The other source types have a precise format set by their authoritative organization and are not AGI-designed formats.

HPOP Satellites

Many of the initial state formats contain spacecraft parameter information (i.e. mass, drag, solar radiation) as well as initial state content. In such cases, when the satellite is an HPOP satellite, those parameters are loaded into the satellite along with the initial state. This replaces any existing values.

The values of the spacecraft parameters can indicate whether drag and solar radiation models are necessary to include during propagation. These settings are loaded into the satellite as well. In addition, when the CCSDS OPM content includes covariance data, it is also loaded into the satellite. This replaces any existing values.

If you use Interpolate for the epoch selection, the parameters are obtained as if you chose ClosestPoint, while the the initial state is found through interpolation.

The tool is accessed through the Orbit page of a satellite's Basic properties or through the Trajectory page of a missile's Basic properties. To display the tool, click Initial State Tool....

This tool is available with some, but not all, propagators.

When the Get New Initial Vector window appears, options are:

Initial state vector options

Option	Value
Source Type	The new source for the initial state of the vehicle. Select one of the following: STK File. Use the button to select a source file. The ephemeris start and stop times and the number of ephemeris points display. Valid file formats are: Satellite (.sa) Satellite with Ephemeris (.sae); used by satellites with STK's Astrogator capability. Ephemeris (.e) Missile (.mi) Launch vehicle (.lv) Propagated Ephemeris The current vehicle's start and stop time and number of ephemeris points display. IIRV T9 File: Improved Interrange Vector Type 9. IIRV T1 File: Improved Interrange Vector Type 1. IIRV File: Improved Interrange Vector. EPV File: Extended Precision Vector. NASA IIRV File: NASA Flight Dynamics Facility Improved Interrange Vector. STK requires that the year be part of the NASA IIRV file name, and that it must start at the 8th character. For example, Sat123_2016.txt. The file name can include additional characters after the year. CCSDS OPM File: The Orbit Message Parameter (OPM) file format as specified by the Consultative Committee for Space Data Systems (CCSDS). Both version 1.0 and 2.0 files are supported in XML and Keyword Value Notation (KVN) formats.
Reload	Reloads the original ephemeris file so that any changes made are negated and the original state is restored.
Epoch Selection	The method by which the new initial state is selected. Interpolate: Calculates a point precisely at the Target Epoch. Specify an interpolation order. Closest Point: Uses the data point closest to the Target Epoch. Closest Previous: Uses the closest data point preceding the Target Epoch. Closest Following: Uses the closest data point following the Target Epoch. First Point: Uses the first ephemeris point. Last Point: Uses the last ephemeris point.
Target Epoch	The epoch to be used as a starting point for initial state. If you choose an Epoch Selection of Interpolate, Closest Point, Closest Previous, or Closest Following, you must specify a Target Epoch. If the Target Epoch lies outside the span of the available ephemeris, the closest ephemeris point is used. For more information on the options available for epoch times, see Time Options.
Interpolation Order	If the method is Interpolate, set the order of interpolation.
Generate New Vector	Click this button to generate the new initial state vector. Results display to the left of the button.
Results	When you click Generate New Vector, the Results pane displays the new initial vector and the new epoch.

If you click OK, the new vector data will display with a CBI Cartesian coordinate system in the Orbit or State page for all central bodies except Earth and Sun. For Earth and Sun, it will display as J2000 CBI.