Initial State Tool

In the Ansys Systems Tool Kit^® (STK^®) application, use the Initial State Tool to set the current vehicle's initial state, including epoch, position, and velocity, from the vehicle's own currently propagated ephemeris, from data in a file, or from a Flight Dynamics Record component in the Component Browser.

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. Most other source types are files containing initial states having data is not dense enough across time spans to provide accurate interpolation. Typically, they have 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. These other source types have a precise format set by their authoritative organization and are not AGI-designed formats. A third source type is a component from Flight Dynamic Records, which are stored in the Component Browser.

HPOP Satellites

Many of the initial state formats contain spacecraft parameter information, such as mass, drag, and solar radiation parameters, 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.

You can access the tool 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 Initial State Import Tool dialog box appears, the options are:

Initial state vector options

Option	Value
Source Type	Select the new source for the initial state of the vehicle. Choose one of the following: CCSDS OPM File: The Orbit Message Parameter (OPM) file format is 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. EPV File: Use the ellipsis () to select an Extended Precision Vector file. Flight Dynamics Record: Use the ellipsis () to open the Flight Dynamics Record folder in the Component Browser, from which you can select a Flight Dynamics Record to set your initial satellite state. IIRV File: Use the ellipsis () to select an Improved Interrange Vector file. IIRV T1 File: Use the ellipsis () to select an Improved Interrange Vector Type 1 file. IIRV T9 File: Use the ellipsis () to select an Improved Interrange Vector Type 9 file. NASA IIRV File: This is the NASA Flight Dynamics Facility Improved Interrange Vector. STK software requires that the year be part of the NASA IIRV file name, and that it must start at the eighth character. An example is Sat123_2016.txt. The file name can include additional characters after the year. Propagated Ephemeris The current vehicle's start and stop time,number of ephemeris points, and central body appear with this option, to help you choose an epoch and target epoch. STK File. Use the ellipsis () to select a source file. The ephemeris start and stop times, number of ephemeris points, and central body appear with this option, to help you choose an epoch and target epoch. Valid file formats are: Satellite (.sa) Satellite with Ephemeris (.sae); used by satellites with the STK Astrogator capability Ephemeris (.e) Missile (.mi) Launch vehicle (.lv)
Reload	Reloads the original ephemeris file so that any changes made are negated and the original state is restored.
Epoch Selection	Choose the method by which the new initial state time 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	Choose 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 Epoch Selection method is Interpolate, set the order of interpolation.
Generate New Vector	Click this button to generate a new initial state vector. Results appear to the left of and below the button, inside the Results pane.
Accept State	Click this button to apply the new initial state vector to the Initial State sequence.

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