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Initial State

Use the Initial State segment to define the initial conditions of your MCS or of a subsequence within the MCS. You can specify the state at a given epoch in a variety of coordinate types and in any coordinate system. You can also configure the spacecraft’s physical values. The segment adds the defined state to the ephemeris and then passes the state to the next segment.

## Selecting a coordinate system

The name of the currently selected coordinate system displays. To select a different coordinate system, click to the right of this field and make the desired selection in the Select Reference dialog box that appears. The name of that coordinate system will then appear in the Coordinate System field. For more information on coordinates systems, see STK Technical Notes.

## Selecting a coordinate type

You can define the initial state using Cartesian, Geodetic, or Spherical elements if the coordinate system is fixed, or by Cartesian, Spherical, and several other element sets if the coordinate system is inertial. Select the desired element set from the Coordinate Type shortcut menu and then define an Orbit Epoch and values for the elements of the selected set.

## Initial State Tool

Click

to do either of the following:- change the initial state of the satellite by reading ephemeris from a file
- move the epoch of the initial state using a vehicle's propagated ephemeris

See the Initial State Tool topic for more information.

## Set Full State

You can define all six elements of the initial state at once using the following steps:

- Click to open an MCS Initial State Input dialog box.
- In the upper left, specify the coordinate system of your input data by clicking and choosing from a list of available types.
- In the upper right, select either Cartesian or Keplerian for the state element type of your input data.
- In the input text box, enter the six elements using km for distances, km/s for velocities, and degrees for angles; you must use these units. You must also follow the input order for the state variables as shown above the input text box. Separate the state elements by commas, spaces, or return characters.
- After entering the initial state into the text box, click to preview the resulting Cartesian state in the coordinate system chosen on the Elements tab of the Initial State segment (not your input data coordinate system).
- If the preview is satisfactory, click to import the result into the initial state.

## Spacecraft Parameters and Fuel Tank

Use the Spacecraft Parameters and Fuel Tank tabs to manually define the Spacecraft Configuration.

## User Variables

Use the User Variables tab to set initial values for user variables that have been defined for the mission.