User Variables

Astrogator is capable of incorporating additional variables during propagate and finite maneuver segments. Within Astrogator, these variables are called "user variables". These variables are carried through the MCS with the rest of the spacecraft state, and are saved at each time step as part of the ephemeris.

To incorporate a user variable, it must be defined in the MCS Options window of the Astrogator satellite and in an EOM Function plugin. In the MCS Options window, the User Variables tab is used to define the variable by name and unit dimension; the name must exactly match the variable name registered in the plugin.

Once you have defined a user variable in the MCS Options window, you can set its initial value in an Initial State, Follow, or Launch segment and you can modify its value using an Update segment. In addition, the initial value and updated values can be selected as independent variables in a Target Sequence search profile.

In propagate and finite maneuver segments, an EOM Function plugin that modifies the user variable can be added to the propagator. The value of the user variable can either be set directly by the plugin or the plugin can give the derivative of the variable and Astrogator will integrate it. Refer to the help for EOM Function in the Programming Interface help system and the example plugin scenario provided with STK for more information.