Astrogator

Here's a simple example that illustrates some of the functionality of the new scripting tool in STK 9.

In this example, a plane-change maneuver is being performed to complete an insertion into geostationary orbit.  A differential corrector is used to find the necessary duration of the maneuver to complete the plane change.  But, the engine that will be used has never been fired before.  Because we're going for a zero inclination, if the maneuver runs hot it will end up flipping the ascending node, which we want to avoid.  So we want to reduce the size of the maneuver from the ideal case - in this case by performing 97% of the maneuver.  On the next orbit the rest of the burn can be performed to finish the plane change, after we see how well the first maneuver performed.

The question is, how do we get Astrogator to model performing 97% of the ideal maneuver?  The answer is: Scripting Tool.

Start by setting up the targeter as if the whole maneuver will be performed.  Set up a differential corrector (DC) profile that targets the necessary burn duration to give you the desired plane change.  This gives us the ideal situation.

Now, add a Scripting Tool profile after the DC in the targeter's list of profiles.  We'll use this profile to modify the burn duration that the DC found.

In the scripting tool, add a segment property called BurnDuration.  Set it to the maneuver segment, and make the attribute FiniteMnvr.StoppingConditions.Duration.TripValue.  That's the attribute that controls the burn duration.  We want to take the value it already has from the previous profile and use 97% of it, so make the script say:

BurnDuration = 0.97 * BurnDuration;

Now when you run the MCS, the DC will find the ideal maneuver for the plane change, and the scripting tool will make the maneuver use 97% of the ideal.  If that multiplication factor might change, you can make a parameter for it and set it initially to 0.97.  Then the script becomes:

BurnDuration = factor * BurnDuration;

With the factor a parameter, it can be changed through Connect or the object model, and also used as a control in an outside targeter.