Interpolation of additional state for SpacecraftState

Orekit usage
1

Hi all,

I had a question regarding additional states attached to a SpacecraftState object and more precisely to the carrying out of the information when transforming an ArrayList<SpacecraftState> into a BoundedPropagator.

Using an external trajectory file, I get the orbital parameters and the thrust generated on each time step to generate a set of SpacecraftState. To have all the information correctly synchronized I was hoping to use additional states to carry the information of the thrust. But when using the BoundedPropagator, the additional states seem to have been erased.

Is there a better way to carry this thrust information?

See below for the code I’m using to create the ArrayList<SpacecraftState> and how I transform it to a BoundedPropagator.

public static ArrayList<SpacecraftState> readTrajectoryFile(File file) throws IOException{

// Array containing all spacecraft states
ArrayList<SpacecraftState> spacecraftStates = new ArrayList<SpacecraftState>();

[...]	

while ((line = reader.readLine()) != null) {

[...]
// Get thrust
thrust = Double.parseDouble(columns[19]);

try {
// Add spacecraft state and convert to J2000
	Transform cirfToJ2000 = frame.getTransformTo(frameJ2000, date);
	KeplerianOrbit orbitJ2000 = new KeplerianOrbit(cirfToJ2000.transformPVCoordinates(keplerianOrbit.getPVCoordinates()), frameJ2000, mu);
	spacecraftStates.add(new SpacecraftState(orbitJ2000).addAdditionalState("thrust", thrust));
} catch (OrekitException e1) {
	logger.error("Orekit error, failed to build SpacecraftState", e);
}
}
reader.close();
return spacecraftStates;

Once this ArrayList<SpacecraftState> is created I then transform it into a BoundedPropagator:

ephemerisReference = new Ephemeris(ephemerisT3D, 3);

Thank you very much for your help!

Kind regards,

B.

2

Hi Benoist,

That is weird, the Ephemeris class should handle additional states.
Could you provide us with a working example showing your issue, like a failing JUnit test ?

Regards,
Maxime

3

Hi Maxime,

I actually just managed to spot where the state gets erased. I checked and as you said when I’m out of the method reading my external file the state does exist. But it is when I add an attitude provider to the ephemeris that the state is erased.

To debug I simply tested:

// Set attitude
logger.info("{}", ephemerisReference.propagate(ephemerisReference.getMaxDate().shiftedBy(-1)).getAdditionalStates());
ephemerisReference.setAttitudeProvider(attitudeReference);
logger.info("{}", ephemerisReference.propagate(ephemerisReference.getMaxDate().shiftedBy(-1)).getAdditionalStates());
System.exit(0);

For which I get:

10:31:12.818 [main] INFO  main.MA_Propagator - {thrust=[D@64f6106c}
10:31:12.819 [main] INFO  main.MA_Propagator - {}

Is there a way to not erase the states when adding an attitude provider?

Otherwise I’ll just use two separate variables as attitude and trajectories are independent - they both are coming from an external file.

Thank you very much for your help!

Kind regards,

B.

4

Hi again Benoist,

I think you found a bug. Thank you for this !
Could you please open an issue on the Gitlab forge ?

The bug is in Ephemeris#basicPropagate (l.222).
Line:

return new SpacecraftState(evaluatedState.getOrbit(), calculatedAttitude, evaluatedState.getMass());

Should be:

return new SpacecraftState(evaluatedState.getOrbit(), calculatedAttitude, evaluatedState.getMass(), , evaluatedState.getAdditionalStates());

In short, the additional state is “forgotten” when adding the evaluated attitude.

Regards,
Maxime

5

Ah okay, no worries! I just opened an issue with your recommendation and a link to this topic for reference.

Thank you!

B.

6

Thanks!

The fix will be provided asap.
If you want and have time you can also contribute it, following guidelines from the contributing guide :wink:
Have a good day.