Tesseral force with DSST propagator

Orekit Python Wrapper usage
1

Dear all,

I’m having trouble using the tesseral forces with DSST.
Here is a code sample:

GravityFieldFactory.addPotentialCoefficientsReader(EGMFormatReader('EGM2008_to2190_TideFree.*',
                                                                                   False))
normalized_provider = GravityFieldFactory.getNormalizedProvider(self._harmonics_degree, self._harmonics_order)
unnormalized_provider = GravityFieldFactory.getUnnormalizedProvider(normalized_provider)
zonal = DSSTZonal(unnormalized_provider)
orekit_itrf = utils.toOrekitFrame('itrf')
tesseral = DSSTTesseral(orekit_itrf, Constants.WGS84_EARTH_ANGULAR_VELOCITY, unnormalized_provider)

Note: toOrekitFrame is just a method that returns a Frame from a name (string).
The zonal forces seem to work fine, however as soon as I add the tesseral terms, I get this during propagation:

orekit.JavaError: <super: <class 'JavaError'>, <JavaError object>>
E           Java stacktrace:
E       java.lang.ArrayIndexOutOfBoundsException: -1
E       	at org.orekit.propagation.semianalytical.dsst.forces.DSSTTesseral.computeNSum(DSSTTesseral.java:858)
E       	at org.orekit.propagation.semianalytical.dsst.forces.DSSTTesseral.access$1100(DSSTTesseral.java:84)
E       	at org.orekit.propagation.semianalytical.dsst.forces.DSSTTesseral$FourierCjSjCoefficients.buildFourierCoefficients(DSSTTesseral.java:1264)
E       	at org.orekit.propagation.semianalytical.dsst.forces.DSSTTesseral$FourierCjSjCoefficients.generateCoefficients(DSSTTesseral.java:1220)
E       	at org.orekit.propagation.semianalytical.dsst.forces.DSSTTesseral.updateShortPeriodTerms(DSSTTesseral.java:561)
E       	at org.orekit.propagation.semianalytical.dsst.DSSTPropagator.computeMeanOrbit(DSSTPropagator.java:843)
E       	at org.orekit.propagation.semianalytical.dsst.DSSTPropagator.computeMeanState(DSSTPropagator.java:676)
E       	at org.orekit.propagation.semianalytical.dsst.DSSTPropagator.computeMeanState(DSSTPropagator.java:647)
E       	at org.orekit.propagation.semianalytical.dsst.DSSTPropagator.getInitialIntegrationState(DSSTPropagator.java:914)
E       	at org.orekit.propagation.integration.AbstractIntegratedPropagator.integrateDynamics(AbstractIntegratedPropagator.java:470)
E       	at org.orekit.propagation.integration.AbstractIntegratedPropagator.propagate(AbstractIntegratedPropagator.java:425)
E       	at org.orekit.propagation.integration.AbstractIntegratedPropagator.propagate(AbstractIntegratedPropagator.java:385)

Moreover, I would say that the normalized provider is fine because I can successfully use a HolmesFeatherstoneAttractionModel initialized with it.

Cheers,
Romain.

2

Hi Romain,

Is it possible to see how do you initialize the initial state and the DSST propagator?
In other words, could you provide the full initialization of the DSST propagator?

Thank you,
Bryan

3

Hi Bryan.

Sure. I handpicked stuff because it is a bit spread out in the code:

self._propagator = DSSTPropagator(hipparchus_integrator, propagation_type)
self._propagator.setMu(mu)
self._propagator.setInitialState(spacecraft_state)
self._propagator.setResetAtEnd(False)
for force in [zonal, tesseral]:
       self._propagator.addForceModel(force)

The main difference I see w.r.t. how I use the NumericalPropagator is that I don’t set the OrbitType and PositionAngle. Also I don’t set an initial step-size for the integrator: is that an issue?

4

I have some additional questions. What are the values of propagation_type, _harmonics_degree, and _harmonics_order? Also, what is the value of the step used by the Hipparchus integrator?

I think the issue is related to the short period terms, but I need the value of these parameters to confirm and find a solution.

Best regards,
Bryan

5

The problem arises no matter the propagation type (OSCULATING or MEAN).
I am testing with self._harmonices_order = self._harmonics_degree = 2.
I am using Dormand-Prince 5 with min. and max. stepsize of 0.01 and 60s respectively, with tolerances computed to “reach” a position error of 0.01m. That may be too stringent for a semi-analytical propagation maybe? I was just reusing values from the full numerical ones.

Edit: I tried Runge-Kutta 4 with a step of 10s and the propagation still crashes.

Cheers,
Romain.

6

Ok, that’s a bug. We have an (old) issue opened for that: https://gitlab.orekit.org/orekit/orekit/-/issues/672

I recommend you to use bigger steps. Because the integrated elements are the mean elements, with DSST you can use integration steps equal to several orbital periods.

Bryan

7

I confirm that when trying a 4x4 geopotential, I do not have an error.
Thank you Bryan for the explanation!

Best,
Romain.