/**
* Method called just before integration.
*
* <p>The default implementation does nothing, it may be specialized in subclasses.
*
* @param initialState initial state
* @param tEnd target date at which state should be propagated
* @exception OrekitException if hook cannot be run
*/
@Override
protected void beforeIntegration(final SpacecraftState initialState, final AbsoluteDate tEnd)
throws OrekitException {
// compute common auxiliary elements
final AuxiliaryElements aux = new AuxiliaryElements(initialState.getOrbit(), I);
// check if only mean elements must be used
final boolean meanOnly = isMeanOrbit();
// initialize all perturbing forces
for (final DSSTForceModel force : mapper.getForceModels()) {
force.initialize(aux, meanOnly);
}
// if required, insert the special short periodics step handler
if (!meanOnly) {
final InterpolationGrid grid =
new VariableStepInterpolationGrid(INTERPOLATION_POINTS_PER_STEP);
final ShortPeriodicsHandler spHandler = new ShortPeriodicsHandler(grid);
final Collection<StepHandler> stepHandlers = new ArrayList<StepHandler>();
stepHandlers.add(spHandler);
final AbstractIntegrator integrator = getIntegrator();
final Collection<StepHandler> existing = integrator.getStepHandlers();
stepHandlers.addAll(existing);
integrator.clearStepHandlers();
// add back the existing handlers after the short periodics one
for (final StepHandler sp : stepHandlers) {
integrator.addStepHandler(sp);
}
}
}
/**
* Conversion from osculating to mean, orbit.
*
* <p>Compute osculating state <b>in a DSST sense</b>, corresponding to the mean SpacecraftState
* in input, and according to the Force models taken into account.
*
* <p>Since the osculating state is obtained with the computation of short-periodic variation of
* each force model, the resulting output will depend on the force models parametrized in input.
*
* <p>The computing is done through a fixed-point iteration process.
*
* @param osculating Osculating state to convert
* @param forces Forces to take into account
* @return mean state in a DSST sense
* @throws OrekitException if computation of short periodics fails or iteration algorithm does not
* converge
*/
public static SpacecraftState computeMeanState(
final SpacecraftState osculating, final Collection<DSSTForceModel> forces)
throws OrekitException {
// Creation of a DSSTPropagator instance
final AbstractIntegrator integrator = new ClassicalRungeKuttaIntegrator(43200.);
final DSSTPropagator dsst = new DSSTPropagator(integrator, false);
// Create the auxiliary object
final AuxiliaryElements aux = new AuxiliaryElements(osculating.getOrbit(), I);
// Set the force models
for (final DSSTForceModel force : forces) {
force.initialize(aux, false);
dsst.addForceModel(force);
}
dsst.setInitialState(osculating, true);
final Orbit meanOrbit = dsst.mapper.computeMeanOrbit(osculating);
return new SpacecraftState(
meanOrbit,
osculating.getAttitude(),
osculating.getMass(),
osculating.getAdditionalStates());
}