[Orekit Users] Additional States

[Sylvain Rouard <sylvain.rouard@astrium.eads.net>]

Hello all,

Thanks to recent improvements added on 2013-04-08 to orekit git repository, the
management of Additional States is much more flexible.
These additional states are managed by propagators using either
AdditionalStateProvider for already integrated states or AdditionalEquations
for states driven by differential equations.
Before, during and after propagation, current values of these additional states
are stored directly inside the SpacecraftState object, which is very convenient
for use in eventHandlers and stepHandlers.

However, i can see one drawback to the current implementation:
Let's say you add an additional state to an initialSpacecraftState before
propagation, then you register your initialSpacecraftState to the propagator
and launch propagation.
If you have not added either an AdditionalStateProvider or an
AdditionalEquation to the propagator, you additional state will be lost during
propagation.
The default behaviour I would expect in this case is to keep the state constant
during propagation and provide it back to the user at the end of the
propagation.
This could be done by adding a constant AdditionalStateProvider to the
propagator when he founds a non-explicitely-managed additional state in its
initial SpacecraftState.

what do you think ?

cheers

Sylvain