what do you guys think is the most elegant way of evaluating the equations of motion with a propagator (either analytical or numerical after initialization with force models, so ideally with the same lines of code)? In other word I would like to get dx/dt at an arbitrary time, where x is the state defined by the orbitType (I care less about the mass).
When spacecraft states are produced by a propagator, they generally include the first time derivatives.
You can retrieve them either using OrbitType.mapOrbitToArray() if you pass a non-null stateVectorDot array to be filled in, or using the getters from each orbit type individually (for example KeplerianOrbit has getADot, getEDot…)