 # Initial Acceleration For Propagator

Hello,

I was wondering if it is possible to get the initial acceleration for an initial spacecraft state that has all of the force models taken into account for a given numerical propagator without actually propagating. The initial state would only be defined by a position and velocity (and attitude, satellite mass, coefficients of drag, etc.).

From what I see, if I get the acceleration of the initial state of the propagator outright (before any propagation has happened), I only get a Newtonian attraction acceleration, even though I didn’t input that directly into the state. However, if I propagate by a miniscule amount then the acceleration reflects all the force models. I checked this by computing the acceleration separately for all the different force models I’m using using the initial state.

Is there a way to get the correct acceleration for all the force models at once for a given state that only has position and velocity (and attitude, satellite mass, coefficients of drag, etc.) defined initially? Or do I need to compute the accelerations for all the different force models separately and add them or propagate the numerical propagator by a very small amount?

Sam

Hi @Sam

The simplest way is probably to call directly the acceleration method from all force models. Something like this:

``````  Vector3D acceleration = Vector3D.ZERO;
for (ForceModel forceModel : models) {