Hi everyony,

I’m trying to set up a numerical propagator in python to propagate the position of one of the Swarm satellites. I want to add a gravity perturbation and a simple exponential atmosphere. I’ve been following the example given for the python wrapper however the forces seem to have no effect on the resultant position. I’m wondering if I’ve added them correctly.

I’ve attached two snippets of my code where I add the forces.

Gravity:

ae = Constants.WGS84_EARTH_EQUATORIAL_RADIUS

f = Constants.WGS84_EARTH_FLATTENING

propagator_num = NumericalPropagator(integrator)

propagator_num.setOrbitType(orbitType)

propagator_num.setInitialState(initialState)

# International Terrestrial Reference Frame, earth fixed

Earth = OneAxisEllipsoid(ae, f, EarthFrame)

gravityProvider = GravityFieldFactory.getNormalizedProvider(8, 8)

propagator_num.addForceModel(HolmesFeatherstoneAttractionModel(Earth.getBodyFrame(), gravityProvider))

Atmosphere:

refAlt = 400e3

density = 2e-12 # 1430.

hScale = .05

atmosphere = SimpleExponentialAtmosphere(Earth, refAlt, density, hScale)

dragForce = DRAG.DragForce(atmosphere, shape)

propagator_num.addForceModel(dragForce)

Thanks