Hi Hank,
I ran in to something vaguely similar to this today. I was trying to
get the state every minute using a propagator in slave mode. It
seems that the internal state of the integrator is not preserved
across calls to propagate. So for every call to propagate the
integrator step sizes ended up as 0.1, 1, 10, 47.9 seconds. I ended
up switching to ephemeris mode to avoid the unnecessary oscillations
in the step size. Though after I made the switch I saw less than 1mm
difference in the ephemeris. What is your tolerance setting for the
propagator? I used very tight tolerances, 1e-7, and the DP853
integrator.
Regards,
Evan
On 06/11/2015 05:34 PM, Hank Grabowski
wrote:
Hello all,
I'm in the process of doing a full up propagator V&V of
the Orekit library. It's mostly gone very well but I hit a
couple of snags today. One snag is with the BoundedPropagator
that gets returned by the getEphemeris. I essentially
generate an ephemeris in two ways. The first way is to
manually walk over the propagation time using the propagate
method on the actual propagator. The second way is to run the
propagation from the beginning to the end in one fell swoop
and then to iterate over the generated ephemeris to generate
the lookup file. I do this for a HEO, GEO, and a LEO orbit
using various force model settings. When I do this with an
earth point mass setting the raw integrated and interpolated
ephemeris match to within 3e-4 meters at GEO after 15 days.
I'm very happy with that. If I do it with an EGM96 70x70
gravity field however the solution over time gets worse and
worse, ultimately being 2 meters off 15 days later. This
happens regardless of the max step size I give the
integrator. I even set it to 60 seconds and reported out the
ephemeris using the generated ephemeris at 180 seconds. The
error seems to be consistent across those settings. The other
orbit regimes have a similar problem.
I am going to investigate this further but I figured I'd
put this out there in case someone had a suggestion for why it
would be happening and how one would address it.
Hank
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