Re: [Orekit Users] 0.1 deg Inclination bias?

["Hammel, Gregory (ASC/CSA)" <gregory.hammel@canada.ca>]

Hello Luc,

Thanks for this. This was actually going to be my next question - how to use LS to convert from osculating to DSST - was digging around the estimation project and was starting to run into a brick wall at the PropagatorBuilder. I didn't realize that my two problems may be actually only one.

If this is the source of the problem, then what purpose does the DSSTPropagator.computeMeanState function serve? Is is intended to be a quick way to get mean states when precision isn't required?

Will give this a go. Thanks,

Greg
________________________________________
From: orekit-users-request@orekit.org <orekit-users-request@orekit.org> on behalf of MAISONOBE Luc <luc.maisonobe@c-s.fr>
Sent: Thursday, July 19, 2018 2:08 PM
To: orekit-users@orekit.org
Subject: Re: [Orekit Users] 0.1 deg Inclination bias?

"Hammel, Gregory (ASC/CSA)" <gregory.hammel@canada.ca> a écrit :

> Hello,

Hi Greg,

>
> This is my first post to this list, so I would just like to start by
> thanking everyone who contributes to this project. Its an incredible
> resource.
>
>
> I am trying to use Orekit for mean state generation for
> stationkeeping using DSST. To that end I want to take in a vector
> from an external source (in this case, STK) read it in, propagate
> it, including manoeuvres, and then use DSST to get pre and
> post-maneouvre mean states. If I take a J2000 vector and provide it
> to DSST to get a mean state, I get an inclination of 97.75 deg.
> However, if I first propagate that same vector and then pass it
> through DSST I get an inclination of 97.65 (in this case, without
> any manoeuvres).
>
>
> I'm using the same methods as outlined in the "MasterMode.java"
> tutorial for my "pre-mean" propagation, but I've modified it by
> including solar and lunar grav and DTM2000 drag.
>
>
> Can anyone explain why there is a 0.1 deg shift in the inclination?
> I can provide the code if it helps.

If you convert starting from a single state vector, and change from
one propagator to another one, you can have this sort of problems.

I'll suggest to look at the propagation.conversion package and
at the associated test cases to do the conversion from a full
time range (say one or two periods) instead of a single state
vector. What this package does is a fitting, trying to ensure
the trajectories stay close to each other, in a least squares
sense.

Hope this helps,
Luc

>
>
> Thanks,
>
> Greg Hammel
>
> ___________________________________________________
> Gregory Hammel
> Analyste de la dynamique de vol
> Contractuel SED a division of Calian Ltd. Utilisation de l'espace
> Agence spatiale canadienne / Gouvernement du Canada
> gregory.hammel@canada.ca / Tél.: 450-926-5138
>
> Flight Dynamics Analyst
> Consultant SED a division of Calian Ltd. Space Utilization
> Canadian Space Agency / Government of Canada
> gregory.hammel@canada.ca / Tel.: 450-926-5138