Re: [Orekit Users] Problem when doing propagation from different point of views

[Quentin Nénon <q.nenon@gmail.com>]

Hi,

I would like to add some comments in order to make the discussion progress.

You will find enclosed another main class using the previously posted ones and it is basically doing the same thing as before but it uses the Venus point of view (and adds the perturbation due to Venus to avoid to use a GM constant of 0., that throws an exception). You can therefore see that the problem is not only due to the definition of the Sun inertially oriented frame. The problem still can be in the definition of all the inertially oriented frames.

Another interesting aspect is when you change the force models you add to the propagators. If for instance you remove the moon or sun perturbation, you have errors on the position and velocity that change. This makes me think that the problem might be in the definition of the perturbative forces ?

If any of the users have an idea of what might be the problem, I would be very happy to discuss it here,

Thank you,

Quentin

2014-03-20 9:57 GMT+01:00 Luc Maisonobe <Luc.Maisonobe@c-s.fr>:

Le 20/03/2014 09:53, Quentin Nénon a écrit :

> Hi,
>
> I would like to complete my answer of yesterday. What I called
> "differential accelerations" is just taking into the relative
> acceleration of the two frames.
>
> You will find enclosed a new main class, step handler and a "MyChart"
> class for the plots. I modified a little the step handler and the main
> and you now have the plots of the difference of position and speed
> between the two propagators over the time.

Hi Quentin,

I will only be able to look at this in a few days, I am very busy with
some urgent matters right now.

Sorry for the delay
Luc

>
> I am using the jfreechart-1.0.17 and jcommon-1.0.21 libraries for the
> plots. You will find enclosed the jar files that should be linked to the
> project to have the plots.
>
> Hope this can help.
>
> Thanks again,
>
> Quentin
>
>
> 2014-03-19 16:10 GMT+01:00 Quentin Nénon <q.nenon@gmail.com

> <mailto:q.nenon@gmail.com>>:

>
>     Thanks again for the fast answer.
>
>     You will find enclosed a MyStepHandler class and a new main class
>     that is using this step handler to keep the positions with an output
>     step of 1000 secondes (you can modify it in the main class if you
>     want). I then write the results in a txt file that I am then used to
>     visualize using Excel. I can create charts if you want.
>
>     I already tried to verify that the problem was not due to the fact
>     the the Earth EME2000 Frame is not inertial. It seems to already be
>     taken into account by using differential accelerations for the
>     ThirdBodyAttraction rather than the actual acceleration created by
>     the perturbative body. It means that the acceleration due to the Sun
>     perturbation in the Earth Frame is equal to the acceleration of the
>     satellite due to the Sun in the Sun frame MINUS the acceleration of
>     the Earth due to the Sun in the Sun Frame. If the Earth Frame was
>     inertial, the acceleration of the Earth in the Sun Frame due to the
>     Sun would be 0. and the acceleration of the satellite would be the
>     same in the Earth and Sun Frame.
>
>     Moreover, if the Earth motion around the Sun was not taken into
>     account, much bigger errors would be expected and all the
>     propagations in the EME2000 would be (I think very) wrong.
>
>     Thank you,
>
>     Quentin
>
>
>     2014-03-19 15:35 GMT+01:00 MAISONOBE Luc <luc.maisonobe@c-s.fr

>     <mailto:luc.maisonobe@c-s.fr>>:
>
>         Hi Quentin,
>
>         Quentin Nénon <q.nenon@gmail.com <mailto:q.nenon@gmail.com>> a

>         écrit :
>
>
>             Hi Orekit users,
>
>             First, let me thank Luc very much for the very fast and
>             effective answer he
>             gave to my last topic. It is very nice and enjoyable to have
>             support and
>             suggestions from the Orekit developer team and users.
>
>
>         Thanks a lot.
>
>
>
>             I have another issue I would like to submit to the Orekit
>             users. I am
>             trying to use Orekit to propagate  an interplanetary
>             trajectory and in
>             order to have the best possible precision, I am creating a
>             manager of
>             sphere of influence. The goal is therefore to be able to
>             propagate the
>             motion of the spacecraft in different frames (first, in
>             inertial frames).
>
>             You will find enclosed a main class that is doing the
>             propagation of the
>             same motion but from two different point of views :
>
>             -The first one is to consider that the spacecraft is turning
>             around the
>             Earth central body and has newtonian perturbations coming
>             from the Sun and
>             from the Moon
>             -The second one is to consider that the spacecraft is
>             turning around the
>             Sun central body and has newtonian perturbations coming from
>             the Earth and
>             from the Moon.
>
>             I am using the Orekit physical data available on the Orekit
>             website. I have
>             Orekit 6.1 and commons math 3.2 as dependances.
>
>             At the end of the two propagations, I have a difference in
>             the position of
>             about 2800 kilometers, that is not very good ... I verified
>             with my own
>             patch that it is not a problem due to the distances between
>             the celestial
>             bodies (see the EarthMoonBarycenter topic).
>
>             Does anyone has an idea of why I have this result ? Am I
>             doing a mistake
>             when I am adding the force models to the propagators ?
>
>
>         I just skimmed over the code and did not see any obvious error.
>         Could you store not only the final position but a few hundreds
>         intermediate points at fixed date (you can use an
>         OrekitFixedStepHandler for that) and create a plot showing the
>         error evolution throughout the propagation?
>
>         I wonder if the problem could not be related to the fact Earth
>         frame is not really inertial (due to motion around Sun) and in
>         this case it shows up.
>
>         best regards,
>         Luc
>
>
>             Thanks again,
>
>             Quentin
>
>
>
>

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