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

2014-03-19 16:10 GMT+01:00 Quentin Nénon <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>:

Hi Quentin,

Quentin Nénon <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

----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.