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

Hello.

Is Orekit designed to allow for motion about an arbitrary cental body?

If so, what characteristics can this central body have?
I am thinking of the paper that Ken Seidelmann updates for the IAU every couple of years. 

Paul

--
Dr. Paul J. Cefola
Consultant in Aerospace Systems, Spaceflight Mechanics, & Astrodynamics
Adjunct Faculty, Dept. of Mechanical and Aerospace Engineering, University at Buffalo (SUNY) 

4 Moonstone Way
Vineyard Haven, MA 02568
USA

508-696-1884 (phone on Martha's Vineyard)
978-201-1393 (cell)

paulcefo@buffalo.edu
paul.cefola@gmail.com

On 03/31/2014 8:27 am, Quentin Nénon wrote:

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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