Mohammed,

Measuring the attitude of a spacecraft (say, with respect to the radio emission of pulsars, or the x-ray radiation from various sources) is much easier than measuring the position of the Earth and the Sun - do you suggest to use occultation of x-ray sources as a means to locate the planets?

I believe that the first challenge has some merit, the second one - I confess - might not be tractable.

Some links:

http://www.asterlabs.com/publications/2006/Sheikh_et_al,_AIAA_JGCD_Jan_Feb_2006.pdf

Note, *position* will not be well-defined given the large distances to most x-ray sources - but atittude is far easier to determine.

thank you Mr;

i have a difficult to simulate the model of the sensor in matelab, because i haven't some data like the position of the sun and earth in the ssb frame . And with out the data i can not calculate the TOA of the pulse

kindregard

Mohammed,

I am still uncertain as to your needs.

Are you trying to determine spacecraft *attitude* or spacecraft *position*?

I try to determine spacecraft *position*

Thank you Mr

Mohammed,

That will be *very * hard for two reasons.

X-ray sources are very distant - and thus the angular change in position will be minute when viewed from locations within the solar system. Let's see: your baseline will be a few dozen AU at most, and for, say, a neutron star (~500 ly away) you have a an angular shift of 0.3 micro radians. I struggle to imagine an x-ray sensor onboard a spacecraft that can resolve to that accuracy.

Even BeppoSax cannot do that.

May I suggest that a more interesting approach might be to look at using pulsar timing as a GPS-like system?

https://www.technologyreview.com/s/515321/an-interplanetary-gps-using-pulsar-signals/

If you are looking for predicted postions of the Earth and Sun wrt the SSB or any other body in any frame, the JPL SPICE system is useful for getting programmatic access to solar system body and spacecraft ephemerides (positions, velocities and attitudes).  The link below points you to the toolkit for Matlab 

The learning curve for SPICE is not trivial, but it is very powerful and there are tutorials and example programs provided.  If you can describe an API (function call with input arguments and outputs) I could probably cobble something together for you pretty quickly.

http://naif.jpl.nasa.gov/naif/toolkit.html

M; Yousfi, pour la position (Terre Soleil, Planètes,...astres.), vous pouvez retrouver les éphémérides (éléments orbitaux), dans référentiel céleste héliocentrique, dans un ouvrage qui s'appelle "la connaissance des temps" qui est publié par l'Observatoire de Paris et calculer la position à un instant donné. Il sera aisé ensuite, si nécessaire, de passer au référentiel terrestre de type ITRF.