Re: [find_orb] Computing orbit from a satellite

Bill Gray Jun 17, 2013

On 06/16/2013 01:22 AM, clark_wayne_1 wrote:
> It looks like find_orb works with observations taken from the Earth only.
> My application is similar, RA/DEC vectors to a target but the observations
> are taken from a satellite in known orbit about another planet. Is there
> a way to manipulated find_orb to do this or is there other software out
> there to do this?

You can get Find_Orb to do this, admittedly with a fair bit of effort.
The only case in which I've done it was to get an orbit for Deimos using
Mars Express data :

http://www.projectpluto.com/pluto/mpecs/deimos.htm

Note that to do this, you'll need to use the current development
version from http://www.projectpluto.com/pluto/devel/find_orb.htm .
That version understands assorted extensions to the "standard"
80-column MPC format. In particular, while the standard format
does allow for satellite observations, it only knows about Earth
and Sun orbiting ones.

For the sake of convenience, I also did things such as storing
times in JD format instead of YYYY MM DD.DDDDD and angles in decimal
degrees. That saved me some reprocessing and reformatting, but be
warned: that's also Find_Orb specific.

Unfortunately, there is no MPC-like central clearinghouse for
natural satellite data (though MPC _does_ provide astrometry for the
irregular gas giant satellites). I've accumulated a bit here and there.
Let me know which object(s) you're after; I may be able to supply some
ground-based data to supplement the satellite data.

The Mars Express data, by the way, is the only data I have taken
from a platform around another planet. I've seen some Cassini data,
but it contained no Cartesian coordinate offset (i.e., it told you
what object was at thus-and-such RA/dec from Cassini at thus-and-such
time, but you had no idea where Cassini was at the time.)

-- Bill