Re: Positional Requirements

Bruce Watson (wats@scicom.alphacdc.com)
Mon, 27 May 96 11:30:33 MDT

>In response to R. B. Minton, Lutz Schindler asked:

>>It is possible to get elements from observations without a
>>previous element set ?

>Yes.  In theory, it takes six independent numbers to geometrically
>define an orbit.  Three positional observations at
>three different times fit this criteria.  Then it's a matter of
>doing a lot of math to get an orbit that fits through these three
>points in time and space.

But for low earth orbits, this method doesn't work unless your
observations are accurate to better than arc-seconds.

For an object with an unknown orbit, it is best to use two widely
separated observations to come up with a preliminary circular solution
and then apply the differential corrections method as used
by elcor and fitelem, including your other observations, to calculate 
an accurate elliptical orbit.