[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Orekit Users] Converting a State Vector to a TLE



Matt,

There is a well established way to do this.

1. you should use the state vector as the initial condition in a Special Perturbation (numerical integration) orbit propagation. If you are considering a LEO orbit, the time interval for the Special Perturbation orbit propagation should be at least 3 or 4 days. You should record the position velocity on a fine grid (say every few minutes).

The 3 or 4 day interval is dictated by the desire to make the integration span long relative to the periodic terms that are neglected in the GP4 theory that is the basis for the TLE.

2. use a least squares process (differential correction) to fit the GP4 theory to the position and velocity that you created with the Special Perturbation orbit propagator.

The results of this least squares process will a set of TLE.

There are lots of fine details to be discussed.

There are documents and software that describe and demonstrate this approach.

The DSST satellite theory is quite ... different ... from GP4.

Send me a note and we can discuss.

regards,

Paul Cefola

--
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 11/14/2014 3:01 pm, matthew.darden@solers.com wrote:
Hi,

I have to take a state vector (in this case a PVCoordinates and AbsoluteDate) and convert it into a TLE (or rather orbital elements that I can make a TLE from). I know the answer will never be very good, but I have to do it. Is
there a good way to make this conversion?

I know that I can just get what I need by creating a KeplerianOrbit from what I have, but those values are osculating and I need the mean orbital elements
if I want the answer to be anywhere near correct. I tried using
OsculatingToMeanElementsConverter with a DSST propagator using different force
models, but nothing really made any difference.

As a test case I took a random TLE, got the PVCoordinates at the time the TLE was created (so that it would be as accurate as possible) and passed those into my method. Which should spit out a generic TLE with orbital values close
to the originals. To test how close the two orbits truly are, I simply
propagated them both every 10 minutes for a 24 hour period, checking the
distance between the two points.

Thank you,
Matt