On the computation of preliminary orbits for space debris with radar observations

Abstract: We introduce a new method to perform preliminary orbit determination for space debris on low Earth orbits (LEO). This method works with tracks of radar observations: each track is composed by $n\ge 4$ topocentric position vectors per pass of the satellite, taken at very short time intervals. We assume very accurate values for the range $\rho$, while the angular positions (i.e. the line of sight, given by the pointing of the antenna) are less accurate. We wish to correct the errors in the angular positions already in the computation of a preliminary orbit. With the information contained in a pair of radar tracks, using the laws of the two-body dynamics, we can write 8 equations in 8 unknowns. The unknowns are the components of the topocentric velocity orthogonal to the line of sight at the two mean epochs of the tracks, and the corrections $\Delta$ to be applied to the angular positions. We take advantage of the fact that the components of $\Delta$ are typically small. We show the results of some tests, performed with simulated observations, and compare this algorithm with Gibbs' method and the Keplerian integrals method.