A re-analysis of the 2009 Iridium-Cosmos predicted miss distance using two-line element derived orbits

On 2009 February 10 Iridium 33 (active) and Cosmos 2251 (inactive) collided at an altitude of 789 km which injected thousands of debris larger than 1 cm into the low-Earth orbit environment. A close approach of 584 metres was predicted before the collision but an orbit manoeuvre was not carried out. In this paper, an analysis of the miss distance prediction between the two objects is presented using the recently developed TLE-OD/OP method. The TLE-OD/OP uses multiple TLE datasets to perform an orbit determination (OD) computation and make an orbit prediction (OP) based on the OD results. The OD and OP computations consider a more complete set of forces than those in the SGP4 algorithm. The smallest close approach of 152.68 metres on February 10 at 16:55:59.92 was obtained from the TLE-OD/OP method, compared to the predicted close approach of 698.72 metres at 16:55:59.80 for SGP4. Leading up to the collision, the results show that the predictions from our method are less variable than the SGP4 propagator predictions. Finally, a method for bias correction is discussed which provides better orbit predictions using limited satellite laser ranging data.