Space Debris in Routine Satellite Operations: Risk Mitigation for Collision Avoidance

Abstract

In recent years, the space debris has gained a lot of interest as part of the space environment due to the increasing population of uncontrolled man-made objects orbiting the Earth. This population is causing a significant and constantly growing risk of collision with operational satellites, as recently proven with the collision of the Iridium33 satellite with the decommissioned Cosmos-2251 spacecraft. Satellite operators are raising their concerns on this risk due to this accident and demand collision risk assessment and mitigation applications for their operational satellites. In addition, each collision or event provokes the appearance of a considerable amount of new debris in space. Currently, there are more than 600,000 objects larger than 1 cm in orbit (according to the ESA MASTER-2005 model) particularly concentrated in the most busy and interesting orbits for current and future missions. The risk of collision of a geostationary satellite with uncontrolled debris or other satellites is currently estimated to be above 1% over the 13 years of a mission lifetime and has increased an order of magnitude in the last decade. Many geostationary satellite operators have started to control this risk in the last few years. HISPASAT, as part of the risk management strategy in the company, implements an active monitoring of the potential collisions with space debris. This monitoring obeys to the increasing sensitivity to implement effective measures of control in front of these uncontrolled objects and to the decision to demonstrate a robust satellite control to the end customers. Another clear example of this interest is the initiative for a future European Space Situational Awareness System and all the precursor and preparatory activities undertaken, to which HISPASAT is interesting. GMV, a recognized leader in the field of Flight Dynamics, has a very extensive knowledge and broad base of experience in the field of space debris. This is due to its collaboration with the European Space Agency in this area over the last decade, as well as the development of customised solutions for operators such as HISPASAT. At the beginning of 2003, GMV was starting the development of a new activity for detection of close approaches between satellites and third-party objects. This activity was based on the information provided by USSTRATCOM as two-line elements (TLEs) plus the operational data available for the operator’s satellites. The tool has eventually evolved into a generic product called focusCloseAp, which is commercialised like a COTS product in different versions, to provide operators with a cost-efficient solution for collision risk assessment. This paper presents experience obtained by HISPASAT while using focusCloseAp to obtain collision approach results, the motivation, kind of problems encountered and the solutions that have been studied and / or applied. focusCloseAp presents a great flexibility in its use and allows the user to modify the satellite orbital and manoeuvre parameters very easily and re-run different analysis cases to check the effects of the proposed modifications. This feature is exploited to find out that there are various options for altering the encounter geometry quite considerably