Analysis of Electric Propulsion for De-Orbiting of Sun-Synchronous Satellites

During the last decades the importance of satellites for the every day life has increased continuously, leading to an increase in the number of satellites deployed into space. Most of the satellites delivered into space are not removed from their operating orbit. Given the growing number of objects in space, especially in the Low Earth Orbit (hereafter LEO) the possibility of collision with recent space debris (satellite or launcher fragments) increases. These collisions could lead, depending on the size of the impact object, to minor damages (no mission failure), to major damages (mission failure), to partial fragmentation (break up of satellite parts) or in the worst case to a total fragmentation of the satellite. The latter can easily produce up to 1000 fragments of various sizes from micrometers to meters in diameter. Therefore, recent and future satellites should be transferred into an end-of-life orbit or de-orbited according to the Space Debris Mitigation Guidelines in order to decrease the amount of space debris and thus guarantee access to space for future generations. Among the various possible orbits in LEO (160 km < h < 2400 km) the most interesting ones with respect to the avoidance of space debris are those with an inclination i>90°, the so-called sun- synchronous orbits (hereafter SSO). Due to the oblateness of the Earth, the right ascension of the ascending node increases and leads to a rotation of the orbit. Assuming a total fragmentation of a SSO satellite, its fragments will encounter different variations in their orbital elements due to the oblateness of the earth and the atmospheric drag. Therefore the fragmentation cloud will envelope the Earth roughly 1 year after the collision, presenting an enormous threat for recent and future objects in space. According to the Space Debris Mitigation Guidelines, a satellite in LEO should be removed 25 years after the end of its operation. Given the recent and possible future advances in the field of electric propulsion together with the fact that an SSO satellite spends most of its orbital time in sunlight, in this paper we investigate the possibility and capability of electric engines for the de- orbiting of SSO satellites.