Analysis and Conceptual Development of a Controllable Drag Sail for Low Earth Orbit Satellites

Kurzfassung

Over the last decade, the number of satellites and space debris on low Earth orbits increased nearly exponentially. In order to preserve the usability of these orbits, the quick and efficient demise offuture satellites shifts into focus. Even more so, since de-orbit requirements demanding a satellite to demise within five years in many cases. One prominent technology that could help greatly with this challenge are drag sails. After deployment, these systems significantly increase the aerodynamic drag surface of a satellite while only adding little mass to the whole spacecraft. However, current systems have no means of atti-tude control and lack efficiency due totumbling and suboptimal pointing. This limits the usability of drag sails to lower orbits and lighter satellites than would technically be feasible. To study the possibilities of a controlled drag sail system, an orbit propagation program was written in Python. With the propagator, satellites with a freely orientable drag surface were simulated and subjected to different sailing strategies. The simulated reference satellites differed in mass and their starting orbits; 2000 kg from an eccentric orbit and 250 kg from a circular orbit. The focus is put on varying the sail attitude, and thereby the effective aerodynamic area, in order to change the eccentricity of the orbit, decrease de-orbit time and provide means for collision avoidance or controlled re-entry. It was found that with a controlled sail system, the de-orbit time could be reduced significantly compared to the natural orbit decay and a non-controlled tumbling drag sail satellites. In some cases, the de-orbit within five years could only be achieved with the controlled sail. Further, up-coming conjunction events could be avoided with a lead time of one day. Also, a targeted re-entry for safe demise could be possible with a changeable drag surface. From the simulation, key properties and sail configurations were derived and discussed under the aspects of complexity, reliability and practicability. Under the conservative assumption of low solar activity, satellites with ballistic coefficients of up to 12 kg/m2 seem demisable within five years from circular orbits of 600 km altitude. From eccentric orbits in a similar altitudes, satellites with even higher ballistic coefficients of up to 84 kg/m2 could be de-orbited. Favourable configurations for de-orbit include dihedral (e.g. quasi-rhombic pyramid (QRP)) sails and black or transparent membrane material to reduce the influence of solar radiation pressure. The overall design space for a reliable and simple controllable drag sail seems limited, yet worthwhile to explore.