Comparison of technologies for deorbiting spacecraft from low-earth-orbit at end of mission

摘要

An analytical comparison of four technologies for deorbiting spacecraft from Low-Earth-Orbit at end of mission\udis presented. Basic formulas based on simple physical models of key figures of merit for each device are found.\udActive devices - rockets and electrical thrusters - and passive technologies - drag augmentation devices and\udelectrodynamic tethers - are considered. A basic figure of merit is the deorbit device-to-spacecraft mass ratio,\udwhich is, in general, a function of environmental variables, technology development parameters and deorbit\udtime. For typical state-of-the-art values, equal deorbit time, middle inclination and initial altitude of 850 km, the\udanalysis indicates that tethers are about one and two orders of magnitude lighter than active technologies and\uddrag augmentation devices, respectively; a tether needs a few percent mass-ratio for a deorbit time of a couple of\udweeks. For high inclination, the performance drop of the tether system is moderate: mass ratio and deorbit time\udincrease by factors of 2 and 4, respectively. Besides collision risk with other spacecraft and system mass\udconsiderations, such as main driving factors for deorbit space technologies, the analysis addresses other\udimportant constraints, like deorbit time, system scalability, manoeuver capability, reliability, simplicity, attitude\udcontrol requirement, and re-entry and multi-mission capability (deorbit and re-boost) issues. The requirements\udand constraints are used to make a critical assessment of the four technologies as functions of spacecraft mass\udand initial orbit (altitude and inclination). Emphasis is placed on electrodynamic tethers, including the latest\udadvances attained in the FP7/Space project BETs. The superiority of tape tethers as compared to round and\udmulti-line tethers in terms of deorbit mission performance is highlighted, as well as the importance of an\udoptimal geometry selection, i.e. tape length, width, and thickness, as function of spacecraft mass and initial\udorbit. Tether system configuration, deployment and dynamical issues, including a simple passive way to mitigate\udthe well-known dynamical instability of electrodynamic tethers, are also discussed. [Acta Astronautica]