Benefits and risks of using electrodynamic tethers to de-orbit spacecraft - results of the AI 19.1 study plan

Pardini C.

Electrodynamic Tethers  Spacecraft De-orbiting  Space Debris Mitigation  J.2 Physical Sciences and Engineering 

Over nine thousand satellites and other large objects are currently in orbit around the Earth, along with many smaller particles. As the low Earth orbit is not a limitless resource, some sort of debris mitigation measures are needed to solve the problem of unusable satellites and spent upper stages. It has been suggested that every satellite deployed should carry extra propellant to bring it down once completed its mission. On the other hand, electrodynamic tethers, potentially able to rapidly remove unwanted satellites and upper stages from low Earth orbits with a low mass requirement, have been recently proposed as an alternative solution. Nevertheless, electrodynamic tethers introduce unusual problems when viewed from the space debris perspective. In particular, because of their small diameter, tethers of normal design may have a high probability of being severed by impacts with relatively small meteoroids and orbital debris. The Inter-Agency Space Debris Coordination Committee (IADC) recognized this demanding task and a new action item (AI 19.1) was opened, in 2001, to investigate the potential benefits and risks of using tethers in space. This action item was successively focused on electrodynamic tethers to de-orbit spacecraft, while a study proposal was addressed to assess the tethers survivability concerns. The institute ISTI of the Italian National Research Council (CNR), together with the Kyushu University, in Japan, and NASA participated in the IADC study. Different models and techniques were developed and applied to compute the fatal impact rate of meteoroids and orbital debris on space tethers in circular orbits, at different altitudes and inclinations, as well as to assess the survival probability of electrodynamic tether systems during some baseline de-orbiting missions. This work compares the results obtained at ISTI with those computed at the Kyushu University and NASA concerning the vulnerability to debris impacts of a specific electrodynamic tether during some typical de-orbiting missions. Besides the single line tether design, double line solutions were analysed as well to reduce the tether vulnerability. The orbital debris and meteoroid fluxes models adopted included ORDEM 2000, MASTER 2001, DAS 1.5.3 and Grun 1985. The results obtained were similar for a single line tether, confirming that the survivability concern is fully justified and that no de-orbiting mission, from the altitudes and inclinations considered, is possible if the tether diameter is smaller than a few millimetres. The survival probability may significantly increase for a double line configuration with a sufficiently high number of loops. The results strongly depend on the debris environment model adopted. The more pessimistic results were obtained with ORDEM 2000. The MASTER 2001 and DAS 1.5.3 fluxes resulted in comparable survival probabilities higher than ORDEM 2000.

Source: Meeting of the Inter-Agency Space Debris Coordination Committee, ESA/ESOC, Darmstadt, Germany, 21-22 April 2005