Are de-orbiting missions possible using electrodynamic tethers? Task review from the space debris perspective

Over 9000 satellites and other trackable 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. De-orbiting devices based on the use of conducting tethers have been recently proposed as innovative solutions to mitigate the growth of orbital debris. However, 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. This paper compares the results obtained at ISTI/CNR, the Kyushu University and NASA/JSC concerning the vulnerability to debris impacts on a specific conducting tether able to de-orbit spacecraft in inclinations up to 75^{{ring operator}} and initial altitude less than 1400 km. A double line tether design has been analyzed, in addition to the single wire solution, in order to reduce the tether vulnerability. The results confirm that the survivability concern is fully justified for a single line tether and no de-orbit mission, from the altitudes and inclinations considered, is possible if the tether diameter is smaller than a few millimeters. The survival probability is shown to grow for a double line configuration with a sufficiently high number of knots and loops. The results are strongly dependent on the environment model adopted and the MASTER-2001 orbital debris and meteoroids fluxes result in survival probabilities appreciably higher than those of ORDEM2000 coupled with the Grün meteoroids model.