Stabilisation of in-plane periodic motion of electrodynamic tether system by combining tether length control and current control

A tether system is a large flexible structure connecting two or more satellites. Libration control methods of a tether system in elliptic orbits have been studied. For electrodynamic tether systems, these have included control of the tether length and the electric current. In previous studies, these two control methods were considered independently. However, by combining them, it is expected that the periodic motion of an electrodynamic tether system can be stabilised using a smaller electric current. The tether satellite system considered in the present study consists of two subsatellites and a mother satellite connected together in series via massless tethers. To stabilise the periodic motion using only a small electric current, two different tethers are used. The first is a non-electrodynamic tether whose length acceleration is varied using bang-bang control, and the other is an electrodynamic tether subject to proportional-derivative or delayed feedback control. The results of numerical simulations show that the proposed control scheme exhibits good performance for stabilising librational motion of the tether system to periodic motion, combining non-electrodynamic and electrodynamic tethers.