Investigating the use of motorised tethers for payload orbital transfer

This paper introduces the concept of symmetrical double-ended motorised spinning tethers for use as orbital transfer vehicles. The orbital elements of a payload released from above and below a hanging, prograde librating and prograde spinning tether are derived and employed to evaluate the effectiveness of the three tether types along with their optimum configurations for payload transfer. A new ratio, the efficiency index, is defined as the altitude gain or loss half an orbit after tether release per tether length. The motorised tether is found to perform best and also most efficiently, improving by two orders of magnitude on the librating tether which, in turn, improves on the hanging tether by a factor of two. A long motorised tether on a circular orbit is found to be able of transferring an upper payload from a low to a geostationary Earth orbit by employing relatively high motor torque and a safety factor on the tether strength close to unity. Multiple tethered stages, for which short tethers are found worthy for consideration, or tethers on elliptic orbits will, consequently, have to be considered for geostationary payload transfer unless expendable tethers are employed.