The μTORQUE Momentum-Exchange Tether Experiment

摘要

Long, high-strength tethers can provide a mechanism for transferring orbital momentum and energy from one space object to another without the consumption of propellant. By providing a highly-reusable transportation architecture, systems built upon such "momentum-exchange" tethers may be able to achieve significant cost reductions for a number of in-space propulsion missions. Before such systems could be placed into operation, however, a number of technical challenges must be met, including flight demonstration of high-strength, highly survivable tethers, demonstration of the ability to control the dynamics of a rotating tether system, and the ability for a tether system to rendezvous with, capture, and then toss a payload. In this paper, we discuss a concept design for a small momentum exchange tether experiment that is intended to serve as the first step in demonstrating these key technologies. The "Microsatellite Tethered Orbit Raising Qualification Experiment" (μTORQUE) will be designed to fly as a secondary payload on an upper stage of a rocket used to deliver a satellite to GEO. The μTORQUE experiment will remain on the upper stage left in a GTO trajectory. After the primary satellite has been deployed into GEO, the μTORQUE experiment will deploy a microsatellite at the end of a 20 km long tether. Utilizing tether reeling and/or electrodynamic propulsion, the μTORQUE system will set the tether in rotation around the upper stage, accelerating the rotation until the tip velocity is approximately 400 m/s. The experiment will then release the microsatellite when the system is at its perigee, tossing the payload into a near-minimum-energy transfer to the Moon. The microsatellite can then utilize a Belbruno weak-boundary trajectory to transfer into a lunar orbit using only a few m/s of delta-V. Preliminary analyses indicate that the tether system could be mass-competitive with a chemical propellant system for the same mission.