Orbital Maneuvering with Electrodynamic Tethers

Abstract

expendables. 1;2 The nearly propellantless nature of maneuvering with electrodynamics tethers could potentially enable new ways of operating in space. Some of these possibilities could be achieved in the near term. For example, techniques for boost and reentry of spacecraft has been developed by several researchers 2i8 and will be demonstrated in the NASA ProSEDS mission. Other applications are also beingconsidered and couldreap tremendous benee t. For example,a satellite servicing vehicle could rendezvous with multiple satellites in different orbits to transfer fuel or replace components to extend the lifetime of expensive space assets. An orbital tug could change the orbits of low-Earth-orbit (LEO) satellites. 9 A space surveillance satellite could obtain intelligence on foreign space assets and even perform counterspace missions if necessary. There are two practical disadvantages to electrodynamic tethers. The e rst is that the ionosphere density is not sufe cient for maneuvering out beyond LEO.Second,for practicalcurrents, forexample, a few amperes, the achievable thrust is low, and maneuvers can take many weeks to realize. Therefore, it is necessary to make an electrodynamic tether as autonomous as possible. When human support is limited for these long-duration operations, the electrodynamic tether concept can be made more cost effective. This paper provides the guidance equations for the tether current to effect a desired change in orbital elements. The guidance is capable of simultaneously changing the orbit size, shape, and plane,thatis,semimajoraxis,eccentricity,inclination,lineofnodes, and argument of perigee. These guidance laws could be used in a mission planner to perform trade studies and to evaluate the performance of a given electrodynamic tether design. The guidance laws may be suitable for onboard implementation as well,