GEOSAIL: Exploring the geomagnetic tail using a small solar sail

Conventional geomagnetic tail missions require a spacecraft to be injected into a long elliptical orbit to explore the spatial structure of the geomag netic tail. However, because the elliptical orbit is inertially fixed and t he geomagnetic tail is directed along the sun-Earth line, the apse line of the elliptical orbit is precisely aligned with the geomagnetic tail only on ce every year. To artificially precess the apse line of the elliptical orbi t in a sun-synchronous manner, which would keep the spacecraft in the geoma gnetic tail during the entire year, would require continuous low-thrust pro pulsion or periodic impulses from a high-thrust propulsion system. Both of these options require reaction mass that will ultimately limit the mission lifetime. It is demonstrated that sun-synchronous apse-line precession can be achieved using only a small, low-cost solar sail. Because solar sails do not require reaction mass, a geomagnetic tail mission can be configured th at provides a continuous science return by permanently stationing a science payload within the geomagnetic tail.