Electric Solar Wind Sail Pole Sitter Spacecraft

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Electric Solar Wind Sail Pole SItter Spacecraft Proposal SummaryA major constraint on the capabilities of conventional spacecraft is the limited amount of fuel they can carry. Trajectories are generally ballistic with modifications by means of short thruster bursts or gravity assists. However, the Sun is a source of unlimited thrust which if appropriately harnessed can allow spacecraft to perform manoeuvres impossible for conventional spacecraft, such as "orbits" entirely out of the plane of the ecliptic. One of these balances the gravity of the Sun and the Earth with dynamic and solar forces, (provided by either the solar photon flux or the solar plasma flux - the solar wind) so that the spacecraft can hover in a fixed position above one of the Earth's poles. This is called a "polesitter" orbit. One type of spacecraft designed to use the solar wind is the electric sail spacecraft (e-sail) consisting of a central hub from which radiate a number (approx 80) of long tethers (approx 20 km) all charged to a high positive potential so as to react against the protons of the solar wind to provide thrust. The whole structure is spun to provide gyroscopic stiffnessThe idea of a polesitter using an e-sail is an exciting new research area which nevertheless has very practical potential applications. One example is northern communications. Above 60 degrees latitude geostationary satellites are of limited value for communications, with the result that expensive constellations of spacecraft in highly eccentric orbits have been seen as the solution thus far. The recent Canadian Polar Communications and Weather (PCW) program of exactly this type, was put on hold when its cost estimates for just two satellites became astronomical. A polesitter, on the other hand, could just hover above the pole as a communications relay satellite and could also monitor the weather from a relatively fixed point. A polesitter would also have many advantages as a remote sensing platform, but perhaps the most significant application would be for monitoring solar weather and warning of geomagnetic storms. The result of solar flares and mass ejections, these events destroy satellites, disrupt communications and knock out power grids at great financial cost and threat to lives. The Ace and SOHO spacecraft, currently our best means of solar weather monitoring, are at Sun-Earth L1, providing 30 to 60 minutes of warning of these events. A polesitter could be parked twice as far sunward as these spacecraft, thus doubling the warning time for us on the Earth.The ultimate objective of this research is a technology demonstration flight of an e-sail pole sitter, but it is necessary first to understand the dynamics and control of this type of spacecraft in such orbits. The e-sail pole sitter of this proposal has never before been considered.The goals of this proposal then are: to characterize the solar plasma thrust on an e-sail; to investigate stability and controllability of e-sail polesitter orbits; to design a control system to hover an e-sail spacecraft at a fixed point above one of the Earth's poles; to design a method to maintain the structural integrity of an e-sail spacecraft; and to investigate a radical new technology, the photonic cavity thruster, which would use laser light pressure for structural control of an e-sail.