Benefits of Solar Electric Propulsion for the Next Generation of Planetary Exploration Missions
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Benefits of Solar Electric Propulsion for the Next Generation of Planetary Exploration Missions Steven N. Williams· and Victoria Coverstone-CarrollAbstract Planetary missions of the future will have increasingly greater energy requirements due to the desire for in-situ investigations and faster flight times. Solar electric propulsion provides a means of more effectively accomplishing these types of missions. The first planetary low-thrust mission will be launched in July 1998, and fly by an asteroid, a comet, and the planet Mars. This mission will demonstrate solar electric propulsion technology, and lay the groundwork for more exciting missions in the future. Three missions representative of the types of future missions for which solar electric propulsion might be used are shown. In each case, the performance of solar electric propulsion and chemical options are compared.
Introduction The strategy of how to explore the solar system is currently undergoing revolutionary changes. Previous missions have visited all the planets except Pluto, including the first encounters with comets and asteroids. These initial reconnaissance missions have returned a wealth of scientific information, but the next stage of exploration will require in-situ investigations with planetary orbiters, surface rovers, and sample returns. This phase of planetary exploration began with missions like Viking, Galileo, and Cassini, and are considerably more challenging from an engineering standpoint than simple flyby missions. There is an obvious desire for larger spacecraft with more instruments to probe every facet of a remote surface. Also, and more directly related to the subject of this paper, the propulsive requirements to perform these missions are considerably more demanding. This
of the Technical Staff, Navigation & Flight Mechanics Section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109. 2Assistant Professor, Department of Aeronautical & Astronautical Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. I Member
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may require a rendezvous and planetary capture or a fast flyby (or impactor) of some object in the outer solar system (Le. Pluto). On the other hand, the need to perform good planetary science on smaller budgets is driving the industry to smaller launch vehicles, less complicated flight systems, and shorter missions. How can the realities of smaller budgets be reconciled with the scientific requirements for more challenging missions? We suggest that part of the answer is more efficient propulsion systems. Current solar electric systems can deliver specific impulses on the order of 3000 s, as opposed to around 310 s for space-storable chemical propellants. Of course one does not get a ten-fold increase in performance, because the long thrust arcs of a solar electric propulsion (SEP) system suffer more from gravity losses. Nevertheless, this difference is too large to ignore for missions with significant post-launch propulsive re
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