Electric Propulsion Options for a Magnetospheric Mapping Mission

Steven OlesonNYMA Inc.NASA Lewis Research CenterBrook Park, OH 44142Chris RussellUniversity of California, Los AngelesInstitute of Geophysics and Planetary PhysicsLos Angeles, CA 90095Kurt Hack and John RiehlNASA Lewis Research CenterCleveland, OH 44135The Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories mission concept was proposed as aMiddle Explorer class mission. A pre-phase-A design was developed which utilizes the advantages of electricpropulsion for Earth scientific spacecraft use. This paper presents propulsion system analyses performed for theproposal. The proposed mission required two spacecraft to explore near circular orbits 0.1 to 15 Earth radii in bothhigh and low inclination orbits. Since the use of chemical propulsion would require launch vehicles outside theMiddle Explorer class a reduction in launch mass was sought using ion, Hall and arcjet electric propulsion system.Xenon ion technology proved to be the best propulsion option for the mission requirements requiring only twoPegasus XL launchers. The Hall thruster provided an alternative solution but required two larger, Taurus launchvehicles. Arcjet thrusters did not allow for significant launch vehicle reduction in the Middle Explorer class.IntroductionThe TEMPEST (Twin Electric MagnetosphericProbes Exploring on Spiral Trajectories) missionconcept was proposed as a Middle Explorer(MIDEX) class mission. Figure 1 presents an earlyconceptual TEMPEST spacecraft. The pre-phase-Adesign utilizes the advantages of electric propulsionfor Earth scientific spacecraft use. TEMPEST isderived from an earlier concept, TROPIX (TransferOrbit Plasma Interaction eXperiment).1Figure 1. Conceptual TEMPEST SpacecraftThe following study draws requirements andconceptual information from the TEMPEST MIDEXProposal. The propulsion system trades that form thebulk of this paper were made during the pre-phase-Aprocess. 30-cm ion thrusters were preliminaryselected for the TEMPEST science mission based ontheir performance.Study Objectives and ApproachThe objective of this paper is to demonstrate theadvantage of using electric propulsion technology forMIDEX class Earth magnetospheric mappingmission. Mission performance comparisons betweenelectric and chemical thrusters are made. Inaddition, specific requirements, impacts and benefitsof using an ion propulsion system (IPS) on an Earthorbital spacecraft are identified.Emphasis is placed on determining the performanceeffects of an electric propulsion system in terms ofreduced launch mass. This study includes anassessment of two solar cell technology options andquantifies the radiation damage encountered duringthe transfer through the Van Allen Belts.The following mission and science descriptions areexcerpts from the TEMPEST MIDEX Proposal. TheyNASA/TM--1998-206303 1