An Electric Propulsion Module (EFM) for interplanetary missions has been studied under ESA/ESTEC contract based on the AGORA mission requirements. AGORA is the synonym for Asteroid Gravity, Optical, and Radar Analysis, representing a 6 years interplanetary mission during the epoche 1993 till 1999 with rendez-vous of the asteroids Vesta, Thetis and Hersilia at approximately 2.5 AU. Because of the large velocity increment of 14 km/s required for such a mission an ion propulsion system has to be applied rather than a chemical system. This report concentrates on the design aspects of the Electric Propulsion Module EPM including solar array whereas the payload module is treated as a 465 kg, 400 W black box. Key element of the EPM is the RIT-35 ion thruster being developped at present at Uni Giessen and MBB. 4 + (2) of these thrusters are mounted on a gimballed platform and provide a maximum thurst of 4 x 0.2 = 0.8 N. Beam voltage and current of each thruster can be varied in the range of 1000 to 2000 V and 1.25 to 2.5 A, rsptly. At BOM total power of 27 kw is provided, decreasing to 6 kw at 2.5 AU. The varying power input requires beam current throttling and sequential switch-off of operating thrusters during transfer, with only 1 thruster being active at 2.5 AU. The accumulated operation time of each thruster will be 11000 hours, compared with 15000 hours qualification time. As propellant 850 kg mercury are provided, stored in 1 single tank of 50 cm diameter. For propellant expulsion under zero-g conditions bladders and GN2 stored in a separate tank are used. For thermal control of thruster electronics heat pipes and louvers as thermal switch are necessary in order to overcome the stringent thermal requirement to radiate 2.5 kw at 1 AU (hot case) and only 0.6 kw at 2.5 AU (cold case).
Electric propulsion module for high energy interplanetary missions
Elektrisches Antriebsmodul fuer Hochenergie-Interplanetare-Missionen
1985
21 Seiten, 24 Bilder, 6 Tabellen
Conference paper
English
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