Perspectives of Electric Propulsion for Outer Planetary and Deep Space Missions

Solar-electric propulsion (SEP) is superior with respect to payload capacity, flight time and flexible launch window to the conventional interplanetary transfer method using chemical propulsion combined with gravity assists. This fact results from the large exhaust velocities of electric low–thrust propulsion and is favourable also for missions to the giant planets, Kuiper-belt objects and even for a heliopause probe (IHP) as shown in three studies by the authors funded by DLR. They dealt with a lander for Europa and a sample return mission from a mainbelt asteroid [1], with the TANDEM mission [2]; the third recent one investigates electric propulsion for the transfer to the edge of the solar system. All studies are based on triple-junction solar arrays, on rf-ion thrusters of the qualified RIT-22 type and they use the intelligent trajectory optimization program InTrance [3]. Mission analysis As electric propulsion scenario for an Europa lander this paper will present at first a two-stage scheme with 33 kW BOM solar power: Up two a solar distance of about 3 AU three ion thrusters with high specific impulse of 6500 s will run. This stage will be jettisoned and two ion thrusters with low specific impulse of 3700 s will continue the transfer to Jupiter and spiral the spacecraft into a parking orbit of 80 RJ. While spiralling down, the magnetosphere of Jupiter can be mapped. The lander will be a transported by a chemical 675 kg stage released from the parking orbit, passing Ganymed. The total launch mass and the total mission duration resulted in 2.71 tons and 5.7 yrs, respectively. With respect to the selection of Laplace as a combination of NASA and ESA missions, the authors intend to investigate the trade-off for reducing the transfer duration by the installation