ISTS 2006-k-35 MISSIONS TO THE EDGE OF THE SOLAR SYSTEM USING A NEW ADVANCED DUAL-STAGE GRIDDED ION THRUSTER WITH VERY HIGH SPECIFIC IMPULSE

A new and innovative type of gridded ion thruster, the “Dual-Stage 4-Grid” or DS4G concept, has been proposed and its predicted high performance validated under an ESA research, development and test programme. The DS4G concept is able to operate at very high specific impulse and thrust density values well in excess of conventional 3-grid ion thrusters at the expense of a higher power-to-thrust ratio. This makes it suitable for ambitious missions requiring very high delta-V capability and high power. Such missions include sub100 kilowatt multi-ton probes based on nuclear electric propulsion to distant Kuiper Belt Object and inner Oort cloud objects, and to the Local Interstellar medium. In this paper, the DS4G concept is introduced and its application to this mission class is investigated. Benefits of using the DS4G over conventional thrusters include reduced transfer time and increased payload mass, if suitably advanced lightweight nuclear reactor technologies are developed. A mission-level optimisation is performed (launch, spacecraft system design and low-thrust trajectory combined) in order to find design solutions with minimum transfer time, maximum scientific payload mass, and to explore the influence of power system specific mass. It is found that the DS4G enables an 8-ton spacecraft with a payload mass of 400 kg, equipped with a 65 kW nuclear reactor with specific mass 25 kg/kW (eg. Topaz-type with Brayton cycle conversion) to reach 200 AU in 23 years after an Earth escape launch by Ariane 5. In this scenario, the optimum specific impulse for the mission is over 10,000 seconds, which is well within the capabilities of a single 65 kW DS4G thruster. Copyright © 2006 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved.