RITA - An Ion Thruster System for Commercial and Scientific Applications

Abstract

Gridded Ion Thrusters are the technology that allows substantial performance improvements for commercial and scientific satellites. Thanks to their high specific impulse capabilities, the systems offer mass savings by reduced propellant consumption station keeping applications for telecommunication satellites or deep space science missions. EADS SPACE Transportation is developing ion propulsion since many years and with the RIT-10 ARTEMIS flight heritage in a regime even exceeding qualification limits could be obtained. Based this EADS-ST has started the development of a high thrust Radiofrequency Ion Thruster Assembly (RITA) in cooperation with European partner companies. The development comprises the RF-Ion Thruster (RIT) including the Frequency Generator (RFG), The Power Supply & Control Unit (PSCU), and the Xenon Flow Controller (XFC). Providing for a nominal thrust range between 100mN and 200 mN at specific impulse of more than 4200s and 4 to 6 kW power consumption (5 kW PSCU baseline), the unit requirements are optimized as well for the use next generation telecommunication satellites, as the needs of future science missions such as ESA's BepiColombo mission to planet Mercury.The core component, the thruster RIT-22 is under development by EADS Space Transportation GmbH. In contrast to other ion engines developed worldwide, the RIT-22 has a unique feature: The propellant is ionized cathodeless by electromagnetic waves. This, so called Radio Frequency Ionisation, guaranties for highest reliability (no life limited cathode inside, intrinsic isolation from the discharge plasma high voltage potential to the surroundings) and flexibility in design. During the last three years, engineering and breadboard Models of the RIT-22 have been build and successfully characterized. The characterization includes the basic performance mapping, extended beam diagnostics and direct thrust measurement. Also tasks, as dual operation of two thrusters in the vacuum test facility to study possible interactions between the engines have been performed. The program is ongoing and advanced tasks (operation at highest ambient temperatures e.g.) will be performed in near future. Of course, the design goal, a specific impulse of more than 4000s for the basic, but most important commercial application, the north-south-station keeping of geo synchronous could be successfully demonstrated early. For north-south station keeping, the nominal thrust is set to 150mN. The thrust range reaches from 25mN up to more than 250mN. The dynamic of more than 1:10 is correlated with an increasing specific impulse with raising thrust. In fact, a maximum specific impulse of more than 6000s could be successfully demonstrated in 2003. Considering interplanetary missions, ESA's corner stone mission BepiColombo, a journey to Venus including an orbiter and lander to the suns nearest planet is one of the most ambiguous challenges for electric propulsion and space engineering in the near future. Especially the extremely high thermal environment forces spacecraft design on the limit. Principally, the rf-technology shows the inherent advantages also under this extreme environment. The avoidance of any cathode inside the thruster which has to be adapted to the high temperatures in its surroundings is a clear advantage. Nevertheless the thermal load for the grid system is extremely high. In the framework of the ESA activity New Grid systems for Ion Engines EADS ST started the design and manufacturing of a grid optimized for the BepiColombo mission.In for future application high and ultra high specific impulse (Isp) electric propulsion becomes from growing attraction as the electrical power