Electric Propulsion System Design basing on HEMP Technology for High Accuracy Geostationary Satellites
- Paper number
IAC-08.C4.4.4
- Author
Mr. Marcel Berger, Astrium GmbH, Germany
- Coauthor
Mr. Jens Levenhagen, Astrium GmbH, Germany
- Coauthor
Mr. Danilo Baldesi, Astrium GmbH, Germany
- Year
2008
- Abstract
For geostationary, scientific satellites with challenging demands in pointing accuracy and scientific duty cycle, high constraints for reaction wheel offloading and orbit maintenance manoeuvres are design driving for an AOCS system. One approach is the use of an electric propulsion system basing on the High Efficient Multistage Plasma (HEMP) Thruster technology. With its simple and robust design the HEMP thruster proposes good performances and simple operations but this has not been analysed before - neither on propulsion system nor on spacecraft level. A high accuracy, geostationary sample mission was used to generate functional requirements for a HEMP system. A generic HEMP system design process has been established and used in order to identify system design options. In this process, a systematic, top down approach has been followed. System architecture options were traded in a first step so that the minimum operations and reliability requirements were satisfied. Thrust performance analysis on system level led to requirements towards Power Supply and Control Unit (PSCU) and Flow Control Unit (FCU). Several PSCU and FCU design options were traded against overall system performance, operations, budgets and complexity. The main design driver for a HEMP system was found to be the thrust noise, which is rather a product of a variation of electrical parameters (anode voltage, neutraliser current) and the propellant massflow than by the thruster itself. Thrust control is typically handled by two approaches: anode voltage or propellant massflow control. Thrust control by electrical parameters leads to fast thrust responses (in the range of milliseconds) and very dynamic thrust behaviour. The penalty of the good thrust performance is a reduced mean specific impulse (Isp) as the thruster is working slightly off its design point. In a detailed AOCS performance analysis the thruster operating performance was traded against pointing requirements of the sample mission. It was shown that with a combination of reaction wheel-off loading and orbit manoeuvres the HEMP system performance in terms of thrust accuracy and noise (< 0.7mN) can meet overall mission requirements. Generic and HEMP specific system design considerations have led to an optimum HEMP system architecture for the sample mission. This is considering 4(+4) HEMP thruster, a nominal thrust of 50mN, a mean specific impulse of 2750s and nominal HEMP system power demand of 7.5 kW. Alternatively, nominal thrust level can be reduced to 30mN so that the overall power demand can be reduced to a total of 4.1 kW.
- Abstract document
- Manuscript document
IAC-08.C4.4.4.pdf (🔒 authorized access only).
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