ESA Science & Technology - Publication Archive
Scientific Coordination: Agustin Chicarro
This ESA Special Publication focuses on the Mars Express scientific instrumentation and its state about a year after launch in order to include some initial scientific discoveries. In spite of the Beagle 2 failure, the lander's payload is also thoroughly described here because it is of the highest scientific value. Furthermore, the orbiter instruments are looking specifically for possible evidence of past or present life. No other mission to Mars since NASA's Viking missions in the 1970s has made exobiology so central to its scientific goals.
Electric propulsion represents one of the most promising technologies for application in future space missions. The knowledge of the plasma plume evolution in the thruster surrounding space is still of fundamental importance, at system design level, for new generation satellites, in order to integrate the propulsive subsystem with the other vehicle subsystems. Furthermore, the necessity to simulate realistic configurations leads to the need of powerful and flexible 3-D tools. Alta S.p.A. and Consorzio Pisa Ricerche developed a three-dimensional particle-in-cell code capable to simulate conditions found both in space and in ground vacuum facilities, for realistic satellite configurations for Hall Effect Thrusters and Gridded Ion Engines. The present article will present a brief description of the PICPluS 3D code, including the various physical models that can be used and the code validation. Numerical results related to the ESA's SMART-1 satellite, launched on 27 September 2003, will then be compared with flight data. Finally, an analysis of the influence of the simulation paramaters on the results will follow.
Onboard the ESA SMART-1 spacecraft, (Small Mission for Advanced Research in Technology), the Xenon feeding system operates since the September 30th 2003. EPS Contractor, ESTEC, and EPS manufacturer, SNECMA MOTEURS, present in detail the major performances of the Pressure Regulation System, with a comparison to the ground tests results. The PPS® -1350 Hall Effect plasma Thruster needs a regulated xenon pressure as input of the flow controller. Such pressure is delivered and controlled by two pieces of hardware, the "Bang-Bang Pressure Regulation Unit" and the "Pressure Regulation Electronic Card". The concept is described as well as its main features: the robustness by design that cannot allow a direct communication between the high-pressure parts (the xenon tank) and the low-pressure parts (the thruster input). The paper highlights the possibility for various parameters to be tuned by telecommands in order to reach different performance levels of the pressure regulation. The real flexibility of the concept allows smoothing the pressure regulation. This paper describes the performances results of the pressure regulation in space environment compared to the ground tests results. It discusses also the advantage of the regulation tuning capability during the first flight phase. This new features of primary electric propulsion subsystem demonstrates its robustness and flexibility toward thruster initial requested tuning to keep the thruster loop fine pressure regulation in an adequate range.
Onboard the ESA SMART-1 spacecraft, (Small Mission for Advanced Research in Technology), the primary Electric Propulsion Subsystem (EPS) operates since the 30th September 2003. EPS Contractor, ESTEC, and EPS manufacturer, SNECMA MOTEURS, present in detail the major performances of the complete electric propulsion system, with a comparison to the ground tests results. The PPS®-1350-G Hall Effect plasma Thruster and its Power processing unit, developed in the frame of the CNES Stentor Program, was tested at Snecma facilities. The main feature of the Smart-1 system is its variable power supply. Integrated into the whole spacecraft the electric propulsion system was tested at ESTEC before the in-flight first firing after the successful Ariane V launch. Results of these main tests demonstrate a good prediction of the in flight EPS behavior including the robust bang-bang xenon pressure regulation for the input pressure and variable electrical power supply. This paper describes the performance results of the PPS®-1350-G firing in space environment. It discusses also the consequences of the Van Allen radiation belt crossing during the first flight phase, particularly the behavior of the floating potential of the thruster with respect to the satellite electrical ground. The initial successful results obtained supports the first technological experience objective of the SMART-1 mission. These new features of primary electric propulsion subsystem and especially the low-power start-up and variable power features can be also a significant added value for any commercial application using electric propulsion for station-keeping and/or orbit transfer.
Present simulation techniques for plasma thrusters plume simulations usually implement a Particle In Cell / Monte Carlo approach to a plasma flow considered in a quasi-neutral state, with the possibility of a residual atmosphere (typical of a vacuum chamber test facility). Nonetheless it is difficult to compare directly results, even with measurements taken in very similar laboratory configurations, because it's not yet achieved the possibility to simulate at the same time realistic chamber geometry, pumping system performance and effect of the sputtering caused by the ion beam impinging the chamber walls. The present article will show the results of a series of PIC/DSMC simulations executed with CPR/Alta codes on HET plumes, considering a wide range of realistic laboratory configurations, and considering also the effect of different physical models; results will be also compared with experimental ones from literature and Alta testing facilities and flight data from the European SMART-1 mission.
Editor: A. Wilson The report for the 35th COSPAR Meeting covers, as in previous issues, the missions of the Scientific Programme of ESA in the areas of astronomy, Solar System exploration and fundamental physics. This year's COSPAR Meeting occurs only weeks after the Saturn-orbit insertion of the Cassini spacecraft - carrying Europe's Huygens probe to explore the atmosphere of Titan - and at the same time as the launch of the second satellite of the Double Star project.
- perform instrument conceptual design and trades
- prepare a preliminary instrument design including budgets and subsystem designs with required performance
- show science requirements compliance
- define critical design issues requiring further analysis
- assess and analyse programme, risk and costs
Electric propulsion represents one of the most promising technologies for application in future space missions; Hall Effect Thrusters (HET's) and Gridded Ion Engines (GIE) are particularly interesting for their relatively high thrust capability coupled with a specific impulse which is up to one order of magnitude higher than latest generation chemical systems. The knowledge of the plasma plume evolution in the thrusters surrounding space is of fundamental importance, at system design level, for new generation satellites, in order to integrate the propulsive subsystem with the other vehicle subsystems: as known, the use of electro-magnetic thrusters can create compatibility problems, due to the electrically charged particle flow, which can interfere with telecommunication signals and generate erosion and insulation loss for critical satellite surfaces (e.g. solar panels, optical instruments and sensors etc.) A number of Hall thrusters plume models have been developed, present simulation techniques usually implement a Particle In Cell / Monte Carlo approach to a plasma flow considered in a quasi-neutral state, with the possibility of a residual atmosphere (typical of a vacuum chamber test facility). In this paper the 3D plume simulation model developed by Alta will be described, and applied to model the SNEMA PPS® 1350 thruster used on the SMART-1 satellite.
|4||Solving the puzzles of Saturn and Titan|
|6||High ambitions for an outstanding planetary mission|
|8||A long and rich journey|
|12||What lies beneath?|
|20||Vehicles of discovery|