Overview of ONERA’s advanced diagnostics for micropropulsion systems
- Paper number
IAC-08.C4.4.11
- Author
Dr. Simone Rocca, ONERA, France
- Coauthor
Dr. Denis Packan, France
- Coauthor
Dr. Jean Bonnet, France
- Coauthor
Dr. Paul-Quentin elias, France
- Year
2008
- Abstract
New space missions such as MICROSCOPE, LISA, LISA PATHFINDER and GAIA require high accuracy and resolution for attitude and altitude control, and they triggered the operational development of new micronewton thrusters. In particular for the MICROSCOPE mission, ALTA SpA is developing a Cesium FEEP (Field Effect Electric Propulsion) thruster, in the range 1µµN - 150 µµN. The goal of the study presented in this paper is to measure with non-intrusive, optical diagnostics the absolute flowrate of cesium atoms expelled by a flight model Cesium FEEP thruster for the MICROSCOPE mission. The atom flowrate is determined by measuring point-by-point the local velocity vector and absolute density of cesium atoms, yielding local surface flowrates, and then by integrating these values over a closed surface encompassing the plume. The velocity vector is measured using a Laser Induced Fluorescence (LIF) Doppler technique along the three axis of the frame of reference. Along each axis, a Lasertechnik TEC-500 extended-cavity laser diode, with a linewidth of 1 MHz, a CW power of 10 mW and a mod-hop-free range of 10 Ghz is tuned to the D2 transition of Cesium at about 852 nm. Using the described optical techniques point-by-point with a 1 mm spatial resolution, the 3D distribution of velocity vector and absolute concentration of cesium atoms in the plume can be measured and the cesium atom flowrate can be determined. An optical setup has been designed and built at ONERA (France) to perform these measurements on a Cesium FEEP thruster provided by ALTA SpA, in the framework of an ESA study. The thruster is mounted on three translation stages so that the optical system can probe different points of the plume. A reference cell is also included in the setup and is kept in a closed container during thruster firing, in order to protect it from the sputtering in the vacuum tank and thus ensure the accuracy of calibration for absolute density. A test of the system has been successfully performed on a source of neutral cesium, or cesium dispenser, and the results are presented. Velocity vectors and absolute number density of thermal cesium atoms were measured along a line 2 mm downstream of the 7 cm long dispenser. The resolution of the measurements can be optimized to better than 10-9 mbar (2x107 cm-3) for the number density, and better than 3 m/s for the velocity.
- Abstract document
- Manuscript document
IAC-08.C4.4.11.pdf (🔒 authorized access only).
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