THERMAL PLASMA MEASUREMENT UNIT FOR PROBA II MICROSATELLITE F. Hruska, J. Base, J. Chum, J … The TPMU is housed in an aluminum box together with the electronics of the Dual … THERMAL PLASMA MEASUREMENT UNIT FOR PROBA II MICROSATELLITE Thermal plasma measurement unit for microsatellites THERMAL PLASMA MEASUREMENT UNIT FOR PROBA II MICROSATELLITE F. Hruska, J. Base, J. Chum, J. Klas, I. Kolmasova, J. Smilauer and V. Truhlik Institute of Atmospheric Physics ASCR,v.v.i. Bocni 2-1401, 14131 Praha 4, Czech Republic THERMAL PLASMA MEASUREMENT UNIT. FOR PROBA II MICROSATELLITE. F. Hruska, J. Base, J. Chum, J. Klas, I. Kolmasova, J. Smilauer and V. Truhlik …

2. MEASUREMENT METHOD The ion measurement is based on retarding potential analyzer (RPA). RPA consists of planar sensor which is directed approximately along the spacecraft velocity vector. The sensor has internal grids. Subsequent steps of positive voltage are applied to the grids to retard the incoming ion flux that reaches the collector. The resulting ion-flux versus retarding potential measurements is used to derive the total ion concentration Ni, the ion temperature Ti and the approximate ion composition. The electron temperature measurement uses another principle and sensor. It is based on radio frequency probe method using the RF signal (~50 kHz) which is modulated by square wave. The amplitude of RF is controlled in such a manner that the shift of probe potential is constant. The probe potential is periodically searched for minimum of electron temperature . The electron temperature is measured under the assumption of Maxwellian distribution. Ranges of measurement: Total ion density: 2.107 – 8.1012 m-3 Electron temperature: 800 – 20000 K Ion temperature: 800 – 10000 K Floating potential of the satellite: ±12 V 3. TECHNICAL DESCRIPTION The TPMU is housed in an aluminum box together with the electronics of the Dual Spherical Langmuir Probe (DSLP) experiment. Both experiments have the Digital Processing Unit (DPU) in common. Digital part of the TPMU is built on the 8051 clone (ADuC845), containing among others single-cycle core 8051-based core running on 12.58 MHz, 62kBytes program memory, 2304 bytes on-chip data RAM, two independent 24-bit ADCs with 8 input channels, 12 bit D/A converter. It provides proper timing and control signals for the analog part, primary data processing and necessary calculations.

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