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Science Requirements

Science Requirements. The FGM shall measure DC and low frequency perturbations of the magnetic field  see performance requirements The FGM shall measure time wave and structure propagation between probes

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Science Requirements

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  1. Science Requirements • The FGM shall measure DC and low frequency perturbations of the magnetic field  see performance requirements • The FGM shall measure time wave and structure propagation between probes • The FGM shall provide information on plasma currents based on instantaneous magnetic field differences on two or more probes, separated by >0.2RE ? modelling requirements?

  2. Performance Requirements • The absolute stability of the FGM shall be less than 1nT • The relative stability of the FGM shall be less than 0.1nT Sensor Characteristics: • offset / time: < 0.1nT/h; < 1nT/year; (+ s/c) • offset / temperature: < 0.1nT/°C • scale value / temperature: 24ppm (0.8nT/°C at 32000nT) • orthogonality / temperature: can be neglected

  3. Performance Requirements • The FGM resolution shall be less than 0.1nT • The FGM science range shall exceed 0-1000nT • FGM provides always 0.01nT resolution independently of the external field • The maximum feedback field (range) is about 32000nT • therefore three 24bit values will be sent to the IDPU • 16 bit will be selected for transmission 10pT if B < 320nT 160pT if B > 2500nT 1.2nT if B > 20000nT

  4. Performance Requirements • The FGM noise level at 1Hz shall be less than 0.1nT • Sensor noise is less than 10pT/sqrt(Hz) at 1Hz • additional “noise” will be generated by the differential nonlinearity of the 12 bit DAC’s (10% of LSB) <1000nT - 50pT(maximum), >1000nT - 1.5nT(maximum) 91pT2/Hz : 9pT/Sqrt(Hz) 26pT rms pT2 pT

  5. Performance Requirements • The FGM frequency range shall exceed DC-1Hz • primary data (FPGA1 -> FPGA2) are 128Hz mean values (128Hz data: 7.5ms measurement, 0.3ms feedback setting) • further averaging will be done by FPGA2 and IDPU • Problem: to find the right compromise between telemetry rate, aliasing errors, and spin period interferences. • Equator-S: aliasing errors are not detected although bandwidth was to high. • Cluster: ratio between spin period and data rate of 100 is sufficient.

  6. Performance Requirements • The FGM calibration shall ensure 1nT absolute accuracy • Determination of 3 offsets and 9 elements of a matrix (scale values, non-orthogonality, sensor orientation) • spin of satellite provides 8 of 12 • offsets perpendicular to spin axis (2): < 0.1nT • relation between scale values perp. to spin axis (1): < 10-4 • non-orthogonality (3): < 5’’ • orientation to spin axis (2): < 5’’ • scale values are sufficient known from preflight calibr. • orientation depends on mech. alignment of sensor (0.1-1°) • spin axis offset is the problem (1nT by known physics)

  7. Resource Requirements • The FGM shall not exceed the allocated mass budget (70g) • 36g sensor • 30g-40g for the housing

  8. Resource Requirements • The FGM shall not exceed the allocated power budget (800mW) • we need • +5Vd & +2.5Vd (FPGA & DAC): 10mA • +8Va (excitation & amplifiers): 40mA (30mA+10mA) • - 8Va (amplifiers): 10mA • +5Va (ADC): 15mA • - 5Va (ADC): 15mA • 600 mW if all voltages will be provided • 800 mW if ADC will be provided by +/- 8V • 1000 mW if only +/- 8V is available

  9. Resource Requirements • The FGM shall meet the following thermal requirement • survival temperature range (no-op): –50°C to +65°C • operating temperature range (op): –20°C to +40°C • cold start: -50°C •  tested for Rosetta and VEX • design and manufacturing of thermal sensor cover is still tbd

  10. Facilities Integration and Tests • Midex Quality Reqiurements • e-parts, see following list • fabrication of sensor in BS (no cleanroom environment) • calibration (no cleanroom environment) in Magnetsrode, Jeserigerhütten ... (outside of civilisation) • calibration facilities for final tests in Graz, Berlin, BS, und Berkeley should be identical, stimulation by coil system to test ranging ... • Schedule has to be reworked

  11. IDPU sense excitation feedback DAC ADC Sensor FPGA e-parts: overview bold - qualified red - preferred DAC: 6 x 8043 6 x 8143 FPGA: 2 x 54SX32 1 x 54SX72 Amplifier: 6 x LT1013 3 x LT1013 & 3 x AD648 ADC: 3 x AD6764 3 x AD7872 Instr. Ampl.: 3 x AD524 3 x AD625 Prec. Resistors.: Megatron MMQ / MMP Voltage Reference: 1 x LT1013 Driver: 1 x HS9-4424 1 x MIC4425 Line Regulators: LM117 & LM137

  12. Contamination Requirement • all instruments shall comply with the MC standard • UCLA responsibility • if necessary we can provide • ESTEC software • turntable to determine magnetic moments • gradiometer mounted on a guide bar to estimate s/c field

  13. operation • operation during ... • all science phases in the same mode • all technically interesting phase (orbit change, eclipse) • FGM should be switched on before boom deployment

  14. IDPU requirements • FGM software • selection of 16bit, orbit controlled or auto-controlled • despin onboard? • relation to other experiments • test data necessary? • responsibility? • FGM hardware • clock / timing

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