Institut für Geophysik und Meteorologie FGS Mechanical Design Hans-Ulrich Auster Institut für Geophysik und Meteorologie TU Braunschweig

Sensor selection Sensor design Test results Fluxgate Sensor (FGS) vector compensated ringcore sensor Sensor design function + material + fabrication of all sensor parts Test results space qualification, parameter tests

Sensors Mars96, EQS, DS, 240g Rosetta Orbiter, DS1, <50g, <10cm³ Observatories, MC, applied Geophysics 3kg Rosetta Lander, MIR, VEX, terrestrial applications. <50g M 1:10 M 1:1

Vector-compensated Ringcore sensor Why this Sensor? Vector-compensated Ringcore sensor Two crossed ringcores for three components Large feedback coil system (Al and Cu only) high thermal expansion coefficient (24ppm) sensor signal not identical for each component low mass homogeneous feedback field lot of flight and ground based applications

Vector Compensation Transfer Function: without feedback: Y X Angle between true Y and Open Loop Y axes Angle between true X and Feedback X axes Angle between true Y and Feedback Y axes Transfer Function: without feedback: _ + with independent feedback coils: with vector compensating feedback coils:

Sensor Design (1) Crossed Ringcores Y X Z Parameters Dimensions: 13mm, 17mm, 24mm in diameter Soft magnetic material: 6-81-Mo Permalloy band of 2mm width and a thickness of 20µm Bobbin: non-ferromagnetic NiMo30 alloy Two ringcores for three components With one ringcore the field can be measured in two directions (ringcore plane). With the second ringcore the third dimension can be measured and one of the other ringcore components is improved.

Sensor Design (2) Pickup Coil systems Parameters X and Y: two oval coils each Z: one ring coil Sensitivity: about 1,5 … 3µV/nT Material: Cu wire isolated by polyesterimid and covered by bond coat (polyamid) Requirements to workmanship Symmetry is necessary in order to reduce contribution of excitation frequency and its odd harmonics. Orientation and stability are not critical because its influence is reduced by the vector compensation.

Sensor Design (3) Support System Mounting elements: Struts: Al, 12g in total Fixation: by glue (UHU Endfest 300) Screws: Brass, M1,5 Sensor PCB: Provider: Straschu GmbH, Oldenburg Material: 1mm epoxy fibreglass compound Features: single layer with vias used as connections

Sensor Design (4) Feedback Coil System Parameters Material: Cu - wire, see pickup Coil constants: X - 13000nT/mA Y - 15000nT/mA Z - 17000nT/mA Thermal expansion coeff.: 24ppm (Cu and Al) Fixation: by glue (Endfest 300) Requirements to workmanship Symmetry is necessary for a real Helmholtz-System. Orientation and stability are necessary because scale value and orthogonality are dependant on it.

Sensor Design (5) Sensor Hut & Interface Parameters Material Hut & base plate: Aluminium Isolation: glassfibre reinforced plastics Screws: titanium Washers: glassfibre reinforced plastics Surface (Al): Alodine 1200 Interface: four M4 screws Mass: 78g Manufacturer: Artec Präzisionstechnik GmbH, Osterode Germany

Qualification Vibration Specs (Qualification): Sinusoidal Vibration: Rosetta - Ariane 5 Venus Express - Sojus/Fregat Sinusoidal Vibration:   5 - 20 Hz: 12mm 20 - 26 Hz: 1.5m/s   26 - 100 Hz: 25g Random Vibration, Grms = 18.07: 20 - 100 Hz: +6dB/Oct 100 - 400 Hz: 0.5 g2/Hz 400 - 2000 Hz: - 6 dB/Oct Quasistatic Acceleration: 25g TV Specs (Qualification): Rosetta: -150°C Venus Express: +100°C Radiation Electronics: Rosetta: 10krad Venus Express: 12krad Radiation Sensor N/A

Qualification EMC Emission of excitation frequency excitation current, 1mV = 1mA EMC Emission of excitation frequency Sensitive on 2 fexcitation M, generates 1nT B, generates by 1mAm² Magnetic Cleanliness for Boom & Sensor Susceptimeter necessary to detect magnetic critical parts

Stability of Parameters Test over 100 days using FGM for absolute measurement of the Earth field Offsets: < +/-1nT Scale values: 0.02% drift Orthogonality: < 0.01% Scale Value Offset Orthogonality