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

2. 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

3. 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

4. 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

5. 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:

6. 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.

7. 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.

8. 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

9. Sensor Design (4) Feedback Coil System Parameters
Material: Cu - wire, see pickup
Coil constants: X nT/mA
Y nT/mA
Z nT/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.

10. 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

11. Qualification Vibration Specs (Qualification): Sinusoidal Vibration:
Rosetta - Ariane 5
Venus Express Sojus/Fregat
Sinusoidal Vibration:
  Hz: 12mm
Hz: 1.5m/s  
Hz: 25g
Random Vibration, Grms = 18.07:
Hz: +6dB/Oct
Hz: 0.5 g2/Hz
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

12. 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

13. 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