1. Solar Probe Plus FIELDS Instrument PDR Search Coil Magnetometer SCM
T. Dudok de Wit & G. Jannet and SCM team: C. Agrapart, P. Fergeau V. Krasnosselskikh, P. Martin, M. Timofeeva-Bouaroua
LPC2E, CNRS and University of Orléans
Contact :

2. Outline
SCM instrument general description, specifications & performances
SCM instrument design
Antenna design
Preamplifier design
Electrical interfaces
Mechanical design and interfaces
Thermal design and interfaces
Calibration
Heritage
Conclusion and main issues

3. Instrument general description
SCM is a search coil magnetometer (inductive type), consisting of:
2 single-band antennas (10 Hz-50 kHz range)
1 double-band antenna (10 Hz-50 kHz & 1 kHz-1 MHz)
4-channel miniaturized preamplifier inside sensor foot
sensor foot
Analogue outputs are processed by 3 modules from FIELDS-MEP
DFB will routinely compute spectral matrices and on demand capture waveforms from the 3 LF channels
RFS will compute spectra from the MF channel
TDS will capture waveforms from the MF channel
3 search coil antennas
3D preamplifier

4. Level 3 Requirements
Measure AC magnetic fields from 9.5 RS to AU
3D magnetic field (LF coil, 10 Hz - 50 kHz)
Min. sensitivity 10-4nT/Hz-1/2 at 3.5kHz ; Max. field intensity 1000nT at 3.5kHz
1D magnetic field (MF coil, 1 kHz - 1 MHz)
Min. sensitivity nT/Hz-1/2 at 100kHz ; Max. field intensity 6nT at 100kHz LF MF

5. Performance expectations
SCM frequency response measured with preamplifier and antennas prototype 3kHz, 100 kHz)
1.3V/nT
0.35V/nT
0.28V/nT
1.78mV/nT
2.51mV/nT
3.16mV/nT
0.09mV/nT
MF frequency bandwidth specification
LF frequency bandwidth specification

6. Instrument design

7. in addition to B3 antenna
SCM design : Antennas
Magnetic core consists of 3C95 ferrite: selected for its stable magnetic permeability (µr) at low temperatures
Coils are performed with the following characteristics :
Each antenna is inserted inside a carbon fiber tube filled under vacuum with STYCAST resin
Finished antenna dimensions: ∅20mm length 104mm
100mm
Metallized epoxy flanges for the link between coiling wire and harness
Function
LF antennas
B1, B2, B3
MF antenna B4
in addition to B3 antenna
Primary coil
13 500 turns
360 turns
Secondary coil
32 turns
3 turns
Wire
∅Cu 80µm
∅Cu 90µm
Ferrite core
Length: 100mm
∅coil: 5mm
∅max (tips): 14mm
Length: 60mm
∅inner: 12mm
∅outer: 14mm
LF coil
MF coil
Ferrite mutual reducer
SCM antennas (TARANIS EM)

8. SCM design : Preamplifier
FM preamplifier
Built in 3D technology and manufactured by 3Dplus (compliant with space- qualified PID reference rev 7)
5 stages of electronic circuits + Pin grid array on top (connection to antennas) and bottom (power supply, signals)
Protection against radiation with 0.5mm of tantalum layers at each tip of the module and a cylinder around the module
DDD protection implemented inside the preamplifier module (RC structure)
Power supply regulation
Dimensions
Height 32.3mm + 2x5mm for in/out pins
Inside a ∅18.7mm cylinder (PCB with octagonal section, width 16mm)
3LF channels
MF channel
Preamplifier FM example (heritage TARANIS)
SCM preamplifier prototype

9. Electrical interfaces
SCM is connected to
DFB, TDS and RFS for signal digitization and processing
LNPS for ±12V power supply & heating

10. SCM design : Electrical interfaces
SCM harness definition
1 shielded and twisted triple (for ±12V) & 9 shielded and twisted pairs
Cables from ESA/SCC series. Temperature range -200°C to +200°C
AWG28 wires for power supply and heaters, AWG30 for the others (flexible & reduced thermally conductive section)
SCM connector
HD-sub 26pins, shell size A
SCM harness accommodation: 30 cm pigtail
20 cm = 1 turn around the foot inside the MLI cavity
outside MLI cavity for connection to boom harness
Cables
4 for LF (X, Y, Z) and MF (X) signals
1 for calibration
1 for heating power
2 for temperature probe dedicated to heating control
1 for HK temperature probe (sent to telemetry)
10 cm pigtail
SCM HD-sub 26 pin connector

11. SCM design : Mechanical structure
Mechanical structure inherited from Solar Orbiter design
SCM mechanical assembly
Orthogonal assembly of 3 antennas (±0.1°)
Preamplifier inside the foot cavity, filled under vacuum with STYCAST resin
Total mass with MLI 680g
Element individual mass
Double band antenna
72g
Mono band antenna (each)
59g
Closing plates (each) 3g
Centering ring
Anti-rotation pin
<1g
Radiation shield
18g
Sensor foot
122g
Insulating bedplate
39g
Preamplifier
25g

12. SCM design: mechanical structure
SCM mechanical interface with the boom
The insulating bedplate must be fixed to the boom before the rest of the instrument N°
Function
Element
Material
Qty
Location
Dimension (mm)
and tolerance 1
Fixing bedplate boom
CHC Screw
Titanium TA6V4 6
On 38 at 60° M4 2
Centering, Anti-shearing
Bedplate pins
PEEK
Centered on ZURF
10 g6 3
Foolproofing, Anti-rotation
Pin
On 38 pointing towards YURF
4mm g6 3 1 2
Bottom view
Top view

13. Mechanical design verification
Current design analysis with Solar Orbiter specifications (simulated with FEM):
First vibration mode: 288Hz
Sinus vibrations: current design can bear 25g sinus with good margins
Random vibrations: Instrument capabilities already validated up to 1.5g²/Hz
Shocks: validated up to 2000g
SCM FEM is ready
analysis shall be performed with specifications for I-boom units
Mode 1 foot bending (along X axis)

14. Thermal interfaces SCM environment SCM temperature ranges
I-boom: -175°C as a worst case (TBD with EDTRD update)
No solar flux during Sun-pointing phases
Suitable thermal interface is required including insulation and heating
SCM temperature ranges
element
Operating
switch-on
non-operating
survival mode
Antennas
-100 to +100 °C
Electronics
-50 to +80 °C
-60 to +100 °C
Harness
-200 to +200 °C

15. SCM design : Thermal interfaces
Passive thermal control
direct heritage from Solar Orbiter design
protection against radiative losses: double 15-layer MLI envelope
protection against conductive losses: insulating bedplate reducing contact surface & decoupling instrument from fixing screws
conduction through harness reduced by a full turn around the bedplate and increased pigtail length
MLI and harness accommodation
Contact area
foot / insulating plate: 504mm²

16. SCM design : Thermal interfaces
Active thermal control
Critical element is preamplifier
Heaters are wrapped around the preamplifier (Flexible polyimide thermofoil by MINCO, space qualified ESCC ), powered by LNPS
Temperature probe for heating control (Lakeshore PT-103)
1 HK temperature probe for transmission to telemetry (Lakeshore PT-103 likely)
Required heating power
Thermal analysis in progress (software compatibility problems)
heater
T probe
control
T probe
monitoring

17. SCM design : Accommodation
Location on I-boom is dictated by EMC requirements
Minimum distance from spacecraft : 3m is acceptable for science if RE-01 requirements are applied on spacecraft bus
Minimum distance from MAG unit : 1m is acceptable (interference tests, June 2012)
Envelope of MAG drive frequency & harmonics
SCM-MF noise floor with MAG at 1m

18. Overall volume with MLI blanket
Summary of resources
Power budget
Instrument power supply: 270 mW ±12V
Heating power: TBC (600mW allocated)
Mass budget
total mass of SCM unit 680g
Instrument: 525g
Harness pigtail: 30g
MLI blanket: 125g
Harness: 55.2 g/m + 15 g/connector
Overall volume with MLI blanket
diameter ∅110mm
height 165mm
Overall volume with MLI blanket
110 85
165
∅77

19. SCM frequency response test bench (mu-metal box)
Calibration
Pre-flight calibration
Frequency response measurement to have SCM gain in V/nT
Sensitivity measurement to demonstrate capacity of measuring small fields.
SCM test bench is composed of :
Network/spectrum analyzer
Mumetal shielding to get a magneticallly clean environment
Helmholtz coil system for magnetic field generation
In-flight performance testing
Onboard verification system
Sensor response to a calibration signal (sine waves) sent by DFB
Exact CAL signal still TBD
SCM frequency response test bench (mu-metal box)
4 layers of µmetal
20cm Helmholtz coils
Flux feedback
CAL signal from DFB
Measmt. signal
Main coil
preamplifier

20. SCM maturity: heritage
Strong heritage from TARANIS & Solar Orbiter SCM
TARANIS heritage
Antenna design: double band concept
3D Preamplifier design and qualification philosophy
Full instrument concept with preamplifier inside the foot has been validated on a fully operational EM
Assembly process
Solar Orbiter heritage
Antenna ferrite core and coiling process
Mechanical interface
Thermal interface: conductive and radiative insulations, heating system implementation
TARANIS EM search coil

21. Conclusions and open issues
SCM meets Level 3 requirements
SCM has good level of maturity thanks to strong heritage from SCM on TARANIS and Solar Orbiter
Open issues (peer review)
EMC requirements impose minimum distance from S/C (RE-01 specification) and from MAG magnetometer. Final orientation of the antennas will be set accordingly.
Thermal model definition and simulation to be done with Solar Probe temperature conditions. Heating power to be set accordingly.
Mechanical and structural analysis to be updated with I-boom specifications to confirm the design

22. Backup slides

23. Performances expectations
SCM sensitivity curves measured with preamplifier and antennas prototype
L3 specifications
10-3nT/Hz-1/2
10-4nT/Hz-1/2
10-5nT/Hz-1/2

24. SCM design: antennas Antenna internal structure
Dimensions: cylinder ∅20mm, length 104mm
Inner volume is filled under vacuum with STYCAST resin (epoxy)
Ferrite mutual reducer
Carbon fiber tube
LF coil
Ferrite core
Harness: 2 twisted and shielded triple
Internal potting with STYCAST resin
Copper foil separation screen
MF coil
Finished antenna with wires and electrostatic shield

25. SCM design : Preamplifier
Radiation protection
Ta layers (0.5mm) at each tip inside the module
Ta cylinder (thickness 0.5mm) around the module
EEE components status
All passive parts are space qualified (MIL-PRF or ESCC)
Active parts
2 space qualified: 1 OpAmp, 1 current diode
5 Commercial parts: heritage from TARANIS and/or Solar Orbiter
Commercial parts selected for performance and dimensions
3D preamplifier qualification
Manufactured by 3Dplus (compliant with space-qualified PID reference rev 7)
FM manufacturing lot to be submitted to Lot Acceptance Tests (LAT), by heritage it will be based on:
burn-in (168h) and life test (1000h at 125°C) on 2 modules and DPA on 1 module
Fast temperature variations (500 cycles -55°C/+125°C) on 2 modules and DPA on 1 module
LAT will be adapted to Solar Probe mission

26. DDD protection
Injection of DDD at preamplifier output: waveform generated by the model proposed by APL
Implemented design: RC filter, a 4.7nF capacitance is added to the current electrical scheme
Working with 150Ω resistor already present
out in
SCM preamplifier output stage
~5.5V at preamplifier output with 150Ω, 4.7nF config.

27. DDD protection Component selection
4.7nV capacitor in 1812 package, ESCC
admissible DC voltage 1000V, dielectric strength 200% ⇒ 2000V pulse acceptable
Resistor: 2 components in 1206 package added to take margin
Routing with SCM preamplifier PCB dimensions
Implementation is feasible on a single additional preamplifier stage
16mm
routing:
3 ½ structures on top and 3 ½ at bottom
Protection structure x7
Top view of protection routing

28. SCM design: mechanical structure
SCM mechanical interface with the boom: 2nd step
The instrument is fixed to the bed plate N°
Function
Element
Material
Qty
Location
Dimension (mm) and tolerance 4
Fixing foot to bedplate
CHC Screw
Titatium TA6V4 6
On ∅40 at 60° M4 5
Centering, Anti-shearing
Ring
PEEK 1
Centered on ZURF
∅10 H7
Foolprofing, Anti-rotation
key
On ∅50 pointing towards XURF
Width 4mm g6 5 4 6
Top view

29. Harness DDD protection
Additional shielding braid option
SCM harness is composed of 10 cables, if an overshield is implemented, required internal diameter braid is ∅8mm.
AXON reference gives a mass of 52g/m
Electronic protection option
Using resistor + capacitors to ground to protect the 4 measurement channels and power supply regulation circuit
Can be implemented on an additional stage inside the 3D preamplifier
This circuit does not protect temperature probes
2 possibilities still in balance
Easiest solution is the additional shielding on harness with the drawback of extra mass and stiffness
Electronic protection is the best possibility in terms of mass. A way of protecting temperature probes shall be found

30. SCM design : EMC test results
MAG-SCM interference test result
Decrease of MAG drive frequency spike with the separation
Measurements of June 2012

31. SCM verification: calibration
Frequency response measurement
Measurement for each channel (3LF and 1 MF) with a Helmholtz coil system and a test bench
Inside a mumetal shield to avoid EMC disturbances
Outside in “free field” to verify “wall effects”
Gives SCM calibration curve (gain in V/nT and phase) used for production of data in physical unit
Power supply
SCM harness
CH2
CH1
Gain control
source
Input signal to Helmholtz coil
Network analyzer
Gain control nT/V
4 layers of µmetal
20cm Helmholtz coils
µmetal shielding boxes

32. SCM verification: calibration
Sensitivity measurement
Measurement for each channel (3LF and 1 MF) with the sensor alone in a mumetal shielding box
Verifies the lowest signals SCM can measure
Power supply
SCM harness
CH1
Spectrum
analyzer
µmetal shielding boxes

33. SCM verification : in flight test
In flight performance verification
Onboard verification system
Sensor response to a signal composed of sinus waves
Signal send by DFB during 4s (TBC)
Verify the correct behavior of the instrument (gain and phase) by comparison with ground measurements
This system can be used as a functional test on ground
Science measurements can be performed at the same time
Duration of CAL sequences and CAL frequencies
Flux feedback
Calibration signal from DFB
Main coil
Measurement signal
preamplifier

34. SCM design maturity Antennas Preamplifier Design is fully defined
Coils for ETU model have been received (coiling operation done by Microspire)
MF coils for the double band antenna will be added at LPC2E
Preamplifier
Electrical scheme is ready
Issue on DDD protection (additional circuit in the module for protection) shall be fixed before starting activities with the manufacturer 3Dplus
Ferrite core and coils for SCM ETU antennas

35. SCM Design maturity Mechanical design and assembly Thermal design
Mechanical structure & machining process (tools and accessories) are defined
Design shall be confirmed by analysis with I-boom mechanical specifications
Assembly process is mastered (TARANIS heritage), necessary tools (vacuum potting, glueing, alignment... ) already exist
Thermal design
Thermal analysis is ongoing to deliver SCM thermal model and defined required heating power (SCM urgent issue)
Heaters definition and implementation process are currently being done (iteration with the manufacturer Minco). Heating power value is needed to finalize the design
SCM mechanical elements kit

36. SCM PA/QA
NASA APL FIELDS
C. Agrapart
E. Cocheteau

37. SCM PA/QA Package of Product Assurance documents available for PDR:
Reference
Product tree, issue 1.0, 03/20/2011
SPP‐SCM‐MNG‐GEN‐PT‐0002‐LPC2E
Product assurance plan, issue 1.0, 11/14/2011
SPP‐SCM‐AQP‐PAP‐PL‐0038‐LPC2E
PAP compliance matrix, issue 1.0, 04/13/2012
SPP‐SCM‐AQP‐PAP‐MT‐0082‐LPC2E
Declared components list, issue 1.0, 06/25/2013
SPP‐SCM‐AQP‐EEE‐LI‐0115‐LPC2E
Declared materials list, issue 1.0, 03/26/2013
SPP‐SCM‐AQP‐MPR‐LI‐0121‐LPC2E
Declared process list, issue 1.0, 03/26/2013
SPP‐SCM‐AQP‐MPR‐LI‐0122‐LPC2E
Failure mode effect analysis, issue 1.0, 04/26/2013
SPP‐SCM‐AQP‐RIS‐TN‐0120‐LPC2E
Documentation management plan, issue 1.0, 04/08/2011
SPP‐SCM‐MNG‐GEN‐PL‐0001‐LPC2E

38. SCM PA/QA Work in progress: Future work: Product assurance plan update
PAP compliance matrix update
Risks list update