Solar Probe Plus FIELDS Instrument PDR Search Coil Magnetometer SCM

1. Solar Probe Plus FIELDSInstrument PDRSearch Coil Magnetometer SCM T. Dudok de Wit & G. Jannetand SCM team: C. Agrapart, P. Fergeau V. Krasnosselskikh, P. Martin, M. Timofeeva-Bouaroua LPC2E, CNRS and University of Orléans Contact : ddwit@cnrs-orleans.fr

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 +0.25 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 3.10-5nT/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 (3000nT @ 3kHz, 6nT @ 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. 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 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 3300-0546 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) • Dimensions • Height 32.3mm + 2x5mm for in/out pins • Inside a ∅18.7mm cylinder (PCB with octagonal section, width 16mm) Power supply regulation 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 • 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) • SCM harness definition • 1 shielded and twisted triple (for ±12V) & 9 shielded and twisted pairs • Cables from ESA/SCC 3901 019 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 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

12. 1 2 3 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 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 • 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

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 4009 003), 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. 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. 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 3300-0546 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 3009 034 • 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. 4 5 6 SCM design: mechanical structure • SCM mechanical interface with the boom: 2nd step • The instrument is fixed to the bed plate 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. Gain control nT/V 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 Input signal to Helmholtz coil source Network analyzer 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 • 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 • 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:

38. SCM PA/QA • Work in progress: • Future work: