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MAGIC Patrick Brown Imperial College London

MAGIC Patrick Brown Imperial College London. MAGIC – Magnetometer from Imperial College. Purpose Dual tri-axial magnetoresistive sensor measures magnetic field vector local to spacecraft in frequency range 0-10Hz Role of magnetometer Contribute to spacecraft attitude determination

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MAGIC Patrick Brown Imperial College London

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  1. MAGIC • Patrick Brown • Imperial College London

  2. MAGIC – Magnetometer from Imperial College Purpose Dual tri-axial magnetoresistive sensor measures magnetic field vector local to spacecraft in frequency range 0-10Hz Role of magnetometer Contribute to spacecraft attitude determination Measurement of local field direction for pitch angle determination Detection and characterisation of local waves and structures Parts Outboard sensor head Electronics board Inboard sensor (on electronics board) Harness (UCB supplied)

  3. Magnetoresistive magnetometer 3axis Fluxgate Single axis MR • Implementation – analogue closed loop • Bipolar driving to maintain optimum detectivity • Requires current pulse of 4A for 2ms • Dynamic Offset compensation employed

  4. Three Axis MAGIC Implementation Note: IB sensor & electronics not identical to OB

  5. MAGIC Requirements (requires updating). See MAGIC ICD (Latest version 04012010) MAGIC Requirements

  6. Sensor Head (Outboard Sensor) CINEMA Boom very light MAG Harness requires at least 17 lines Boom can only support very thin gauge wire Line loss on 4A pulse too large Solution MAGIC Sensor Head Install sensor drive electronics with sensor Inboard sensor in mounted directly on PCB MAGIC Test Harness

  7. Hybrid three axis sensor • Since KHU meeting – have discovered some head parts are magnetic (lead frames, capacitors) • Solution: Implement sensor drive circuit at die level • Funded by ESA to manufacture prototype demonstrator for separate project • Design assessment currently ongoing – awaiting quote for EM manufacture Three axis head (home made) Ceramic Hybrid

  8. MAGIC Power Default Science Mode

  9. Performance testing – Fluxgate vs AMR 8nT ptp 2Hz Square Wave 2nTptp 2Hz Sine Wave

  10. Test results on most recent design Note MR bridge is this instance only 5V – a considerable power saving over a 12V bias. Saves ~130mW per axis. Compare to 16V flipping power ~ 120mW for all three axis

  11. Sensor head mechanical interface design led by UCB Harness supplied by UCB Magnet wire with Aracon outer braid Aracon slightly magnetic Last 10cm near head will be silver over copper Original Provisional Integration Plan UCB Manufacture harness with flying wires Imperial integrate harness to sensor head/add non magnetic braid piece Imperial install MAGIC connecter for test and calibration Imperial remove bus connector prior to delivery UCB or Imperial add bus connector following head installation on boom IS THIS STILL VALID – CAN WE DELIVER UNREMOVABLE CONNECTOR ? Harness Connector at MAGIC PCB – MDM25Way Sensor head mass: <20g (if potted) MAGIC Mechanical Strain Relief No Connector Prototype Sensor Head: Dimensions 2x2x2cm • Inboard sensor in mounted directly on MAGIC card • MAGIC PCB Single PC104 card, Mass ~ 150g, clearance 1cm and 0.5cm alternate side (TBC)

  12. MAGIC Harness Connections Connections to bus Sensor Harness connections

  13. MAGIC Data & Command Interface Interface to bus via ADS1216 8 channel, 24 bit Delta-Sigma architecture with 8 I/O registers Has the required channel number, range and H/W control potential Control interface via SPI PGA, and on board Sinc filters Low power consumption ~ a few mW Issues MAGIC requires the bus to sample the MAGIC data at some TBC rate i.e. switching the MUX at the required cadence Baseline that MAGIC filtering is performed on board ADC No CS needed on dsPIC33 if ADS1216 only SPI device To minimise processing load on bus controller recommend dedicated bus connections for NDREDY and ADC RESET

  14. MAGIC CMDH Bus Requirements Channel switching of ADC add acquisition of data 7 channels in total OB (Bx, By, Bz) IB (Bx, By, Bz) OB Temp Not all channels accessed in all modes (default mode is OB and Temp only) Potential switching of sinc filter, read of ADC register status MAGIC commanding via SPI to ADC Commanding only defined at functional level ADC Configure Switch channel (OB sensor (3), IB Sensor (3) or Temperature) Switch between Attitude, Science and Gradiometer Modes Data Rates Attitude Mode 1 vector per second (65 bits per second) Science Modes 10 vectors per second (578 bits per second) Timing interface – Vectors assumed to be stamped by bus

  15. Development • Single axis analogue design exits since 2008 • Three axis analogue design ready since Dec 2009 • Waiting for ADC test before migration to PCB • ADS1216 8 channel ADC board currently under development • ADC Board 1 – developing SPI code connection to analogue MAG • ADC Board 2 – to interface to CubeSat board to develop flight pseudo code • Expect MAG ADC interface test to take place later this week • Proposed Schedule Milestones • MAGIC EM PCB Layout from 12th Feb • EM Test & Evaluation starts 26th March • FM Manufacture starts 26th April • FM Test & Cal starts 18th June • Delivery to UCB 5th August • Schedule include milestone for ADC code, STM and ETU delivery Development Plan (1)

  16. STM Sensor • Idea is to deliver a potted sensor head for early stage deployment firing to test robustness of harness termination in potted sensor head • Senor head would be dummy i.e. potted set of 17 resistors • Would require delivery of sensor harness from UCB. Sensor chassis would be manufactured by IC • Proposed delivery date 1st April • EM model • Single axis MR with ADC for interface testing prior to FM deliver • Would require ADS1216 SPI MAG pseudo-code • Proposed delivery date 30th April Development Plan (2)

  17. MAGIC Internal Schedule

  18. Current Issues ADC ADS1216 development work ongoing SPI comms sampling at 100Hz on three MUXed channels now working Controlled by PC with LabView Next step is to connect to MAG three axis board Still a difficult interface. Only 0- 2.5V range so need to add attenuator to MAG board Looking into alternate ADC as a nuclear option (AD1217, ADS1256) ADS1217 – identical interface but bigger range (0-5V) ADS1256 – faster sampling and lower noise but at expense of power ~38mW Will connect ADS1216 to MAGIC board this week in any case and assess. Sensor Head MOSFET Lead frames and capacitor are magnetic Solution: Hybrid sensor built with component die Connectors Is it OK to deliver MAGIC with sensor harness with un-removeable connector? Calibration MAGIC Three Axis sensor not yet calibrated due to broken facility Detailed performance testing waiting for operational ADC interface

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