MAGIC Interface Issues Patrick Brown, Blackett Laboratory, Imperial College

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)

Magnetoresistive magnetometer (Single axis) 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 3

MAGIC Instrument Datasheet Characteristic Requirement Mass 25g (outboard sensor); 150g (inboard sensor and electronics) (TBC) Power 100mW (attitude mode); 500mW/750mW (science modes) (TBC) Volume OB Sensor head 10cm3 (2x2x2.5cm) Electronics 162cm3 (9cmx9cmx2cm) Sensitivity 25nT in attitude mode, <10nT/2nT (science modes) Cadence Typical: 4 vector/s (TBC) (attitude mode); 20 vectors/s (TBC) (science modes) Telemetry ~ 238bits/s (attitude mode at 4Hz) and ~ 1150 bits/s (science mode at 20Hz) Range +/- 65536nT Resolution 0.25nT (assuming 19bit transmission) Noise Density <150pT√Hz- at 1Hz Temperature -50oC to +120oC Two instrument modes – Science A/B (high res) and Attitude (lower res) Switch to science modes when power allows

Note: IB sensor & electronics not identical to OB

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 Plastic packages (most likely implementation) Ceramic version MAGIC Test Harness

Mechanical Interface Issues Strain Relief 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 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 Harness Connector at MAGIC PCB – MDM25Way Sensor head mass: <20g (if potted) No Connector Prototype Sensor Head: Dimensions (cm) 2x2x2.5(h) Inboard sensor in mounted directly on MAGIC card MAGIC PCB Single PC104 card, Mass ~ 150g, clearance 1cm each side Latest UCB Drawing

MAGIC Harness Connections 17 wires 3 x 2 Differential Sensor out (Bx, By, Bz) 3 x 2 Feedback (Bx, By, Bz) 1 x Thermistor (RTN reference to GND) 1 x Bridge Voltage (12V or 5V reference to GND) 1 x Drive Clock 1 x Drive Voltage (16V RTN reference to GND) 1 x GND

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

ADS1216 testbed now operating at Imperial after some initial difficulties Currently accessed at an individual sample level via a Linux box Next step is continuous sampling via Linux and connection to MSP430 Envisage uplink of ADC pseudocode to CINEMA FTP server

MAGIC Bus Interface Connections Pin EST Current Load (TBC) Remark/Issue + 12V (14+7.5)mA per axis Powers Bridge in Science Mode A. + 5V (5.6+7.5)mA per axis Always on for bridge relay + 3.3V 3mA for 3axis Always on for ADC + 16V 7.5mA for 3 axis Only required for flipping (OB in Science Mode B or IB after a sensor set command). ANL GND DIG GND Serial Data In (SPI) Serial Data Out (SPI) Data CLK (SPI) CS not required if MAGIC has sole use of one of the dsPIC33 SPI buses ADC Master CLK 5MHz ADC RESET Could be implemented in bus software. Prefer dedicated hardware line NDREDY Connector – Pins on a standard PC104 connector are OK but if opportunity exists for a smaller dedicated connector would take that option

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 Packetization and time stamping MAGIC commanding via SPI to ADC but also prefer if commanding can control rail switching on the bus Mode Sensor Live Rails Power Consumption Remark Attitude OB or IB 5V, 3.3V 210mW Science A OB only 5V, 3.3V, 12V 788mW Can 12V be switched by bus? Science B 5V, 3.3V, 12V,16V 908mW Can 16V be switched by bus? Currently investigating whether Attitude can run on 3.3V and Science A/B can run at 5V Bridge to get ~ 75mW and 420mW saving in Attitude and Science Mode A/B respectively

MAGIC Functional Commanding Assume: 1. MAGIC On when 5V and 3.3V rails are up 2. 12V and 16V are switched off by bus on start up Command Rail Status from bus ADC Action Attitude OB On, IB Off 12V & 16V Off, 5V & 3.3V On IB Switched Off Attitude IB On, OB Off OB Switched Off Attitude with flip IB ON, OB Off 12V Off, 16V, 5V & 3.3V On Switch on IB Flip CLK Attitude OB ON, Attitude IB ON ADC Switches power to both bridges Science Mode A OB On, IB Off 16V Off, 5V & 3.3V On Switch Bridge from 5V to 12V Science Mode B OB On, IB Off 12V &16V On, 5V & 3.3V On Set Bridge to 12V & OB Flip CLK ON

ICD Clarification: Current Efforts ADC ADS1216 development work ongoing Have switched relay via I/O lines Priority task to get continuous sampling (up to 200Hz) by MSP430 over SPI Then start MAGIC code development MAG Investigating if Attitude Mode can be run on a 3.3V Bridge Finalise Functional Block Diagram Generate Three axis schematic Build three axis breadboard Calibration and Interference test of proto-sensor head THERMAL Initial thermal mode indicated in-flight temp range of -50oC to +120oC Once three axis calibration complete temp test will be made with unpotted and potted sensor Other Issues for Discussion – Schedule & Magnetic Cleanliness Plan