1. MAGIC Interface Issues
Patrick Brown,
Blackett Laboratory,
Imperial College

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 (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

4. 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
+/ nT
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

5. Note: IB sensor & electronics not identical to OB

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

7. 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

8. 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

9. 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

10. 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

11. 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
( )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

12. 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

13. 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

14. 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