The application of a fluxgate magnetometer for Mars space

environment exploration in CHINA

Jindong Wang, Bin Zhou, Xin Zhang, Hua Zhao

Center for Space Science and Applied Research, Chinese Academy of Science, Beijing, China

contents

Magnetic field of Martian Space Environment

Introduction of the fluxgate magnetometer (FGM)

Calibration & EM tests

Spacecraft residual magnetic field

Summary

Orbit & Martian space environment

orbit：elliptical, periapsis (nearest point) 800km，apoapsis (furthest point) 76,000km, period 72hours.

“YH-1” orbiter will pass through bow shock, magnetosheath, magnetic pileup boundary, magnetic pileup region, and magnetic tail.

Martian magnetic field Mars lacks an appreciable global magnetic field (<0.5 nT equatorial

surface field) Based on the Mars Global Surveyor (MGS), magnetic field at 800km

altitude is dominated by external fields arising from the interaction of the solar wind with Mars.

This external field is highly variable, ranging from a few nT to as much as (rarely) ∼100 nT.

Design parameters Measurement range: ±256nT Resolution: 0.01nT Noise: <0.01nT/√Hz@1Hz Operating temperature range：-120~+70 ℃ Mass: <2.5kg

Block diagram of FGM

FMG sensor A

FGM sensor B

PCB of FGM ACPU

ofspacecraft

PCB of FGM B

On the Boom Electronic box of FGM

F1/2

ClockDrive

16bitA/D

8bitD/A

DPUWith

DigitalFilter

3-Axis Sensor Analogue Fluxgate Magnetometer Electronics Digital Part

Feed Back

Operating modes Default mode

Acquires vector magnetic field measurements up to 10 samples/s in orbit;

Measurement range: -256~+256nT, resolution 0.01nT

Compensation mode Only used in ground testing; Measurement range: +/-65000nT

Self-calibration mode Every time starting FGM Self-calibration every 18 hours

0 2 4 6 8 10 12 14 16 18 20-200

-150

-100

-50

0

50

100

150

200

时间（s）

磁场

强度

（

nT）

Instrument design Integrate 3 fluxgate sensors

into a small casing;

Can be divided into two independent instruments.

Simulation of structure stress

20℃15g acceleration

X Y Z

Max stress (MPa) 3.17 1.77 9.26

Displacement (μm) 6.21 0.353 12.5

-180℃15g acceleration

X Y Z

Max stress (MPa) 8.18 3.79 15.2

Displacement (μm) 12.6 2.16 21.3

75℃15g acceleration

X Y Z

Max stress (MPa) 7.62 2.28 13.2

Displacement (μm) 9.34 1.15 18.4

Performance Measurement range

-256nT~+256nT -65000nT~+65000nT

Resolution 0.01nT

Noise <0.01nT/√Hz@1Hz

Sample rate 10 Hz

Mass 2.5kg

Power consumption 6W YH-1 FGM, flight model

Calibration & Test

Linearity and resolution Noise Stability Thermal stability

Linearity and resolution Laboratory for calibration:

National Institute of Metrology, Beijing, China； 3-axis criterion coil system; magnetic clean and thermostatic

test room.

Linearity（%）

Range（nT）

Sensitivity(nT)

X 0.041 >±256 0.098

Y 0.031 >±256 0.097

Z 0.116 >±256 0.099

-400 -300 -200 -100 0 100 200 300 400-3

-2

-1

0

1

2

3x 10

4

磁场强度 （nT）

磁强计读数

Linearity, sensitivity and resolution of FGM ALinearity of FGM A, axis X

Calibration for FGM sensor——National Institute of Metrology, Beijing, China

FGMsensor

Turntable

Coilsystem

Linearity, sensitivity and resolution of FGM, flight mode

Axis Sensitivity（1/nT） Resolution （nT/1） Linearity（%）

A

X 101.58 0.0098 0.041

Y 103.32 0.0097 0.031

Z 103.80 0.0098 0.116

B

X 103.06 0.0097 0.052

Y 104.19 0.0096 0.083

Z 101.23 0.0099 0.045

-300 -200 -100 0 100 200 300

-30000

-20000

-10000

0

10000

20000

30000

正样A机 Y轴线性度及偏差

磁场强度(nT)

磁场

测量

值

-240 -210 -180 -150 -120 120 150 180 210 240-50

0

50

磁场强度(nT)

线性

偏差

参考点

拟合点

拟合直线

Noise

0 1 2 3 4 50

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

频率（H z）

功率

谱密

度（

1/√Hz）

正 样件A机功率谱密度

X 方向

Y方向

Z方向

Laboratory for noise test Ming-Tombs Geomagnetic Station, Institute of Geology and Geophysics,

China Academy of Sciences, Beijing, China Space Research Institute, Austrian Academy of Sciences, Graz, Austria

PSD noise of FGM sensor, CAS, Beijng & IWF, Graz

Stability

Stability of FGM, flight mode

FGM Axis stability（nT/24hours）

A

X 0.035

Y 0.116

Z 0.096

B

X 0.057

Y 0.105

Z 0.110

Laboratory for stability test CSSAR, Beijing, China Space Research Institute,

Austrian Academy of Sciences, Graz, Austria

Thermal stability

Sensitivity VS Temperature

Temperature（℃） -80 -60 -40 64

Axis Y, FGM A flight mode

Measurement 13276 13253 13238 13279Error 0.11% 0.06% 0.18% 0.13%

During eclipses, temperature of FGM sensors could drop to about -210℃;

Temperature drift must be calibrated so that we could fix the data measured in orbit.

-100 -80 -60 -40 -20 0 20 40 60 80-15000

-10000

-5000

0

5000

10000

15000

温度 （ ℃ ）磁

场测

量值

X方向测量数据

X方向拟合曲线

Y方向测量数据

Y方向拟合曲线

Z方向测量数据

Z方向拟合曲线

Thermal test devices

Block diagram of thermal test equipment

Spacecraft residual magnetic field In case of limited boom length, the spacecraft residual magnetic field

could be simplified as a dipole; Use gradient magnetic data by two sensors, we can eliminate the

influence of residual magnetic field of the spacecraft; Multi-pole magnetic field can be ignored because it weaken by 5-th

power of distance.

Sensor A

LBLA

33

33

BA

BBAAM LL

BLBLB−−

=

Sensor B

Current of Solar Wing Current on the solar wing

generates electromagnetic interference;

An analyses model was established in order to remove these interference;

Typical case： W1=W3=0.2A W2=0.1A，

Result: 1.97nT at Sensor A 8.38nT at Sensor B

SensorA

SensorB

Summary Time and Space Resolution

Time resolution: 0.1s Space resolution: better than 0.3 km

The speed of YH-1 spacecraft is about 3km/s at perimartian (nearest point ), so in most case space resolution will be better than 0.3 km.

Performance

Hz/ HznT /008.0

Performances Design specifications Measured indicators

Range -256nT～256nT -270~270nTResolution 0.01nT 0.0099nTPSD noise 0.01nT @1Hz @1HzRMS noise <0.1nT <0.03nTAccuracy <0.125nT <0.09nT

Thank you