Inertial Sensor and Its Application for Space Fundamental Experiments Ze-Bing Zhou ( 周泽兵 ), Jun Luo ( 罗俊 ) Center for Gravitational Experiment, Huazhong University of Science and Technology 3rd ASTROD, July, 2006, Beijing

2 Outline Principle of inertial Sensor Principle of inertial Sensor Space application of inertial sensor Space application of inertial sensor Progress of inertial sensor in HUST Progress of inertial sensor in HUST Summary Summary

3 1 、 Principle of Accelerometer/Inertial Sensor x r =x - y k m y x If To obtain the acceleration of the mobile objects by monitoring the relative motion of the proof mass w.r.t. it; Lower of natural frequency (softer linkage), higher sensitivity

4 Accelerometer Structure Test Mass Senor Open- Output Test Mass Actuator Controller Closed- Output Sensor Linkage ： Mechanic, Electrostatic, Magnetic, Optical Position Sensor: Optical, Capacitance, SQUID Force Actuator: Electromagnetic, Electrostatic, Piezo- Control Unit: simulative, digital, mixed

5 Electrostatic Suspension/Space Accelerometer Capacitance transducer + Electrostatic Actuator One Proof Mass with Six degree-of-freedom measurement

6 Superconducting Inertial Sensor SQUID technique Optical Suspension Inertial Sensor Optical read out (phase) and control (power) Inertial sensor with atom-interferometer

7 AccelerationMeasurement Model Model InertialReferenceModel(Geodesic) Test mass tracks with spacecraft Spacecraft tracks with test mass Operation modes in space applications 2 、 Space Application of Inertial Sensor

CACTUS 1996 ASTRE: µgravity survey 2000 STAR : CHAMP 2002 SuperSTAR : GRACE 2006? GRADIO GOCE 2009 ? MICROSCOPE 2015 LISA Ref. ONERA Space Application of Inertial Sensor

9 CHAMP GFZ,Germany GRACE NASA/GFZ Projects of EGF Measurement 3*10 -9 m/s 2 3* m/s 2 Accelerometer provided by P. Touboul, ONERA, France

10 MICROSCOPE (ONERA-ESA 2009?) Proof-mass material : Platinum - Titanium Pt/Pt - 186g/500g Pt/Ti - 186g/106g Expected Precision: 5* m/s 2

11 Predicted Accelerometer Noise: 3× m/s 2 /Hz 1/2 0.1mHz ~1mHz Inertial Sensor for LISA Univ. Trento, Italy, * m/s 2 /Hz 1/2 at 3mHz

12 3 、 Development of inertial sensor in HUST Member of ASTROD-1: Inertial sensor research TISS: Test of Inverse-law Square in Space proposed by Prof. Jun Luo Background: Present status: Preliminary progress of CESA on ground (Chinese Electrostatic Suspension/Space Accelerometer)

13 Terrestrial Scheme for Electrostatic Suspension Inertial Sensor/Accelerometer ONERA, France, * m/s 2 /Hz 1/2 [RSI ] Univ. Trento, Italy, m/s 2 /Hz 1/2 [PRL ] High-Voltage Suspension Fiber Suspension Main difficulty: 1g Earth’s gravity acceleration limit

14 Fiber Suspension Electrostatic feedback CESA Scheme

15 Turntable Probe Fiber Experimental setup Vacuum: 100Pa. Position in center of +10um Preamplifier in vacuum Digital PID Control Original prototype

16 Free motion of the torsion pendulum

17 Experimental parameters Proof Mass M Al, g ; ( ) * ( ) * ( ) mm 3 Inertial moment I ( )*10 -4 kg m 2 Suspension fiber Tungsten, Φ50um *(960+1)mm Torsion constant K f ( ) * Nmrad -1 Free period T s Quality factor Q ≈382 (about 100Pa) Capacitance electrode 19.5mm*40.1mm, gap: 0.81±0.10 mm; Capacitance in balance C pF

18 Calibration steps: (1) To change the capacitive electrodes position with respect to the test mass by the rotate table; (2) The capacitive sensor detects the relative motion, and then acts an electrostatic torque on the test mass; (3) The test mass follows the capacitive electrodes, and its rotational angle is simultaneously monitored by an optical level. * In this case, the electrostatic torque is equal to the fibre restoring one.

19 Sensitivity: Calibration Result Feedback voltage variety (0.170V) Angle variation (5.173mrad)

20 Preliminary Result (8th July,2006) Resolution: 3* Nm/Hz 1/2 at 1mHz 2.4* m/s 2 /Hz 1/2 at 1mHz 1SD=1.5mV

*10 -8 Nm Dynamic range: + 2.8*10 -8 Nm Dynamic range measurement Feedback voltage Error signal

22 Predicted of Inertial sensor for ASTROD-1 Capacitance gap: 0.8 mm 1 cm (156 times) TM: 320g (Al) 1.68 kg (5*5*3.5cm 3, Au-Pt) 3* m/s 2 /Hz 1/2 (5 times) 2.4* m/s 2 /Hz 1/2 at 1mHz If the capacitance sensor keeps same resolution

23 Disturbance model F sp,g F sp,ng XsXs xaxa F pm,g F pm,n Capacitance Transducer H s Controller H c Electrostatic Actuator H a Coupling K cp V fed VnVn Coupling K cp XnXn V err TM SC Thruster H t TnTn Intrinsic noise Disturbance on TM Coupling between TM and SC

24 Key of further research: To add translation control To improve the vacuum To add vibration isolation To analyse and test the disturbance effects To change probe parameters for ASTROD-1 condition: TM material, capacitance gap ….

25 Inertial Sensor/Accelerometer is one of key technologies for space fundamental experiments. It will be developed with the requirement of space mission, and inversely then it will push the space mission. Electrostatic suspension/space accelerometer has been studied for over 30 years, and succeed to be used in space. CESA should be studied step by step, too much disturbances need be analyzed, tested, and suppressed. 4. Summary

26 Thank you very much!