Gravity Advanced Package (GAP) : a «null bias» electrostatic accelerometer for fundamental physics missions in the Solar System

Transcription

1 Gravity Advanced Package (GAP) : a «null bias» electrostatic accelerometer for fundamental physics missions in the Solar System B. Christophe (ONERA, Châtillon, France) on behalf of the GAP Instrument Team (Zarm, DLR-RY, LKB, JPL, Onera) GPhys KO Colloquium, Les Houches, October 2009

2 Interest of Accelerometer for Fundamental Physics Solar radiation pressure S/C S/C Dynamic Orbit Determination Process Post Einstein Gravity Modification in 2 nd sector Signal Signal Propagation Doppler Solar Radiation Other NG forces Gravitation Solar Plasma Atmosphere Deviation GAP GAP Fit Accelerometer Fit parameters General Relativity Model Model Deviation? Troposphere Meas. Meas. Bi-frequency By courtesy of LKB 2

3 GAP : Accelerometer with null bias Accurate accelerometer in DC domain for fundamental physics MICROSTAR Sensor Unit Front-End Electronic (ONERA) Bias Rejection System Rotative stage (ZARM/DLR) ICU ONERA heritage GRACE - GOCE Volume = 3 l Mass = 3 kg Consumption = 3 W Data rate = 300 bits/10s Heritage of space rotary stage or filter wheel 3

4 ONERA Electrostatic Accelerometer Earth Observation: geodesy, geophysics, oceanography, hydrography, climatology CHAMP (CNES-DLR), July 2000 Range : 10-3 ms -2 Noise : ms -2 /Hz 1/2 MBW : [ mhz] Bias : ms ms -2 / C GRACE (NASA-JPL), March 2002 Fundamental Physics: test of the Equivalence Principle,... MICROSCOPE (CNES-ONERA) Range : ms -2 Noise : ms -2 /Hz 1/2 MBW : [ mhz] Bias : 10-8 m/s ms -2 / C (Elec) ms -2 / C (Meca) Range : ms -2 Noise : ms -2 /Hz 1/2 MBW : [ mhz] Bias : ms ms -2 / C GOCE (ESA), March 2009 Range : ms -2 Noise : ms -2 /Hz 1/2 MBW : [5 100 mhz] Bias : m/s ms -2 / C (Elec) ms -2 / C (Meca) 4

5 GOCE DRAG FREE PERFORMANCE GOCE drag free performance, verified in commissioning phase (June GOCE: Space technology for the reference Earth gravity field determination, A.Allasio, D.Muzi, B.Vinai, S.Cesare,G.Catastini, M.Bard, J.P. Marque, EUCASS 2009, Versailles France. DFAC noise estimated through redundant acceleration measurements 6 3 The common mode of the two accelerometers voltages measures the non gravitational forces at the middle of their axis, located at the center of gravity of the satellite N = 2/sqrt(3) [ acc14x (acc25x +acc36x)/2] Actuation noise (DAC + DVA ) main contributor in [ 10 mhz 100 mhz ] MBW Detection noise (detector + ADC1) main contributor in [ 0.5 Hz 5 Hz ] MBW 5

6 Accelerometer control loop goldwire Capacitive Detection Proof mass Det Controller Vp,Vd Gel Gel +DVA -DVA ADC Electrostatic Action Science output Readout circuit ADC 6

7 MICROSTAR Accelerometer Design Proof-mass in ULE 20x20x20 mm 3 Electrode plates in ULE 40x20x10 mm 3 Aluminum box Stops Electrodes Getter Hermetic housing Electronics PCB Core Sole-plate 7

8 Bias rejection: principle Periodic flip of Microstar ±180 bias Frequential Domain Measured acceleration a ext harmonics a ext f mod noise Demodulated acceleration Ground processing: a ext bias harmonic a ext + bias Demodulation Low-pass filtering noise Error on acceleration estimation noise 8

9 Accelerometer Performance Noise of MICROSTAR Noise (m/s 2 /Hz 1/2 ) 1.E-08 1.E-09 1.E-10 1.E-11 1.E-12 Modulation frequency Total Detector Wire damp dt Bias ADC CPD Bias fluc. Thermal environment stability of 0.6 K pp over 1 day Vp = 7 V Vd = 5 V Gap = 600 µm Proof-mass in ULE Gold wire Ø 5µm 1.E-13 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 Frequency (Hz) Range: 20 µm/s 2 Bias rejection Bias: 5 µm/s 2 20 pm/s 2 Noise: 1 pm/s 2 1 mhz ± 0.1 mhz 9

10 Bias rejection: simulation verification ±180 Acceleration JGO at 3 AU (h) Modulation Accelerometer Measure (s) (s) Ground processing Estimated Acceleration Estimation error (h) Error < 5 pm/s2 (h) 10

11 Bias rejection: ground verification Accelerometer 1-axis Q-Flex QA-700 Measured acceleration with bias rejection modulation Estimated acceleration Newport Rotary Stage CNES CNES funding funding in in 2008/ /

12 Missions for GAP GAP on EJSM/JGO Deep Space Gravity Flyby Anomaly Gravity field of Ganymede GAP on Odyssey Deep Space Gravity Flyby Anomaly Eddington parameters Gravity field of Planets or Moons 12