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NGGM ASSESSMENT STUDY Progress Meeting 2 TUD, Delft, 24-25 March 2010

NGGM ASSESSMENT STUDY Progress Meeting 2 TUD, Delft, 24-25 March 2010. WP 2121 Measurement Technologies (ONERA). Input for accelerometer technology review (1/1). Radial (Z). 2. Sat - Sat line (X). 1. Cross-track (Y). WP2121. Accelerometer accommodation. Angular acceleration around X:

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NGGM ASSESSMENT STUDY Progress Meeting 2 TUD, Delft, 24-25 March 2010

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  1. NGGM ASSESSMENT STUDYProgress Meeting 2TUD, Delft, 24-25 March 2010

  2. WP 2121 Measurement Technologies (ONERA)

  3. Input for accelerometer technology review (1/1) Radial (Z) 2 Sat - Sat line (X) 1 Cross-track (Y) WP2121 Accelerometer accommodation Angular acceleration around X: from aZ1 – aZ2 Angular acceleration around Z:from aX2 – aX1 Linear acceleration (now) Linear acceleration (previously) Angular acceleration Cross-track axis Y Radial axis Z Around cross-track axis, Y Sat-Sat axis, X

  4. Input for accelerometer technology review (2/2) Radial (Z) 2 Sat - Sat line (X) 1 Cross-track (Y) WP2121 Accelerometer accommodation Angular acceleration around X: from aZ1 – aZ2 Angular acceleration around Z:from aX2 – aX1 2 1 Linear acceleration (previously) Scale factor stability Linear acceleration bias Bias along Y < 210-7 m/s2 Bias along Z < 210-7 m/s2 Sat-Sat axis, X Cross-track axis Y Radial axis Z

  5. Low-frequency noise of GOCE gradiometer Thermal drift of the accelerometer from GOCE model It is difficult to assess the thermal stability of the accelerometer from the trace behaviour at low-frequency

  6. Temperature stability in GOCE 1/f3 1/f3 1/f2 1/f3 1/f 1/f3

  7. Bias thermal stability in GOCE Detector bias thermal sensitivity: 30 µV/K => 8.7 10-13 m/s2/K • Radiometer effect depends on: • pressure inside ASH (0.3 Pa) • temperature gradient at I/F Telec(f)=3.45 K/Hz1/2 x (1 mHz/f)2

  8. Gradiometer core temperature 4 7 Y X 5 Z 6 Don’t take into account the radiative filtering to ASH Not representative at high frequency (accuracy of reading)

  9. Electronic temperature FEEU1+ TA1 FEEU1+ TA2 FEEU1- TA1 FEEU1- TA2 FEEU1+/- TC Not representative at high frequency (accuracy of reading 12 bits)

  10. Bias on GOCE Requirement NGGM: Bias < 210-7 m/s2 Bias along ultra-sensitive axis : 1.3 10-7 m/s2 (due to gold wire stiffness) Bias along ultra-sensitive axis : 1.2 10-5 m/s2 (due to gold wire stiffness)

  11. Bias rejection - Principle ±180° Frequential Domain Periodic flip of Accelerometer Measured acceleration aext harmonics aext bias fmod noise Demodulated acceleration harmonic aext+ bias bias aext Ground processing: Demodulation Low-pass filtering noise Error on acceleration estimation noise

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

  13. Bias rejection: ground verification Accelerometer 1-axis Q-Flex QA-700 Measured acceleration with bias rejection modulation Estimated acceleration Newport Rotary Stage CNES funding in 2008/2009

  14. Scale factor stability GOCE Performance vs NGGM requirement Need improvement of the ADC reference voltage stability Need improvement of the thermal stability and better CPD thermal sensitivity

  15. Other concepts LS axis US axes GOCE with 2 ring-plates • Advantages: • Control of 2 angular motions with US • More redundancy (capability to controlangular motions with LS or US axes) • Disadvantages: • Weight of the proof-mass (if PtRh10) • Degradation of performance if lighter proof-mass (TBC) Radial (Z) Sat - Sat line (X) Cross-track (Y)

  16. Other concepts Capacitance with surface variation • Advantages: • Perfectly linear in detection • Perfectly linear in action • Disadvantages: • Reduced range • Coupling with vertical motion • Use in Microscope accelerometer

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