Stanford Modular Gravitational Reference Sensor MGRS Technology Development

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• Stanford Modular Gravitational Reference Sensor
  (MGRS) Technology Development

A. J. Swank, B. Allard, G. Allen, S. Buchman, R.
L. Byer, J. W. Conklin, D. DeBra, D. Gill, A.
Goh, S. Higuchi, P. Lu, N. A. Robertson, K-X.
Sun
Stanford University Hansen Experimental Physics
Laboratory
June 22, 2006
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Stanford LISA Team
Robert L. Byer Sasha Buchman Dan DeBra Norna A.
Robertson Ke-Xun Sun
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Drag-Free Satellite History
STEP
Future

• 1972

LISA
Triad/DISCOS
BBO
1975-1988
Triad 2
TIP 3
NOVA I-III
2004
Gravity Probe B
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MGRS Design
External Laser Beam To/From Telescope
Optical Sensing
Grating Angular Sensor
Single Proof Mass
UV LED Charge Management
Large Gap
Sun et al. CQG (22) 2005 S287-S296, LISA 5.
Sun et al. JPCS (32) 2006, 137-146
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Optical Sensing
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
Grating Fabrication Patrick Lu
ES Modeling Surface Studies Allex Goh Norna
Robertson
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Graham Allen
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Internal Optical Sensing

• Sensor Goals
• High Precision
• 1 pm/?Hz in LISA band
• Low Disturbance
• lt 10 ??W optical power
• Compact
• Fiber optics

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Optical Sensor
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Optical Sensor

• Sensitivity 10 pm/ vHz
• 100 ?W incident power

• New photodetector will improve performance

Finesse 5, PDH linear range 100 nm
Optical measurement at 3 kHz, Low frequency
performance limited by environmental noise.
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Grating Angular Sensor
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
ES Modeling Surface Studies Allex Goh Norna
Robertson
Grating Fabrication Patrick Lu
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Grating Angular Sensor
Special Thanks to Dr. Robert Spero at JPL DRDF
Program
Sun et al. JPCS (32) 2006 167-179, Amaldi 6
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Grating Angular Sensor
Angular Sensitivity 1 nrad/vHz
1 nrad/vHz
Special Thanks to Dr. Robert Spero at JPL DRDF
Program
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Grating Fabrication
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
Grating Fabrication Patrick Lu
ES Modeling Surface Studies Allex Goh Norna
Robertson
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Patrick Lu
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Grating Fabrication

• Dielectric grating
• e-beam lithography
• Gold grating
• Transfer-imprinting of dielectric gratings
• Focused ion beam milling
• Precise control over grating duty cycle

Dielectric grating (AFM Image)
Gold Gratings, (SEM Images)
Imprinted
Focused ion beam milled
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Mass Center Determination
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
ES Modeling Surface Studies Allex Goh Norna
Robertson
Grating Fabrication Patrick Lu
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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John Conklin
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Mass Center Determination

• Optical sensing (100 ns accuracy)
• Different initial phases average out rail
  irregularities

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Mass Center Determination

• Initial accuracy
• 2-3 ?m
• Future lt 1 ?m

Tests with Calibration sphere
Conklin et al. Accepted for ASPE Monterey, 2006
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Mass Attraction
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
Grating Fabrication Patrick Lu
ES Modeling Surface Studies Allex Goh Norna
Robertson
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Aaron Swank
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Gravitational Self-Attraction

• Density inhomogeneities and geometrical
  variations lead to uncertainty

?FGrav, FGrav f ( Mass, Mass Center, Inertia,
... )

• Goal Measure inertia to below 1 part in 104
• Includes mass property uncertainties

Swank et al. Accepted for ASPE Monterey, 2006
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Gravitational Self-Attraction
Spectral resolution lt 1 mHz
Q 1500 f 2.715 Hz
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LED UV Charge Management
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
Grating Fabrication Patrick Lu
ES Modeling Surface Studies Allex Goh Norna
Robertson
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Sei Higuchi
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UV LED Charge Management
UV LED
GP-B Mercury Lamp
Sun et al. CQG (23) 2006 S141-S150, Amaldi 6
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UV LED Lifetime Tests
Spectral Intensity Measurement
Power Stability Measurement
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Surface Studies
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
ES Modeling Surface Studies Allex Goh Norna
Robertson
Grating Fabrication Patrick Lu
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Patch Effects

• Patch effects have been studied with a Kelvin
  probe at GSFC
• Many samples precision coated in-house at Stanford

Kelvin probe at GSFC
Special Thanks to Dr. Jordan Camp at GSFC
Robertson et al. CQG (23) 2006 p2665
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Surface Potential Distribution
Spatial variations over 1 cm square
Special Thanks to Dr. Jordan Camp at GSFC
Robertson et al. CQG (23) 2006 p2665
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Surface Potential
1 mV/vHz
Variation of surface potential with time
Amplitude spectral density of variations
Larger gap size mitigates patch effects
Special Thanks to Dr. Jordan Camp at GSFC
Robertson et al. CQG (23) 2006 S2665
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Allex Goh
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Electrostatic Modeling
Analytical solution exists!
relative force
coating gap depth (mm)
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Thermal Control
Optical Sensing Graham Allen
Grating Angular Sensing Ke-Xun Sun
Thermal Control Sei Higuchi
Grating Fabrication Patrick Lu
ES Modeling Surface Studies Allex Goh Norna
Robertson
Mass Center John Conklin
UV LED Charge Management Sei Higuchi
Mass Attraction Aaron Swank
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Thermal Control
LISA Spacecraft
Solar Radiation
GRS

• LISA Thermal Stability 3x10-5 K/vHz for f gt
  0.01 mHz
• Low frequency disturbance input
• Time-delays

GRS
Daily Ambient Temperature Variation
Ground Verification System
Higuchi et al. J. Physics (32) 2006 S125-S131,
Amaldi 6
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Thermal Control
Experimental Results
Control Signal
Ambient
Output
Smith Regulator Control
Stability 1 mK/vHz for f gt 0.7 mHz
Higuchi et al. Accepted for ASPE Monterey, 2006
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Summary
Optical Sensing 10 pm/vHz
Grating Angular Sensing 1 nrad/vHz
Thermal Control 1 mK/vHz
ES Modeling Surface Studies 1 mV/vHz Analytic
Solution
Grating Fabrication Gold Dielectric Surfaces
Mass Center lt 3 ?m
UV LED Charge Management gt 1000 hrs
Mass Attraction ?I lt 10-3
Graduate Students Supported by Stanford Deans
Office of Research