The Relativity Mission, Gravity Probe B Results and Lessons 2013. 4. 16.¢  The Relativity...

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Transcript of The Relativity Mission, Gravity Probe B Results and Lessons 2013. 4. 16.¢  The Relativity...

  • 1

    The Relativity Mission, Gravity Probe B

    Results and Lessons Learned

    Sasha Buchman for the GP-B team

    Q2C, Quantum to Cosmos #5

    Köln, October 9th 2012

  • 2

    Outline

    1. Experiment description

    2. Patch effects

    3. Data models and analysis techniques

    4. Results, uncertainties and cross-checks

    5. Lessons learned

  • 3

    Gravity Probe B Concept

    ee e

    FD ωRω R

    R

    Rc

    IG Ω

     

     232

    3

    vR Rc

    MG Ω eG

     322

    3

    Guide STAR

    IM Pegasi

    HR 8703

  • 4

    Expected Gyroscope Behavior

    Newton

    Newton

    Geodetic effect*

    (-6571 marcsec/yr)

    Frame-dragging effect*

    (-75 marcsec/yr)

    *includes solar GR effects and guide star motion

  • 5

    The Science Instrument

    Nothing could be simpler then GP-B;

    just a gyroscope and a telescope

    William Fairbank

    Telescope Quartz Block Gyro 4

    Science Instrument Assembly

  • 6

    Probe, Dewar, and Satellite

    http://einstein.stanford.edu/gallery/dewar/slides/dewar_arrival.html

  • 7

    GP-B Gyroscope Requirements

    1 marcsec/yr = 3.2×10-11 deg/hr = 1.5 10-16 rad/sec

    Electrostatic gyro

    uncompensated

    (10-1 deg/hr)

    Electrostatic gyro

    with modeling

    (10-5 deg/hr)

    39 Frame dragging effect

    0.50 GP-B requirement

    ~10 -6

    102

    10

    1

    10-1

    10-2

    103

    6,606 Geodetic effect

    103

    104

    105

    106

    107

    108

    109

    1010

    Laser gyro

    (10-3 deg/hr)

    m a rc

    s e c /y

    r

    Spacecraft gyros

    (3x10-3 deg/hr) m

    a rc

    s e c /y

    r

  • 8

    Ensuring Gyro Performance

    1. Optimize Geometry

    I. Gyro asphericity R/R < 10-6

    II. Gyro mass unbalance dMU/R < 10 -6

    III. Housing asphericity RH/RH < 10 -5

    2. Reduce Environmental Disturbances

    I. Residual acceleration atrans < 10 -11 ms-2

    II. Magnetic field B < 10-10 T

    III. Gas pressure P < 10-11 Pa

    IV. Electric charge Q < 10-11 F

    V. Patch effects dpatch < 10 -6 m

    3. Shift Frequency and Average Signal

    I. Roll satellite 77.5 s

    II. Use polhode averaging ~ 3,000 s

    III. Multiple gyroscopes (4) 4 gyros

    4. Use Natural Calibrations

    I. Daily aberration ~ 5 arcsec

    II. Yearly aberration ~ 20 arcsec

    5. Ground Testing Capability 10 ms-2 to 10-11 ms-2

  • 9

    Gyro Description

     Components

     Rotor

     Housing

     Read-out loop

     Spin-up nozzle

     UV fixtures

     Suspension cables

     Read-out cable

     Functionality

     Electrostatic suspension

     Capacitance rotor position

     Forcing charge measurement

     London moment read-out

     Helium spin-up

     Cryogenic operations

     UV charge management

    Gap = 32.5 m

  • 10

    Gyro Spin-up

    Differential Pumping Requirement:

    1) spin channel ~ 10 torr (sonic velocity)

    2) 2) electrode area < 10-3 torr

    Gyro f (Hz) df/dt

    (μHz/hr) (yr)

    1 79.4 0.57 15,900

    2 61.8 0.52 13,600

    3 82.1 1.30 7,200

    4 64.8 0.28 26,400

    0 0.5 1 1.5 0

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    Time (hours)

    S p in

    r a te

    ( H

    z )

    Gyro 1

    Gyro 2

    Gyro 3

    Gyro 4

    Gyro 1 spun-up last; spin-up

    of one gyro causes spin

    down of the other gyros

    0 0.5 1.0 1.5 Time (hours)

    S p in

    S p e e d (

    H z )

    100

    80

    60

    40

    20

    0

    Spin-up half

  • 11

     London moment read-out with dc SQUIDs

     Superconducting pickup on gyroscope housing

     < 8 10-29 J/Hz (

  • 12

    Gyroscope Readout Single Orbit

    0 10 20 30 40 50 60 -6

    -5.8

    -5.6

    -5.4

    -5.2

    -5 Output of SQUID Readout Electronics, Gyroscope 3, Orbit 6200, June 15, 2005

    O u

    tp u

    t( V

    o lt

    s )

    0 10 20 30 40 50 60

    -6

    -4

    -2

    0

    2 Optical Aberration due to Orbital Motion

    A rc

    S e c

    Time (minutes) After Acquisition of Guide Star

  • 13

    Post Science Calibration Anomaly

    0 0.2 0.4 0.6 0.8 1 0

    0.5

    1

    1.5

    2

    2.5

    3

    3.5

    4

    Angle of Misalignment (degrees)

    D ri

    ft R

    a te

    ( a s

    /d a

    y )

    Magnitude of Drift Rate vs. Angle of Misalignment

    Gyro 1

    Gyro 2

    Gyro 3

    Gyro 4

  • 14

    The Patch Effects:

    1.Gyro acceleration along the roll axis

    2.Gyro acceleration at spin frequency

    3.Gyro spin down

    4.Gyro polhode damping

    5.Misalignment torque

    6.Resonance torque

    7.Charge measurement bias

    The Patch Effect

    Explanation of anomalies: Patch Effect

    Mechanical, magnetic, suspension effects ruled out

     Variation of electric potential over the surface

    Can arise due to the polycrystalline structure

    Can be affected by presence of contaminants

     Patch fields present on gyro and housing walls

     Cause forces and torques between surfaces

    d

    Gyro surface

    Housing surface

    Schematic of surfaces with patches

    Complicate

    Data analysis

  • 15

    3 Complications due to Patch Effect I

    Misalignment Torques

     Proportional to spin to roll angle

     Magnitude up to 2.5 arcsec/yr

     Orthogonal to misalignment plane (roll & spin axes)

  • 16

    3 Complications due to Patch Effect II

    Polhode damping

     Caused by power dissipation in housing resistances to ground

     Changes trapped flux orientation to the spin axis

     Complicates scale factor Cg determination

    Time (days from Day #1; Apr. 20, 2004)

    P o lh

    o d e P

    e ri o d (

    h o u rs

    )

    140 190 240 290 340 390 440

    140 190 240 290 340 390 440 140 190 240 290 340 390 440

    140 190 240 290 340 390 440

    Time (days from Day #1; Apr. 20, 2004)

    G y ro

    1

    G y ro

    4

    G y ro

    3

    G y ro

    2

    4

    3

    2

    1

    20

    15

    10

    5

    1.8

    1.7

    1.6

    5.5

    5.0

    4.5

  • 17

    3 Complications due to Patch Effect III

    Gyro 2 per orbit orientation

    142 139 140 141 145 144 143 138 146

    sEW

    res. m

    E W

    o ri e n ta

    ti o n ,

    s E W (

    a rc

    s e c )

    Date (2005)

    Roll-polhode Resonance Torque

     ‘Jumps’ occur when harmonic of polhode rate coincident with roll rate

     Up to 200 marcsec discontinuities in data

     Long term oscillatory behavior polhroll ff

    m 1

  • 18

    Raw & Processed Flight Data (Gyro 2)

    Jan 8 Jan 28 Feb 17 Mar 9 Mar 29 Apr 18 May 8

    Jan 8 Jan 28 Feb 17 Mar 9 Mar 29 Apr 18 May 8

    date (2004)

    –0.5

    0.0

    0.5

    1.0

    1.5

    2.0

    1.64

    1.66

    1.68

    1.70

    1.72

    1.74

    E W

    o ri e n ta

    ti o n (

    a rc

    s e c )

    N S

    o ri e n ta

    ti o n (

    a rc

    s e c )

    EW uniform drift

    NS uniform drift

    Gyro 2, orientations – Newtonian torques

    –1

    +1

  • 19

    Gyroscope Performance

    700 marcs

    Patch effects

    1 marcsec/yr = 3.2×10-11 deg/hr = 1.5 10-16 rad/sec

    Electrostatic gyro

    uncompensated

    (10-1 deg/hr)

    Electrostatic gyro

    with modeling

    (10-5 deg/hr)

    39 Frame dragging effect

    0.50 GP-B requirement

    102

    10

    1

    10-1

    10-2

    103

    6,606 Geodetic effect

    103

    104

    105

    106

    107

    108

    109

    1010

    Laser gyro

    (10-3 deg/hr)

    m a rc

    s e c /y

    r

    Spacecraft gyros

    (3x10-3 deg/hr) m

    a rc

    s e c /y

    r

    ~ 1%

    Data Analysis

  • 20

    Science Data Segments and Anomalies

    Aug Sept Oct Nov Dec J