A Space-Based Gravitational-Wave Detector with Geometric Suppression of Spacecraft Noise(LAGRANGE)

Kirk McKenzie1, Robert E. Spero1, William M. Klipstein1, Glenn de Vine1, Brent Ware1, Michele Vallisneri1, Curt Cutler1, John Ziemer1, Daniel A. Shaddock2, Ruth Skoug3, and John Steinberg3

1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 2 Department of Physics, The Australian National University, Canberra, Australia 3 Los Alamos National Laboratory, Los Alamos, New Mexico

2011

Document does not contain sensitive or proprietary information.

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Gravitational Wave Detector with Geometric Suppression

• Remove: high-risk technologies; that drives spacecraft requirements

• Replace Drag-free (GRS + microNewton Thrusters) with radiometer + solar wind monitor(or GOCE accelerometer)

• 3 Spacecraft with LISA-like interferometrySeparation is 4 x LISA separation

• Reduced (but interesting) sciencefor reduced cost

• 4 rather than 6 interferometer links

2

Workshop Q’s and A’s 1.

• Q: What forces are you aware of that you are not measuring?  

• A: Nothing significant

10 4 10 3 10 2 10 1 100

10 15

10 14

10 13

10 12

Frequency [Hz]

Acce

lera

tion

[m/s

2 /rtH

z]

Calibrated Acceleration Noise in X

Radiation PressureSolar WindThermal RadiationLaser RecoilLorentz Force

Laser recoil, Lorentz force analyzed:

Also small: •transverse orbit coupling,• s/c dipole coupling to magnetic field gradient

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Workshop Q’s and A’s 2.

• Q: What about internal distortions?

• A: Needs study, but expect these effects can be made small by palce the beamsplitter fiducial at spacecraft center.

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Workshop Q’s and A’s 3 (performance risks).

• Q: Risk 1: Unmodeled forces

• A: LAGRANGE s/c vs. LISA’s GRS:

• Requirements relaxed a little

• Benefit from larger mass (though smaller mass/area)

• Q: Risk 2: Inaccurate models

• A: The noise couplings are simple enough that the risk seems low

• Q: Risk 3: Sensor failures

• A: Needs  study,  but  the  radiometer  and  solar  wind  monitors  have  very  good  reliability  records.

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Workshop Q’s and A’s 4.

• Q: Is calibration with an on-board accelerometer critical?

• A: No.

10 4 10 3 10 2 10 1 10010 20

10 19

10 18

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Frequency [Hz]

Stra

in [1

/rtH

z]

LISA Science RequirementSolar Wind Monitor + RadiometerRadiometer + AccelerometerAccelerometer+ Solar Wind Monitor

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End of Q & A

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Sensitivity

• Spacecraft noise is reduced through:

• Geometry (factor of 100)

• Calibration (factor of 100)

• Low frequency limit: Residual Solar-Wind Acceleration

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LAGRANGE

LALALALAGRGRGRGRANANANANGEGEGEGE ((((40404040cmcmcmcm))))

LAGRANGE (40cm)

LAGRANGE (40cm)

Science

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Noise Budgets

10 4 10 3 10 2 10 1 10010 15

10 14

10 13

10 12

10 11

10 10

Frequency [Hz]

Acce

lera

tion

[m/s

2 /rtH

z]

Acceleration Noise on a single spacecraft

Radiation PressureSolar WindThermal RadiationLaser RecoilLISA Proof Mass

10 4 10 3 10 2 10 1 10010 15

10 14

10 13

10 12

10 11

10 10

Frequency [Hz]

Acce

lera

tion

[m/s

2 /rtHz

]

Acceleration Noise in X

Radiation PressureSolar WindThermal RadiationLaser RecoilLISA Proof MassLISA Shot

10 4 10 3 10 2 10 1 10010 15

10 14

10 13

10 12

10 11

10 10

Frequency [Hz]

Acce

lera

tion

[m/s

2 /rtH

z]

Calibrated Acceleration Noise in X

Radiation PressureSolar WindThermal RadiationLaser RecoilLISA Proof MassLISA Shot

GeometricSuppression

Calibration

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Instruments

• Solar wind monitor

• Radiometer

• Accelerometer

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SWEPAM

McCOMAS et al, Rev Sci Inst1998

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GOCE Accelerometer

• Only one axis needed

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The highly variable solar wind (1)

• Variable in magnitude and direction:

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The highly variable solar wind (2)

Angle of the solar wind - Histogram

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Orbits, 2 year data

0 100 200 300 400 500 600 7002

2.05

2.1

2.15

2.2 x 1010

Time [days]

S/C

Sep

arat

ion

[m]

0 100 200 300 400 500 600 700150

100

50

0

50

100

150

Time [days]

Rel

ativ

e S/

C v

eloc

ity [m

/s]

S/C 1 S/C 2S/C 3 S/C 2

S/C 1 S/C 2S/C 3 S/C 2

0 100 200 300 400 500 600 700163.6

163.7

163.8

163.9

164

Time [days]

Mic

hels

on a

ngle

[deg

rees

]

0 100 200 300 400 500 600 70088.5

89

89.5

90

90.5

91

Time [days]

Sun

Lin

k An

gle

[deg

rees

]

Sun S/C 1 S/C 2Sun S/C 3 S/C 2

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Orbits, 5 year data

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Cost Estimate

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Solar wind - SWEPAM instrument minimum performance

• Look for when the windis quite - plot spectra

• This appears to occur when the wind is low velocity (~330km/s vs 800km/s max)

• This gives worse case levelfor SWEPAM measurementperformance, but may stillbe actual wind.

• This level is less than a factor of10 from LAGRANGE assumptions

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SW Noise Components

• Look at: ∆rho, ∆v, ∆theta,hold other terms constant,calculate acceleration spectrum

• Density noise is largest.

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