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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.
1
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
3
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.
4
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.
5
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
10 17
10 16
Frequency [Hz]
Stra
in [1
/rtH
z]
LISA Science RequirementSolar Wind Monitor + RadiometerRadiometer + AccelerometerAccelerometer+ Solar Wind Monitor
6
End of Q & A
7
Sensitivity
• Spacecraft noise is reduced through:
• Geometry (factor of 100)
• Calibration (factor of 100)
• Low frequency limit: Residual Solar-Wind Acceleration
8
LAGRANGE
LALALALAGRGRGRGRANANANANGEGEGEGE ((((40404040cmcmcmcm))))
LAGRANGE (40cm)
LAGRANGE (40cm)
Science
9
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
10
Instruments
• Solar wind monitor
• Radiometer
• Accelerometer
11
SWEPAM
McCOMAS et al, Rev Sci Inst1998
12
GOCE Accelerometer
• Only one axis needed
13
The highly variable solar wind (1)
• Variable in magnitude and direction:
14
The highly variable solar wind (2)
Angle of the solar wind - Histogram
15
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
16
Orbits, 5 year data
17
Cost Estimate
18
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
19
SW Noise Components
• Look at: ∆rho, ∆v, ∆theta,hold other terms constant,calculate acceleration spectrum
• Density noise is largest.
20