testing gravity with lunar laser ranging doe site visit james battat august 21, 2006
TRANSCRIPT
Testing Gravity with Lunar Laser Ranging
DoE Site Visit
James Battat
August 21, 2006
Testing Gravity with Lunar Laser Ranging
New Mexico, near White Sands. Note SDSS
3.5 m
APOLLO
UCSD:Tom Murphy - PIEric MichelsenAdam Orin
Harvard:Christopher StubbsJames Battat
U. Washington:Eric AdelbergerErik SwansonC. D. HoyleLarry Carey
JPL:Jim WilliamsJean DickeySlava Turyshev
Lincoln Lab:Brian AullBernie KosickiBob Reich
Northwest Analysis:Ken Nordtvedt
Mapping the lunar orbit to 1 millimeter
APD detectors
Ephemeris
Why Push Gravity Tests Further?
• Order of magnitude in constraints
• Dark energy, w
• Scalar field modifications to GR– Predict non-GR effects
• Brane-world cosmology– Gravitons leaking into bulk modify gravity at
large scales
LLR is a Powerful Test of Gravity
With one millimeter range precision:
• Weak EP a/a 10-14
• Strong EP 3×10-5
• Gravitomagnetism 10-4
• dG/dt 10-13•G/year• Geodetic precession 3×10-4
• Long range forces 10-11 × the strength of gravity
* In each case, LLR currently provides the best limit.
LLR is a Powerful Test of Gravity
With one millimeter range precision:
• Weak EP a/a 10-14
• Strong EP 3×10-5
• Gravitomagnetism 10-4
• dG/dt 10-13•G/year• Geodetic precession 3×10-4
• Long range forces 10-11 × the strength of gravity
* In each case, LLR currently provides the best limit.
Nordtvedt Effect
Nordtvedt, Phys Rev, 169, 1014, 1968
Nordtvedt, Phys Rev, 169, 1017, 1968
Nordtvedt, Phys Rev, 170, 1186, 1968
Synodic period = 29.35 days
r = 13 cos(D) meters
Avalanche Photodiode Array
= 30m
-Courtesy of MIT Lincoln Lab
3.5 meter telescope
Good seeing
APOLLO: Reaching 1 mm
Laser Ranging Apparatus: Transmit
2.3 Watt NdYAG laser2.3 Watt NdYAG laser20 Hz, 20 Hz, = 530 nm = 530 nm < 100 ps pulse width< 100 ps pulse width110 mJ per pulse110 mJ per pulse
APD arrayAPD array
START
3.5m primary3.5m primary
LASER
Corner cubeCorner cube
Laser Ranging Apparatus: Receive
2.3 Watt NdYAG laser2.3 Watt NdYAG laser20 Hz, 20 Hz, = 530 nm = 530 nm < 100 ps pulse width< 100 ps pulse width110 mJ per pulse110 mJ per pulse
APD arrayAPD array
STOP
3.5m primary3.5m primary
LASER
25 km
4 km
~1017 attenuation
MOON
Interpretation Requires Sophisticated Modeling
Measure telescope-to-reflector distanceWant center-to-center separationThrough the atmosphereNeed precise ephemeris information – JPL collaboration
MLRS: The Old Way
28 photons in 42 minutes
Enter APOLLO
1,500 photons in 13 minutes
1 mm statistical uncertainty
Current Status
Millimeter precision dataReturns from all 3 Apollo arraysRemote operations
• Enter campaign mode (October)1-2 hours every 2-3 nights
• Improve site coordinates
• New constraints on gravitational params
The End
THE END
EXTRA SLIDES
APOLLO: Reaching 1 mm
• Large-aperture, good seeing– Figure of merit goes like (D/)2
• Incorporate modern technology– Detectors, precision timing, laser
• Re-couple data collection to analysis/science
LLR Targets
Gravitational Self-Energy + SEP
Object mSE/m
1 kg sphere, 6” diam 5 x 10-27
Moon 0.2 x 10-10
Earth 5 x 10-10
APOLLO Random Error BudgetExpected Statistical Error RMS Error (ps) One-way Error (mm)
Laser Pulse (95 ps FWHM) 40 6
APD Jitter 50 7
TDC Jitter 15 2.2
50 MHz Freq. Reference 7 1
APOLLO System Total 66 10
Lunar Retroreflector Array 80–230 12–35
Total Error per Photon 105–240 16–37
Nordtvedt, Class. Quantum Grav., 15, 3363, 1998
Lunar Phase Coverage
• EP violation has a null at Quarter moon and maxima at Full and New Moons
• Same data, uniform coverage gives tighter
No measurements at max signal
Current PPN Constraints
1
0.998 10.999 1.001 1.002
1.002
1.001
0.999
0.998
Lunar Laser Ranging
Mercury Perihelion Shift
Mars Radar Ranging
VLBI & combined planetary data
Spacecraft range & Doppler
Basic phenomenology:
measures curvature ofSpacetime
measures nonlinearity of gravity
= (2.1 § 2.3) x 10-5
= (1.2 § 1.1) x 10-4
= (4.4 § 4.5) x 10-4
Solar System Parameters• Separation
– Moon-Earth 0.38 million km– Sun-Earth 150 million km
• Mass– Sun 2 x 10^30 kg– Earth 6.0 x 10^24 kg– Moon 0.073 x 10^24 kg
• Radius– Sun 695,000 km– Earth 6380 km– Moon 1740 km
• Gravitational Constant6.67 x 10^-11 m^3 kg^-1 s^-2
Testing Gravity with Lunar Laser Ranging
Historical Accuracy of LLR Data
30 cm
0 cm
1970 present
Laser Ranging Apparatus
2.3 Watt NdYAG laser2.3 Watt NdYAG laser20 Hz, 20 Hz, = 530 nm = 530 nm < 100 ps pulse width< 100 ps pulse width110 mJ per pulse110 mJ per pulse
APD arrayAPD array START
3.5m primary3.5m primary
LASER
Corner cubeCorner cube
2.3 Watt NdYAG laser2.3 Watt NdYAG laser20 Hz, 20 Hz, = 530 nm = 530 nm < 100 ps pulse width< 100 ps pulse width110 mJ per pulse110 mJ per pulse
APD arrayAPD array
3.5m primary3.5m primary
Laser Ranging Apparatus
LASER
STOP