Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session H7: Laboratory and Space Tests of Gravitation |
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Sponsoring Units: GGR Chair: Eric Adelberger, University of Washington Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Rose Garden |
Sunday, April 13, 2008 8:30AM - 9:06AM |
H7.00001: Pioneer Anomaly: Status of New Investigation Invited Speaker: The Pioneer 10/11 spacecraft yielded the most precise navigation in deep space to date. However, their radiometric tracking data received from the distances between 20-70 astronomical units from the Sun has consistently indicated the presence of a small, anomalous, Doppler frequency drift. The drift is a blue frequency shift that can be interpreted as a sunward acceleration of $a_{P}$ = (8.74 $\pm $ 1.33) $\times $ 10$^{-10}$ m/s$^{2}$ for each particular spacecraft. This signal has become known as the Pioneer anomaly the nature of which remains unexplained. New Pioneer 10 and 11 radio-metric Doppler data recently became available that span a longer interval compared to the data used in previous investigations. A thermal model of the Pioneer vehicles is being developed to study possible contribution of thermal recoil force acting on the two spacecraft. The current status of these investigations will be discussed. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration. [Preview Abstract] |
Sunday, April 13, 2008 9:06AM - 9:42AM |
H7.00002: APOLLO: A Comprehensive Test of Gravity via Lunar Laser Ranging Invited Speaker: The fundamental incompatability of quantum mechanics with general relativity together with our well-quantified ignorance of large-scale gravity (dark energy, dark matter) strongly suggests that we intensify our tests of gravity. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is a new project that will bring about order-of-magnitude improvements in testing several fundamental aspects of gravity. Using a 3.5 meter telescope to bounce laser pulses off of the retroreflector arrays left on the moon by the Apollo astronauts, APOLLO is capable of one-millimeter range-precision. By determining the exact shape of the lunar orbit, it will be possible to test the equivalence principle, the time-rate-of-change of the gravitational constant, gravitomagnetism, geodetic precession, and the inverse-square law to at least ten times better precision than currently tested. Details of the technique, millimeter-scale challenges, and performance to date will be presented. [Preview Abstract] |
Sunday, April 13, 2008 9:42AM - 10:18AM |
H7.00003: Precision Test of the Equivalence Principle Invited Speaker: We used a torsion balance instrument installed on a continuously rotating turntable to measure the acceleration difference of beryllium and titanium test bodies towards sources at a variety of distances. Our result $\Delta $a$_{N,Be-Ti}$ = (0.6$\pm $3.1)$\times $10$^{-15}$ m/s$^{2}$ improves previous limits on equivalence-principle violations with ranges from 1 m to $\infty $ by nearly an order of magnitude. The E\"{o}tv\"{o}s parameter is $\eta _{Earth,Be-Ti }$= (0.3$\pm $1.8)$\times $10$^{-13}$. By analyzing our data for accelerations towards the center of the Milky Way we find equal attractions of Be and Ti towards galactic dark matter, yielding $\eta _{DM,Be-Ti}$ = (-4$\pm $7)$\times $10$^{-5}$. Space-fixed differential accelerations in any direction are limited to less than 8.8 $\times $ 10$^{-15}$ m/s$^{2}$ with 95{\%} confidence. [Preview Abstract] |
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