Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session K4: Earth, Sky and Moon: Gravity Tests Across 13 Orders of Magnitude |
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Sponsoring Units: GGR GPMFC Chair: John Gillaspy, National Institute of Standards and Technology Room: Thurgood Marshall North |
Sunday, February 14, 2010 3:30PM - 4:06PM |
K4.00001: Laboratory Tests of the Inverse Square Law of Gravity Invited Speaker: Newton's inverse square force law of gravity follows directly from the fact that we live in a 3-dimensional world. For sub-millimeter length scales there may be undiscovered, extra dimensions. Such extra dimensions can be detected with inverse square law tests accessible to torsion balances. I will present an overview of two experiments that are being conducted at the University of Washington to search for gravitational-strength deviations from the inverse square law for extra dimension length scales smaller than 50 micrometers. One experiment is designed to measure the distance dependent force between closely spaced masses, whereas the second experiment is a null experiment and is only sensitive to a deviation from the inverse square law of gravity. The first experiment consists of a torsion pendulum that is suspended above a continuously rotating attractor. The attractor and the pendulum are disks with azimuthal sectors of alternating high and a low density. The torque on the pendulum disk varies as a function of the attractor angle with a 3 degree period. The amplitude of the torque signal is analyzed as a function of the separation between the pendulum and the attractor. The second experiment consists of a plate pendulum that is suspended parallel to a larger vertical plate attractor. The pendulum plate has an internal density asymmetry with a dense inlay on one half facing the attractor and another inlay on the other half on the side away from the attractor. If the inverse square law holds, the gravitational field of the attractor is uniform and the torque on the pendulum is independent of the gap between pendulum and attractor. The attractor position is modulated between a near and far position and the torque difference on the pendulum is recorded and analyzed for a possible inverse square law violation. [Preview Abstract] |
Sunday, February 14, 2010 4:06PM - 4:42PM |
K4.00002: ESA's GOCE gravity gradiometer mission Invited Speaker: In the present decade, three space gravity missions, CHAMP, GRACE and GOCE provide unique information about mass and mass redistribution in the Earth system with a wide range of scientific returns like global ocean circulation, ice mass balance, glacial isostatic adjustment, continental ground water storage. On board the four satellites of these missions, similar electrostatic space inertial sensors deliver continuously, during quite nine years for the older, the accurate acceleration data needed for the missions. The sensor operation remains on the six axes electrostatic suspension of one solid metallic mass, which is servo-controlled motionless at the centre of the highly stable set of gold coated silica electrode plates. All degrees of freedom are measured with very sensitive capacitive sensors down to a few pico-m and the applied electrostatic forces to pico-N. With similar sensor design and technologies, full scale range and resolution can be adjusted according to the satellite environment and the mission requirements. The CHAMP and GRACE accelerometers have demonstrated their in orbit performance. They provides measurements of the satellite non gravitational surface forces like the atmospheric drag and radiation pressures in order to extract from the satellite measured orbital position and velocity fluctuations, the effects of gravity anomalies. The six GOCE accelerometers compose the three axes gradiometer, combined to the SST-high-low GPS tracking to provide higher precision and resolution of the Earth static field. They contribute also to the satellite attitude control and drag compensation system, allowing the heliosynchronous orbit at the very low 260 km altitude. So, the accelerometers are designed to exhibit a full range of 6.5 10$^{-6~}$ms$^{-2}$ and a resolution of 2 10$^{-12}$ ms$^{-2}$ Hz$^{-1/2}$. Since the gradiometer switch on in April 09, they deliver data leading to the components of the gravity gradient tensor. The main characteristics of the GOCE accelerometers and the mission are depicted in comparison to the previous ones, exhibiting the increase of performance and the limits. First in orbit results are mentioned like in particular the satellite drag free fly. The future gravity mission configuration is envisaged as well as other fundamental physics applications of such sensors. [Preview Abstract] |
Sunday, February 14, 2010 4:42PM - 5:18PM |
K4.00003: Advancing Tests of Relativity via Lunar Laser Ranging Invited Speaker: Laser range measurements between the earth and the moon have provided some of our best tests to date of general relativity and gravitational phenomenology--including the equivalence principle, the time-rate-of-change of the gravitational constant, the inverse square law, and gravitomagnetism. APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is now collecting measurements at the unprecidented precision of one millimeter, which will produce order-of-magnitude improvements in a variety of gravitational tests. Experimental performance, evidence for degradation of the reflectors, project status and science outlook will be discussed. [Preview Abstract] |
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