Space opens unique opportunities to perform new fundamental experiments not possible on Earth, especially in gravitational physics. I shall describe two: the NASA Gravity Probe B Relativity Gyroscope Mission (GP-B) launched on 20 April 2004, now in the final stages of data analysis, and the proposed NASA-ESA Satellite Test of the Equivalence Principle (STEP).
GP-B tests:
1) the 6.6 arc-s/year geodetic effect due to the motion of the gyroscope through the curved space-time around the Earth;
2) the 0.039 arc-s/year 'frame-dragging' effect due to the rotating Earth. The mission has required the development of cryogenic gyroscopes with drift-rates 7 orders of magnitude better than the best inertial navigation gyroscopes and one dramatic consequence is the immediate appearance of the geodetic effect in the data at the 1% level. More sophisticated analysis to be described is expected to reach two orders of magnitude beyond that.
STEP, which aims to test the equivalence of gravitational and inertial mass to a part in 1018 or better, is currently in an advanced state of technological development. In addition to describing the science and technologies of GP-B and STEP, some account will be given of the real-life experience of setting up and operating a physics experiment in space, relevant to other future missions, including the proposed Laser Interferometer Space Antenna (LISA).
Coffee and cookies before the presentation at 3:15 pm, and refreshments after the presentation will both be served in Room 128.