General relativity experiments in space Original Research Article

Space technology has led to increased accuracy in the measurements of the gravitational redshift and the Shapiro time delay, has permitted the first measurements of the Nordtvedt effect and geodetic (or de Sitter) effect to be made, and has further constrained the parameters in the Parameterized Post Newtonian formalism. These important made, and has further constrained the parameters in the Parameterized Post Newtonian formalism. These important experimental tests of the general of relativity would not have been possible without the capability of launching instruments into space, accurately tracking spacecraft with dual frequency transponders, landing spacecraft on Mars, placing retroreflectors on the surface of the moon, and making precise range measurements to those retroreflectors. The reasons why this technology has been essential are examined. In light of this experience, a number of planned and proposed experimental tests of general relativity are discussed. Increased accuracy in measurements of the geodetic effect and tests of the weak equivalence principle, the first measurements of the Lense-Thrrring effect, and detection of gravitational radiation in space are expected in the next decade.