A ug 2 00 9 On possible a - priori “ imprinting ” of General Relativity itself on some tests aimed to test it

We investigate the effect of possible a-priori “imprinting” effects of general relativity itself on satellite/spaceraft-based tests of it. We deal with some performed or proposed time-delay ranging experiments in the Sun’s gravitational field, and with the attempts to measure the Lense-Thirring effect with the LAGEOS satellites orbiting the Earth. It turns out that the “imprint” of general relativity on the Astronomical Unit and the solar gravitational constant GM⊙, not solved for in the so far performed spacecraft-based time-delay tests, induces an a-priori bias of the order of 10 in typical solar system ranging experiments aimed to measuring the space curvature PPN parameter γ. It is too small by one order of magnitude to be of concern for the performed Cassini experiment, but it would affect future planned or proposed tests aiming to reach a 10 − 10 accuracy in determining γ. General relativity, neither modelled nor solved for in the GRACE-based models of the Earth’s geopotential, “imprints” them at a non-negligible level. This translates into a bias of the LAGEOS-based tests as large as the Lense-Thirring effect itself. Subject headings: Experimental studies of gravity Experimental tests of gravitational theories Ephemerides, almanacs, and calendars Lunar, planetary, and deep-space probes Satellite orbits Harmonics of the gravity potential field