A Priori ※Imprinting§ of General Relativity Itself on Some Tests of It?

作者：Lorenzo Iorio

来源：Advances in Astronomy, 2010.

DOI：10.1155/2010/735487

We investigate the effect of possible a priori ※imprinting§ effects of general relativity itself on satellite/spacecraft-based tests of it. We deal with some performed or proposed time-delay ranging experiments in the sun%26apos;s gravitational field. It turns out that the ※imprint§ of general relativity on the Astronomical Unit and the solar gravitational constant , not solved for in the so far performed spacecraft-based time-delay tests, induces an a priori bias of the order of in typical solar system ranging experiments aimed to measure the space curvature PPN parameter . 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 accuracy in determining . 1. Introduction Several space-based tests of the Einstein＊s General Theory of Relativity (GTR) have been performed, or attempted, in the more or less recent past by following an ※opportunistic§ approach, that is, by suitably analyzing existing data sets of artificial satellites or interplanetary spacecrafts almost always built and launched for different original purposes (e.g., satellite geodesy, geodynamics, planetology, etc.). A cornerstone result was the Cassini radio science experiment [1] which led to constraining the deviation of the PPN parameter from its general relativistic value of unity at a level [2, 3] through the measurement of the general relativistic time delay affecting the electromagnetic waves linking the Earth and the Cassini spacecraft during its journey to Saturn when they were in superior conjunction, that is, aligned and on opposite sides of the Sun. Many other high-precision space-based tests, aiming to reach accuracy levels as high as in determining , have been proposed [4每8]. Indeed, some theoretical scenarios predict deviations from GTR at such a level [9每12]; for a recent overview see, for example, [13]. In this paper we wish to critically discuss certain subtle issues pertaining the consistency of such data analyses interpreted as genuine tests of GTR. In Section 2 we outline the problem in general terms. We will move to concrete examples in Section 3 in which we will deal with the Cassini-like ranging experiments (Section 3.1). Section 4 is devoted to the conclusions. 2. The Issue of the a Priori ※Imprinting§ of GTR Itself in Tests Dedicated to It: General Considerations In general, in such tests huge data sets from man-made interplanetary probes are confronted with the corresponding predictions computed from given dynamical models of their motion in which the