PROBING SPACE–TIME IN THE SOLAR SYSTEM: FROM CASSINI TO BEPICOLOMBO

Abstract

Spacecraft radio science techniques can be used for precision solar system tests of relativistic gravity, as was demonstrated by the measurement of the Doppler shift of radio signals with the Cassini mission. Similar experiments are planned for the BepiColombo mission to Mercury. Recent theoretical developments based on string theory and inflationary cosmologies link the validity of general relativity to the expansion of the Universe and indicate that violations may be within the reach of future, precise experiments. In spite of the uncertainty of the theoretical scenarios, the motivations for further tests of gravitational theories are stronger then ever: string theory, new cosmological observations, the hypotheses of dark matter and dark energy, all point to the need for a new and more profound understanding of the Universe and its laws, including the laws of gravity. This paper describes experiments for probing space–time in the solar system with the Cassini and BepiColombo missions, and discusses the experimental limitations of microwave systems used for these tests, including attitude motion and nongravitational accelerations of the spacecraft, propagation noise, and mechanical noise of ground antenna.