Physics
Scientific paper
May 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999cqgra..16.1487t&link_type=abstract
Classical Quantum Gravity, Vol. 16, No. 5, p. 1487 - 1502
Physics
Gravitation Theory: Tests, Space Missions: Gravitation Theory
Scientific paper
Testing alternative metric theories of gravity with an accuracy much better than the present level has recently drawn great attention, in particular in relation to the search for a very weak scalar field, which is a possible remnant of an early inflationary cosmology. The gravitational deflection of electromagnetic waves is controlled by the dimensionless post-Newtonian parameter γ, which takes a value of unity in general relativity. Here, the authors claim that the accuracy in the measurement of γ can be substantially improved by measuring the Doppler frequency shift of a microwave beam transponded back to the ground by an interplanetary spacecraft near solar conjunction. In this kind of experiment, the dispersion due to the plasma in the solar corona is the crucial difficulty, which, however, can be essentially overcome using skilful combinations of carriers with different frequencies. The spacecraft Cassini, launched in 1997, has a sophisticated radio system, including a Ka-band link at 32 - 34 GHz, which makes this possible. The authors discuss the noise budget for two experiments to be carried out with Cassini in 2002 and 2003. In particular, the authors consider the contribution of the solar corona, the non-gravitational accelerations, and thermal noise due to solar radio emission. They estimate that an accuracy in γ of about 10-5 is achievable.
Anderson John D.
Bertotti Bruno
Giampieri Giacomo
Tess L.
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