Experimental test of general relativity using time-delay data from Mariner 6 and Mariner 7
Range and Doppler data from Mariner 6 and Mariner 7 have been analyzed for purposes of measuring the effect of the sun's gravity field on S-band radio transmissions to the spacecraft. The prediction of general relativity, that the round-trip time delays between the station and the spacecraft will be increased by about 200 microsec near superior conjunction, has been verified with an uncertainty of 3 per cent or less. The dominant error source on the experiment is the stochastic nongravitational forces which act on the spacecraft and which limit the accuracy of the determination of the Mariner orbits. Effects of free coronal electrons on the round-trip propagation also make the measurement difficult, but the coronal contribution to the error is only about 1 per cent. Separate analyses of data from Mariner 6 and Mariner 7 yield two values near unity for the parameter gamma* which differ by about 0.3 per cent from each other. This and other considerations suggest that the error in the experiment is perhaps less than 3 per cent.