The Galileo solar redshift experiment

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Abstract
From the October 1989 launch to the first December 1990 Earth gravity assist, we regularly obtained frequency measurements of the spacecraft clock—an ultrastable crystal oscillator (USO) supplied by Frequency Electronics Inc. The solar gravitational redshift in frequency was readily detectable, and because of the unique variations in heliocentric distance, we could separate the general relativistic effects from the USO’s intrinsic frequency variations. We have verified the total frequency shift predicted by general relativity to 0.5% accuracy, and the solar gravitational redshift to 1% accuracy. This is the first test of the solar redshift with an interplanetary spacecraft.