Testing the Einstein equivalence principle with two Earth-orbiting clocks

We consider the problem of testing the Einstein equivalence principle (EEP) by measuring the gravitational redshift with two Earth-orbiting stable atomic clocks. For a reasonably restricted class of orbits we find an optimal experiment configuration that provides for the maximum accuracy of measuring the relevant EEP violation parameter. The perigee height of such orbits is similar to 1000 km and the period is 3-5 h, depending on the clock type. For the two of the current best space-qualified clocks, the VCH-1010 hydrogen maser and the PHARAO cesium fountain clock, the achievable experiment accuracy is, respectively, 1 x 10(-7) and 5 x 10(-8) after 3 years of data accumulation. This is more than 2 orders of magnitude better than achieved in Gravity Probe A and GREAT missions as well as expected for the RadioAstron gravitational redshift experiment. Using an anticipated future space-qualified clock with a performance of the current laboratory optical clocks, an accuracy of 3 x 10(-10) is reachable.

Automated summary

This study explores testing the Einstein equivalence principle by measuring gravitational redshift with two Earth-orbiting stable atomic clocks, and finds an optimal experimental configuration for maximum accuracy. For a restricted class of orbits, the experiment achieves significant accuracy in measuring the relevant EEP violation parameter.