Development of Software to Measure the Gravitational Redshift with RadioAstron

The incompatibility of General Relativity (GR) and quantum theory continues to be a stumbling block in the unification of our understanding of the physical world. Tests of the Einstein Equivalence Principle, lying at the core of GR, are vital to constrain new theories that require departures from GR's predictions. One such test is measuring the gravitational redshift using RadioAstron – a space-VLBI mission launched in 2011 into a highly elliptical orbit. Utilizing the onboard H-maser frequency standard along with a Doppler compensation scheme that minimizes systematics, the gravitational redshift is anticipated to be determined with a relative accuracy of 10^-5. A third-order dynamical model has been implemented to predict frequency shifts in the spacecraft's carrier signal needed to conduct the experiment. The theory behind this model is developed, the software implementation described and third-order effects necessary to achieve the desired measurement accuracy are discussed.