Testing the gravitational redshift during VERITAS cruise phase

Abstract

The NASA Discovery-class mission VERITAS, selected in June 2021, will be launched towards Venus in 2027. In addition to the science instrumentation that will build global foundational geophysical datasets, VERITAS proposed to conduct a technology demonstration for the Deep Space Atomic Clock (DSAC-2). A first DSAC successfully operated in low-Earth orbit for more than two years, demonstrated the trapped ion atomic clock technology, and established a new level of performance for clocks in space. DSAC-2 would have further improvements in size, power, and performance. It would host a 1×10-¹³ grade USO to produce a frequency output with short-term stability of less than 2×10-¹³/√T (where τ is the averaging time). In this work, we investigate the possibility of leveraging DSAC-2's frequency stability to measure possible discrepancies in the redshift predicted by General Relativity. With its capability of establishing a one-way downlink Doppler link with Earth stations, DSAC-2 would enable precise tests of the dependency of the redshift on the location and velocity of the spacecraft and the Earth, thus providing improved tests of the Local Lorentz Invariance and Local Position Invariance. We perform accurate simulations of the experiment that would take place during the VERITAS cruise phase. We consider different parametrizations of the possible violations of the General Relativity, different operational conditions, and a wide spectrum of expected measurement performance assumptions. We show that DSAC-2 onboard VERITAS would provide new and improved constraints with respect to the current knowledge.