Preliminary Sensitivity Study for a Gravitational Redshift Measurement with China's Lunar Exploration Project

TL;DR

This study proposes a high-precision measurement model for testing gravitational redshift using China's Lunar Exploration Project, demonstrating potential for high-accuracy tests if frequency offset issues are addressed.

Contribution

It introduces a Doppler cancellation-based measurement approach for gravitational redshift testing with space-ground clock comparisons in lunar missions.

Findings

Potential to reach an uncertainty of 3.7×10⁻⁶ after 60 days

Effective error reduction in space-ground clock comparison

High-precision onboard H-maser stability enables accurate tests

Abstract

General relativity (GR) is a highly successful theory that describes gravity as a geometric phenomenon. The gravitational redshift, a classic test of GR, can potentially be violated in alternative gravity theories, and experimental tests on this effect are crucial for our understanding of gravity. In this paper, considering the space-ground clock comparisons with free-space links, we discuss a high-precision Doppler cancellation-based measurement model for testing gravitational redshift. This model can effectively reduce various sources of error and noise, reducing the influences of the first-order Doppler effect, atmospheric delay, Shapiro delay, etc. China's Lunar Exploration Project (CLEP) is proposed to equip the deep-space H maser with a daily stability of $2\times10^{-15}$, which provides an approach for testing gravitational redshift. Based on the simulation, we analyze the space-ground clock comparison experiments of the CLEP experiment, and simulation analysis demonstrates that under ideal condition of high-precision measurement of the onboard H-maser frequency offset and drift, the CLEP experiment may reach the uncertainty of $3.7\times10^{-6}$ after a measurement session of 60 days. Our results demonstrate that if the issue of frequency offset and drift is solved, CLEP missions have a potential of testing the gravitational redshift with high accuracy. This manuscript has been accepted for publication in Classical and Quantum Gravity. DOI 10.1088/1361-6382/ad4ae2