# Test of the Gravitational Redshift with Galileo Satellites in an Eccentric Orbit

## TL;DR

This paper reports a three-year analysis of Galileo satellite data with hydrogen masers, providing a highly precise test of the gravitational redshift predicted by general relativity, surpassing previous experimental accuracy.

## Contribution

It presents the first test of gravitational redshift using Galileo satellites in eccentric orbits, achieving over four times improved precision compared to prior experiments.

## Key findings

- Reduced uncertainty in gravitational redshift measurement by over 4 times
- Confirmed general relativity's predictions within experimental error
- Demonstrated the scientific value of eccentric satellite orbits for fundamental physics

## Abstract

On August 22, 2014, the satellites GSAT-0201 and GSAT-0202 of the European GNSS Galileo were unintentionally launched into eccentric orbits. Unexpectedly, this has become a fortunate scientific opportunity since the onboard hydrogen masers allow for a sensitive test of the redshift predicted by the theory of general relativity. In the present Letter we describe an analysis of approximately three years of data from these satellites including three different clocks. For one of these we determine the test parameter quantifying a potential violation of the combined effects of the gravitational redshift and the relativistic Doppler shift. The uncertainty of our result is reduced by more than a factor 4 as compared to the values of Gravity Probe A obtained in 1976.