EQUS researchers have developed a compact absolute laser-frequency reference for future space-based geodesy missions.

Satellite-based geodesy relies on inter-spacecraft laser interferometry. To accurately track climate-induced movements of water and ice around Earth over long timescales (months to decades), ranging measurements require long-term absolute laser-frequency stability to calibrate the data.

The EQUS team have investigated a technique to provide long-term absolute laser-frequency data for future space-based gravity missions (such as GRACE and GRACE Follow-On) with minimal changes to existing flight-qualified hardware. The simple and robust technique applies additional gigahertz modulation to the laser,

revealing information about the length of an optical cavity. This information is then used to correct for changes in laser frequency over time.

This result represents an enabling technology for laser interferometry on future space-based gravity-sensing missions, the next of which is expected to launch within the decade. The next step is to test and validate the technique to ensure the readout scheme is ready for inclusion in the next mission.

EQUS Chief Investigator Kirk McKenzie helped to build the satellites for the GRACE Follow-On mission, while working at NASA’s Jet Propulsion Laboratory.

A prototype of the team’s system is being developed in collaboration with CEA Technologies and NASA, with support from an Australian Space Agency Grant and the ARC Centre for Excellence for Gravitational Wave Discovery.

In 2021, EQUS funded a research translation project to upgrade flight-like test capability for this prototype.

This story was first published in the 2021 EQUS annual report, and was written by Kristen Harley.