Lasers in space, at the quantum limit

EQUS research allows laser power reduction for future NASA climate missions

Tracking lasers on satellites need to remain extremely stable over long periods of operation, and they need to be extremely power efficient.

Put into terms we might use at EQUS: What is the quantum limit of the lasers? What is the very lowest level of power at which a laser can reliably remain within necessary operation parameters?

An ANU/EQUS team has developed new technology to determine the power limits of the GRACE-FO flight laser.

The innovation enables future climate-monitoring and astrophysics missions to operate with ten times less energy than previously required.

The project was facilitated by the EQUS Translational Research Program.

How Low Can You Go? Finding the Power Floor for Space Lasers

Space missions have stringent requirements on laser stability over periods of months or years, as well as desperately tight power ‘budgets’.

Inter-spacecraft interferometers, lasers are used to track changes in spacecraft separation to the nanometre level over distances hundreds of kilometres long. This is a challenging task that places stringent requirements on the lasers used.”

Test-bed technology designed and built by the EQUS team at ANU, and deployed at JPL in California, has enabled a tenfold reduction in the laser’s necessary power output.

The ANU team’s portable optical testbed was designed to determine the minimum optical power at which a laser can be used for phase metrology, and revealed that the GRACE-FO flight laser could be used down to a received optical power level of 200 femto-Watts, a factor of ten below the previously determined limit.

“The results allow JPL to lower the required optical power of inter-spacecraft interferometric measurements on all future missions,” says EQUS PhD candidate Callum Sambridge, recently returned from two weeks in California with the JPL team.

“This significantly reduces operational costs, helping make critical climate-monitoring missions more accessible,” says Callum. “They also enable a wealth of novel mission configuration previously thought infeasible under the old optical power requirements!”

From Lab to Launch: The Role of Translation

“The Ultra-Low Optical Power Tracking technology comes from core EQUS research,” ANU lab head and EQUS CI Prof Kirk McKenzie explains. “We developed techniques to track laser phase at the quantum limits.”

“We wanted to know: how quiet can we make lasers?”

The project received funding in 2023 through EQUS’s Translational Research Program (TRP) to quantify the performance limits of inter-satellite laser links.

By understanding the phase tracking control system and where the system becomes non-linear, the team could demonstrate the boundaries of phase tracking. This has been done with hardware-in-the-loop simulations and optical experiments.

The TRP project was extended based on its initial successes, and the team were able to expand their demonstration from only the JPL flight laser to encompass other possible flight lasers operating at 1550nm.

“The EQUS Translation Program was a key part of the success of the project,” says Callum. “The ease of access to the Program, and speed with which the finances were dispersed, allowed us to work on the tight timelines that the project had.”

“It was a great experience, and I wish I had engaged with it earlier.”

Subsequent to the TRP seed funding, the team were able to secure a Moon to Mars Initiative Demonstrator Mission Grant for Laser Technology worth over $6M for the next GRACE mission, to produce laser-stabilisation technology for next-generation gravity-sensing missions, in collaboration with industry partner CEA Technologies.

EQUS’s research translation program has facilitated EQUS researchers identifying over 50 technologies with commercialisation potential across diverse sectors from satellite communications to hydrogen fuels. From less than $3 million invested into translation, it has attracted $4.1 million in cash or in-kind and generated over $80 million in subsequent economic activity. The program has also incubated a new generation of entrepreneurs such as Callum, and delivered at least 10 new startups to date. See EQUS.org/translation for more.