For NASA’s next generation of deep space exploration missions, spacecraft may need to refuel in Earth orbit before pushing farther into the solar system. Similar to how a gas pump needs a nozzle to fit your fuel tank, future spacecraft could require a special device in order to fill up prior to departure, known as a cryocoupler.

Cryocouplers would allow spacecraft to connect to future orbital propellant depots, which would serve as the gas stations of space. The technology comes with the challenge of reliably transferring cryogenic, or super-cold, fluids without losing propellant or performance. Cryogenic propellants like liquid hydrogen and liquid oxygen must stay chilled to hundreds of degrees below zero Fahrenheit, placing strict demands on the materials, seals, and mechanisms that move them.

“In-orbit cryogenic refueling between two spacecraft has yet to be done and remains one of the toughest engineering challenges in spaceflight,” said Travis Belcher,  cryocoupler project manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “These propellant transfers are essential for the kinds of missions NASA wants to fly in the future, so developing a coupler that can handle ultra-cold propellants is a critical step toward making that capability real.”

Ground-based couplers like those used to fill the SLS (Space Launch System) for Artemis missions are not an option for orbiting propellant transfers. Those couplers release quickly while a rocket is launching and must be manually reconnected for the next flight. They also are not designed to operate in the harsh environment of space and are much larger than what would be used to refill an orbiting spacecraft’s fuel tank.

To meet these challenges, NASA tested a cryocoupler developed by L3Harris.

“The cryocouplers we’re working on can attach and detach multiple times and are fully automated, so astronauts won’t have to perform a spacewalk to transfer propellant,” said Belcher. “They’re rigorously designed to withstand space and sized for the expected tank designs.”

A joint NASA and L3Harris team recently conducted two types of tests at NASA Marshall. To ensure the cryocoupler can handle the extremely cold temperatures it will be exposed to, they ran liquid nitrogen at minus 321 degrees Fahrenheit through multiple connected and disconnected configurations to observe how the coupler reacts to thermal contraction, flow, and significant temperature differences between propellant and materials.

The team also put the cryocoupler through operational tests to determine its performance limits. In this setup, one coupler half was mounted to a robotic table that could move and rotate in any direction, allowing it to simulate misaligned docking with the other half, which remained stationary above the table. The cryocoupler is designed to accommodate some misalignment in case a spacecraft and depot are not perfectly aligned when docking.  

“These cryocouplers are very early in development, so the testing is mostly focused on basic functionality,” said Belcher. “Future test campaigns will design them for specific missions and assess them more meticulously based on that mission’s requirements.”

The cryocoupler testing was done as part of a 2022 Announcement of Collaboration Opportunity, a partnership where NASA centers provide select companies with expertise, facilities, hardware, and software at no cost.

The Cryogenic Fluid Management Portfolio project, a cross-agency team based at NASA Marshall and NASA’s Glenn Research Center in Cleveland, oversees cryocoupler development.

To learn more about cryogenic fluid management, visit:

https://go.nasa.gov/CFM