The French space agency CNES has issued a call for proposals to develop and demonstrate in-orbit cryogenic propellant storage and refuelling technologies as part of its CRYOSTARS initiative.
Launched under the Space Transportation Solutions stream of CNES’s Priority Innovation Vectors programme, the initiative is aimed at advancing technologies that support sovereign access to space. These include reusable launch systems, satellite servicing, and in-orbit refuelling.
The first phase will assess potential use cases, including applications outside the space sector in areas such as naval and aeronautical operations. CNES has outlined several areas for exploration, including long-term liquid hydrogen storage for nuclear thermal propulsion, refuelling of upper stages and orbital vehicles, and cryogenic propellant depots for electric propulsion systems.
Cryogenic propellants such as liquid hydrogen and liquid oxygen are widely used in spaceflight for their high specific impulse – which means a rocket uses less fuel to generate the same amount of thrust – and energy density. These gases must be stored at extremely low temperatures (-253°C for liquid hydrogen and -297°C for liquid oxygen) posing technical challenges for long-duration missions and in-orbit transfer.
The ability to refuel cryogenic systems in space could extend the lifespan of satellites and reduce the need for redundant hardware launches.
Several private companies are also targeting this emerging segment. US-based Eta Space is developing cryogenic fluid management and in-orbit refuelling systems, including plans for satellite servicing.
The company’s LOXSAT project, set to launch in 2026, is designed to test the transfer of liquid oxygen in microgravity.
Eta Space is developing in-orbit refuelling systems.
Refuelling capabilities are becoming more critical as satellite constellations expand. Most satellites are currently deorbited or left inoperative once they run out of fuel, contributing to orbital debris.
These dead satellites can break up or drift uncontrollably, posing collision risks to other space assets. The International Space Station has had to manoeuvre over 30 times in the past two decades to avoid debris.
Proposed technologies under the CRYOSTARS programme must reach at least technology readiness level 6, which means successful demonstration in a relevant environment. CNES recommends participants aim for level 9, which corresponds to full system qualification in an operational setting.
The move follows a similar initiative by the European Space Agency, which in February announced funding to support in-orbit refuelling demonstrations using green, self-pressurising propellants. ESA’s programme is targeted at supporting multi-orbit satellite constellations, including the EU’s IRIS2 system.
