New Test Brings Europe Closer to Reusable Rocket

ArianeGroup and SSC Space completed the second "wet fill" test of the European Space Agency's experimental reusable vehicle "Themis" at the Esrange facility in Sweden, according to an announcement by the agency on October 7.

The test actually took place on September 29, during which the vehicle was loaded with liquid nitrogen instead of real fuel, cooling it to approximately minus 200 degrees Celsius, simulating the behavior of tanks and pipes under actual launch conditions.

The experiment tested automated ground control systems necessary for reusability, including robots to drain remaining fuel from a vehicle that landed after a mission—a crucial step toward making the rocket ready for a new launch faster and at lower cost.

At least one more rehearsal is expected using liquid oxygen and liquid methane before testing the firing of the "Prometheus" engine. This program comes as part of the 42.8 million euro EU-funded "SALTO" project, which aims to build a European capacity to recover and reuse stages.

What do these terms mean?

Wet Fill: A test in which the rocket body is filled with cryogenic liquids without igniting the engine, to verify tanks, pipes, and safety systems before launch.

Reusable Vehicle: A rocket or stage designed to return, land, and relaunch again, rather than being expended in a single flight.

Cryogenic Fuel: Liquids kept at very low temperatures to remain in liquid state inside the rocket, such as liquid oxygen and liquid methane.

Engine Firing: A test of actually running the engine on a test stand before integrating it with the vehicle and certifying it for a real flight.