Starship In-Space Refueling Technology Is Getting Real

NASA’s recent update confirms SpaceX’s progress toward a pivotal milestone: the in-space refueling of Starship, slated for demonstration next year. This advancement is crucial for utilizing the Starship to transport humans back to the lunar surface, as part of the Agency’s Artemis Program.

Amit Kshatriya, NASA’s deputy associate administrator for the Moon to Mars Program, shared insights during a recent session with the NASA Advisory Council’s Human Exploration and Operations Committee, held on April 26.

He confirmed that SpaceX accomplished a significant step towards Starship refueling during the latest Starship test flight on March 14.

The outcome of Starship’s third flight demo

Under a NASA Tipping Point contract from 2020, SpaceX conducted an in-flight propellant transfer demonstration, aiming to transfer at least 10 metric tons of liquid oxygen from a header tank to the main tank within the Starship upper stage while in space.

Although SpaceX appeared to confirm the success of the demonstration on the same day of the flight, no further updates were shared afterwards. Space Voyaging asked NASA for a confirmation or a comment on the test the following day, but we didn’t receive any answer.

No details were provided during the call, but he confirmed the success of the demonstration. “On Flight 3, they did an intertank transfer of cryogens, which was successful by all accounts,” he said. Further analysis of the results are underway.

The next milestone on the agenda is a planned 2025 demonstration where two Starships will dock in orbit, with a propellant transfer from one to the other. This phase has already cleared a flight system review, ensuring readiness across mission architecture and key subsystems, according to Kshatriya.

During this demonstration, a designated “target” Starship will launch first, entering orbit and awaiting. Subsequently, a “chaser” Ship will follow “three to four weeks later”. The chaser vehicle will then dock with the target, and transfer propellants. Post-demonstration, the two Starships will undock and initiate the descent and deorbit phase.

“It’s just docking with ourselves. Not trivial, but certainly easier than docking with the Space Station, which is far more complex,” said Elon Musk on X.

However, ahead of this test, SpaceX has still work to do. The biggest challenges, according to NASA, are the understanding of propellant dynamics during maneuvers, and the determination of the optimal thrust for propellant flow post-docking.

For SpaceX, in-space refueling is the key

Propellant transfer technology is integral to SpaceX’s ambitions beyond Earth orbit, particularly for the Human Landing System (HLS) version of Starship, which aims to land astronauts on the moon as part of the Artemis III mission, tentatively scheduled for September 2026.

The mission has already been delayed from its original schedule and, while it’s certainly not the time-driving item, SpaceX not being ready in time could still be a showstopper for its new launch target.

While the exact number of refueling launches remains uncertain, Kshatriya emphasized the need for further analysis to refine this aspect of the process. Factors like propellant boiloff, leakage, and transfer efficiency require thorough investigation to determine the optimal approach.

Following the in-space propellant transfer test, an uncrewed demonstration mission of the HLS Starship is planned, featuring fueling procedures and a lunar landing.

Additionally, an “ascent demo” has been added to verify Starship’s capability to lift off from the lunar surface. This was originally not present in NASA’s requirements for the demo mission.

Elon Musk, CEO of SpaceX, underscored in a post on X once again the importance of achieving full and rapid reusability of booster and ship, along with orbital refilling. These milestones, targeted for completion by the end of next year according to Musk, are way more complex than a booster catch attempt on the tower, which is “highly likely” this year.