This article is about the propellant transfer demo between Starship vehicles. For the initial propellant transfer demo between tanks on a single vehicle, see Starship flight test 3.
The SpacexStarship Propellant Transfer Demo is a demonstration of essential capabilities required for refueling a Starship in low-Earth orbit. It is expected to occur in 2026.[1] A somewhat similar test occurred during the Starship flight test 3, though the transfer during that test was between two tanks on the same vehicle.[2] The ability to refuel a Starship in low orbit is critical for the NASAArtemis program,[3] as Starship HLS (Human Landing System) requires approximately ten tanker launches of propellant to a depot in orbit to refuel a Starship sufficiently to then reach the lunar surface.[1]
Eventual expected use of Spacex propellant tankers and propellant depot in the Artemis 3 mission: A Low Earth orbit – 'B' Near-rectilinear halo lunar orbit – 1 Launch of the Starship propellant depot – 2 Launch Starship tanker (x 10+) – 3 Ship-to-ship propellant transfer between Starship tanker and Starhip propellant depot (x 10+) – 4 Launch of Starship HLS – 5 Ship-to-ship propellant transfer between Propellant Depot and Starship HLS – 6Orion launch with crew – 7 Crew transfer from Orion to Starship HLS – 8 Starship HLS stays on the Moon – 9 Crew transfer from Starship HLS to Orion – 10 Crew return to Earh.
The mission profile for the Starship Propellant Transfer Demo will begin with the first launch. This launch will deliver the upper stage into orbit around the earth, while the first stage returns to the launch site for a catch by the launch tower. The second launch will repeat this profile three to four weeks later, and dock with the first Starship.[4] Once docked, the vehicles will use a pressure differential between them to force propellant from the second vehicle into the first.[1] After this is complete, the two ships will undock, reenter the earth's atmosphere, and be caught by the launch tower.[1]
Payload
The second launch in the propellant transfer will fly an unknown amount of propellant as its payload.[1] In order to prevent the propellant from boiling during the vehicle's time in orbit, significant insulation and vacuum jacketing will be added to the propellant lines inside the vehicle.[1] This change was introduced on the first Starship Block 2 vehicle, S33.[5]
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