SpaceX’s Starship generates over twice the thrust of the Saturn V rocket, yet after 13 integrated test flights as of July 2026, the vehicle has not yet demonstrated in-orbit ship-to-ship refueling—a critical technical hurdle that remains essential for future missions to the Moon and Mars.
Thrust Scale Versus Orbital Architecture
SpaceX’s heavy-lift vehicle cuts an imposing figure on the pad, but raw force does not equate to interplanetary readiness. The Starship V3 configuration leaves its launch pad with roughly 18 million pounds of thrust. For comparison, NASA credits the historic Saturn V with 7.6 million pounds at liftoff, meaning the modern stack produces well over twice the power of the rocket that carried Apollo astronauts toward the lunar surface.
That scale establishes Starship’s immense physical capacity rather than its operational readiness for deep-space missions. While Saturn V discarded three stages in sequence and sent a relatively small spacecraft stack onward to the Moon, Starship is designed to recover and rapidly reuse both its Super Heavy booster and its upper stage. However, that reusability requires carrying massive tanks, heat shielding, flaps, and landing systems that expendable vehicles never needed to haul home.
The Flight Campaign and the Refueling Void
By the completion of the vehicle’s 13th integrated test flight on 24 July 2026, SpaceX had built up a substantial operational record. The flight campaign—which began with the first full Starship and Super Heavy launch in April 2023—has demonstrated hot-stage separation, controlled atmospheric entry, planned ocean splashdowns, in-space engine relights, payload deployment, and catches of Super Heavy boosters using the launch tower. Flight 13 itself featured a clean flight plan for the V3 vehicle, deploying 20 next-generation Starlink satellites and successfully relighting a Raptor engine in space before an Indian Ocean splashdown.
Yet a gaping hole remains in the flight manifest. No two Starships have ever met in orbit, docked, and passed propellant between them. Because an upper stage consumes the vast majority of its launch load simply climbing away from Earth, an interplanetary craft cannot depart from low-Earth orbit with a full complement of fuel unless it is refueled aloft.
Single-Ship Tests Versus Interplanetary Demands
SpaceX did achieve a partial fluid-management milestone during Flight 3 in March 2024. Backed by NASA’s Tipping Point programme, the ship transferred approximately five tonnes of liquid oxygen from a smaller header tank into its main oxygen tank while coasting in space. NASA’s TechPort record marks that project complete, noting it provided crucial data about pressure control, subcooled oxygen, and cryogenic fluid behaviour in free fall.
But that experiment happened entirely within a single vehicle. The source tank, receiving tank, and connecting plumbing were installed inside the same hull before launch. Nothing had to rendezvous, and no coupling had to join two independently moving spacecraft in orbit.
NASA and SpaceX engineers continue to analyze the underlying physics required for a true multi-ship transfer. Watson-Morgan points to complex variables like ullage, tank collapse, fluid slosh, guidance, navigation, control, and the mechanical stability needed to keep two docked ships steady.
“Things like ullage, for tank collapse, for slosh, for how the fluids should go from one ship to the other, the guidance navigation and control, how the two ships are going to hold steady.”
Watson-Morgan, NASA
The Artemis Lander Equation and Tanker Fleets
The unresolved refueling milestone directly impacts NASA’s human lunar return timelines under the Artemis program. A planned flight demonstration under a $53 million Tipping Point award aims to transfer 10 metric tons of liquid oxygen between tanks on a Starship vehicle, serving as a stepping stone toward a future multi-ship propellant transfer demonstration.
Until that demonstration succeeds, key questions about the Starship human landing system remain unanswered. Watson-Morgan has suggested that the total number of tanker launches required to support a single Artemis landing mission could land in the high single digits to the low double digits, though exact figures depend heavily on boil-off rates and vehicle sizing still being refined by SpaceX. While CEO Elon Musk has previously floated expanding Starship’s capacity with larger propellant tanks to cut down on required tanker flights, the entire architecture hinges on mastering autonomous fuel transfers in low-gravity orbit—a feat that has never been done successfully in orbit.
