Starship's Thirteenth Flight Test *REDUX*
SpaceX, Starship, and lofty goals for the future
Running in Place
SpaceX had a slight mishap with their planned launch of Starship Flight 13 last Thursday. We wrote about the mission goals then, and invite readers to review the piece for the basics.
They were originally hoping to launch this Monday, the 20th, then updated that to target yesterday, Thursday, and are now preparing to go today, Friday, July 24th, with the 90-minute launch window opening at 6:45 p.m. EST.
Last Thursday’s attempt was scrubbed because some of the Super Heavy booster's Raptor engines failed to ignite during the final seconds of the countdown. In a post on X, Musk said they needed to replace two of them.
If the new launch goes ahead as announced, it’ll help, maybe, to get SpaceX caught up on its timelines as part of the NASA Artemis program. But more likely not. A successful launch is more likely to help the SpaceX stock price regain some ground, but that’s about it.
Early next year, SpaceX is scheduled to send a Starship to land on the Moon. The landing test will be uncrewed, but there’s a lot of development to be done before that happens. Late 2027, Starship (and Bezo’s Blue Origin) is supposed to perform a docking test with the Orion spacecraft, with astronauts.
Before any of that happens, SpaceX has to demonstrate cryogenic refueling, the process in which a tanker-supply-version of Starship will link up with a stationary tanker-depot-version of Starship and demonstrate that they are able to re-fuel the tanker in orbit. This is one of the prerequisites for Starship even reaching the moon, and essential to the future of the platform.
If Starship can’t prove refueling, Starship can never be the Starship Elon has promised. Without Starship, the core of the entire space part of SpaceX (since Falcon is scheduled to be wound down to make way for Starship), the “space exploration” part, is is effectively dead in the water. Starship, if it then survives as a program, will be demoted to transporting next-generation Starlink satellites to low earth orbit.
The problem is, the refueling test is supposed to happen this year and ship-to-ship cryogenic refueling is still an unproven technology.
Room-temperature, storable hypergolic propellants are routinely transferred in space, such as on the International Space Station, but the transfer of super-chilled cryogenic fluids between two independent spacecraft in orbit has never been successfully demonstrated.
SpaceX isn’t going in completely blind. They did achieve a baseline step by demonstrating a small-scale internal transfer of roughly 10 metric tons of liquid oxygen between two tanks within the same vehicle back in March, 2024, during Starship Flight Test 3. Blue Origin has also tested mechanical utility transfer mechanisms in Earth-based thermal vacuum chambers.
Without diving into the details of the fascinating world of fluid dynamics, let it suffice to say that without gravity, things get…complicated.
In the Flight 3 test, SpaceX was able to get some data on how the liquid oxygen shifted and settled when the ship's small roll-control thrusters fired to create ullage.
Ullage is the unfilled space or the pocket of gas at the top of a container of liquid. Gravity is your friend here. In zero gravity, liquids float freely inside the tank as floating blobs mixed with gas bubbles. If a rocket engine sucks in gas bubbles instead of pure liquid it can cause pump cavitation (implosion), which could cause what SpaceX refers to as “rapid unscheduled disassembly.”
SpaceX did not test much else that needs to be done properly before they can achieve in-flight fuel transfer.
They did not test any external docking ports. The pump connections they eventually use have to be able to seal perfectly in space without leaking fluid into a vacuum.
They also got no data on transferring supercooled liquid gas into dry, empty transfer lines between two completely different ships. The process can cause rapid thermal contraction, warping or fracturing the pipes.
Additionally, 10 tons of liquid oxygen is a fraction of the actual requirement. The lunar landing mission requires transferring hundreds of tons of fluid rapidly across multiple consecutive Starship-tanker flights, while the lunar transport Starship waits in orbit.
We also don’t know exactly how many tanker flights will be required to fill the depot ship, because we don’t know how much “boil-off” (liquid oxygen and methane returning to a gaseous state, requiring venting to keep the tank from exploding under the enormous pressure buildup as the gases expand) there will be between flights. The boil-off rate for the “Methalox” fuel mix SpaceX uses for an uninsulated Starship is about 2.5% per day, giving SpaceX a limited window (4-6 weeks) for tanking up the depot ship, and then tanking up the lunar Starship.
The SpaceX plan is to insulate the ship, and install giant “cryo-coolers”. While the tech exists, current ones are relatively tiny, weigh only a dozen pounds, and require around 200 watts of power. They are engineered to lift milliwatts of heat away from miniature electronic chips, not cool massive fuel tanks in space.
NASA is testing larger scale systems and SpaceX has updated Starship’s core internals to feature a high-voltage, electrically actuated cryogenic recirculation loop, with SpaceX ground crews subjecting redesigned Starship V3 structural plumbing to intense "cryoproofing" cycles by loading thousands of tons of sub-cooled liquids into the tanks under severe structural and thermal stresses to ensure the seals and recirculation valves hold up to rapid pressure spikes, but this is all on the ground testing with no data from an actual orbiting spacecraft.
With all that yet to do, and time running out on getting it done by the end of the year, it’s somewhat concerning that none of the technologies required for the refueling test will be tested on today’s flight. Except for Flight 3, none of the other Starship flights have involved any testing related to the refueling mission.
Whatever happens later today, SpaceX still has mountains to climb before they hit these rapidly approaching deadlines.
Flight 14 is planned for late August or September. They are aiming for the first orbital insertion of a Starship vehicle, the first actual deployment of next-generation Starlink satellites, the first landing and tower "catch" of the upper stage rocket, and the first booster recovery.
Lofty goals, given the modest scope of today’s test. As always, we wish everyone at SpaceX the best of luck.
They need all they can get.
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