This test took place during Starship’s 3rd flight on March 14, 2024, but the company did not report its results until a month later. Elon Musk said in a speech at the end of April that a demonstration of Starship refuelling in space could take place “next year”. Thus, the year 2025 is mentioned, which cannot but cause some concern about the timing of the Artemis-3 mission, which involves the landing of astronauts on the Moon. Let me remind you that not so long ago these terms were already shifted “to the right” by almost 1 year. Today, it is assumed that the mission will take place no earlier than September 2026.
It is worth noting that fuel pumping in space is one of the key technologies on which the possibility of carrying out a mission to land on the moon depends. The fact is that the landing module of the mission – Starship HLS – is not even capable of simply going to the Moon, let alone landing on it, without refuelling in Earth orbit. Moreover, the required amount of fuel is calculated in hundreds of tons.
That is why, already in the third test flight of the Starship/Super Heavy system, SpaceX attempted to pump fuel in space flight conditions. It was planned to transfer at least 10 metric tons of liquid oxygen from the collection tank to the Starship’s main tank during the flight.
According to NASA, a test to transfer fuel between tanks on Starship during its March test flight was successful.
After the flight, SpaceX said the test had been completed, but neither the company nor NASA released any details. And now, almost 40 days later, information has appeared that after analyzing the telemetry there is every reason to believe that the test was successful.
In addition to Elon Musk, this was also reported by Amit Kshatriya, NASA’s deputy assistant administrator for the Moon-Mars program, in his speech on April 26 before the Human Exploration and Exploitation Committee of the NASA Advisory Board.
“On flight 3, they did a cryogenic transfer between the tanks, which, according to general opinion, was successful,” he said, adding that the analysis of the received data is ongoing.
However, during the last flight, the fuel was transferred inside one ship and in a rather small amount, so the next important step on the way to the moon should be tested during which two Starships will dock in orbit and one of them will transfer fuel to the other. This test, according to Elon Musk, may take place in 2025.
It is assumed that the “target” ship will be launched first, and after three to four weeks the “tanker” ship will launch. After docking in Earth orbit, fuel will be pumped. The Starships will then undock and de-orbit.
The stages of working out the fuel pumping technology are presented in the picture below.
It is worth noting that the company has to solve several difficult problems related to the suppression of fuel fluctuations in the tanks during Starship manoeuvres, as well as determining the amount of “stabilizing thrust” necessary to ensure the transfer of fuel between ships.
Why do the company’s plans to conduct tests in 2025 cause fears about the disruption of the Artemis 3 mission?
Well, let’s try to pretend. If Musk is talking about “next year”, then, most likely, it could be the middle or even the end of 2025. The fact is that, taking into account “Elon time”, the terms of everything shift noticeably “to the right”.
Let’s assume that the tests will be quite successful. In this case, SpaceX will begin a demonstration mission of the Starship HLS ship (in unmanned mode), which involves refuelling the ship and sending it to the Moon for landing and subsequent launch from it. Agree that this is quite a difficult task, and its success is by no means guaranteed. But even if everything goes without any problems, the realization of this flight requires a considerable number of Starship/Super Heavy system launches. According to SpaceX – from 4 to 8, according to NASA – about 20. How long will it take to simply refuel Starship HLS for a flight to the moon? The answer is obvious: several months.
And then the system will have to make the same number of flights to bring the fuel into orbit for the actual Artemis 3 mission.
But there are still such problems as leakage and boiling. In addition, it is still not clear exactly what amount of fuel can be brought into orbit in 1 tanker flight and, what is extremely important, pumped into the “orbital refuelling station”.
Elon Musk also understands this. “Complete and rapid reusability of the launch vehicle and ship, as well as orbital refuelling of the ship, are two fundamental technologies that we aim to implement by the end of next year,” he wrote on April 26 on social networks.
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