Shulou(Shulou.com)11/24 Report--

On Saturday, local time, NASA decided to postpone the launch of the unmanned lunar mission Artemis-1 after the mission team encountered a leak while filling a space launch system (SLS) rocket with liquid hydrogen. In response, SpaceX founder Elon Musk (Elon Musk) commented and even gave suggestions for improvement.

According to NASA, the leak occurred on an eight-inch supply line called Quick disconnect, which is used to inject propellant into the core level of SLS. This means that there have been four liquid hydrogen leaks since the giant lunar launch vehicle was pushed onto the launch pad of the Kennedy Space Center.

Although liquid hydrogen is considered to be a more efficient fuel for rocket launch, it is very difficult to manage it because it is the lightest element in the world. Even the tiniest openings allow tiny hydrogen atoms to escape, which is one of the reasons Musk decided to switch to methane for SpaceX rocket engines.

Musk wrote on Twitter: "the Raptor engine was designed with liquid hydrogen, but then switched to methane. Methane is the best combination of efficiency and ease of operation." He added that when using liquid hydrogen and methane as propellants, the speed difference is small, and methane requires smaller containers and less insulation.

In addition, methane is more likely to be produced on Mars, which is very important for launch missions. SpaceX was one of the first companies to use liquid methane and liquid hydrogen as rocket fuel. Musk hopes to build a self-sufficient city on the red planet in 20 years' time, and his company is preparing to use starships to transport people and goods to the moon, Mars and beyond.

So far, SpaceX has developed five engines, Merlin, Kestrel, Draco, SuperDraco and Raptor, for its Falcon 9 rocket, dragon spacecraft and starship. In addition to methane, SpaceX uses liquid oxygen and rocket-grade kerosene (RP-1) propellant for the Merlin engine on the Falcon 9 rocket, while the Raptor engine on the starship uses a combination of methane and liquid oxygen as fuel.

Although the task of handling and preserving liquid hydrogen during the refueling operation is cumbersome, NASA can only continue to use liquid hydrogen because of a mandatory policy of the United States Congress. It is reported that in 2010, Congress instructed NASA to use the types of engines and propulsion systems used in other SLS hardware, which were used in the space shuttle program many years ago.

Currently, NASA allows up to 4 per cent of liquid hydrogen to leak during propellant filling into the rocket. Recently, however, the leakage of liquid hydrogen on Saturday was more than twice the maximum threshold. Despite these troubles, however, liquid hydrogen is considered a viable propellant option because it provides better thrust for the rocket during launch. The core stage tank of the SLS rocket has a liquid hydrogen capacity of 538606 gallons and a liquid oxygen capacity of 19000 gallons.

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