NASA successfully conducted tanking demonstration tests for its Artemis 1 mission on September 21 but during the test, it once again faced an issue that has been plaguing the mission: a liquid hydrogen leak. The second launch attempt had to be scrubbed because a liquid hydrogen leak appeared multiple times. If this fuel is so difficult to work with, why has it become the rocket fuel of choice for space expeditions? Let’s find out.
Liquid hydrogen and liquid oxygen are both cryogenic gases, meaning that they can only be liquified at extremely low temperatures. Due to this, the fuel poses enormous technical challenges. Liquid hydrogen must be stored at about minus 217 degrees celsius and should be handled with extreme care.
The tanks of rockets fuelled with liquid hydrogen must be insulated from all sources of heat, including the exhaust from the rocket’s engine and air friction during flight. But despite these challenges, Hydrogen offers some inimitable advantages.
It is the element with the lowest molecular weight amongst all known substances and burns very intensely, at higher than 2,600 degrees Celsius. When combined with liquid oxygen, liquid hydrogen yields the highest specific impulse (or efficiency) with respect to the amount of propellant consumed.
According to NASA, one of the first and most important projects that tested using liquid hydrogen as fuel was conducted by the United States Air Force between 1956 and 1958. Even though very few people were aware of it at the time, and even now, the Air Force spent over a hundred million dollars on the project. That is more than a quarter billion in today’s dollars.
The test project was codenamed Suntan and it was an effort to develop a hydrogen-fueled aeroplane that was aimed at being a successor to the Lockheed U2, which was the spy plane of choice for the Air Force at the time. Even though the project was cancelled before completion, it led to the development of the first rocket engine that flew using hydrogen.