Helium

About Helium: 

• It is an inert gas and does not react with other substances or combust.
• Its atomic number is 2, making it the second lightest element after hydrogen.
• Helium also has a very low boiling point (-268.9° C), allowing it to remain a gas even in super-cold environments.
• The gas is non-toxic, but cannot be breathed on its own, because it displaces the oxygen humans need for respiration.

How is it used in Rockets?

• Helium is used to pressurize fuel tanks, ensuring fuel flows to the rocket’s engines without interruption; and for cooling systems.
• As fuel and oxidiser are burned in the rocket’s engines, helium fills the resulting empty space in the tanks, maintaining the overall pressure inside.
• Because it is non-reactive, it can safely mingle with the tanks’ residual contents.

Is it prone to leaks?

• Helium’s small atomic size and low molecular weight mean its atoms can escape through small gaps or seals in storage tanks and fuel systems.
• But because there is very little helium in the Earth’s atmosphere, leaks can be easily detected - making the gas important for spotting potential faults in a rocket or spacecraft’s fuel systems.

Q1: What are inert gases?

These are gases which are chemically inactive, so will not undergo chemical reactions with many materials. Inert gases are used for many purposes in a wide range of industries - for example in welding, chemical processing, and as filler gases in light sources.

Source: What is helium and why is it used in rockets?