How Industrial Gases Applied in the Aerospace Industry?

Nitrogen
Nitrogen can be used as a power source for pneumatic valves; high-pressure nitrogen is used as a power source to drive the turbo pump when the rocket engine starts.
Nitrogen is an economical purge gas. It is used to blow out the instrument cabin on the rocket and blow out the explosion-proof electrical equipment required for firefighting on the ground.
Nitrogen is used to blow out the ground pipeline system and seal it.
Nitrogen is also used to check the airtightness of rocket propellant tanks, engine systems, etc.

Oxygen
Oxygen is a necessary gas for humans in space. Oxygen and hydrogen produced by water electrolyzers can ensure the necessary gas supply in space.
Liquid oxygen is used before rocket launches and in engine testing.

Helium
Helium can be used as a pressure agent and booster for rocket liquid fuel, and is widely used in missiles, spacecraft and supersonic aircraft.
Helium is used as a protective gas during smelting and welding, which is very important in shipbuilding and the manufacture of aircraft, spacecraft, rockets and weapons.
Helium has excellent permeability and is used for cooling nuclear reactors, leak detection of some pipelines of rockets and nuclear reactors, and electronic and electrical devices.
Helium is a gas with ideal gas properties and is an ideal gas for vapor pressure thermometers at extremely low temperatures.
Helium has low mass density and weight density and is not flammable. It can be used to fill light bulbs and neon tubes. It is also an ideal gas for balloons and airships.
Liquid helium can achieve low temperatures close to absolute temperature (-273°C) and is used to manufacture superconducting equipment.

As a kind of inert gas, its solubility in blood is lower than that of nitrogen! Therefore, its anesthetic property is lower than that of nitrogen, so helium is often mixed with oxygen as a breathing gas for divers.

Krypton
As a propellant for electric propulsion technology, it is used for tasks such as satellite orbit maintenance and adjustment, emergency collision avoidance, etc. Krypton gas, as a propellant for Hall thrusters, is not only used in my country's aerospace projects, but also adopted by the "Starlink" program of SpaceX, an American space technology exploration company.