What Gases Power NASA’s Artemis Rockets?

NASA’s Artemis rockets run primarily on liquid hydrogen (LH₂) and liquid oxygen (LOX), the same propellant combination that powered the Space Shuttle. But propellant is only part of the picture. Helium pressurizes the fuel tanks and purges the lines. Nitrogen keeps ground systems safe and inert. Together, these four gases make every Artemis launch possible.

What Is the Artemis Program?

Artemis is NASA’s program to return astronauts to the Moon for the first time since Apollo 17 in 1972 and establish a long-term human presence there, then use the Moon as a proving ground for eventual crewed missions to Mars.

The hardware at the center of it all is the Space Launch System (SLS), the most powerful rocket NASA has ever built, paired with the Orion spacecraft designed to carry crew beyond low Earth orbit. The long-term vision includes the Lunar Gateway, a small space station orbiting the Moon that will serve as a staging point for surface missions and deep-space operations.

Artemis I launched successfully in November 2022 as an uncrewed test flight. Artemis II launched on April 1, 2026, carrying four astronauts on a ~10-day crewed lunar flyby mission without landing. Artemis III is the one everyone’s watching: the first crewed lunar landing in over 50 years.

Why Does the SLS Run on Liquid Hydrogen and Liquid Oxygen?

The SLS runs on liquid hydrogen and liquid oxygen because no other propellant combination delivers as much energy per pound of fuel burned.

The SLS core stage uses four RS-25 engines—the same engines that powered the Space Shuttle for 135 missions. Each one produces over 500,000 pounds of vacuum thrust by burning liquid hydrogen (the fuel) with liquid oxygen (the oxidizer) in a staged-combustion cycle. The result is a specific impulse of 452 seconds in vacuum, one of the highest ratings of any rocket engine ever flown.

Specific impulse is essentially fuel efficiency for rockets. Higher numbers mean more velocity per unit of propellant. At 452 seconds, the RS-25 outperforms kerosene-based engines like the Falcon 9’s Merlin (311 seconds) by a wide margin.

The tradeoff is temperature. Liquid hydrogen has to be stored at -253°C (-423°F). Liquid oxygen sits at -183°C (-297°F). At those temperatures, the core stage’s propellant tanks physically shrink after fueling, requiring flexible mounting hardware that adjusts as the metal contracts.

The core stage holds over 733,000 gallons of these two propellants combined. During launch, the RS-25 engines consume roughly 1,500 gallons per second across an eight-and-a-half-minute burn to reach orbit. The solid rocket boosters handle about 75% of the thrust in the first two minutes, then the LH₂/LOX engines carry the rest.

NASA has called the RS-25 “the Ferrari of rocket engines.” With over a million seconds of cumulative test-fire time and more than 99% reliability, the nickname fits.

What Role Does Helium Play in a Rocket Launch?

Helium keeps the propellants moving and the fuel lines clean, two jobs that sound simple until one goes wrong and a multibillion-dollar mission gets delayed.

The SLS core stage carries multiple large helium tanks inside the engine section. That pressurized helium does three critical things: it pressurizes the liquid hydrogen and liquid oxygen propellant tanks so fuel feeds smoothly to the engines, it purges the engine plumbing before and after propellant flows to prevent dangerous gas mixtures from forming, and it powers the pneumatic systems that open and close the large valves controlling propellant flow throughout the rocket.

Helium gets the job because it’s completely inert, meaning it won’t react with hydrogen, oxygen, or anything else on the vehicle. It also has the lowest molecular weight of any inert gas, which matters when every pound on the rocket counts.

The upper stage (called the Interim Cryogenic Propulsion Stage, or ICPS) has its own separate helium system. Those bottles pressurize the upper stage’s propellant tanks and purge its engine before the burn that sends Orion toward the Moon.

The risk isn’t theoretical. In February 2026, a helium flow interruption in the Artemis II upper stage forced NASA to roll the rocket back to the Vehicle Assembly Building for troubleshooting. The issue was traced to a dislodged seal in a quick-disconnect fitting that obstructed helium flow.

Where Does Nitrogen Fit Into Launch Operations?

Nitrogen is the ground crew’s gas, used almost entirely on the pad and in pre-launch processing rather than onboard during flight.

Before any cryogenic propellant gets near the rocket, technicians perform an air-to-gaseous-nitrogen changeover inside the SLS’s cavities. This displaces atmospheric oxygen and moisture, creating an inert environment that prevents accidental ignition when liquid hydrogen and liquid oxygen start flowing. During Artemis II preparations, this changeover was one of the final steps before fueling operations began.

Nitrogen also purges the oxygen side of the RS-25 engines to remove moisture before chill-down. (The fuel side gets purged with helium, since liquid hydrogen is cold enough to freeze nitrogen solid, and frozen nitrogen particles running through a turbopump would be catastrophic.)

On the pad itself, nitrogen pressurizes pneumatic systems, actuates valves, and purges hazardous areas around the vehicle. NASA teams responsible for propellants and ground systems monitor nitrogen and helium pressures from control consoles during the countdown.

The key distinction from helium is that nitrogen is cheaper, more abundant, and works perfectly for ground-side inerting where temperatures stay above its freezing point. But it can’t go everywhere helium goes. Anywhere liquid hydrogen is involved, nitrogen becomes a liability instead of a safeguard. That’s why the two gases divide the work so cleanly between ground operations and flight systems.

How Do These Same Gases Show Up in Everyday Use Cases?

The gases behind a Moon launch are the same ones running through commercial and industrial operations every day, just at a different scale.

Liquid Oxygen

Liquid oxygen is one of the most widely used industrial gases on the planet. Hospitals pipe it through their facilities to supply patient rooms and surgical suites. Steel mills and metal fabricators use it for cutting and welding. Wastewater treatment plants inject it to speed up biological processing. The LOX in a hospital’s bulk tank is chemically identical to the LOX in the SLS core stage.

Liquid Hydrogen

Petroleum refineries use massive quantities of liquid hydrogen for hydrocracking and desulfurization. The semiconductor industry relies on ultra-high-purity hydrogen in chip fabrication. And hydrogen fuel cells are gaining traction in transportation, from forklifts in warehouses to long-haul trucking pilots.

Helium

Helium shows up anywhere you need an inert gas with unique physical properties. Leak detection in manufacturing, MRI machines in hospitals, shielding gas in tungsten inert gas (TIG) and metal inert gas (MIG) welding, and controlled atmospheres in fiber optic production. When a welder runs helium-argon mix to get a cleaner bead on aluminum, they’re relying on the same inertness that keeps an SLS fuel line safe.

Nitrogen

Nitrogen is the workhorse. Food packaging operations flush it through bags of chips and sealed meat trays to displace oxygen and extend shelf life. Chemical plants blanket reactive materials with it. Electronics manufacturers use it in soldering and reflow ovens. Breweries push beer from kegs with it. The applications are nearly endless because nitrogen is abundant, inert at normal temperatures, and cost-effective in bulk.

Same Gases, Different Mission

NASA spends years qualifying every gas system on the SLS because a failed valve or a contaminated line can ground a multibillion-dollar launch. Even if you aren’t sending anything to the Moon, the principle holds: the right gas, at the right purity, delivered when you need it, is what keeps everything running.

Lawrence Haynes

Currently serving as Marketing Director at WestAir Gases & Equipment in San Diego, CA Lawrence leverages his expertise in industrial gas solutions and equipment marketing. With a proven track record in cross-industry marketing strategy, he brings a specialized experience in content development, marketing automation, and partner relations to the industrial gas sector.