Explainer-What is helium and why is it used in rockets?

investing.com 07/09/2024 - 04:17 AM

NASA Astronauts’ Extended Stay on ISS

By Nivedita Bhattacharjee

BENGALURU (Reuters) – Two NASA astronauts aboard Boeing (NYSE:BA)’s Starliner will stay on the International Space Station (ISS) for several months due to a faulty propulsion system that included helium leaks. Meanwhile, SpaceX’s Polaris (NYSE:PII) Dawn mission has also been delayed because of helium issues affecting ground equipment.

Boeing’s Starliner spacecraft returned uncrewed to a New Mexico desert late Friday.

Previous missions plagued by helium leaks include ISRO’s Chandrayaan 2 and ESA’s Ariane 5. This raises a question: why do spacecraft utilize helium, and what challenges does it pose?

Why Helium?

Helium is inert, with an atomic number of 2, making it the second lightest element after hydrogen.

To achieve specific speeds and altitudes for orbit, rockets require optimal fuel use. Heavier rockets demand more energy and, in turn, more powerful—and expensive—engines.

Helium’s very low boiling point (-268.9°C or -452°F) allows it to remain gaseous even in extremely cold conditions, which is vital as many rocket fuels must be kept at those temperatures.

While helium is non-toxic, it cannot be breathed because it displaces the oxygen necessary for human respiration.

How Is It Used?

Helium serves multiple roles in rockets:
Pressurizing fuel tanks: It ensures that fuel flows uninterrupted to the engines.
Cooling systems: As fuel and oxidizers are consumed, helium fills the void in the tanks, maintaining overall pressure.

Because of its non-reactive nature, helium can safely mix with residual substances in tanks.

Is It Prone to Leaks?

The small atomic size and low molecular weight of helium make it escape through tiny gaps within storage tanks and fuel systems. Fortunately, there is very little helium in Earth’s atmosphere, so leaks can be easily detected—making it crucial for identifying potential issues in a rocket’s fuel systems.

For example, on May 5, prior to Boeing’s Starliner spacecraft’s first crewed launch attempt, tiny sensors identified a helium leak in one of the spacecraft’s thrusters. NASA analyzed the leak, which was determined to pose low risk.

Additional leaks occurred in space after the Starliner launched in June, prompting NASA’s decision to return Starliner to Earth uncrewed.

The prevalence of helium leaks has urged some engineers to call for innovations in valve designs and tightening mechanisms across the industry.

Are There Alternatives?

Some rocket launches have experimented with gases like argon and nitrogen, which are also inert and can be cheaper. However, helium remains extensively used in the industry.

Europe’s new Ariane 6 rocket replaced helium with a new pressurization system that converts a small portion of its primary liquid oxygen and hydrogen propellants into gas for pressurization. Unfortunately, this system failed during the final stage of Ariane 6’s debut launch in July.

This underscores the extensive challenges the global rocket industry faces concerning pressurization.




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