Helium, the second lightest element on the periodic table with an atomic number of 2, is essential in space missions, playing a critical role in the operation of rockets and spacecraft. Its unique properties, such as being inert, having a very low boiling point, and non-toxicity, make it indispensable for various functions in space travel. However, its small atomic size and low molecular weight also make it prone to leaks, which have been a persistent challenge in the aerospace industry. Recent issues with NASA’s Starliner and SpaceX’s Polaris Dawn missions underscore the complexity and importance of managing helium in space exploration.
Why Helium?
Helium is favored in the aerospace industry primarily because it is chemically inert. It does not react with other substances, combust, or cause corrosion, making it ideal for pressurizing fuel tanks and cooling systems without posing a risk of explosion or chemical reactions. Rockets need to achieve specific speeds and altitudes to reach and maintain orbit, and pressurizing the fuel tanks is crucial for this. Helium ensures that the fuel flows smoothly to the engines without interruption, even as fuel levels decrease during a flight. As fuel and oxidizers are consumed in the rocket’s engines, helium fills the empty space in the tanks, maintaining the overall pressure inside. Its non-reactivity allows it to mingle safely with residual contents in the tanks, avoiding any dangerous reactions.
Another advantage of helium is its extremely low boiling point of -268.9°C (-452°F), which allows it to remain in a gaseous state even in the super-cold environments of space, where many rocket fuels are stored at similar temperatures. This property is particularly important because it ensures that helium can perform its role effectively in pressurizing systems without freezing or liquefying, which could compromise the function of the rocket’s fuel delivery system.
The Challenges of Helium Leaks
Despite its advantages, helium’s small atomic size and low molecular weight make it notoriously difficult to contain. Helium atoms are so small that they can escape through minuscule gaps or imperfections in seals and storage tanks, leading to leaks. These leaks can compromise the integrity of a rocket’s pressurization system, potentially leading to mission delays or failures. For instance, NASA’s Starliner spacecraft experienced helium leaks on multiple occasions, including just hours before its first crewed launch attempt. Although NASA eventually deemed the leak low-risk, the issue highlighted the broader challenge of managing helium in space missions.
In another example, Boeing’s Starliner was brought back to Earth uncrewed after detecting additional helium leaks in space. These incidents have prompted calls within the aerospace industry for innovation in valve design and more precise valve-tightening mechanisms to mitigate helium leakage.
Alternatives and Innovations
Some rocket systems have experimented with other inert gases, such as argon and nitrogen, which can sometimes be cheaper and easier to manage than helium. However, helium’s unique properties often make it the preferred choice despite these alternatives. Europe’s new Ariane 6 rocket, for example, moved away from helium, opting instead for a novel pressurization system that converts a small portion of its primary liquid oxygen and hydrogen propellants into gas. This gas is then used to pressurize the rocket’s fuel systems. Although this system marked an innovative departure from traditional helium-based pressurization, it faced its own challenges during Ariane 6’s debut launch, underscoring the complexities of rocket pressurization technologies.
The Future of Helium in Space Exploration
The frequency of helium leaks across various space missions highlights the need for continued advancements in containment and pressurization technologies. While alternative gases and innovative systems are being explored, helium remains a mainstay in the industry due to its unmatched properties. As the global rocket industry continues to evolve, addressing the challenges associated with helium leaks will be crucial for ensuring the safety, reliability, and success of future space missions.
