Context: Two NASA astronauts aboard Boeing's Starliner will remain on the International Space Station for an extended period due to a malfunctioning propulsion system, which has been plagued by helium leaks. Meanwhile, SpaceX's Polaris Dawn mission has faced delays due to helium-related problems with ground equipment. This issue with helium leaks is not unique; similar problems have impacted past missions, including ISRO's Chandrayaan 2 and ESA's Ariane 5.
Helium’s unique properties:
- As the second lightest element after hydrogen, helium has an atomic number of 2 and is chemically inert-meaning it does not react with other substances or combust.
- This makes it ideal for pressurization and cooling systems in rockets and spacecraft.
Inert gases:
- An inert gas is a type of gas that resists reacting chemically with other substances.
- These gases are less likely to form chemical compounds due to their low reactivity.
- The primary function of inert gases is to prevent unwanted chemical reactions, such as oxidation and hydrolysis, which can degrade sensitive samples.
Typically, the term ‘inert gas’ includes:
- Noble Gases: Helium, neon, argon, krypton, xenon, and radon.
- Pnictogen: Nitrogen.
- Chemical Compound: Carbon dioxide.
- However, the classification of gases as inert can be context-dependent.
- While noble gases are generally considered inert due to their stable electron configurations, some of them, including nitrogen and carbon dioxide, can react under specific conditions.
- Argon is the most frequently used inert gas. Its popularity is attributed to its high natural abundance (making up about 1% of the Earth's atmosphere) and its relatively low cost.
The non-reactivity of these gases is largely due to their complete valence electron shells, which contribute to their general stability.
- Additionally, helium has an extremely low boiling point of -268.9°C, which allows it to remain in a gaseous state even in the extremely cold environments where rocket fuels are stored.
Importance in rocketry:
- Achieving the requisite speeds and altitudes for rockets to reach and maintain orbit, demands highly precise and efficient fuel management.
- Heavier rockets necessitate significantly more energy to achieve and sustain their trajectories. This increased energy demand leads to higher fuel consumption and requires more powerful engines.
- The development, testing, and maintenance of these advanced engines are not only more complex but also more costly.
- Helium is crucial in addressing these challenges due to its unique properties and essential functions:
- Helium is used to pressurize fuel tanks, ensuring that fuel flows continuously and smoothly to the rocket’s engines throughout the mission. As the rocket’s fuel is consumed during flight, helium replaces the volume left behind, maintaining consistent pressure and preventing any interruptions in fuel delivery.
- In addition to pressurizing fuel tanks, helium is integral to cooling systems, especially in environments where rocket fuels and oxidizers are stored at extremely low temperatures. Helium’s low boiling point ensures it remains a gas even in these frigid conditions, facilitating effective cooling and temperature management.
- As fuel and oxidizers are depleted, helium fills the resulting voids in the tanks. This ongoing replenishment of helium helps maintain stable internal pressure, which is crucial for the efficient operation of the rocket’s fuel systems and overall performance.
Usage and safety:
- Helium’s non-reactive nature makes it suitable for interacting safely with the residual contents in fuel tanks.
- It is also employed in cooling systems to manage temperatures and prevent overheating.
- Despite being non-toxic, helium can displace oxygen, making it unsuitable for breathing in high concentrations.
Prone to leaks:
- Helium’s small atomic size and low molecular weight make it prone to escaping 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.
- For instance, in May, shortly before Boeing’s Starliner was set to launch its first crewed mission, sensors detected a minor helium leak in one of the spacecraft’s thrusters. NASA assessed this leak as low-risk but it contributed to subsequent issues.
- Additional leaks were detected in space after Starliner launched in June, contributing to NASA’s decision to bring Starliner back to Earth without its crew.
- The frequency of helium leaks across space-related systems, have highlighted an industry-wide need for innovation in valve design and more precise valve-tightening mechanisms.
Alternatives and industry trends;
- In response to helium-related challenges, some space missions have explored alternative gases such as argon and nitrogen, which are also inert and potentially less expensive.
- However, helium remains the dominant choice due to its specific advantages.
- A notable attempt to move away from helium was Europe’s new Ariane 6 rocket, which replaced the helium system of its predecessor, Ariane 5, with a novel pressurization system.
- This system converts a small portion of its primary liquid oxygen and hydrogen propellants into gas for pressurizing these fluids.
- Despite this innovation, the system experienced failure during the final phase of Ariane 6’s inaugural launch, illustrating the ongoing difficulties in achieving reliable pressurization systems without helium.
Missions mentioned in the news:
Boeing Starliner:
- The Boeing Starliner, also known as CST-100, is a spacecraft developed to transport crew members to and from the International Space Station (ISS) and other low-Earth orbit destinations.
- Designed under NASA's Commercial Crew Program (CCP), the spacecraft comprises a reusable crew capsule and an expendable service module.
- Slightly larger than the Apollo command module or the SpaceX Crew Dragon, but smaller than the Orion capsule, the Starliner is capable of carrying up to seven astronauts.
- The Starliner can remain docked to the ISS for up to seven months and is launched aboard an Atlas V N22 rocket.
- The Crew Flight Test (CFT), launched in June 2024, encountered multiple malfunctions, including helium leaks and failures in five of the eight aft-facing reaction control system thrusters during its approach to the ISS.
- Consequently, NASA deemed it too risky for returning astronauts to Earth on Starliner.
- The uncrewed Starliner CFT-1 ultimately landed in September 2024.
Polaris Dawn:
- Polaris Dawn is an upcoming private human spaceflight mission operated by SpaceX, commissioned by Shift4 CEO Jared Isaacman.
- It is the first of three planned missions in the Polaris program, marking the 14th crewed orbital flight of a SpaceX Crew Dragon spacecraft.
- The mission will carry a four-member crew.
- The crew will be launched into a highly elliptical orbit, reaching up to 1,400 kilometers (870 miles) from Earth-the farthest human distance from Earth since NASA's Apollo program.
- This trajectory will allow the crew to pass through portions of the Van Allen radiation belts, providing a unique opportunity to study the effects of space radiation and spaceflight on human health.
- The Van Allen radiation belts are zones of energetic charged particles, primarily from the solar wind, trapped by Earth's magnetic field.
- They form a barrier that prevents the most energetic electrons from reaching Earth.
- The belts consist of two main regions:
- Outer Belt: Contains high-energy particles from the Sun, trapped within Earth's magnetosphere.
- Inner Belt: Formed by interactions between cosmic rays and Earth's atmosphere.
- The belts were discovered in 1958 by American physicist James A. Van Allen using instruments on Explorer 1, the first U.S. spacecraft.
- This discovery marked the beginning of space physics, as it revealed previously unknown radiation zones around Earth.
- One of the key objectives of Polaris Dawn is to conduct the first-ever commercial spacewalk.
- This mission not only aims to push the boundaries of private space exploration but also to advance scientific understanding of how the human body is affected by the unique conditions of deep space.
Chandrayaan-2:
- Chandrayaan-2, is India's second lunar exploration mission, developed by the Indian Space Research Organisation (ISRO) after Chandrayaan-1.
- The mission includes three components: a lunar orbiter, the Vikram lander, and the Pragyan rover, all designed and developed in India.
- Its primary objective was to map the lunar surface, study its composition, and locate lunar water deposits.
- The mission was launched in July 2019 from the Satish Dhawan Space Centre in Andhra Pradesh using a LVM3-M1 rocket.
- Chandrayaan-2 entered in August 2019. An attempted landing by the Vikram lander in September 2019 failed due to a software error.
- Despite the crash, the lunar orbiter continues to function in orbit around the Moon.
- A subsequent mission, Chandrayaan-3, was launched in 2023 and achieved a successful lunar landing.
Also read: Pragyan rover reveals signs of magma ocean on ancient moon
Ariane 6:
- Ariane 6 is a European expendable launch vehicle developed by ArianeGroup for the European Space Agency (ESA) and operated by Arianespace.
- It serves as the successor to the Ariane 5 within the Ariane launch vehicle family.
- Ariane-5 Rocket has been used to launch ISRO’s communication satellites like GSAT-11, GSAT-30, GSAT-31, ESA’s Juice mission and NASA’s James Webb Space Telescope (JWST).
- The rocket is a two-stage design that employs liquid hydrogen and liquid oxygen (hydrolox) as fuel.
- The first stage is powered by an upgraded Vulcain engine from the Ariane 5, while the second stage is driven by the Vinci engine, created specifically for Ariane 6.
- The rocket is available in two variants: Ariane 62, which includes two P120 solid rocket boosters, and Ariane 64, which uses four.
- Chosen in 2014 over an all-solid-fuel alternative, Ariane 6 was finally launched in 2024.
- The flight of Ariane 6 successfully placed nine cube-sats into orbit, including NASA's CubeSat Radio Interferometry Experiment (CURIE) and other satellites focused on studying Earth's climate and weather patterns.
- The Vinci engine is capable of multiple restarts, enabling the deployment of payloads into several distinct orbits.