Why Helium Leaks Postponed Boeing Starliner Astronauts' Return

The cosmos is a realm of infinite mysteries and challenges, and for space agencies worldwide, one such challenge lies in the use of hydrogen to operate their rockets. Recent issues with Boeing's Starliner spacecraft due to faulty propulsion systems that included helium leaks have once again brought this matter into focus. This incident is not an isolated one; past missions like ISRO's Chandrayaan 2 and ESA's Ariane 5 have also been affected by similar problems. 
 
Helium holds an integral position in rocket science owing to its unique properties. As the second lightest element after hydrogen, it does not react with other substances or combust—a crucial requirement given the highly volatile nature of fuel used in rockets. A heavier rocket would require more energy, leading to increased fuel consumption and necessitating powerful engines, which are expensive to develop, test, and maintain. 
 
Another advantage offered by helium is its remarkably low boiling point (-268.9°C or -452°F), allowing it to stay gaseous even at extremely cold temperatures where many rocket fuels are stored. It also happens to be non-toxic but cannot be breathed on its own as it displaces oxygen required for respiration. 
 
In the context of space exploration, helium has two main uses: pressurizing fuel tanks and cooling systems. When fuel burns in a rocket engine, creating empty spaces within the tank, these voids are filled up by helium, thereby maintaining consistent pressure inside them while safeguarding against any possible chemical reactions due to its inertness. 
 
However, dealing with helium isn't without challenges, primarily being prone to leaks because of its small atomic size and low molecular weight, which makes escape through tiny gaps or seals quite easy—another reason why there was a delay in SpaceX’s Polaris Dawn mission too, apart from the recent issue faced by Boeing’s Starliner. 
 
Despite these setbacks, helium still remains indispensable since any leak can easily be detected due to the to the presence of very little quantity in Earth's atmosphere, thereby helping to spot any potential faults in the fuel systems of rockets or spacecraft. 
 
Several engineers working on space-related systems believe that these frequent helium leaks underline an industry-wide need for innovation, especially concerning valve design and more precise valve-tightening mechanisms. 
 
While there have been experiments with other inert gases like argon and nitrogen as alternatives due to their lower cost, helium still remains the preferred choice within the industry. Europe's new Ariane 6 rocket has tried a different approach by adopting a unique pressurization system that converts part of its primary liquid oxygen and hydrogen propellants into gas, which then pressurizes those fluids for the rocket engine; however, even this faced failure during its debut launch. 
 
These incidences underscore the fact that, despite being an integral component in driving our ambitions towards space exploration, dealing with helium is not without complexities. It is evident that continued research and innovation are imperative to overcome such challenges while ensuring safety and efficiency in future missions.