Helium is used in rockets because it is inert, lightweight, and non-combustible, providing the necessary speed and power to reach specific altitudes. It pressurises fuel tanks and cools systems, while its low boiling point keeps it as a gas in extremely cold environments. However, helium leaks have impacted missions like ISRO's Chandrayaan 2, ESA's Ariane 5, and SpaceX's Polaris Dawn.