Despite the years of rigorous testing preceding the launch of Boeing’s CST-100 Starliner, the crewed mission that took flight in early June, has run into some fairly serious setbacks that could postpone the astronauts’ return to Earth. Much like the liquid methane/liquid oxygen explosion that delayed the commercial operation of the SpaceX Dragon in 2019, a helium leak has rendered the Strainer unable to complete its mission and bring two astronauts home.

Helium, an inert and non-reactive gas, is used to pressurize fuel tanks. In spacecraft, fuel and oxidizer tanks need to be pressurized to feed the propellants into the engines, especially in the vacuum of space where there is no atmospheric pressure.

Concern for the safety of the two astronauts, Butch Wilmore and Sunita Williams, is foreshadowed by the death of Kalpana Chawla — an Indo-American astronaut that died aboard the Columbia space shuttle in 2003, and friend of Sunita Williams.

“We are taking our time and following our standard mission management team process,” said Steve Stich, manager of NASA’s Commercial Crew Program on Friday. “We are letting the data drive our decision making relative to managing the small helium system leaks and thruster performance we observed during rendezvous and docking.”

At a June 18 press conference, officials reiterated that the ship needs seven hours of helium to make it home and has 70 hours’ worth aboard. However, if the leaks turn out to be so bad that the supply is not sufficient to return to Earth, the Starliner’s crew could stay at the ISS until it can catch another ride home. Regardless of how the return is executed, and despite the current contingency, NASA spoke about a potential return on the 26th — based on the opportunity at that time to reach the White Sands Space Harbor in New Mexico.

Now aboard the ISS, the two astronauts await further instruction from NASA with the Starliner docked and helium tanks turned off — preventing further loss of the gas. The data collected while docked will be highly useful for post-flight trouble shooting.