What happened to Boeing’s spacecraft?

Two NASA astronauts will remain aboard the International Space Station until February after their Boeing spacecraft encountered problems during its journey into orbit.

Boeing’s Starliner capsulewhich was due to undock and return to Earth without a crew on Friday, has been sidelined by Faulty thrusters and helium leak.

Engineers on the ground spent months assessing the issues, but NASA ultimately opted to return the spacecraft to Earth without anyone on board. The two astronauts, Butch Wilmore and Suni Williams, will spend more time in space before returning home aboard a SpaceX Crew Dragon capsule.

The Starliner test flight marked the first time a human crew was on board. The mission, originally scheduled to last about eight days, was to be the final step before NASA could certify Boeing’s spacecraft to make routine trips to and from the orbiting outpost.

Here’s what happened with Boeing’s Starliner capsule.

The vehicle encountered two separate problems: one with a set of thrusters and the other involving helium leaks in its propulsion system. Either could have affected the Starliner’s ability to return Wilmore and Williams to Earth.

The astronauts took off on June 5thThe setbacks began the very next day.

As Starliner approached the space station, five of its 28 reaction control system thrusters malfunctioned, delaying the docking process by almost an hour.

These thrusters are located on the spacecraft’s service module and are used to move the capsule in orbit, including adjusting its position when docking and undocking from the space station.

Four thrusters were eventually restored, allowing the astronauts to complete their arrival at the space station, but the problem prompted NASA to launch an investigation into the cause of the thrusters’ shutdown.

Engineers from NASA and Boeing used a test engine at the space agency’s White Sands Test Facility in New Mexico to study thruster performance. The teams subjected the engine and its thrusters, which were developed for future Starliner flights, to conditions similar to those the capsule experienced on its way to the space station.

Mission managers also conducted a “hot-fire test” in space, firing the Starliner’s thrusters in short bursts while it remained docked with the space station.

Preliminary results showed that all but one of the thrusters in the reaction control system were functioning well, but NASA said various tests showed that a tiny Teflon seal appeared to swell under high temperatures, which could block the flow of propellant into the thrusters. The space agency said the expanding seals could be the cause of the thruster problems that occurred during docking.

However, Steve Stich, manager of NASA’s Commercial Crew Program, said in August that the team “cannot prove with certainty that what we see in orbit is exactly what was replicated on Earth.”