Boeing and NASA have found the cause of the problem, but no date has yet been set for the astronauts' return.

It’s progressing…slowly. After weeks of testing aimed at replicating the problems that plagued Boeing’s Starliner, NASA and Boeing officials are still not ready to announce when the two astronauts who pilot the spacecraft will return for its first crewed flight. But engineers are beginning to understand what caused the malfunctions that plagued the Starliner on its maiden voyage: helium leaks and thrusters that suddenly stopped en route to the International Space Station (ISS).

Astronauts will return to Earth, but probably not in Starliner

Engineers recently conducted more than 1,000 engine test runs to recreate the conditions encountered in flight. Those tests recreated the propellant degradation seen in orbit, and discovered that heat buildup inside the thrusters could cause Teflon seals to swell, restricting the flow of propellant. Despite the progress, officials have yet to confirm that Starliner will be used to return astronauts Butch Wilmore and Suni Williams to Earth.

Meanwhile, engineers have made progress in understanding the helium leaks that have hampered Starliner’s first stage. Additional tests of the spacecraft’s thrusters, while docked with the ISS, are scheduled for the end of this week to better understand what’s happening. The tests are intended to see if the leaks have worsened since Starliner docked with the ISS.

Already 50 days in space

Meanwhile, Wilmore and Williams, who arrived at the International Space Station on June 6 for an eight-day mission, have spent about 50 days in space. While they remain optimistic and busy with their science and maintenance missions, their return will depend on the results of ongoing tests and inspections.

NASA and Boeing hope to conduct a review of the Starliner mission as early as next week, but astronauts will remain in space until all safety safeguards are in place.