For the past few weeks, Nasa astronauts Butch Wilmore and Suni Williams have been stuck on the International Space Station (ISS) after the first crewed voyage of Boeing's new Starliner spacecraft hit a snag. Concerns raised by Boeing and Nasa over thruster problems and several helium leaks (helium is used in Starliner's engine system) have prevented the craft from making the return journey as scheduled. Nasa has now said the astronauts may have to stay put until the next scheduled crew switchover in August – potentially on another ship.

Boeing and Nasa are trying to put a positive spin on the extension by saying they are testing systems required for longer Starliner missions. But the project has already suffered several delays, having originally been set to lift off for the first time with crew in 2017. This, combined with the latest problems raise questions over the whole Starliner programme.