The launch of Boeing’s Starliner, which was heading for the International Space Station (ISS), was called off two hours before lift-off because of a problem with the spacecraft’s rocket.

The CST-100 Starliner was scheduled to lift off from Cape Canaveral in Florida yesterday (6 May), in its first crewed test flight.

The two Nasa astronauts – Butch Wilmore and Suni Williams – were heading to the ISS, where the Starliner would dock for around 10 days before returning to Earth.

The two astronauts were in position ready for blast-off, but the decision was taken to halt the flight because of a potential issue with an oxygen relief valve in the Atlas rocket, which sits beneath the Starliner.

According to the BBC, flight engineers discovered that the valve in the Atlas rocket, which is run by the United Launch Alliance (ULA) , had been rapidly opening and closing in the period before launch and so the countdown was aborted.

ULA will now examine the data, and if it is discovered that the energy...