The Boeing Starliner is a capsule designed to transport crew and equipment into space.
Nasa asked Boeing – which is a private company that makes planes – to develop the Starliner so they could have a US-made spacecraft to transport crew to and from the ISS.
However, before the spacecraft had set off for the ISS, Nasa discovered a number of issues, including several helium leaks in its capsule.
The launch went ahead on 5 June, as engineers thought the small leaks would not affect the mission.
But further leaks happened during the mission and there were problems with some of its thrusters.
Nasa has been carrying out checks and on Saturday announced the plan to return the astronauts using a SpaceX ship next year.