Nasa and its commercial partners, Boeing and SpaceX, are nearing the end of their programme to develop new crew capsules that will act as taxis between Earth and the International Space Station (ISS).
Two final uncrewed test flights have been confirmed for next year, which will be followed by the first astronauts in the summer.
The US has been without the domestic means to launch its astronauts since 2011, when the Space Shuttle was retired. Since that time, it has been relying on Russian Soyuz craft to carry Americans into space.
In tandem, Nasa has been developing capsules as part of the commercial crew programme. That effort is reaching the final stages. On 7 January, SpaceX will launch its first Crew Dragon spacecraft, which will be an uncrewed test flight to the ISS that will pave the way for the first crewed flight in June.
In March, Boeing will perform a similar test of its CST-100 Starliner in the run-up to a crewed launch in August. Before the manned flights, the two companies will perform launchpad and inflight-abort tests. Nasa is also conducting a review of its workplace safety culture at the companies.
