It will be the first manned US launch to the orbiting research laboratory since the space shuttle programme was retired in 2011, forcing US astronauts to hitch costly rides aboard Russian Soyuz spacecraft. A flight on Boeing spacecraft is set to follow in August 2019.
“This new process for reporting our schedule is better; nevertheless, launch dates will still have some uncertainty, and we anticipate they may change as we get closer to launch,” said Phil McAlister, director of Commercial Spaceflight Development at Nasa headquarters.
“These are new spacecraft, and the engineering teams have a lot of work to do before the systems will be ready to fly.”
Both missions are considered tests: the two astronauts transported in each flight will spend two weeks aboard the orbiting ISS before returning to Earth.
In the long term, Nasa will use SpaceX and Boeing to take astronauts to the ISS for regular missions, which last about six months. SpaceX will carry out an uncrewed test in January 2019, and Boeing in March 2019.
SpaceX will use its Falcon 9 rocket for its launch with a Crew Dragon capsule attached on top.
Boeing’s Starliner ship will be propelled into space by an Atlas V rocket made by the United Launch Alliance, a joint venture with Lockheed Martin. Nasa is depending on the success of both missions as its contract with the Russian space agency expires in November 2019.
Back in January, Nasa said Boeing would fly two astronauts on its first crewed launch this November, followed by SpaceX the next month.
Now, the space agency predicts SpaceX will fly astronauts first, in April 2019, and Boeing after that, in mid-2019.
SpaceX is in line to beat Boeing to uncrewed flights too, which will be carried out and evaluated before Nasa astronauts come on board.
Nasa said that SpaceX will launch an uncrewed test flight in November of this year, followed by Boeing in late 2018 or early 2019.
Officials at both SpaceX and Boeing have avoided publicly describing their efforts as a race, but being the first to return human spaceflight to the United States would bring either company major prestige.
American astronauts have not launched from US soil since 2011.
To reach the International Space Station, where they live and work for six months at a time, they’ve hitched rides on Russia’s Soyuz spacecraft, which costs the US government between $70 million and $80 million a seat.
When the space shuttle stopped flying nearly a decade ago, US officials promised that this arrangement would be temporary.
The country, they said, would soon find another, American-made way to transport people to space.
In 2010, Nasa solicited proposals from commercial-spaceflight companies for astronaut-transportation systems.
By 2014, the space agency had two frontrunners, SpaceX and Boeing, and officials awarded the companies a combined $6.8 billion to develop and test their concepts: the Crew Dragon for SpaceX, which will launch atop the company’s Falcon 9 rocket, and the CST-100 Starliner for Boeing, on an Atlas V rocket made by the United Launch Alliance.
At first, Nasa predicted both companies would complete their spacecraft, fly uncrewed and crewed tests, and be ready for regular missions to the ISS by the end of 2017.
Neither company has been able to stick to the original timeline.