Both Boeing and SpaceX are building spaceships to transport astronauts and restore U.S. access to the space station, a capacity lost when the shuttle program was retired in 2011, as planned after 30 years of operation.
Mulholland said the Atlas V launch vehicle for the mission is launch-ready and should ship to Florida before the end of this year.
Boeing has also developed a state-of-the-art spacecraft, the Crew Space Transportation (CST)-100 Starliner.
NASA's Commercial Crew Program is working with the American aerospace industry as companies develop and operate a new generation of spacecraft and launch systems created to carry crews safely to and from low-Earth orbit. Coupled with the technical challenges inherent in any human spaceflight development program, the systems have been repeatedly delayed and NASA's dependence on Russian Federation extended.
The NASA statement did not disclose reasons for either company's delays, and SpaceX did not respond to questions about its revised schedule.
An engine flaw discovered during a launchpad test of Boeing's Starliner spaceship, created to carry humans to the International Space Station, has delayed its first crew test flight until next year. But the vast majority of Americans said government should play a major role in space exploration, while only 38 percent said the same for private-sector companies.More news: ‘Vaginal Rejuvenation’ Devices Have Serious Side Effects, Unproven Claims: FDA
Now, however, the SpaceX uncrewed flight is scheduled for November 2018 and its crewed successor for April 2019 - edging in front of Boeing's planned launches.
Among the options being considered by NASA is to use the crewed flight test as a crew rotation flight by adding a third astronaut to the mission and extending its stay from two weeks to as long as six months. He made the announcement via telecon.
Before today's announcement, NASA had officially planned for both SpaceX and Boeing to fly uncrewed test flights of their capsules - known as Crew Dragon and the CST-100 Starliner, respectively - this month. Four NASA astronauts were selected in 2015 for training.
NASA is about to name the first eight astronauts ever to fly Boeing and SpaceX's brand-new spaceships. For Crew Dragon, both will be NASA astronauts. Flights without any people are expected before the end of 2018, followed by two crewed missions sometime in 2019. Boeing will conduct a manned Starliner flight in mid-2019.
In light of Boeing's schedule adjustment, will that crew arrive on a Starliner or on SpaceX's Dragon spaceship?
NASA plans to announce its final decision on the crews - two astronauts for each of the four crewed test flights - on Friday morning.