"The launch of this commercial space system designed for humans is a phenomenal demonstration of American excellence and is an important step on our path to expand human exploration to the Moon and Mars", he said.
The mission's first launch try on Wednesday was called off with less than 17 minutes remaining on the countdown clock. Though the weather has improved, a NASA spokesman said that there was still a 50/50 chance of a second delay.
Its success will open the door for 16 operational flights to the Space Station using a SpaceX rocket and crew dragon capsule. This was the first manned space launch from United States territory in nine years.
After successfully docking, the crew will be welcomed aboard the International Space Station, where they will become members of the Expedition 63 crew, which now includes NASA astronaut Chris Cassidy.
Behnken, 49, and Hurley, 53, former military test pilots who joined the USA space agency in 2000, are to blast off from Launch Pad 39A.
Nasa chief, Jim Bridenstine, told a news conference on Friday that "back-to-back wet dress rehearsals" disrupt the astronauts' sleep cycles.
If successful, Saturday's takeoff will mark the first crewed space mission since the shuttle program was retired in 2011. Boeing's spaceship, the Starliner capsule, is not expected to fly astronauts until early 2021.
SpaceX and NASA officials were holding off on any celebrations until after Sunday's docking - and possibly not until the two astronauts are back on Earth sometime this summer.
The spacecraft was detached from the rocket 12 minutes after lift-off.
"We've got the coronavirus pandemic, we've got other challenges as a country but I hope this moment in time is an opportunity for everybody to reflect on humanity and what we can do when we work together", he said. The three space station residents trained cameras on the incoming capsule for flight controllers at SpaceX headquarters in Hawthorne, California, as well as NASA's Johnson Space Center in Houston.
Musk, the South African-born high-tech entrepreneur who made his fortune in Silicon Valley, is also CEO of electric carmaker and battery manufacturer Tesla Inc. U.S. President Donald Trump watched the launch from the space center. The "Launch America: Mission to Space Live" coverage will also be available to stream on a variety of other platforms, including Hulu; the Roku Channel; YouTube TV; Amazon's news app on Fire tablets and Fire TV devices; Sling TV; Facebook; Twitter; ABCNews.com; and the ABC News and ABC mobile apps.
The Crew Dragon is scheduled to dock with the ISS at about 10:29 a.m. "One of the things we've done is create the Space Force".
Wednesday's first human flight was originally targeted for around 2015. A SpaceX capsule exploded on the test stand a year ago.
SpaceX's Dragon aced all of its objectives, while Boeing's Starliner capsule ended up in the wrong orbit and was nearly destroyed because of software errors.