SpaceX, the private rocket company of billionaire entrepreneur Elon Musk, launched two Americans toward orbit from Florida on Saturday in a mission that marks the first spaceflight of NASA astronauts from US soil in nine years.
A SpaceX Falcon 9 rocket lifted off from the Kennedy Space Centre at 3.22pm EDT (7.22am NZT) launching Doug Hurley and Bob Behnken on a 19-hour ride aboard the company's newly designed Crew Dragon capsule bound for the International Space Station.
The mission's first launch try on Wednesday was called off with less than 17 minutes remaining on the countdown clock due to stormy weather around the Kennedy Space Centre at Cape Canaveral in Florida.
The forecast for the reattempt was likewise precarious with a 50-50 chance of launch. Mission managers plan to make an earlier decision on weather hazards in a bid to avoid unnecessarily wearing out the crew with another suit-up and full day of launch preparations.
"Back-to-back wet dress rehearsals" disrupt the astronauts' sleep cycles, NASA chief Jim Bridenstine told a Friday news conference.
The launch pad is the same one used by NASA's final space shuttle flight, piloted by Hurley, in 2011. Since then, NASA astronauts have had to hitch rides into orbit aboard Russia's Soyuz spacecraft.
As the crew bid goodbye to their families before getting into a specially-designed Tesla for the ride to the launch site, Behnken told his young son, "Be good for mom. Make her life easy."
Bridenstine has said resuming launches of American astronauts on American-made rockets from US soil is the space agency's top priority.
For Musk, the launch represents another milestone for the reusable rockets his company pioneered to make spaceflight less costly and more frequent.
And it marks the first time commercially developed space vehicles - owned and operated by a private entity rather than NASA - have carried Americans into orbit.
The last time NASA launched astronauts into space aboard a brand new vehicle was 40 years ago at the start of the space shuttle program.