SpaceX is aiming for a Sunday-night launch of four astronauts to the International Space Station, although the prospects of good weather were just 50-50 and its leader was sidelined by Covid-19.
Vice President Mike Pence was expected at Nasa’s Kennedy Space Centre for the long-awaited start of regular crew rotations aboard privately owned and operated capsules.
It also marked only the second time in nearly a decade that astronauts were set to rocket into orbit from the US.
“Game day!” tweeted Nasa astronaut Mike Hopkins, the crew commander.
As nearby towns braced for an onslaught of spectators, SpaceX founder and chief executive Elon Musk disclosed via Twitter that he “most likely” has a moderate case of coronavirus, despite mixed test results.
Nasa policy is that anyone testing positive for the virus to quarantine and remain isolated.
“Astronaut launch today!” Mr Musk tweeted on Sunday morning, adding he had symptoms last week of a minor cold but currently felt “pretty normal”.
The launch of three Americans and one Japanese — all but one of them former space station residents — comes just three months after a pair of Nasa test pilots successfully concluded SpaceX’s first occupied flight of a Dragon crew capsule.
The crew led by Mr Hopkins, an Air Force colonel, includes physicist Shannon Walker and Navy Cmdr and rookie astronaut Victor Glover, who will be the first black astronaut to spend an extended period aboard the space station — a full five to six months.
Japanese astronaut Soichi Noguchi will become only the third person to rocket into orbit aboard three different kinds of spacecraft.
They named their capsule Resilience given all the challenges in 2020, most notably the global pandemic.
The 50-50 forecast focused only on the local weather for the planned 7.27 pm local time lift-off, not the wind or sea conditions all the way up the east coast or across the north Atlantic to Ireland.