The latest in a recent line of space-obsessed billionaires is set for lift-off with three less wealthy private citizens along for the ride aboard a SpaceX rocket ship, seeking to become the first all-civilian crew launched into Earth orbit.
The quartet of amateur space travellers, led by the American founder and chief executive of e-commerce firm Shift4 Payments Inc, Jared Isaacman, were due for blast off as early as 8pm on Wednesday from the Kennedy Space Centre in Cape Canaveral, Florida.
SpaceX's senior director of human spaceflight, Benji Reed, told reporters that "everything looked great" following a final "static" test-firing of the rocket engines on Monday.
"Right now the weather is trending well" for an on-time launch, he said.
The flight, with no professional astronauts accompanying SpaceX's paying customers, is expected to last about three days from liftoff to splashdown in the Atlantic.
They will fly aboard a SpaceX Crew Dragon capsule, dubbed Resilience, perched atop one of the company's reusable Falcon 9 rockets and fitted with a special observation dome in place of the usual docking hatch.
Isaacman, 38, the trip's benefactor, has forked over an undisclosed but presumably hefty sum to fellow billionaire and SpaceX owner Elon Musk to send himself and his three crewmates aloft.
Time magazine has put the ticket price for all four seats at $US200 million ($A272 million).
The so-called Inspiration4 mission was conceived by Isaacman mainly to raise awareness and support for one of his favourite causes, St. Jude Children's Research Hospital, a leading paediatric cancer centre in Memphis, Tennessee.
It marks the debut flight of Musk's new orbital tourism business, and a leap ahead of competitors likewise offering rides on rocket ships to well-heeled customers willing to pay a small fortune for the exhilaration, and bragging rights, of spaceflight.
Inspiration4 is aiming for an orbital altitude of 575km above Earth, higher than the International Space Station or Hubble Space Telescope. The capsule will circle the globe once every 90 minutes at roughly 22 times the speed of sound.
Rival companies Virgin Galactic and Blue Origin inaugurated their own private-astronaut services this summer, with their respective founding executives, billionaires Richard Branson and Jeff Bezos, each going along for the ride.
But those suborbital flights, lasting a matter of minutes, were short hops compared with Inspiration4's spaceflight profile.
SpaceX has already launched numerous cargo payloads and astronauts to the International Space Station for NASA.
Despite some largely honorary titles, the Inspiration4 crew will have no part to play in flying the spacecraft, which will be operated by ground-based flight teams and onboard guidance systems, even though two crew members are licensed pilots.
Isaacman, who is rated to fly commercial and military jets, has assumed the role of mission "commander," while geoscientist Sian Proctor, 51, a former NASA astronaut candidate, has been designated as the mission "pilot."
Rounding out the crew are "chief medical officer" Hayley Arceneaux, 29, a bone cancer survivor turned St. Jude physicians' assistant, and mission "specialist" Chris Sembroski, 42, a US Air Force veteran and aerospace data engineer.
The four crewmates have spent five months in rigorous preparations, including altitude fitness, centrifuge (G-force), microgravity and simulator training, emergency drills, classroom work and medical exams.
Inspiration4 officials stress that the mission is more than a joyride.
Once in orbit, the crew will perform a series of medical experiments with "potential applications for human health on Earth and during future spaceflights," the group said in media materials.
Biomedical data and biological samples, including ultrasound scans, will also be collected from crew members before, during and after the flight.
"The crew of Inspiration4 is eager to use our mission to help make a better future for those who will launch in the years and decades to come," Isaacman said in a statement.
Australian Associated Press