It sounds like the beginning of a bad joke.

A billionaire, a physician’s assistant and an Air Force veteran are launched into space. How many days will they spend in orbit before realising none of them are astronauts?

Except the unlikely trio are joined by a geoscientist – and they already know.

A SpaceX rocket ship blasted off from its Florida base on Thursday, carrying a group of civilians into orbit for the first time in history.

A billionaire e-commerce executive has chosen three less-wealthy private citizens to join him in the first all-civilian crew ever launched into earth orbit.

Tweet from @SpaceX

Financial services boss Jared Isaacman, accompanied by his hand-picked team of amateur astronauts, lifted off just before sunset on Wednesday (local time) from the Kennedy Space Centre in Cape Canaveral, Florida.

A SpaceX webcast showed Mr Isaacman, 38, and his crewmates – Sian Proctor, 51, Hayley Arceneaux, 29, and Chris Sembroski, 42 – strapped into the pressurised cabin of their SpaceX Crew Dragon capsule, dubbed Resilience.

Thumbs-up were on display as the capsule streaked into the sky, perched atop one of the company’s reusable two-stage Falcon 9 rockets.

The Crew Dragon, fitted with a special observation dome in place of its usual docking hatch, reached orbit almost 10 minutes after the 8.03pm (1003 AEST) blast-off.

The rocket’s first-stage booster, after separating from the spacecraft’s top half, descended back to earth and touched down safely on a landing platform floating in the Atlantic.

The flight, marking the first crewed mission to orbit with no professional astronauts along for the ride, is expected to last about three days from launch to splashdown in the Atlantic.

It marks the debut flight of SpaceX owner Elon Musk’s new orbital tourism business, and a leap ahead of competitors offering paid rocket ship rides.

The four civilians blasted off from the Kennedy Space Centre on September 16. Photo: Netflix

Mr Isaacman paid an undisclosed sum to fellow billionaire Musk to send himself and his three crew mates up and away.

The mission, called Inspiration4, was conceived by Mr Isaacman to raise awareness and support for St Jude Children’s Research Hospital, a pediatric cancer centre in Memphis, Tennessee.

He used a Super Bowl advert for his company, Shift4Payments, to recruit candidates.

Inspiration4 is aiming for an orbital altitude of 575 kilometres, higher than the International Space Station or Hubble Space Telescope, and the furthest any human will have flown from earth since the end of NASA’s Apollo moon program in 1972, according to SpaceX.

The Crew Dragon will circle the globe once every 90 minutes at 27,360km/h.

Rival companies Virgin Galactic and Blue Origin inaugurated their own private-astronaut services in recent months.

Respective founding billionaires Richard Branson and Jeff Bezos were among the first to board.

The Inspiration4 crew has no part to play in flying the spacecraft, which is operated by ground-based flight teams and onboard systems.

Tweet from @DrSianProctor

Mr Isaacman, who is rated to fly commercial and military jets, is mission “commander”, while Dr Proctor, a geoscientist and former NASA astronaut candidate, is the “pilot”.

Rounding out the crew are “chief medical officer” Ms Arceneaux, a bone cancer survivor turned St Jude physician assistant. And mission “specialist” Mr Sembroski, a US Air Force veteran and aerospace data engineer.

For anyone wishing they could be a fly on the wall, as reported by The New Daily, streaming giant Netflix will turn the whole journey into a docu-series. 

The crew have spent five months in rigorous preparations, including altitude fitness, simulator training and medical exams.

They will perform medical experiments with “potential applications for human health on earth and during future spaceflights”, according to SpaceX.

-with AAP