A SpaceX Falcon 9 rocket sits on Kennedy Space Center’s Launch Pad 39-A in Cape Canaveral, Florida. AP

The challenge SpaceX has set for itself when it launches its first tourism mission on Wednesday, the first time a crew of exclusively private citizens will orbit our planet.

The weather seems cooperative and the passengers are raring to go: SpaceX's first space tourists were a picture of calm on Tuesday as they prepared to blast off on a three-day mission to orbit the Earth. A five-hour launch window for "Inspiration4" opens from local time 8:02pm.

The four would-be citizen astronauts poised to ride a SpaceX rocket ship around the globe as the first all-civilian crew launched into orbit said on Tuesday they were eager for liftoff on the eve of their flight, feeling only "the good kind" of jitters.

The Inspiration4 crew of Chris Sembroski, Sian Proctor, Jared Isaacman and Hayley Arceneaux poses in Florida. Reuters

As part of an astro-tourist team poised to make history the four passengers are supposed to embody the opening-up of space to everyone, giving the mission its name: Inspiration4.

A billionaire, Jared Isaacman, is behind the project. It was he who chartered the mission, at his own expense, inviting three anonymous people to join him, via a rather original selection process. Each seat has been assigned to represent a specific value.

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The "Inspiration4" mission caps a summer that saw billionaires Richard Branson and Jeff Bezos cross the final frontier, on Virgin Galactic and Blue Origin spaceships respectively, a few days apart in July.

"I was just worried that this moment would never come in my life. Let's get going, let's do it," said Sian Proctor, 51, a geoscience professor, artist and lifelong space enthusiast who was a 2009 finalist in NASA's astronaut candidate program before she was cut.

Proctor also disclosed she and her flightmates received a telephone call from one of her personal heroes, former first lady Michelle Obama, wishing them well, an honor she said "would stay with me the rest of my life."

A new construction surrounds the SpaceX Crew Dragon capsule at Kennedy Space Center in Florida. Reuters

The crew vehicle is set for blastoff from NASA's Kennedy Space Center atop one of Musk's reusable Falcon 9 rockets, with a 24-hour targeted launch window that opens at 8pm EDT (0000 GMT) on Wednesday. That window will be narrowed, or possibly altered, a few days before, depending on weather.

SpaceX has already given no fewer than ten astronauts rides to the ISS on behalf of NASA — but this will be the first time taking non-professional astronauts.

Lift-off is scheduled for Wednesday from 8pm Eastern Time (0000 GMT) from launch pad 39A, at NASA's Kennedy Center in Florida, from where the Apollo missions to the Moon took off.