WASHINGTON (AFP) - SpaceX's all-civilian Inspiration4 crew are "healthy, happy and resting comfortably," the company said on Thursday (Sept 16) in its first update since the pioneering mission blasted off from Cape Canaveral the night before.

The four American space tourists "travelled 5.5 times around Earth, completed their first round of scientific research, and enjoyed a couple of meals" before going to bed, Elon Musk's company said.

Musk tweeted that he had personally spoken with the crew and "all is well."

After waking up, they will get their first look out of the Dragon ship's cupola - a large observation dome that has been fitted onto the vessel for the first time, in place of a docking mechanism.

Billionaire Jared Isaacman, physician assistant Hayley Arceneaux, geoscientist Sian Proctor and aerospace data engineer Chris Sembroski are orbiting the globe at an altitude that at times reaches 590 kilometres.

That is deeper in space than the International Space Station, which orbits at 420 kilometres, and the furthest any astronauts have ventured from our planet since a 2009 maintenance mission for the Hubble telescope.

The mission aims to raise US$200 million (S$270 million) for St Jude's Children's Research Hospital, and study the biological effects of deep space on the astronauts' bodies.

Its main goal, however, is to prove that space is accessible to ordinary people as the United States and private companies like SpaceX seek to further commercialise the cosmos.

The space adventure bookends a summer marked by the battle of the billionaires Richard Branson and Jeff Bezos to reach the final frontier.

But these flights only offered a few minutes of weightlessness - rather than the three full days of orbit the Inspiration4 crew will experience, before splashing down off the coast of Florida on Saturday.