A crew of four private astronauts on Tuesday were in the final stages of preparation for a risky SpaceX mission to attempt the first-ever private spacewalk using the company’s new spacesuits and a redesigned spacecraft, Reuters reported.

A billionaire entrepreneur, a retired military fighter pilot and two SpaceX employees are poised to launch at 03.38 ET (11:38 UAE time) from NASA’s Kennedy Space Centre in Florida aboard SpaceX’s Crew Dragon capsule, the spacecraft’s fifth private space mission so far.

An attempt to launch last month was postponed hours before lift-off over a small helium leak in ground equipment on SpaceX’s launchpad. SpaceX fixed the leak, but the company’s Falcon 9 was then grounded by US regulators over a booster recovery failure during an unrelated mission, further delaying the Polaris launch.

Permitted to resume Falcon 9 flights, the Polaris mission is now set for a pre-dawn launch Tuesday, but with only a 40 percent chance of favourable weather, according to US Space Force launch weather modelling. SpaceX has other launch opportunities Tuesday at 05.23 and 07.09 local time.

The SpaceX mission, called Polaris Dawn, will last about five days in an oval-shaped orbit that passes as close to Earth as 190 km (118 miles) and as far as 1,400 km (870 miles), the farthest any humans will have travelled since the end of the United States’ Apollo moon programme in 1972.

The spacewalk is planned for the mission’s third day at 700 km in altitude and will last around 20 minutes. SpaceX’s Crew Dragon craft will slowly depressurise its entire cabin – it has no airlock like the ISS – and all four astronauts will rely on their slimmed-down, SpaceX-built spacesuits for oxygen.