• The Polaris Dawn crew will attempt to reach heights higher than humans have traveled since NASA's Apollo program in the 1970s and will also conduct the first-ever commercial spacewalk.
• The Falcon 9 rocket carrying the Dragon is now slated to take off between 3:38 and 7:09 a.m. ET Wednesday from NASA’s Kennedy Space Center in Florida.
• "Falcon and Dragon remain healthy and the crew continues to be ready for their multi-day mission to low-Earth orbit," SpacX said on social media.

A SpaceX capsule carrying four commercial astronauts hoping to conduct a pioneering spacewalk won't be launching at least until Wednesday morning.

The Polaris Dawn mission, an ambitious five-day journey to the upper reaches of Earth's orbit, had been slated for a Tuesday liftoff before a detected helium leak forced a delay, SpaceX said Monday night on social media site X.

When the crew does launch aboard a SpaceX Dragon, it will be the second trip to space for billionaire entrepreneur Jared Isaacman, who funded the mission along with Elon Musk's company. Isaacman previously ventured to orbit in 2021 on Inspiration4, the mission that became the first-ever private orbital spaceflight.

Isaacman will command a crew that includes pilot Scott “Kidd” Poteet and SpaceX engineers Sarah Gillis and Anna Menon, both mission specialists. During the mission, the Polaris Dawn crew will attempt to reach heights higher than humans have traveled since NASA's Apollo program in the 1970s and will also conduct the first-ever commercial spacewalk.

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When will Polaris Dawn launch?

The Falcon 9 rocket carrying the Dragon is slated to take off between 3:38 and 7:09 a.m. ET Wednesday from NASA’s Kennedy Space Center in Florida.

The launch delay – the second since the Polaris Dawn crew arrived last week in Florida – was necessary to give ground crews time to take “a closer look at a ground-side helium leak” on a piece a equipment designed to detach from the rocket during takeoff, SpaceX said on X.

The Boeing Starliner spacecraft, which is competing with the SpaceX Dragon for NASA approval to make routine orbital trips, also experienced a helium leak on its journey to the International Space Station. The leak, combined with thruster troubles, ended up requiring NASA to scuttle the crew's return trip to Earth aboard the Starliner.

SpaceX, though, appears more optimistic that the helium leak wouldn't threaten an imminent launch of its own proven craft, which has already been reliably transporting astronauts to orbit since 2020.

"Falcon and Dragon remain healthy and the crew continues to be ready for their multi-day mission to low-Earth orbit," the company said.

If another mission scrub is necessary, the launch could still take place Thursday morning, according to SpaceX.

What is the Polaris Dawn mission?

The crew eventually plans to spend five days in orbit testing technology on behalf of SpaceX that could prove crucial as NASA and other space agencies set their sights on deep-space exploration, including destinations like Mars.

During the crew's first day in orbit, they will blast off to a height of 870 miles above the surface – higher than any human has traveled since NASA’s Apollo lunar program came to an end in the 1970s. The trajectory will take the capsule through the treacherous inner regions of Earth's Van Allen radiation belts before descending to a new cruising orbit about 435 miles above Earth.

The Van Allen belts pose one of the largest hazards to future spacefarers venturing deep into the cosmos. But for future expeditions to the moon and Mars to be possible, astronauts will have to be able to safely fly through them.

While in orbit, the crew will complete some 40 scientific experiments – many of which are to understand the human body's reaction to long spaceflights – and test a new laser-based satellite communication system using Starlink.

Menon, of Houston, also plans to read a children's book she co-authored, "Kisses from Space" – inspired by her experience preparing for the Polaris Dawn mission – to her two young children while in orbit.

On the sixth day of the mission, the SpaceX vehicle will reenter Earth's atmosphere and splash down at one of seven sites off the Florida coast.

Conducting a risky spacewalk

Without a doubt, the climax of the Polaris Dawn mission will come on day three, when the crew hopes to become the first ever nongovernment astronauts to complete a spacewalk.

The complex orbital maneuvers have only ever taken place in craft with airlocks that negate the need to depressurize an entire capsule.

But because the Dragon does not have an airlock, the entire spacecraft will have to be depressurized when the hatch is opened. Even though only Isaacman and Gillis plan to exit the craft, the entire crew will still be exposed to the vacuum of space.

For this reason, all four astronauts will be wearing Extra-Vehicular Activity (EVA) suits designed by SpaceX to receive oxygen through tethers. The purpose of the operation, which should take about two hours, is to test the suit's capabilities for SpaceX.

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at [email protected]