Embarking on a new chapter of private space exploration, the Polaris Dawn mission is poised to make history this week by launching four private citizens into ultrahigh orbit and attempting the first civilian spacewalk.

Led by billionaire Jared Isaacman and in collaboration with SpaceX, the crew aims to reach as far as 870 miles above Earth, the highest altitude of any human spaceflight mission in more than a half-century since the Apollo program.

SpaceX announced Monday that the Falcon 9 rocket that will carry the Polaris Dawn crew to orbit could launch as early as Wednesday at 3:38 a.m. ET from NASA’s Kennedy Space Center in Florida. The launch was delayed 24 hours from the planned pre-dawn Tuesday blast-off.

The delay is due to a ground-side helium leak on the Quick Disconnect umbilical, SpaceX said.

Umbilical systems employ fluid connectors known as quick disconnects to transfer fluids into a vehicle, according to NASA.

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

There are two additional launch opportunities within the four-hour window on Wednesday at 5:23 a.m. and 7:09 a.m. ET. If needed, backup opportunities are available on Thursday, Aug. 29 at the same times, according to SpaceX.

Isaacman, the CEO of the payment-processing company Shift4, will be joined by former Air Force pilot Scott “Kidd” Poteet and two SpaceX engineers, Anna Menon and Sarah Gillis.

During the historic mission, which is set to span five days under normal conditions, two of the crew members will exit the spacecraft in the first commercial spacewalk at an altitude of 435 miles above Earth.

During a press briefing last week, Isaacman shared details on the ambitious mission, which will see all four crew members exposed to the vacuum of space due to the absence of an airlock on the SpaceX Dragon capsule.

The spacewalk will also serve as a critical test for SpaceX’s new Extravehicular Activity spacesuits, an evolution of the intravehicular activity suit.

This new design includes a heads-up display, helmet camera and enhanced joint mobility. It also features thermal insulation, solar protection and a suspension system that allows you to pressurize the suit, put on a harness and actually go through operations as if you are weightless.

The Dragon spacecraft has undergone significant modifications, including upgrades to the life support systems to supply more oxygen during spacewalks, according to the Polaris Program. Environmental sensing has been improved, and a new nitrogen repressurization system has been installed.

The Polaris Dawn mission will be Isaacman’s second journey to space.

In 2021, he funded his first mission to orbit Earth. The project was billed as a childhood cancer fundraiser, garnering $250 million for St. Jude Children’s Research Hospital, and marked the first all-civilian mission to orbit.

Looking to the future, Isaacman believes the SpaceX vehicles could unlock a new frontier in commercial space travel.

“It could very well be the 737 for human space flight someday,” he said of the company’s Starship vehicle. “But it’ll certainly be the vehicle that will return humans to the moon and then on to Mars and beyond,” he added.

ABC News’ Ayesha Ali contributed to this report.