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Aug. 27 (UPI) -- SpaceX has again delayed its historic launch of the four-person Polaris Dawn crew who are to fly father than any human has flown since the end of the Apollo missions. SpaceX was targeting a Wednesday 3:38 a.m. EDT liftoff of Falcon 9's Polaris Dawn to low-Earth orbit from NASA's Kennedy Space Center in Florida, but canceled the launch Tuesday night due to weather forecast for the spacecraft's return to Earth.
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"Due to unfavorable weather forecasted in Dragon's splashdown areas off the coast of Florida, we are now standing down from tonight and tomorrow's Falcon 9 launch opportunities of Polaris Dawn," SpaceX said on X only hours before the launch was to commence.
Billionaire philanthropist Jared Isaacman, who is leading the mission, explained online following the scrubbing of the launch that their launch criteria is "heavily constrained" by splashdown weather conditions.
"With no ISS rendezvous and limited life support consumables, we must be absolutely sure of re-entry weather before launching," he said, referring to the International Space Station by its common initialism.
"Polaris Dawn is a challenging mission with critical objectives, so we'll wait for the best opportunity to ensure success."
The mission was initially supposed to launch Monday, but was pushed to Tuesday to allow additional time for preflight checks. Then Tuesday's launch was scrubbed hours before liftoff after a helium leak was discovered.
Now it appears that Friday would be the next possible launch date as SpaceX ruled out Thursday's back-up opportunities as well.
"Teams will continue to monitor weather for favorable launch and return conditions," SpaceX added.
The announcement comes after SpaceX earlier Tuesday said weather was 85% favorable for liftoff, but teams were "keeping an eye on recover weather."
Once eventually launched, the plan is for the Polaris Dawn crew aboard the SpaceX Dragon capsule to spend five days orbiting Earth where they will conduct the first commercial spacewalk in history.
The crew are expected to fly to an initial maximum altitude of about 870 miles before dropping back to a lower cruising orbit. The maximum height is well into the inner band of Earth's Van Allen radiation belts, which start at around 600 miles in altitude.
The all-civilian crew's spacewalk is scheduled to occur on the third day to test the function of SpaceX's new spacesuits, which feature enhanced thermal control materials and technologies. The entire spacewalk from cabin depressurization through repressurization will last approximately two hours.
The Dragon capsule does not have an airlock so the spacewalk will take place closer to Earth, about 435 miles in altitude, where the astronauts will be exposed to the vacuum of space.
On the fourth day, the crew is planned to connect to SpaceX's Starlink satellite network to transmit a "surprise" message down to Earth, before preparing to return for a splashdown at one of seven sites off the coast of Florida.
The Polaris Dawn crew is led Isaacman, who is funding the mission in partnership with St. Jude Children's Research Hospital. Retired U.S. Air Force Lit. Col. Scott "Kidd" Poteet will pilot Polaris. The mission also includes two of the first SpaceX employees to travel to space, Medical Officer Anna Menon and Mission Specialist Sarah Gillis.
"Sometimes, the hardest journeys require the most patience, and we're ready to wait for the right moment," Isaacman wrote after Wednesday's scrub on X.
"We know many have traveled to see the launch, and we're grateful for your support."
