• The cancellation is due to bad weather forecasted around the time that the Polaris Dawn crew would be returning to Earth in the Dragon for a splashdown landing off the Florida coast.
• Last week, SpaceX moved the launch window back from Monday to Tuesday to give teams time for preflight checkouts. On Monday, a since-fixed helium leak forced another delay.

SpaceX has again delayed the potentionally-historic Polaris Dawn commercial spaceflight mission that aims to send a four-member crew further into space than humans have been in more than 50 years.

The mission was set to take off early Wednesday morning before SpaceX announced on social media site X that the launch had been called off because of "unfavorable weather" forecasted for the crew's return to Earth. The possibility of a Thursday launch is also now a no-go due to the predicted conditions off the Florida coast, where the SpaceX Dragon capsule intends to make a water landing with the crew when the mission is complete, the company said.

The latest delay is the third since billionaire entrepreneur Jared Isaacman arrived with his crew more than a week ago at the Kennedy Space Center in Florida to prepare for the imminent launch. Isaacman, who funded the mission along with Elon Musk's company, will command a crew that includes pilot Scott “Kidd” Poteet and SpaceX engineers Sarah Gillis and Anna Menon, both mission specialists.

The crew's ambitious spaceflight will attempt to take them to higher altitudes than humans have traveled since NASA's Apollo program in the 1970s. While in orbit, the Polaris Dawn crew will also conduct the first-ever commercial spacewalk and test SpaceX technology that could set the stage for future deep space exploration.

Polaris Dawn mission:What to know about historic commercial spacewalk mission for SpaceX

Why was Polaris Dawn delayed this time?

The Falcon 9 rocket carrying the Dragon was slated to take off between 3:38 and 7:09 a.m. ET Wednesday before SpaceX scrubbed the launch Tuesday night.

The cancellation came after SpaceX officials detected bad weather in the forecast around the time that the Polaris Dawn crew would be returning to Earth in the Dragon for a splashdown at one of seven sites off the Florida coast.

Three launch delays so far, 1 for a helium leak

The delay is the third since the Polaris Dawn crew arrived in Cape Canaveral to make the final preparations for the mission.

Last week, SpaceX moved the launch window back from Monday to Tuesday to give teams more time to complete preflight checkouts. Then when Monday came, a detected helium leak on a piece a equipment designed to detach from the rocket during takeoff forced another delay.

Isaacman, founder of payments platform Shift4, said Wednesday night on X that the helium leak was repaired and the weather for the launch itself was ideal, if not the weather for the landing.

When will Polaris Dawn launch?

It's unclear yet just when SpaceX would be targeting a new launch window, but it won't be Wednesday or Thursday.

"Teams will continue to monitor weather for favorable launch and return conditions," SpaceX said.

Sharing SpaceX's post, Isaacman added that "we’ll assess day by day."

"As Elon mentioned, Polaris Dawn is a challenging mission with critical objectives, so we’ll wait for the best opportunity to ensure success," Isaacman posted. "Sometimes, the hardest journeys require the most patience, and we’re ready to wait for the right moment."

The mission of Polaris Dawn

Polaris Dawn is the first of three human spaceflights under the Polaris Program, all of which are intended to test SpaceX technologies needed to carry humans deep into the cosmos.

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.

The launch itself should take the SpaceX Dragon capsule to a height of 870 miles above the surface – a trajectory that will take the crew through the treacherous inner regions of Earth's Van Allen radiation belts.

Once Polaris Dawn descends to a new cruising orbit about 435 miles above Earth, the crew will attempt to become the first nongovernment astronauts to conduct a spacewalk.

Because the Dragon does not have an airlock, the entire spacecraft will have to be depressurized when the hatch is opened, exposing the entire crew to the vacuum of space. All four astronauts will be wearing Extra-Vehicular Activity (EVA) suits designed by SpaceX to receive oxygen through tethers, which they will test on behalf of the company.

The crew will also 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.

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