SpaceX's historic Polaris Dawn astronaut mission has been delayed again.

Polaris Dawn was originally scheduled to launch early Monday morning (Aug. 26) from NASA's Kennedy Space Center in Florida, but SpaceX pushed things back a day to perform more preflight checkouts. The company then called the planned Tuesday (Aug. 27) attempt off after detecting a helium leak, targeting Wednesday (Aug. 28) instead. But now Mother Nature has foiled that plan.

"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. Teams will continue to monitor weather for favorable launch and return conditions," SpaceX announced Tuesday evening via X. 

Polaris Dawn will send four people to Earth orbit in a SpaceX Crew Dragon capsule, which will depart the planet atop one of the company's Falcon 9 rockets. 

The crewmembers are commander Jared Isaacman, pilot Scott "Kidd" Poteet and mission specialists Sarah Gillis and Anna Menon. Isaacman is a billionaire entrepreneur who's funding Polaris Dawn; Poteet is a former lieutenant colonel in the U.S. Air Force, and Gillis and Menon are both SpaceX engineers.

The upcoming mission will make history in several ways. Isaacman and Gillis will conduct the first-ever private spacewalk, for example, and Polaris Dawn aims to send the Dragon to a maximum altitude of about 870 miles (1,400 kilometers) — higher than any crewed mission since the Apollo era.