SpaceX on Monday pushed back the historic launch of an all-civilian crew on an orbital expedition set to mark a new chapter in space exploration with the first spacewalk by private citizens.

The Polaris Dawn mission, organized by billionaire entrepreneur Jared Isaacman, was set to lift off early Tuesday from NASA’s Kennedy Space Center, but is now targeting early Wednesday after a late technical hitch.

“Teams are taking a closer look at a ground-side helium leak on the Quick Disconnect umbilical,” Elon Musk’s company wrote on X. Umbilicals connect a tower with a rocket, while helium is a non-flammable gas often used to pressurize fuel lines.

Riding atop a Falcon 9 rocket, the SpaceX Dragon capsule is set to reach a peak altitude of 870 miles (1,400 kilometers) — higher than any crewed mission in over half a century, since the Apollo era.

Mission commander Isaacman will guide his four-member team through the mission’s centerpiece: the first-ever commercial spacewalk, equipped with sleek, newly developed SpaceX extravehicular activity (EVA) suits.

Rounding out the team are mission pilot Scott Poteet, a retired US Air Force Lieutenant Colonel; mission specialist Sarah Gillis, a lead space operations engineer at SpaceX; and mission specialist and medical officer Anna Menon, also a lead space operations engineer at SpaceX.