Aug 27 (Reuters) - The launch of SpaceX's four-person

Polaris Dawn mission will be delayed by at least a day because

of a helium leak in ground equipment at Kennedy Space Center,

the company said on Tuesday, hours before the scheduled liftoff

of its Crew Dragon capsule.

The highlight of the five-day mission is expected to come

two days after launch, when the crew embarks on a 20-minute

spacewalk 434 miles (700 km) from earth, in history's first such

private spacewalk.

The company now aims to launch the spacecraft, carried by a

Falcon 9 booster, at 3:38 a.m. (0738 GMT) on Wednesday, it said

in a posting on X.

"Teams are taking a closer look at a ground-side helium

leak," it added in Tuesday's post. "Falcon and Dragon remain

healthy and the crew continues to be ready for their multi-day

mission to low-Earth orbit."

Only government astronauts have performed spacewalks to

date, most recently by occupants of the International Space

Station, who regularly don spacesuits to perform maintenance and

other checks of their orbital home.

The first U.S. spacewalk was in 1965, aboard a Gemini

capsule, and used a similar procedure to the one planned for

Polaris Dawn: the capsule was depressurised, the hatch opened,

and a spacesuited astronaut ventured outside on a tether.

Polaris Dawn's crew will be testing SpaceX's new, slimline

spacesuits during the spacewalk.

Only two of the four - billionaire Jared Isaacman, mission

pilot Scott Poteet, a retired U.S. Air Force lieutenant colonel,

and SpaceX employees Sarah Gillis and Anna Menon, both senior

engineers at the company - will leave the spacecraft.

Isaacman, the founder of electronic payment company Shift4,

bankrolled the mission; he has declined to say how much he has

spent, but it is estimated to be more than $100 million.