The launch of a SpaceX rocket ship with two Nasa astronauts on a history-making flight into orbit has been called off with 16 minutes to go in the countdown because of the danger of lightning.

Liftoff is rescheduled for Saturday (Sunday, 7.22am NZT).

The spacecraft was set to blast off Wednesday afternoon for the International Space Station, ushering in a new era in commercial spaceflight and putting Nasa back in the business of launching astronauts from US soil for the first time in nearly a decade.

Ever since the space shuttle was retired in 2011, Nasa has relied on Russian rockets to carry astronauts to and from the space station.

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Space veterans Doug Hurley and Bob Behnken were scheduled to ride into orbit aboard the brand-new Dragon capsule on top of a Falcon 9 rocket, lifting off at 4.33pm EDT from the same launch pad used by the Apollo moon missions a half-century ago.

Smiling, waving and giving the traditional thumbs-up, the two men met with cice-president Mike Pence and said farewell to their families — pantomiming an arms-wide hug for their sons from a coronavirus-safe distance — before setting out for the launch pad in a gull-wing Tesla SUV, another product from SpaceX's visionary founder, Elon Musk.

Thunder could be heard rumbling as the convoy of vehicles made its way toward the rocket.

The flight would mark the first time a private company sent humans into orbit. It would also be the first time in nearly a decade that the United States launched astronauts into orbit from US soil.

Ever since the space shuttle was retired in 2011, Nasa has relied on Russian spaceships launched from Kazakhstan to take US astronauts to and from the space station.

The SpaceX Crew Dragon capsule after its arrival to the Kennedy Space Center in Cape Canaveral, Florida. AP Photo / SpaceX
The SpaceX Crew Dragon capsule after its arrival to the Kennedy Space Center in Cape Canaveral, Florida. AP Photo / SpaceX

At midday, though, with four hours remaining before liftoff, launch controllers put the chances of acceptable weather for liftoff at just 50-50 because of rain, clouds and thunderstorms at Nasa's Kennedy Space Center. A tropical storm farther up the East Coast also complicated matters.

A woman walks to her spot along Indian Creek Lagoon in a Titusville, Florida to watch the launch of SpaceX Falcon 9. AP Photo / Charlie Riedel
A woman walks to her spot along Indian Creek Lagoon in a Titusville, Florida to watch the launch of SpaceX Falcon 9. AP Photo / Charlie Riedel

In the event of a postponement, the next launch opportunity would be Saturday.
The preparations took place in the shadow of the coronavirus outbreak that has killed an estimated 100,000 Americans.

"We're launching American astronauts on American rockets from American soil. We haven't done this really since 2011, so this is a unique moment in time," Nasa Administrator Jim Bridenstine said.

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With this launch, he said, "everybody can look up and say, 'Look, the future is so much brighter than the present.' And I really hope that this is an inspiration to the world."

The mission would put SpaceX in the same league as only three countries — Russia, the US and China, which sent astronauts into orbit in that order.

Musk, wearing a mask and keeping his distance, chatted with the two Nasa astronauts just before they left for the launch pad.

Nasa pushed ahead with the launch despite the viral outbreak but asked spectators to stay at home to lower the risk of spreading the virus. Beaches and parks along Florida's Space Coast are open again, and local officials and businesses put out a socially distanced welcome mat. Signs along the main beach drag wished "Godspeed SpaceX".

Hours before the launch, cars and RVs already were lining the causeway in Cape Canaveral, with prime views of the pad.

President Donald Trump also planned to fly into Kennedy, where the guest list was exceedingly limited because of the pandemic.

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Among the sightseers was Erin Gatz, who came prepared for both rain and pandemic. Accompanied by her 14-year-old daughter and 12-year-old son, she brought face masks and a small tent to protect against the elements.

She said the children had faint memories of watching in person one of the last shuttle launches almost a decade ago when they were preschoolers.

Nasa astronaut Bob Behnken in his spacesuit at SpaceX headquarters in Hawthorne, California, on May 27, 2020. AP Photo / SpaceX
Nasa astronaut Bob Behnken in his spacesuit at SpaceX headquarters in Hawthorne, California, on May 27, 2020. AP Photo / SpaceX

"I wanted them to see the flip side and get to see the next era of space travel," said Gatz, who lives in Deltona, Florida. "It's exciting and hopeful."

Hurley, 53, and Behnken, 49, are both two-time shuttle fliers.

Nasa hired SpaceX and Boeing in 2014 to transport astronauts to the space station in a new kind of public-private partnership.. Development of SpaceX's Dragon and Boeing's Starliner capsules took longer than expected, however. Boeing's craft is not expected to fly astronauts into space until early 2021.

"We're doing it differently than we've ever done it before," Bridenstine said. "We're transforming how we do spaceflight in the future."

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At a park in Titusville with a clear view of the Kennedy Space Center launch pad 24km away, hundreds of spectators sheltered from an off-and-on drizzle under tents and umbrellas on lawn chairs in the hours before the scheduled launch.

Cars park in a vacant lot to watch the launch of SpaceX Falcon 9 with NASA astronauts Doug Hurley and Bob Behnken in the Dragon crew capsule. AP Photo / Charlie Riedel
Cars park in a vacant lot to watch the launch of SpaceX Falcon 9 with NASA astronauts Doug Hurley and Bob Behnken in the Dragon crew capsule. AP Photo / Charlie Riedel

They turned out to witness the first launch with astronauts from Florida in almost a decade, and the first by a private company, SpaceX.NASA and SpaceX had urged spectators to stay at home for safety reasons. But officials in Brevard County, home to the Kennedy Space Center, rolled out the welcome mat in an effort to jump-start a tourism industry hit hard this spring by coronavirus-related lockdowns.

About a third of the people at the Titusville park wore masks as encouraged by health officials to help stop the spread of the new coronavirus. The Brevard County Sheriff's Office asked visitors to practice social distancing as they watch the launch of astronauts Hurley and Behnken on a test flight of SpaceX's Dragon crew capsule.

President Donald Trump and Vice President Mike Pence traveled to Kennedy for the launch, while the number of visitors inside was drastically curtailed.

About two hours before the scheduled launch, a downpour sent many spectators running to their cars to wait out the storm. A short time later, a tornado warning was issued for the area.

SpaceX CEO Elon Musk talks to the media and NASA personnel, after astronauts Douglas Hurley and Robert Behnken departed for launch. AP Photo / John Raoux
SpaceX CEO Elon Musk talks to the media and NASA personnel, after astronauts Douglas Hurley and Robert Behnken departed for launch. AP Photo / John Raoux

Mike Rine, who set up a folding chair before the storm to watch the launch at Space View Park in Titusville, found the mixed message about attending a bit confusing, so he came but left his elderly father at home in Leesburg, Florida.

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"If the president and the vice president can come...," said Rine, who was wearing an Apollo 11 anniversary T-shirt. "But I've got a mask."

For Scott and Lisa Ward, to be able to watch a launch from Florida after a nine-year absence was worth a 125-mile drive from Okeechobee in the heart of Florida. Scott Ward had watched several launches in person during the shuttle era. "That's what it's about, getting back to exploration," said Scott Ward, who is retired.

Patricia Gottenger and Nelly Marro tied a rocket ship balloon to their lawn chairs as they set up to watch the launch a bit away from the rest of the crowd at Space View Park.

A NASA helicopter escorts the crew to Launch Pad 39-A at Kennedy Space Center in Cape Canaveral. AP Photo / David J. Phillip
A NASA helicopter escorts the crew to Launch Pad 39-A at Kennedy Space Center in Cape Canaveral. AP Photo / David J. Phillip

The Venezuelan natives wore face masks and acknowledged they picked a spot on the edge of the park as a safety precaution to watch their first launch.

"This is historic," said Gottenger, who drove up from South Florida for the day with Marro.

Erin Gatz came prepared for both rain and pandemic. Accompanied by her 14-year-old daughter Regan and 12-year-old son Gavin, she brought face masks and a small tent.

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The children have faint memories of watching one of the last shuttle launches almost a decade ago when they were small. "I wanted them to see the flip side and get to see the next era of space travel," said Gatz, who lives about an hour away in Deltona.

"It's exciting and hopeful." - AP