CAPE CANAVERAL, Fla. — A seemingly wayward boat, high winds and a rocket valve problem forced a one-day postponement in the maiden launch of NASA’s Orion capsule on Thursday. The string of glitches added suspense to the first test of a spacecraft that’s designed to take humans farther than they’ve ever gone — including to Mars.

The planned 4.5-hour mission — known as Exploration Flight Test 1, or EFT-1 — isn't supposed to carry people. It's an uncrewed flight, meant to check critical systems that can't be fully tested on Earth, including the craft's heat shield and parachutes.

The data gathered from more than 1,200 sensors will be factored into the construction of more flightworthy Orion spaceships, with the aim of flying astronauts for the first time in 2021. If NASA holds to its schedule, the cone-shaped spacecraft would send crews to a near-Earth asteroid by 2025, and to Mars and its moons starting in the 2030s.

"We're now on the way to Mars, and that's what's most important," NASA Administrator Charles Bolden told NBC News in advance of liftoff.

NASA expected more than 20,000 spectators to turn out for the launch, and astronauts on the International Space Station were watching closely as well.

"It's a thrilling prospect when you think about actually exploring the solar system," station commander Butch Wilmore said from orbit. "Who knows where it will take us, who knows where it will go? We'll find out as time goes forward, but this first step is a huge one."

Last-minute snags

Minutes before the scheduled launch time of 7:05 a.m. ET, NASA said a boat was in a restricted area of the range, east of the launch pad at Cape Canaveral Air Force Station. That forced a 12-minute delay in liftoff.

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Just as the countdown resumed, ground winds gusted higher than allowed — which led to another hold. "This is not a show-stopper," launch commentator Mike Curie said. Similarly, mission managers determined that an alarm that flashed due to the delay could be ignored.

A second attempt to restart the countdown was stymied again by high winds, and yet another countdown was aborted when sensors indicated that some of the fill-and-drain valves on Orion's United Launch Alliance Delta 4 Heavy rocket were not fully closed. That was the show-stopper: The launch team couldn't resolve the valve problem before time ran out at 9:44 a.m. ET.

For now, the schedule calls for the next attempt to take place Friday, with liftoff scheduled once again to take place at 7:05 a.m. ET. That schedule could change, however, depending on the weather outlook.

During a post-scrub news conference, Dan Collins, chief operating officer for United Launch Alliance, said the boat that started all the trouble on Thursday turned out to be "in a safe spot."

As for the technical issue that finally forced the scrub, Collins said the Delta 4 Heavy rocket's valves became "a little sluggish in their performance" after prolonged exposure to cold fuel temperatures. "This is something that we have seen on one previous heavy launch where we had a long window. ... The most likely path forward is that we would employ some type of operational procedure in order to mitigate the risk of this happening," Collins said.

A far-flying trip, a fiery return

The Delta 4 Heavy is the biggest and arguably the most expensive rocket in America's space fleet. Launch costs account for a significant portion of the $370 million price tag for EFT-1. But the massive rocket is required to loft the 23-ton Orion on a two-orbit trip that will loop out as far as 3,600 miles.

Orion's flight would mark the first time since the Apollo 17 moonshot in 1972 that NASA has sent any kind of spacecraft eventually meant to carry people that far away from Earth.

On the way down, the craft will blaze through the atmosphere at 20,000 mph, or 80 percent of the speed that a craft returning from the moon would experience. The heat shield will have to withstand temperatures as high as 4,000 degrees Fahrenheit.

The flight plan calls for Orion to splash down in the Pacific Ocean, about 600 miles west of Baja California. Two recovery ships and an array of helicopters are stationed to pick up the spacecraft and bring it in to Naval Base San Diego. The Orion craft is due to be trucked back to Kennedy Space Center in Florida by Christmas, NASA officials said.

Years of testing ahead

This Orion is flying without some critical pieces, such as a working launch abort tower and service module. Those components are still being developed, and they'll be integrated into the spacecraft for Orion's next test flight in 2018. That flight, known as Exploration Mission 1 or EM-1, will also mark the first use of NASA's Space Launch System — which will trump the Delta 4 Heavy as the world's most powerful rocket.

EM-1 is due to send an uncrewed Orion around the moon and back, in preparation for the first crewed flight in 2021.

Some observers have criticized Orion and the SLS rocket as too costly and slow to build. NASA's program manager for the Orion program, Mark Geyer, told NBC News that development costs for the spacecraft amount to about $1 billion a year — and that budgetary rather than technical considerations are driving the development schedule.

Once Orion and SLS are fully tested, NASA is planning to mount one SLS launch per year, and the giant rocket may be used for robotic interplanetary missions as well as crewed exploration missions.

At the same time, NASA is working with U.S. commercial partners on less expensive space taxis that would be used to transport astronauts to and from the International Space Station. The space agency's current scenario calls for SpaceX and the Boeing Co. to begin such flights in 2017, a year before the next Orion test is scheduled.