"We got really close today, and the team did a phenomenal job," said Steve Stich, NASA manager for the commercial crew program, told reporters during a post-launch attempt news conference.

"This is kind of the way that spaceflight is," he added. "Every time you go to the pad for a crew flight or any flight, you've got a chance for scrubbing."

A computer launch sequencer problem with the United Launch Alliance Atlas V rocket triggered a hold less than four minutes before the first crewed launch of the Boeing Starliner spacecraft was to occur.

NASA test pilots Sunita "Suni" Williams and Barry "Butch" Wilmore are attempting the first crewed mission of the Boeing Starliner spacecraft .

The Atlas V rocket was set to launch the Starliner into space from the Space Launch Complex 41 at the Cape Canaveral Space Force Station in Florida at 12:25 p.m. EDT Saturday.

Starliner's next launch opportunity is 12:03 p.m. EDT Sunday.

Prospects for Saturday's launch initially looked good despite a minor setback.

Around 10 a.m., teams found a loss of data from ground valves responsible for replenishing the liquid oxygen and hydrogen to the second, or upper stage, of the Atlas V rocket.

A redundant system worked as intended, which didn't halt or slow the launch.

At 3 minutes and 50 seconds before launch, the computer launch sequencer triggered an automatic launch hold, which scrubbed the day's launch.

The Atlas V rocket uses three large computers to monitor launch conditions and provide triple redundancy if something fails, ULA CEO Tory Bruno told reporters during news conference.

Triple redundancy means there are three ways to do the same task in case one or two other systems fail.

"That ended up scrubbing the mission," Bruno said, adding that it will take up to four hours to remove fuel from the rocket before a team can analyze the problem.

"If it's as simple as replacing a card, we'll do that" and prepare for a Sunday launch at 12:03 p.m., Bruno said.

If it's something more complicated, like a network problem, he said the next available launch window is Wednesday with Thursday as a backup launch date.

Bruno said the team has until about 12:30 a.m. Sunday to determine if a launch attempt can be done Sunday afternoon.

Williams and Wilmore are giving the Starliner its final shakedown run, which includes a week-long stay while docked at the International Space Station.

The test pilots will spend a day traveling to the ISS, where it will dock and remain for about a week while testing the Starliner's ability to support a crew in space.

The Starliner will return to Earth with a soft landing planned in the U.S. desert Southwest.

The Starliner is designed with a service life of 10 launches and landings.

Earlier test launches were delayed for many reasons, including the use of flammable tape in the Starliner capsule, a buzzing noise detected on the launch pad, a defective pressure valve on an upper-stage oxygen tank and a helium leak in the service module.

If the 10-day test flight proceeds successfully, NASA likely will certify the Starliner for use.

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