WALLOPS ISLAND, Va. -- The countdown for the first launch of the Orbital Sciences Corp. Antares rocket was halted 12 minutes before liftoff Wednesday after an Ethernet umbilical cable prematurely disconnected from the booster.

The Antares rocket on the launch pad at Wallops Island, Va. Credit: Stephen Clark/Spaceflight Now

Engineers will have to troubleshoot the umbilical before proceeding with another try, and Orbital Sciences officials said Wednesday that Friday is the earliest the rocket would be ready for a second launch attempt.

The abort occurred after a smooth countdown with no major problems. Worries over an iffy weather forecast proved unfounded as sunny skies and light winds swept over the Antares launch site at NASA's Wallops Flight Facility on Virginia's Eastern Shore.

"LC, we've had a premature separation of the umbilical on stage two so we're going to have to abort for the day," a launch controller said on the countdown communications loop.

"OK, copy that," the launch conductor said. "This is LC on countdown one, abort, abort, abort. This is LC on countdown one, abort, abort, abort, proceed to abort safing procedures."

With a brief launch window limited to 10 minutes by constraints on the temperature of liquid propellant, officials immediately declared a scrub for the day.

"You learn a little bit from every launch attempt," said John Steinmeyer, an Orbital project manager. "We'll take the lessons learned today and move into another launch attempt as soon as it's safe to do so."

Frank Culbertson, executive vice president and general manager of Orbital's advanced programs group, said launch controllers noticed a data dropout in a link with the rocket's flight computer at 4:44 p.m. EDT, about 16 minutes before the target launch time.

Launch officials decided to postpone the launch once it became clear the umbilical was disconnected.

Culbertson, a former NASA astronaut, said the Ethernet cable is one of several power and data connections in a bundle running between the launch pad's servicing mast and the Antares rocket. All of the other connections appeared to remain in place, he said.

The Ethernet connection allows the launch team to communicate with the flight computer mounted on the Antares second stage, Culbertson said.

"There is a set of umbilical cables that go into the second stage that provide communications between the ground and the flight computer that's on the second stage," Culbertson told reporters after the scrub. "There's two-way communications sending information to the vehicle about where we are in the count, and then the vehicle actually is controlling some aspects of the countdown itself."

The cables attach to the rocket in a matrix similar to the way audio and video wires connect to the back of a television. Culbertson said engineers aren't sure what made the umbilical come loose.

"We're not sure exactly what caused that," Culbertson said. "We're going to go in as soon as we can get to the pad and look at the connector. The connector is a collar-type connector that has a lanyard that pulls the collar at the right time so that it releases, kind of like what you have on a TV connection."

The cable is supposed to disconnect at liftoff.

The weather forecast for Friday was bleak, predicting gusty winds, thunderstorms and cloudy conditions. The weather rules for the Antares rocket call for winds of less than 20 knots, no cloud ceiling below 6,000 feet, and no chance of lightning.

"The weather forecast is not good for Friday, but we're going to march down the road as if we're going to make a launch attempt on Friday," said Barry Beneski, an Orbital Sciences spokesperson.

Beneski said engineers will meet at 8 a.m. EDT Thursday to assess the technical status of the umbilical repair. A weather briefing later Thursday will give managers an updated forecast for Friday before officials make a decision on when to make another attempt.

Crowds of onlookers gathered at the eastern Virginia launch site. The Antares rocket is the largest vehicle to ever launch from Wallops in its 68-year history.

Wallops Flight Facility has launched more than 16,000 rockets, mostly missiles and sounding rockets for military and engineering research.

Orbital's Antares rocket and Cygnus cargo freighter are designed for resupply flights to the International Space Station. The first Antares test launch will only demonstrate the rocket, while another mission this summer will rendezvous with the space station to prove out the Cygnus spacecraft.

NASA is paying Orbital Sciences up to $288 million in an agreement under the Commercial Orbital Transportation Services, or COTS, program. The COTS agreement covers development and testing of the Antares and Cygnus vehicles, and a separate contract with NASA worth $1.9 billion covers at least eight operational resupply flights to the space station.

Culbertson said he was pleased with the performance of the launch team Wednesday.

"The whole team was working together superbly," Culbertson said. "For our first launch attempt, I thought it was as good as I have seen."

"Not only is this a test of the vehicle, this is a test of the team," said Alan Lindenmoyer, NASA's COTS program manager. "This was their first time for a launch attempt, and observing this team in action was very impressive."