James Dean

FLORIDA TODAY

Note: Atlas V successfully launched at 10:30 a.m. Eastern time. Read more here.

United Launch Alliance’s Atlas V rocket returns to action Friday after a close call three months ago, when its main engine quit firing six seconds too soon.

The early shutdown imperiled a launch of International Space Station supplies that reached orbit safely thanks to an extra minute of work by the rocket’s upper stage.

ULA says it has fixed a valve problem that restricted fuel flow on that March 22 flight, leaving a significant amount unused.

Now the most powerful version of the Atlas V is poised for a 10:30 a.m. blastoff from Cape Canaveral Air Force Station’s Launch Complex 41 with a large, military communications satellite.

“We’re confident we’re ready to support this mission and have cleared the vehicle for flight,” said Laura Maginnis, ULA’s vice president for custom services.

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For only the seventh time, the base of the 20-story Atlas V is ringed with the five solid rocket motors — the maximum possible — which will combine with the RD-180 main engine to generate 2.5 million pounds of thrust at liftoff.

All that power is needed to boost the Navy’s fifth Mobile User Objective System, or MUOS, satellite on its way to an orbit 22,300 miles over the equator.

The 15,000-pound satellite built by Lockheed Martin will complete the space-based portion of the $7.7 billion MUOS program, which also includes four ground stations and software still being integrated with Army and Navy radios that will be deployed on the ground, at sea and in aircraft.

“This launch is a significant event for the entire MUOS team, because it will complete the five-satellite constellation,” said Navy Capt. Joe Kan[CQ], the program manager.

ULA and the Air Force would not discuss in detail the last Atlas V mission's engine issue, citing proprietary supplier information, or say how close the launch came to failure.

They said investigation and testing resulted in a minor hardware change to the valve system that controls the mixture of kerosene fuel and liquid oxygen flowing through the Russian-made RD-180 engine.

“We’re very confident that we have the likely cause,” said Walt Lauderdale, the Air Force mission director. “Looking forward, we have high confidence for future missions.”

This launch had been planned for early May before the engine glitch occurred.

Atlas V ready for Friday flight from Cape Canaveral

The fifth MUOS satellite, like the first four, will bolster a constellation of six older satellites providing a network critical to forces from every service who are on the move and working in difficult terrain, from mountains to forests to dense city streets.

The new constellation eventually promises to expand the network’s capacity by 10 times and to deliver smart phone-like features. Mobile troops will be able to make clearer calls while simultaneously sending e-mails, texts or mission data, even when the users are not located beneath the same satellite.

But those improvements, which may start to be rolled out later this year, won’t be widely available until user radios are ready and deployed over the next year or two.

For those advanced features, the satellite launching Friday will serve as a spare in case another MUOS spacecraft runs into trouble.

“If anything were to happen to one of the four satellites in orbit, we will be prepared to maintain coverage around the world,” said Kan.

Contact Dean at 321-242-3668 orjdean@floridatoday.com.And follow on Twitter at@flatoday_jdeanand on Facebook atfacebook.com/jamesdeanspace.

Launch Friday

Mission: U.S. Navy’s fifth Mobile User Objective System communications satellite (MUOS-5)

Rocket: United Launch Alliance Atlas V 551

Launch Time: 10:30 a.m.

Launch Window: 44 minutes, to 11:14 a.m.

Launch Complex: 41 at Cape Canaveral Air Force Station

Weather: 80 percent “go”

Visit floridatoday.com at 9:30 a.m. for countdown chat and updates, including streaming of ULA’s launch Webcast starting 20 minutes before liftoff.