CAPE CANAVERAL, Fla. -

A Delta IV rocket carrying a spy satellite launched into space from Cape Canaveral on Friday morning after being delayed three times.

[PHOTOS: Delta IV rocket launches into space]

The rocket launched at 9:15 a.m., more than three hours after the initial launch time.

The initial launch time of 6:13 a.m. was pushed back when an alarm was triggered by an incorrect battery voltage reading while the countdown clock was at T-minus 3 minutes, 44 seconds.

The second and third delays were prompted when a drain valve did not close properly.

The nation’s most powerful rocket blasted off with a little added oomph.  The liftoff of United Launch Alliance’s 232-foot Delta IV heavy rocket was the first by upgraded engines powering each of the rocket’s three first-stage boosters.

“We’re getting more miles per gallon and more thrust overall due to these improvements,” said Steve Bouley, vice president of launch vehicle and hypersonic systems for engine maker Pratt & Whitney Rocketdyne.

A question officials involved in the National Reconnaissance Office mission won’t discuss is why the extra performance is needed.

One theory holds that the payload could be the last of a Cold War-era program of stealth imaging satellites designed to disguise their location, and could include a decoy sent to a different orbit.

Ted Molczan, an amateur astronomer who specializes in tracking secret payloads, says clues point to launch of a third “Misty” satellite, as the program came to be known.

Molczan believes the mission was once slated for an earlier-generation rocket that would have placed the satellite in low Earth orbit, and that the heavy-lift Delta IV’s extra power will help send a decoy to a higher orbit.

The first two launches of Misty satellites — on the shuttle in 1990 and on a Titan IVB from California in 1999 — both employed deception tactics that hobbyists later figured out.

The exposure in 2002 of the second mission’s decoy “may have provided some of the motivation to enhance the ruse” on a third launch, Molczan wrote in a post on the “SeeSat” listserv.

“There are less demanding options that do not involve the use of a decoy, but the ruse probably would be far less convincing,” he wrote.

But Jeffrey Richelson, who reported details about the Misty program in his 2001 book, “The Wizards of Langley: Inside The CIA’s Directorate of Science and Technology,” doubts Molczan is right.

Richelson believes the Misty program was canceled after 2005, before a third spacecraft was ever built. Lawmakers questioned the benefits the stealth technology provided and the vehicle’s staggering cost — reportedly nearly $10 billion.

“Even for spy satellites, that’s a lot,” said Richelson, a Los Angeles-based senior fellow at the National Security Archive.

Richelson suspects the upcoming mission involves a heavier signals intelligence satellite bound for an orbit roughly 22,000 miles above Earth, where it could intercept voice communications or telemetry from missile tests.

Work to upgrade the RS-68 main engines flown by Delta IV rockets began in 2006.

That year, a RAND Corp. report noted that the Delta IV Heavy needed the performance improvement for a single NRO mission then expected to launch before 2010. It estimated the upgrades would cost around $200 million.

Whatever this mission’s purpose, the rocket’s three RS-68A main engines fired with 702,000 pounds of thrust, nearly 40,000 pounds more than the original engine. The extra power enables the rocket to lift over 1,000 pounds more payload to high orbits, according to ULA.

Launch viewers didn't notice the difference, but engine designers likely felt great satisfaction watching the world’s most powerful liquid hydrogen-fueled engines take flight.

“When it’s a first-of-a-kind launch, it carries even a little bit more something special to it,” Bouley said. “There’s always some degree of risk associated with changes, but there’s a benefit and a gain from that, and so to watch the first and see it operate successfully is truly a great thing.”