The United States has launched a vast reconnaissance satellite reputed to be the largest eavesdropping device ever sent into space. The largest unmanned American launch vehicle, the Delta-4 Heavy rocket, roared into the the night sky in Cape Canaveral, Florida on Sunday carrying the mysterious satellite on a mission, dubbed NROL-32.

The National Reconnaissance Office did not disclose the purpose of the satellite but widespread reports in the US media suggest it is for eavesdropping on enemy communications.

"This second Delta IV Heavy launch for the NRO is the culmination of years of hard work and dedication by the combined NRO, air force, supplier and ULA team," United Launch Alliance vice-president Jim Sponnick said.

"ULA is pleased to support the NRO as it protects our nation's security and supports our warriors defending our nation around the world."

It was only the fourth time the Delta-4 Heavy - the most powerful liquid-fuelled rocket booster with a massive two million pounds of thrust - has flown.

The launch of the NROL-32 had been moved back from October 19 due to delays for undisclosed reasons.

One cannot overstate the importance of Friday night's Delta 4-Heavy launch from Cape Canaveral to national security, a mission by the massive rocket that will deploy "the largest satellite in the world" to hear the whispers of evil.

United Launch Alliance's Delta 4-Heavy is America's biggest unmanned rocket currently in service, capable of lofting the largest and heftiest cargos. The mammoth vehicle is created by taking three Common Booster Cores -- the liquid hydrogen-fueled motor that forms a Delta 4-Medium's first stage -- and strapping them together to form a triple-barrel rocket, and then adding an upper stage.

The nighttime blastoff should be visually spectacular, lighting up the Space Coast with three distinct pillars of fire from the main engines trailing more than 200 feet long. Ideal viewing spots include off SR401 at Port Canaveral, along the 528 causeway or on the riverbanks in Titusville.

Thundering eastward across the open Atlantic, the rocket will soar out of sight within a few minutes as it embarks on a multi-hour mission to serve the U.S. National Reconnaissance Office, the agency responsible for the country's fleet of intelligence-gathering satellites.

The NRO's diverse spacecraft, including telescope-like observers and communications collectors, uncover looming dangers to the nation and provide surveillance over the world's hot spots.

"Always vigilant, the NRO's eyes and ears give America's policy markers, intelligence analysts, warfighters and homeland security specialists the critical information they need to keep America safe, secure and free," the agency says.

The clandestine payload going up this time, known only by its launch identification number of NROL-32, is widely believed to be an essential eavesdropping spacecraft that requires the powerful lift provided by the Delta 4-Heavy to reach its listening post.

In an address to the Air Force Association conference in September, NRO Director Bruce Carlson, a retired Air Force general, said this rocket launch would carry "the largest satellite in the world on it."

The NRO has flown various types of communication-interceptors since the dawn of the space age, and analysts say it is virtually certain this Delta 4-Heavy is hauling another.

"I believe the payload is the fifth in the series of what we call Mentor spacecraft, a.k.a. Advanced Orion, which gather signals intelligence from inclined geosynchronous orbits. They are among the largest satellites ever deployed," said Ted Molczan, a respected sky-watcher who keeps tabs on orbiting spacecraft.

Destined for geosynchronous orbit 22,300 miles above the planet, this new spacecraft supposedly will unfurl an extremely lightweight but gigantically huge umbrella-like antenna to overhear enemy communications and aid U.S. intelligence.

"The satellite likely consists of sensitive radio receivers and an antenna generally believed to span up to 100 meters (328 feet) to gather electronic intelligence for the National Security Agency," Molczan said.

Observers think the mesh antenna's diameter is the size of a football field, comparable to the International Space Station's remarkable width. That explains why satellite-tracking hobbyists say these Mentor craft are "by far the brightest" in the high-flying geosynchronous orbital perch to see from the ground, outshining conventional television relay birds, weather sentinels and the like.

Although NRO satellites are secretive by nature, the spacecraft are visible by just looking up. Molczan is member of a hobbyist group that routinely finds and watches the craft while monitoring the skies with precision.

But despite the identity of this particular satellite being obvious, exactly where in the geosynchronous belt it will be positioned and what part of the globe it will cover are details that remain hush-hush.