Heavy-duty Delta 4 rockets now stand atop the nation's two launch pads in Florida and California for vitally important missions carrying clandestine spy satellites.

File image of a Delta 4-Heavy rocket launch. Credit: Pat Corkery/United Launch Alliance

The back-to-back launches are targeted for October 19 from Cape Canaveral Air Force Station and January 15 from Vandenberg Air Force Base.

Although the identities of both payloads are hush-hush, analysts are assessing what each satellite will do.

Experts widely believe the Florida rocket is deploying the next high-flying eavesdropping spacecraft to intercept communications for national security. The West Coast launch will place a telescope-like imaging craft into orbit.

The flights come with official designations of NROL-32 and NROL-49, respectively, since their customer is the National Reconnaissance Office. The agency is responsible for flying the country's fleet of intelligence-gathering satellites.

United Launch Alliance's Delta 4 rocket program, which took flight in November 2002, has performed 13 missions to date. Three of those launches used the massive Heavy configuration capable of lofting the biggest and heftiest cargos.

The Delta 4-Heavy is America's largest unmanned rocket currently in service. 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-body rocket, and then adding an upper stage.

After a demonstration test flight in December 2004, the first operational mission in November 2007 delivered a missile-warning satellite for the U.S. military. The NRO's first use of the vehicle came in January 2009 and orbited a geosynchronous eavesdropper.

The two upcoming Heavy rockets carry with them new satellites considered critical to the intelligence community, experts say.

"NROL-32 likely consists of sensitive radio receivers and an antenna perhaps 100 meters (328 feet) in diameter, used to gather electronic intelligence for the National Security Agency. The upcoming launch may replace one of the older spacecraft in the series, or augment the fleet by occupying a new location in geosynchronous orbit," said Ted Molczan, a respected sky-watcher who keeps tabs on orbiting satellites.

There's always a chance the educated speculation about the payload for NROL-32 could be overturned by a surprise spacecraft. Time will tell.

"It is generally accepted that NROL-49 is an electro-optical imaging intelligence satellite of the KH-11 lineage, which were built by Lockheed Martin," Molczan also said.

Although NRO satellites are supposed to be secretive, the spacecraft are visible to anyone looking up. Molczan is member of a hobbyist group that routinely finds and watches the craft while monitoring the skies with remarkable precision.

The California liftoff early next year marks the Heavy's debut from the West Coast, something that has required extensive modifications to the Space Launch Complex 6 pad. The rocket was erected in late January in preparation for several fueling tests and countdown rehearsals to work out any bugs.

The Florida team, already seasoned with the three previous Heavy missions, rolled out the launcher for October's flight this week.

File image of a Delta 4-Heavy rocket arriving at launch pad 37B. Credit: Carleton Bailie/United Launch Alliance

Resting horizontally on its motorized transporter, the orange and white machine traveled from the assembly hangar to pad 37B yesterday afternoon, then spent the night waiting for a lift that it received this morning to stand upright on the launch table.

Delta 4-Heavy continues the tradition of hauling the nation's mega-buck reconnaissance birds that the now-retired Titan 4 rockets used to handle. The Air Force phased out the Titan a few years ago in favor of the modular designs offered by the Evolved Expendable Launch Vehicle program.

Smaller NRO satellites not requiring the triple-barrel power of the Heavy have flown four times on Medium versions of the Delta 4 and Atlas 5. The next one is planned for September 20 from Vandenberg using an Atlas with a big nose cone and no strap-on boosters.

The Atlas 5 family has another Medium-style NRO launch targeted for March from California and a Delta 4-Heavy featuring upgraded main engines flies for the first time next year from the Cape.