Preparations for the next launch of America's largest unmanned rocket are underway at Cape Canaveral's Complex 37 following the recent rollout of the Delta 4-Heavy vehicle from its assembly hangar.

Credit: Carleton Bailie for United Launch Alliance

Resting on its transporter, the mammoth orange and white rocket stretching about 170 feet in length emerged from the Horizontal Integration Facility on March 26 for the short drive to pad 37B.

The Heavy is the biggest booster -- in size and stature -- for the Air Force's Evolved Expendable Launch Vehicle family of rockets. It is capable of carrying the military's largest payloads that once relied upon the now-retired Titan rocket fleet.

The Delta 4-Heavy 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 arriving at the launch pad, technicians readied the rocket to be raised vertically. The pallets in which the rocket was cradled were tied down to the Fixed Pad Erector. The diesel-powered transporter used to drive the rocket to the pad then disengaged from the pallets and pulled away.

On March 27, the erector system and its hydraulic pistons lifted the rocket upright, putting the vehicle on the pad's launch table.

Several pages of photography are available:

• Panoramas inside the hangar
• Vehicle before rollout
• The trip to pad 37B
• Rocket goes vertical

Once the rocket was set, technicians could unhook the booster from the pallets. That allowed the erector, along with the pallets, to be lowered back to the ground. The transporter then returned to retrieve the pallets for reuse on another mission.

United Launch Alliance engineers will spend a few months putting the rocket and its systems through pre-flight tests. A highlight of the checkout period will be the countdown dress rehearsal that includes fully fueling the rocket with liquid hydrogen and liquid oxygen propellants.

Launch is targeted for July 25.

The U.S. Air Force is overseeing the flight, which is known as the NROL-26 mission. The rocket will deploy into space a classified satellite payload for the National Reconnaissance Office.

Earlier plans had called for a May 9 liftoff, but the launch date was pushed back at the request of the NRO customer, Air Force officials said.

This will be the third launch of the Delta 4-Heavy rocket. A test flight was conducted in December 2004, followed by the first operational launch last November that delivered a missile-warning satellite into orbit for the U.S. military.

After the NROL-26 mission is flown this summer, the Cape's Delta 4 team will ready a Medium version of the rocket for launch of the GOES-O civilian weather satellite. That launch is targeted for around November 5.

Those two launches are the only ones planned for the Delta 4 program in 2008. The classified NROL-25 mission from Vandenberg Air Force Base in California, which was once scheduled for August, has been postponed beyond this year, Air Force officials told Spaceflight Now. A new date for that NRO flight has not been established.