Dec. 6, 2004 — After months of delays for technical issues and a trio of hurricanes that blew through Central Florida in August and September, one of the biggest rockets ever built in the United States has been cleared for liftoff on Friday.

Aside from two tiny science satellites, there is nothing but dead weight sitting atop the Delta 4 Heavy, the latest incarnation of an expendable line of boosters manufactured by Boeing.

For all its time, trouble and multi-hundred-million-dollar investment, the Air Force will be flying a 6.5-ton dummy payload and two university-built experimental nanosatellites. The prime cargo, dubbed DemoSat, has no function other than to reach orbit.

The real purpose of the flight is to demonstrate that Boeing's new booster has the right stuff to carry expensive national security payloads to space.

"First and foremost (the goal) is to place the payload into its proper orbit," said Dan Collins, vice president of Boeing Expendable Launch Systems.

The rocket is based on Boeing's successful Delta 4 Medium booster, a design that debuted two years ago as the launcher for a European communications satellite. Two more successful missions occurred in 2003.

The Delta 4 family is built around common liquid hydrogen-burning boosters powered by a newly developed main engine built by Rocketdyne. The heavy-lift version of the rocket, which will be making its maiden flight, includes three of Boeing's so-called Common Booster Cores strapped together to form a triple body and a powerful upper-stage motor.

The rocket is almost 235 feet long, about 50 feet longer than a space shuttle.

Delta 4 Heavy is designed to carry 50,000 pounds into low-Earth orbit and about 29,000 pounds to geostationary orbit, an altitude used by communication satellites and other spacecraft that is about 22,300 miles above Earth. Spacecraft at this altitude basically can stay in a fixed position relative to the ground.

Together, the trio of boosters generate almost two million pounds of thrust at liftoff, with each rocket consuming about a ton of propellants per second, or about five tanker trailers' worth of fuel per minute.

While the Air Force views the rocket as a likely replacement for its retiring Titan 4 vehicles, NASA is considering Boeing's heavy-lifter for flying its next-generation space capsules to the International Space Station. Another option is Lockheed-Martin's biggest booster, the Atlas 5.