The upcoming demonstration of Boeing's heavy-lift Delta 4 rocket will feature a booster-separation event soon after liftoff and a long-duration main-engine burn during which the thrust will be throttled up, down and back up again.

Those are the major differences between the flight profile of the heavy-lift Delta 4 and the standard variant, said Dan Collins, vice president of Boeing Expendable Launch Systems of Huntington Beach, Calif. The heavy-lift vehicle, with three core stages in a side-by-side configuration, is designed to loft up to 13,000 kilograms to geosynchronous-transfer orbit, twice the capacity of its single-core cousin.

The demonstration flight, which will carry an instrumented payload to measure vehicle performance, is on track for Dec. 10 from Cape Canaveral Air Force Station, Fla., Collins said. "We are 70 to 80 percent confident" of that date, he said. "There's always the possibility we may find something that wasn't quite what we expected and could give us a little bit of a hiccup, but we're pretty good at working things out."

The Delta 4 rocket family was developed under the U.S. Air Force Evolved Expendable Launch Vehicle (EELV) program. Boeing has launched a medium-lift version of it three times, giving engineers good data on the performance of the vehicle's RS-68 core-stage engine -- the first large, liquid-fueled rocket engine developed in the United States in more than 20 years, Collins said.

"We have a good idea after three launches of how the common booster cores will react," Collins said.

The two strap-on booster cores will be jettisoned about 100 seconds into the mission, Collins said. The engine in the center booster core, which supports the vehicle's upper stage and payload, will be throttled down for the separation event and then powered back up to fire for another 100 seconds, he said.

The center core's RS-68 will burn for a total of about 330 seconds, about 70 seconds longer than the engine fired during previous flights, Collins said. The mission also marks the debut of Boeing's 5-meter fairing, he said.

The Air Force and Boeing will review the data gathered by the satellite in preparation for the first Air Force launch, a Defense Support Program missile warning satellite scheduled for fall 2005, Collins said.

"We've given ourselves plenty of time to make the normal types of adjustments you would see after a first flight," Collins said. "I think with a successful payload separation of [the demonstration satellite], there will not be any issue with launching" the Defense Support Program satellite.

The Air Force is paying Boeing between $140 million and $170 million for the demonstration mission, according to the U.S. Federal Aviation Administration's Office of Commercial Space Transportation. Collins would not confirm the price of the launch.

The heavy-lift Delta 4 was designed primarily for lofting large U.S. military payloads into orbit, but Boeing remains hopeful that other markets will develop.

The commercial market for the EELV rockets as a whole has collapsed, and the heavy-lift vehicles were designed mainly with the Air Force in mind, said Phil McAlister, program manager for the space and telecommunications industry analysis unit at Bethesda, Md.-based Futron Corp.

"On the commercial side, there is no demand for a big launcher right now or in the next five years," McAlister said. "None of the private-equity guys [who have purchased several large commercial satellite operators] are looking at monster satellites, especially if the only ride is on a relatively unproven rocket.

"Collins said the most likely market for the heavy-lift Delta 4 outside the Air Force is NASA's new space exploration initiative, which is targeting manned missions to the moon by 2020 and eventually missions to Mars.

"As NASA looks toward their exploration initiatives, here's a heavy-lift vehicle that will be flight proven," Collins said. "When looking at program as complex as the exploration program is going to be, to know that you're starting from a foundation that isn't a paper rocket, but has flown successfully, just brings a lot of confidence."

"NASA and the moon and Mars missions are the wild card," McAlister said. "Nobody knows how to handicap the market right now, but it's something everybody is looking at."