Although Boeing and Lockheed Martin plan to combine production of their respective Delta 4 and Atlas 5 rockets in the near future, for now the companies are pushing separate solutions based on those vehicles to help NASA achieve its goal of returning astronauts to the Moon by 2020.

The U.S. Air Force spent a decade and well over $1 billion developing the Delta 4 and Atlas 5 under its Evolved Expendable Launch Vehicle (EELV) program, and the White House and Department of Defense want NASA to leverage that investment in carrying out U.S. President George W. Bush's vision for space exploration. The alternative is a vehicle that uses the propulsion elements of NASA's space shuttle orbiter - its main engines, solid-rocket boosters and giant external tank.

Both companies would have a major role if NASA ultimately selects a shuttle-derived vehicle to meet its anticipated launch needs, as would ATK Alliant Techsystems of Edina, Minn., builder of the solid-rocket boosters. But for Boeing's Delta 4 team and their counterparts at Lockheed Martin, the focus is on finding a stable government customer for the EELV besides the Air Force, which is straining to keep both rockets in service.

"Lockheed Martin is a full participant in the shuttle-derived industry team and we also have the Atlas 5. We will be participating either way," said George Sowers, director of advanced programs and strategic development for space transportation at Lockheed Martin Space Systems of Denver. "As the Atlas 5 advocate, which I am, we think there are advantages to the EELV-derived solution. One of them is commonality with what the Air Force uses."

Both Lockheed Martin and Boeing officials stress sharing the cost of launch infrastructure with the Air Force as one of the big advantages of EELV-derived solutions. That position is shared by White House officials who crafted a U.S. space transportation policy that nudges NASA toward using the EELV for its future launch needs, which include placing some 100 metric tons of hardware into Earth orbit for lunar missions. The policy, released in January, also bumps the decision for meeting that heavy-lift requirement up to the White House and directs NASA and the Pentagon to come together on a joint recommendation.

U.S. Defense Secretary Donald Rumsfeld and NASA Administrator Mike Griffin are expected to meet toward the end of June and Washington sources say the agenda is devoted to that very issue.

Griffin has not stated publicly a preference for using EELV versus shuttle hardware to launch the planned Crew Exploration Vehicle (CEV), which will replace the space shuttle orbiter as NASA's human space transportation system. But he has said on numerous occasions that he favors a shuttle-derived vehicle for the heavy-lift requirement associated with Moon missions.

Griffin is slated to receive before the end of the month the results of a 60-day exploration systems study that will recommend an overall approach to going back to the Moon as well as the kind of CEV and launch vehicles need to support that approach. But lunar expeditions are not the only factors to be considered as NASA mulls its launch options: Griffin also plans to use the CEV to ferry astronauts to and from the international space station as soon as possible after the space shuttle fleet is retired in 2010.

The range of Atlas 5 and Delta 4 modifications required to support NASA's anticipated needs run the gamut from the addition of crew safety systems for CEV missions to the development of what in effect would be next-generation vehicles rivaling or even surpassing the lift capacity of the Apollo-era Saturn 5 rocket. Everything will depend on decisions NASA has yet to make about the CEV itself and the agency's overall approach to lunar exploration.

"At one point the CEV was 20 metric tons," said Jim Harvey, director of advanced NASA programs at Boeing Launch Services of Huntington Beach, Calif. The current heavy-lift variant of the Delta 4, known as Delta 4 Heavy, could handle such a vehicle, he said.

"When you start talking 25-30 metric tons, we find ourselves being one upgrade away from meeting that requirement," Harvey said.

The "most straightforward approach" to boosting the Delta 4-Heavy's performance would be to add six solid-rocket strap-on boosters, Harvey said. But given that some NASA officials are less than enthusiastic about adding a half-dozen solids to a rocket launching humans, Boeing has done extensive analysis of two other upgrade options: modifying the Delta 4's upper stage or upgrading the RS-68 engines that power the rocket's main stage.

The Delta 4's upper stage is powered by a single RL10 engine capable of producing 22,000 pounds of thrust. Harvey said a Delta 4-Heavy could lift a 25-30 metric ton CEV with a new upper stage that uses three RL10 engines or one of the 60,000-pound-thrust engines that Boeing has on the drawing boards. Alternatively, Boeing could replace the RS-68 main engine's ablative nozzle with a lighter-weight regenerative nozzle to get the performance boost needed for the CEV mission.

With solid boosters and modifications to both the main engine and upper stage, Harvey said, the Delta 4-Heavy could deliver about 50 tons to low Earth orbit. Getting above 50 metric tons would require much more extensive modifications and a new launch pad and infrastructure. Getting above 100 metric tons would require building what Boeing considers a next-generation Delta with bigger engines and a wider first stage, which would require new production facilities.

Harvey acknowledged that the expense of such an approach would be substantial and likely NASA's alone to bear. "The reason we prefer enhancing the existing heavy is that it takes advantage of existing infrastructure, which is a very big part of the cost," he said.

Lockheed Martin also would have to build essentially a new rocket and launch pad to be able to launch over 100 metric tons to low Earth orbit. So Lockheed Martin Atlas 5 officials, like their Boeing counterparts, think NASA would be better off using multiple launches to lift its Moon-bound payloads and then assemble the hardware in orbit.

A shuttle-derived vehicle, on the other hand, could loft 100 metric tons in a single launch.

Lockheed's Sowers said the current heavy-lift variant of the Atlas 5 - which has been designed but not built - lends itself to upgrades to meet NASA human and cargo launch needs. With a wider Centaur upper stage outfitted with one or more RL10 engines, the Atlas 5 could lift the 25-30 metric ton CEV. By combining the wider Centaur with a wider main stage, the Atlas 5 could lift 70-80 tons of payload and still operate out of its existing launch facilities, he said.

"This is the option we've told NASA is the most attractive for human space flight because it's the simplest," Sowers said. "It's two stages to orbit, it's all liquid so you don't have the catastrophic failure modes and it has engine out capability. It comes the closest to meeting the exact letter of the human rating requirements of anything I've seen."

Sowers acknowledged that NASA appears to be heading toward a shuttle-derived solution for its heavy-lift needs but said it is possible that the agency will take a mixed fleet approach, using an EELV-derived system for some missions and the shuttle-based system for others.

Either way, Sowers said he hopes NASA won't make a final decision without opening it up to a competition.

"Normally when a government agency has multiple good answers, and I think that is the case here, the way to get the best value is to compete it," Sowers said. "But that's a personal opinion."

Neither Sowers nor Harvey would discuss cost estimates associated with the various upgrade options for the Atlas 5 and Delta 4. Alliant Techsystems, which has the most to lose if NASA opts for an EELV-based solution, similarly will not divulge cost estimates for vehicles based on space shuttle propulsion hardware.