WASHINGTON -- The U.S. Department of Defense has signed off on NASA's plan to use major space shuttle components as the basis for separate vehicles that will launch the agency's new crew transport and 100-ton loads of Moon-bound cargo.

The U.S. Space Transportation Policy issued by the White House in January requires NASA to coordinate its future launch vehicle plans with the Pentagon and submit a joint recommendation to the president on the nation's next heavy-lift rocket.

NASA Administrator Mike Griffin and U.S. Air Force Undersecretary Ronald Sega, the Pentagon's top space official, sent the White House a letter Aug. 5 outlining a joint strategy for the use and development of national launch systems. The letter, a copy of which was obtained by Space News, was addressed to John Marburger, director of the White House Office of Science and Technology Policy. Senior U.S. government officials copied on the letter include National Security Council Director Steve Hadley, Deputy Defense Secretary Gordon England, and White House Office of Management and Budget Director Josh Bolten.

The two-page letter says "NASA will initiate development of a Crew Launch Vehicle derived from Space Shuttle solid rocket boosters with a new upper-stage for human spaceflight missions in the 25-30 metric-ton-class following retirement of the Space Shuttle in 2010. NASA then plans to develop a new 100 metric-ton-class launch vehicle derived from existing capabilities with the Space Shuttle external tanks and solid rocket boosters for future missions to the Moon."

The letter also says NASA and the Pentagon will use the Atlas 5 and Delta 4 rockets developed under the U.S. Air Force's Evolved Expendable Launch Vehicle (EELV) program "for all intermediate and larger payloads for national security, civil, science, and International Space Station cargo re-supply missions in the 5-20 metric-ton-class to the maximum extent possible."

The letter further noted that new commercially developed launchers, should they become available, will be allowed to compete for such missions.

NASA and the Pentagon, according to the letter, have agreed to complete a joint cost benefit analysis in the coming months of phasing out Boeing's Delta 2 rocket in favor of the EELV. Although the Air Force has largely moved on to the EELV, the smaller Delta 2 remains NASA's workhorse for launching medium-sized science satellites and interplanetary probes.

Also according to the letter, the Pentagon will consider using NASA's proposed heavy-lift launcher for any future military missions that might require such a powerful rocket. But it is unlikely, the letter says, that the Pentagon would endorse a shuttle-derived vehicle as an EELV back-up "due to the significant risk, reliability, and cost of modifications required to [Defense Department] satellites and infrastructure."