With White House approval secured, NASA is set to unveil a long-awaited human space exploration roadmap that calls for landing four astronauts on the Moon by 2018.

NASA intends to spend $100 billion and the next 12 years building the spacecraft and rockets needed to accomplish that feat, a critical first excursion in what the U.S. space agency envisions as a sustained space exploration campaign meant to lead mankind to Mars and destinations beyond.

The exploration plan is set to be unveiled Sept. 19 by NASA Administrator Mike Griffin at a press conference in the auditorium at the agency’s headquarters here. U.S. President George W. Bush appeared in the same setting in January 2004 when he called for the United States to return to the Moon by 2020 as the first major step in a broader space exploration vision aimed at extending the human presence throughout the solar system.

NASA has been working intensely since April on an exploration plan that entails building a 5.5-meter blunt body crew capsule and launchers built from major space shuttle components including the main engines, solid rocket boosters and massive external fuel tanks.

That plan, called the Exploration Systems Architecture Study, was presented by Griffin, his space operations chief Bill Gerstenmaier and several other senior agency officials Sept. 14 to senior White House policy personnel, including an adviser to Vice President Dick Cheney and the president’s Deputy National Security Adviser J.D. Crouch.

NASA’s plan, according to official briefing charts obtained by Space News, envisions beginning a sustained lunar exploration campaign in 2018 by landing four astronauts on the Moon for a seven-day stay.

The mission would begin, these charts show, by launching the lunar lander and Earth departure stage (essentially a giant propulsion module) on a heavy-lift launch vehicle that would be lifted into orbit by five space shuttle main engines and a pair of five-segment shuttle solid rocket boosters.

Once the Earth departure stage and lunar lander are safely in orbit, NASA would launch the Crew Exploration Vehicle capsule atop a new launcher built from a four-segment shuttle solid rocket booster and an upper stage powered by a single space shuttle main engine.

The CEV would then dock with an expendable lunar lander and Earth departure stage and begin its several-day journey to the Moon.

NASA’s plan envisions being able to land four-person human crews anywhere on the Moon’s surface and to eventually use the system to transport crew members to and from a lunar outpost that it would consider building on the lunar south pole, according to the charts, because of the regions elevated quantities of hydrogen and possibly water ice.

If NASA’s plan bears a close resemblance to the approach the United States took during the Apollo Moon program more than 30 years ago, space agency officials say that is because the physics of spaceflight have not changed since then. While the overall approach has much in common with Apollo, NASA officials and others familiar with the plan said it represents significant advances over Apollo.

According to NASA’s briefing charts, these include: double the number of crew to the surface, four times the number of lunar surface crew-hours, the ability to land anywhere on the Moon and return at any time, and a significant improvement on overall safety and reliability.

One of NASA’s reasons for going back to the Moon is to demonstrate that astronauts can essentially “live off the land” by using lunar resources to produce potable water, fuel and other valuable commodities. Such capabilities are considered extremely important to human expeditions to Mars which, because of the distances involved, would be much longer missions entailing a minimum of 500 days spent on the planet’s surface.

NASA’s Crew Exploration Vehicle is expected to cost $5.5 billion to develop and the Crew Launch Vehicle another $4.5 billion, according to sources knowledgeable about the plan. The heavy-lift launcher, which would be capable of lofting 125 metric tons of payload, is expected to cost between $5 billion and $10 billion to develop, according to these sources.

Two industry teams, one led by Lockheed Martin and the other by Northrop Grumman, are competing for a contract to build the CEV. NASA expects to select one team in April 2006 as a prime contractor.

NASA’s plan also calls for using the Crew Exploration Vehicle, equipped with as many as six seats, to transport astronauts to and from the international space station. An unmanned version of the Crew Exploration Vehicle could be used to deliver a limited amount of cargo to the space station.

The Crew Exploration Vehicle, NASA and other source said, will touch down on land with the aid of parachutes and airbags and will be capable of being reused as many as 10 times with refurbishment that includes replacing the capsules’ ablative heat shields.

For trips to the space station and back from the Moon, the Crew Exploration Vehicle will be propelled by pressure-fed liquid oxygen- and methane-burning engines that NASA and industry will have to develop. The Crew Launch Vehicle will require development of a new liquid oxygen- and liquid hydrogen-fueled upper stage that, according to NASA’s plans, will be powered by a single space shuttle main engine that will have to be modified to start in mid-flight.

NASA would like to field the Crew Exploration Vehicle by 2011 — about a year after it plans to fly the space shuttle for the last time. Development of the heavy-lift launcher, lunar lander and Earth departure stage would begin in 2011. By that time, according to NASA’s charts, the space agency would expect to be spending $7 billion a year on its exploration efforts, a figure projected to grow to more than $15 billion a year by 2018, the date NASA has targeted for its first human lunar landing since Apollo 17 in 1972.

Brian Berger is editor in chief of SpaceNews.com and the SpaceNews magazine. He joined SpaceNews.com in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...