At the moment, two teams at the National Aeronautics and Space Administration are studying booster rocket design concepts.

One team, assembled by the space agency's Exploration Directorate, has been examining rocket designs from the top down, according to Michael Lembeck, who heads the directorate's Requirements Division.

At the same time, Lembeck explained, a second team at NASA's Launch Services group is conducting a bottoms-up review, meaning the services group, which purchases launch vehicles for NASA missions and payloads, is accumulating background on and analyses of all available U.S. boosters and their capabilities.

NASA is not yet wedded to any specific type of moon booster, either for the planned manned craft - called the Constellation Crew Exploration Vehicle - or the large cargo carrier that might be needed to support the moon landings and subsequent bases.

We have yet to develop an opinion on launch vehicles and continue to refine the requirements for launch systems before we look around to see what could fulfill those requirements, Lembeck told United Press International.

That opinion may be established by this fall, he said.

Along with the spacecraft it will carry aloft - the cargo or crew version - the principal driver of the booster's design will be the method by which it will fly from Earth to the moon.

Mission modes are influenced by the going-in constraints and not having a Saturn V class vehicle readily available is a new constraint, Lembeck said. It may influence the ultimate lunar architecture.

Whatever NASA decides, it will be worth billions of dollars in development contracts for the shrinking US launch industry.

That industry is vastly different from the time when NASA developed the Saturn family of launchers for Project Apollo four decades ago, however. Then, the huge Saturn V, standing 365 feet tall, could lift 250,000 pounds into Earth orbit and send nearly 100,000 pounds to the moon.

Today, NASA's largest rocket, the Boeing-built, Delta IV Heavy - which makes its maiden flight this fall - can lift 50,000 pounds into orbit. Right behind it is Lockheed Martin's Atlas V 500 series, which can launch about 45,000 pounds to orbit.

Both rockets are slightly more powerful than the Apollo Saturn IB, the smaller of Wernher Von Braun's Saturn series. The Saturn IB stood 224 feet tall, compared with Delta IV's 235 feet.

From 1961 to 1975, NASA launched 33 Saturn 1, IB, and V boosters with a 100 percent success rate.

The huge, heavy-lifting Saturn V represented a larger and perhaps healthier U.S. rocket industry. From tip to tip, the Apollo Saturns reflected many companies, several of which no longer exist as separate corporations.

For example, Apollo's emergency escape rocket was a product of Thiokol and Lockheed. The command and service modules were built by North American Rockwell. Grumman furnished the lunar lander.

Of the Saturn V's three stages, the third was built by McDonnell-Douglas, the second by North American, and the booster by Boeing. All three stages used engines built by Rocketdyne.

Since then, Rocketdyne, McDonnell-Douglas and North American have been absorbed by Boeing. Thiokol was acquired by Alliant Techsystems, and Northrop bought Grumman to become Northrop Grumman.

Lockheed, Martin Marietta and the rocket-making part of General Dynamics all merged into Lockheed Martin.

With all the changes and consolidations, the U.S. space propulsion industry has shrunk to the Rocketdyne part of Boeing; Pratt & Whitney, which provides engines for the Lockheed Martin Atlas V; ATK-Thiokol, which builds the boosters for the space shuttle, and Aerojet, which makes both solid and liquid rocket engines and motors.

Most rocket suppliers in the United States still in existence are affiliated with either Boeing's Delta launchers or Lockheed Martin's Atlas family.

NASA's new, moonbound space booster most likely will be a variation of the Delta or Atlas families or, perhaps, from the elements that have made up the space shuttles. The Exploration Directorate is studying how different parts of the shuttles could form an entirely new launcher for Constellation payloads or the CEV.

Planners are studying several alternatives. One uses a solid rocket booster adapted from the shuttle to lift the CEV, and an escape rocket similar to the one used in Apollo.

Another uses the shuttle's huge external fuel tank and attaches a new rocket stage on top to power Constellation cargo flights. Either an expendable variety of the shuttle's liquid engines, or engines adapted from the Delta boosters, might provide thrust to orbit.

Still another idea would employ both the tank and solid boosters along with a payload pod that replaces the winged shuttle orbiters. One advantage of adapting shuttle components, developers say, is reduced design costs and the availability of the shuttle's trained and experienced workforce.

Lembeck's task has been complicated by the aggressive schedule NASA wishes to follow in developing the CEV and the rocket to lift it. His team's planners are using guidelines that call for the final requirements for the crew vehicle to be completed this fall.

Those requirements will drive the detailed competition for the moonship's builders, which will begin when the Request for Proposals for the ship's design are issued early next year.

The types of rockets needed for the human-rated launcher and a heavy-lift vehicle are supposed to be finalized by the middle of next year and the two winning CEV designs should begin development by the fall.

The first stripped-down CEV is to be launched with a candidate booster rocket in 2008, and the two teams are to test their separate designs for the moonship and its launchers in a fly-off competition the same year.

By the third quarter of 2008, NASA plans to select a final design for the moon vehicle and its mission mode. First flight of the winning design without a crew should occur in 2014, and the first flight carrying astronauts is scheduled for 2015.

That puts the first possible landing on the moon with astronauts as early as 2015 -- but no later than 2020.

Despite their phenomenal success, Apollo-style boosters are unlikely this next time around, given the tight budget and timetable set by President George W. Bush last January.

Lembeck said NASA was making use of the surviving veterans of the Apollo design era in other ways, however. It is hoped Apollo's creators can provide an experienced review of whatever ideas the current generation of designers develops for the upcoming lunar missions - and the spacecraft that may, finally, resume the explorations that Apollo began.

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