ATK Thiokol is preparing to begin work on a more powerful variant of the space shuttle solid-rocket motor it has long produced as part of a streamlined NASA exploration plan that would land astronauts on the Moon in early 2017, a year earlier than previously envisioned.

Thiokol is not yet under contract to design and build the five-segmented solid boosters NASA now plans to use on both its crew and lunar-cargo launchers. NASA announced in December, however, that it had selected the Promontory, Utah-based firm as prime contractor for the Crew Launch Vehicle's first stage. At the time, NASA still was planning to launch Moon- and space station-bound astronauts atop a rocket based on a modified version of the four-segmented booster that Thiokol has produced for the space shuttle for the past two decades.

Although NASA has yet to publicly unveil the details of the revised approach, dubbed "Lunar Sooner," internal documents obtained by Space News show that the agency's Exploration Systems Mission Directorate has laid out a program that would achieve the first human lunar landing since Apollo by March 2017--a full three years ahead of the 2020 date U.S. President George W. Bush set in announcing the exploration effort 2004. When it unveiled its lunar exploration implementation plan last year, NASA envisioned a 2018 landing date.

In order to minimize its long-term costs, NASA has since decided to reduce the amount of hardware development it intends to take on in the years ahead. Skipping the four-segmented solid rocket booster in favor of the five-segmented version is one example.

Another is the scuttling of plans to modify the space shuttle main engine to serve as the Crew Launch Vehicle's upper stage. NASA will instead go with an updated version of the Apollo-era J-2 engine, which NASA planned to develop anyway for the Earth departure stage of its unmanned, heavy-lift lunar cargo launcher. Because the J-2 is less powerful than the main engines that help lift the shuttle, NASA will pair it with a five-segmented solid-rocket booster to launch the astronaut-carrying Crew Exploration Vehicle (CEV) into orbit.

The CEV is targeted for a first flight in 2012, but that date is in question due to near-term budgetary pressures facing NASA. That, in turn, has implications for the Lunar Sooner plan.

"It's not clear yet whether the 2007 budget will allow a CEV by 2012," said John Logsdon, director of the Space Policy Institute at George Washington University here. "There is a complex interplay between the fiscal 2007 budget in particular, the date for initial CEV availability and the potential for accelerating return to the Moon."

Mike Hecker, director of the Constellation Program at NASA headquarters here, said in a Jan. 27 interview that the revised approach will lower the life cycle costs of the agency's exploration program, but noted that the near-term costs are essentially unchanged. The Constellation Program encompasses the hardware NASA must develop to return to the Moon.

Any costs associated with accelerating the five-segmented booster and modified J-2 development programs will be offset in part by dropping plans to develop a liquid-methane fueled engine for the CEV, Hecker said. "From a budget standpoint, it came up as a wash," he said. "We're not asking for more dollars."

Hecker said the new launcher approach also should not impact the CEV's schedule one way or the other, although he added that the analysis was ongoing.

While the White House and Congress hash out NASA's 2007 budget in the year ahead, companies like ATK Thiokol are standing by for marching orders.

Michael Kahn, ATK Thiokol's vice president of space launch systems, said the five-segmented booster for the Crew Launch Vehicle is not that much more complicated from a developmental standpoint than the four-segmented version.

Both efforts would require computer modeling and flight tests to certify that the booster works just as well as a single-stick core stage as it does in pairs strapped to either side of the shuttle. Similarly, Kahn said, either will require a different separation system than the one used to jettison spent shuttle boosters today.

But there are important differences, Kahn said. Upgrading the parachute-recovery system for the five-segment booster will be "a more significant modification because when it separates, it is going higher and faster" than the four-segment booster, he said.

In addition, the bigger booster will require a different nozzle and propellant-casting shape than the four-segmented booster, Kahn said.

ATK Thiokol ground tested a five-segment motor for NASA in October 2003. Although that development effort initially was undertaken as a potential space shuttle performance upgrade, Kahn said that by the time of the firing, the rationale for the test had changed to show that the existing booster's components had plenty of safety margin built in--enough to handle the additional thrust produced by the 135,000 kilograms of propellant the extra segment added.

Kahn said pairing a five-segment booster with an updated J-2 engine for the Crew Launch Vehicle is an approach that should prove more economical in the long haul than the previous plan. "Even though it's a little more challenging and costly upfront, in the long term it makes a lot of sense," he said.

Meanwhile, sources familiar with the Lunar Sooner plan said NASA and J-2 engine builder Pratt & Whitney Rocketdyne likely are facing a six-year modification effort. The J-2 has not flown since the 1970s, although its components have been pulled into other development efforts, including the linear aerospike engines for NASA's experimental X-33 rocket, which never got off the ground.

Pratt & Whitney Rocketdyne spokesman John Mitchell said Jan. 25 that officials with the DeSoto, Calif.-based company declined to talk about the status of the J-2, what has been done with it since the 1970s, or what would have to be done to get the engine ready to serve as the Crew Launch Vehicle's upper stage.