NASA engineers are hard at work on a lunar spacecraftexpected to be the first in a wave of robotic probes that will pave the way forfuture human missions.

The spacecraft, called the Lunar ReconnaissanceOrbiter (LRO), is the first mission out of the gate under NASAs space vision ofsending more robot and human explorers beyond Earth orbit.

This mission is the first concrete step in layingthe groundwork for humans to go back to the moon, said Jim Garvin, the leadscientist for moon and Mars exploration at NASA headquarters in Washington. Sotheres a lot resting on its shoulders.

Set for a 2008 launch, the probe is expected tocircle the moon for at least one year and return detailed maps of the lunarsurface, data on the moons radiation levels and an in-depth look at its polarregions for resources that could be tapped by future astronauts.

But everything is still on paper, and projectengineers have a narrow window in which to design, build and integrate thespacecraft to meet their intended launch date.

Engineers at NASAs Goddard Space Flight Center inGreenbelt, Md., are designing the actual spacecraft bus, while the instrumentpayload will be provided by private industry. An Acquisition of Opportunity forthe payload was announced June 18 and a final design is expected to be in handin November.

This is certainly a quick development mission,Garvin said in a telephone interview. Theres not a lot of time to generate ahigh-reliability flight mission.

Exactly how LRO will make its moon measurements isstill an unknown, though mission planners can envision a number of routesprivate payload designers might take.

This is not a science mission, its a measurementmission, Garvin said. For example, we dont have any lunar maps at the scaleof a landing site since the Apollo missions, but there are a variety of ways tomake them.

LROs topographic map-making instruments may includeone or more of the following: conventional radar, laser-based range systems likeLight Detection and Ranging, or a system known as synthetic aperture radar thatcombines radar measurements with computer analysis to make detailedmeasurements.

High-resolution cameras similar to those used in theone-meter resolution Ikonos satellites owned by Space Imaging Inc. will berequired to photograph the lunar surface. Part of LROs mission is to identifypotential landing sites for future missions and any nearby hazards, such asboulders, which could shift and knock a lander or human down, Garvinsaid.

LROs imaging system also is expected to be able tolook into permanently shadowed regions of the moon and its polar regions to lookfor signs of large water ice deposits on the scale of football fields thatcould be viable resources in future missions.

A critical part of any prolonged human stay on themoon is the amount of radiation astronauts will be subject to during a mission.LROs instrument set also should be able to determine the biological effects ofthat lunar radiation environment.

Jim Watzin, lunar exploration program manager atNASAs Goddard Spaceflight Center, said NASA engineers have already begunpreliminary design work on the spacecraft.

Even without a final payload in hand, Goddardengineers have been able to define some of the parameters their spacecraft mustmeet.

Since time is of the essence, LRO will make use ofconventional technology instead of untested tools. That means a chemical-fueledrocket will push the spacecraft moonward as opposed to more exotic approaches,such as an ion engine or other propulsion methods.

A conventional approach also keeps costs down, animportant point since the missions total budget from development throughfirst-year operations is set at about $90 million.

Were constrained to be a Discovery class [mission]in cost, so we have to limit ourselves to a Delta 2 launch vehicle, Watzinsaid.

Because of that rocket limitation, project engineersknow their final spacecraft must weigh about 1,000 kilograms (2,200 pounds),half of which will be propellant to not only push LRO to the moon, but keep itin the proper lunar orbit once it arrives, Watzin said. And because thespacecraft will be making detailed maps from an altitude of about 50 kilometers(31 miles), LRO will need to be able to accurately point itself in anydirection, he added.

The spacecraft will also require a robust power andcommunications system to relay large amounts of data to Earth and sustain itsscience instruments.

Were pushing the spacecraft design as far as we cango knowing, in general, what the capabilities it needs and having some idea onthe classes of instruments it will have, LRO project manager Craig Tooley saidin a telephone interview.

Lunar pathfinder

The future of NASAs lunar exploration exploits mayride heavily on the data LRO sends back to Earth.

If LROs lunar maps point out an obvious point ofinterest on the surface, the space agency may choose a robot lander mission todrop on the area for a more detailed study. A second possibility would be asecond orbiter, armed with more science instruments, to conduct morereconnaissance.

The early months of [LRO] would target things thatthe second mission would follow in this lunar robotic program, Garvin said.But were talking about moderate-class missions here, not billion-dollar,100-yard wandering rovers.