HOUSTON -- Behind 18 inches of concrete in stainless steel cabinets flushed with pure nitrogen rests a material rarer than gold, more valuable than diamonds.
Not even NASA curator Gary Lofgren knows both combinations to the Johnson Space Center's vault that contains 600 pounds of lunar rocks and soil.
Of late, Lofgren has noticed something unusual - there's been a run on moon dirt. Gram by precious gram, he has been doling out samples to researchers around the world eager to study the desolate orb again.
Thirty-four years after the last Apollo astronaut walked on the lunar surface, a new space race is under way.
It will be a long race, with humans unlikely to set foot on the moon again in the next 10 to 15 years. But countries are gearing up to take their first steps.
India's 20,000 space workers are readying a lunar orbital mission set for 2007. Japan plans to send a robotic rover to the lifeless rock by 2013, and the European Space Agency has a probe, SMART-1, orbiting the moon.
Although many countries are talking about sending people to the moon, only two, the United States and China, have set dates for manned lunar landings. NASA says its next manned mission will be after 2018; China says it wants to land "taikonauts" - as Chinese astronauts are called - as early as 2017.
"There is a lunar armada" on the way back to the moon, said James B. Garvin, head of NASA's Lunar Reconnaissance Orbiter project, scheduled to lift off in 2008.
It's an unlikely renaissance of lunar exploration after decades of sending robots to distant planets while human explorers busied themselves building a space station in low-Earth orbit.
Each country is going for its own reasons - some commercial, some strategic, some for national pride. But if the plans come to fruition, the moon could become a busy extraterrestrial outpost for scientists, engineers and possibly ordinary citizens. It would also serve as a vital way station for man's long-dreamed-of trip to Mars.
Leading the way is the only country that has set foot there before, the United States.
In 2008, NASA will begin launching probes to search for landing sites and potential water sources at the moon's south pole. Work is under way on new lunar projects, including a souped-up rover and a $38-million project to extract breathable oxygen from moon dust.
All this has gotten NASA's work force, which has been demoralized by the frustrations and tragedies of the ill-fated space shuttle program, fired up in ways it hasn't been since the 1960s.
