It's as though time has stood still on the Moon--and also in the human space exploration program. "In the past 30 years, no human being has set foot on another world or ventured farther up into space than 386 miles, roughly the distance from Washington, D.C., to Boston, Massachusetts," President George W. Bush said in announcing a major U.S. space initiative on January 14. Soon, though, he vowed, humans will head "into the cosmos"; his new space policy calls for sending astronauts back to the Moon by 2020. Exactly how they will get there remains to be seen, but many experts agree on one thing: Like those footprints on the Moon, the technology of human spaceflight has changed surprisingly little in 30 years. Improvements in materials, electronics and solar power have made spacecraft lighter, smarter and more energy efficient than in the Apollo days, but with few major advances in propulsion technology since the advent of chemical rocket engines powered by cryogenic liquid fuels, human spaceflight isn't significantly faster or cheaper than it was in the 1970s.