I was talking to a friend the morning the space shuttle Columbia exploded over the skies over Texas. We both felt that in the early hours after the disaster, at least, NASA had done a pretty good job of handling the crisis. But then he said something that made me think a little deeper about the role of PR in the disaster - not in handling it, but in creating it."Remember when President Kennedy told Americans he was going to put a man on the moon," he says. "Eight years later, we had a man on the moon. It was a remarkable achievement. But since then, what have we accomplished?" The question was interesting for its underlying assumptions. Because if you talk to serious scientists, many of them consider Neil Armstrong's stroll on the lunar surface little more than a publicity stunt. It focused popular attention on the nation's space program, it turned astronauts into heroes, and it enabled us to thumb our collective noses at the Russians, but it returned little in the way of meaningful new knowledge. Which, in turn, raises questions about the purpose of the space program. Does it exist to add to the sum of human comprehension, to expand scientific and medical knowledge, as well as our understanding of the universe in which we live? Or is it just a kind of national adventure, designed so ordinary Americans can bask in the heroism of a handful of astronauts? That's the next big question NASA will have to answer after it has dealt with the aftermath of this latest catastrophe. Space exploration has long been marketed as an adventure. Coverage of the space program often focuses on the human element - from high school teachers to wealthy individuals who want to buy their way on board the shuttle - perhaps at the expense of the real benefits, which are often more mundane and less telegenic. That's not to say there's no scientific benefit from manned space flight. But NASA needs to focus more energy on explaining the payoff from its efforts, detailing all the advances that have been made because of the space program. Such an effort was launched five or six years ago by a consortium of aerospace companies. Known as Mission HOME, it was supposed to explain how America - and the world - had benefited from space exploration. A Factiva search covering the past two years finds no mention of Mission HOME in major media. Now would be a good time for that effort to be revived, to focus on the substance rather than the sizzle of space, to make sure our expectations are more realistic, and our understanding of the value of exploration is more complete.