Should the U.S. halt human space flight? The Columbia accident has revived the debate on whether the rewards of human space exploration are worth the risks.

YES Anything we want to do in space we can do more efficiently, more economically, and more safely with automated spacecraft than with astronauts. It is now impractical and unsafe to send humans into space.

The space shuttle is the world's most sophisticated launch vehicle, but also the most expensive, the most fragile, and the most unreliable. Seven astronauts died in the Columbia accident and another seven died when the Challenger exploded in 1986. The shuttle will never achieve the vision of sending humans to Mars.

Whatever we are trying to do in space costs 10 times as much if we send astronauts along for the ride. The primary mission of all human space flight is getting the crew back alive, and so we burden the spacecraft with life-support equipment and we limit where it can go. Nothing that astronauts contribute can compensate for the weight and safety penalties imposed as a result.

For the past 25 years, NASA has been trying to re-create the golden age of the Apollo program, which aimed to send a man to the moon--and did so six times between 1969 and 1972.

Since then, the world has undergone a computer revolution.

Technology has taken over many human activities on Earth, from manufacturing to surgery. Only the space program--supposedly the center of our most visionary science and technology--remains wedded to the idea of keeping people in jobs that machines do better. NASA should turn its considerable talents to developing a safer and more reliable launch vehicle. Until then, we should stop risking people's lives by sending them into space.

NO I was a teacher when men first landed on the moon in 1969, and I remember how it moved my students and this country. It is now more than 30 years since the last American left the surface of the moon and returned to Earth. And we haven't ventured outward since then. That's 30 years too long! America's human space-flight program is adrift, with no clear vision or goals beyond the completion of the International Space Station.

I want NASA to establish a phased series of goals over the next 20 years, including human visits to asteroids that cross the Earth's orbit, establishing a research and living facility for humans on the moon, and human expeditions to the surface of Mars and its moons. Astronauts are key to this expanded exploration.

An astronaut is today's Christopher Columbus, who sailed into the unknown and discovered the Americas. The knowledge we gain from having actual people exploring can never be replaced by robots. Our ability to send humans into space and have them return gives us amazing information about ourselves and our universe. Robots are useful, but humans can do things that robots can't.

The real obstacle we face in overcoming the drift in the nation's human space-flight program is not technological and it's not financial--it's the lack of commitment to get started.

The lesson from the Columbia accident is not that humans don't belong in space. Instead, we should honor the memory of the lost astronauts by pushing our exploration of space further.