NASA HAD no choice but to suspend indefinitely any more shuttle flights after it discovered during Discovery's takeoff Tuesday that the agency had not solved the deadly problem of foam insulation debris falling off the external fuel tank. The more difficult issue is what this latest mishap means for both the future of the shuttle and for President Bush's plan to send astronauts to the moon and Mars.
While manned space exploration should continue to be a long-term goal of American science, the failure of the shuttle program argues strongly for concentrating on Mars robotic rovers, the space probes, and the Hubble space telescope, which are providing a wealth of new information about Earth's planetary neighbors and the universe.
The shuttle never met expectations. Even apart from the two fatal accidents and this week's revelation that only luck kept a piece of debris from damaging Discovery's heat-shield tiles --as with Columbia in 2003 -- the shuttle failed to deliver on the original vision: a low-cost, reusable means of transportation to the space station and a lab for experiments in a gravity-free environment.
After the Columbia catastrophe, a board of inquiry faulted NASA for treating the shuttle as though it had become a reliable space 747 instead of a work in progress, which it was then and still is. NASA engineers' inability to solve the falling debris problem after more than two years and hundreds of millions of dollars is a strong argument for dropping the shuttle program completely.
The Russians' Soyuz vehicles can be relied on to keep the space station in service, as long as international scientists believe there is genuinely worthwhile work to be done on it. Without the larger shuttles as transports to the station, it would be impossible to expand it to the dimensions originally planned.
In 2004, President Bush announced a goal of sending astronauts first to the moon and then to Mars. The risk is that funding for this would leave too little money for the unmanned projects to Mars and deep space that have proven so productive scientifically.
More unmanned rovers on Mars might help lay the base for a decades-off flight to the planet by astronauts. Some scientists believe it would make sense to skip a return to the moon and go straight to Mars after robots prepare a base there for human use. Alternatives like this are worth exploring, but it would be a mistake to invest billions now in a crash program to put an American back on the moon, especially if the project is motivated by a desire to do so before the Chinese reach the moon. The camera eyes and shovel hands of probes and rovers have proven to be first-rate and affordable -- and safe -- decipherers of distant worlds.