Scuttle the Shuttle?

If NASA operated like a day-care center with zero-tolerance for risk, it would have hailed Tuesday's successful return of the spacecraft Discovery and then called it quits for the shuttle fleet, five years short of its planned retirement.

The arguments to ditch both the shuttle and the international space station remain strong, and will for some time. After all, despite more than two years of repair work, NASA failed to fully fix the falling-foam problem that led to Columbia's breakup in 2003. A bit of loosened foam from the fuel tank just missed Discovery in its launch this time, and then a dangerous spacewalk was needed to repair a filler between the heat-shielding tiles.

Dicey stuff, even for risk-taking astronauts.

Fixing these problems may delay the next launch of the Atlantis shuttle to the point that money and political will in Congress simply run out. Wayne Hale, the shuttle deputy program manager, likened the aging shuttles - first flown in 1981 - to "an old truck I own."

With just three shuttles left and the necessity for one of them to always be ready for launch in case a space rescue of another one is needed - NASA's margin for mistakes is getting thinner. And with Congress being so miserly on space funding, the shuttle's rising costs are eating away at NASA's other missions, many of them more spectacular to the public and far less risky.

The space station, too, remains half built, unable to perform much of the promised bio-science. Completing the orbiting laboratory will take at least 15 more shuttle flights, billions of dollars, and perhaps a humble US request of Russia to once again use the ever-ready Soyuz rocket for transporting crew and supplies (although not new space-station modules).

Yet NASA has several valid reasons to keep the shuttle going to the end.

For one, Congress hasn't fully committed the money for a new generation of replacement vehicles which, in their current design, may not be as versatile as the shuttle anyway, only safer.

After two shuttle accidents that killed 14 crew members, NASA has also learned a lot about how to reduce risks, mainly by improving the agency's management style. NASA's previous "broken safety culture," in which it was too complacent about risks, has been overhauled with a much more meticulous safety-check approach.

Despite nearly a quarter century of flights with a 98 percent success rate, the shuttle still remains an experimental vehicle, not the reliable workhorse envisioned. It's the most complex machine ever built and a constant source of lessons for how earthlings can achieve regular space exploration. It's inspired a private industry in low-orbit launchers, and pumped up continuing passion among young people for manned space flight.

Without the shuttle, the expected human repair of the Hubble Space Telescope will not be completed, ending the life of the most stellar of NASA's achievements, sooner than it should. A planned servicing mission would help Hubble keep providing many more views on the universe, and insights on its origins.

Most of all, however, the shuttle is needed to fulfill the Bush vision of manned missions to the moon and Mars. It's essential in transporting more modules to the space station in order to complete it, allowing medical scientists to study the impact of space radiation and long-term weightlessness on the body. Without designing ways to counteract those effects, space travel to Mars and beyond could be far more dangerous than a shuttle flight. Better to take the risks with the shuttle today than deal with greater risks of planetary travel tomorrow.

Abandoning the shuttle, and thus the International Space Station, would also require abandoning commitments to Canada, Europe, Japan, and Russia, partners in the station. How could NASA again line up space partners, and keep its costs down, having failed on this commitment?

If NASA were asked to be risk-free, it would never launch a rocket again.

But space science and exploration still require rockets and spacecraft. And the best beast of burden for now remains the shuttle.