Apprehension inevitably haunted the Fourth of July celebration of shuttle Discovery's successful return to space. Fears will doubtless linger until the orbiter and its crew land back on Earth in 10 days or so. That's as it should be. Space travel is still far too experimental to be taken for granted, as the tragic explosions of shuttles Challenger and Columbia at the beginning and end of their missions, respectively, attest.
Despite continuing concerns about breakaway chunks of foam insulation of the sort that damaged Columbia three years ago, NASA Administrator Michael Griffin made the correct calculation to OK Tuesday's launch. After all, space flight is by definition risky, and further delays might well have grounded the costly and controversial shuttle fleet permanently.
This journey is among the last voyages of the shuttle, in any case. The fleet is scheduled to retire in 2010 as NASA shifts its attention to manned flights to the moon and Mars. But vital work for the shuttle remains.
Most immediately, Discovery will bring supplies, new equipment and a new crew member to the International Space Station, arriving there today. Four additional trips a year over the next four years may also be required to complete construction of the space station - one of NASA's major objectives for the shuttle.
At least equally important from a scientific standpoint is the shuttle's expected repair mission to the Hubble Space Telescope, which needs a team of astronauts to fix its failing batteries and gyroscopes. Without that, this amazing window into the secrets of the universe will likely go dark within two years, and a replacement telescope is not scheduled for launch until 2015.
Mr. Griffin has not yet committed to sending astronauts into space just to repair Hubble, saying he wants to wait until after successful completion of Discovery's current trip. But as a rocket scientist who formerly directed the Johns Hopkins Applied Physics Lab, he is in a position to understand more keenly than most the extraordinary value of the pictures and information beamed back from the telescope, which is directed from Baltimore.
Enhancing knowledge and understanding not only of the universe but of Earth itself is the real payoff from the nation's investment in space travel. Nobody gets that better than a scientist on a budget.