Any lingering doubts about the need to retire NASA’s space shuttle fleet should be fully erased by the troubles getting the Discovery orbiter off the ground for its final mission. A planned Nov. 1 launch was scrubbed five days in a row due to weather and technical issues, and in the process technicians discovered a more serious problem: cracks in the orbiter’s external tank hardware. That unwelcome discovery pushed the launch to late November, then into December and now to no earlier than Feb. 3.

As a result, the last shuttle mission on NASA’s official manifest, which had been scheduled for Feb. 27, has been bumped to April 1 at the earliest. This may or may not affect the timing of the additional shuttle mission Congress directed NASA to fly no earlier than June in the 2010 NASA Authorization Act. But the yet-to-be-funded final mission could face delays completely unrelated to manifesting issues, further postponing the end of a program that costs NASA more than $200 million per month.

NASA officials say the flight ordered up by Congress is necessary to bring critical supplies to the international space station given delays to the commercial cargo delivery vehicles now in development. Congress had other motivations, namely, to stave off the loss of thousands of jobs associated with the shuttle program, but political and operational imperatives do converge from time to time.

But Discovery’s saga validates the 2004 decision to retire the shuttle fleet, which in April will mark three decades of flight operations. The sooner that happens, the sooner NASA can field new human spaceflight systems that are simpler, less costly and more robust. Space transportation should be a means to an end, not an end in itself.