Although NASA's budget has risen about 7 percent over the past two years, its responsibilities have grown much faster. First, NASA must safely resume the flights of its space shuttles, which have been grounded since the loss of Columbia in 2003. Second, the agency plans to continue assembling the International Space Station, the half-built orbital outpost currently occupied by a two-person crew and supplied by Russian spacecraft. And third, President George W. Bush ordered NASA last year to develop the Crew Exploration Vehicle (CEV), a new craft designed to take astronauts back to the moon and ultimately to Mars.

Unsurprisingly, the agency's renewed commitment to human exploration is now impinging on its program of unmanned missions. Since the unveiling of NASA's budget request for the 2006 fiscal year, the impending cuts to Earth-observing satellites and interplanetary probes have led scientists to raise their voices in protest [see "Feeling the Pinch," by Mark Alpert, News Scan]. Of course, researchers have a tendency to defend their projects to the death, no matter what their value, and NASA must sometimes make sacrifices to ensure that its limited funds go to the missions that return the best science. But the fact that the agency is even considering canceling the Voyager probes, which are now breaking through the boundaries of the solar system, is a sign that NASA's priorities are seriously out of whack.

The shuttle and space station programs would be better targets for cost-cutting. NASA originally planned about 25 shuttle flights over the next five years to deliver the trusses, solar arrays, docking nodes and laboratory modules needed to complete the station. The shuttle and station consume 40 percent of NASA's budget and will burn through at least $40 billion between now and their scheduled phase-out dates (the shuttle in 2010, the station in 2017). In contrast, the Voyager mission costs only $4.2 million a year.

When the assembly of the station began in 1998, NASA justified the expense by noting the potential benefits of conducting materials science and protein crystal experiments in orbit. Today agency officials say medical studies of station astronauts will help NASA prepare for manned missions to Mars. Yet neither argument stands up to scrutiny. Most scientists say the results from station experiments are not worth the cost of putting the laboratories in orbit. And the primary obstacle to human travel to other planets is the threat of ion bombardment in deep space, a danger that cannot be fully investigated at the station, which lies within Earth's protective magnetosphere.

Cutting the shuttle and station budgets could pose diplomatic problems: the European and Japanese space agencies have already built expensive laboratory modules and made barter agreements with NASA to ensure their delivery to the station. Those agreements can be renegotiated, however. If NASA limits the number of shuttle flights to the station to six or seven--enough to finish the core assembly--the freed-up funds could bolster both human and robotic exploration. NASA could accelerate the development of the CEV and new heavy-lift rockets intended to launch components for interplanetary missions as well as modules for the space station. A 2004 study commissioned by the Planetary Society advocated exactly this strategy; one of the leaders of the study team, Mike Griffin, became NASA's administrator in April. We urge Griffin to put this plan into effect.