WASHINGTON — As things stand now, U.S. manned spaceflight is dead in the water.

A combination of budget woes, disagreements over where in the heavens to go next and the absence of a clear set of goals has reduced the once-supreme U.S. manned space program to a space transport and maintenance operation in low-Earth orbit that's scheduled to end next year with the retirement of the Space Shuttle. That leaves only the International Space Station, and no way for the United States to get there without Russian help. Moreover, the station has drained tens of billions of dollars from NASA's coffers over the last two decades, hamstringing the space agency's other manned spaceflight operations.

By contrast, NASA's unmanned missions to Mars, Mercury and the rest of the solar system have yielded astonishing advances in humankind's knowledge of the universe. With budget shortfalls expected to continue for the foreseeable future, many experts advocate exclusive reliance on machines to explore space, providing humanity with a "tele- presence" in orbit or on the surface of planets, moons and even near-Earth asteroids.

Note: Launchers are not shown to scale. Colored bars beyond launchers indicate their relative scale. Click on image to enlarge.

Two things are clear. First, the United States can no longer afford to mount, say, a manned mission to Mars on its own. Nations must find new ways to pool technological and financial resources, while overcoming narrow political differences and rivalries, to explore the solar system.

Second, a clear set of goals, including a firm timetable, is needed to move beyond low-Earth orbit. Almost without exception, veterans of early U.S. manned spaceflight agree that President John F. Kennedy's challenge to land humans on the moon by the end of the 1960s was the unifying principle that took humans to the moon nine times between 1968 and 1972.

"The question kind of boils down to: What are you going back into space for?" said John Aaron, the legendary NASA flight controller who worked extensively on planetary exploration after the U.S. Apollo program. "Are you going back into space to stay, or are you going to focus on landing people on Mars and come home? If the philosophy is that we are going back into space to stay, then resources and operational experience are paramount."

Aaron and many former astronauts agree that returning to the moon represents, in the words of former Apollo 11 crew member Michael Collins, a "technological briar patch" that would take our eye off the ball. Both Aaron and Collins believe returning to the moon only delays the day humans reach Mars.