In low Earth orbit, the main attraction of human spaceflight was spacewalks, whose novelty soon wore off. Some of the recent ones, requiring astronauts to juggle tons of Erector set components in constructing the space station, are as difficult as any ever attempted, but the nuances of this arcane skill are lost in the viewing. The painstaking movements that unfold so slowly in the weightlessness of space sap the tension from these events. Spacewalking, 42 years after it was invented, is about as spectator-friendly as croquet.

The torch of novelty passed to the robots. The unmanned missions proved their worth early with probes like the Soviets' Venera, which in 1975 descended through clouds of sulfuric acid toward the surface of Venus, withstanding temperatures of 900°F (482°C) and pressures equivalent to 90 Earth atmospheres in order to transmit the first images of the surface of another planet. NASA's Voyager 1, launched in 1977 and still transmitting today from the frontier of interstellar space, sped past Saturn and turned backward on February 14, 1990, for a final snapshot: a first ever family portrait of the solar system from the outside looking in. "After that we shut the cameras off," recalls Voyager project manager Ed Massey. "There was nothing left to shoot."

Recent years have brought, among many other triumphs, the rovers Spirit and Opportunity, driving on the surface of Mars since 2004; Cassini, currently touring Saturn and its moons; and Deep Impact, which dropped an 820-pound (372 kilograms) projectile into the path of a comet in 2005, then analyzed the resulting crater and debris plume to determine its composition. Orbiting observatories, beginning with the Hubble Space Telescope, provide a never ending supply of breathtaking images of the cosmos.

Despite its shifting fortunes, manned space exploration still retains a viselike grip on the human imagination. Indeed, although it is impossible for all but VIPs, reporters, and NASA employees to get really close to a space shuttle launch at the Kennedy Space Center, crowds still gather on the banks of the Indian River 11 miles (18 kilometers) away to witness a heart-stopping event that never disappoints—more than seven million pounds (three million kilograms) of thrust in a controlled explosion hurling a 4.5-million-pound (two million kilograms) object into the heavens at 25 times the speed of sound.