ON OCTOBER 11, 2000, THE SPACE SHUTTLE DISCOVERY took off from Kennedy Spaceflight Center at Cape Canaveral. Two days later, it docked with the International Space Station, setting the stage for eight clays of construction work. At the moment of docking, the shuttle/station complex, including the three modules that made up the station at that time—Zvezda, Zarya, and Unity—weighed more than 160 tons and spanned a length of more than 150 feet. Bringing structures like this together in space seems almost routine today. Zvezda, the station’s first habitable module, docked automatically with the station in July 2000 with no problems, and as of last June American astronauts have docked the shuttle to the station nine times. Before that, shuttle and Soyuz dockings with the space station Mir happened in an almost humdrum manner.

Successes like these can make docking a space vehicle seem about as challenging as backing a car into a garage, but in fact it is vastly more complicated. A better analogy would be to a driver trying to attach his four-ton truck to the tow hitch of another 16-wheeler while both are racing down the highway at night, without lights. Even this greatly understates the difficulty, because in earth orbit the task happens in three dimensions and at speeds greater than 17,500 miles per hour. Moreover, the driver has to use a joystick instead of a steering wheel, and no help is available from friction.

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