A mechanic crawls under an Army tank with a computer strapped to his belt and a keyboard on his wrist. A tiny camera clipped to a futuristic headset beams pictures back to colleagues, who whisper repair instructions through the headset speaker. The once-fictional vision of Dick Tracy’s wearable computers has given way to reality at the Army’s Fort Monmouth in New Jersey and at other military repair depots nationwide where such devices are now in daily use. Government officials impressed with their miniaturization and speed already are envisioning new uses that would take wearable computers to the battlefield and beyond. “Wearable computers may be the future not only for Mars expeditions, but for many future space missions,” said Pascal Lee, project scientist with the National Aeronautics and Space Administration. NASA researchers are testing ways to fit the devices into Mars space suits, and the computers will be used for a mock Mars mission this year. NASA and the SETI Institute, which is dedicated to the search for extraterrestrials, will test space gear on Devon Island in northern Canada. The frigid site is the world’s largest uninhabited island, and mirrors some of the extreme conditions on Mars.