Spacecraft That Refuse to Quit

Engineers design probes with a certain lifespan in mind, but some hardy robots just keep going. The tradition begun by the Voyager twins, which outlasted their missions to Jupiter and Saturn by decades and are now reporting from the edges of the solar system, continues today: In March a combination of luck and solid engineering allowed the Stardust probe to complete its second comet-chasing mission. Here is how it and two other plucky space explorers have defied retirement.