A satellite resembling a shiny spinning drum and orbiting 21,156 miles above Earth celebrated its 41st birthday in November, astounding engineers and scientists, some of them the children of those who built it. For years, the satellite has served as an emergency communications link for rescue operations, including the 1985 Mexico City earthquake and the 1980 Mount St. Helens volcanic eruption. It was supposed to live for only three years when it was launched in 1967.