When the first X-ray detectors revealed many places in the universe that are too hot to be seen by optical and radio telescopes, pioneering X-ray astronomers realized they were onto something big. They knew that a large X-ray observatory must be created if they were ever to understand such astonishing phenomena as neutron stars, supernovas, black holes, and dark matter. What they could not know was how monumental in time, money, and effort this...