On April 30, 2015, a spacecraft weighing over 1,100 kilograms struck Mercury at roughly 8,700 miles per hour, leaving a 52-foot crater. It was not a failure but the planned end of one of NASA's most successful missions. This episode tells the biography of MESSENGER, beginning with the 30-year gap after Mariner 10 and the brutal physics that kept Mercury unexplored: a spacecraft falling toward the Sun arrives far too fast to brake into orbit with any launchable amount of fuel. We explain Chen-wan Yen's 1985 solution, a 4.9 billion mile route using reverse gravity assists at Earth, Venus, and Mercury itself to shed velocity over nearly seven years.

We cover the tense 2009 safe mode event during a Mercury flyby, the March 2011 orbital insertion, the Nextel ceramic sunshade, and the highly elliptical orbit that let the probe cool off between pa ...