Who is the Villain in Mars Sample Return?

Last month I wrote about the demise of Mars Sample Return, NASA’s most ambitious planetary science mission. What’s fascinates me about sample return is that it’s a human mission in miniature. The goal is to land a large spacecraft on Mars and return its contents safely to Earth. The criterion for success is binary—either the sample gets back safely to Earth, or it doesn’t. The mission has a mix of American and European spacecraft launching over several synodic periods, interacting with equipment that has been pre-positioned on Mars years in advance. And the program as a whole consumes a substantial fraction of each agency’s exploration budget, spanning multiple election cycles. This makes sample return a different animal from normal planetary science missions, which are set up so that there is a partial science return even if important components break, and whose costs tend to be front-loaded ahead of a single launch. For that reason, the demise of sample return may give us some clues…