Another significant anniversary: the Mars Exploration Rover-B (“Opportunity”) has been on that cold planet for ten years now– count ’em, a decade. That’s especially significant when you consider the mission was 90 days. Count ’em, the rover has outlived its design by more than a factor of 40. By “its design,” I technically mean the failure criteria; most people privately guessed the rover would last at least 91 days. But if it didn’t, someone would be penalized, after an investigation of some sort. You can think of 90 days as the rover “warranty.” Cars typically keep on going right past their warranty expirations… two or three times.
You may be asking about that other rover. Spirit (MER-A) is long frozen, though well past its mission criteria. It lasted over five years- no slacker by any standard. The Martian nights cause freeze-thaw cycles, which are bad for electrical connections and poorly-designed mechanisms. On shorter scales, one big freeze may pop something. Spirit, stuck in a sand patch and unable to bask in a Sun-facing direction, simply lost something over the Martian winter. This is despite RHUs (Radioisotope Heater Units). Many spacecraft carry little pellets of radioactive metal. Heat from the radioactivity pretty much guarantees a little thermal power. In this case, the RHUs simply couldn’t keep up.
And yet, both Spirit and Opportunity succeeded outright, and in principle. We flattered them with an imitation, MSL. A smarter, sharper, more incisive rover. And its bigger body should retain heat better through temperature swings; the mission location (Gale Crater) seems to have milder temperatures anyway, possibly due to a bowl shape retaining heat. One project member estimates over a decade of mission, perhaps fourteen years. Of course, that would still include stationary operations, if the electronics survive but the wheels grind still or something. Let’s find us a something.