Well, it’s about 1000 days past the planned mission end date, and the Martian rovers are in serious trouble.
I’m finding it hard to get excited about this, Spirit and Opportunity have done yeoman work, and exceeded any possible reasonable expectations for thier capabilities and longevity. I hope that they won’t be lost to this season’s dust storms, but if we do lost them, they’ve still earned a place on the long list of phenomenally successful NASA unmanned missions.
Just figured that I’d share this news with the Teeming Millions.
Not to rain on anyone’s parade, but the “design life” is a bit of a misnomer. The “ninety days” given is “merely” how long the rovers have to last for the mission to achieve it’s primary objectives. They’re designed as rugged as we know how to make them. Given that guys doing engineering work for NASA were probably inspired by one Montgomery Scott, I can imagine that even their “official” estimates of the rovers lifespans contain a good bit of fudge. Personally, I wouldn’t be surprized if they didn’t survive the “coming of the Martian night winds” when NASA expects them to be dead.
The 90 day planned lifespan of the Mars Exploration Rovers was based upon anticipated erosion and dust cover on the photovoltaic arrays, which were expected to degrade power delivered to about 30% of original capability in that time period, which would render them marginally operable. However, because of unusually clear atmospheric conditions, dust removal via winds, and a lower-than-ancipated level of battery and solar cell degradation they still pull in better than 300 watt-days of energy after three years.
That limit aside, conditions on Mars are not terribly hards; while their is wind to power erosion, it’s very thin, and there is essentially no surface water to form a conduit for corrosion. There’s also enough of an atmosphere to prevent lubricants from rapidly evaporating and to prevent the vacuum adhesion or cementing that can occur in space. Regarding how “rugged” the vehicles are, knowing that they would be beyond any possible mechanical or electrical repair they were no doubt designed with as high a structural margin and with as much a degree of redundancy as payload mass would allow. Since they have a much reduced weight in the Martian gravity field (although they still have the same inertia) many the loads on them are lower than they’d be on Earth, so it doesn’t require massive overbuilding to ensure that the structure and locomotion systems last substantially longer than their planned operational lifespan.
NASA and the JPL like to lower expectations by reminding people that 75% of all missions ever launched from Earth to Mars have failed, but they are usually kind enough not to point out that the vast majority of those failures were not American missions.
As the OP of the Bad Design in Everyday Life Thread:
I would just like to say I am officially in awe of the guys who designed those rovers, most especially the first one. Their rovers were designed for theoretical conditions, and they lasted for a very long time. So often, conditions on the ground are not what the designer imagined: witness all the designers of something as simple as dishes, who apparently never considered the consequences of those dishes being left in a dishwasher, upside down.
Well, if they need a break from all that rocket science, they could always take a crack at our most pressing civilian design emergency, the automobile cupholder problem. If anyone can solve it, they can.
