No matter how much brilliant work the folks at NASA and JPL put into their planetary exploration robots (and it’s a lot of brilliant work), eventually, inevitably, they break down. It’s rare that these breakdowns are especially complicated, but since the robots aren’t designed for repair, there isn’t much that can be done. And even if (say) the Mars rovers did have the ability to swap their own wheels when they got worn out, where are you going to get new robot wheels on Mars, anyway?
