The media keeps talking about how amazing it is that engineering can send this Mars Pathfinder to Mars, millions of miles away, and hit a target within a few miles. They say, it's like hitting a hole in one from Houston to LA. I contend that this is a horrible analogy. When you play golf or football or any similar sport, you hit or throw the ball and let it fly. Suppose you try to hit a hole in one from Houston to LA. You calculate exactly what angle and how hard to hit it and then do just that. You'll never get a hole in one. There is an uncertain atmosphere to go through the whole way. Also, if a gust of wind blows while the ball is in the air, you can't adjust. With the Mars Pathfinder, you can. They didn't just shoot the thing off and hit it that exactly. They made a number of burns on the way to correct the trajectory to get it just right. Also, it is much easier to predict the trajectory of an object through the near-vacuum of space, than through our atmosphere. So, in my mind, getting Mars Pathfinder to land on Mars is a case of using feedback control. Shooting a hole in one is "open-loop" and doesn't really compare.