What's more of a motivator: making something that goes to Mars, or making a machine that works perfectly?
Both of them are great motivators. From my perspective as a mechanical engineer, making a machine that works perfectly is always a goal, and then working on Mars is that extra little tidbit that puts it over the top, it's the icing on the cake.

I started off when I was seven years old going, I want to be Jordie LaForge from "Star Trek, the Next Generation," that'd be cool: he's an engineer, he gets to build motors... and say "The dilithium crystals are discharged," or whatever it is, "The matrix isn't working." Now I've come to the point where we're getting ready to send something to another planet, it's going to be this huge elation, that says, "Gee, I have hardware that I built on the way to another planet." I can't wait till that happens...it's an amazing thing.