What has been the most exciting or memorable moment working as a Rover driver?
My first drive will always stay with me, of course. It wasn't much, just seven metres, but when I went home I simply couldn't sleep. I realised that right at that moment, a hundred million miles away, there was a robot on the surface of another planet doing what I had told it to do. I still have never gotten over that feeling.
But for me, the greatest moment of the mission was when Spirit reached the top of Husband Hill. We took our little Rover -- just the size of a golf cart -- and drove it all the way to the top of a hill that's about as tall as the Statue of Liberty in New York. Spirit had to climb that hill to look for evidence of water because most of the crater it landed in had been covered by a lava flow billions of years earlier, hiding any possible water evidence. Our hope in driving Spirit up Husband Hill was that it'd discover rocks that had been altered by water but not subsequently covered over by lava -- and it did just that, almost as soon as it started climbing.
But it didn't stop there. Plucky Rover that it is (and plucky team that we are), it kept on going, all the way to the top, even though it took months and it suffered some heart-breaking setbacks on the way -- times when it had to give up hard-won altitude so it could attempt a different ascent path. As hard as that was, it was worth it. Coming in one morning and seeing the images from our latest drive, realising that our courageous little robot had fought its way to the top at last, filled me with unending pride in the robot and in our team.
What has been one of the more humorous moments at work?
Early in the mission, we nearly lost Spirit due to a problem with its flash file system -- in PC terms, it couldn't boot normally because we'd filled up the Rover's hard drive. (Instead of a hard drive, the Rovers use flash drives -- essentially the same technology that's used by the USB drive on your key chain -- because they have no moving parts.) When we had diagnosed and fixed the problem, cleaned up the flash drive, and knew that the danger was safely past, someone wrote this on one of our white boards: "Spirit was willing, but the flash was weak."
What has been the most challenging aspect of your work, technically?
Working around hardware failures. The Rovers have now survived more than 15 times as long as they were built to, in an extremely harsh environment. There's lots of radiation, fine dust lurks everywhere, and temperatures swing from mild to Antarctic -- often in the same day. In the face of this, some of the Rovers' parts have just plain worn out, and there's obviously nobody around to repair them (though I'd go if they'd send me!), so we have to muddle through.
A perfect example is when Spirit's right front wheel seized up just before the onset of the previous Martian winter. Imagine trying to cross the desert pushing a shopping cart with one stuck wheel -- suddenly, that's what driving Spirit was like. We couldn't get to our planned safe haven for that winter -- it was on the wrong side of a sandy patch that our hobbled Rover could no longer cross.
So now we have winter coming on. The Rover's going to die if we can't get it to safety, and we have to learn to drive it in a whole new way. Thankfully, we have a copy of the Rovers in a testbed here on Earth, and we use it for just such occasions. We went down to our testbed, invented techniques to drive Spirit successfully despite the hardware failure -- with Martian winter edging closer all the while - then found a relatively nearby spot where we could park it safely, and somehow managed to drag it there.
That was a stressful time, but it was also enormously rewarding. The guys who worked out those driving techniques saved a priceless scientific asset. And even better, because Spirit survived that winter, it ended up making the biggest scientific discovery of the entire journey the next Martian spring, discovering a patch of silica-rich rocks. Silica-rich rocks thrill our science team because they're excellent evidence for past water exposure -- exactly what we're on Mars to find.