Spirit Sol 454

We've recovered from the weekend's fault, and the downlink shows we're in pretty much the state we expected: somewhat dug in. A small potato hovers by the left front wheel, and another possible potato -- the scientists bet strongly it's just a dirt clod, not a rock -- sits in the left rear wheel. So it'll be tricky just to get away.

Fortunately, we have a little more time than expected. On the large scale, that is: "There's nothing magic about sol 500 any more," Steve declares at the SOWG meeting. This had previously been the date by which we had to make it to the summit, before the sun angle started to favor south-facing slopes. The resulting lack of energy on our current north-facing slope would mean we'd face serious consequences. In the benign scenario, we'd have less and less time to drive each day, making the top farther and farther away. In the less benign scenario, we'd freeze to death.

But the dust devil that cleaned the solar panels bought us more time than I'd thought: even with the reduced energy level, we can last well past sol 500 now. The pace is now to be driven by the Martian terrain and scientific discoveries, not a mad scramble for the top.

Which is a good thing, because we haven't exactly been making a lot of progress lately. The next thing we're going to try is cross-slope driving. The last drive failed because it was fighting directly uphill -- the same mistake we made around Wopmay, back on the other side of the planet. This time we're going to try to drive at about a 45-degree angle to the slope instead. Before we can even do that, we have to carefully back away downhill, to extricate ourselves from our dug-in position. If you thought the going had been slow recently, just think what it would be like if we picked up another potato ....

Just a few meters away, the slope breaks, and should be easier going. Once the rover gets that far, the drive aims a little more uphill, to avoid a gap in the terrain mesh (representing an area we can't quite see from our current position, and therefore can't evaluate).

This is the first drive I've written for Spirit in quite some time. I have this fantasy of coming downstairs and magically putting everything back into shape, coming up with some brilliant scheme that puts the rover on the top of this hill in no time. Awing the crowd. But no such thing will happen: the guys who've been doing this are plenty smart already, and if there were any such clever trick, they'd have thought of it. Getting to the top is just going to be a long, tough slog, and it's really possible that we just won't make it.

I have a talk coming up in a few days, down in Anaheim at the USENIX 2005 conference. I'll be talking about how to drive a Mars rover. I spend some time thinking about how to put the audience in the right mindset. This is what I come up with:

You're 450 sols into a 90-sol mission. Threats surround you; every path is blocked. You're chasing the sun to the top of a hill and if you don't beat it you'll die. Welcome to Mars.

A little too dramatic, I think; I decide not to use it. But it sounds cool.