Spirit Sol 238

I'm running late and there's no parking, but I still manage to make it up to the SOWG room right on time. Where I find an ongoing meeting. Turns out they revised the schedule, bumping up the meeting half an hour. So I'm not barely on time, I'm horribly late. That's always a great way to start your day.

It also turns out they've changed the plan, again without telling me. (Though to be fair, maybe I'd have known this earlier if I'd known when the SOWG meeting was and I'd been able to get there on time.) We're going to make up for our lost sol by compressing the two drive sols into one: we'll drive to Anasazi_station, image Anasazi, and drive to Tikal, all in the same sol. But I don't learn this until after the SOWG meeting, so the duration estimates we use for the plan are way too short, which means we have to replan later.

I complain about all this to John (thisol's floating RP), and he just grins and says, "This is so cool ...." Once again, this simple phrase snaps me back into a good mood. Bastard!

So we need another thirty minutes for the extra driving (it's only about three meters and some turning, but visodom slows things down a lot), and this simply breaks the plan -- there's not enough energy to do it all. The science team decides to nix the dogleg to Anasazi_station, as well as the associated PANCAM imaging. (Thus disappointing Heather, who's already built the PANCAM sequences. But as always, she's a good sport about it.) This leaves us with a straight drive to Tikal and plenty of time to do it.

The more complex drive was already built, but I decide to follow Heather's example and be a good sport about it. Wincing internally, I rip out about three-quarters of the drive sequence and redo it as a straight drive to Tikal. The rest of the work is mainly analysis, to see whether we're going to be at a good solar tilt if we error out, and stuff like that. Turns out there's nothing to worry about: the insolation maps -- colored terrain overlays showing the goodness of our sun-relative tilt at each point in an image -- show the path from us to Tikal as being completely safe. In these maps, blue is good, green is so-so, red is bad. And the path from here to Tikal is a big blue highway.

Though still under the weather, Mark Adler is back as thisol's Mission Manager. Every Mission Manager has his own style. Mark's is to ask a few really tough questions to see if you seem to have your shit together. If you pass the test, his comfort level increases and he leaves you alone.

Thisol he decides to make the test open-book: he writes the questions down on the MERboard, and announces that this is what he's going to be asking at the CAM. Nearly all of them are for me, to wit: (1) What tilt limit was chosen for this drive? (2) How was that limit derived? (3) If the drive faults out due to a tilt error (or any other error), how will we recover in time for conjunction? (4) What is our insolation along the drive path?

Having the list in advance makes my life about a zillion times easier. I make time before the CAM to discuss my answers with Mark. (Which is the way to do it -- early, I mean.) As I'm talking to him, I watch the comfort level rise above his critical threshold. He visibly relaxes, and the drive is on.

I'm glad I've already gotten this out of the way when, ten minutes or so before the CAM, John and I notice a rock-ringed depression just in front of the rover and along our drive path. (Indeed, the encircled depression looks uncannily like a fire pit.) To a first approximation, it's not a drive obstacle. It's only about 20cm deep, from the top of the tallest rock to the lowest spot we can find. But there are some aspects of its shape that worry us. For one thing, the path from the bottom of the depression to the top of that tallest rock is nearly vertical -- a mini-cliff, which the rover would have a hard time scaling. Moreover, the area immediately in front of the mini-cliff is just about one wheel diameter across. This reminds me of a "feature" of the rover, a problem that arises because it can't lift its own weight. You can build a kind of rover trap, a hole just big enough for one wheel, which the rover will have a hard time extricating itself from. Put all six wheels in such a trap, and the rover turns into a lander.

We soon deduce that if the rover gets stuck in the fire pit, we'll be able to get it back out -- eventually. Probably, we could just have it turn in place and it would climb out the side. The problem is that we don't have any sols we can afford to spend doing this; if we get stuck in the fire pit, we may have to remain stuck until after conjunction. That's assuming that the attitude change induced by dropping a wheel into the pit doesn't blow our insolation, causing the rover to drain its batteries during conjunction and freeze to death. In which case, we'll still be there after conjunction ... and for a long time afterward. (OK, so that's a worst-case scenario. But worrying about worst-case scenarios is what they pay me for.)

Ultimately, we conclude there's no reasonable risk. The depression is quite near us, only about a meter away, so we won't accumulate much uncertainty before we reach it. The likely case is that we'll just drive straight over it, mostly straddling the depression, and in particular straddling the worst-case area.

Ah, it's always something.

Courtesy NASA/JPL-Caltech. The rock-ringed depression we started to worry about is straight up the middle of this image.

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