Opportunity Sol 625 (Spirit Sol 646)

I've switched rovers once more. Back in the Land of Opportunity, they've backed away from the northern part of Erebus Crater -- pretty far away, as in 100m or so -- and now we're planning a drive to the west side of Erebus Crater. They had to back off so far because of the enormous ripples they encountered in the crater's immediate vicinity, and we're going to keep our distance as we head west.

Or that's what Frank and I think. The scientists would like to complicate things by adding a stop to the tour: in the orbital images, we can see a large expanse of outcrop at the northwest part of the crater. Can we stop by on the way?

Frank puts it to them bluntly: we can drive south to that outcrop, but if the ripples there are like they are elsewhere near the crater, we won't be able to go directly from there to the point where they're thinking of entering Erebus. Instead, we'll have to drive north from the outcrop before we can drive west to the point where we can drive south to get to the west entrance. Just thinking about it is enough to make your head spin, and it'll definitely make our wheels spin for an extra week or more.

This leads to the usual lengthy back-and-forth, and eventually to a compromise solution: we'll drive a little south of west, at an azimuth of 240 or so, hoping it will help us reconnoiter without driving all the way to the outcrop. If what we see tells us that the outcrop would be an expensive journey, we'll skip it; else we'll go there.

No matter how we do it, this will be a lot of driving. So I suggest to Frank that Opportunity revive an old trick, one Spirit uses often but Opportunity hasn't used for quite a while: autonav. We're in such a benign zone right now -- no ripples over 15cm, and nearly all under 10cm or so -- that we ought to take advantage of it to get as much extra distance per sol as we can.

Frank readily agrees. In fact, as it turns out, he and Jeng tried to do just this a few weeks ago, but that drive stopped for other reasons before it got to the autonav section. Nevertheless, it's a straightforward matter to add an autonav section to thisol's drive sequence.

When we actually do the math ... even with about two and a half hours to drive, the visodom-based slip checks are just so time-consuming that autonav is going to end up giving us only 5 or 10 meters. That's discouraging, but, well, it's something. Five meters here, 10 meters there, pretty soon you're talking about ... well ... it's something.