Spirit Sol 797

Our Spirit drives keep doing the same thing: we can execute the turns just fine, but when we start to move, we bog down pretty quickly. That happened again as we tried once again to power up this slope.

"Slope," ha! It's about four degrees of tilt. But this, combined with the soft, loose soil under our wheels, is too much for poor gimpy Spirit now.

The only nearby patch of ground that looks at all promising is a berm about 60deg off to one side of us, starting about 3m away. Obviously, we already know how to aim toward it, and we're going to try to haul ourselves up onto it if we do so.

But then what? When we look at the images, it looks like this berm is the near edge of a sort of island of possibly navigable -- hard-packed, sometimes gravelly -- material rising out of a sea of soft sand. The island is maybe 15 to 20m across, so that's great. The problem is what to do when we get to the far side, where the sand sea resumes?

If we're lucky, it's flatter over there and we'll be able to drag ourselves across it. If we're unlucky, we're just going to pull ourselves out of this frying pan, only to walk straight into that fire.

We could tell whether it's worth even trying, if only we had PCAM coverage of that area. But we don't, and the NCAM range data runs out just before that region starts.

On the other hand, if we don't go there, where can we go? Back to Home Plate? We already think that's hopeless -- even if we made it there, there's nowhere safe to park for the winter.[1] Our only other option would be a strategic retreat; reverse course for 10m or so, then take the "scenic route" along a lengthy path that circumnavigates the shore of the sandy sea.

This depends on some critical assumptions. First, that we can in fact back out. If we're really mired down here, we might not be able to do even that. And second, it depends on the assumption that the scenic route even exists. We don't have good imaging of that area, so maybe there are showstoppers. What we can see of either end of that route suggests we'll have to navigate for tens of meters around rover-killing rocks, with a rover that doesn't steer very well.

My gut feeling is that we're going to have to sound retreat. And if we're going to do that, we're going to have to do it now. Jake Matijevic says we've got about two weeks in which we can tolerate the occasional drive that leaves us with poor northerly or even small southerly tilts.

We can't do it now now, as in today, of course; since we don't know the scenic route exists, we don't know that retreating toward it does us any good. So for today we go with what we know: we'll try to drag ourselves up onto the nearby berm, but we'll also take pictures of the far side of the island and of the scenic route. That way, when we get our downlink, we'll know what we need to do.

If we get onto the berm and the imaging shows the sea on the far side of the island is flat enough, we'll try to continue directly toward McCool Hill. If we can prove the existence of the scenic route, we'll try to take it.

And if neither one pans out -- well, better not to think about that.

[Next post: sol 800, April 3.]


[1] False. Indeed, that's exactly where we spent the next winter, hanging off the north side of Home Plate. But we didn't know about that area then.

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