Spirit Sol 706

The good news is, Ashitey was right: we did make contact on the first retry with the tweaked surface normal -- none of the fancy new stuff was even needed. The bad news is, the resulting RAT brush was fairly poor, so they had to redo it last week. The good news is, the second one worked, and they drove away already.

And a nice job they did of it, too: 71m on the first sol, 47m on the second (autonav-only) sol. (Incidentally, this was Spirit's first such back-to-back drive.) The bad news is, the drive was sort of perpendicular to Home Plate, so our radial distance to our long-term goal remains more or less unchanged, even as time wasteth. Not that I'm worrying about it.

Anyway, as a result, we're only about 40m from El Dorado, and John and I are looking to get the rest of the drive today. Happily, it's just about as simple as it could be -- there are practically no obstacles here, just a nice flat zone. Just before El Dorado begins, there's a slight rise, so we'll have to be on autonav for the last part, but it shouldn't be any problem at all.

The big question is whether we should enter El Dorado or not. Our goal here is to find out what this thing is made of, which we intend to do by digging a trench. If we enter it thisol, then tomorrow we'll know a lot more about what it's made of and what we can expect from the trench. The problem is, maybe we'll know too much -- maybe we'll be bogged down in it, just as Opportunity was at Purgatory. And with winter coming on, and us already behind the curve ....

On the other hand, if we're going to trench the thing, we've got to enter it sometime, at least with the front wheels. Ideally, we'd stop with just the front wheels in it, but it's 40m away (or so -- our range data is poor, compounding the problem) and if we want to plant the front wheels only, we'd have an error budget of only 50cm or thereabouts. We just can't drive these vehicles that precisely. (They were designed for two-meter approaches. We do a lot better than that, but 40m really is out of the question.)

Fortunately, of course, we've got world-class experts to help us answer these questions. I ask both Brenda Franklin and Rob Sullivan about what we can expect from El Dorado. They agree that the material is coarse-grained (you can tell because it's dark -- dust is light). Brenda thinks the stuff is likely relatively compact, though maybe not; Rob's not even that sure. At least it's not likely to be quicksand -- so-called "foo-foo dust," which we'd just sink right into.

John and I decide we're going to proceed with caution. We'll just zoom right over the stuff we can see, but when we're about 10m from El Dorado, we turn on autonav and start doing slip checks every 2-3m (as opposed to the usual 10-15m between checks on this vehicle). That way, we can't get more than about a vehicle length into a trouble zone. And we make the slip checks pretty paranoid; if they fail to converge, we bail on the whole drive -- a common practice on Opportunity, but not something we usually bother with on Spirit. By the time we're done messing with it, we've got a drive that's likely to give up early for one reason or another. But better that, than be lost forever in El Dorado.

Mark Adler keeps discovering more about how things have changed since he was here last. "You're not doing anything during the 11 minutes of drive heating?" he asks incredulously. We used to pack the sol as full as possible; we'd have found something to do during those 11 minutes.

"It's not like it used to be," I shrug. "It grated on me for a while, but I got used to it. We have to make compromises to get out of here in shorter amounts of time, and to keep people from burning out." Sad, but true. I'd been thinking about just this when walking in this morning. When we changed the mission from a sprint to a marathon, we adjusted our pace accordingly. It was the right choice, and yet I regret being unable to use the vehicles to their fullest capacity -- it seems such a waste of a priceless scientific resource that the limiting factor in their operation would be us humans. I suppose that's a lesson to take forward to MSL: engineer them (and the ground tools, and whatever) so that they can be used to their fullest capacity in an eight-hour planning cycle.

But Mark remains stubbornly old-school in another way. "I'm gonna play a wakeup song," he announces. "It's 'El Dorado,' by ELO." He plays it for us. I'm sorry to say it's a pretty lousy song. But it's nice to have the old days back, even in such a small way, all the same.

[Next post: sol 710, January 1.]

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