2010-08-04

Opportunity Sol 543 (Spirit Sol 564)

"Wow, Scott, you're batting a thousand this week." Jeff Favretto is right: I'm on a roll and I know it. Once again, Opportunity is right where she's supposed to be, peeking over (and actually perched on) a small ripple, with a patch of outcrop just on the other side, lying dead center in the next trough.

The science team, having been long denied any rock targets to sink the rover's teeth into, wants us to put 'em right on top of it. So that's our plan. We could head straight for it, but if we did that we'd be crossing the ripple somewhat obliquely, and the right side would pass through a patch of relatively soft-looking stuff, which can hurt our precision. So we settle on a different approach, turning left and scooting directly across the ripple where we are, then turning right and heading down the trough onto the outcrop.

And now we have naming of parts. Larry asks for a name for the target we're trying to get into our IDD workspace in this drive. I point out that from overhead the outcrop looks like an ice-cream cone -- we're going to be driving along the cone and parking with the scoop in the IDD work volume. What I didn't realize was that Larry was asking one of the scientists to suggest a name. He suggests "Mound" -- the target being slightly raised, like a pitcher's mound.

"Yeah, that's original," I say off-mike, to the amusement of listeners in the room. "Let's go with that." (Later, Larry agrees with me, and they end up naming the IDD targets with an ice-cream theme.)

Well, they can't stop me from calling stuff what I want to call it. My uplink report speaks of crossing Fudge Ripple and driving along Rocky Road.

Mmmm, ice cream ....

Just before the walkthrough, Jeng and I get concerned about the precision of the drive. It's only Wednesday, so they can bump on Thursday if we don't get this right, and still be able to IDD over the weekend. But I want to get it right -- for the sake of my pride, and because this is my last Opportunity shift for a while, and, oh yeah, because sols cost a million dollars a day and my job is to make them go as well as possible.

Our concern is the first part of the drive, where we're crossing Fudge Ripple. If we're going to slip appreciably, we're going to do it here, and the rest of our drive depends on that part going correctly. After some discussion, we end up turning on visodom for that segment of the drive. Because of the leftward turn, we can't look back at our tracks, but there's a whole bunch of juicy outcrop in this area, so we point visodom at that instead. If it doesn't converge, we're no worse off than if we weren't using visodom at all, and if it does converge, it will help the drive go a lot better. So we'll probably win, and can't lose. Unless one of the dozen or so last-minute changes completely screwed something up.

I guess we'll see.

After I return to the Spirit World, Opportunity will spend a few days, possibly a week, IDDing this outcrop. Then she'll stow and continue toward Erebus.

She'll probably make it to Erebus in about two weeks. Or not. I've been joking that Erebus is a sort of anti-Wopmay and will always be two weeks away. I'm not actually sure that I'm joking, come to think of it. Last week or so, we thought Erebus was a little less than two weeks away, only to find that our position in the orbital mesh was wrong. The corrected position put us 75m farther from the crater -- adding another two or three days of driving, and putting us back to a full two weeks. See? If necessary, the whole planetary surface will move in order to keep Erebus two weeks away. And of course, as long as we sit here at the outcrop, Erebus will remain two weeks away.

I elucidate this theory for Jeff Favretto, who agrees sagely. "So you're saying it's some sort of Martian Groundhog Day. Every day you come in and plan pretty much the same drive, and when you come back the next day, you're still as far away as when you started."

Exactly!

[Next post: sol 573, August 13.]





Courtesy NASA/JPL-Caltech. Our start-of-drive position -- right where we were supposed to be.

2 comments:

ermanno said...

About 2 weeks on Mars...
Have you heard about the "Achilles and the turtle" paradox?
Achilles was the fastest man in the world (so they say) but he couldn't reach a turtle because for every step Achilles did, the turtle moved a bit more than Achilles's step.
Ok. Search it with Google. It's surely explained better than my writing.

Ciao and.. come in Italy for "the better ice cream" ;-)
Ermanno

AySz88 said...

I remember getting very confused by that paradox at a younger age; I only felt it was intuitively solved by realizing this:
Aristotle is complaining that Achilles has to finish an infinite number of tasks. Note that the story has divided a finite distance into an infinite number of "steps". So apparently it's okay to split a finite thing into an infinite number of smaller things. But the steps take less and less time and work - the time and work in each "step" are also an infinite number of smaller and smaller things. Why couldn't you reverse the logic that allowed you to split a finite thing into an infinite number of things? Recombine the infinite slivers in the "steps", and it can add back up to some finite amount of work. It's no more difficult to do that infinite number of tasks than to do that original task in the first place!

Of course, this doesn't work for every sequence of decreasing numbers - only the sequences that could come from somehow splitting up a finite number into an infinite number of pieces.

IIRC, the formalization of all this is in Calculus or pre-calc (wherever you learn the infinite series stuff).