Spirit Sol 48

Yestersol we dug a hole. This is a pretty cool maneuver, a variation on the one I watched Jeff and Mark rehearsing in front of the NBC cameras a few weeks ago: the rover holds five wheels steady and spins the sixth, digging it down a little way into the soil. Then it turns in place a little way back and forth, packing down the soil on either end of the hole. Then it returns to its starting point and digs a little further. The result, as in our case, is a hole as wide as a wheel and as deep as we have patience to make. (In this case, that's about 6 or 7cm. Opportunity's hole, by contrast, was nearly 10cm deep, and they needed less than half as much energy to dig it. Which would tell me something about the differing soil composition between the two sites, if I were that kind of person.)

They decided to dig in this spot because when they got the images after the drive that took us here, they spotted polygonal structures in the soil that, on Earth, indicate water. "But we're on Mars," shrugs Dave Des Marais, who's filling me in, "so we'll see."

Now that they've dug the trench, the plan is to IDD it. This makes me nervous, since it means all kinds of new ways to screw up. Fortunately, Bob is going to be RP-2 tonight, and he knows the arm like, uh, the back of his hand. So I won't be able to screw up too badly, anyway.

The scientists are excited, and the downlink assessment meeting is fairly upbeat. LTP reports that Spirit has now covered 131.1m, and we've now explored the number of different locations (four) needed for minimum mission success. Also, our recent aggressive drives have brought us within "kissing distance" (as Dave phrases it) of the path that will take us to Bonneville by sol 60. We'll hang out by the trench a while first, spending a couple of sols here, then we're driving again.

Ray Arvidson has shown up for the meeting, partly because he's going to be the SOWG chair for a couple of sols starting tomorrow, and partly because there are specific observations he wants us to make at this trench. It's a rare chance for an interplanetary comparison, in which we'll do science observations that complement the ones Opportunity made at its trench. We'll also be prototyping drive science for the extended mission (and it's weird to me that they're already planning the extended mission; but here we are, past the halfway mark already).

The conclusion Ray pushes them to is to do a couple of long APXS and MB integrations on the trench, along with several MI observations. I suggest that they pick backup targets within the trench just in case their primary targets aren't reachable, which was a practice that saved us at Mimi and might do so here as well, since it's hard to safely maneuver the IDD in the trench.

They're going to have a lot of questions I won't be able to answer without using RSVP, so by the SOWG, I'm already sequencing. This works out perfectly; they keep asking me questions I've just gotten the answers to. At the end of the meeting, one of the MI guys comes over to ask if we're going to be able to put the MI on their preferred target, and I say, "Well, why not see for yourself?" And I show him an animation of the IDD doing exactly what he wants. ("You guys are so good at your jobs," he tells me and Art wonderingly. Apparently, this mission also has an unusually close rapport between the engineers and scientists -- I've never been on a mission before, so I don't really know, but he and Art talk about other projects they've been on in which the two groups were at each other's throats.)

Just to make my life more complicated, the RAT guys want another picture of the RAT magnets. Apparently there was something strange about the last picture they got, and they want to know if it was real or an image artifact. So I work out a position in the sequence where we can just flip the wrist a little bit and get them a nice shot of the magnets, and they're happy. As it turns out, we have a bunch of other imaging we need to call from our sequence, so this ends up fitting right in.

The handover to Bob goes more smoothly than usual. I finish writing up the handover documentation just as he arrives, and I manage to get the sequences into just about the perfect shape: close enough to finished to satisfy my persnickitude, but with a few tweaks still needed so he'll have something to do. This isn't going to get much better, so I decide to leave.

But right then the midnightly science talk starts, so I stay for that. This one is given by Larry Soderblom, who talks about what they found at Opportunity's trench. Opportunity landed in clean black sand, which is largely free from the sulfur and chlorine that glues Gusev's sand together. Over time, lighter sand has been blown out of the crater, leaving the sand we see -- and the ubiquitous Marsberries. (Which, as it turns out, are more nearly brown than blue in true-color images.) These Marsberries come in three types: the blue and spherical kind I've seen the most of; a yellow, gumdrop-shaped kind (which Larry calls "Kix"); and a third kind that are sandblasted, pitted, and darker in color (Larry calls these "grape-nuts" -- somebody's hungry). Opportunity's trench contained Marsberries, too, and while these are shiny like the ones on the surface, they lack the frosted appearance of the surface spherules -- possibly, this is simply because they're not on the surface, being rolled around and smacked with grit.

In addition, as Opportunity dug its trench, they confirmed their observations about its soil. It's like putting your hand in a bag of dry cement -- it retains a perfect imprint, showing that its particles are very fine.

Not long after the science talk finishes, I leave. On the way out I stop to pick up my mail, which I haven't done for weeks, and discover a letter from a kid in Long Island, addressed to me personally. I assume he got my name out of a newspaper or something, or maybe off the Web site. He asks me a couple of questions about the rovers, and encloses a couple of pictures he drew, and asks if he can have a poster of the rover. I think about when I was a kid his age, watching the Voyager missions on TV. About how much it meant to me to know that the world was so much bigger than the little town I lived in, that there was this huge universe out there, waiting for people to explore it. How I wanted to grow up to be one of those people. And here I am.

You bet you can have a poster, kid.