Spirit Sol 239

The project's in a bit of a tizzy. The email server that handles all of the MER ops mailing lists was cracked a couple of days back, and as the system administrators scramble to get it back online, email service has become woefully unreliable. We rely on email to communicate meeting schedules, and the science teams use it to coordinate their planning, and nothing's getting through to anyone reliably.

So it's a bit of a minor miracle that the SOWG takes place at all, but take place it does. We still haven't gotten the downlink, so we have no idea whether yestersol's crucial drive went as planned. Consequently, we're planning in the blind -- and what a plan they come up with. Yestersol I left with the impression that -- assuming the drive worked -- we'd maybe do a bump drive if need be, and then sit still for conjunction. Somehow that plan flew out the window (or maybe I just didn't get the email), and they've decided to stuff in a bunch of complex IDD work before the drive.

I decide to take this as a challenge, and (despite my irrational but unshakable misgivings about the drive's chances) start sequencing the IDD work as fast as I can, while the SOWG meeting is still going on. I get help from an unexpected source: balky communication equipment. The science teams are mostly remote now, so the project invested in some fiendishly sophisticated hardware and software to enable us to interact. When it's all working, the remote teams are audible through the conference phones and visible on the big projection screens.

When it's all working. Which it mostly isn't. The system fails every few minutes, causing Brenda Franklin, the unlucky scientist stuck with running this stuff, to scramble madly around the room, apologizing to people, whacking buttons, and whispering urgently on her cell phone.

She's not happy. Neither is Ray Arvidson, who's annoyed even when the system is working at its best, because of the audio delays. There's a second or two of lag in the audio, just enough to make conversation difficult. One end of the conversation will sound like this: "I think -- I think we should -- sorry, go ahead -- okay, I think we should -- sorry, go ahead ...." The other interlocutor is saying much the same thing, but offset by a second or so, so they spend more time negotiating who should talk next than they do talking. (I think up a simple protocol: when there's a collision, the person who should proceed is the one whose name is alphabetically first. Arvidson would like this, but I doubt we can sell it to Squyres.) It's like when the anchorman talks to a reporter via satellite phone -- or, more apropos, like when Mission Control talks to an astronaut near the moon. And Houston, we have a problem.

Well, the good news is that I get all of the IDD sequences built even before the first bit of the downlink arrives -- all I need is for the scientists to pick a target, and I can plug that into the sequence and I'm done.

When the downlink starts flowing, I promptly pull up the final front HAZCAM and check out the coordinates in the image header. They're (0, 0, 0) -- we didn't move. Oh, fantastic. We are so boned. I knew I'd fuck something up.

Oh, wait. It's (0, 0, 0) in the new site. And, duh, the terrain is different. Holy shit, we did move.

By the time I've figured this out, the penultimate HAZCAM is down. This one will actually be more useful to me, since it contains the rover's estimate of its position near the end of the drive. That'll give me an idea of whether we got anywhere close to the destination. It's a trivial bit of math to plug in the numbers and -- we're about 1.25m from the destination. Which is excellent -- yestersol, we estimated we'd take this HAZCAM from about 1m or 2m away from the target, depending on slip, so we're right in line with expectations. Unless the rover wigged out in the last couple of drive steps, we should have made it.

When Jeng works it out more precisely, it turns out that we hit the bullseye. Yestersol's goal was to put the rover within 70cm of Tikal -- that is, we had a bullseye with a 70cm radius. Our actual distance to Tikal after this drive: 68cm. Jeng says it's the best drive he's seen in the last month, which might be unfair to the other rover drivers but makes me feel great anyhow.

Not much more data has come down, and a couple of minutes later we learn why. We screwed up the data volume predicts yestersol. It turns out our final attitude is very poor for getting data back for this comm pass (we estimated we'd get 55 Mbits, but we got only about 15), so we're going to have to plan everything using the HAZCAMs and not much else. In particular, the post-drive NAVCAMs aren't coming down. But we probably don't need them. We have acceptable NAVCAM coverage of this area from the previous sol -- we didn't drive that far, after all -- and the penultimate HAZCAM shows us the near field in good detail. We were planning to drive only a meter or so thisol anyhow, and I think we can do it with what we have.

To make matters worse -- or better, depending on your point of view -- part of the right-eye image of the final front HAZCAM was lost in transit due to the poor quality of the comm pass. This leaves us without stereo data for the region immediately in front of the rover, which means we can't plan IDD work for the sol -- without knowing exactly where the ground is, we can't safely move the arm. Consequently, all the work I did building the IDD sequences was a total waste -- but the upside of that is, I can focus all of my energy and attention on the drive, which remains in the plan.

The goal of this drive is twofold. The first goal is simple: if possible, further improve our energy position -- the more we can tilt the solar panels to face the sun, the better. The second goal results from some disputed observations from early in the mission. Some of the scientists think that when we were inadvertently stuck at Adirondack, some interesting things happened to the soil under the rover. (I'm not clear on what these interesting things were, but I think they had to do with the effect on the soil of the way the rover disturbs the wind.)

So the scientists want to use conjunction to do a soil experiment: before conjunction, we image a patch of dirt and drive onto it, disturbing it as little as possible with the wheels. (The interesting stuff will be the soil under the rover body; we just have to be careful not to turn in place or do anything else with the wheels that would disturb that part.) After conjunction, we back out the way we came in, and see what happened.

The resulting drive is, shall we say, elegantly simple. We'll turn 30 degrees to the left -- causing us to face down a short north-facing slope, so that damn near anywhere we stop on the slope will be a good solar attitude -- take some pictures, and drive a meter and a half. (It ends up being slightly more complex than that, as we need to pause halfway through to acquire some MTES images as well.) We get to associate a short name with every sequence; since this is the bump-drive that will take us to Conjunction Junction, I name this one "Conjunction Bumpin'." Then I sit and wait ... and wait ... and wait ....

Because meanwhile, life has been sucking for the rest of the uplink team. We have some unexpected heating requirements, which end up blowing the sol's energy budget and forcing Kevin and the TAP/SIE to replan the sol. (Happily, the drive is untouched, so I can ignore all this except for the delays it introduces.) In the end, they settle for just blowing the damned energy budget; they'll end the day with a net loss in the batteries, but they'll still be above critical levels. They'll make up for it nextersol. This all leads Kevin to declare thisol "The Suckiest Sol Ever."

Kevin's the type to muse aloud about his setbacks. "I think I was too nice today," he says. "I should have said at the SOWG, 'This plan is ridiculous, go change it' .... Tomorrow, I'm gonna be a dick!"

It's so important to have a plan of action.

So the CAM starts three hours late. This exposes yet another problem with remote science teams -- they're all in later time zones than ours. Ray's on Central Time, for instance, so our 22:30 CAM starts at 00:30 for him. He sounds snippy and pissed, not that I blame him.[1]

It's not the kind of sol where you want to find a problem at the CAM. Mindful of this, I keep my voice down when I point out a problem to John (who's floating again thisol). The slope we're heading down is a short one; if we slip too much, we'll reach the bottom and level out, leaving the solar panels aimed straight up, not at the (northerly) sun. This will make things worse for us -- much worse.

I roll my chair over to him. "You think we're going to have a problem if we slip too far?" I ask him quietly.

"I wouldn't worry about it," says John.

"OK, that's what I wanted to hear," I say, and I roll my chair away. I think about it. No, that won't do. I roll my chair back. "OK, why wouldn't you worry about it?"

"If we start to level out," he points out, "we'll stop slipping."

Duh. I roll my chair away again.

And I think about that answer. No, that won't do, either; by the time we've leveled out enough to stop slipping, our solar attitude will already be terrible. I need to know this, or I'm not going to be able to sleep, so I model 10% and 20% slips in RSVP. The results have to be taken with a grain of salt since our terrain data is so limited thisol, but ... 10% slip is fine; 20% slip isn't as good as the no-slip case, but it still leaves us with a good solar attitude.

And that's what I wanted to hear.

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Footnotes:

[1] As I've learned since then, Ray is a classic morning person. He hates late hours, and like most morning people, he really hates Mars time. That didn't stop him from living on Mars time as the science team lead for Phoenix a few years after this, though.