Opportunity Sol 371 (Spirit Sol 392)

Oddly, we have no images from sol 369. We know the rover's not dead; we have images from sol 370. But for 369, nothing but thumbnails. It makes an odd gap in the data -- I don't remember ever seeing that happen before. They'll come down eventually, but not until our downlink improves.

Thisol we're going to finish up with the damn trench already. Still, we're not ready to leave. (Hell, we wouldn't want me to drive somewhere -- I might get a chance to break a record. Grumble, grumble.) Since we couldn't IDD the scuff we made earlier, we're going to make another one and IDD that. The last one appeared to dig farther into the soil than they'd wanted, so this one's going to be simpler and shorter: we'll just run the left front wheel back and forth a bit, then back off and turn.

Or that's Rob Sullivan's plan. But Julie points out that that will leave the rover at an azimuth of 210 degrees -- not bad for comm, but we could do better. "Better" would be a radically different heading, 80 or 90 degrees -- split the difference and say 85 -- where we'd get 100 Mbits more downlink each sol. 100 Mbits is a lot of saved-up images, so I start thinking about how to accomplish this.

We can't scuff just anywhere, we need to ensure that the wheel's not on a ripple. Our view of the immediate area isn't that great, so to ensure success, we really want to scuff the spot where the left front wheel is now. In order to be at 85 and IDDing the scuff, the spot we need the rover to be in is in front of us and to the right of where we are now. If we scuff and then drive to that spot, we'll either drive through the scuff, contaminating it, or through the trench, which they haven't finished imaging yet.

It's time for a creative solution, and I think of one: don't scuff with the left front wheel, scuff with the left rear wheel, after putting it where the left front wheel is now. That is, instead of scuff/drive forward/turn/back off, we could drive forward/scuff (with rear wheel)/turn/back off. By design, the trench is just a bit narrower than the wheel base, so we can even do this without disturbing the trench -- we'll just straddle it.

While Jeff writes the IDD sequences, Jeng and I develop the drive, but in the end it simply proves too complex. This is already our second try at the scuff, and nobody wants to have to make a third -- even the scientists are ready to drive on. As much as I love my idea (and I'm not the only one), it's not The Simplest Thing That Could Possibly Work. So we revert to Rob's original plan: scuff, back off a bit, and turn. Simple, effective -- and, unfortunately, 100 Mbits/sol less downlink.

In refining the scuff part of the drive, we introduce an unusual move. The original idea was to run the left front wheel backward, to kick away any material it might have tracked in underneath it, then run it forward to create the scuff, and then back up. But in order to help create a clean scuff, we need to drive the rover back very slightly, just a centimeter or so.

At first, Jeff's not even sure such a short drive will work. But it works fine when we run it through the simulation, so he shrugs and blesses it. He turns to me and says, "I don't think we've ever done a drive that short on Mars. Hey, I guess you got to set a record after all!"

Gee, I'm so proud.

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