Opportunity Sol 535 (Spirit Sol 555)

I don't remember the last time this happened. We appear to have entirely lost the first part of the pass, leaving us nearly blind. We got the side-looking NAVCAMs and all of the PANCAMs, but we don't have any front HAZCAMs, the final rear HAZCAMs, or the center NAVCAMs -- not even thumbnails.

So the question is, can we drive anyway? The last drive aimed for the entrance to a particularly broad and flat zone, so if we can prove that that's where we ended up, we're fine. In an ideal world, this would be mostly a problem of triangulation -- first, find several landmarks in the images we do have, and estimate azimuth and range to those. Then do the same for the same landmarks in the previous sol's images, and compare the two results. That will tell us for certain where we are with respect to where we started.

There's only one small problem: the landmarks. In large measure, every part of Meridiani looks like every other part. How do you pick out the same point on the top of a ripple in two images taken 30m apart? We're able to find a couple of Scotty-like cobblestones in both the old and new images, but they're very distant in the older images and won't provide solid enough data for a convincing solution.

Things aren't looking good. Even if we get a good fix on our relative location, we won't be able to drive farther than about 20m with the data we have. But they managed to get an urgent retransmit request up to the spacecraft, so if we wait until tomorrow, we'll have all the data we normally have for a drive. It's less risky that way. And the way things work out with the restricted sols, we'll actually make more distance for the week with that approach.

So we reluctantly bag it. Beth Dewell breaks the bad news to Steve, who shrugs it off. "If that's the consensus at your end, then that's OK with me," he says. They replan the sol to do nothing but remote sensing, and we're released for the day; we'll come back tomorrow to plan the drive when we have the data. Well, I'd been planning to take a vacation day tomorrow, but what the heck. I figure I'll just take the rest of the day today instead.

A couple of hours later, Beth Dewell calls me at home. It turns out we had the needed data on the ground all along. Due to some kind of ground processing error, it was just stuck at the DSN. It's too late to change our minds today, so we're just continuing with the current plan.

What can you do? I just laugh.

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