Opportunity Sol 266 (Spirit Sol 287)

Seriously, what does it take to get out of here? The downlink brings unwelcome news: we appear to be stuck on another submerged rock. ("The Presumptive Son of Bane," Andy dubs it.) The good news is that the drive was doing what it was supposed to do, right up until we got stuck. The bad news is, that happened less than halfway through the drive. After turning, we made maybe 4m uphill before we got hung up.

Worse, we have a motion error, which is the flight software's way of telling us something went physically wrong. This turns out to result from a stall in the left front wheel, which occurred because the rover dug itself a nice deep hole under that wheel while trying to push uphill. At some point, while trying to perform a turn to reinforce its heading, the sides of the hole kept the wheel from steering to the needed position, and the rover declared a fault and gave up.

To make things more complex, we don't have imagery showing the rock. We don't even know we're on a rock, though the motor current data suggests that's what's happening. If we are on a rock, we don't know where it is with respect to the vehicle, so we're not sure how we can get away from it.

Looking at Mark Maimone's drive plot clears up part of the mystery, at least. By looking at the rover's heading, we can see that as it tried to drive straight backward, it would yaw clockwise. This suggests that whatever's blocking us is behind one of the left-side wheels. That means we should rotate clockwise to get away from it.

The drive Brian and I work out is, in its way, a thing of beauty. We first turn in place to get the left front wheel out of the hole. (To do this, we have to temporarily disable that wheel's steering actuator so it won't just repeat the stall from yestersol, but luckily it's already mostly in the turn-in-place position, so that won't matter much.) Then Brian comes up with a series of twisty little arcs that, with the help of slip, will wiggle the vehicle around the hole it dug, so the other wheels won't get stuck there. Then we turn to face uphill and somewhat away from Wopmay. (As we slip through this turn, RSVP shows, we'll end up with Bane dead ahead of us -- perfect for a HAZCAM! But we let the opportunity go.) After that, we drive uphill at an angle -- if slip were wind, we'd be tacking across the slope -- before turning once more and driving directly uphill.

It's a more complex drive than I'd like to shoot for in this area in a single sol, but I can't wait to see it happen.

Along with the drive, we have IDD sequences to do. It's a Friday, meaning it's a three-sol planning day. So they plan to spend two sols using the APXS and MI on the filter and capture magnets, and do the drive on the third sol.

But Andy thinks of something at the walkthrough. "If we know the terrain under the rover has changed, and we don't have a picture of it," he asks, "how do we know it's safe to deploy the IDD?"

Damn, I should have thought of that.

Which is not to say I think there's a problem. Andy suggests that we might have dislodged a rock in such a way that the rock is in the space the IDD moves through while deploying, making the rock invisible to the HAZCAMs but a threat to the arm. But in order for this to have happened, all of the following would have to be true:

  • The left rear wheel, which is drawing the highest current -- suggesting it's the wheel directly against the dislodged rock -- would have to be drawing more current for some other reason. The rock (Presumed Son of Bane, or PSOB) would have to be under the left front wheel instead, which is not showing a particularly high current draw. (That would mean it's moving a rather large mass around without giving us any evidence.)

  • PSOB would have to be half a meter or so long, in order to extend from the left front wheel into the unseen part of the IDD work volume. This would make it about twice as large as Bane, maybe bigger.

  • Rather than being pushed straight back in Opportunity's direction of travel, PSOB would have to have rotated more or less 90 degrees, and find a convenient fulcrum underneath it that would cause it to extend diagonally upward toward the IDD at an angle of about 60 degrees.

  • This would have to have happened in a way that left no traces in what we can see -- nothing in the numbers, nothing around the left front wheel itself. No shadow, no cracking, no evidence of disturbed soil, nothing.

So I don't believe this for a nanosecond. But I should have thought of it anyway, if only to dismiss it.

Unfortunately, I can't seem to convince anyone else I'm right. As soon as Andy raises the idea, Steve gets nervous, and that makes Jim Erickson (who's been hanging around a lot ever since we nearly collided with Wopmay) nervous. We have a big debate about it, with me the only defender of the proposition that it's safe to deploy. ("I'd bet my job on it," I declare at one point. "And you know how much I love my job.") Even Brian joins them. In the end, I'm heavily outvoted.

OK. Well, what the hell. We can do this science later -- wherever we go, we take the magnets with us. Anyway, having only the drive to worry about simplifies my job. And who am I to force science down the throat of the project's principal investigator? If he doesn't want to do it, we won't do it. I graciously concede defeat, and the IDD sequences are dropped from the plan.

When it's all over, Saina announces: "New rule!" She mock-glares at Andy. "No more thinking during the walkthrough!"

[Next post: sol 290 (Opportunity sol 269), October 26.]


AySz88 said...

FYI, the sol numbers in the title of this post are reversed. Also, Opportunity sols 265 and 264 are identical posts?

Scott Maxwell said...

Yikes! The second is a classic copy-and-paste error; the first, classic stupidity. :-) Thanks!

(Actually, see, it was a glitch in the Matrix that caused exactly the same thing to happen two sols in a row ....)