Spirit Sol 340

"Do you know what happened?" Matt Golombek asks me. I sigh inwardly. As I figured out a long time ago, that's never good news.

Indeed it isn't. We appear not to have moved -- we turned, but we didn't go anywhere. The data's only just starting to come down, and I can't tell them anything useful without more analysis, so I slip out of the SOWG meeting and head downstairs to the SMSA. Jeng, Khaled and I quickly work out that the right rear wheel is dug in -- looks like another Wopmay situation. Well, I figure we can jog downhill a bit and then head back up, much like what we did on the far side of the planet. So I rush back upstairs and tell them we'll have to work out the details but it looks like we can do a semi-normal drive.

I start looking more closely at the images, and just as the meeting ends I notice something weird, something that looks like a clod of dirt in the right rear wheel. Or -- uh-oh. A rock.

I remember Jeff Biesiadecki telling me early in the mission how we could get a rock of the right size stuck in the wheel, jamming the wheel permanently. This rock's the right size, and it's in the right spot. And it's jammed against the steering actuator.

I go back down to the SMSA to tell them the bad news, but it looks like they've already discovered it: there's a whole crowd of mechanical and mobility experts, plus a mission manager or two, peering at the images and arguing with each other. There's already consensus on what happened: it looks like we picked up the rock while turning at the very beginning of the drive, and as the right rear wheel spun, it shoved our little passenger up against the steering actuator. That got it stuck, and as the wheel continued to try to turn, it drew additional power. Eventually, the current draw exceeded the defined limit, and the rover shut itself down for safety's sake.

But while there's no controversy about what happened, how to fix it is a matter of contention. I do what I usually try to do in these situations: facilitate. For the most part, this means "shut up." But I have a talent for noticing when two people aren't communicating well and getting them back onto the same page, so I pipe up from time to time to do that. When the discussion starts to go in circles, I summarize and ensure everyone agrees on the plan. Step one is to spin the stuck wheel one radian[1] in the opposite direction, in the hope of unjamming the potato (as Jeff Biesiadecki dubs the oblong rock). Step two, steer the wheel straight (it's currently cocked in, in its turn-in-place position). Finally, we'll drive away. Each step will take a sol, and we'll take high-quality images in between to assess our progress. If things aren't going well, we'll stop.

Well, there's no hope of hitting that 4km mark now.

Now that we've agreed on what to do, building the sequence is easy. The guts of it is just one command, turning the now-stuck wheel. The rest is just decoration, sprinkling in a bit of visual odometry just in case the rover actually moves during this operation (highly unlikely). And, as in comedy, timing is crucial: we schedule the sequence to execute late in the sol, when we'll have the best lighting. I spend about half an hour picking the perfect time.

At least I can have any time I want. The rover doesn't have much else to do thisol.

I'm RP-1 thisol and John is RP-2 -- that's been a while. We also have Khaled Ali, our RP-in-training, shadowing us thisol. And Jeff Biesiadecki takes time to carefully review and inspect the sequence. That's a lot of RPs for one command. I hope, between the four of us, we can manage to turn this stupid wheel and dislodge the potato.

I really do.


[1] For those of you who aren't so much into math, a radian is a unit of angular measuremen. It's a little less than 60 degrees. Because it's computationally convenient, Spirit and Opportunity measure all angles in radians, so we humans on the project do the same here and there.


George said...

ot but quite important: on sol 2117 (yesterday) Spirit's stucked front right wheel rotated a lot!! What was your first reaction? I just can't wait five years to know from the blog...

Thanks for your great work & insight on MER!

Scott Maxwell said...

@George It's certainly nice to see a piece of hardware we thought was dead show signs of life at such a critical time. We certainly can't count on seeing that wheel continue to work, but at the moment I'll take any asset I can get. I tend to discuss the real-time stuff more on Twitter (where I'm @marsroverdriver), incidentally.

Many thanks for your continued interest and support!