The scientists are happier than I am. In and of itself, that's an okay state of affairs; I'd rather have it that way than the reverse.
The scientists are happy because they have a nice scuff to play with. I'm unhappy because the scuff isn't where it was supposed to be. It's on the wrong side of the dune -- the far side, not the near side. This is an error of maybe half a meter; we should have been a lot more precise than that.
Chris works out what happened. In the main drive sequence (the "backbone," as we call it), we had several clauses that were intended to help us execute the drive more precisely. They checked if we were close to our defined target, and if not, they commanded a short step in its direction.
The problem arose because of our obstacle-check helper. For that part of the drive, we were running the helper explicitly as needed (as opposed to just letting it execute in the background) because the same "variable" that it uses to check whether we're too close to each obstacle is also used to check whether we're close enough to a goal. We wanted to be sure that the helper and the backbone didn't stomp on each other's use of this shared resource. The problem that escaped both Chris's and my notice was this: the backbone didn't reset the variable's value after calling the helper. So the helper stomped on the value, then we neglected to reset it to what we wanted.
The outcome we got -- a perfectly scientifically useful scuff half a meter away from the intended position -- was just about the least bad thing that could have happened. This mistake will be the subject of an automated check very shortly.
But not as soon as I'd like, I'm afraid. I'm going in for shoulder surgery Monday and will be unable to work for at least a couple of days. Chris is already covering my Monday shift, and John agrees to take my Tuesday shift. I already had Wednesday off, so I plan to just take those days off altogether and come in Thursday to help Jeng drive Opportunity -- one-handed, for my part.
It looks like I'll be leaving the rover in some increasingly capable hands. Since I had to meet with the surgeon and have some labwork done this morning, Paolo filled in for me until I was able to get here. I was a little worried about it since we're planning IDD work thisol, and Paolo has told me he's a lot less comfortable with the IDD than he is with driving. But I ask him to walk me through the sequence, and he knows it just about perfectly. He's even able to sketch out the process of doing it; he'd probably have been able to build the sequence himself, or come close, if John hadn't been here to do it.
[Next post: sol 613, September 23.]
Courtesy NASA/JPL-Caltech. The scuff, right in front of us.