Opportunity Sol 383 (Spirit Sol 403)

We got the downlink from the first of our weekend drives. This is the combined blind + autonav drive. Mark Maimone and I sit in the SMSA, looking at the downlink. The images show that the way ahead is totally clear, all the way to the horizon. So whatever else we see in the downlink, this is pretty much enough to tell us we should proceed on the next sol.

But how far did we get?

"177.5m total," Mark reports. "About 105m blind, 72m more autonav."

Oh, well, I say to myself philosophically. It would have been nice to set the record, but at least -- "Hey, wait a minute!" I exclaim. "That is a record!"

And it is. Indeed, it's at least two records. The previous single-sol total was 156.55m, so we beat the heck out of that. And the previous single-sol blind-drive record was about 92m; we beat that too. I don't know what the single-sol autonav record was, but I wouldn't be surprised if that's a third record broken. They won't last long, but it's nice to hold the records once again.

We actually got some bonus blind driving. In order to help the rover keep itself safe, we increasingly tightened its suspension limits the farther out it got: if it tried to drive over something too tall, or into something too deep, the suspension would articulate beyond the limit and the blind drive would stop. Then the sequence would automatically clear the error, back up into presumably safe territory (it had just driven through that area successfully), and continue on autonav. That way, even if the blind drive faulted out, we'd be able to use autonav to salvage part of it.

As it happened, the suspension limit triggered at the very end of the blind drive, as the rover was turning around to switch from blind driving to autonav. So it had already completed the entire planned blind drive, and then we got a few bonus meters on the wheels as it backed up.

We simply couldn't have planned this. Art agrees, when I call him to tell him the great news: "This is just too good!"


Anonymous said...

Wait, so...it was supposed to back up into presumably-safe already covered territory, but you had the suspension fault occur during a final turn and it backed into uncovered territory?

I mean, good luck that it wasn't a problem, but couldn't that have easily been a problem?

Scott Maxwell said...

@Anonymous There was a flaw in our thinking, though not quite that one -- the sequence wouldn't tell Opportunity to "back away" in whatever direction she happened to be facing, mid-turn. Instead, the sequence loosened the suspension limits in order to complete the turn in place before backing away from whatever had tripped the suspension limits to begin with.

Now, this was good in that we'd drive away from the scary thing in a known-good direction, but bad in that the suspension limits were loosened first: if it really wasn't safe to be driving over something big enough to trip the tighter limits, then we shouldn't have loosened them for the turn. The limits were not completely relaxed, mind you, but we still probably should handled this differently -- and, looking back at subsequent sequences, it seems we recognized the mistake at the time and immediately fixed it.

I suspect, though I don't actually recall, that we designed the sequence to handle the case where the suspension limits were tripped during the turn-in-place, without really taking seriously the possibility that they would be: we would have considered it much more likely that the limits would be tripped during the 100 meters of driving preceding the turn than during the turn itself. We also knew that the limits were so tight that there was no danger we were actually going over something that was a threat. Even so, if I had it to do all over again, I'd do it differently, and I'm happy to see we reached the same conclusion at the time.

Anonymous said...

I must be misunderstanding this sentence, then: "As it happened, the suspension limit triggered at the very end of the blind drive, as the rover was turning around to switch from blind driving to autonav."

As always: fascinating stuff. Damn cool, and a very fine job done by everyone.