"Our objectives today," Steve announces, "are to drive like the wind and then get the uplink team home in time to watch Texas beat USC." It's Rose Bowl Day, and Steve, in case you hadn't guessed, is a Texas fan.
Spirit made a respectable showing for her second Earth-birthday: 65m, most of it in the direction of Home Plate. It's not as terrific as I was hoping for, but it's sure not bad. Slowly but surely, the drive-metric graph is starting to look less scary.
She made it a good chunk of the way through the dune field that yesterday lay between us and Lorre Ridge, but a slip check measured 70% slip -- apparently real, not a visodom artifact -- and stopped the drive a little earlier than it would have otherwise.
Looking at our tracks, we can see that we really are slipping a lot. Rather than leaving nice, widely spaced cleat marks, the wheel tracks are all bunched up. However, we're not digging in, so Chris and I agree that it's safe to drive away.
Which will be fun. The path out of the dune field is relatively obvious, and firmer terra (marsa?) is only about 12m away, but on the way is a 30cm rock pile we definitely don't want to climb. With that, and the fact that we're slipping so much, there's only one way out: visodom. It'll be slow, but we've got a whopping four hours to drive, so we've got plenty of time for it. And after that we have a short blind segment followed by autonav until the time-of-day limit. (I'd rather spend the four hours on an 80m blind drive followed by a three-hour autonav segment, but we aren't in that kind of terrain. Mars wins.)
And there's something we need to do before we even get on the road. For the last few sols, we've been getting intermittent stall warnings from the left front wheel. We got another batch yesterday, and Matt Heverly and Terry Huntsberger work out that it happens whenever autonav decides to take a sharp left, meaning that that wheel is steered almost to the extreme counterclockwise position.
This probably isn't a failing actuator, but it could be. More likely, it's either a miscalibrated actuator or some junk physically jammed into the wheel. Hoping for the former, we start the drive with some commands to recalibrate the wheel, steer it to the troublesome position (to see if we get more stalls), then straighten the wheels and install new soft-stops that will prevent Spirit from steering that wheel back to the position where we get the warnings (for the rest of the day, giving us a chance to look at the data before she tries to go there again). If we see no warnings tomorrow, then the recalibration likely fixed it. If we do see warnings, well, we'll make the new soft-stops permanent. The new limit is only about one degree away from the old limit, so that won't compromise Spirit's driving appreciably anyway.
All the same, I'm hoping it'll go away and stay gone. One rover with a bad steering actuator is plenty.
[Next post: sol 719 (Opportunity sol 698), January 10.]
Courtesy NASA/JPL-Caltech. Spirit's tracks look a little closely spaced -- this is different terrain, probably with somewhat looser soil, than we normally drive her in. Still and all, though a little worrisome, it's traversable.