At first blush, the data look encouraging. We don't have any drive errors, which is definitely good news. But when we get a little more data, we can tell that the drive didn't complete -- Opportunity's nowhere near the predicted final location. In fact, she's only about three or four meters from where she started.
Plugging the reported position into RSVP makes one thing clear. Yestersol's drive consisted of a short downhill leg, a cross-slope leg, then an uphill leg. Opportunity appears to be around the start of the third leg, as if she'd gone down and across, but not very far back up.
That strangled groan you hear is coming from me.
We get a front HAZCAM -- since we're driving backward uphill, this shows the downhill view -- which shows the front wheels dug into the sand. The current-draw plot doesn't show anything suspicious -- but that tells us something. If one of the wheels were hung up on a rock, we'd expect its current draw to be much higher than the others; since we're not seeing that, we can tentatively conclude the rover's just spinning its wheels in dirt.
This is getting monotonous. But Jeng comes up with another approach we can try: switchbacks.
That's how Opportunity got out of Eagle Crater, the one they landed in. Trying to power straight up the crater wall didn't work, so they used a switchback technique to climb out more gradually, and this worked great. Not only might this help us climb the wall, it would also tend to help keep us from getting hung up on rocks: if we were unable to progress past a particular rock, we wouldn't just keep trying to push past it. By the nature of the switchback, at some point we'd turn and head the other way.
This idea has real merit. I pitch it to Frank, who agrees.
But we might not get a chance to try it. "I'm not sure we can do this," Art says. "If we have to go 25 or 30 meters cross-slope in 100% slip territory, we might just not be able to make it." I think this is premature, but I have to admit things haven't been going so well lately. (Not that it isn't par for the course in the Land of Opportunity, but still.)
Frank and I talk to the Mobility/IDD team about how to proceed. The general consensus is, basically, to take a sol off. Because of ongoing ground processing problems, we don't have the rear HAZCAM, which means we don't have an uphill view, and we don't want to proceed in that direction without one. The same rationale that kept us from deploying the IDD on Friday applies today, so we can't do that either. Instead, we'll take the time to prepare a test drive for the next sol, probably a switchback maneuver of some kind.
The next step is to have a long and painful meeting about this. The meeting draws in Daniel Limonadi, Jim Erickson (it's always good news when the project manager gets involved), Jake Matijevic, Jeng Yen, and Rich Petras, along with Frank and myself. Steve Squyres teleconferences in. The subject is, broadly, what the hell do we do now -- not just tomorrow, but beyond that: do we want to keep trying to get around Wopmay to Burns Cliff or give up and go for something else? Jim Erickson, for one, doesn't seem to think we can make it to Wopmay at all along the proposed route. He seems to have begun to adopt Art's view that we should quit trying now.
My take is that the nervous Nellies are giving up too easily. We haven't tried every weapon in our armory yet, so it's too early to give up on a high-value science target. (To be fair, one of the proposed approaches is not to give up, but to exit the crater, go around, and re-enter directly above Burns Cliff. But this would take a long time, several weeks at least, and it's still too early, IMHO, to decide to do all that when we have more things we can try cheaply in situ.)
My opinion is bolstered, at least in my own view, by the rear HAZCAM, which popped out of the ground system pipeline at last. The image shows the right rear wheel on a small rock. But Opportunity doesn't appear to have been struggling very hard with this rock. It's entirely possible we were already nearly at the slip limit and the rock was just enough to push us up to 100% slippage. Here's why I see this as good news: the vehicle is doing what we want, except when it runs into things we can't see. The switchback approach helps us avoid things we can't see, or rather minimize their effect, so it's very much worth giving it a try.
I try to make this point, but, like the vehicle, I rapidly cease to make headway. I give up in frustration, and it occurs to me that it's a mistake to push for continuing on the current path anyway. To put it another way, it's a mistake to get invested in any particular plan. This is the science team's vehicle, I just drive it. Maybe I've lost sight of that.
Instead, I just sit there with my mouth closed and wait for the naysayers to talk themselves out and leave. Then Frank and I work out the drive.
The first thing we need to do, we realize, is spend a sol evaluating different approaches. The point of this drive will not be to get us uphill (though if that happens, so much the better). Rather, we'll spend the time trying different strategies, figure out which one worked best, and then use the best strategy to get us uphill so we can get around Wopmay and on our way.
We decide to start out with "wiggles," small turns-in-place followed by short uphill arcs. We'll turn just to one side of the slip vector, take a short uphill step, turn just to the other side of the slip vector and take another step, and so on. The theory behind the wiggles is that our uphill drives are working except when we get stuck on something, and the small turns could help us drive around any little obstacles. We also try a couple of curvy wiggles -- building the heading change into the uphill step itself.
After that, we'll switch to a switchback test, experimenting with 2m legs at different angles to the slip vector.
I draw this out on a whiteboard as we build it, and the result reminds me of the shape of the rat-tail-shaped carmen figuratum in Alice in Wonderland.
Okay, I guess you have to be me to get the connection.
Frank was up earlier than I was, so he goes home and I work out a prototype of the drive.
Courtesy NASA/JPL-Caltech. The downhill view, showing the wheels -- particularly the right front wheel -- dug in fairly badly.