[X] My Assistant

[nasaman58]

I'm thrilled that Oppy's out of the dune, and I'll admit that I have not scoured and computer processed the raw pictures like good forum members should, but I think I still raise a good question: Do any of you have any ideas as to how on Earth (or Mars, rather) Oppy will be able to get to Erebus or Victoria given that it looks like the terrain leading up to these astrogeological treasure troves is the same as what got Oppy stuck in the first place? Does it sound viable to drive around the culprit dune staying in the valleys inbetween to get there? It seems this would be a majorly long and inefficeint switch-back driving method, but honestly, is there any other foreseeable way?

[Jeff7]

If it dangles freely though, it might not make for a good driving wheel at all. At least now, it does have the ability to help push or pull the rover, albiet with slightly higher friction than the other wheels. But it still can do something. Who knows, maybe with trying to turn in place, all the grinding on the ground might jar it loose. I was hoping that the time in the trench might have somehow helped that, but it'd probably need something more solid than fluffy sand to have any effect.

[dvandorn]

As I recall from Spirit's wheel problems, though (which had nothing to do with the steering actuator), the wheels cannot be left to just turn freely. When Spirit was trying not to use its one bad wheel, that wheel was simply turned off and Spirit dragged it along. That's why Spirit had to drive backwards -- it could maintain good speed and controllability dragging a "back" wheel, but not a front wheel.

In Oppy's case, the wheel turns fine, it just can't be straightened out. As I understand it, it can move from its seven degree toe-in position all the way hard over in the same direction, and back, but no further the other direction.

When Oppy got stuck, it was using its bad wheel but it was driving backwards to lessen the impact of that wheel's toe-in position. The controllers had run into some issues making Oppy drive straight in this configuration, and had made some changes that helped, just before we got stuck. That *may* be one reason we got stuck -- Oppy has to make smal "turns" as it drives backwards just to keep moving straight; it may have made one of those small turns with its "front" wheels just at a point where such a slight turning of the wheels caused them to dig in to the drift it was traversing. I'm sure that's one of the things the MER Team will be examining when it takes a very close look at Purgatory Dune.

-the other Doug

[Jeff7]

As I understand it, it can move from its seven degree toe-in position all the way hard over in the same direction, and back, but no further the other direction.

-the other Doug

Really? Have they tried exercising the wheel? Rotate it to one side, give it a spin one way, two the other way, and then rotate it a little straighter, spin it again, and keep trying somewhat in that fashion?

[dvandorn]

Yes -- as I understand it, they moved the wheel from its seven-degree toe-in position to what looked in the pics I saw about 90 degrees to straight forward (continuing in the toe-in direction), then moved it back as far as it would go, which was back to the seven-degree toe-in. It won't move any farther towards a toe-out position.

They don't want to exercise it a lot further, since it's now only a partial actuatior failure. I guess the theory is that it could become a full failure at any time, and that, of the positions they can get that wheel into right now, the seven-degree toe-in is the "least bad." Moving it *at all* runs the risk of it getting stuck in a worse position.

-the other Doug