Spirit Sol 699

Yestersol's IDD sequence had mixed results. The RAT failed to establish solid contact with the bumpy surface of this rock, so we didn't do the brush. Instead, the sequence simply proceeded to take MIs of the unbrushed surface and place the MB there.

This isn't the worst thing that could have happened. The MB is pretty good at seeing through the dust anyway, so we'll still get good science results from it even though the brushing never took place. However, the APXS can't see through the dust, so we really need to brush the darn thing thisol. We're falling farther and farther behind our drive metric all the time, and with Christmas coming this weekend, a failure to brush now could end up blowing most of a week. And that really wouldn't be good.

What happened yesterday was complex: almost exactly at the nominal contact position, the RAT's contact switches tripped briefly, but then rapidly gained and lost contact several times in less than a second. The initial firing of the contact switches stopped any further motion toward the rock face, but the sequence's subsequent check for contact failed because the switches had changed state by the time that check happened.

Clearly, we need some approach that checks whether we've made contact and autonomously tries again if it hasn't. The solution Frank and Matt Heverly and I come up with is something we've never tried before; we call it the "phased approach." First we'll try to place the RAT the same as we did yesterday, only without attempting any overdrive. (This will probably work, since we contacted 2mm early yestersol.) Then we'll have the sequence check for contact, and if it doesn't see contact, it'll push forward 5mm and check again. If still not in contact, it'll push forward 5mm and try again, then yet again, for a total of three tries (and 1.5cm total overdrive, about the most we dare command). And if we're still not in contact after all that, we'll try the whole routine again on an alternate target -- the same position, but with a slight tweak to the surface normal, so that we'll come in at a different angle.

If we're still not in contact, well ... then we give up. But at least we will have tried, and tried hard.

Though this approach sounds pretty complex, it's reasonably simple to sequence. I'm a good chunk of the way through it when Ashitey arrives to object. At first he's not comfortable brushing at all, since this switch-bouncing behavior isn't something we've seen before. He ultimately relents there, but still has problems with what we're up to.

"I think what you're doing is too complicated," he says. "You're doing things we've never done before." He doesn't say so outright, but this is clearly a sort of threat -- if we want to do what we're doing, he's going to make enough of a stink that we'll have to run it by Project management. "You should keep it simple -- just try again one time, with the tweaked surface normal."

"Besides," he continues, "you know it'll make contact if you just try again with the tweaked target."

But I don't know that. And I don't really think what we're doing is unreasonably complex, especially considering the downside: we have to stay here until we get this done, and since Home Plate is slipping farther and farther away every day, we should make every effort we can to get this to work (consistent with the safety of the vehicle, as always). And while it's true that we're doing something we've never done before, all of the parts of it are things that we have done before. "We invent techniques all the time without taking them to the Project level," I point out. "You think we should involve Jim Erickson every time we add something to a slip check?"

Ashitey backs off on the "first-time activity" line, but still pushes to make the thing simpler. We argue about it for a while, and perversely, our eventual compromise is even more complex than what we had when he came in. Now, we're first going to try the usual-style (non-phased) approach on the tweaked target. If that fails to make contact, we go to the original plan: try a phased approach on the original target, and if that fails to work, we try a phased approach on the tweaked target -- and only then, only if all that fails, we give up.

I'm not sure how that happened, but that's where we wind up.

All of this arguing pushes us pretty late -- by the time we're done, it's approaching 08:00, rover time, only an hour or so before we uplink. Someone remarks on this, but it fails to impress Mark Adler. "Ah, that's nothing," he says. "We used to CAM during the uplink window."

Well, I know they did that once. But it's not something anyone wants to repeat, you may be sure.

[Next post: sol 706, December 28.]

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