Spirit Sol 85

So this is our first sol on Earth time. At least they've chosen to keep things simple thisol.

In case you can't tell, that's sarcasm. The plan for thisol is to do a complex RAT-brush mosaic, making a big dust-free spot on Mazatzal for the MTES, then back up about 85cm so the MTES can see it. After that, we'll drive about 15m, following the path I worked out in advance yestersol, and then autonav as long as they'll let us.

Or should I say, that was the plan. Then word comes that yestersol's IDD sequence faulted out, and all the images look wrong, and nobody knows why. Since we're on Earth time, nobody's around, so I start looking into the problem myself. I quickly discover that my ability to do this is limited. I have no problem finding the list of warnings and errors that the spacecraft has sent back, but since I never look at them, I don't really know what's normal and what isn't. I write down a particularly suspicious subset and ask for help from Jessica Collisson -- who graciously works on analyzing the problem with me, even though she's on Opportunity and right now they have an anomaly of their own.

This doesn't look good. The rover says one of the IDD tools had a contact switch in an unexpected state. Jessica and I don't know which switches are reporting contact, because we're not experienced enough to decode the data we're looking at, but knowing this much leads me to an alarming possibility. We had a frustrating problem during one of the PORTs[1] when we left the APXS contact switches enabled after opening the APXS doors; a sequence failed that should have worked perfectly, because the switches falsely signaled a contact. The vehicle thought the arm had whacked into a rock or the ground and set an error flag, which caused the rest of the sequence to refuse to move the arm. It turns out that those switches are flaky; they often spuriously signal a contact when the doors are open, so we have to disable them after opening the doors (when we are actually going to place the instrument and therefore might see real contact) and re-enable them when the doors are closed. I know Bob correctly added commands to disable the switches after the tool change, but he forgot to save the state, so when the rover wakes up again, the switches will be enabled. If that's what bit us, we're going to be really embarrassed.

But then I work out, with some relief, that that can't be the problem: the sequence faulted out in the middle of the MB-to-APXS tool change -- before the APXS doors were opened, so the APXS switches were in their reliable state.

Well, that's good, at least. Especially if I'm right, which we still don't really know. But something went wrong.

Bob would know which switch was the culprit just by glancing at the data. I go up his office and don't find him, but Mark Maimone is around, and he has access to the flight software, so he checks it out for me. It turns out, if we're reading it right, that the software was complaining that one of the Moessbauer switches was in contact.

That's fine, except for not making any sense. The tool change stopped in the middle, after the MB had retracted from the rock. The documentation images clearly show the IDD retracted cleanly from the surface; the switches shouldn't be reporting contact.

But as it turns out, Mark got it right (as usual). The MB contact switch didn't release when the IDD retracted from the rock, probably because it was so cold -- because the APXS gets its best data when it's cold, the tool change happened just before dawn, the coldest part of the sol. The cold must have caused the switch to stay stuck closed. (As it turns out, the switch unstuck itself three minutes later, but by then the damage was done. Still, we jokingly claim credit for a self-repairing IDD.) There's a reasonably simple way to work around this, now that we know there's a problem -- it's similar to what we already do for the APXS -- so it shouldn't bite us again.

Best of all, it wasn't my fault.[2]

But this throws our plans for a loop. Since yestersol's sequences didn't execute, we need to redo them today. Which theoretically means it'll be an easy sol, although of course the scientists change their minds about what they want (they take advantage of the fact that we'll be here another sol to stick in another MB integration, among other changes), so we have to change a lot of stuff around. But that's OK, it's what we're here for.

Andy's back today -- he's been on Earth time for a while, and in a sense we're catching up with him. He looks bored, and is casually interviewing people for his book. His publisher wants him to write a chapter about MER for the paperback edition. "I have to describe all of MER in ten pages," he says. "Without sounding bitter."

Sadly, this is Bob's last sol. (Or ... is it? Dah-dah-DAAAH!) I shake his hand. "Pleasure working with you," I tell him, and he says: "Likewise." And that's it. See you, Bob.


[1] An operational readiness test -- one of our many dress rehearsals for operating the rovers.

[2] Sigh. Stuck on that again, are we? Oh, five-years-ago self, won't you ever learn? Well, yeah, I guess you will. But it'll take you a while.

1 comment:

Anonymous said...

I can only imagine the problems we'll have investigating even colder bodies, like the Jovian or Saturnian moons. When even contact switches stop working, things are too freaking cold.