Opportunity Sol 921 (Spirit Sol 942)

Grim news from the Land of Opportunity today. The drive's off, because yestersol's IDD work on the trench failed. On the very first IDD move of the sol, we got a joint-1 stall at 80 ohms, which we haven't seen before. And the most likely interpretation of that is that the IDD has continued to degrade, and we're about to see a whole lot more failures. We might have lost the shoulder joint altogether. Jake Matijevic looks unhappy, which is never a good sign. "I'm concerned whether we'll ever be able to reliably stow again," he mutters to me sotto voce.

The only ray of hope is that the 80 ohms value isn't necessarily a magic number. It's a number we picked because it was supposed to work 90% of the time, or something like that. And if this is the first time it's failed in lots and lots of tries, maybe we just had some kind of bad luck, a purely transient failure due to ambient temperature or something. It has been particularly cold lately.

And Kirk Fleming makes a good point. "The first move of the day can be kind of sludgy," he notes as we're sitting in the fishbowl reviewing the data. "The stall doesn't seem to be resistance-related, or we wouldn't have hit the current limit. So either something else is wrong with the same actuator, or we just had a transient glitch."

Well, that is good news, and real reason for hope at last. Anyhow, we'll know more tomorrow than we do today. We're planning a test of the IDD in which we do a series of small shoulder-az motions, at increasing resistance values, until we get a success. That, of course, is hoping we do get a success, which is by no means assured at this point.

After a lot of discussion, we end up with a fairly simple scheme. We're going to repeat a test at three different times of day, so that we can test at different temperatures. Each test moves the IDD to the left and right with a rotor resistance of 80 ohms, then 90, then 100, the max we can command. If we succeed in moving it both directions at a certain resistance setting, we don't try the next-higher setting, since that's potentially dangerous.

And we'll take lots of pictures as we do it. Lots of pretty pictures. Which, we hope, will -- like the other data -- show nothing anomalous. That would leave us, perhaps, with a mystery. But given the alternatives at this point, it's a mystery I think I could live with.

[Next post: sol 946 (Opportunity sol 925), August 31.]

No comments: