I think this is the first time I've done IDD work on Opportunity -- other than the post-drive stow and unstow, that is -- for something like six months, when she had the IDD anomaly to start with. Not much IDD work has been done at all, in fact, and I'm somewhat out of the loop. And today's not just a simple tool placement, it's the whole MI/RAT/MB/APXS/MI/MB campaign over three sols, and I'm RP-1.
So I load up the sequences from the previous time we did IDD work, a couple of weeks ago, and start looking through them. They have a couple of features that surprise me. Last I heard, we were keeping the joint-1 rotor resistance to 58 ohms unless we had a fault; these sequences are using 80 ohms for almost everything except the RAT placement, which uses 75. And last I heard, the shoulder azimuth joint was supposed to stay in a range of about five or 10 degrees from the center so that the arm would be relatively decently positioned in case we lost the shoulder-az joint entirely, but these go to about 25 degrees from the center.
Clearly, I'm not up to speed here. Paolo (who's RP-2 today and is as confused as I) has the right suggestion: go ask Ashitey.
We do that, and Ashitey puts it to us like this: they're working on the extended-extended-extended-extended (or whatever we're up to now) mission proposal, and they want to include a picture of Victoria Crater in it. They don't want to blow a whole lot of sols on the way there, so they've gone ahead and raised the joint-1 rotor resistance limit to ensure that the IDD does not fault out.
I understand this, and of course I'd like to get renewed funding. But, as I point out to Ashitey, if we destroy the arm because we set the resistance value inappropriately high, we'll lose a whole lot of sols. He grins -- it's clear he had the same argument and lost it, and if he lost it, I have no hope. But I decide to try anyway, which means talking to Jake Matijevic.
When I talk to Jake, I decide I really just want one question answered. I put it to him bluntly: "Is this a safety risk to the hardware?"
He shrugs. "We probably don't really need to raise the rotor resistance from 58 ohms at all; if anything, we've seen a possible indication of some recoupling in the motor windings." That would mean we'd need only the nominal amount of current; we could reset the rotor resistance back to its nominal value of 29 ohms and the IDD would work fine -- at least, while the winding was connected. "But is there a risk to the vehicle? No, not really."
He also says it's fine to move the azimuth out of the 5-10-degree band. ("Whatever science wants," are his exact words.) I have enormous respect for Jake and for his knowledge of the spacecraft, and if that's what he tells me, I'm going to believe it. So we go ahead with that. I'm keeping my fingers crossed, just the same, though.
The sequencing itself is a bit tricky but not terribly bad. Some of it I can copy from the stuff they did two weeks ago, which helps. I'm surprised to find that I'm a little rusty, but it all starts coming back to me.
Since this is a multi-sol plan -- 804, 805, and 806 -- we have to have our usual worry about what happens if one (or more) of the sols' IDD sequences is not activated. Obviously, there's no risk to Opportunity's safety if the 806's IDD sequence doesn't make it. If 805's sequence doesn't make it, we'll be OK, since 806 starts with a tool-change command that will do the right thing whether 805's sequence ran or not.
But if 804's sequence doesn't make it ... huh. We've always been protected against the first sol's sequence's not running by the fact that we need to unstow on that sol; if we're not unstowed, the other IDD commands are smart enough not to do anything at all. But since we're unstowing at the end of every Opportunity drive now, there's no such protection any more.
So Paolo and I have to take a careful look at it. After a great deal of to-and-fro-ing, we work out that we're just fine as it stands. The IDD is at the ready position, with the turret held just in front of the vehicle, APXS pointing forward and slightly down. Both sols 805 and 806 begin with a tool change command that will first retract the active tool -- the APXS, as it happens -- 13cm. But in its current configuration, if the rover tries to retract the IDD 13cm, the IDD would collide with the body. The rover's smart enough to know this, and it would refuse to execute that or any subsequent IDD motion command until the fault was explicitly cleared from Earth.
Thus, we're fine, and we can rest easy. With our fingers crossed.
[Next post: sol 828 (Opportunity sol 807), May 2.]