Spirit Sol 1079

I haven't worked with Khaled for a while. He's in fine form, still struggling a little but well on his way to being a full RP again. Today is all IDD work, and it should give him a decent workout.

The first sol's nothing: just pick the APXS up and put it down about 1cm away. It's the second sol that causes all the trouble.

We've got three IDD targets to choose from, spread across the face of the ridge that forms part of the Troll feature. Target 1, off to the right, is the science team's preferred target, and we can reach it pretty well, though we have to disable the wheel-volume collision checks to do it. Target 2, off to the left, is at the very limit of reachability, and is in fact unreachable by the APXS. Target 3, in the middle, is easy to reach but least interesting to the scientists. So we go with Target 1.

Only we discover, partway through sequencing, something we really should have noticed at the outset. There's a projecting knob of rock to the right of Target 1, so when we put the MB on that target, the APXS nearly collides with the knob. Bloody hell. Target 3, here we come.

With that under control, I go up to the Land of Opportunity to help resolve a question raised by one of the mission managers, Rich Morris. The planned Opportunity drive uses a waydisc that's mostly inside of Victoria -- in particular, the center of the waydisc, the waypoint, is inside Victoria. Now, the rover is aimed straight at the waydisc, and it'll stop when it reaches the waydisc's edge, which happens well before it enters Victoria. But theoretically, the rover's mobility code could decide to wander far off to the side, head into Victoria, and enter the waydisc from the side.

Now, we have various guards against that happening. They've already given the rover so-called keepout zones, which are like stringing up "Police Line -- Do Not Cross" tape around the terrain. If the rover crosses the line, it'll stop, and there's no way for it to get into Victoria without crossing one of these lines. In addition, there's a set of reactive checks, where the rover will look at its tilt and suspension and freak out if it appears to be going over a cliff. And, of course, there's our years of experience driving the vehicle, which tell us that it'll do the nominal thing.

But ... a while back, as a defensive measure, I wrote up "Rules of the Rim," which are similar to the "Rules of the Road" in which we documented our best practices for driving through the etched terrain. These rules are meant to document our best practices for driving around Victoria, and one of them says not to sequence drives such that the drive could nominally go into the crater. Rich's question is, does today's planned drive violate that rule?

It's a tough call. Realistically, the answer is no. But technically, we're violating both the letter and the spirit of the rule. And, grimly, because I know this means more work for the RPs on shift -- and, in the real world, pointless work -- I have to tell the truth. Yeah, it's against the rules. And moreover, it's against the rules for a good reason. We really shouldn't do this.

Happily, Paolo Bellutta, one of the RPs on shift, comes up with an elegant fix. There's a knob you can twiddle to tell the rover that it's only allowed to drive so far toward a waypoint. This means we can turn the normal, unbounded-distance command into a command whose nominal behavior constrains the rover to a circle around its starting point. By correctly choosing this setting, we can be that much more sure the rover won't enter the crater; it puts us within the letter and spirit of the rules, and it's a low-effort change. Paolo's brilliant, and everyone's happy.

So I'm back downstairs, back to my own rover. And just in time to hear John Callas point out something I hadn't noticed, and I used to keep fairly close track of this. Today we're doing a three-sol plan, for sols 1079 through 1081. Sol 1080 will be 12 times our prime mission of 90 sols.

Every month a year long, if you see what I mean. And we just keep going.

[Next post: sol 1082, January 18.]

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