The problem is that we don't know where we're driving. Well, our basic options are to go across Home Plate, or to go down so that we can go around it one way or the other. So in the couple of hours we have before the end-of-sol meeting, I sketch out the waypoints for each path.
Meanwhile, other members of the team are pointing out that we won't do much driving for the next few days. Monday was a holiday, and we're still in restricted sols, so we can drive on either Thursday or Friday but not both. Or, of course, we could delay the drive until the weekend -- the point is that between Thursday and Sunday, we can do only one drive. We'll have an IDD sol, a drive sol, and two sols of remote sensing and/or recharging. Since the latter are, from a planning perspective, basically free, and we don't have a pass Monday, Saina proposes we do something we've never done before: a four-sol plan, where we come in tomorrow (Thursday) to plan Friday through Sunday all in one day. (This seems like a lot to me, but when she slyly adduces that some people think it's impossible to do a four-sol plan, I'm suddenly enthusiastic. It's like the four-minute mile of rover planning.) If we succeed, that would also mean we'd have Friday off: we'd plan all four sols tomorrow -- Thursday. If we fail, we could just drop the last sol out of the plan and come in Friday to do that one.
Squyres tells her he's for it, too: "Home Plate is the most interesting and exciting science target Spirit's seen so far. I don't want to end up simplifying or cutting science in order to do this. As long as you and I agree we fall back by cutting sols and not science, I'm up for that. It's a deal! Sounds like fun! Let's do it!"
The end-of-sol meeting is an uncommonly interesting one. The topic is where to go from Home Plate, and how to get there. Squyres leads off with a presentation showing Emily and Jake's analysis of our driving situation. We were supposed to leave Home Plate by sol 760 and spend roughly 25 sols driving to our winter home. Curiously, if we delay our exit until sol 780, we get more drive sols in the 25 sols following (thanks to restricted sols and interference from MRO in the earlier period), though the 780 start leaves no time or power for science. "If we leave at 780, there's no stopping even for dinosaur bones," is how he puts it.
There are three big contenders for our winter home:
- A flatiron slope to the southwest. This would offer good northern exposure, but the path to it may be blocked, it's far away, and it doesn't look too scientifically interesting.
- Von Braun Hill, just south of Home Plate. Its base is readily accessible, but the interesting stuff, a huge caprock, is likely out of reach because the slopes leading to it are too steep. What's left is insufficiently scientifically interesting for a 200-sol winter.
- The north flank of McCool Hill, our original plan. This turns out to have at least three huge bedrock exposures (named Korolev, Oberth, and Faget, all after rocketry pioneers). It's farther away than Von Braun, but offers us good tilts and great science.
So McCool Hill wins. But the next question is how to get there -- across Home Plate, down and clockwise, or down and counterclockwise. That's one for me, and I tell them how I see it.
"Any of our three paths to McCool could be blocked. We could drive all the way across Home Plate, only to find there's no way down the other side. From orbital and Husband Hill imagery, we can't prove that we can get around Home Plate, either to the clockwise or counterclockwise directions, without running into a cul-de-sac and needing to come back. Therefore, despite your sol-780 scheme, we need margin: we need to get moving now, and keep moving.
"Of the three paths, I favor crossing Home Plate. Any of the paths could be blocked later, but backing down off of Home Plate will take a sol, maybe two, where we don't make any real progress toward our goal. My next choice would be the clockwise path, since that's better for energy reasons -- we'll have a more easterly tilt. Counterclockwise is my last choice."
Guess which way the science team wants to go? No prize for the right answer. The counterclockwise path will offer significantly better geology. The west side of Home Plate -- the side the counterclockwise path will take us along -- is apparently a much taller face, with more stratigraphy exposed. So Steve punts, asking if we can consider the question Friday, after we've had a chance to do more analysis of the power differences between the clockwise and counterclockwise paths. (The top of Home Plate doesn't appear to offer us anything of comparable interest to either of those paths, so it's out of the running in his mind. Naturally, I've already picked out the waypoints for our first drive along the top. Sigh.)
Well, this gives us enough direction to get ahead on tomorrow's sequencing. We know we're going downhill, so I go ahead and pick out the waypoints for that drive. Plus, they sketch out the IDD work they'll be asking for tomorrow, and Ashley gets that sequence in the bag. Our Monday pass comes back on the table after all, so they drop the four-sol plan -- tomorrow we'll do a three-sol plan, planning Thursday through Sunday and coming in Monday as normal. But we'd have been ready for it. It would have been awesome.