100 Sols on Cape York — An Absurdly Brief (Read: Long) Summary (Part 5/8)

Part 5: The Trek North — Shoemaker Ridge

Sols
2735 to 2763

"tl;dr" Description
Power started to look tight. It was time to go find those north-facing slopes.

Highlights from Matt's Notebook

Sols 2756-275:

> Science wants a "quick" detour to the western apron of Cape York. This will cost us 2 or 3 drive sols, at the most.

Sols 2760-2762:

> LTP reports that we haven't found much in the way of science on this detour to the northwest. Tosol we will hit the apron dead-on and turn NE.

Details ("the deets")

Here, traverses became important and meaningful again. We'd been hanging out at Tisdale and Chester Lake so long we were, for all intents and purposes*, as the same spot. As such, this part of the story is all about traverse maps and miles under our feet. The hunt for tilty goodness led us in the direction of Shoemaker Ridge, a newly-named formation that forms the backbone of Cape York.

We were in such a hurry that we actually had to forego some systematic and detailed observations of the Ridout boulder perched on the eastern edge of the small Odyssey Crater.

I'll summarize from my own words:

The primary reason for the trek north was, of course, to find those slopes that give us good sun angles for good power. All estimates point to Opportunity surviving the winter with plenty of margin. However, margin can easily be eaten away by the unknown unknowns. With that in mind, we tried to reason how quickly we'd need to find a parking spot. January seemed a good last-minute date to aim for, if push came to shove. With that date in mind, we considered one other major factor: The launch of the Mars Science Laboratory on November 25.

The view periods of the MSL spacecraft after launch mean that they happen to just interfere with all other Mars missions. Immediate post-launch priority for DSN coverage of a spacecraft is very high; Opportunity, being much older and of a much lower status for requesting DSN time, gets the short end of the stick along with everyone else. This means that we may very well lose the time we've already scheduled with the DSN. Some more strategic analysis showed that if we did not finish mapping Cape York's northerly slopes by the time MSL launched, December and January would not provide us enough time to do that mapping because the incoming solar power would be too low.

We had made it clear: Thanksgiving or bust.

There is some confusion about why we went to the north for power. The reason is because that's where the north-facing facing slopes of Cape York happened to be, and it had nothing to do with them being closer to the equator where there is more incident solar energy on our arrays. In fact, as far as some of our analysis tools are concerned, we're in the same place that we landed in 2004**. Even over some 30+ kilometers, there is no discernible difference in solar power than we can measure, all else (like tilt) being equal — and we can certainly expect the same for the few hundred meters that Cape York spans north to south. We also looked to the south towards Cape Tribulation, where there were even better north-facing slopes; they were too far away for us to make it in time for winter.

It's worth keeping in mind that our long-term strategy is go south towards Cape Tribulation because the strongest signals of sciencey things (smectites) were seen from orbit near its peak. The MER team — both science and engineering — kept this concept at the front of the conversations concerning where to park for the winter. After some long and fruitful discussions, it was obvious that Cape York hadn't given up all of its fruits yet. It was an entirely new type of formation with clues of some real juicy stuff at the Tisdales and Chester Lake. Putting on our 20-20 hindsight glasses, we now know that to go south for the winter would have meant a big missing piece of the puzzle that tells us about water on Mars. Without those glasses, we had to make a decision. We went north to the small "lily pads" that the orbital imagery and elevation maps identified as having 15 degrees or more of northerly tilt. Some of these lily pads were at least the width of the rover and there appeared to be some other targets worth our time, such as a nice set of outcrop or a perch spot for a high-resolution Endeavour Crater panorama. 

Backing out for context: Our arrival point at Cape York, by now some 60 sols ago; the suspected smectite goodies from orbital observations; and the suspected location of the north-facing lily pads for winter hunkering.

We greased the wheels up (literally, actually — we heat those suckers to get the lubrication flowing) and boogied on out of Chester Lake, climbing a very slight hill and crossing over the region of negative northerly slopes to the region of positive northerly slopes. The next half dozen or so drives along the Shoemaker spine were relatively uneventful, with the exception of a jut to the west and back to capture a small indent:

This area in the green is, in a way, a dead zone of Cape York. Not a lot of interesting things going here. At about this time, the science team started looking closely at those orbital images and making hypotheses: maybe there was an exposed "vein" in the rough? maybe we could snap a few images as we see them? maybe we could even poke at them? The RPs had made such good time cutting along Shoemaker Ridge (that green area) that we had bought ourselves a week (in sols) of margin for mapping the north-facing slopes with local imaging by the rover. 

Whaddya know, we found a good vein as we approached the western apron on Cape York (here, I maintain the same labeling for context):

As seen by Oppy on the approach:

Mmm. More in Part 6, a part I never really did in detail the first time around.

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*Not, apparently, "for all intensive purposes," as I found out probably two years ago. It unnerves me that I didn't know this for the first 23 years of my life. I can't tell if this is on the same level as an Ecam PUL not knowing who Robert Plant is, or a Mission Manager telling me they thought "God bless you" was actually something like "kuh-bless-ya" until they were 12.

** Blasted typos. "I assume that is because we landed through some weird subspace wormhole and went back in time right?" Mike the Mission Manager is ever watchful.