23 April 2012

The Joys of Fake Geology

Posted by Ryan Anderson

Well, I survived Operational Readiness Test 8 (ORT)! Prior to this week, my only experience with rover operations was as payload downlink lead (PDL) for the color cameras on the Mars Exploration Rovers (MER). I joined MER well into the extended mission, when all of the bugs had been worked out and the planning process was very efficient and streamlined.

My day as a Pancam PDL is pretty easy: take a look at the pictures that came down, check to make sure that the cameras are healthy and that we took pictures of the right things, write down the results of those checks in a short report, and then attend a ~45 minute telecon to tell the team what I just typed in my report. I never experienced the joys of the uplink side for MER.

For this ORT, among other roles I was the second-shift science Payload Uplink Lead (PUL) for ChemCam, which means that I finally got to experience the rest of the planning day that I always missed as a Pancam PDL. The uplink role is split into two shifts because it would be cruel and unusual punishment to make one person work from when the data comes down in the morning until the next day’s commands are sent up to the rover, late at night. Also, people working for that long would start to make mistakes, and we don’t want to damage the rover because someone needed a nap.

After the early meeting where the PDLs report on the data received, the science teams run off with the data and come up with a list of things that they want to do the next day. Then those requested activities are compiled into one big plan that inevitably would require way more power, time, or data volume than is available. So then comes the Science Operations Working Group (SOWG) meeting, where everyone crams into one room and we go through the list of proposed activities and figure out how to make things fit. Usually some observations have to be cut, or shortened. After the SOWG, the PULs for each instrument go off to make minor changed to the plan.

Once refinement is done, there are some smaller meetings, followed by the Activity Plan Approval Meeting. At APAM, we step through the plan line by line again, and make sure that everything is approved. At this point things are pretty much solidified and so we also review more accurate predictions of how much power, data, and time the plan will require. Once APAM is over, the first shift PULs leave and the second shift takes over to turn the plan into actual sequences, which are the actual sets of code that tell the rover what to do.

Once the sequences are written, the second shift PULs have to check to make sure that they do what is intended and don’t violate any “flight rules”. For example, ChemCam isn’t allowed to zap the rover, so we have to double-check the laser pointing. ChemCam actually has separate engineering and science PULs: the engineering PUL generally writes the sequences and the science PUL checks the pointing and makes sure that the laser will hit the right targets. The science PUL also has to check and make sure that the observations are “sun-safe”. ChemCam is a big telescope, and that means that if it is pointed too close to the sun while focused, it can damage the optics. Even when the telescope is defocused, it can’t point at the sun for more than a few minutes because it still heats up the optics too much. (You might be wondering why we would ever want to point at the sun: Sometimes it is necessary to point the cameras at the sun to make atmospheric measurements, and ChemCam points in the same direction as the other cameras on the mast.)

The PUL finished writing the sequences and then “delivers” them so that they can be combined into one big plan. There are two more meetings at the end of the day where the team once again steps through every sequence, and then through every line of code that is going to be uploaded to the rover. In case you couldn’t tell, we are really careful about what gets sent to the rover!


Of course, the thing that makes all those tedious meetings worthwhile is the science, so let’s revisit that step of the process in more detail. The science team is split up into several “theme groups”, each of which takes a look at the data that was downlinked from the previous sol and comes up with a list of things to do. The theme groups are: geology (GEO), mineralogy (MIN), volatiles and isotope geochemistry (VIG), environment (ENV). I was the “keeper of the plan” for the MIN group twice this week, which means I got to put together the requested activities to be passed on to the SOWG meeting. The science theme group meetings tend to be a barely-controlled chaos of speculation and debate and bad science jokes and lots of meandering side conversations.

For this ORT, we were placed a few feet away from a really spectacular “outcrop” of rocks. This was actually a pile assembled by some folks at JPL, but they managed to get some really interesting chunks of rock to keep the scientists nice and busy. Unfortunately, I don’t think I’m allowed to share images from the testbed rover, but I can give you similar examples. There was a big block full of pisolites, sort of like this:

There was also a light-toned rock with thin, darker layers that I am 99% sure came from the evaporite sequence that I visited during the Mars Sedimentology and Stratigraphy workshop a couple of years ago. In fact, I have photographic evidence that the lead engineer for the MSL drill took a bunch of rocks like this back to JPL.

There was also a nice slab with symmetric ripples on its upper surface:

And another that had some weird deformed ripples, sort of like this but much more dense and jumbled-looking:

And on and on it went. And then at the base of the outcrop was a patch of lighter-toned soil that was the target for our scooping activity on Friday. Of course, the science team had a field day trying to interpret this outcrop and patch of soil. In the afternoons while the PULs are going through some of their meetings, the science team gathers for the science discussion meeting, where people can give presentations about their latest hypotheses. On Saturday we had several fun presentations presenting hypotheses for how such a wide variety of rocks might end up in one place. One suggested that they were deposited as a debris flow from the crater rim. Another hypothesis suggested that the outcrop was “intelligently designed” to have pieces representative of the major rock types that you might expect if you had an alluvial fan deposit interfingering with lake sediments (something that is entirely possible for our landing site in Gale crater). Another presentation focused on the patch of salty soil and came to the conclusion that it is very geologically strange, and that it is almost like it was carried from elsewhere in some sort of container and dumped at its current location!

All of these got some laughs, but they also were great practice for the real mission. Someone brought up the very real and important point: what if we found a pile of disparate rocks like this one? Even though they are out of place, each rock has a fascinating story to tell. Would we spend months analyzing every single interesting thing in one jumbled up outcrop, when there is a 5 km high outcrop waiting for us in the form of Mount Sharp? How do we prioritize?

We also had the beginnings of some great discussions about what types of additional measurements would we want to make if we had more time at this outcrop? For example, APXS analysis showed that the light-toned soil that we scooped was high in sodium and chlorine (almost as if it were a pile of rock salt!), but there are minerals other than halite that have high Na and Cl and the APXS spot is large so it got a mix of materials. The scooped sample will also be a mix of the light-toned stuff and the surrounding dark gravel, but ChemCam would be able to analyze individual grains to get their composition.

Likewise, the chaotic arguments in the science theme groups were a great illustration of where some better organization might help make discussions during the primary mission more productive. We learned that sometimes it makes sense to combine certain theme groups when they have similar objectives, and that it is nice to have a Keeper of the Plan, but that people need to not crowd around them and stress them out.

The week was also riddled with minor and major problems that were lovingly referred to as “test-isms”. These ranged from bugs in the software that we were using, to getting permission to exceed our power budget so that all the instruments could get more practice, to the fact that some of the instruments (such as ChemCam) were getting fake data since they aren’t currently installed on the test-bed rover.

It has been a really exhausting week, and I can only imagine how hard it will be when we are on Mars and we have months and months of living on Mars time. But this week was also a great learning experience and an exciting taste of things to come. For all the “test-isms”, the team is really getting better at operating the phenomenally complicated machine that is on its way to Mars right now. It’s going to be a blast once we are on the surface and we have a real outcrop to argue about!