This behavior had varied in our two sample test venues (one is a full-scale rover mockup operated at ambient, the other is an environmental test chamber with a different arm) and is fundamentally non-linear. However, it ended up remarkably well-behaved and reasonably repeatable on Mars. It is well worth noting that this environmental testing is part of an entire parallel campaign at JPL called Qualification Model Dirty Testing (QMDT) with a team including many original designers that continues to work feverishly to scoop and drill a wide array of plausible materials under more realistic pressure, humidity and temperature (and to a certain extent electrostatic) conditions. Their characterization testing has informed most of the system sample processing architecture, as sample flows unrealistically at Earth ambient conditions compared to those of Mars.

Vibe dynamics (which plays a significant role in how sample flows and packs) are somewhat tricky. One of our commissioning phase activities attempted to characterize vibe dynamics in a couple of critical poses for comparison, to confirm that the behavior on Mars was not too dissimilar from our experience here on Earth. We don't have accelerometers on the turret, so we read the tea leaves of vibe actuator current plots over a set of ascending voltage step functions, looking for discontinuities indicative of resonant peaks. The vibe pulses help us to discretize the leveling and tend to remove sample more predictably, reducing the impact of variability in dynamics. Vibe dynamics depend primarily on vibe rate and arm orientation (and by extension the axis of rotation of the vibe actuator relative to the arm, as vibe is induced by a spinning eccentric mass). As such it is infinitely variable. On Earth, we acclimate our ears to this range, and speak of "well-behaved vibe" (something like a raspy blender) and "naughty vibe" (something like a lilting two–stroke motor). There's a pretty wide spectrum with a number of variations on the theme.

For our first four scoops (but not for the fifth), we enforced a conservative ground-in-the-loop process before closing the scoop, assessing images to confirm that we didn't have pebbles on the lip or in the scoop and that our scoop sample volume was appropriate. This self-imposed cycle cut the day’s arm activities short and contributed another component to the length of our stay (driven to a large extent as it was by fully completing a set of arm activities). Furthermore, the amount of arm activity per sol is still modest, at a few hours or so a day. In large part, this imposes a ceiling on perceived complexity, to which many in the review process are sensitive, especially for first-time activities.

But there were additional constraints that tended to pare a sol’s activity to size. Every day, each command has to be reviewed three times along the way in the sol’s planning cycle. We always plan around our one to several Odyssey and/or Mars Reconnaissance Orbiter afternoon communications passes, during which other activity stops. These passes can be variable in number and spacing with each new sol and make robustness to sol slips and any sort of activity packaging optimization a challenge. Conservative projected actuator heating windows mean we only start arm ops near mid-sol currently. Cleanup windows and duration margins have to be allotted for each comm pass and sleep/wake cycle. Margined power budgets can sometimes cut arm activity short, especially when performing instrument analyses overnight, which is otherwise a period of battery recharge. As we often were taking images, suitable lighting dictated that we could not operate into the early evening. The conservative use of windows for dropoff with the least disadvantageous wind effects also tended to limit the day’s arm activities. There were several additional ground-in-the-loop cycles for some planned and unplanned activities. In addition, I’ve not even scratched the surface of all the science activities, which had their own set of constraints that had to be interwoven with those of the engineering activities, with some sols at Rocknest allotted entirely to instrument checkouts and prep, or remote or contact science.

Decontamination of the polished interior surfaces of CHIMRA was a primary purpose and consumer of time at Rocknest. Terrestrial organic contaminants composed of fine particulates in the air are deposited in even the best of clean rooms here on Earth. Those remaining attached through launch and EDL loads require additional stimulus for removal. That stimulus is essentially an extended period of contact with vibrating sample, in turn on all the amenable facets of CHIMRA's interior. Contaminants are scrubbed loose to be swept away and diluted into sample dumped to the side of the rover. Reducing the concentration of these particles in this decontamination activity helps to prevent subsequent, undesirable removal into sample bound for an instrument during our nominal sample preparation activities, which also make use of significant amounts of vibe. The SAM instrument is extremely sensitive, and without the steps we took, our models indicated that we could far exceed their threshold for allowed contamination. These models were calibrated by swab tests in ATLO, projected outgassing and other effects during launch, cruise and descent, and empirical testing of contaminant transfer coefficients under vibing sample. (Note that CHIMRA’s interior surfaces are but one of several potential vectors for introduction of contamination into SAM).

Not only did we perform this activity once, we executed it three times to meet our target, with interstitial thwacks to further help clear loosened contaminants. These three iterations, from acquisition to the cleaning and imaging performed at the end of a cycle, took nearly 20 hours of execution time (performed across 10 or so nonconsecutive sols). And this bespoke activity was about as complex from a commanding and sample management perspective as our entire nominal sample process chain, which has been in work for years. Finally, we spent many sols acquiring the fifth scoop and dropping to SAM repeatedly, again to Chemin, and to the observation tray for APXS and MaHLI analysis. It adds up.

As part of the dectontamination activity, on sols 64 and 78 we actually took two videos with the left Mastcam of sample falling from the portion tube, up high and to the port side of the rover where we could see, as opposed to directly over the inlet covers. They were taken at about 9 to 10 frames per second (frame rate is a function of several factors, and this particular rate is a product of some compromises).