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Almost Ready for the Real Thing
By Jeffrey Marlow

Following an intensive period of soil scoop testing, Curiosity has begun to use its new capability to feed on-board scientific instruments samples from the martian surface. Recent scoop payload was distributed to the CheMin instrument for X-Ray Diffraction analysis, and the camera teams have been measuring grain size distributions. And now, the Sample Analysis at Mars (SAM) instrument is gearing up for its first look at the soil.

If organic molecules are to be found in Gale Crater, it's SAM that will do the finding: the instrument is an analytical powerhouse capable of sniffing out part-per-billion concentrations of certain molecules. Benny Prats is an engineer at Goddard Space Flight Center, and a SAM collaborator since 2007. He was manning the instrument team room on sol 79, reviewing the set of commands that will occupy SAM for the next three sols.

1st Sol: Clean one of the instrument's 54 empty sample cups.
2nd Sol: Move the cup underneath the sample input funnel. (When things get real, this is where a carefully apportioned pinch of soil will enter the instrument. On the upcoming trial run, no such transfer will occur.)
3rd Sol: Perform the analysis - an elaborate, carefully choreographed process of heating here, cooling there in order to shuttle various fractions through the plumbing at just the right times.

Of course, the actual coded commands are a bit more complicated, the product of years of optimization and testing. But as such programming goes, SAM's operating system is relatively straightforward. "The scripts are written in Basic computer code," says Prats, "so they're very easy to understand." This simplicity proved useful for the team, as it removed a traditional barrier to collaboration between scientists and engineers: if the coding aspect is overly complicated, the two groups are effectively speaking different languages, and important details can get lost in translation. "Scientists can easily write these codes," Prats says, with the tone of a seasoned engineer.

At the end of the three-day test, the team will have a reliable "blank" of martian operating conditions. The instrument and its analytical innards have been calibrated - extensively - on Earth, but "we're so sensitive to any signal that we need to know how the baseline is different in each situation," says Prats. For example, differences in atmospheric composition, pressure, and temperature could all cause different molecular building blocks to elute at different times, and it's important to not mistake such discrepancies for actual signal from the surface material.

In the coming weeks, SAM will use its newly acquired background measurement to inform its initial investigation of martian soil, an experiment that has everyone on the edge of their seats. "This is a full-scale dry run," Prats explains, "so that we can get our act together for the real thing."