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Martian Diaries

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How a Science Camera Supports Curiosity's Scooping Efforts
By Jeffrey Marlow

As Curiosity continues its romp through the martian sandbox - scooping up sand and sifting it into different size fractions - scientists are eagerly anticipating a new data set.

But not all instrument teams are sitting on their hands. The Mars Hand Lens Imager (MAHLI) is playing a central role in the scooping effort, serving as a key link between scientists and engineers.

Curiosity's Robotic Arm Camera MAHLI

MAHLI is a 2-megapixel camera attached to Curiosity's robotic arm that is meant to simulate a geologist's hand lens and show fine scale details of martian materials. It can focus on targets as close as 0.9 inches or as far as the horizon. Features such as precise grain shape or rock weathering textures tell scientists a great deal about environmental conditions and mineralogy. Indeed, the discovery of sand-sized grains on Mars was only proved with a similar camera on the Mars Exploration Rovers in 2004, confirming key aspects of the planet's geological system.

MAHLI also has a motor that adjusts the configuration of the lenses to focus on a particular target, and this feature - called a "stepper motor" - has proved particularly useful for arm and scoop engineers.

Ken Edgett is the MAHLI Principal Investigator. In the moments before the first post-scoop downlink - when the team will know for sure if the process worked - Edgett is the only member of the science team around, sitting alone amid rows of power cord strips and empty desks. He's running through the camera's commands again, and tapping "refresh" every few seconds to see if the critical images have been transmitted yet.

First Scoop by Curiosity
This pairing illustrates the first time that NASA's Mars rover Curiosity collected a scoop of soil on Mars.

In the days leading up to the first scoop, MAHLI was used to determine just how far the robotic arm was from the target sand dune. The imager auto-focused on the claw-shaped tool, and by counting the number of incremental turns on the focus motor, Edgett and his team were able to give the engineers a precise location. "We know how the number of steps on the motor correlates with focus position," he said. "So we can look at that motor count and run it through an equation to get the distance."

When the numbers were crunched, it turned out that the scoop was within one millimeter of its pre-calculated goal. By using MAHLI in this range-finding way, engineers gained confidence in the programmed movement commands, setting the stage for Curiosity's triumphant initial scoop.