Scooping up soil blind could damage the scoop on Mars. To avoid this happening the Mars Hand Lens Imager (MAHLI) is playing a central role. This is an instrument where engineers and scientist have to work very closely together for best results.
MAHLI is a 2-megapixel camera attached to Curiosity’s robotic arm. Curiosity’s robotic arm serves as the geologist arm and MAHLI is the hand lens that any geologist would whipp out to view a sample of soil or a rock from close up. MAHLI can focus on targets as close as 2.2 centimeters (0.9 inches) or as far as the horizon.
This capabilities make it possible for us on Earth to look at fine grains and their shape. This is important as precisely this information tells scientists a great deal about environmental conditions and mineralogy. As ’seeing is believing’ being able to take such precise images by MAHLI helps the science on Mars make leaps and bounds. In 2004 a similar precise camera on the Mars Exploration Rovers told us a lot of the geology of Mars by showing us sand sized grains of soil.
Now how does MAHLI work?
MAHLI has a motor that adjusts the configuration of the lenses to focus on a particular target. Before a scoop of soil is taken MAHLI zooms in to tell us exactly what we are going to scoop up and sift in the belly of Curiosity. Seeing this upclose is ofcourse an enormous bonus for the engineers controlling the arm and scoop of Curiosity.
Ken Edgett is the MAHLI Principal Investigator. In the moments before the first post-scoop downlink Edgett is tapping “refresh” every few seconds to see if the critical images have been transmitted yet.
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.