MSL Picture of the Day: T-31 Days: instruments: MAHLI

MSL Picture of the Day: T-31 Days: instruments: MAHLI

Ken Edgett is the principal investigator for MAHLI. Edgett works at Malin Space Science Systems (MSSS), San Diego, California. He is a geologist who has helped run cameras on several Mars orbiters.

The Mars Hand Lens Imager, or MAHLI, is one of 4 cameras designed, built and operated by Michael Malin and his team. It will not surprise you to know that this camera shares some traits with the three other cameras on Curiosity from the same company.

Like the other cameras it uses a red-green-blue filter grid, just like the one on commercial digital cameras for obtaining a full-color image with a single exposure. Its image detector is a charge-coupled device with an array of 1,600 by 1,200 active pixels, which will give us square images of Mars of 1,200 by 1,200 pixels. It stores images in an eight-gigabyte flash memory, and it can perform an onboard focus merge of eight images to reduce from eight to two the number of images returned to Earth in downlink-limited situations. It is this focus merge that makes up for the lack of megapixels each of these cameras have. Merging the pixels from other images taken exactly the same object gives Michael Malin and his team the chance to dazzle us with much sharper and more detailed images. The instruments supplied by Michael Malin are run by a unified imaging-science team which combines experience in geologic field work, Mars exploration and space cameras.

the MAHLI is a focusable color camera on the tool-bearing turret at the end of Curiosity’s robotic arm. Researchers will use it for magnified, close-up views of rocks and soils, and also for wider scenes of the ground, the landscape or even the rover. Essentially, it is a hand-held camera with a macro lens and autofocus.

The investigation takes its name from the type of hand lens magnifying tool that every field geologist carries for seeing details in rocks. Color, crystal shapes, mineral cleavage planes and other visible details from such close-up observation provide clues to a rock’s  composition.

In sedimentary rocks, the sizes and shapes of the grains in the rock, and the scale of fine layering, provide information about how the grains were transported and deposited. Sharp-edge grains have not been worn down by tumbling long distances, for example. The size of grains can indicate whether the water or wind that carried them was moving quickly or not.

These clues garnered from MAHLI images can aid both in selection of which targets to analyze with other instruments and in directly reading the environmental history recorded in the rocks and soils the rover encounters.

As a close-up magnifying camera, MAHLI resembles the Microscopic Imager instrument mounted at the end of the robotic arm on each of the twin Mars rovers Spirit and Opportunity. MAHLI has significantly greater capabilities than those predecessors, however: full color, lights and adjustable focus. Also, it sits on a longer arm, one that can hold MAHLI up higher than the cameras on the rover’s mast for seeing over an obstacle or capturing a rover self-portrait.

When positioned at its closest range — about  21 millimeters( 0.8 inch) from its target — the camera’s images have a resolution of slightly less than 14 microns (one one-thousandth of an inch) per pixel. The field of view for that close-up is a rectangle about 2.2 centimeters   (0.9 inch) by 1.7 centimeters (0.7 inch).

This MAHLI image shows a 26.2 by 19.7 mm (1.03 by 0.78 inches) area on a rock imaged at a scale of 16.4 microns (0.0006 inch) per pixel. The rock is a dense zinc ore from Franklin, New Jersey; the red mineral is zincite (zinc oxide, ZnO4). The 1 mm scale bar equals about 0.04 inch. The picture was taken during MAHLI camera head post-vibration testing on 3 September 2008.
Image credit: NASA/JPL-Caltech/Malin Space Science Systems

The camera can be held at a series of different distances from a target to show context as well as detail by adjusting the focus. At about 1 meter (3 feet) from a target, it still has a pixel resolution of half a millimeter (about 0.02 inch) in a view covering an area about 2 feet (70 centimeters) wide. By manipulation of arm position and focus, the camera can be used to examine hardware on the rover or record time-lapse views of activities such as opening a sample inlet cover.

MAHLI has two sets of white light-emitting diodes to enable imaging at night or in deep shadow. Two other light-emitting diodes on the instrument glow at the ultraviolet wavelength of 365 nanometers. These will make it possible to check for materials that fluoresce under this illumination.

Curiosity carries a vertically mounted calibration target for MAHLI, for checking color, white balance, resolution, focus and the ultraviolet illumination.

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