Two instruments at the end of the robotic arm on NASA's Mars rover Curiosity will use calibration targets attached to a shoulder joint of the arm.

Two instruments at the end of the robotic arm on NASA's Mars rover Curiosity will use calibration targets attached to a shoulder joint of the arm. One of these is the Mars Hand Lens Imager (MAHLI), which is an adjustable-focus color camera. The other is the Alpha Particle X-Ray Spectrometer (APXS), which can identify chemical elements in rocks and soil. This photograph, taken in August 2011 as the spacecraft was being prepared for launch, shows the MAHLI calibration target positioned above the APXS calibration target.

The location of these targets is also visible in photographs of the whole rover at and . They are attached to the azimuth actuator of the shoulder, which is the one that moves the arm left or right, rather than the shoulder's elevation actuator, which moves it up or down.

The MAHLI calibration target includes a penny at the center of this image, plus color chips, a metric standardized bar graphic, and (just below the penny) a stair-step pattern for depth calibration.

The coin is from 1909. That was the first year Lincoln pennies were minted and the centennial of Abraham Lincoln's birth. The penny is a nod to field geologists' informal practice of placing a coin as a size reference in close-up photographs of rocks, and it gives the public a familiar object for perceiving size on Mars easily.

Patches of pigmented silicone on the upper portion of the MAHLI target serve as aids for interpreting color and brightness in images. Five of them -- red, green, blue, 40-percent gray and 60-percent gray -- are spares from calibration targets for the Panoramic Camera on NASA's Mars rovers Spirit and Opportunity. The sixth contains a fluorescent pigment that glows red when an ultraviolet light source on MAHLI shines on it.

The target's bar graphic is adapted from a standardized U.S. Air Force chart for testing camera resolution. Numbers on it refer to how many of the black-white cycles fit into one millimeter. For example, in the largest set of bars, labeled 1.0, each black bar is one-half millimeter wide and each white space between bars is another one-half millimeter. One millimeter is about 0.04 inch. Applied Image Inc., Rochester, N.Y., made the portion of the MAHLI calibration target with this chart and other graphics on opal glass. One of the graphics, just above the left edge of the penny, is a tiny cartoon figure called "Joe the Martian."

The APXS calibration target is a slab of well-characterized basaltic rock surrounded by nickel plate. While Curiosity is working on the surface of Mars, this target will be used periodically to check the continuing performance and calibration of the APXS instrument. The basaltic sample in the target is from near Socorro, in central New Mexico.

NASA's Mars Science Laboratory mission launched on Nov. 26, 2011, and will deliver the rover Curiosity to Gale Crater on Mars in August 2012. With MAHLI, APXS and eight other science instruments, Curiosity will investigate whether the area has ever offered environmental conditions favorable for microbial life.

Malin Space Science Systems, San Diego, supplied MAHLI and three other cameras for the mission. APXS was supplied by the University of Guelph, Ontario, Canada, with funding from the Canadian Space Agency and manufacturing by MDA, in Brampton, Ontario, Canada. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, in Pasadena, manages the Mars Science Laboratory mission for the NASA Science Mission Directorate, Washington, and built Curiosity.




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