Mars Science Laboratory (MSL)
Mars Hand Lens Imager (MAHLI)

Instrument Description

The MSL MAHLI consists of a camera head, which will be mounted on the end of MSL's Sample Acquisition Arm, and an electronics box, which will be housed inside the MSL rover body.

The Mars Hand Lens Imager (MAHLI) will be mounted on the end of the MSL Sample Acquisition Arm. Its purpose is to acquire very high resolution and microscopic color images of materials on the martian surface--rocks, fines, and frost. It will be used to help characterize the geology of the site investigated by MSL, and it will be used to document the materials being examined by MSL's geochemical and mineralogical experiments.

The Mars Exploration Rovers (MER), Spirit and Opportunity, each carried a Microscopic Imager (MI). The MI images resulted in a revolution in Mars science, permitting geologists to see martian surface materials at a scale that was not available on previous Mars missions. For the first time, MI images confirmed the presence of sand-sized grains (sand is defined by geologists as grains of 62.5 to 2000 micrometers in size) on Mars. Sand was long suspected but not confirmed to occur on Mars until the 2004 missions acquired MI data. The MI instruments have greatly contributed to the understanding of the geology and geologic history of the Spirit and Opportunity landing sites.

MER MI images are grayscale (black-and-white) and observe materials at about 30 micrometers per pixel. This resolution is sufficient to see sand-sized grains on Mars, but insufficient to characterize the nature of the smallest sand grains. Having a good look at sand grains provides key evidence to help geologists decipher the history of a sand-bearing material, such as a dune, ripple, or sandstone. The desire to resolve details on the finest sand grains led to the requirement that the MSL MAHLI will be capable, if placed close enough to the target material, of obtaining images of 12.5 micrometers per pixel.

The basic characteristics of MAHLI are as follows:

• MAHLI consists of two hardware elements: a camera head, mounted on the Sample Acquisition Arm, and an electronic box, housed in a temperature-controlled environment inside the rover.
  
  
• MAHLI shares common elements in terms of design, parts, and labor, with the other MSSS cameras for MSL, the MastCam and MARDI.
  
  
• MAHLI uses a Bayer Pattern Filter CCD array to obtain natural color pictures of a quality just like that of commercial digital cameras. Most color systems flown to Mars previously require at least 2 or 3 images acquired by looking through different visible light filters to obtain color, and then there is always the inevitable question, "Is this what the human eye would see?" With MAHLI, MastCam, and MARDI, the Bayer Pattern Filter CCD array permits an answer to this question, an answer of "Yes". For MAHLI, specifically, having color provides an improvement, relative to the MER MI, for the geologists' ability to interpret the mineralogy of the material being studied.
  
  
• The CCD array used by MAHLI is 1600 by 1200 pixels in size. MAHLI uses all 1600 by 1200 pixels for each color image.
  
  
• MAHLI has a motor that allows the position of the lenses to be adjusted, so that the camera can focus on its target. The MER MI did not have a focus mechanism, and thus focusing was done by moving the rover's robotic arm to a distance from the target that was known to provide in-focus images.
  
  
• When taking close-up images like the MER MI and MSL MAHLI can do, often there will be features in the image that are not in focus, especially if the target being imaged is somewhat lumpy or varied in texture. MI solves this problem by having the MER robotic arm move the camera a few steps into and out of focus, and a suite of pictures is returned to Earth and fused together mathmatically to provide a best, in-focus image. MAHLI will do this, too, but it will not require the robotic arm to move, it will use its focus mechanism. In addition, software in MAHLI's electronics box will fuse the images into the best-focus picture and compute a range map, based on the distances indicated by each focus position.
  
  
• MAHLI has a suite of white light LEDs and a suite of ultraviolet (~355 nanometers) LEDs to provide illumination of the targets it is imaging. The white light LEDs permit the instrument to operate at night and allows the science team to avoid problems of shadowing during daytime imaging. The ultraviolet LEDs provide an opportunity to look for minerals that fluoresce. Many fluorescent minerals on Earth are the very same types that may indicate the past presence of water at a given site.
  
  
• MAHLI can focus at infinity. This means that, in addition to being able to get microscopic views of surface materials at the 12.5 to 75 micrometers per pixel scale, MAHLI can also be used for other purposes, including self inspection of areas on the rover that the rover team may want to examine as the mission progresses. MAHLI will also be usesd to characterize the granular materials that have been prepared for study by the geochemical and mineralogical instruments of MSL's Analytical Laboratory.
  
  
• Stereo (3-d) views of selected targets can be acquired by taking 2 images of a target from different looking angles. This is achieved by moving the robotic arm to place the camera in the two different positions.
  
  
• MAHLI has a dust cover, to protect the optics from becoming coated by fine dust and dirt. The MSL Project is planning to provide a contact sensor that will protect MAHLI from accidentally touching a target surface when the dust cover is open.