The MAGI Group - Beagle 2 Page
Mars Atmosphere and Geology Imaging
Lunar and Planetary Lab, University of Arizona
Tucson, Arizona
Page last updated 2000/03/24
Background:
The European Space Agency is preparing to launch a Mars lander in 2003. One of the lander's objectives is to examine rocks up close and to drill/grind through the surface weathering layer using a grinder and drill on the end of a robotic arm. To examine the rock structure up close a microscope is also mounted on the end of the arm. Because of our experience in designing and building the microscope in the MECA instrument for the NASA/JPL 2001 Mars Lander, we were asked to design the optical head for this microscope. The optical head incorporates the lenses and the LED illumination system. The majority of operations will be at night to conserve power. The illumination system will allow imaging at night and in color. This system can also be used to image soil and rock samples brought up by other instruments.
For more information on the Beagle 2 mission
Optical Head:
The optical head will image the rock surface onto a CCD, the resulting images will be digitized and be sent back to Earth. The CCD module has a monochrome CCD. In order to generate color images, the head will be able to illuminate the rock or soil in three colors, Red at 635 nm, Green at 534 nm, Blue at 472 nm. A full color image can then be generated by taking an image with each LED color on, sending the three images back to Earth, and then combining then into a full color image. In addition, there are UV LED's radiating at 370 nm that can cause rocks to fluoresce, which may help in identifying the minerals present. The CCD has 1K x 1K - 14 micron pixels. The magnification of the lens is 3.5. The gives the microscope 4 micron resolution over a 4 mm x 4 mm field of view. The optical head assembly is about 45 mm in diameter, 27 mm long, and weighs 46 grams. It is designed to be powered by a 6 volt supply. The typical current for a single LED is 13 ma.
STM3 - Structural Test Model 3 - Prototype Optical Head:
To test the vibration characteristics of the camera and to get some initial imaging experience, a prototype optical head was designed and built. The head differs from the flight design in that it has a commercial cemented doublet lens instead of an air ( really mars atmosphere ) spaced triplet design. The windows are plain glass instead of sapphire. The doublet lens has a curved focal surface at the object and has much lower resolution than the flight lens in the corners. The flight lens will have a flat focal surface at the object, and the corner resolution will be almost as good as the center. The doublet is also a much slower lens, F/# 6.2 vs. F/# 2.6 for the flight. This makes the exposures about 5 times as long, but gives about 2.5 times the depth of focus. The doublet also has slightly lower magnification, 3.2 vs. 3.5 for the flight.
Pictures of the prototype optical head - STM3:
Links to some images of the prototype assembly.
Side view of optical head and cable
3/4 view of optical head on adapter for CMOS-PRO camera.
Imaging with the prototype optical head:
The prototype optical head was mounted to an active pixel sensor camera, the CMOS-PRO. This camera generates a monochrome 960 x 800 pixel image. The camera has 11 micron pixels so the resolution is slightly higher and the field of view smaller than the flight sensor. Several images were taken and the individual monochrome images combined into full color images. An image of 1 micron silica was used for white balance, i.e., the balance of the three colors were adjusted to make a well lit area of this sample have the same value for all three colors. Most of the samples were also imaged in UV, although very few of them produced any fluorescence. Three known fluorescent rocks were tested, however, some were so dim that the camera had difficulty detecting it. Exposures longer than 1 second resulted in noisy images, from thermal noise in the sensor. The exposures shown for the UV images were calculated based on multiplying the actual exposure by the amount the image was stretched to make a viewable picture. The actual operating conditions at night on Mars are very cold, (-90 C), so there will be no thermal noise to limit long exposures.
Test images of soils and particulates:
Links to some images of soil samples and particulates taken with the STM3 prototype optical head assembly and the CMOS-PRO camera.
Soil sample from Death Valley at Mars Polar Lander test site.
Soil sample with black rock from Death Valley at Mars Polar Lander test site.
Soil sample from Hawaii, Palogonite ( fines )
Soil sample from Hawaii, Palogonite ( coarse )
Soil sample from Wilcox Playa, Arizona ( fines )
Soil sample from Wilcox Playa, Arizona ( coarse )
Soil sample from the Mars Garden at Lunar and Planetary Lab, Tucson, Arizona
Test images of rocks:
Scapolite ( variation of Meionite) ( Fluorescent rock)
This page created and maintained by Roger Tanner, please email comments to me at rtanner@lpl.arizona.edu