Mast Camera (Mastcam)
PI: Michael C. Malin, Malin Space Science Systems
The Mast Camera is a two-instrument suite of imaging systems mounted on the MSL rover's Remote Sensing Mast (RSM), with the boresight ~1.97 m above the bottom of the wheels when the rover is on a flat surface. As proposed and as late as the instrument Critical Design Review (CDR) in February 2007, the Mastcam consisted of two identical area-array digital cameras each with a 6.5-100 mm (15:1) variable-focal length (VFL) (zoom telephoto) lens, whose electronics were identical to the electronics of the MARDI and MAHLI cameras, also provided by Malin Space Science Systems. These cameras would have provided same focal length binocular vision for stereoscopic studies at all focal lengths as well as 14 filter positions for scientific multispectral studies. In September 2007, NASA directed that the zoom capability be removed from the cameras. Between November 2007 and January 2008, new, fixed-focal length (FFL) Mastcam designs were generated, based on using the MAHLI focus mechanism design; these cameras are described below. In early 2010, NASA reconsidered the VFL cameras and work resumed on assembling these cameras, which will replace the FFL cameras described here if the work is completed in time and the instruments meet their requirements.
The FFL Mastcams (we use the plural here because the “eyes” of the FFL Mastcam investigation are not identical) as built and delivered consist of two cameras with different focal lengths and different science color filters. The stereo baseline of the pair is ~24.5 cm. One camera, referred to as the Mastcam-34 (M-34), has a ~34 mm focal length, f/8 lens that illuminates a 15° square field-of-view (FOV), 1200 × 1200 pixels on the 1600 × 1200 pixel detector. The other camera, the Mastcam-100 (M-100), has a ~100 mm focal length, f/10 lens that illuminates a 5.1° square, 1200 × 1200 pixel FOV. Both cameras can focus between 2.1 m (nearest view to the surface) and infinity. The M-100 IFOV is 7.4 × 10^-5 radians, yielding 7.4 cm/pixel scale at 1 km distance and ~150 µm/pixel scale at 2 m distance. The M-34 IFOV is 2.2 × 10^-4 radians, which yields a pixel scale of 450 µm at 2 m distance and 22 cm at 1 km. A strict definition of “in focus” is used for these cameras wherein the optical blur circle is equal to or less than one pixel across.
Fixed-focal length (FFL) Mastcams. The only distinguishing difference in outward appearance between the cameras is the aperture size in the front baffle.
Each camera has an 8 gigabyte internal buffer that permits it to store over 5,500 raw frames. Each camera is capable of losslessly compressing the images, or applying lossy JPEG compression, in realtime during acquisition and storage, although it is more likely that images will be acquired raw and compressed just prior to downlink to Earth. The 8 gigabytes is equivalent to a full-scale mosaic of 360° × 80° imaged in 3 science color filters with >= 20% overlap between adjacent images. With minimally lossy JPEG compression (e.g., a factor of 2), a mosaic including all science filters could be acquired. This is much more than can be transmitted back to Earth under normal communication limitations. Subframing of images is only available at acquisition, not during later processing. Color thumbnail images of 150 × 150 pixels can be created simultaneously with the acquisition of full scale images, or during processing just prior to downlink.
Both FFL Mastcams are color imagers. Integrated over each detector is an RGB Bayer pattern filter (GR/BG unit cell). A broadband (IR cutoff) filter through which RGB imaging will occur is included in one of the 8 filter positions within each camera's filter wheel. Both cameras also include a narrow band filter with 10^5 neutral density attenuation to image the Sun for atmospheric studies. The filters are distributed between the M-34 and M-100 to ensure each camera can address some of the compositional objectives of the investigation should the other camera fail. The science filters are imaged through the RGB filter array. For some science filters, the throughput in some pixels of the unit cell will be poorer than in other pixels, but beyond 700 nm, all three Bayer colors have nearly identical throughput (i.e., they have large IR leaks, which we are using to our advantage). The figure below shows examples taken with the Flight FFL M-100 and its Bayer filter array throughout the IR-cutoff filter and through a 1035 ± 50 nm IR science filter. In-flight calibration uses the MER Pancam spare calibration target with magnets mounted beneath the four color chips and "white" and gray surfaces to provide dust-free spots (following the approach of the Phoenix SSI team).
Mastcam color filter passbands.
Relative passbands of the science color filters, RGB color filter array, and quantum efficiency of the CCD detector. The latter two are not shown to scale.
Mastcam hardware and internal processing permit a wide range of operational flexibility. Each camera is capable of acquiring images at very high frame rates compared to previous missions, including 720p high definition video (1280 × 720 pixels) at ~10 frames per second, and full science frames at somewhat greater than 5 fps. The full range of focus requires between 45 and 60 seconds, but autofocus around a predicted focus point can be accomplished much faster. Changes to consecutive filter positions take 5-8 seconds. It takes between 30 and 45 seconds to rotate the filter wheel a full 360°. Mosaic acquisition is paced by the time it takes the RSM to move and for motion-induced vibration to settle (<< 5 seconds between movements). The cameras include auto- and commanded-focus capability and auto- and commanded-exposure control. Radiometric accuracy is < 10-15%, and precision 5-8%. Exposure times are expected to vary from a few tens of msec to a couple of hundred msec, depending on the band-pass filter and the desired signal-to-noise ratio.
Two Mastcam-100 images, both taken with the Bayer color filters. Left image shows the single image RGB capability. Right image shows the uniform spectral response in the IR as viewed by the Bayer filters.
The primary objectives of the Mastcam investigation are to characterize and determine details of the history and processes recorded in geologic material at the MSL landing site. Both Mastcams can acquire panoramic, color, multispectral images and together are able to acquire stereoscopic observations to address the following specific objectives:
- Observe landscape physiography and processes in order to provide a full description of the topography, geomorphology, and geologic setting of the MSL landing site and the nature of past and present geologic processes at the site
- Examine the properties of rocks (i.e., outcrops down to clasts as small as 0.15 mm) and the results of interaction of rover hardware with rocks to help determine morphology, texture, structure, mineralogy, stratigraphy, rock type, history/sequence, and depositional, diagenetic, and weathering processes for these materials
- Study the properties of disaggregated materials (fines as small as 0.15 mm) to determine the processes that acted on these materials and individual grains within them, including physical and mechanical properties, the results of interaction of rover hardware with fines, plus stratigraphy, texture, mineralogy, and depositional processes
- View frost, ice, and related processes, if present, to determine texture, morphology, thickness, stratigraphic position, and relation to regolith and, if possible, observe changes over time; also examine ice-related (e.g., periglacial) geomorphic features
- Document atmospheric and meteorological events and processes by observing clouds, dust-raising events, properties of suspended aerosols (dust, ice crystals), and (using the video capability) eolian transport of fines
- Support/facilitate rover operations, analytical laboratory sampling, contact instrument science, and other MSL science by assisting rover navigation, acquiring images that help determine the location of the Sun, horizon features, and provide information pertinent to rover trafficability (e.g., hazards at hundreds of meters distance), and for other MSL science instruments, provide data that helps the MSL science team identify and characterize materials to be collected or studied in situ.