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Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

Imaging the Surface of Mars

Photo Courtesy Ball Aerospace
The HiRISE telescope.
Photo Courtesy University of Arizona
This HiRISE image shows the Mars Exploration rover Opportunity near the rim of "Victoria Crater," an impact crater -800 meters (about half a mile) in diameter at Meridiani Planum near the equator of Mars. Opportunity has been operating on Mars since January, 2004. When viewed at the highest resolution, this image shows the rover itself, wheel tracks in the soil behind it, and the rover's shadow, including the shadow of the camera mast.
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Ball Aerospace & Technologies Corp. (Boulder, Colo.)
University of Arizona (Tucson)
Lockheed Martin Space Systems (Bethesda, Md.)
Lightworks Optics, Inc. (Tustin, Calif.)
ATK Space Systems (Edina, Minn.)
E2V Ltd. (Chelmsford, U.K.)
Research Electro-Optics, Inc. (Boulder, Colo.)

The Challenge

In sending the Mars Reconnaissance Orbiter to the Red Planet, scientists intended to produce images at resolutions never before seen in planetary exploration missions. To do so, they needed the largest telescope ever built for any deep space mission. To that end, Ball Aerospace & Technologies Corp. designed and built HiRISE, the 0.5 meter reflecting telescope for the University of Arizona. One of the most versatile instruments aboard MRO, it was designed to take color, stereo pictures of swaths of the surface up to 6 km wide, with an ability to resolve objects as small as one meter (about 3 feet) across from 300 km above the surface while orbiting Mars at a speed of 3.4 kilometers per second.

The Solution

From the beginning, HiRISE was designed to be a high resolution camera. It consists of a 12-meter focal length three-mirror telescope, as well as a large charged coupled device (CCD) detector assembly. Because of this, it achieves a pixel field-of-view of 1 microradian, or 0.3 meter/pixel at a height of 300 km. It can image in three color bands, 400-600 nm (blue-green or B-G), 550-850 nm (red) and 800-1,000 nm (near infrared or NIR). Red color images are up to 20,264 pixels wide (6 km in a 300 km orbit), while the Green-Blue and NIR images are up to 4,048 pixels wide (1.2 km).

HiRISE is a pushbroom imager, i.e. it uses time delay and integration (TDI) to increase the signal-to-noise ratio as it reads out image lines in time with the orbiter's ground speed. The total number of lines, or the image height, is limited by the onboard 28 Gb memory capacity. A nominal high-resolution red image is 20,000 40,000 pixels, or 800 megapixels and 4,000 40,000 pixels (160 megapixels) for the narrower images of the B-G and NIR bands. A single nominal red image will use 16.4 Gb. However, these images can be compressed, down to a total size of 5 Gigabits.

The Tools Used

  • The Ball Aerospace imager design, an all-reflective three-mirror telescope with light-weighted Zerodur optics and a graphite-composite structure. The optical system provides a diffraction limited modulation transfer function (MTF) on 12 um pixels for all 14 HiRISE detectors.
  • Lightworks Optics, Inc. 50 cm diameter primary mirror
  • ATK Space Systems telescope structure
  • E2V Ltd. focal plane assembly housing 14 CCD detectors (2048 x 128 TDI), which are staggered to provide full swath coverage without gaps
  • Research Electro-Optics, Inc. multilayer color filters

The Difference It Made

The HiRISE camera is designed to view surface features of Mars in greater detail than has previously been possible. This allows for the study of the age of Martian features, the evidence of past or present water, the climate record and identification of landing sites for future robotic and manned missions. Images returned by HiRISE since its insertion in the Mars orbit in 2006 have exceeded expectations. NASA's Phoenix lander mission, to be launched in the summer of 2007, has already been using HiRISE images to identify hazards that were not discernible in previous images from orbit.

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