The Mars lander, the Pathfinder, and its smaller rover, Sojourner, use everyday photonics technologies not only to provide startling images of Mars but also to analyze that landscape for hints about Mars' past.
A stereo imaging system developed by a team from the University of Arizona, the Lockheed Martin Fairchild's CCD group in Tustin, Calif., and the Max-Planck-Institute for Aeronomy in Lindau, Germany, captured the sweeping images of the Martian terrain. The Imaging for Mars Pathfinder consists of several components including a camera head with stereo optics, a charge-coupled device (CCD) and its brain, the CCD data card.
The CCD imager is a front-illuminated frame transfer array with 23- µm2 pixels. The image section is divided into two square frames, one for each half of the stereo fields of view. Each has 256 3 256 pixels.
"It's a stereo camera, so they're actually taking two images at once," said Ed Jakl, a staff design engineer who worked on developing the CCD data card at Lockheed. Like other technology aboard Pathfinder, the CCD imager was neither expensive nor the most advanced available. "The resolution is equivalent or less to a television, but they're making the most of it, and, with the cameras in stereo, it's just like human vision," Jakl said. By comparison, the latest CCD chips produced by Lockheed have a resolution of 9216 3 9216. Richard Bredthauer, director of advanced CCD technology at Lockheed, said a chip that advanced simply wouldn't have been practical.
Sojourner unwrapping from Pathfinder.
"It would have cost them a fortune for the chip, and it would have been overkill for what they were looking to do," Bredthauer said. "The chip [in Pathfinder] isn't really high resolution, but it was technology already in hand." Problems of bandwidth and slow data transfer speeds would have hampered attempts to use a higher-resolution chip. In addition, NASA cut costs by acquiring surplus CCDs designed for the Huygens Probe Descent Imaging Spectroradiometer.
While this isn't the first trip into space for Lockheed Martin's CCDs -- the Hubble Space Telescope and the ill-fated Mars Observer used them -- it clearly has captured the most public interest. "You know it really was amazing," Bredthauer said.
While the photographs taken of Mars' surface took center stage, several CCD sensors in conjunction with lasers kept the Pathfinder's rover on track as it navigated over the Martian surface. Two types of Kodak area interline sensors are aboard the rover, the KAI-0371 monochrome sensor and the KAI-037M color sensor. Two KAI-0371 sensors serve as Sojourner's eyes, measuring the topography and recording visual maps of the surface. The sensors continuously capture images of the terrain in front of the rover and transmit them to Earth. Using the information provided by these and other sensors, the Jet Propulsion Laboratory in Pasadena, Calif., steers the rover around rocks and other obstacles to a specified destination.
The KAI-037M sensor delivers full-color images of the ground and soil samples. Using a color CCD with square pixels, the sensor provides 640 3 480-pixel still images, which are eventually transmitted to Earth for analysis.
As with the CCD chips in the imager, the monochrome and color sensors are neither state of the art nor unusually expensive. Commercially available for the last 15 years, the sensors are commonly found in machine vision, medical diagnostics and cameras. It was the sensor's durability that convinced NASA.
"NASA was simply interested in sensors that could withstand the rigors of space travel," said James W. Meyer, chief technical officer and senior vice president of Kodak. Meyer added that the sensors were neither custom-made nor modified to withstand Mars' cold climate, which often drops as low as 260 °F, actually enabling the CCD to perform better by reducing background noise.
So far, the sensors have worked as planned. "This has been almost picture perfect. There's a certain pride in having our sensors on the rover and to actually see everything work as planned," Meyer said.
Photonics' future in space
Though the public eye is now focused on Pathfinder, the Cassini mission to Saturn in October will feature another CCD chip produced by Lockheed. Mars Surveyor, which will use Lockheed's CCD chips to map the Red Planet's surface, is set to enter Mars' orbit in September. This much is certain: Space remains a mystery.
"On Saturn, it's anyone's guess," said Justin Maki, a researcher at the Jet Propulsion Laboratory. "There are probably methane lakes and mountains."
Maki, like others involved at NASA and the Jet Propulsion Laboratory, noted the resounding success of Pathfinder's instruments and said the trend toward lower-cost sensors and CCDs is likely to continue. There is little doubt photonics technology will continue to play a quiet but crucial role in the exploration of space.
"Most things we do in scientific applications don't show up in front of the public," Bredthauer said. "It's incredible seeing the images coming back from chips we had a hand in designing. We didn't realize the implications [this mission] would have."