To get these images, scientists choose which filters to take the image with out of 11 available color filters. These filters help them acquire and reconstruct a reasonably accurate color image and, more importantly, determine the composition of rocks and soil on the martian surface. An additional two filters are included to help photograph the Sun. This not only helps scientists determine the dust abundance in the atmosphere, but also allows each camera to serve as a "solar compass" to determine a rover's orientation.
"The rovers really are like robotic geologists," said JPL Senior Test Engineer Tom Elliot. "What the cameras are seeing on Mars is very similar to what we would see if we were there looking around."
The camera team included specialists from five major disciplines: optics, charge coupled devices, electronics, mechanicals, and assembly and testing.
With valuable input from key contractors, the optics team at JPL designed, built and tested the tiny camera lenses, each custom-tailored to the function its camera was to perform. To meet their requirements, the team had to carefully consider using smaller consumer parts, some of which weren't capable of handling a journey to Mars.
"One of the stressful things about being an optical designer is that you have to be one of the first ones finished so other engineers in the mechanical and thermal areas may do their work," said Principal Optical Engineer Ed Hagerott. "All the people who worked on this project put in very long hours and did a super job of meeting the requirements, sometimes even ahead of schedule."
Step Two, Three and Voila! Images!
While the optics team developed the lenses, a second team designed, built and tested charge coupled devices, the "electronic film" which would convert the optical images (patterns of light, or an image as we would normally see it) into patterns of electronic signals. These signals would then be radioed to Earth and reconstructed into pictures.
Meanwhile, a third team developed the electronics that would operate the camera and process the charge coupled devices' electronic signal. This provides electronic images to the rover computer for transfer to Earth, often via spacecraft that are orbiting Mars.
"Acquiring the images using the rover cameras isn't the black magic that it seems," said Elliot. "The operations team has to decide which filters to use, command the camera, and then process the resulting image after it has been transferred to earth. In fact, the rover cameras, in many ways, are less complicated than consumer digital cameras."
Practice Makes Perfect
"By the time the mission team got the cameras, it was like buying a new car with 25,000 miles already on it," Schwochert said. Prior to delivery, the camera team performed a rigorous series of tests and reviews, referencing designs from Sojourner, Viking and other missions for ideas and problems that they might encounter, such as whether dust would accumulate on the lenses.
"Different missions have different ways of fulfilling their requirements, and it was helpful for us to look at what was successful and where problems were encountered in the past," Elliott said. "Of course, we had our own bag of tricks."
The team conducted camera and rover tests in vacuum chambers and in JPL's In Situ Instruments Laboratory, a building that contains a patch of realistic "Mars" terrain. Camera testing included operation at temperatures as low as -120 degrees Celsius (-184 degrees Fahrenheit), even though the rover cameras on Mars are typically operated at temperatures above -45 degrees Celsius (-49 degrees Fahrenheit).
"After days of electrical testing and retesting under the most rigorous conditions that I could think of, I knew that the camera electronics design was solid, but in this business there always room for more testing," said Lead Camera Electronics Engineer Arsham Dingizian. "I wanted to be prepared for the worst because no design is perfect. To my surprise, although they didn't work properly at -120 degrees Celsius, the cameras electronics survived and worked perfectly at above -55 degrees Celsius (-67 degrees Fahrenheit). This proved to me that the camera electronics design not only met its specifications but also exceeded them. At that moment I knew that the camera electronics could handle almost anything Mars could come up with."
After the cameras were built and thoroughly tested to ensure mission success, the camera team turned them over to the Assembly, Test, Launch and Operations team, who placed them on the rovers. Members of the camera team have since moved onto other projects, although a handful of them still work daily with the Mars Exploration Rovers.
"There was so much riding on these missions, I found myself waiting, like everyone else, into the early hours of the morning until the first images came down," said Elliott, who no longer works with the rovers but is now helping develop the navigation camera on the 2005 Mars Reconnaissance Orbiter and the 2009 Space Interferometry Mission.