Cassini Space Probe Goes Down in Blaze of Glory with Materion Filters Unfailing

After 20 years in space, the Cassini-Huygens satellite, a collaboration of NASA, the European Space Agency and the Italian Space Agency, has entered the final phase of its epic mission to observe and explore Saturn.

Launched in 1997, Cassini completed its nominal mission in July 2008, which was followed by several mission extensions. The aging orbiter is currently swooping gloriously in and out of gaps between the planet and its inner rings at 77,000 miles per hour, capturing otherwise unobtainable images and data before it dives into the planet’s atmosphere and meets its planned demise on Friday morning, September 15th.

In late 2004, the orbiter jettisoned the Huygens probe for a 20-day journey to the huge moon Titan where it made a successful descent and soft landing on the frozen surface. Titan's thick atmosphere had hidden its surface from view by earlier passing satellites. The probe transmitted data to the orbiter for later delivery to Earth for seven hours until its battery gave out.

The Cassini-Huygens mission made some amazing discoveries, including seven previously unknown moons, and close-up images revealing that Saturn’s mysterious rings are composed mostly of ice particles, with sprinkles of pink dust and rocks that range in size from pebbles to house-sized “moonlets.”

Now the orbiter is running out of fuel and some systems are failing. “Its bearings are almost out of lubricant; its reaction controls are wearing out; and the power supply for one sensor has failed,” the Wall Street Journal reported.

But the optical filters on the cameras and other instruments that produced all or virtually all of the images and optical data continue to perform flawlessly—greatly assisted or enabled by filters supplied by Materion Precision Optics.

Tom Mooney, Engineer and Product Manager at Precision Optics in Westford is proud of that. He worked on the Cassini project back in the late 1980s and early 1990s when Precision Optics bid on and won the contract.

Designing, building and testing the filters started years before the launch. Including the circuitous seven-year flight to Saturn, “the filters were already pretty old by the time they got used. We built them to exceed the intended life,” he said.

Precision Optics supplied all of the filters on the Cassini orbiter’s main imaging system, including 18 filters on the wide-angle camera and 24 on the narrow-angle cameras. We also supplied multi-band filter arrays on the Visible and Infrared Mapping Spectrometer. The Huygens probe included Materion filters on an infrared imager and on the solar sensors and ultraviolet photometers on the Descent Imager/Spectral Radiometer. The filters enable the imagery by distinguishing colors, said Tom. “The photos are pretty amazing just as imagery, but they also reveal valuable scientific information.” 

As the Huygens mission manager said in 2005 when the first pictures of Titan’s surface were received, “You have enough information in this one photo to produce several scientific papers.”
Maybe even more important than the pictures is the ability to capture images outside the visual spectrum using infrared and ultraviolet light and to sense the presence or absence of various chemicals by their “spectral signatures,” or “optical spectrum fingerprints,” he said.

Perhaps the biggest discovery of the Cassini mission is the evidence that three of Saturn’s moons could support the chemistry of life as we know it. The Materion filters contributed directly to these discoveries by enabling remote chemical analysis of the atmospheres of the moons and of Saturn.

On a March 2008 flyby of the moon Enceladus, the spectral filters aboard Cassini sampled geyser plumes and found they were made of water laced with ammonia, methane and carbon dioxide. At the same time, infrared filters detected surface features indicating the presence of liquid water not far below the surface. Based on these and other findings, NASA places Enceladus “among the most likely places in the Solar System to host alien microbial life.”

Fortunately for the advance of science, the optical filters on Cassini represented the latest technology of the time. But that almost didn’t happen, Tom recalled. “We had developed some new coating processes at that time that were more expensive but much more reliable than the existing technology,” he said. The processes had been tested in simulations, but they had not actually flown in space.

“In these major space missions, you have one shot,” Tom explained. “Failure is not an option. NASA wants to know the flight heritage, that something has been subjected to the actual space environment.”

As Tom related the story, Precision Optics’ customers for the filters—Lockheed and NASA’s Jet Propulsion Laboratory (JPL)—went back and forth on this with Cassini’s mission managers. “At one point, one of the two cameras on the main imager was going to have filters made with the old process and the other would have filters made with the new process.

“Finally, one prominent engineer at JPL who was an advocate for us, stood up and said, ‘This is crazy. Why are we even having this conversation? The new process is better. Just because it hasn’t flown in space is not a reason not to use it.’ They told NASA they would stand behind it and the new-process filters were approved.”

Once those next-generation filters were on Cassini, said Tom, “It was smooth sailing. As soon as you can say something is ‘space qualified,’ all the questions go away.”
And those questions have been gone for a long time. “We routinely use those same processes on all kinds of things even today,” noted Tom.

For more on Cassini, please check out NASA’s website.