In a brilliant streak of light, NASA's Cassini spacecraft fell from orbit and disintegrated in the atmosphere of the planet Saturn on the morning of Sept. 15, concluding a 20-year mission that saw it make discoveries about the ringed planet and its …
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In a brilliant streak of light, NASA's Cassini spacecraft fell from orbit and disintegrated in the atmosphere of the planet Saturn on the morning of Sept. 15, concluding a 20-year mission that saw it make discoveries about the ringed planet and its moons that scientists will study for generations.
A few hundred million miles away in Littleton, Lockheed Martin engineer Kevin Johnson watched on a live feed as one of the crowning achievements of his career came to a fiery end.
“It was a bittersweet moment,” Johnson said. “It's been a heck of a good mission.”
Johnson helped design and build Cassini's propulsion system, which was crucial in performing the complex “gravity assist” maneuvers that allowed the craft to travel to Saturn: two slingshots around Venus, one past Earth, and another past Jupiter to build up sufficient speed to get to its destination. It took seven years.
The craft's achievements were numerous: it sailed through Saturn's rings multiple times, launched a probe that landed on the moon Titan, and discovered geysers on the moon Enceladus, according to NASA.
“Watching it, it felt like I was exploring the universe,” Johnson said.
As Cassini's fuel dwindled, NASA decided to send it hurtling into the planet — partly to gather previously undreamed of atmospheric and climate data, and partly to prevent the spacecraft from one day plowing into one of the moons and possibly contaminating a virgin environment with Earth-born microbes.
So, flight engineers fired Johnson's propulsion system one last time. Monomethylhydrazine and nitrogen tetroxide blasted from twin valves, combining to form a hot blast that slowed the craft's orbit, and it entered a long, gentle careen to forever join the planet it had spent years discovering.
In Littleton, Johnson and the colleagues who worked with him on the mission got together to celebrate.
“We hoisted a cold one to Cassini and to a job well done,” Johnson said.
Johson started working on Cassini when he was 36. He's 61 now, and an LM Fellow — a leader and mentor for the younger set.
“I think inspiring and educating the future generations of scientists and engineers is one of the big paybacks of missions like Cassini,” Johnson said. “People can get online anywhere in the world and look at the data. We need to inspire people, because there's a whole solar system and galaxy to go explore.”
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