In 2005, Huygens completed its mission by landing on Titan, thus becoming the first human-made object to touch down on a moon other than our own. On Friday, it was Cassini’s turn to take the plunge. The orbiter started a scheduled descent through the hazy brew of hydrogen and helium making up Saturn’s atmosphere and lost contact with Earth.
NASA named the Cassini-Huygens mission after the Italian mathematician and astronomer Giovanni Domenico Cassini, who discovered four of Saturn’s 53 moons and also the gaping void between its rings, and Dutch astronomer Christiaan Huygens, who studied the planet’s rings. The probe arrived at the solar system’s second-largest planet in 2004 and spent the last 13 years studying its surface, atmosphere, moons and rings. NASA reported that its finding allowed scientists to “expand our understanding of the kinds of worlds where life might exist,” see “the physical processes that likely shaped the development of our solar system, as well as planetary systems around other stars,” and “reveal Saturn’s moons to be unique worlds with their own stories to tell,” among other things.
The Cassini-Huygens mission was originally designed to last only through 2008. But the spacecraft kept sending back images and data for almost another decade. The instruments on board drew power from a special power plant called the RTG, or radioisotope thermoelectric generator.
Originally designed by GE’s Space Division (now part of Lockheed Martin) in King of Prussia, Pennsylvania, this model of RTG has powered U.S. spacecraft since the Ulysses probe was launched in 1990. The electricity from the RTG doesn’t propel the spacecraft, which uses inertia from the launch and gravity slingshots around planets, but it’s necessary for the missions to snap pics, gather data and phone home.
The RTG takes advantage of the predictable decay of plutonium-238, a radioisotope supplied to NASA by the U.S. Department of Energy. The heat given off by the plutonium, which is in the form of 18 fire-resistant ceramic pellets, is transformed into electricity by a process known as the Seebeck effect.
GE-designed RTGs also powered the Voyager 1 and 2 spacecraft, which are now at the edge of the solar system; the New Horizons probe, which buzzed Pluto last year; and other space vehicles.
“Cassini represents a staggering achievement of human and technical complexity,” NASA wrote. Take a moment tonight to look at the sky, take pride and let your mind wander.