This is where Cassini plunged into Saturn’s atmosphere in a blaze of glory. After 19 years and 335 days in space—most of it spent spinning around the Saturnian System—Cassini took this one last photo as she descended into the atmosphere of the ringed planet. “This is where I will die, my friends,” I can imagine her thinking as she patiently beamed it back to Earth, “It was good while it lasted, right?”
And good it was. Actually, it wasn’t just good. It was amazing. Awesome. Zoeylalafantaboulous. There’s no hyperbole that can do justice to the endless list of Herculean tasks completed by Cassini–and her buddy Huygens, the “little” European probe that touched down on the surface of Titan (the furthest from Earth that any human-made spacecraft has ever landed), confirming the existence of lakes made of liquid hydrocarbons and taking the first pictures from the surface of a celestial body in the outer Solar System.
And that was just one part of the mission. Cassini discovered two oceans in Titan and Enceladus (the latter with the potential of harboring life); documented three seas and hundreds of lakes in Titan; found six new moons; revealed that Iapetus was made by the Evil Galactic Empire and had an inexplicable ridge of mountains all around the planet, near the equator; studied the “temperature, composition, and distribution of Saturn’s rings” for the first time; obtained data about how the rings were formed and how they interact with their moons; photographed the planet’s mysterious hexagon cloud system on its North Pole… The list is overwhelming, and everything was done while taking stunning photos while traveling as fast as 70,000 miles per hour.
This ship completed 293 orbits around Saturn, with 162 targeted moon flybys, 127 Titan flybys, 23 Enceladus flybys. It processed 2.5 million computer commands, and sent back a grand total of 453,048 photos. Those numbers illustrate the complexity and scope of its mission, which ran on hardware just marginally smarter than a Donkey Kong arcade machine.
The reason for that? Cassini was built in the 1990s with technology from the ’80s. When it comes to designing for space, you have to use tested components that you know will be reliable. You also have to contend with very long development times. This means that you’ll never be on the cutting edge of technology. For instance, take Cassini’s processor, a 16-bit CPU that was released in 1980. Slow and thoroughly tested for military and space applications, this radiation-hardened brain controlled an staggering 1,630 electronic modules interweaved in a spider web of 22,000 wire connectors and 8.7 miles of cabling.
Every scientific instrument was bulky, since they hadn’t reached the level of miniaturization that came in later decades. What’s more, Cassini’s engineers had to figure out how to fit everything into a package small enough to fit in the nose of a Titan IV rocket. Because the mission was so ambitious, that included 12 scientific instruments, from a magnetic field detector to moon-mapping radar to spectrometers that detect chemical elements to the Imagine Science System, a big wide-angle and a narrow-angle digital camera that could record visible light and some infrared and ultraviolet wavelengths with 1 megapixel sensors.
It also included two rocket engines for propulsion—one as a back-up, because in space everything mission critical must have a back-up. Those rockets had been designed for the Apollo program in the ’70s, yet another example of having to work with old, tried-and-tested technology. Plus three radioisotope thermoelectric generators, a type of power source that uses the radiation of plutonium to generate energy. Those generators also required massive, heavy shielding made of graphite, because you don’t want a giant cloud of extremely radioactive dust falling all over Florida if the rocket launcher explodes. Oh, and add the 703 pound Huygens probe to the entire package, because why not try to land something on one of Saturn’s moon since we’ll be orbiting around it, right?
Many people thought it couldn’t be done, but a group of scientists and engineers played the most complex game of Tetris ever and managed to package everything to fit atop the rocket. Sure, the package was the size of a school bus—the largest deep space vessel ever made by NASA. But it worked.
And it worked continuously for almost two decades (in space!) sending data and images back to Earth (from space!) at a glacial 110,000 bits per second (that’s 107 kilobits per second versus the 5,000 to 12,000 kilobits per second of a modern cellphone connection) while dodging particles, zipping between Saturn’s rings, and surfing the salt-water geysers of Enceladus.
For all the criticisms of its bureaucracy and budget, it’s astonishing that NASA was able to put together such a complex ship three decades ago with such limited resources. After the deep pockets of the Apollo era, the agency only had scraps to solve these engineering problems. In that way, Voyager, the Mars Curiosity Rover, and Cassini are all epic technological achievements on par with the Moon landing. So let’s applaud the magnitude of that achievement–the clockwork precision of the design and construction of these magnificent beasts is a testimony of what human ingenuity can achieve, from flying to the Moon to landing on Titan. This is our little homage to these designers and builders, without forgetting the people that make it tick in mission control and the scientists who analyze the data.
Cassini’s death may have happened today at 7:55 a.m. EDT, just as NASA had planned, as she sent her last love letter to science loaded with data about the planet that killed her–but her legend, and the legend of those who made her and her companion, will live on.