The end is coming to an old friend. JPL’s Cassini mission (or originally named Cassini-Huygens in combination with a long since released probe) will end this Friday with a very quiet whimper nearly 900 million miles away from here. Cassini is a two story tall orbiter that is currently racing it’s way towards the upper atmosphere of Saturn. Nearing the end of it’s battery life, and with fears of potential contamination if the orbiter crashes into one of Saturn’s moons, the Cassini team decided to turn it’s child into the planet to burn up quickly in a controlled manner. That time has come, and preparations are underway for the event.
Of course, with our luck, it’s happening at a really crappy time of day.
The path to Friday began so long ago, that some of the engineering reports still show the outline of taping typewritten words against poorly sketched graphs. The first hint of what became Cassini were in a call for mission proposals in 1982; and was tagged with the 17th Century astronomer (Giovanni Domenico Cassini, who discovered that Saturn had multiple rings, not just one flat disc) around 1984. Yet it wasn’t until 1997 before the 2-1/4 ton, 22 foot tall orbiter was launched. In fact, the run up in the last few months almost caused the whole mission to be scrubbed by an outpouring of fear over a potential launch failure – because Cassini was nuclear powered and folks thought that would mean fall out or a mushroom cloud or something like that, who knows, folks are crazy like that.
Yet even after the flawless launch, it took nearly 7 years for the orbiter to make it to Saturn and begin the real work. Later that year, it dropped the Huygens probe that made the first landing on another planet’s moon as it did so into the hyrdrocarbon slushes of Titan. Since then, it’s made 294 orbits of Saturn, traveled over 4 billion miles, executed 2-1/2 million commands, collected 635 gigabytes of data, and snapped over 450 thousand photos. In that time, it discovered the strange ‘hexagonal storm’ on Saturn’s pole; caught geysers of methane from the moon Enceladus, and raised questions of the vast oceans on Titan under it’s surface. Voyager 1 & 2 both took a swing by the planet in the early 80s, but they describe those missions as peeling the first layer of an onion away. While there are many layers left to go in learning about Saturn and it’s moons, they are many layers into this onion, and far deeper than anyone expected to go. There isn’t a mission currently slated to head back to Saturn currently but some are banging around to peel back that onion even more.
As far as Friday goes, there really isn’t much too it. Last Friday, Cassini began a full data dump, sending every bit of information in it’s memory banks back to Earth to make sure we have it all. Monday, it gave a ‘goodbye kiss’ to Titan as it swung by the largest moon in the solar system one last time; and with it making the final course correction to head into it’s end. Tomorrow around lunchtime, Cassini will take it’s last photograph – we aren’t sure of what yet. Shortly after that point, a communication link will be made with the orbiter and will lock onto it through the end of it’s life. Around midnight here, Cassini will make it’s last maneuver, a roll to point an instrument at the planet so that it can collect as much of Saturn’s atmosphere as it can analyze in the waning moment.
Friday morning, at about 3:30am Pasadena time (or just about when the rest of y’all are waking up out east), over the course of a little over a minute, Cassini will breach the Saturn atmosphere, increase it’s thrusters from 10 to 100%, give one last signal to Earth before it begins to tumble, and finally disintegrates into nothing but particles and gas. Due to the time it takes for the signal to cross the nearly 900 million miles here, we won’t recieve that last signal until about 4:54 am PDT (or about 8am out on the East Coast, or 7am in the Central).
It doesn’t look us normal JPLers will be doing anything special for it. It is a regularly scheduled Friday off on-lab; which is probably good with all the media traffic that we expect to have. NASA will be live on YouTube and TV for the event, with live shots at JPL Mission Control (aka ‘The Center of the Universe’). My friends and I talked about a Crash Party, but I guess it may fall through because people are expecting me to clean the house before then … plus how to you stay drunk until 5am when the bars close at 2.
It’s also a bitter sweet sad ending. Cassini was launched in the middle of a number of NASA failures, and so many worked so hard to make it a success that it’s hard to see it end. A common statement made was: “this mission was nothing but throwing toast in the air, and each time it came down butter side up”. Now, they have to do what they have been hoping would never happen. Still, it is better to say goodbye on our own terms, than see something end with nothing but questions.
So goodbye Cassini … and thanks for all the cool pics.