Looking Back: Cassini–Huygens

Nearly 20 years ago, the Cassini space probe and Huygens lander were launched into space on a Titan IV rocket. On September 15th, signal was lost, marking the end of a 4.9 billion mile-long mission.

As I heard the news of the mission’s end drawing near, I experienced feelings of pride, nostalgia, and a bit of sadness about the end of an era. I started my engineering career over 20 years ago as a NASA intern, working on the ground mission planning software suite for Cassini.

Cassini-Hyugens: By The Numbers

Image Credit: NASA

In my youth, I always dreamed of working in the space program somehow, and having recently graduated from college was excited to have the opportunity to do so. I grew up hearing about NASA’s big robotic space probes – Explorer, Mariner, Ranger, Voyager, Viking and Galileo. These missions were historic expansions of the boundaries of mankind; I finally had a chance to be part of it.

Reality was a bit different than I expected. I learned that there are an uncountable number of details to get right in order to successfully design, build, and operate a space craft – and Cassini was the most ambitious one to date. To build a system robust enough to survive the 7 year journey to Saturn, and operate for 4 (later extended to 13!) years, requires a hearty design.

Wherever possible, each subsystem had a redundant backup, and the spacecraft was cross-wired to be able to hot-swap any backup system at any time. There were 2 main flight computers, both running at all times. Each piece of the propulsion system also had a redundant backup, so imagine the complexity required to maintain the ability to swap out any arbitrary valve with its backup and still get the system to run. In a way, Cassini was built like a conjoined twin!

I worked on the analysis software for the Power and Pyrotechnics subsystem. My main workspace was a computer lab that literally looked onto the famous mission control dark room, which was awesome. My job was to get the data related to power consumption on all of Cassini’s subsystems. Cassini was powered by 3 RTGs (radio isotope thermal generators,) which at launch time could provide about 800 watts of electrical power. Try to draw more than that and bam! System failure. We had to make sure that no activity involved turning on too many devices at once.

Cassini RTG Before Installation. Image Credit: NASA

The fuel for the RTGs was about 72 pounds of Plutonium, which as you all know from Doc Brown is a shitload, and not quite available in every corner store in 1995. It was actually quite controversial at the time, due to the risk of putting that much radioactive material on top of a large rocket and shooting it through the upper atmosphere. I can actually say that I had to cross a picket line of protestors to get to work (but that’s another story). 

Great Scott!

My part in this project was miniscule. Cassini was made possible through the tremendous skills of the scientists and engineers of JPL who started planning this mission before I was even born. It was awesome to see some of my former colleagues on TV and in the newspapers as they brought the mission to a successful conclusion. I hope that we will continue to explore our solar system and beyond. Learning about Saturn and its rings & moons is wonderful, and teaches us about our own origins.

More importantly to me; thinking about on a grand scale, about things like space exploration, encourages us to think big about everything else.

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