The Radioisotope Batteries on Cassini Orbiter

We have been following spaceship Cassini as she loops through Saturn’s rings on her final date with destiny. When she launched from mother ship earth on October 15, 1997, her seven-year journey seemed impossibly long, After she dropped her lander Huygens off on Saturn’s Titan Moon, the tiny craft settled down to orbiting around the planet. The power behind this achievement was in the radioisotope batteries she carried as payload.

How the Radioisotope Batteries Explored Saturn’s Rings

The project relied on energy stored on board, at such a distance from the earth. Cassini Orbiter would have otherwise needed two panels the size of tennis courts had she relied on solar. Their weight alone was problematic. NASA engineers therefore decided to use energy stored in radioactive plutonium-238 instead.

Cassini carried three general-purpose head-source modules with her containing the fuel in ceramic pellets. These were similar to those on the Galileo, Ulysses, and New Horizons vehicles. Their energy converted into electricity via thermoelectric blankets as the plutonium-238 gradually decayed.

When the mission launched the radioisotope batteries produced a combined 292 watts. After this had deteriorated beyond any practical value 20 years later, the highly successful mission was over.

Lithium Sulfur Dioxide Batteries Land on Titan Moon

The Huygens lander module was destined for a short sharp burst of fame. It could thus afford to rely on five short-lived LiSO2 batteries with total power of 1,800 watts. Cassini bore Huygens ‘like a baby in its womb sustaining it with its own energy’ throughout the long journey. When it finally released it Huygens descended to the surface, bounced a bit, and settled down to revealing Titan’s secrets for 90 minutes.

Huygens has long fallen silent after its lithium sulfur dioxide batteries died. The radioisotope batteries have almost run out of power on Cassini by now. Today, September 12, 2017 Cassini has completed her final slingshot around Titan. In three days’ time, the orbiter will radio back its last secrets as it disintegrates in Saturn’s mysterious atmosphere.