Cassini prepares for mission’s end

NASA’s Cassini spacecraft is quickly nearing the end of its mission — and its life. Already in the aptly named Grand Finale portion of its mission, Cassini has begun its final five orbits around the ringed planet. The probe is also preparing for its final encounter with Saturn’s largest moon, Titan — an encounter that will seal Cassini’s fate.

On August 13, Cassini completed the first of five close passes over Saturn, skimming the giant’s atmosphere at a height of just over 1,000 miles (1,600 kilometers). That’s close enough to require the spacecraft to utilize its thrusters to maintain its course as it travels through denser portions of the atmosphere than before. However, Cassini has had practice at such maneuvering, thanks to previous close passes over Titan, which itself is shrouded in a thick atmosphere.

Cassini’s last encounter with Titan will take place September 11, when the moon’s gravity will be used to tug the spacecraft into a trajectory that will end with its death plunge into the atmosphere of Saturn on September 15. That final encounter is the last chapter in a story that’s included numerous gravity assists from the moon, which have, in large part, made the mission what it is. Thanks to the ability of Cassini to use Titan’s gravity to modify its orbit, the spacecraft was able to carry less fuel and use that fuel more sparingly, increasing the science return possible from this landmark mission.

But Titan has provided more than a gravitational tool — it’s also been a primary science target throughout the mission, and the landing site of Cassini’s Huygens probe in 2005. During its time at Saturn, Cassini has revealed the surface of the surprisingly Earth-like moon, peering through the veil of its thick clouds to show mountains, dunes, and even seas of liquid hydrocarbons, where future probes may someday sail.

Cassini’s last close pass to the moon was April 22, when flew 608 miles (979 kilometers) above the surface to take radar data. That data added detail to the growing global picture of Titan, and included coverage of some of the very first terrain imaged during the spacecraft’s first flyby of the moon in 2004. Scientists will use the most recent radar data to measure the depths of some of Titan’s north polar lakes, as well as determine whether they contain liquid methane or ethane.

Even as the end of its mission nears, Cassini will continue to return never-before-seen information about Saturn to Earth. And during its September 15th swan song, its instruments will transmit data for as long as possible, offering a momentary glimpse beneath the tops of Saturn’s swirling clouds.