Monday, the Cassini spacecraft gave its final "kiss goodbye" to Titan, the moon of Saturn it has been orbiting as a part of its two-decade exploration of the planet.
Cassini flew by the moon nearly 75,000 miles out, but "the nudge from Titan's gravity however, even at that distant fly by approach distance was enough to seal Cassini's fate," said Todd Barber, lead propulsion engineer on the Cassini Mission.
That fate is for Cassini to crash down to Saturn on Friday, Sept. 15, where it can end its long flight while also protecting the planet's moons and sampling its atmosphere.
Cassini's final trip past Titan was done for a "gravity assist," Barber said, which means the spacecraft got close enough for the planet's gravitational force to pull it into the planet. It will fly between Saturn's rings on its way to its final resting place.
"I think there will be a few tears on Friday," Barber said of the end of the mission he has dedicated much of his career to. "We've learned so much more from Saturn than we ever dreamt possible back when we arrived in 2004. It's this mixture of poignancy, sadness, but with a heap of pride and a sense of accomplishment on the mission."
Indeed, the mission went far beyond what scientists expected when Cassini launched in 1997. The spacecraft reached Saturn in 2004, and orbited the planet for four years. Through increased funding and extended propellant use, they were able to help the mission survive until 2017 and a full seasonal change on the planet.
As Cassini approaches its crash on Friday, it will be taking an orchestrated path that will ensure the bacteria-laden robot won't run into Titan or Enceladus, Saturn's moons that scientists discovered may be able to support life.
"Cassini is a victim of its own success," Barber said of the bacteria that has attached to the craft as a result of its extended use. If Cassini crashes into one of the moons, the bacterial spores could contaminate them.
"We can't allow that," Barber said. "We have to take pristine beautiful new spacecrafts, sterilized, to those worlds to answer the most fundamental question in human history: Are we alone in the universe?"