It’s been fifteen years since Cassini launched to Saturn. A joint program with the European Space Agency and the Italian space agency, the Cassini-Huygens mission left Earth on October 15, 1997. It flew by Venus twice, swung back by Earth, then went onward to Jupiter before settling in around Saturn in 2004; the Huygens probe landed onto the surface of Titan in 2005. In all, the spacecraft covered more than 3.8 billion miles on the seven year journey, and has spent the last eight years returning stunning images of, and incredible science from, the ringed planet and its moons.
It wasn’t a simple path to take. In fact, Cassini’s trip to Saturn was a long and very winding road. And things didn’t get easier for those plotting its route once it’s arrived at Saturn. “Cassini… has been flying the most complex gravity-assisted trajectory ever attempted,” program manager at NASA’s Jet Propulsion Laboratory Robert Mitchell said. “Each flyby of Titan, for example, is like threading the eye of the needle. And we’ve done it 87 times so far, with accuracies generally within about one mile, and all controlled from Earth about one billion miles away.”
The trajectory’s ongoing complexity comes largely from Saturn’s busy system. Cassini lines up to visit more than a dozen of Saturn’s 60-plus moons in one pass before working its way back to an orbit around Saturn’s equator. The directions mission planners write also have to factor in the gravitational influences of the moons and the spacecraft’s limited fuel supply.
Even if it’s hard keeping the spacecraft on track so far from home, Cassini doesn’t look like it will run into problems anytime soon. “I’m proud to say Cassini has accomplished all of this every year on-budget, with relatively few health issues,” Mitchell said. “Cassini is entering middle age, with the associated signs of the passage of years, but it’s doing remarkably well and doesn’t require any major surgery.”
So far, Cassini has sent back 444 gigabytes of scientific data and over 300,000 images. Scientists have used this return well. That data has gone into more than 2,500 scientific papers describing some of the most noteworthy discoveries like the plume of water ice and organic particles spewing from the moon Enceladus, the first views of the hydrocarbon-filled lakes of Saturn’s largest moon Titan, and the atmospheric upheaval from a monstrous storm on Saturn.
Saturn and its moons are currently undergoing a change in season – it’s turning into spring – giving Cassini a chance to gather data on seasonal changes. This is the first time a spacecraft has had the opportunity to observer a global change on a giant planet.
The team see no indication that the redundancies on Cassini’s critical engineering systems have failed, so they expect to get millions more bytes of data on the remainder of the mission. And it’s about to get really fun.
In November 2016, Cassini will manoeuvre its way closer to Saturn’s outer F ring. Then in April 2017, a close encounter with Titan will nudge Cassini on a trajectory that will take it inside Saturn’s innermost ring. The end of the mission will come that September. After 22 close passes, the planet’s gravity will overtake Cassini, bringing into its atmosphere where it will be crushed by the pressure and temperature.
“Cassini has many more miles to go before it sleeps, and many more questions that we scientists want answered,” said Linda Spilker, a Cassini project scientist at JPL. “In fact, its last orbits may be the most thrilling of all, because we’ll be able to find out what it’s like close in to the planet, with data that cannot be gathered any other way.”
It will be sad to see Cassini go, but it’s going to go out with a scientific bang.