NASA’s Cassini orbiter zoomed inside Saturn’s rings overnight for the first time in its 20-year-long flight – and lived to tell about it.
Signals received by the Deep Space Network’s Goldstone radio antenna in California confirmed that the bus-sized spacecraft survived its closest-ever encounter with the ringed planet.
Cassini zoomed as close as 1,900 miles to Saturn’s cloud tops and within about 200 miles of the innermost visible edge of the rings, at a relative speed of 77,000 mph, NASA reported in an update early today.
Computer modeling showed that any concentration of ring particles in the gap between the visible rings and the clouds should be no more dense than smoke, but mission planners had no way of knowing for sure. They said there was a chance Cassini could be damaged if the particle concentration had been denser than they expected.
“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” Cassini project manager Earl Maize of NASA’s Jet Propulsion Laboratory explained in today’s status update.
As a precaution, Cassini’s high-gain antenna dish was turned into the rush of particles to serve as a shield, and that meant the spacecraft had to be out of communication during the critical phase of the crossing.
Cassini captured data and images as it flew through the gap, and transmitted them back to Earth after contact was re-established.
Cassini’s successful passage this first time around reassured the team that the craft would survive 21 more precision passes inside the rings, scheduled to occur between now and the end of the mission in September.
That’s when the probe will be sent deliberately to crash through Saturn’s dense atmosphere. Cassini’s controlled destruction is meant to make sure there’s no contamination of the planet’s mysterious moons, such as ice-covered Enceladus. Enceladus could become the focus of a future space mission aimed at investigating what scientists believe is an ocean beneath the ice.
The plutonium-powered Cassini probe was launched in 1997 and went into Saturnian orbit in 2004. Since then, it has beamed back a wealth of data about the planet and its myriad moons.
Correction for 9:50 p.m. PT April 27: An earlier version of this report referred to Europa, an ice-covered moon of Jupiter, but Cassini’s planetary protection policy is aimed more directly at safeguarding moons such as the Saturnian moon Enceladus.