NASA''s Cassini completes first dive between Saturn''s rings

Washington

NASA's Cassini spacecraft has successful executed its historic first-ever dive through the narrow gap between the planet Saturn and its rings, marking the beginning of the 'Grand Finale' of the 20-year-long journey.

The spacecraft is in the process of beaming back science data collected during its passage, through NASA' Deep Space Network Goldstone Complex in California's Mojave Desert.

"In the grandest tradition of exploration, NASA's Cassini spacecraft has once again blazed a trail, showing us new wonders and demonstrating where our curiosity can take us if we dare," said Jim Green, director of the Planetary Science Division at NASA in the US.

As it dove through the gap, Cassini came within about 3,000 kilometres of Saturn's cloud tops and within about 300 kilometres of the innermost visible edge of the rings.

While mission managers were confident Cassini would pass through the gap successfully, they took extra precautions with this first dive, as the region had never been explored.

"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," said Earl Maize of NASA's Jet Propulsion Laboratory in the US.

"I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape," said Maize.

The gap between the rings and the top of Saturn's atmosphere is about 2,000 kilometres wide.

The best models for the region suggested that if there were ring particles in the area where Cassini crossed the ring plane, they would be tiny, on the scale of smoke particles.

The spacecraft zipped through this region at speeds of about 124,000 km per hour relative to the planet, so that small particles hitting a sensitive area could potentially have disabled the spacecraft.

As a protective measure, the spacecraft used its large, dish-shaped high-gain antenna four meters across as a shield, orienting it in the direction of oncoming ring particles.

This meant that the spacecraft was out of contact with Earth during the ring-plane crossing on April 26.

Cassini was programmed to collect science data while close to the planet and turn toward Earth to make contact about 20 hours after the crossing. Its next dive through the gap is scheduled for May 2.

Launched in 1997, Cassini arrived at Saturn in 2004.

Following its last close flyby of the large moon Titan on April 21, Cassini began what mission planners are calling its "Grand Finale."

During this final chapter, Cassini loops Saturn approximately once per week, making a total of 22 dives between the rings and the planet.

Data from this first dive will help engineers understand if and how they will need to protect the spacecraft on its future ring-plane crossings.

The spacecraft is on a trajectory that will eventually plunge into Saturn's atmosphere — and end Cassini's mission — on September 15. — PTI