Nasa's Cassini aircraft on Saturn mission makes first ring-gazing plunge

Nasa said its Cassini spacecraft has successfully made the first close dive past the outer edges of Saturn's rings since beginning its penultimate mission phase on November 30, but did not obtain views of the planet near the time of closest approach.

"Cassini's imaging cameras obtained views of Saturn about two days before crossing through the ring plane, but not near the time of closest approach," Nasa said in a statement on Monday.

"The focus of this first close pass was the engine manoeuvre and observations by Cassini's other science instruments. Future dives past the rings will feature some of the mission's best views of the outer regions of the rings and small, nearby moons," it added.

Cassini crossed through the plane of Saturn's rings on Sunday at a distance of approximately 91,000 kilometres above Saturn's cloud tops.

This is the approximate location of a faint, dusty ring produced by the planet's small moons Janus and Epimetheus, and just 11,000 kilometres from the centre of Saturn's F ring.

About an hour prior to the ring-plane crossing, the spacecraft performed a short burn of its main engine that lasted about six seconds.

About 30 minutes later, as it approached the ring plane, Cassini closed its canopy-like engine cover as a protective measure.

A few hours after the ring-plane crossing, Cassini began a complete scan across the rings with its radio science experiment to study their structure in great detail.

"It's taken years of planning, but now that we're finally here, the whole Cassini team is excited to begin studying the data that come from these ring-grazing orbits," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California.

"This is a remarkable time in what's already been a thrilling journey," Spilker said.

Each of Cassini's orbits for the remainder of the mission will last one week.

The next pass by the rings' outer edges is planned for December 11.

The ring-grazing orbits -- 20 in all -- will continue until April 22, when the last close flyby of Saturn's moon Titan will reshape Cassini's flight path.

With that encounter, Cassini will leap over the rings, making the first of 22 plunges through the 2,400-kilometre gap between Saturn and its innermost ring on April 26.

On September 15, the mission will conclude with a final plunge into Saturn's atmosphere, NASA said.

Launched in 1997, Cassini has been touring the Saturn system since arriving there in 2004 for an up-close study of the planet, its rings and moons.