An unmanned NASA spacecraft, Cassini, is poised to plunge into the gap between Saturn and its rings, a pioneering journey that could offer an unprecedented view of the sixth planet from the Sun.

The first of the spaceship's 22 deep, daring dives between Saturn and its innermost ring is scheduled for April 26 at 5:00am Florida time (09:00 GMT), NASA said.

If everything goes to plan, the spacecraft will offer the closest-ever views of Saturn's rings - but first NASA faces a nail-biting wait.

Communications with the spacecraft will go dark during the dive and for about a day afterwards, while it makes scientific observations of the planet.

If Cassini survives the trip, it could make radio contact with Earth as early as 3:05am (07:05 GMT) on April 27.

NASA said that images and other data are expected to begin flowing in shortly after communication is established.

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Cassini is a 20-year-old joint mission of NASA, the European Space Agency, and the Italian Space Agency.

The 6.7-metre spacecraft launched in 1997, back when Bill Clinton was president, and began orbiting Saturn in 2004.

Cassini's latest adventure is a swansong for the spacecraft, as it is running low on fuel, and will make a death plunge into Saturn's atmosphere on September 15.

But first, Cassini has to complete its most perilous feat.

'A dangerous moment'

Venturing between the planet and its rings for the first time represents "a dangerous moment for the mission," Luciano Iess, Cassini team member at Italy's Sapienza University of Rome, said at a meeting of the European Geosciences Union in Vienna.

Skimming above Saturn at an altitude of about 3,000 kilometres, the spacecraft will be closer than ever to the band of ice and space rocks that encircle Saturn.

The debris moves at speeds of around 109,000 km/h.

The rings around Saturn – a gas giant second in size in our solar system only to Jupiter – are thousands of kilometres wide, but only around nine to 90 metres deep.

The spacecraft's final dives aim to offer a fresh look at the rings, potentially revealing more about their mass and whether they are old or new.

Some scientists believe that rings could have formed after asteroids smashed into some of Saturn's moons, creating a trail of debris.

Earlier this month, ESA called for increased international cooperation to head off a threat posed to its network of satellites by debris flying around space .

"No country can stand or act alone," Jan Woerner, the chief of ESA, told an international conference in the western German city of Darmstadt.

"It's clear to us that the issue of space debris is serious," he said at the opening of the four-day summit..

Life on Saturn?

Saturn has more than 60 moons, and Cassini has made new discoveries on some of them, which may have conditions suitable for a form of life.

Cassini dropped a European probe on Saturn's massive moon, Titan, and revealed its surface of liquid methane seas, including a complex system of methane rain and runoff.

It discovered that the icy moon, Enceladus, conceals a sub-surface, salty ocean beneath its crust, and may be able to support living microbes.

The decision to end Cassini's mission was made in 2010, as scientists feared the spacecraft could crash into and damage moons like Enceladus, which could be explored for signs of life in the future.

Cassini also observed storms, lightning and clouds around Saturn for the first time.

Cassini has made "a wealth of discoveries," said Nicolas Altobelli, Cassini project scientist with the European Space Agency.

"We will have to rewrite many textbooks on planetary science."