The Cassini spacecraft - now just weeks away from the end of its mission - is due to begin the first of five final orbits around Saturn.
Cassini will enter new territory when it goes into the final orbits starting with its pass over Saturn starting at 0222 AEST on Tuesday.
It will come as close as 1,630km above Saturn's cloud tops when it executes the five passes, the US space agency said, describing the passes as "ultra-close" through Saturn's upper atmosphere.
The five final orbits will allow scientists to learn what Saturn looks like on the inside and get high-resolution images of the planet's rings.
The spacecraft is expected to encounter atmosphere dense enough to require the use of its small rocket thrusters to maintain stability.
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The Cassini team is confident they understand how the spacecraft will behave at the atmospheric densities expected because the conditions are similar to those encountered during many of Cassini's close flybys of Saturn's moon Titan.
The mission, formally known as the Cassini-Huygens mission, is a co-operative project of NASA, the European Space Agency and the Italian Space Agency. Its mission is due to end on September 15.
