"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 Cassini project manager Earl Maize of NASA's Jet Propulsion Laboratory, in a statement.
Cassini was out of radio contact with Earth as it became the first spacecraft to enter the gap between Saturn and its rings.
In its first dive Wednesday morning around 5 a.m., Cassini used its high-gain antenna as a protective shield as it passed through the ring plane.
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.
After nearly 20 years of calling space home, NASA's Cassini Spacecraft will embark on its final performance before completing what has been dubbed in the spacing world the "Grand Finale". The spacecraft came within 1,900 miles of Saturn's cloud tops and 200 miles of the planet's innermost ring, shooting a gap between the top of Saturn's atmosphere and its rings that is about 1,500 miles wide.
The spacecraft flew through the ring plane at 77,000 miles per hour (124,000 kph) relative to the planet, and at that speed tiny particles could have posed a large threat to its sensitive instruments without the shielding.
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The 22-foot-tall (6.7 meter) spacecraft launched in 1997 and began orbiting Saturn in 2004.
The spacecraft is on a trajectory that will cause it to plunge into Saturn's atmosphere - ending Cassini's mission - on September 15, 2017, the statement said. Another objective is to take new measurements to better determine the total mass of Saturn's rings.
Early story from Scientific America: Running low on fuel, NASA's Cassini spacecraft has begun the final - and most daring - phase of its epic mission to Saturn. That's why the spacecraft had no contact to Earth during the maneuver.
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. Although this will end the spacecraft, Saturn's moons will be protected.
NASA's Cassini-Huygens spacecraft was created with the bold of spirit of adventure in mind, which will soon see it descending into Saturn's innermost ring. Saturday's flyby with Titan was the mission's last opportunity to see the moon close-up. The view was captured by the spacecraft during its first Grand Finale dive past the gas giant on April 26, 2017.
Eventually, NASA plans to dump Cassini in Saturn's clouds before it collides with one of the planet's 53 moons.
Cassini mission project manager Earle Maise said the risk puts them at a 97 percent chance of success.
Over her life, Cassini has dedicated herself to sharing with us the wonders that is Saturn through data and photography.