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Saturn-orbiting Cassini spacecraft faces fiery finish

  • The planet Saturn, as seen from the Cassini spacecraft. After a 20-year trip, Cassini will dive into Saturn Friday. nasa image

  • FILE - In this Friday Sept. 20, 1996 file photo, NASA's Jet Propulsion Laboratory engineers and technicians lower the 3,420-pound Cassini Spacecraft into the Launch-Vehicle-Adapter at JPL in Pasadena, Calif. After a 20-year voyage, the spacecraft is poised to dive into Saturn on Friday, Sept. 15, 2016. (AP Photo/Frank Wiese) Frank Wiese

  • This June 9, 2017 image made available by NASA shows bright methane clouds drifting in the summer skies of Saturn's moon Titan, along with dark hydrocarbon lakes and seas clustered around the north pole, as seen from the Cassini spacecraft. (NASA/JPL-Caltech/Space Science Institute via AP)

  • This Feb. 3, 2017 image made available by NASA shows Saturn's shadow on its rings as seen from the Cassini spacecraft. During its deliberate plunge Friday, Sept. 15, 2017, Cassini will keep sampling Saturn's atmosphere and beaming back data, until the spacecraft loses control and its antenna no longer points toward Earth. (NASA/JPL-Caltech/Space Science Institute via AP)



AP Aerospace Writer
Tuesday, September 12, 2017

CAPE CANAVERAL, Fla. — After a 20-year voyage, NASA’s Cassini spacecraft is poised to dive into Saturn this week to become forever one with the exquisite planet.

There’s no turning back: Friday it careens through the atmosphere and burns up like a meteor in the sky over Saturn.

NASA is hoping for scientific dividends up until the end. Every tidbit of data radioed back from Cassini will help astronomers better understand the entire Saturnian system — rings, moons and all.

The only spacecraft ever to orbit Saturn, Cassini spent the past five months exploring the uncharted territory between the gaseous planet and its dazzling rings. It’s darted 22 times between that gap, sending back ever more wondrous photos.

On Monday, Cassini flew past jumbo moon Titan one last time for a gravity assist— a final kiss goodbye, as NASA calls it, nudging the spacecraft into a deliberate, no-way-out path.

During its final plunge early Friday morning, Cassini will keep sampling Saturn’s atmosphere and beaming back data, until the spacecraft loses control and its antenna no longer points toward Earth. Descending at a scorching 76,000 mph (122,000 kph), Cassini will melt and then vaporize. It should be all over in a minute.

“The mission has been insanely, wildly, beautifully successful, and it’s coming to an end,” said NASA program scientist Curt Niebur. “I find great comfort in the fact that Cassini will continue teaching us up to the very last second.”

Telescopes on Earth will watch for Cassini’s burnout nearly a billion miles (1.6 billion kilometers) away. But any flashes will be hard to see given the time — close to high noon at Saturn — and Cassini’s minuscule size against the solar system’s second largest planet.

The plutonium on board will be the last thing to go. The dangerous substance was encased in super-dense iridium as a safeguard for Cassini’s 1997 launch and has been used for electric power to run its instruments. Project officials said once the iridium melts, the plutonium will be dispersed into the atmosphere. Nothing — not even traces of plutonium — should escape Saturn’s deep gravity well.

The whole point of this one last exercise — dubbed the Grand Finale — is to prevent the spacecraft from crashing into the moons of Enceladus (ehn-SEHL’-uh-duhs) or Titan. NASA wants future robotic explorers to find pristine worlds where life might possibly exist, free of Earthly contamination.