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The Cassini spacecraft during processing.
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Courtesy of NASA

Cassini Flyby Dangerous for Earth
News story originally written on August 16, 1999

The Cassini space probe will use the Earth's gravity to increase its speed while zooming towards Saturn. NASA's most expensive unmanned spacecraft has already made a flyby of Venus during its two-year trip in space. After passing Earth, it has one more flyby of Jupiter in 2000 before reaching Saturn in 2004. NASA probes have completed successful flybys of Earth since 1973, but this one attracts more attention than usual because the probe carries plutonium.

Plutonium is used in Cassini to power all of its instruments. Solar energy, which is the usual source of power, cannot be used because Cassini is going to Saturn. It would need solar panels the size of tennis courts in order to absorb enough energy. The satellite will come within 725 miles of Earth, which could possibly endanger lives if something happens to the spacecraft.

Plutonium is a radioactive chemical which can cause lung cancer if inhaled. The plutonium is stored as pellets in special cartons aboard Cassini, but if an error occurs, the satellite could burn up in the atmosphere and disperse the harmful chemicals. Scientists say the chance of a problem occurring is less than 1 in a million. Still, the chance of disaster upsets many around the world.

If a pellet breaks up into powder high in Earth's atmosphere, it will be dispersed all over the globe. Such a small amount will not be harmful. However, if a cannister makes it to Earth and crashes, the chemicals would be concentrated in one area.

Still, NASA believes the rewards are much greater than the risks.

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