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P A S A D E N A, Calif., Aug. 14 -- A two-story, $3.4 billion spacecraftcarrying a load of deadly plutonium will zoom within 725 miles ofEarth this week to gain momentum for the final leg of itsmeandering, seven-year voyage to Saturn.
Cassini’s return, two years after NASA launched the largest andmost expensive unmanned spacecraft ever, poses virtually no risk,mission officials say.
But anti-nuclear activists, concerned over the 72 pounds ofcarcinogenic cargo, aren’t so sure.
“The fact is space technology can and does fail,” said BruceGagnon of the Global Network Against Weapons and Nuclear Power inSpace. “And when you start using nuclear materials in increasingnumbers, the odds of an accident increase.”
The flyby at 8:28 p.m. PDT Tuesday will use Earth’s gravity tochange the probe’s direction and speed relative to the sun. Withoutthe “gravity assist” and two previous close encounters with Venus and a future flyby of Jupiter, the probe would never reach itsdestination in 2004 to study Saturn’s rings and moons.
Chances of Re-Entry Small
The probe will approach Earth at about 35,000 mph. Its speedwill increase by about 11,000 mph after the swingby. At its closestpoint over the South Pacific, the probe might be visible fromPitcairn or the Easter islands.
NASA has used planets’ gravity to fling its probes through spacesince 1973. The plutonium-powered Galileo probe to Jupiter twiceswung by Earth in the early 1990s at altitudes much lower thanCassini’s closest point.
The chances of an accidental re-entry of Cassini are about 1 in1.2 million, according to a NASA estimate.
“It’s just not a credible event,” said Bob Mitchell, Cassini’sprogram manager at NASA’s Jet Propulsion Laboratory in Pasadena.“I’m not telling you it’s impossible, but it’s just notcredible.”
Activists fear that some sort of navigation or human error couldcause the craft to burn up in the Earth’s atmosphere, showering theplanet with deadly plutonium dioxide.
