Cassini
Probe To Swing by Earth
By MATTHEW FORDAHL, AP
LOS
ANGELES (AP) - Worrying anti-nuclear activists, a
plutonium-powered NASA spacecraft hurtled toward a close
encounter with Earth on Tuesday in order to use the
planet's gravity to sling it toward Saturn.
The $3.4 billion Cassini probe was scheduled to
fly within 725 miles of Earth, over Easter and Pitcairn
Islands in the southeastern Pacific, at 8:28 p.m. PDT.
Anti-nuclear activists feared that some kind of
error would cause the 22-foot Cassini and its 72 pounds of
plutonium to plunge into the Earth's atmosphere and shower
the planet with deadly radioactive debris.
But NASA officials said there was only a
1-in-1.2 million chance of accidental re-entry. And even
if that happened, the plutonium was well-protected, they
said.
The swingby was designed to give the spacecraft
momentum for the final leg of its seven-year journey to
Saturn and its moons. Cassini will also make a
December 2000 flyby of Jupiter before reaching its final
destination in 2004.
In June, demonstrators protested against the
flyby, but most activists conceded there was no way to
prevent it. Before Cassini's launch in 1997, protesters
filed lawsuits and threatened to chain themselves to the
pad.
``NASA
said in order to explore you have to take risks, like
Columbus took risks,'' said Bruce Gagnon of the Global
Network Against Weapons and Nuclear Power in Space. ``But
Columbus only risked himself and his crew. In this case,
they're risking people all over the world.''
NASA has used ``gravity assists'' of Earth and
Venus since 1973 to fling other spacecraft to their
destinations, including the plutonium-powered Galileo
probe that went to Jupiter. Galileo twice flew close to
Earth without incident.
Cassini doesn't use the plutonium for propulsion
but to power its dozen instruments. Heat from the
element's decay is converted into electricity.
NASA's Russian Roulette
By Ligia Giese
This October NASA plans to launch the
Cassini space probe to explore the planet of Saturn and
one of its moons. A frightening payload, unfortunately,
will accompany the space flight. In addition to an array
of scientific instrumentation, Cassini will carry 72.3
pounds of plutonium-238. Plutonium-238 is extremely
carcinogenic. When inhaled, less than 30-millionths of a
gram causes lung cancer. Plutonium also moves throughout
the circulatory system, where it eventually causes many
types of cancer including leukemia, bone and liver cancer.
The possibility of a Challenger-like explosion
makes the plutonium-powered Cassini probe a significant
health risk for the people of Florida and the entire
world. On the morning of October 6 the probe is scheduled
to be launched using a Titan IV rocket. Not the most
reliable vehicle, in 1993 a Titan IV rocket blew up during
a launch from California. Furthermore, recent problems
with fuel leaks and rips in the capsule's insulation will
delay the launch. It is worth noting that the space
shuttle Challenger was scheduled to carry plutonium on the
flight following its tragic accident. If the plutonium had
been on board when the Challenger exploded, the tragedy
would have been on a much larger scale.
Another opportunity for the release of
plutonium-238 from the Cassini probe is a
"fly-by" within 312 miles of the earth's surface
in 1999. In order to shorten the time to reach Titan, a
moon of Saturn, Cassini will first orbit Venus and then
return to Earth to get the "sling-shot" effect
of the earth's gravitational force. If for any reason
Cassini re-enters the earth's atmosphere, the probe's heat
shield will be destroyed and the plutonium-238 will be
released into the atmosphere. If dispersed as a fine
aerosol and then inhaled, it would be "astonishingly
hazardous", to quote John Pike, director of space
policy for the Federation of American Scientists, and
potentially affect millions of people. The fact that the
Russian Mars 96 space vehicle spread a half-pound of
plutonium over the border of Bolivia and Chile in November
of 1996 seems not to have deterred NASA from planning to
use this dangerous energy source.
The Cassini launch is a high stakes gamble and
the potential health risk it poses to all of us seems
greater than the benefit of using plutonium-powered space
vehicles. Why use plutonium-driven generators when solar
generators of marginally greater weight have been recently
developed in Europe? NASA is not currently willing to
retrofit the Cassini probe using this new technology, nor
does it intend to alter plans to launch a dozen more
plutonium-driven space vehicles in the future. The Jet
Propulsion Laboratory web site states, "While it is
estimated that the probability of a Cassini launch failure
is about 1 in 20, most failures would not result in a
release of plutonium."
It continues: "Though more detailed
assessments are underway, initial estimates are that
approximately 1 in 25 Titan IV/Centaur failures could
result in the release of small quantities of plutonium
dioxide to the environment. It is possible that there
could be small releases of plutonium dioxide particles
from some RTG components, but if the components strike
water there would be no release. None of the releases are
expected to result in any cancer fatalities in the exposed
population."
Although retrofitting Cassini would no doubt be
expensive and time-consuming, are estimates of the chances
of plutonium release and its consequences adequately small
for us to take this risk? As a future physician, I do not
wish to treat cancers borne of preventable man-made
exposure. I urge you to tell your parents, teachers, news
editors and elected representatives about the Cassini
launch and future launches using radioisotopes as an
energy source. Only President Clinton has the authority to
postpone the Cassini launch until further investigations
can be undertaken. Action on our part and that of our
representatives will help us to avoid a future health
crisis of catastrophic proportions.
Related Links:
Cassini:
Mission to Saturn
