Anti-nuclear groups wrong on supposed dangers of Cassini

July 08, 1999|By M. Jack Ohanian

ONCE the dream of interplanetary romantics, the idea of traveling hundreds of millions of miles to Saturn by powering a spacecraft with a compact nuclear generator is well on its way to becoming a reality. But NASA's Cassini spacecraft's voyage has generated much controversy.

Even before it thundered off the launch pad at Cape Canaveral, Fla., 19 months ago, anti-nuclear groups had protested NASA's plutonium-powered spacecraft, exploiting public fears about radiation.

Now such groups are planning demonstrations timed to coincide with Cassini's orbital loop, when it flies within 800 miles of the Earth in mid-August. These activists maintain that the Cassini spacecraft might break apart as it nears Earth, showering the planet with radioactive fallout. They say that, if all the plutonium in the spacecraft's power source was dissipated in the atmosphere, man-made radiation would double.

What this ignores, however, is the fact that man-made radiation is but a very tiny part -- a small fraction of 1 percent -- of total background radiation; nature bathes us in radiation from minerals and from space. So, if an accident released all of the plutonium, it would hardly change the world's radiation levels, and never produce a detectable health effect.

Though the anti-nuclear activists' allegations are not based on a rational analysis, but rather on hysterical claims that have no basis in fact, the so-called "radiation controversy" is at the center of the public debate on the space program. Proposed legislation to ban the use of nuclear power in space is now before Congress.

This is not a routine nuclear dispute. If such mischief is allowed to influence public policy-making on radiation applications, the results would be far-reaching and devastating: Exploration of the solar system would be stalled, testing of new power systems for use in space would be stopped and industrial and military uses of radioisotopes in satellite systems would be stifled. Congressional action could determine not only the immediate fate of radioisotope thermoelectric generator or RTGs, but also an advanced radioisotope power system for future missions in NASA's outer planets project.

Plutonium-238 -- an isotope of plutonium that is not used in weapons -- is the only practical source of electrical power for spacecraft traveling to five of the nine planets in our solar system.

Sunlight at those distances is too faint to supply solar power, and batteries will not last the many years it takes to get to these destinations. RTGs are reliable and long-lived. During the past four decades, nuclear devices have powered 26 U.S. space missions, including the Apollo moon landings and the Voyager, Galileo and Ulysses probes of the solar system. These missions are the core of the space program.

When Cassini arrives at Saturn July 2004, its mission will truly begin. The craft will orbit the ringed planet for four years, plumbing the dynamics of the rings themselves, the magnetic field environment, Saturn's biggest moon, Titan, and all its icy moons.

The scientific benefits will be incalculable. Scientists will be rewarded for their seven-year wait with a wealth of scientific data and breathtaking, full-color, real-time pictures. The mission will help scientists find out how Saturn and its rings and moons formed and evolved, and may provide clues as to the origin of our solar system.

One future mission that might use an advanced radioisotope power system is the Europa Orbiter. Intrigued by the amazingly detailed images of the Jovian moon transmitted by the Galileo spacecraft, NASA scientists want to know more.

In its tour around Jupiter, Galileo, powered by two 285-watt RTGs, photographed the surface of Europa, the planet's fourth-largest satellite. In the view of many astronomers, these pictures reveal a sheet of ice on the surface beneath which a liquid ocean could exist.

But does it? To answer that question, NASA plans to send a craft to Europa, where it would bounce radio waves through the miles-thick ice sheet to determine the depth of the ice. To run its on-board computers, which operate the craft and gather, process and transmit data, the Europa Orbiter may well rely on an advanced radioisotope power system. If the orbiter does find an ocean -- which could contain the building blocks of extra-terrestrial life -- a follow-up mission, Europa Lander, could include remote-controlled submarines to melt through the ice and explore the undersea realm.

Irrational opposition to nuclear power should not be allowed to block its use in space missions that probe the deepest secrets of the cosmos. The real question is whether we will let groundless fears keep us rooted to the Earth, or let our spacecraft explore the outer reaches of space.

M. Jack Ohanian is a professor of nuclear and radiological engineering at the University of Florida and past president of the American Nuclear Society.

Pub Date: 7/08/99

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