Probe to Saturn Is on Track
On Monday, NASA will launch the Cassini space probe to Saturn, the huge planet whose hundreds of lightly colored rings and 18 known moons resemble a miniature version of the solar system itself. The mission is one of indisputable scientific benefit and considerable public angst.
In recent months, critics opposed to the use of nuclear power in space have launched a campaign against Cassini, warning that the probe’s 72 pounds of plutonium could prove deadly if the rocket carrying it were to explode on launch or if Cassini were to crash to Earth during a planned 1999 fly-by on its way to Saturn. The chance of the second scenario occurring is in the range of 1 in a million, say NASA scientists and others.
But the first scenario is conceivable, for the Titan rocket that will launch Cassini has failed once in 20 launches. Most scientists, however, are satisfied that NASA has fixed the flaw that caused that single failure and have protected the plutonium pellets in Cassini’s batteries by encasing them in heat-resistant ceramic shells (plutonium is deadly only if it is ingested or inhaled).
Even if the shells fail and plutonium dispersion does occur, the expected radiation dosage a person might receive is 1 millirem, a small dose considering that each of us absorb 300 millirem of natural radioactivity annually from cosmic rays and the Earth itself.
The dangers posed by Cassini are significantly lower than those posed by other, less recognized nuclear safety risks, like California’s plans to store nuclear waste in Ward Valley. Nevertheless, Cassini’s critics have done a public service by reminding Americans that nuclear power has its dangers, even if Cassini, relatively speaking, isn’t one of them.
Respected nuclear watchdog groups like the Bulletin of Atomic Scientists support Cassini, while sensibly opposing the Defense Department’s far more dangerous plans to put nuclear reactors in space. Plutonium power systems similar to Cassini’s have been used without public objection in most space missions, from Apollo to Pioneer and Voyager.
They are far more essential in Cassini because Saturn is so distant from the sun (almost a billion miles, twice as far from the sun as Jupiter) that even the most advanced solar panels could not begin to collect enough power to fuel the mission and others like it to deep space and its unknown mysteries. Cassini will focus much of its attention, for example, on Titan, a moon whose uniquely rich mixture of carbon and nitrogen is likely to bear more resemblance to early Earth than the Earth itself does today.
