Thrawn Rickle 21

Radioisotope Thermoelectric Generators

© 1995 Williscroft

RTGs are incredibly simple and safe.  Certain substances are naturally radioac­tive—the atoms of these substances spontaneously change from time to time into sim­pler substances.  When these changes happen, one or more relatively high energy neu­trons are released.  Because of their high energy, these neutrons can be harmful to living matter, just as bullets or energetically thrown rocks can be.  This natural process of atomic change is called radioactive decay.

One group of substances generates an especially large number of neutrons during this decay process—plutonium and some of its oxides.  This is why plutonium is used in nuclear explosives.  When a sufficiently large amount of plutonium is concentrated in a special way, neutrons can be forced into a very rapid chain reaction where each neu­tron creates more neutrons, so that in a fraction of a second incredibly high energies are produced.

Under normal circumstances this cannot happen.  In an RTG, a small amount of plutonium dioxide (essentially plutonium rust), far less than the critical mass for a bomb or even that needed to sustain a reactor, is placed inside a container designed to trap the emitted neutrons as heat.  With the plutonium is a simple electrical device with no moving parts that produces electricity when it gets warm.  Since the plutonium can produce heat for a hundred years or more, RTGs can produce electricity that long.

RTGs are especially useful in deep space probes.  Solar power could be used, of course, but the collector panels are less efficient, are subject to damage from external sources, and they only work well near the sun.

Approximately four years ago, several “environmental” groups expressed serious opposition to using RTGs in space.  They  publicly decried the “dangers” of nuclear en­ergy, and they insisted on  keeping space free of such “dangers.”  On one hand they seemed to know nothing of the true nature of the space environment:  the sun is a con­tinuously exploding hydrogen bomb millions of times the size of the whole earth; our solar system is filled with high energy particles, neutrons, cosmic rays—at times it is like the inside of a nuclear reactor. Nothing humans could ever do would have the slightest effect on this environment.

On the other hand, they seemed equally ignorant of the benign character of RTGs.  The only possible risk from RTGs could result from scattering the thimbleful or so of plutonium into the atmosphere.  This is a non-problem for two reasons:  RTGs are de­signed to withstand an uncontrolled return through earth’s atmosphere without break­ing up; even if one did break up, however, the amount of plutonium is so small that it is extremely unlikely it could even be detected, let along harm anybody.

The irony is that the focus of ULYSSES, the space probe these groups were object­ing to, was solar variability and its effect on earth’s atmosphere, most notably the greenhouse.  This is a crucial concern to everyone on earth, and a special interest to many environmental groups, including those protesting.

Once again anti-nuclear groups are trying to prevent the “contamination of space with nuclear energy,” this time objecting to the launching of the Saturn-bound CASSINI spacecraft.  Scheduled for launch in October 1997, CASSINI will be powered by three RTGs.  Since this $3.4 billion spacecraft will be traveling near Saturn, almost a billion miles from the Sun, RTG power is unequivocally the best choice for this craft.  CASSINI will study Saturn and its satellites for at least four years, and will parachute a small probe dubbed HUYGENS onto the surface of Saturn’s largest moon, Titan.  It is the twenty-fourth U.S. space mission to carry RTGs—which included the manned Apollo lunar landings.

The problem here is not the twenty-three eminently successful prior RTG powered missions, nor the forthcoming CASSINI mission, but the incredible ignorance demon­strated by the leadership of the anti-nuclear environmental coalition that continues to resist these launches.  Their legal interference in the launch of ULYSSES delayed its de­ployment and increased its cost by nearly double.  They have the potential for causing the same kind of legal mischief during the work-up period prior to CASSINI’s launch in 1997.

In a free society even uninformed people have the right to express their opinions.   The leaders of the anti-nuclear environmental coalition have failed to edu­cate themselves even to the most rudimentary level of knowledge regarding RTGs and the space environment.  I trust the courts will recognize this failure in finding for NASA, and that they will assign responsibility for the financial cost of the proceedings and the subsequent delays squarely in the lap of those responsible.