Comments by Ross McCluney, Ph.D.,on:
the article that appeared in SPACE NEWS
(Feb 16-22, 1998, p.3), by James E. Oberg

By Ross McCluney, Ph.D., is Principal Research Scientist at Florida Solar Energy Center and a member of the NoFlyby Advisory Board [Please note these are Ross McCluney's views and not necessarily those of the University of Central Florida or the Florida Solar Energy Center]:

Regardless of the cause of the failure, the ICBM destruction mentioned in the article serves to illustrate that putting important, and dangerous objects into space is not 100% safe.

The discipline known as probabilistic risk assessment seeks to weigh both the probability of a bad action and the magnitude of its outcome. As the theory goes, if either the probability or the magnitude of a consequence are "vanishingly small", then even if the other or these two is very large, the risk is not high and the threat is of little consequence, so little needs to be done to protect society from the event.

There are a couple of fallacies with this argument, however. One is that we don't always know the true probability of an event, with high certainty, at very low levels of probability. Among other things, the probability quoted depends upon the assumptions used, the ones ignored or not realized, and the accuracy of the mathematics of the process. Errors in any of these can result in the real probability being much higher than the quoted figure.

Let's define probability. If one repeats a process a large number of times, the probability of any particular outcome, if the process is random, is the ratio of the number of times the outcome is recorded to the total number of times the process is repeated. With small probabilities, and with cases where we cannot easily repeat the experiment a large number of times, stated low probability estimates are highly uncertain in their accuracy or validities, even if everything was done right to compute the actual probability figure.

The second fallacy with the argument is this. If the unwanted outcome of an even minuscule risk can be horrifically terrible, such as destroying life on Earth, or, more reasonably, killing a large fraction of its human population, then no matter how low the computed probability, if it DOES occur, the consequence is so terrible that reasonable humans react with horror to even the minute possibility of it. The expert in probabilistic risk assessment, however, says that this position is not rooted in scientific fact and is therefore an unreasonable reaction. Wiser heads, on the other hand, might say that humans have a right to their fears, no matter how much the scientist may say they are unreasonable. Whose life, after all is in jeopardy? Those at risk have a right to seek to avoid perceived risks, no matter how minuscule the scientists may say are their probabilities.

Applying this to the Cassini fly-by, we hear that the risk of killing large fractions of the human population, or of radioactive contamination of large areas of the Earth, is minuscule. Do we trust these claims? No. Especially when we hear of examples of failures of space probes near to the Earth, for known and for unknown reasons, as with the recent loss of a U.S. ICBM. How do you assign a probability to an unknown reason for failure? Do you chalk it up to UFOs? What probability do you assign to UFOs targeting our space vehicles?

Although this may sound ridiculous, it is no more ridiculous than NASA's claim that the risk of a catastrophic failure of the Cassini space probe upon its Earth fly-by event is sufficiently small to be "acceptable risk." This is why I call on the Congress to stop this dangerous event. Just say no, to risking the Earth for modest gains in our understanding of distant planets.

Ross McCluney, Ph.D.
Principal Research Scientist
Florida Solar Energy Center,
1679 Clearlake Rd., Cocoa, FL 32922-5703
NoFlyby Advisory Board Member

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