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Comment by dalke | Hacker News Reader

Because it's launched from the earth, and rockets have an unfortunate tendency to blow up at times. That's why the RTG's are designed to re-enter safely even if there's an explosion.

Even after it leaves orbit, the probes loop back to use the Earth for gravitational assist and there's a minuscule chance that it will crash; with odds something like 1:1000000. In the absolute let's-imagine-the-impossible worst case scenario, an additional few thousand people are expected to get cancer.

Summarize that as "but if it crashes into the Earth, thousands of people will die!"

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How about if the rocket blows up on launch? Wouldn't the launch pad area be covered it aerosolized plutonium?

No. Most of it would be in ceramic chunks, which are much less dangerous.

Even the hugely improbable worst case scenario of an RTG powered spacecraft impacting the Earth during a flyby is unlikely to lead to any increased deaths per se. In such a scenario (again, astronomically unlikely) the RTGs fuel would vaporize in the upper atmosphere and ultimately add a very tiny additional contribution to the global background radiation level.

This is a pretty thorough analysis of the risks/outcomes along those lines: http://www.dartmouth.edu/~chance/course/Syllabi/97Dartmouth/...

That document estimates 120 extra cancer deaths, should the nearly-impossible flyby reentry occur. However, a better text is the Cassini Final Environmental Impact Statement, chapter 2 (http://saturn.jpl.nasa.gov/spacecraft/safety/chap2.pdf). Table 2-8 estimates 4500 deaths, assuming there is no lower limit for radiation exposure, or 15 deaths if you exclude those with under 1/1000 rem exposure.

> In such a scenario (again, astronomically unlikely) the RTGs fuel would vaporize in the upper atmosphere and ultimately add a very tiny additional contribution to the global background radiation level.

In that case, the media would spend all their time talking about how many billions of becquerels of plutonium got released into the ocean (or atmosphere, or wherever), not having any directly-attributable deaths to point to or any other large measurements to use.

The media can't do math, they'd try to compare it to some other thing (like Three Mile Island, Chernobyl, or Hiroshima) and probably get it wrong by a factor of 1,000 one way or another.

What's funny is that they even get Three Mile Island wrong, everyone regularly confuses it with a movie The China Syndrome that was released around the same time.

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