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PRI's Environmental News Magazine


Air Date: Week of September 5, 1997

Next month NASA plans to launch a plutonium-laden spacecraft on a mission to Jupiter, this one carrying 72 pounds. Steve Curwood spoke with John Pike, Space Policy Director of the Federation of American Scientists about the risks involved with this flight.


CURWOOD: It's Living on Earth. I'm Steve Curwood. Fear gripped Australia last fall when it seemed a Russian space probe bound for Mars and loaded with a half pound of deadly plutonium might crash on the island nation. In the end, the near-panic passed as the satellite probably went down in Bolivia or Chile, and so far no traces of plutonium have been found. Today there are new concerns. This fall, NASA plans to launch its own plutonium-laden spacecraft: a mission to Jupiter, and this one carrying 72 pounds. I asked John Pike, space policy director of the Federation of American Scientists, about the risks involved with this mission, and why NASA needs a nuclear generator to power it.

PIKE: Traditionally, NASA has been of the view that when they're flying missions to the outer planets, much further away from the sun than the Earth is, that solar power just isn't an option that far away from the sun. They use the plutonium on Cassini not the way you build a bomb or build a reactor here on Earth, but basically from the natural decay of the plutonium. That gives off a lot of heat. And they use thermocouples, which in turn generate the electricity that's required to power the spacecraft.

CURWOOD: The concern comes from people saying that an accident could disperse this probe's plutonium into the Earth's environment. How would that happen and how likely is that?

PIKE: Well, there are basically 2 major accident scenarios that people are concerned about. The first one is that the Titan rocket that it's being launched on could explode or otherwise break up shortly after launch with a radiological release around the Kennedy Space Center, Cape Canaveral Air Force Station area in Florida. The other possibility is that some time after launch, when the Cassini spacecraft loops around the sun and then comes back by the Earth in order to get a gravitational assist to get it all the way out to Saturn, there's a concern that it might be slightly off course, and rather than passing a few hundred miles above the Earth's atmosphere, re-enter the Earth's atmosphere, burn up, and the plutonium could be dispersed either over a large area or perhaps globally. The problem is that it's difficult to quantify both the probability of either of those accidents happening, or the extent to which plutonium would be released. It's fairly easy to say that the odds of the Titan rocket having a launch accident are about 1 in 20. There have been 20 Titan launches, one of them's blown up.

CURWOOD: You're saying that just in the launch phase there's a 1 in 20 chance that the rocket carrying the spacecraft, which is loaded with all this plutonium, could blow up and here the plutonium might be dispersed?

PIKE: Well certainly, there have been 20 Titan IV launches. One of them had a launch accident and its spy satellite payload wound up in the Pacific Ocean. And 1 in 20 is a typical number for expendable launch vehicles. NASA's calculations suggest that the radioactive power source on Cassini is built to withstand the sort of conditions that it would encounter in such an accident. Of course the problem is that they don't have an awful lot of experimental data on this. But I think that we're basically in a situation where, with a launch vehicle accident there's a relatively high probability that something's going to go wrong with the launch vehicle, a relatively low probability that the plutonium is dispersed. In the second scenario, the probability that the spacecraft swinging back by the Earth would accidentally re-enter the atmosphere is probably fairly low. On the other hand, NASA's studies conclude that if it did accidentally re-enter the atmosphere, the odds are pretty high that a lot of plutonium would get scattered around.

CURWOOD: And what would that mean for people's health, for wildlife, for the planet's health if that happened?

PIKE: Well, that's where the controversy comes in. NASA's assessment of the risk is that as many as a few thousand people might die as a result of Cassini re-entering the Earth's atmosphere. Other estimates place the numbers in the millions. And since we don't have very much experience with this sort of Earth fly-by, there is considerable uncertainty associated with that.

CURWOOD: I'm wondering, haven't there been some pretty substantial advances in solar technology that NASA should be able to take advantage of, compared to when they first looked at the solar option?

PIKE: Well, there have certainly been major advances in solar electric power technology over the last several decades. Particularly in the last 5 or 10 years, there have been significant improvements. Back in the 1960s, when NASA first started flying missions like this, I think the case for nuclear power was much clearer than it is today. The main thing that's driving the nuclear rather than solar option here is the well-founded fear on the part of the Cassini scientists that if they stopped their program for a few years, put solar power on it, that there's a real risk that NASA or the Congress would cancel it and it would never get to fly.

CURWOOD: John Pike is space policy director of the Federation of American Scientists. Thank you, sir.

PIKE: Thank you.



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