The Daily Revlution

Why We Should Stop Cassini

by Russell D. Hoffman

at sunset.
Taken by Hubble.
Soon, NASA plans to launch a space probe called Cassini. Cassini is designed to go to Saturn by way of Venus, Earth, and Jupiter. It will use each planet in one or more "gravity assist maneuvers" to attain the speed necessary to make it all the way to Saturn. When Earth is used for the Gravity Assist (EGA), NASA will fly Cassini just 496 miles above the surface of the Earth, at about 43,000 miles per hour (19.4 Kilometers per second, or 63,600 feet per second). The actual stated height above Earth which NASA will use has changed many times, and was 312 miles for several years prior to the latest published number.

To say Cassini is a risky mission is an understatement. It will contain over 72 pounds of Plutonium Dioxide consisting of over 60 pounds of pure plutonium 238. This is a health risk of virtually unprecedented proportions. In the past, all the weapons testing, which the world felt it was necessary to do, put an incredible amount of plutonium in the atmosphere. But that was a WAR -- albeit, a cold (blooded) one, but it was war nonetheless.

If such actions were inexcusable (and this writer and many others believe that the vast majority of past nuclear weapons testing was certainly inexcusable) then it surely is inexcusable to risk the same sort of contamination of our home turf (Earth) for NASA's next science experiment. But that is just what Cassini is capable of if an accident occurs during the launch, late launch, or during the gravity assist.

This is not a peaceful use of the mighty atom (if indeed there can be such a thing).

The purpose of 99% of the plutonium on board Cassini is to provide merely 745 watts (nominal) to power the science experiments. It is not for propulsion, it is not a "fuel" for attitude control or anything like that: it is just a small heat source used to create a very modest amount of electrical power via thermocouples. Is it necessary? No. While NASA claims that the current mission objectives would be severely hampered by insistence on a reliance on solar, in truth, there is little doubt that one of the following solutions would work:

1) NASA could reduce the mission objectives to power requirements that could be supplied by solar.

2) NASA could work harder on perfecting solar options -- with continuance of the Cassini mission, and the benefits to mankind of better solar technology, as two powerful incentives.

3) NASA could realize that mankind, while we love the quest for knowledge, does not want to take unnecessary risks, and Cassini is too risky RIGHT NOW. Therefore, in addition to perfecting the solar option, NASA should redesign the scientific tools to be used on the mission to have even lower power requirements. Probably within 10 years NASA would be able to fly the exact same mission with one tenth or at most half the power requirements -- then they could use solar options. We have waited over two decades to return to the moon -- we can wait for NASA to perfect its tools. Cassini is not necessary RIGHT NOW.

Cassini, if it is not stopped, will be launched some time in October or November of this year (1997), with a number of backup launch opportunities extending to the year 2001. Holding up Cassini will not do. It must be permanently prohibited until it can be launched with solar alternatives.

In 1964 NASA had a mission abort of a nuclear-packed mission that resulted in 17,000 Curies of plutonium being intentionally incinerated in the upper atmosphere. Opposition estimates range to hundreds of thousands of people -- or more -- who may have died from that one accident, known as SNAP-9A. In 1967, in response to a worldwide atmospheric test ban treaty, NASA changed its policy of intentional incineration of nuclear fuel packs, so that their newest RTG (Radioisotope Thermoelectric Generator) design does not intentionally incinerate.

But now, NASA is carrying many times more plutonium. Cassini is scheduled to carry about 406,000 Curies of plutonium! In an EGA reentry accident during the Earth Gravity Assist (EGA) maneuver of Cassini, NASA estimates that 4/5ths of the time there will be a fuel release. According to NASA, in an EGA reentry accident, 3/4's of the time about 13,000 Curies of the fuel will be released at high altitude, and several times more than that will be released near Earth's surface if the plutonium pellets impact on hard surfaces. But unlike the SNAP-9A, this time, somehow, it will be considered an accident! Yet virtually the same amount is EXPECTED to be released in a flyby reentry accident as was released in the SNAP-9A intentional incineration! That's some accident!

How does this work? What NASA does is it puts the plutonium into 108 separate units called GISs (Graphite Impact Shells). These units are then placed in pairs into 54 units called GPHSs (General Purpose Heat Sources). 18 of these are packed into each of 3 RTGs.

If a reentry accident occurs, the RTGs are expected to melt away and release the GPHSs. Then, the GPHSs are expected to slow down, and also melt a bit, but not entirely. Most of the time. But it's not expected to work 100% by any means.

If the GPHSs are cracked or smashed in some way while still traveling at high speed (for example, by smacking into each other or other pieces of the disintegrating spacecraft) then the GISs and the plutonium within will probably melt and be released. Every one of those 54 GPHS's must remain intact, since each one contains over a pound of deadly plutonium. But even NASA admits that it is unlikely that all of them will remain unbroken. Current NASA estimates are that 1.7 of the GPHSs will crack or "ablate" (melt away) sufficiently to release their GISs (two in each GPHS). Those GISs are expected to release their plutonium contents as vapor and small particles.

What does NASA do about this? While they could give up and go to a solar option, instead they consider this to be okay! And how do they do that? NASA does not think that a slight increase in radioactivity is anything to worry about. Since "background radiation" is already about 360 millirem per year per person, adding a fraction of a millirem to everybody is A-OKAY.

But it isn't.

Plutonium 238 is a highly radioactive (i.e. "hot") substance. It is 280 times more radioactive than plutonium 239. This means that a given weight of Plutonium 238 emits about 280 times more "alpha particles" per second than the same amount of Plutonium 239 does. So a given mass of Plutonium 238 is much more dangerous, especially when inhaled, than the same mass of Plutonium 239. A Cassini reentry accident can create literally billions and billions of respirable pieces, and both sides -- pro and con -- agree that inhaling even a millionth of a gram of plutonium is a fatal dose. But NASA would risk spreading anywhere from several pounds to many pounds of this stuff in an accident. The half-life of Plutonium 238 is 87.75 years; while the half-life of Plutonium 239 is about 24,400 years. About 10% of the nuclear fuel will be plutonium 239 and most of the rest will be plutonium 238.

NASA claims that the chance of a reentry accident is less than one in one million -- but NASA bases this number on complex mathematical estimates based on "educated guesses". Past NASA flight experience suggests a much greater danger. Yet every time NASA figures out what it did wrong on a previous disaster, it discounts the obvious fact -- that they blew it again!

For example, the Titan booster rocket that NASA plans to use for the Cassini launch has successfully been used just 18 times -- and failed catastrophically once. Yet NASA's estimate of a Titan launch failure is one in several hundred -- not one in 19!

Furthermore, they have based their guess that usually only 1.7 of the GPHS units will break apart on studies done with very, very few actual units and a lot of simple computer modeling. (While very time consuming to run, the actual programs do not appear to be terribly complicated.)

When Boeing or Airbus do computer simulations prior to launching a new airplane, they risk their businesses and they risk the lives of perhaps 500 people in an accident -- both high risks. But NASA numbers, if in fact 3.4 GPHS's will desintegrate rather than 1.7 of them, would mean hundreds of thousands more deaths! This is a much greater risk! Also, the possible deviation from this number is quite high depending on many accident scenario factors. In reality, no one knows what will happen if a flyby reentry occurs. It could be that only a few pounds will be vaporized in the upper atmosphere as NASA suggests, but then again it could be more like 10 or 20 pounds -- it could even be more. And it would be very hard to tell what actually had happened, even if over the years millions of deaths were to occur from the accident.

There are many things that need to be done to stop this madness, because NASA is in no mood to stop it themselves. We have made many attempts to present NASA with an alternative viewpoint to what they consider "acceptable risk". But NASA intends to launch.

People need to learn about this awful thing. This writer is personally shocked by how surprised even the staunch environmentalists he talks to are when they learn what NASA is trying to do. The average person, today, might know what PATHFINDER is and what planet it whet to, but they are sure to say "What's Cassini?" if you ask them about NASA's upcoming mission.

The public needs to hear the truth. Anyone reading this message should feel free to republish it as they see fit. President Clinton needs to be contacted, so that he knows that people care about today's Earth more than they care about NASA's weak scientific arguments for the Cassini mission.

People need to contact their congresspeople and ask for their help in stopping Cassini as the mission is presently planned, with its deadly plutonium payload.

People need to stand up and say they ARE AWARE of Cassini, and they want it stopped -- "what is Cassini?" is not a sufficient answer for the general public who funds this sort of thing. NASA loves to promote its successes, but has an amazing ability to hide its failures behind complex scientific jargon, and a dearth of press releases. We the public should not be able to say later: "Who knew?"

People need to shout: "NASA IS PLANNING TO LAUNCH 72+ POUNDS OF PLUTONIUM IN OCTOBER, 1997 -- AND WE HAVE TO STOP IT." For more information and more "to do" ideas, please visit our web site at:

Russell D. Hoffman