What divides the experts is:
All parties are agreed that such an event is unlikely. It may happen that the Cassini mission may be a resounding, flawless success. However, it's only a matter of time before some disaster strikes. Instead of relying on misleading computer programs which tell you what you want to hear, one should carefully examine the actual track record of accidents in the space program, with numerous booster rocket failures and space probes which malfunction.
Unfortunately, the true risks from such an accident and the consequences have been downplayed. In a democracy, the American people can make rational decisions only on the basis of scientific truth, not simplistic, misleading press releases. It is inevitable that there will be spectacular accidents with the space program, some involving casualties, and the American people have a democratic right to know what the true risks are. Thus, it is a matter of scientific interest to go over line-by-line the calculation of the FEIS.
NASA calculates in its FEIS that up to 2,300 people might come down with fatal cancer over a 50 year period from the dispersal of plutonium-238 over a populated area. More recently, it has lowered this figure to 120. However, the calculation of these figures depends on three important steps, each of which has been underestimated by NASA:
The FEIS admits that plutonium in the RTGs will be subject to three extreme conditions during a launch phase accident: high temperatures, shrapnel, and explosive over-pressure. However, the essential problem is that NASA engineers have failed to perform a full-scale, realistic test of an explosion involving the RTGs.
In other areas of engineering, we have a good understanding of what happens when many different types of catastrophes happen, e.g. plane crashes and train wrecks, because we have a large body of experimental data. However, we have no experimental data by which to estimate the true dispersion of plutonium during a launch phase explosion because no realistic tests have ever been conducted.
NASA, however, has conducted some partial tests, which already reveal the vulnerability of the RTGs to extreme environments. The FEIS in fact, concedes that plutonium will escape the RTGs during a launch phase explosion, but its analysis is purely hypothetical and results in only a rough estimate.
In particular, we find:
Several conclusions can be drawn:
The point is that a full-scale test involving the simultaneous conditions of high temperature, shrapnel, and over-pressure has never been done. It is likely that the combination of all three will cause severe rupturing of the RTGs.
In spite of all these factors and uncertainties, the FEIS on p. 4-48 confidently concludes that a maximum of 28.7 curies, or less than .01% of the plutonium, will escape during a launch phase accident.
Several points can be made:
In addition, actual experiments have shown that micron-sized particles of natural uranium, U-238, can be dispersed by the wind over 25 miles. In nuclear power plant accidents, radiation has been dispersed several thousand miles from the original accident. (For example, in the Windscale disaster in England in 1957, which was completely hushed up by British authorities, the radioactive cloud emerging from the carbon-moderate reactor was tracked going over London, sailing over the English channel, and finally dispersing over Cairo, Egypt. More recently, the radiation from Chernobyl was widely tracked over Europe and even the U.S.)
However, what is rather remarkable is that the FEIS totally ignores wind conditions and merely postulates that the plutonium will be dispersed, in one scenario, within an area of 7.18 x 10^-2 square miles. This is a roughly a square area 1,000 feet on each side. Again, the fact that this is presented without any error bars, and to three significant figures, shows the ignorance of the engineers who calculated this number.
But what is revealing is that the FEIS assumes that almost all the plutonium will be confined to the launch facility. According to the FEIS, no plutonium is expected to leave the launch pad area. In other words, NASA engineers have discovered a new law of physics: the winds stop blowing during a rocket launch.
But anyone who lived through the Challenger explosion, the Delta rocket explosion, etc., will realize that debris has been pulverized and spread over a significant area. Eyewitness accounts of the recent Delta rocket explosion indicated debris scattered over several miles.
In fact, experiments conducted on metal oxides have shown that a significant percent of the inventory can be pulverized into a fine dust of micron-sized particles, which can then be blown miles from the original site by the winds. These micron-sized particles are especially dangerous because they stay lodged deeply in the lungs for decades, where ciliary action is useless in expelling these particulates. Thus, these particles can emit radiation at close range to nearby lung tissue for decades to come, causing cancer.
However, what is in dispute is the fact that the FEIS assumes a rather average density of people per square mile. This is therefore not a maximum credible accident, which would assume that the winds blow the plutonium into a major city.
For example, the FEIS assumes that, for a Phase 5 accident over Africa, the expected health risk would be 1.5 x 10^-4 over a population of only 1,000 people. This is low even for Africa. Not to mention that the rocket may misfire during the launch phase and tumble in a partial orbit, thereby landing almost anywhere on the earth, rather than in Africa.
A Phase 1 accident would release plutonium in an area populated by only 100,000 people. But if the winds blow, then the area affected within 5 counties of the launch site could total over a million people.
The FEIS then calculates how much plutonium may actually land on the earth, and again underestimates the real risks.
The FEIS first divides the source term into three parts: a rock impact, soil impact, and water impact, and then calculates the percent distribution of each on the planet earth. For example, the FEIS estimates that 4% will hit rock, 21% will hit soil, and 75% will hit water.
This is a rather odd way of calculating maximum risks, because it confuses probability of an accident with the consequences of that accident. The calculation of how much surface area of the earth is divided into rock, soil, and water belongs in a calculation of the probability of mishap, not in the calculation of maximum risk.
The calculation of maximum credible risk necessarily assumes maximum risk by definition, i.e. that all the plutonium will hit rock, since that is the maximum credible scenario. Rather than 4% of the plutonium hitting rock, one should assume that all of it does.
Second, the FEIS calculates the percent of plutonium that can be released on impact with rock, soil, and water. Again, these numbers are simply pulled out of a hat, with no justification. For example, in one scenario, it assumes that all of the plutonium will be dispersed if it hits rock, 25% of the plutonium hitting soil will escape, and none hitting water will escape. However, no justification is given for these estimates, because there are none.
The important point is that no one has ever done an experiment calculating the effect of entering the atmosphere with RTGs at 40,000 miles per hour. Until this experiment is done (using a replacement for plutonium), all these numbers are purely speculative.
More recently, on April 1997, the Supplemental Environmental Impact Statement has revised the early estimate of cancer fatalities from 2,300 to 120 (p. 2-19). This may seem strange, until one realizes that their assumptions have become even more conservative. Instead of assuming that land contamination can be 2,000 sq. km, the new estimate puts it at a surprisingly small area of 7.9 sq. km. This is a square about 1.7 miles on each side. In other words, the new EIS assumes that the Cassini probe, coming down in flames from outer space at 40,000 miles per hour, will hit a bull's eye and then remain there, without any winds whatsoever.
This is a remarkable reduction by a factor of 250, which once again is pulled out of a hat, without any justification. Not surprisingly, the casualty figures have also dropped significantly, from 2,300 to 120, a factor of 20.
Although these methods are standard for the field, these methods have largely been discredited by the actual operating record of nuclear power accidents. Three Mile Island, for example, was a Class IX accident which was largely unforeseen by MIT's WASH-1400, the standard reference within the industry, which largely ignored small pipe breaks.
The methodology is flawed for several reasons:
The actual track record of accidents shows that computer calculations are often misleading and give a false sense of confidence:
Meteorite damage is of a real concern, but human and technical flaws are much more likely to cause failure. For example, it has been recently estimated that the International Space Station Alpha may suffer a 50% probability of a catastrophic meteor impact during its 15 year life span. This is certainly a significant danger. But actual operating experience has shown that in almost all space missions, the real danger comes from human and technical flaws, i.e. sending the wrong instructions to space probes, failure of transmitters and solar panels to unfurl correctly, etc. These are almost impossible to model by computer.
There is no question that, in deep space, there is not much sunlight. At the distance of Saturn, there is only 1% of the solar flux found on the planet earth (in watts/sq. meter). The debate revolves around whether solar/fuel cells can make up the 800 watts necessary to run the mission.
The FEIS on p. 2-56 claims that, if the Cassini is equipped with massive, bulky solar panels, the probe will be 130 pounds too heavy for lift-off. (The Titan IV can lift 13,743 pounds of payload to Saturn). However, the calculation is incomplete, since it does not consider some simple options:
Cassini is therefore a left-over from the old NASA philosophy of doing big space shots once every 10 years. Since space probes were so infrequent, this philosophy resulted in space craft that were overloaded with experiments, and hence the RTGs seemed a natural solution. But the new philosophy of NASA should generate small, frequent, and cheap probes to Saturn which are well within the capability of solar power.
But the difference with the Cassini mission is that we voluntarily put ourselves at risk when traveling. However, no one asked the American people if they wanted to put themselves in danger. NASA bureaucrats, not the American people, are making this decision.
Second, if we are in a car accident, only a handful at most will die. But no one told the American people that thousands may die if a plutonium accident takes place.
Similarly, the FEIS justifies the figure of 2,300 cancer deaths by stating that that figure is lost in the background cancer levels found world-wide. This is a strange argument. That same argument can be used to justify mass murder. Since thousands die violent deaths in the U.S., it makes no difference if a few hundred more die by a serial killer. They will be lost in the background noise.
Of course, we all want a healthy, vibrant space program to explore the universe. However, it should also be made safe. Since the American taxpayers are paying for it, they have a right to know the true risks, and should be informed of the debate concerning accident risks within the scientific community.
Unfortunately, the American people, being constantly told that the probability of an accident is on the order of one in a million or a one in a billion, will feel betrayed when a catastrophic accident does occur in space. Such a space tragedy could cause a backlash from the American people, who will correctly feel that they were lied to by NASA bureaucrats. This could be the end of the space program, which would be a disaster to science.
Furthermore, there is no mention of property damage in such an accident. The Three Mile Accident, for example, reputedly released just 13 curies of iodine (compared to 400,000 curies in the Cassini mission) yet it generated two billion dollars in law suits.
Even if no significant amounts of radiation are released in a plutonium accident, property values are expected to plummet. And if significant amounts of plutonium are released, then whole areas must be quarantined, earth dug up and placed in 55 gallon drums, houses hosed down with fire trucks, crops impounded, etc. That was one terrible lesson from Chernobyl. The loss to home owners and the agribusiness in the area around the Cape could amount to tens of billions of dollars.
Therefore, the mission of a critic is to save the space program from NASA bureaurcrats.
Unfortunately, NASA commits the worst mistake that a scientist can ever make: believing your own press release. A casual observer, reading the FEIS, may be deceived into thinking that a careful analysis has been done. But when actually reproducing the calculation, the observer will be shocked at how many guesses, hidden assumptions, and minimizations of risks there are in the FEIS.
A true scientist carefully writes down the error bars and the confidence level he or she places in their figures. A careful scientist does not do what NASA has done:
This borders on scientific dishonesty.
It is no accident, therefore, that the FEIS comes up with consistently low numbers for a maximum accident.
The simplest way to solve our problem is to use solar cells with fuel cells. This will require downsizing the space craft by at least 130 pounds. But this is also in tune with the new philosophy of faster, better, and cheaper. The Cassini mission, however, is a relic of the old thinking of slower, more expensive, less frequent.
A new program to explore the planets would have these probes downsized and launched much more frequently, using non-nuclear energy sources.
In the interim, this may cost more and cause some delays, but it may also have the lives of thousands, prevent law suits numbering in the tens of billions, and save the space program from NASA bureaurcrats.
He received his B.A. in physics from Harvard in 1968. He graduated summa cum laude (with highest honors), Phi Beta Kappa, and number one in his physics class.
He received his Ph.D. at the Radiation Laboratory at the Univ. of Calif. at Berkeley in 1972. He was a research associate at Princeton University in 1973, and has been a professor at CUNY for the past 25 years. He has been a visiting professor at Cal Tech, the Institute for Advanced Study at Princeton, and New York University.
He has published 9 books and 70 articles in the scientific literature (including Nuclear Physics, Physical Review, Physics Letters, Physical Review Letters).
He is a Fellow of the American Physical Society, and honor held by the top 10% of physicists in the U.S.
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