Thanks for your email. Our responses must have crossed in email-land last night...
Regarding your comments in your latest email:
However, the main plan for mission objectives covers the 11 years, but after those main objectives are accomplished, there's a variety of options, provided that the spacecraft is still functioning well after years of pummelling by Saturn's radiation belts. One option is to aerobrake it into orbit around Titan for ongoing study of that moon. I believe all this is covered on the JPL web page.
Of the 11 years, 7 of them are just getting to Saturn. It's actually a 4-year mission at the site. If Saturn's radiation belts can pummell Cassini into failure mode, that certainly seems worth studying too. In other words, that should be a reason to let the mission proceed longer just to see what the radiation pummelling can do, and how well they protected against it. The point is, once we get there, I think we should stay MUCH longer.
The real question is, why do you believe that the fins on the RTGs will help pull them apart? Let's see facts, instead of opinions. Facts in the form of solid modelling, finite element analysis, atmospheric density and the induced bending force vs. tensile strength of the particular alloy used in the fins and the casing, etc, etc.
I answered this extensively in my previous post to you from last night. I realize you might still feel that that answer is a cop-out -- I stated in part that to do a "proper" analysis I would need NASA's cooperation, which so far I have (of course) not received. Certainly, you also have not answered my charges. I have gone EXTENSIVELY into what I think will be the sequence of events. Do you think NASA has told me the "tensile strength of the particular alloy used"?
I have NASA's rough drawings and anyway (as I state in me previous email) NASA's already done this investigation and I challenge them to show us their proof. You can't possibly be calling those fins aerodynamic, are you? Not to mention that since at 43,000 mph Cassini will be the fastest manmade object ever [propelled past Earth in a flyby manuever], one has to wonder how much of the solid modeling that can be done is guesswork anyway, and 72 pounds of Pu-238 is too much to be guessing about. Many re-entry angles are very shallow, in fact, the most likely ones are the most shallow ones. The RTGs are going to incinerate at least partially in those cases -- even NASA admits this with their percentage of burn values. So NASA expects the RTGs can and will be breached. It's a pretty delicate question to be asking me to resolve the issue of just how much without full NASA cooperation. I think my claims are pretty clear and if NASA wanted to, they could present the data needed to prove their opinion.
Do you have a web page reference for this? [NASA "Final" EIS from June '95]
I don't have a web page for the EIS from NASA, but you can write or call them and ask for it...
Mark R. Dahl, Program Executive,
Cassini Mission & Payload Development Division
Office of Space Science, Code SD
Washington DC 20546-0001
Phone: (202) 358-1544
Thanks for taking the time to talk to me. I hope you're enjoying my previous correspondence.
Russell D. Hoffman
I'm the same. I guess the things we're concerned about just differ.
Instead I get a half-page letter sending me to a web site that is totally basic. I don't think an engineer at NASA even saw my documentation or my inquiries. Instead it appears that it was passed directly to someone in the PR department. Usually, my inquiries go the other way! I am quickly passed from the PR person to the engineer. I challenge NASA to show me the proof about the RTGs. Instead you ask me to start from scratch. Sir, I do not think that is fair.
You ask me to "crack open [my] thermodynamics textbook and do the math" but I don't think NASA has provided the data I would need, so it would do no good.
I agree with the dearth of technical information that's been provided about the specific details of the construction of the RTG. I too would like some engineering and materials information, and the web page just doesn't cut it. One person you might want to contact who I've talked to is Bev Cook at the Dept. of Energy, the agency in charge of procuring the RTGs. Her e-mail address is "email@example.com". She's very overworked, so it may take a while to get a response out of her, but she's overall fairly friendly.
I haven't pressed her for detailed specs, but she might be able to help you there or put you in touch with one of the engineers. Who knows, maybe through some convoluted bureaucratic web it's classified information, in case the Iranians wanted to build a plutonium generator. ;-)
Those ICBM's are pretty secret stuff. How do I know that the way they survive re-entry is not by melting off the outer few hundred pounds of whatever kind of special super-secret metal they are made of? If so, that would actually indicate that the RTG's could melt away too. But that's not as important as this point:
Good thing, because common sense would tell you that if they melted and disintegrated on their way in, it would be hard for the bomb to go off. ;-) But really, you seem to be reaching here. *If* there's some heretofore unknown material that ablates away from ICBMs, then Cassini has a problem. Kind of a longshot, I'd think, since the Russians have ICBMs too, and half a dozen other nations are working on develping them.
My understanding is that the temperatures an ICBM survives on re-entry are in the neighborhood of 14,000F, well above the 4442F and 4861F temperatures you talk about. The plutonium cores in the GPHS modules are at 1100C. The outermost part, the "outer shell of the RTG" is at 270C when heated by the plutonium dioxide within. When additionally heated and burned off by the heat of re-entry, the 1100C cores will soon be exposed, I fear. See page 3-5 of the Nuclear Safety Analyses for Cassini Mission Environmental Impact Statement Process (April 1997) and your email below for the source of the above numbers. For the "14,000F" number, I have a book published and compiled by the Editors of Air Force Magazine called Space Weapons. Copyright 1959. Old news, but I doubt the potential temperatures of ICBM's on re-entry has changed much. But that's not as important as the next item:
The Heuygens probe into Titan will reach a temperature of around 21,632F, about twice the surface temperature of the Sun, and will hit Titan's atmosphere at 13,725mph, per http://www.jpl.nasa.gov/cassini/Spacecraft/probe.html. If they can design a probe to withstand that kind of punishment using space-shuttle style tiles (well-proven existing technology) and silica fibers, why do you suppose that they can't do the same to the RTGs?
The ICBM you mention re-enters Earth's atmosphere at about 1/3rd the speed of Cassini during the flyby. Temperatures will be very significantly hotter for Cassini.
But the thing is, you don't know *how* much hotter, or for how long it'll be that temperature, since you haven't done the math. I haven't either, but I'm not the one with the doom-and-apocolypse web page. If the bulk of the atmosphere is 50 miles thick, a Cassini travelling at 45,040mph would take 0.00111 hours, or about four seconds, to pass through it. I doubt four seconds is enough time for the heat impulse to pass through the insulating material.
The exact properties of the RTGs are impossible to determine from the available drawings, although I find it hard to believe that you are actually asking me to compare the aerodynamic nose cone of an ICBM to the vaned contraptions that surround the RTGs.
Again, see if you can get Bev Cook to send you more details.
When the outside's hotter than the inside (as will be the case if a re-entry occurs) the vanes will do basically the opposite of what they do when the temperature gradient's the other way around, won't they? Won't they permit heat to enter, having been designed to permit heat to escape when the temperature gradient's is the other way around? Not to mention, I expect them to be ripped and burned and melted off, leaving gaping holes for heat to enter--to enter to a core that's already at 1100C. As vanes they will channel and eddy the heat so that again, gaping holes can form. Not like a nose cone at all which is designed specifically to spread the heat out evenly along the surface.
Whether they're burned off depends on how the aerodynamic friction affects them during the four second blast through the earth's atmosphere.
Even with all that knowledge, the actual calculations would require hundreds of thousands or even millions of dollars and hundreds of hours (or more) on super-computers. It would produce real data. Data NASA in theory already has but HAS NOT PRODUCED. Why am I being asked to duplicate this effort?
I think you're mistaken in saying that they haven't produced this data, and that you're overstating the difficulty of the calculations. Remember, they built the SR-71 Blackbird in the 60's.
So far, NASA has merely summarized it as having passed their tests... Actually, they didn't even do that. My reading of page 2-19 of the "FINAL EIS ON THE CASSINI MISSION" (June, 1995) is that it failed explosion testing, fire testing, and fragmentation testing. Conditions in all three areas can easily exceed the tested points of failure.
I'd be interesting in seeing a copy of that. Thanks for the address, I'll request a copy.
If each of them were answerable, then perhaps it would be time to open the books. I don't believe those RTGs will survive a re-entry, and in any event, there is no way NASA (or you) should be asking me to do the study. NASA has already done the study, has computer-generated videos, etc. All they have given us is a summary claim of what the data showed them, in their minds. Have you asked for NASA for this information so that you can explain it to me? I would not mind. I will apologize when and if (and where) I am shown to be wrong.
Maybe it's time to twist their arm a bit to get them to release the technical details, rather than vague drawings on the web site. I'd be happy to assist in the arm-twisting.
Let me first state how absurd I find this, to be arguing that the RTG's are designed to fail, with people who claim that they are not, who also are the same people who claim that such failure would be the safest way to design the things, the most humane, the best way in the interests of the United States' financial balance book for sure -- do you deny any of these things?
If you had it to do, would you design the RTGs to incinerate or would you not?
First of all, the possibility that they would re-enter is so absurdly remote, requiring such an improbable sequence of failures, that it's hard to believe that anyone is arguing about it at all. However, I think that it would be prudent to prevent the release of plutonium, just as it would be prudent to prevent the release of chlorine gas, gasoline, or any number of other poisonous substances in common use today. Although plutonium is not as dangerous as most people make it out to be, you wouldn't want to grind it up and snort it anymore than you'd want to snort arsenic or lead.
On the other hand, if it were the case that the airborne concentration of plutonium from atomic bomb testing is already, say, 10 ppb, and the Cassini probe's complete incineration would add another 0.1 ppb in the re-entry vicinity, I'd probably opt to design it to incinerate. See what I mean?
Because if they partially incinerate on the way back to earth, then truly, that can have the horrendous IMMEDIATE AND OBVIOUS health effects many would call a "WORST CASE SCENARIO". A streaming, partial incineration will leave a plume no one can like. And by the way, NASA officially predicts just such a partial incineration if a re-entry occurs, usually anywhere from 1% to 30% of the RTGs, but virtually never 0% or 100%. A partial incineration is particularly scary from the point of view of financial liability and immediate effect.
30% meaning that graphite heat and impact shells? What percentage has to be incinerated away before exposing the plutonium ceramic? There's multiple layers of protection, and 30% of the RTG does not mean 30% of the plutonium ceramic. Most of the mass of the RTGs is the plutonium dioxide, since it's about twice as heavy as lead.
If as NASA contends, low level radiation is really such a minor problem, then a complete upper atmosphere incineration on the other hand would mean virtually no one gets hurt. And certainly the financial burdens of a failure will disappear if the Pu 238 incinerates in the upper atmosphere. So why not build them that way on purpose?
Because it's wrong. Humanity STOPPED atmospheric testing of nuclear weapons precisely because it was unhealthy. A Cassini re-entry incineration would be a catastrophe. So comparing 72 pounds of Pu 238 dioxide, which is 280 times more radioactive when inhaled, to the "11,000 pounds" of mostly far lower grade plutonium, I see as absurd. Just because mankind has poisoned the planet terribly does not mean that mankind should continue to do so. Besides, this one accident, if it's a complete incineration, would put the "radioactive equivalent" of 20,000 pounds of a less radioactive grade of plutonium into the atmosphere at once! Nearly double the effect of your "11,000 pounds" from atmospheric testing. How many millions died and will die from the atmospheric testing?
What lower-grade plutonium? Where do you get your "radioactive equivalent" notions? Pu238 is a low-level alpha emitter, which is not the case with some other isotopes, as well as the menagerie of other fallout from atmospheric tests. My father was instructed by the US government to not eat snow during a few winters when he was growing up, in fact. Plutonium was not the only radiation source generated by bomb tests.
For example, look how long it took to even figure out the cigarettes were dangerous! A few tobacco executives still do not believe it, but even they are coming around... You ask me to prove a far more subtle killer. Scientists have shown time and again, a multitude of mechanisms by which the killing and other destruction can work. (It's not just about killing. It's also about breast cancer, infant and fetal illnesses and deformities, and genetic damage, not just to humans but to other living things as well.)
If it's so subtle, maybe it's not causative. Humans have been living in a sea of radiation for millions upon millions of years.
But the scientist's theorems and explanations of the mechanisms are not enough for you, you want some kind of statistical proof. Does NASA want such proof as well? Then they should go and get it: Read Dr. Sternglass's books, and Dr. Gofman's, and Dr. Gould's and Dr. Caldicott's and Dr. Morgan's and on and on and on. As far as I can see, there is scientific literature and scientists to back up my point of view.
Now I know where you're coming from. I should have guessed. Sternglass, Gould, and Caldicott are idealogical axe-grinders and paranoid conspiracy theorists who wish to see the end of everything having anything to do with radioactivity, probably even sunlight. They blur the distinction between weapons and nuclear electricity, and bend facts and statistics to suit their own shrill idealogical dogma. They hardly qualify as objective sources, and it may be charitable to call them "kooks." Sternglass and Gould are used by Greenpiece to give their pseudo-scientific tripe a veneer of legitimacy.
Please read the following links carefully:
There have been countless concerted conscious efforts (and now, with information recently declassified, conspicuous efforts at that) over the years to thwart such research, starting with the Army keeping double books about real and reported soldier exposures during bomb testing. No. Before that. Starting with estimates of acute radiation damage PRIOR to Hiroshima and Nagasaki. ("NONE." The official estimate prior to dropping the bombs was that everyone who might otherwise die of acute radiation sickness would be dead by being hit with a brick or something first.)
Call Oliver Stone, eh? Maybe it's just because nobody truly knew how dangerous the material they were dealing with actually was, rather than a vast cover-up. Do you believe that OJ Simpson was innocent?
I disagree, of course, with the "six ways from Sunday" portion, but that I have gone into repeatedly at the web site. I personally do not trust NASA's estimate of the unlikelihood of an accident being anywhere near one in one million.
Okay, in order for the Earth flyby phase to fail, since the launch phase is not a real threat to the integrity of the RTG units as demonstrated by Apollo, the following would have to happen:
Next, the flight computer would have to recieve a command on its properly working communications systems to adjust the trajectory to perform the Earth flyby, and fail at *that very instant* in just such a way that the delicate trajectory adjustment yeild a trajectory a miniscule percent too shallow that would impact Earth, a target a few thousand miles wide, eight months and millions of miles later, instead of going to wide or too shallow, and fail in just such a way, in all the redundant systems, that the trajectory could not be further adjusted after that specific failure.
If it fails before December 1998, the trajectory can't be adjusted, and so the probe misses Earth by tens of thousands of miles, or the failure is detected by diagnostic systems and adjustments are made in the probe's software or course-adjustment instructions to accomodate it. If it fails after the trajectory adjustment, the probe flys by Earth as planned, and continues on to Saturn, and flies right past it at tens of thousands of miles per hour since it would be unable to do its braking maneuver.
However, your point about comparing Cassini's 'threat' to the daily damage of coal-burning power plants to me just shows you have a very limited argument at best, or even one which dooms you and your side to philosophical failure. The very act of trying to use coal as the comparison is a poor choice, I think. It's the pot calling the kettle black.
Nuclear advocates have always used coal-fired power plants as their whipping boy. Always, a properly operating nuclear plant is shown to be clean compared to a properly operating coal plant. But one has to recognize that a major accident at a coal plant is a rather minor event in the scheme of things, while a Chernobyl-type accident is not. And, the as-yet-unexperienced process of decommissioning the plant and then storing the waste for a quarter million years has also not been included in the comparison.
A coal plant is an ongoing nuclear accident, day in and day out. See the following URL:
The point is that radiation released by dispersal of a mere 72 pounds of plutonium, granting the highly unlikely possibility that it would be dispersed, pales in comparison to the daily tonnage of uranium and thorium radiation that's released by coal plants. If you're truly concerned about radiation in the environment, go chain yourself to the gate of a coal power plant.
And about 70 plants have reached the end of their operational life and have been decommissioned. As I recall, the first commercial nuclear plant in the US has been returned to a grass field. And nuclear materials, including plutonium and other fission products, have been stored in the Earth's crust for hundreds of millions, if not billions of years. And by recyling nuclear waste, the danger zone of storage shrinks to about 500 years. See the various articles at:
Part of the heat of the Earth's mantle comes from radioactive decay. Decomissioning is a well-understood and practiced process, and the only obstacles to safe nuclear waste disposal are political, fueled by the dubious propoganda of Sternglass, Caldicott, and their ilk.
I do not find value in arguing such a comparison. I do not believe one anti-nuker, or one environmentalist, supports coal OR nuclear power.
Compare it with, say, the ridiculously low energy density of solar panels, of which the manufacture generates toxic chemical wastes? I think that by overblowing the damaging potential of the Cassini probe, you're coming to some unwarranted conclusions about the relative risks and values of this probe.
Energy drives the world, it always will, and there are good reasons to risk damage to the environment to produce energy to supply the needs of an existing or anticipated populace. Not that coal OR nuclear can justify themselves, they cannot, but they can more so I think than Cassini can. As a species, we must choose our energy sources wisely and we have not done that. Coal pollutes too much. Nuclear pollutes too much. And oil? Oil has far too many uses to simply burn it! Renewables are the only reasonable choice. Don't compare to coal.
Nuclear *pollutes* too much? Except for Chernobyl, every last fuel pellet ever used in commercial nuclear power is right where it was warehoused. You call that pollution?
or on other missions. The potential science benefit does not justify the health risk.
Only if you inflate the heath risk to monumental proportions.
And so that one little plutonium particle goes 'round and 'round again... The average plutonium dioxide molecule will last for more than 87 years... After 500 years, out of 72 pounds of Pu 238, there will still be more than a pound of "the deadliest substance known to man" on Earth. Even after a thousand years, there will be enough to kill off whole countries, "when properly distributed". Randomly throughout the environment and the food chain is one "proper" method of distribution.
Calling it "the deadliest substance known to man" is nothing but more of Gould, Sternglass, & Caldicott's ridiculous emotional hyperbole. Try ingesting a gram of pure caffiene and a gram of finely ground plutonium, and see what kills you first.
My understanding is that if Chernobyl released 72 pounds of Pu-238 into the atmosphere (which it could not actually do, but just for arguments's sake--) it would have been a significant portion of the overall health hazard. Emotional fear-mongering? Absolutely. I'm scared. Re-examine your understanding. Far more deadly, as has been demonstrated, was the radioactive iodine that was released.
The exact nature of the underlying statement is that if you were to divide a pound of plutonium into some 5.8 billion particles, and then placed one of those particles on a person's lung tissue, that person will surely develop lung cancer, without question. It's that deadly. So the only thing "saving us" from such a death is the fact that many of the particles will NOT be inhaled if a flyby re-entry accident occurs.
Lung cancer does not have 100% mortality, and I understand the logical basis of that statement. However, it's like saying that a single male ejaculation could impregnate the entire female population of the US. Technically true, but still a ridiculous practical assertion.
evaporation... Will NOT become part of the food chain (it looks like iron to most biological systems, which they need, but it isn't)... There are 5.8 billion people on this earth. That is far too many to risk giving them each a chance at ingesting or inhaling a plutonium particle.
So instead they risk dying of starvation in North Korea, or of malnutrition in Northern Africa, or of bodily trauma from a car crash in the US, and a mission that would return a vast wealth of information about the universe we live in is scuttled on the vague, improbable off chance that some of these people *might* develop lung cancer in a certain specific failure scenario sometime in the next 50 years. Right.
Thank you, again, for your email. Although I cannot entirely say I have enjoyed the exercise of responding, I can say that I believe it has done me good and I appreciate your efforts and your challenges, and, after my #1 hope that I have actually swayed you, my #2 hope is that at least you do not feel I have wasted your time. I will be interested to read any response, either of which of us might of course freely publish. I will presumably include any additional response you offer in anything I might publish...
It's tiring to debate, I agree, but it's been said that one teaches best what one most needs to learn. I've learned a lot from our exchange. Let's team up and get NASA to release blueprints and technical specifications.
If you would like to include your affiliation or a brief c.v. of some sort, I would be curious and I'm sure others would appreciate it as well.
I'm a computer systems administrator by trade. I'm 26 years old, and I attended the University of Michigan Engineering school, and later transferred into the Computer Science department since I'd been programming computers since fifth grade. I was born and raised in Ann Arbor, Michigan, and I've always had a keen interest in science and spaceflight, since I learned to read at a young age and space books were quite engaging.
Thanks for your email. This note is just to let you know I've received AND READ your response and appreciate it tremendously.
I will work on an answer, of course. Since you've also sent me to several web sites, and since the DEIS deadline is May 27th, it might unfortunately be two weeks before I can entirely respond in the manner fitting the care and attention to detail your response just received demands and deserves. (Please don't show that sentence to an English major.)
My initial response, of course, is that while many of your arguments are good, when you remind people that lung cancer is not always fatal, you are standing on loose soil. No one I know with less than two full-sized lungs feels all THAT far from death. And no one without good modern medical care ($$$) IS that far from death. Talk about specious arguments! I don't think lung transplants are a good solution to the problem of plutonium's hazards.
Anyway, yes, I confess that now, I AM enjoying corresponding with you (it is no longer just a chore!) It's hard, but it's worth the effort. I think perhaps both sides will benefit in the end from our digging so deeply into each other's beliefs...
However, some of your arguments do seem to simply bounce back some of your original statements. For us both to enjoy this exercise, we will need to not let that happen. (But I bet I do it too!) I'll be specific later, I promise.
Regarding the incineration of the RTGs, you talk about the probe taking "four seconds" to fall through the atmosphere -- that's if it comes in at 90 degrees, just about the least likely scenario of all. Gimme a break! That's obvious obfuscation. Overall, I find your answers to the RTG question actually quite weak, but I'll get into that in my later response. I will probably contact Beverly Cook soon as you suggest and I hope you do as well...
As to Oliver Stone and O.J., please don't get me started... Those were both unfair remarks which I believe you should retract and hope you will refrain from in the future.
I watched at least 98% of the O.J. trial (I was, at the time, doing a lot of computer animation (drawing) so it was pretty easy to leave it on T.V. and listen) which is probably a lot more than any of the jurors watched. I understood exactly what [the defense] was doing... Lying with statistics. Or did you miss that? The defense would have you (and the jurors) believe things like: that a match that is likely to be wrong only 7 in 100 times, figured with a separate 7 in 100 match and another 7 in 100 match is 21 in 100 chances of being wrong... In fact it is 21 in 1,000,000.
I consider O.J. to be one of the meanest men in America, who would help to divide this nation on color lines to save his own tail. And guilty. He's no Rodney King.
O.J. got off in the criminal case because the jury could not understand statistics... Maybe it's relevant, after all! (Oh, yes -- and the glove fit just fine. Ron Goldman, a hero, was able to pull one off PRECISELY because they had shrunk (leather gloves WILL do that) and O.J. didn't have them on completely. All he wanted to do was cover his fingerprints and palm prints anyway. That, they were big enough to do. They were probably a little tight, having sat around and shrank, and he just had them lying around, until he "needed" them.)
So there's my take on O.J., at least, briefly. Are you glad you brought it up?
Oliver Stone's films? I haven't watched one in years, not since NBK (which I also didn't see.) But as to conspiracies and obfuscations and such -- well, have you had any luck getting accurate technical data on the RTGs from NASA? I bet you won't. They already know I want it...
Again, thank you for taking the time to engage my mind. I am happy to be "teaming up with you" to discover any truths we can find. If in the end we still agree to disagree (which of course I'm sure we both suspect will happen) I'm sure I will be improved by the exchange and I hope it benefits you as well. As to what happens to our respective "movements" by such corroboration, well, I think time tells the truth, and we are moving forward to blow away some of the smoke and break some of the mirrors. I wish you good luck in our continued war of letters...
Russell D. Hoffman