Lets see, you said: " The CANDU heavy water system is genuinely fail-safe. The coolant doubles as the moderator. That means if you loose one you loose the other and the reaction is halted.
And later you said: "In control theory we would simply call what you are refering to as decay heat a time lag. There are time lags in pretty much every process control loop and being able to both control them and understand their effect is critical. Decay heat might be an immutable physical process but the implications are certainly not."
Were you trying to imply that the CANDU is a fail-safe reactor except that it requires a means of decay heat removal just like any nuclear reactor? Not exactly the way that I'd define fail-safe. I fail to see what how the heavy water prevents core damage (as required in the definition of fail-safe) in this regard.
Note, decay heat removal is only one aspect that I was pointing out that makes the CANDU reactor *not* fail-safe. There are many others, but just one contradiction is required to disprove any argument. I thought it was clear that this was the way my argument was progressing. I hope this clears up any confusion.
Let me summarize my arguments: 1. The CANDU reactor is not fail-safe because there exists a contradiction to the definition of being fail-safe: lack of decay heat removal will cause core damage. 2. It is my *opinion* that the nuclear power industry has learned its lesson and changed its culture to minimize the probability of a future accident, and therefore deserves a second chance. 3. I argued that personal insults were irrelevant in an argument. Of course, I failed to mention that my first statement was fairly arrogant and while not in my opinion a personal insult, was fairly belittling. Oops, well worse has happened on Slashdot in the past and worse will happen in the future, but nonetheless, I apologize.
You said: "The point I was making is that it is people rather than technologies that are unsafe. Your inane repetition of 'decay heat', an irrelevant snippet of data that you appear to have read in a magazine article would seem to reinforce my point."
Decay heat is not an irrelavant snippet. Decay heat is a key concept in reactor safeguards. I know you probably won't trust my words for it (and there's nothing wrong with that), so I'll give a reference. If you want to see more, go to the NRC's reading room, or google for "decay heat and reactor safeguards". It was only decay heat that physically caused the TMI-2 nuclear accident. Everything else just contributed to not being able to remove it.
Ok, let me now address your point. People are safe if well trained. It is possible to construct a nuclear plant in a way that no people operate it. The reason that most future designs have operators is that people, if well trained, are flexible enough to handle unforseen events. While many people feel that the nuclear industry is the same as it was 25 years ago, that is completely wrong. The NRC used to be a good 'ol boys organization. It covered up the Brown's Ferry nuclear accident in 1975 for example. Much like the rest of the US changed after 9/11, the nuclear industry drastically changed after March 28, 1979. How can I prove this in words? I can't. You have to go talk to the regulators and the operators to understand. We haven't abandoned the airline industry even though some incredibly horrific accidents have occured over the past couple of years. I say we shouldn't abandon the nuclear industry because there is not another industry in the world that cares more about safety.
Am I an apologist? Hardly. I've just always wondered from a young age on how the US could abandon such an amazing technology for others that are so inferior. How could we abandon a technology that could dramatically increase the quality of life of the entire world? How could we chose technologies that cause global warming and spread vast amounts of pollution rather than nuclear power? To me its as silly as saying that we want to abandon the microprocessor! There are pros and cons with every technology. If the pros outweigh the cons, then the technology is worthwhile, and I think the pros do by a dramatic margin (even though the cons are significant).
By the way, many of your comments are aimed at attacking my credibility (like saying that I read about decay heat in a magazine). I have intentionally withheld credentials because it only confuses the issues (i.e. persons are more likely to agree with an authority figure or a person with significant credentials than someone who doesn't) and doesn't strengthen the facts. The facts are all that matter. But since this argument is over I will tell you that I am a reactor operator, have operated multiple nuclear reactors shutdown and critical, and my prime job is to ensure reactor safeguards. Reactor safeguards are 90% of my job. When it comes to reactor safety, I know what I am talking about (and I train others on it).
You said: "Yeah, yeah, I have a doctorate from Oxford Univ. Nuclear Physics Lab. Where is yours from? I have also worked as a control engineer.
From your tone you sound like an ex-nuclear power employee who just has to spend their time writing self-justifications on the Internet. Sorry, you have no more credibility with me than the rentacops who used to do airport security here in Boston before 9/11. You guys screwed up real bad, you lost the public trust, that is because you deserved to."
Wow. Being that you have a doctorate from Oxford I would have assumed that you would realize that personal attacks during arguments don't win the arguments. They only distract people from the points. Only the truth will win an argument, and if it comes from a trashman or Neils Bohr himself, it doesn't matter.
As a person who has a doctorate in nuclear physics how could you miss that the CANDU reactor, just like every other nuclear reactor is going to produce decay heat? TMI's core damage all occured after the reactor was scrammed, so how would getting rid of the moderator have helped?
Are you trying to say that the CANDU reactor can't have a temperature induced runaway reaction? Big deal, it's not the first reactor with a negative temperature coefficient of reactivity. And any water moderated reactor will have a negative void coefficient, so I don't see how CANDU is that special. CANDU is a neat reactor, don't get me wrong, but its hardly failsafe. It has a pressure vessel: brittle fracture and the game is over. If it ejects a control rod and goes prompt critical, the fact that it can dump its moderator isn't going to save it. It'll still blow up because heat transfer to make gas bubbles in the moderator will take too long.
Ok, since noone has told you, here's whats special about heavy water: its nucleus doesn't have excited states so it doesn't resonantly absorb neutrons. Since H-1 will, deuterium will be a better moderator. This is pretty much required in low enriched plants like CANDU. Any plant with significant enrichment will use light water or graphite as a moderator because it is far cheaper. Just putting it in your plant doesn't work as a magic potion to prevent meltdowns.
You also said: "You might be correct in claiming that it would be possible to design a safe PWR. I don't care, if anything that looks like a PWR is built it will be run and staffed by the same discredited establishment that gave us Three Mile Island and Chernobyl."
TMI? That was 25 years ago, all those people have retired. Chernobyl? You understand that the lobbying group for nuclear power was not the same in Soviet Russia as it was in Capatalist USA, right?
You said: " The balls expand and move the fuel away from each other. The reactor cools and the balls contract and heat up again but if there is no coolent then they expand and reach an equilibrum. No coolent is needed as long as you don't want to use the power"
You are aware of the processes of creep and swelling right? A pebble bed reactor is not designed for the pebbles to swell. It is designed for them to be strong enough to prevent and fission product gas release under any planned accident condition. This makes PBR's very safe. But if there is a loss of coolant casuality, the reactor fuel is useless afterwards due to creep and swell.
You assert that the balls will expand and contract. This isn't their purpose and if they did they would breach the pressure boundary.
Many articles on the internet assert that the pebble bed reactor will be able to cool itself down prior to melting of fuel. How is this done? The MH-GTR, for example, uses natural circulation air cooling. Other reactors suggest ideas vaguely similar to ECCS (where has something similar failed before--oh yeah TMI). They also assert that since the PBR's have a larger surface to volume ratio, they will be able to cool down easier. Of course what they don't mention is that a PBR is going to use a gaseous coolant like CO2 or He, and for that coolant to be useful it must be at a higher temperature than conventional PWR's are run at. What's the big deal about this? Well if the pressure vessel ruptures and exposes the PBR to the environment (many PBR's are not planning containment structures because they believe they are so safe) and temperature rises high enough, both hydrogen gas will develop due to airborne H20 and the graphite will burn if a pebble has defects. Lets not forget Windscale and Chernobyl on the effects of what a graphite fire in a reactor can do. If this occured it would be catastrophic. And before you say defects are unlikely, a rupture of a pressure vessel causing a loss of coolant casuality would be a violent event, as well as a hydrogen fire.
One thing I do think about PBR's is this: they are extremely safe reactors if they have both natural circ. air cooling and a containment structure pressurized with N2 gas.
You said: "The truth is that the better designs of forty years ago could have made safe nuclear power. The CANDU heavy water system is genuinely fail-safe. The coolant doubles as the moderator. That means if you loose one you loose the other and the reaction is halted."
This shows the naivety of some people who are not nuclear scientists or reactor operators regrarding nuclear power. Let me give you a quick lesson.
A reactor can be in several operational states: shutdown, starting up, at power, or shutting down. During startup the reactor will in a state known as supercritical. This means that for every neutron that causes fission in a uranium atom, more than 1 will cause fission in others. This allows reactor power to increase. Once desired power is attained the reactor will again be made critical (where there is a 1 to 1 ratio). When you want to shut down the reactor you make it subcritical. All of this can be controlled by control rods (among other things).
Chernobyl blew up because they had an accident that made the reactor very very supercritical. Power increased until the core exploded, shutting it down.
Now here's the shocker: TMI-2 was shut down when it partially melted down. Control rods were fully inserted. This means that the fission reactons for the most part had stopped (though they would still be occuring at trillionths the rate that they occured while critical). So fission was not generating any heat.
So what partially melted and reorganized the core? Decay heat. When fission occurs fission fragments are the result. These fragments fall away from the line of stability, hence rapidly beta- decay. Obviously this is governed by thier half-lives and the resulting fission products from any fission are pretty much random (though there are statistical proportions). This means some products will have short half-lives, others long, etc. And most products will probably go through many beta and perhaps alpha decays before reaching a stable point. This means that decay heat will be greatest right after shutdown, but will decrease over time.
This is why TMI-2 partially melted down. The reactor was critical, it was shut down, but the decay heat wasn't removed, so the reactor melted. It could happen to CANDU just as easily if they lost the ability to remove decay heat (which is why loss of coolant or loss of pressure control casualities in nuclear plants are big casualities).
You said: "Today there are vastly better designs, like the pebble bed reactor that MIT and others have been looking at."
There is no design that magics away decay heat. Sorry.
"The incoming also creates a small amount of 'heavy water' in the oceans. The creation process I've been told is forever as long as the sun shines, and has long ago, as in billions of years, reached an equalibrium point."
Wrong. In the Big Bang about 90% of all matter formed hydrogen-1, about 10% formed helium-4, and about 0.15% formed hydrogen-2 (deuterium). This value has been confirmed in theory and observations of very old stars. In any given star, it will preferably use deuterium vice hydrogen-2 as a fuel due to the lower energy requirement. This leads to a deficient deuterium spectra when older stars are observed. Once the first stars supernova'd (known as population I stars), the remnants of the star (which only had elements up to roughly iron since that is all that fusion can produce exothermically, higher is endothermic) was ejected at incredible speeds (up to 0.3 c in some cases). This ejecta sometimes collided with interstellar gasses with such force that it transmuted the elements up to uranium rarely. Later this gas formed a population II star, and then a population III star, in our case the solar system. There is no deuterium production in the earth, and it is at the ~0.15% level naturally since large stars that supernova rarely eject burnt fuel, just their outer layers. But the deuterium in the universe is constantly decreasing. Neutron absorption reactions in nuclear reactors can occasionally produce it, but that is the only way that I know if its production.
"The one item I can't drag up from memory is the byproducts of its fusion"
D + D -> He-3 + neutron + lotsa energy (~50% chance) D + D -> T (H-3) + proton + lotsa energy (~50% chance) D + D -> He-4 + energy (rarely, less than 1%)
"Maybe its time some of the people playing with this gave us a progress report?"
ITER is expected to break even in a couple of years.
You said: "I'm curious -- why? Laws the prevent public disclosure always bother me, so I'd like to know."
In the Atomic Energy Act of 1954, Title 1 Chapter 12 (warning--big pdf) Control of Information, certain data such reactor designs, nuclear weapons designs, etc. are designated as Restricted Data. While you might think much of this wouldn't apply to a nuclear reactor you have to remember that civil nuclear reactors produce a small amount of plutonium and therefore also fall under any of the weapons restrictions in that chapter. Certain exemptions exist as listed in section 144 but they are difficult to get (requires Presidential approval). This basically makes everything about the technology of a nuclear power plant classified--hence radiation levels will also fall under this guidance. The NRC issues accident reports that declassify much data in the case of accidents or incidents because they feel it is good for public review. Of course they have section 144 approval to do so.
You said: "sorry, 2R/yr is the administrative limit. That is, if you get above 2R/yr the radiation safety officer has to work with you to alter your work pratices to decrease your anual dose. At the same time, it is true that you can have 5 R years."
Administrative limits are different from legal limits. For example, I have an administrative limit a fraction of the legal limit and a local control limit that is a fraction of that (though extensions that allow up to my administrative limit are allowed). If certain work permits and waivers are signed, I can go up to the full 3 rem/qtr or 5 rem/yr (but they are difficult to get). In casualities I can go up even higher depending upon whether equipment or lives are at stake.
The purpose of these limits is to follow the ALARA (as low as reasonably attainable) campaign. If I was to work in a radiation area of 5 mrem/hr and had a local limit remaining of perhaps 10 mrem (hypothetically--obviously this is very low to be considering doing any high radiation work), I should probably leave the area to check my dose at about an hour (having used up about 5 mrem) or when my self-indicating dosimeter reads 5 mrem. If the job is so complex that it requires more hours, additional shielding and cycling other personnel through would prevent any one person from exceeding their local control limit. If I had exceeded my 10 mrem of local control limit left, I would be blocked from additional radiation work until I could get an extension to my local limit.
You said: " You do realize that Three Mile Island was the single lamest nuclear "disaster" in history, right? Standing with my hand on the reactor, I would get the same amount of radiation from said reactor in one second as I get from the rest of the environment in one second. Compare to smoking, which (on average) quadrouples your radiation dose."
No. This is not true.
You could not do that for a small plant, and TMI-2 (anniversary is on the 28th btw), was a big plant (~3GW thermal). The Atomic Energy Act pretty much makes it impossible for me to give you any real numbers for the radiation levels outside the reactor pressure vessel shutdown or critical (though they may be published somewhere), I can tell you that it is not background. Civil nuclear plants typically start up, operate for 18 months at full power, shutdown to refuel and perform maintenance, and then repeat. Since TMI-2 was in the operating stage when its accident occured, there was a significant amount of fission products in the reactor core at the time of the accident. If you are standing next to the reactor core you do not have the full amount of radiation shielding that the general public has, so the radiation dose will be much higher. Also considering that some fission products escaped from the fuel and circulated through the coolant (of which some was released into the containment structure due to the pressure relief which set of the radiation alarms during the casuality), there will be alot of radiation in the general area not coming from the reactor vessel (which again will be significantly higher than background).
You said: " Yeah, potasium iodide, they are saying it keeps radiation out of your system for X amount of dollars, like this: http://www.nukepills.com/"
Potasium iodide doesn't 'get the radiation out of your system'. Please understand that radiation is the transmittal of energy through EM-wave or various particles (betas, alphas, neutrons). Radiation may pass through your body (perhaps doing harm) but it won't stay. Contamination is some radioactive substance that emits radiation governed by its half-life. If you drive by the a site that has alot of contamination you will get some radiation dose. As long as you don't ingest any of the contamination you will not get a dose when you leave.
The purpose of potassium iodide is to minimize the dose to your thyroid. One characteristic radionuclide from nuclear reactors and nuclear weapons is radioactive iodine (typically I-129 and I-131). Your thyroid can absorb a certain amount of iodine before it become saturated. If you use iodine pills, your thyroid will absorb a non-radioactive nuclide. This means that when you ingest radioactive iodine following a casuality, little of it will be absorbed into the thyroid, reducing the dose to the thyroid. Please note though, that the thyroid isn't the only organ that can kill you if it gets exposed to a significant amount of radiation. Its just the only one that there is an effective preventive measure for. If you are in the area of radioactive fallout, it will increase your chances of survival slightly, but it won't make you a radiation-resistant superman.
You said: " Wait a second! she is showing readings of less than 1 mR/hour. Power plant workers can work in 1 mR/hour for the entire year and not exceed NRC's strict 2 R/year limit. In otherwords, this is nothing. Parent poster doesn't know what he is talking about."
The NRC limit (see 10 C.F.R.) is 3 rem per quarter, and 5 rem per year. A rem is a weighted roetgen (R). The weighting factors are used because while a roetgen measures the energy deposited, a rem measures the physical damage (exposure versus dose). An example of a weighting factor is a gamma will have a factor of 1, while a fast neutron may have a factor of 20. So a 1 mR/hr exposure rate will give you 1 mrem/hr for gammas, and 20 mrem/hr for fast neutrons.
You said: "For example, the last paragraph about the kinetic energy of neutrons and whether you want fast or slow neutrons for a bomb or reactor is complete bullshit. A given nucleus has an optimum range of energy for neutron absorption, whether that nucleus is in a bomb or a reactor."
The microscopic cross section for absorption varies depending upon energy. But a nuclear bomb will not work with slow neutrons. The reason is very simple: neutrons created from fission are fast neutrons, so in order for them to become slow neutrons they must slow down by hitting a moderating substance. Slowing down takes time, hence, there is time for the bomb to transfer thermal energy and expand. This will destroy the critical geometry and make the bomb fissible vice boom. This is exactly the reason that discouraged early atomic bomb pioneers.
You said: "Further, breeding and/or refining nuclear fuel is not an exact process -- you're going to get quanties of other elements and isotopes according to the amount of fission, neutron capture and impurities in the original material -- the analysis will look at things like strontium, gadolinium, other fission byproducts and their isotopic ratios."
When you seperate plutonium from a uranium breeder or uranium from a thorium breeder reactor, it is a chemical process. One substance precipitates out of the pot and the other doesn't. You can get extremely precise results doing this. Please reread my post if you don't understand the difficulties in determining fission products.
You said: " I don't know if they can id specific weapons, but can't they already identify the reactor of origin for the nuclear materials used?"
The nuclides currently of interest in making a nuclear weapon are U-233, U-235 and Pu-239. U-233 can be made from neutron absorption of Th-232 (and subsequent double B- decay), U-235 occurs about 0.7% as natural U, and Pu-239 can be made by neutron absorption of 238 (and susequent double B- decay). The reason these nuclides are of interest is that if one of them absorbs a neutron, due to the quirks of physics, it now has enough energy for the nucleus to break apart without requiring any kinetic energy from the neutron. This is not true for most other common radionuclides.
So, if the bomb used U-233, it came from a thorium breeder reactor, U-235 came from some type of seperation plant (which requires advanced materials--tends to indicate a fully industrialized country), and Pu-239 would come from a uranium breeder reactor. Since U-233 and Pu-239 would be chemically seperated from the rest of their respective reactors' fuel, you aren't really going to get any good design information about their breeder reactors that created the U-233 or Pu-239. A U-235 bomb is the only one that you can really tell based on environmental impurities or irregularities in the U-234, U-235, and U-238 concentrations where the U was mined.
So how can you tell if the bomb was created with U-233, U-235, or Pu-239? Well, there is a statistical distribution of fission products created during fission of any fisionable nuclide. This distribution will vary from nuclide to nuclide. Each of these radionuclides will have a half-life (and branching ratios) as it decays to various radionuclides. If you know when the bomb detonated, you should be able to determine its type by the radionuclides left over at the point of detonation, right? Not exactly, for 2 reasons. First, some radionuclides are gaseous (once cooled to ambient temperature) prior to a decay and solid afterwards or vice versa, so environmental factors have to be taken into account (or just measuring radionuclides that will be solid at all points in their decay chains). Second, and most important, a nuclear bomb has lots of neutrons flying around. Depending upon the size of the bomb, the tamper, they type (atomic bomb, thermonuclear bomb, etc.), --basically the design--the concentration of neutrons in time for the bomb will vary. Whats important about this is not that all the fissionable material will be used up--thats the point of the bomb--but that the fission fragments will also be exposed to a neutron flux and transmuted.
What does this mean? Based on the fallout you can determine what the fissionable material is and the design of the bomb within your mathematical models.
Finally one point that I think needs pointing out: U-233, U-235, and Pu-239 are selected because they require no kinetic energy of a neutron hitting them to cause fission. Thats useful for a nuclear reactor where you want to control the fission rate, but in a nuclear bomb you have to use neutrons that are travelling very very fast; therefore, there will be a significant kinetic energy imparted upon an absorbing nucleus that one of these fast neutrons hits. Meaning: other nuclides (other than U-233, U-235, and Pu-239) could potentially be used in an advanced (but probably very large) nuclear bomb.
You said: "The cleanup after a fail safe event would be difficult and expensive because of its design, but the design also meant that a meltdown was just about impossible."
You realize that TMI-2 was shutdown when the fuel actually started melting, right? Even when you shutdown a nuclear reactor there will be some decay heat that decreases based on the different half-lives of fission products. If you are unable to remove the decay heat the reactor complex *will* fail, like TMI-2 on 28 March 1979.
You said: " How does the moon have military value? I'm no expert, but doesn't it take like six days to go up there? Not to mention the costs. From a military perspective, wouldn't a base in orbit around earth be more practical?"
Its like a man on a hill versus a man downslope. On the moon you have the ability to see every point on the Earth in time, but the 'dark side' (of course its not always dark) of the moon is never seen from Earth. It would be possible to stockpile weapons on the 'dark side' and then move them to a suitable base on the other side to attack the Earth. Additionally, if you are trying to defend the dark side, there is a very narrow cone-ring that you'd have to survey. But on the Moon you could easily attack any point on the Earth with a gigantic area that they'd have to defend against. And, of course, I haven't even started to talk about gravitational advantages.
You said: "The PC adventure market is mostly dead. No reason to go into reasons why, but who in their right mind would fund a game in a dead market? Sometimes a game comes along that can surprise everybody, but not that often."
Funny thing. You could have substituted adventure for RPG six years ago. Now you can't swing a dead cat around without hitting someone who is talking about their RPG characters or the RPG that they just bought or are playing, etc. The release of Baldur's Gate and its sequels, in my opinion, completely revived the market (though some might argue it was Everquest). The point I'm trying to make is that while the adventure market may be dead for now, if the right game comes around and it inspires people, the adventure market could come back in a flurry. Some company might get rich off of it (look at Bioware), but they won't get rich if they cancel the games.
You said: " Has it occurred to anyone that the reason the X Prize hasn't been won yet is becuase of the size of the prize? I mean, if I'm going to invest (and have others invest in ME) I think there needs to be a reasonable expectation of a return on that investment. 5, 10, 20 mil just doesn't seem to be enough to me."
This is only part of the reason. I think the bigger part is that the 2 week time between launch and subsequent relaunch is too short. Not even the space shuttle could qualify to win the X-prize with that restrictive of a time-table. I think the team that will win the X-prize will not win it with innovative launch technologies (it will probably be very similar to the 'booster pack' that the Space Shuttle uses) but with a rapidly replacable heat shield (one that won't take months to repair unlike the Space Shuttle's tiles).
You said: "Sure it can--you must not be aware of the advances in adaptive optics. There's a reason that the next-generation space telescope isn't designed for visible-light observations--advances in ground-based technology have overtaken the advantages of a space-based platform."
If a photon is absorbed by the atmosphere, it doesn't matter how large your telescope is or how advanced the adaptive optics are, you still won't see that photon. Space based telescopes always will be able to see that photon, that is why they are continuing to be developed.
You said: " The suits are actually nowhere near sterile. . . . taking enough of those chemicals to sterilize the suit everytime you go out could get both very heavy AND very expensive."
It is probably not that important to worry about not contaminating the Martian environment because it is believed that the unshielded UV radiation has createdsuperoxides in the oxygen bearing Martian minerals. This would be lethal to any organisms, and this is the main reason it is believed there is no life on the surface of Mars. It could be argued that organisms could be picked up in the wind and carried far across the planet, but those organisms would be killed due to superoxides in the iron-heavy airborne Martian dust (its really too small to call sand). The main area where we would have to be careful is while digging, and then only in that particular local area. I would reckon to guess that a couple of hours in the Martian environment (being pelted with superoxide laden dust) would be as effective at killing terrestrial organisms as the sterilizing chemicals that could be brought onboard.
You said: "On Mars, with the presence of gravity, this bulky, massive suit would just be plain useless. Instead, a more sleek body suit might be prefered. Something like a scuba suit here on earth, ribbed with heating and cooling and bio-sensors, and instead of zipping or snapping or locking, make it skintight and put on simply by crawling in. Put on a sterile helmet and air supply."
There are a couple of reasons I don't think this would work. (1) Since Mars has no method of shielding UV radiation, the chemistry in the soils has become very reactive, so that it is believed that contact with the soil would cause chemical burns. A 'breathable' suit would allow injury. (2) Martian air pressure is less than 1% of what it is on Earth. What this means is that any exposed water will rapidly evaporate into the air if it doesn't have a chance to freeze first (and then it will probably sublimate). This may be an undesired condition for your skin. (3) I think you underestimated the coldness of Mars. Air temperatures typically range from -20 to -90 C. The surface rocks are typically warmer in the day and colder at night, and rocks under the surface are typicically colder than surface rocks. This means that your suit must be able to able to heat across at least a 140 C difference (and you can't say the low specific heat of the low pressure air will act as a great insulator because you must also take into account that the astronaut may want to sit down). This will take some thick tubing and insulation.
You said: "Just to play a devil's advocate: what business do we have throwing our limited resources to other planets when we have so many problems already down here?"
I can answer that with a simple quote from Larry Niven: The dinosaurs went extinct because they didn't have a space program.
Its a silly quote but its very true. The probability of humanity being destroyed or anhillating itself will drop dramatically once we have a self-sustaining colony on an extraterrestial object. Its like insurance for humanity in a way.
Mars Rover Sample Return (MRSR) has been in development since the 1980's. Initially the Pathfinder program, which eventually spawned the Pathfinder mission, was designed to demonstrate the technologies for the MRSR. MRSR is classic vaporware. It has gone through several complete revisions including one that had a 1100 pound rover and a cost of $10 - $13 billion. MRSR if it ever launches will probably take place after the Mars Science Laboratory mission (if it ever launches). While it sounds like a cool idea to bring back rocks to give intense scientific analysis, I think it is more practical on science earned per dollar cost to invest other technologies such as a rover or lander that can drill far beneath the surface for samples, multiple advance seismic detectors, or rovers with ground penetrating radar. Many of these mission could be done for the same cost and a fraction of the failure probability of MRSR.
You said: "I think that the problems with Spirit and Opportunity might show we need to take it at a cautios pace before sending folks out there. Its been pointed out that these rovers took 10's of G's just to get there and land, and thats gotta be rough. Most pilots and astronauts to this point have seen about 10G's worst case, and for very short periods of time."
Your comparison is not valid because you are assuming that the same design requirements apply to a manned mission and an unmanned mission, and that the same implementation will be used. You realize that the first shots we took at the moon were unmanned machines with a camera that rammed the surface of the moon. You could make the argument that humans couldn't take the 1000s of G's of force imparted when colliding with the surface of the Moon. Of course, this is missing the point that a manned spacecraft that will land on the Moon (or Mars) will be of different design than a robotic mission.
You also said "One of the largest concerns about space travel is radiation exposure."
There are only 3 things you can do about radiation: time/distance/shielding. You can minimize the time of the exposure by flying a fast rocket. Since the primary source of radiation in the Solar System is the Sun, you can't really get far enough away to make it safe for the distance aspect. Finally you can beef up your shielding. It should be noted that if your rocket is long and faces away from the Sun with the persons in the cone of the rocket, you will have a significant amount of shielding just from the rocket materials (at least from the Sun). This would require orientating the rocket to face away from the Sun after all of your thrust for a particular stage of the mission has been imparted.
There is no current plans for a nuclear propelled Mars spacecraft. There is a plan for the Jupiter Icy Moons Orbiter (JIMO). This spacecraft will use a nuclear reactor coupled with an ion engine. The nuclear reactor assembly makes electricity and the ion engine uses it to propel the spacecraft with the scarce propellant that it brings with the spacecraft. Note that this is very much unlike the direct nuclear propulsion idea of using a propellant in the nuclear reactor as coolant and venting it to space after it is heated by the reactor. This second idea will produce alot of thrust for a very short time (as propellant is rapidly depleted) compared to the ion engine producing little thrust but for a very long time.
Since neither idea requires that the nuclear reactor ever start up prior to enterring space, there will be very little radioactive fission products in the reactor core. What this means is that the only really radioactive item in the core at launch (the stuff that can go into the atmosphere if the launch fails) is uranium. Since uranium has a long half life (7e8 years for U-235, and greater than 1e9 years for U-238), the cooresponding radioactivity will be that much less.
Note that JIMO will be the second US nuclear reactor placed in space (the first in 1965).
You said: "We don't know what happened before the Big Bang, and we will almost certainly never know. It's quite possible the question makes no sense, as time itself may be an artifact of the Big Bang"
Correct. Time and space was *defined* by the Big Bang. Just like the x- and y- dimensions don't make sense in 3-D space without the z-dimension, space-time makes no sense without the time dimension. To a beam of light, there is no difference between a light-second of distance and a second of time.
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Lets see, you said: " The CANDU heavy water system is genuinely fail-safe. The coolant doubles as the moderator. That means if you loose one you loose the other and the reaction is halted.
And later you said: "In control theory we would simply call what you are refering to as decay heat a time lag. There are time lags in pretty much every process control loop and being able to both control them and understand their effect is critical. Decay heat might be an immutable physical process but the implications are certainly not."
Were you trying to imply that the CANDU is a fail-safe reactor except that it requires a means of decay heat removal just like any nuclear reactor? Not exactly the way that I'd define fail-safe. I fail to see what how the heavy water prevents core damage (as required in the definition of fail-safe) in this regard.
Note, decay heat removal is only one aspect that I was pointing out that makes the CANDU reactor *not* fail-safe. There are many others, but just one contradiction is required to disprove any argument. I thought it was clear that this was the way my argument was progressing. I hope this clears up any confusion.
Let me summarize my arguments:
1. The CANDU reactor is not fail-safe because there exists a contradiction to the definition of being fail-safe: lack of decay heat removal will cause core damage.
2. It is my *opinion* that the nuclear power industry has learned its lesson and changed its culture to minimize the probability of a future accident, and therefore deserves a second chance.
3. I argued that personal insults were irrelevant in an argument. Of course, I failed to mention that my first statement was fairly arrogant and while not in my opinion a personal insult, was fairly belittling. Oops, well worse has happened on Slashdot in the past and worse will happen in the future, but nonetheless, I apologize.
You said: "The point I was making is that it is people rather than technologies that are unsafe. Your inane repetition of 'decay heat', an irrelevant snippet of data that you appear to have read in a magazine article would seem to reinforce my point."
Decay heat is not an irrelavant snippet. Decay heat is a key concept in reactor safeguards. I know you probably won't trust my words for it (and there's nothing wrong with that), so I'll give a reference. If you want to see more, go to the NRC's reading room, or google for "decay heat and reactor safeguards". It was only decay heat that physically caused the TMI-2 nuclear accident. Everything else just contributed to not being able to remove it.
Ok, let me now address your point. People are safe if well trained. It is possible to construct a nuclear plant in a way that no people operate it. The reason that most future designs have operators is that people, if well trained, are flexible enough to handle unforseen events. While many people feel that the nuclear industry is the same as it was 25 years ago, that is completely wrong. The NRC used to be a good 'ol boys organization. It covered up the Brown's Ferry nuclear accident in 1975 for example. Much like the rest of the US changed after 9/11, the nuclear industry drastically changed after March 28, 1979. How can I prove this in words? I can't. You have to go talk to the regulators and the operators to understand. We haven't abandoned the airline industry even though some incredibly horrific accidents have occured over the past couple of years. I say we shouldn't abandon the nuclear industry because there is not another industry in the world that cares more about safety.
Am I an apologist? Hardly. I've just always wondered from a young age on how the US could abandon such an amazing technology for others that are so inferior. How could we abandon a technology that could dramatically increase the quality of life of the entire world? How could we chose technologies that cause global warming and spread vast amounts of pollution rather than nuclear power? To me its as silly as saying that we want to abandon the microprocessor! There are pros and cons with every technology. If the pros outweigh the cons, then the technology is worthwhile, and I think the pros do by a dramatic margin (even though the cons are significant).
By the way, many of your comments are aimed at attacking my credibility (like saying that I read about decay heat in a magazine). I have intentionally withheld credentials because it only confuses the issues (i.e. persons are more likely to agree with an authority figure or a person with significant credentials than someone who doesn't) and doesn't strengthen the facts. The facts are all that matter. But since this argument is over I will tell you that I am a reactor operator, have operated multiple nuclear reactors shutdown and critical, and my prime job is to ensure reactor safeguards. Reactor safeguards are 90% of my job. When it comes to reactor safety, I know what I am talking about (and I train others on it).
You said: "Yeah, yeah, I have a doctorate from Oxford Univ. Nuclear Physics Lab. Where is yours from? I have also worked as a control engineer.
From your tone you sound like an ex-nuclear power employee who just has to spend their time writing self-justifications on the Internet. Sorry, you have no more credibility with me than the rentacops who used to do airport security here in Boston before 9/11. You guys screwed up real bad, you lost the public trust, that is because you deserved to."
Wow. Being that you have a doctorate from Oxford I would have assumed that you would realize that personal attacks during arguments don't win the arguments. They only distract people from the points. Only the truth will win an argument, and if it comes from a trashman or Neils Bohr himself, it doesn't matter.
As a person who has a doctorate in nuclear physics how could you miss that the CANDU reactor, just like every other nuclear reactor is going to produce decay heat? TMI's core damage all occured after the reactor was scrammed, so how would getting rid of the moderator have helped?
Are you trying to say that the CANDU reactor can't have a temperature induced runaway reaction? Big deal, it's not the first reactor with a negative temperature coefficient of reactivity. And any water moderated reactor will have a negative void coefficient, so I don't see how CANDU is that special. CANDU is a neat reactor, don't get me wrong, but its hardly failsafe. It has a pressure vessel: brittle fracture and the game is over. If it ejects a control rod and goes prompt critical, the fact that it can dump its moderator isn't going to save it. It'll still blow up because heat transfer to make gas bubbles in the moderator will take too long.
Ok, since noone has told you, here's whats special about heavy water: its nucleus doesn't have excited states so it doesn't resonantly absorb neutrons. Since H-1 will, deuterium will be a better moderator. This is pretty much required in low enriched plants like CANDU. Any plant with significant enrichment will use light water or graphite as a moderator because it is far cheaper. Just putting it in your plant doesn't work as a magic potion to prevent meltdowns.
You also said: "You might be correct in claiming that it would be possible to design a safe PWR. I don't care, if anything that looks like a PWR is built it will be run and staffed by the same discredited establishment that gave us Three Mile Island and Chernobyl."
TMI? That was 25 years ago, all those people have retired. Chernobyl? You understand that the lobbying group for nuclear power was not the same in Soviet Russia as it was in Capatalist USA, right?
You said: " The balls expand and move the fuel away from each other. The reactor cools and the balls contract and heat up again but if there is no coolent then they expand and reach an equilibrum. No coolent is needed as long as you don't want to use the power"
You are aware of the processes of creep and swelling right? A pebble bed reactor is not designed for the pebbles to swell. It is designed for them to be strong enough to prevent and fission product gas release under any planned accident condition. This makes PBR's very safe. But if there is a loss of coolant casuality, the reactor fuel is useless afterwards due to creep and swell.
You assert that the balls will expand and contract. This isn't their purpose and if they did they would breach the pressure boundary.
Many articles on the internet assert that the pebble bed reactor will be able to cool itself down prior to melting of fuel. How is this done? The MH-GTR, for example, uses natural circulation air cooling. Other reactors suggest ideas vaguely similar to ECCS (where has something similar failed before--oh yeah TMI). They also assert that since the PBR's have a larger surface to volume ratio, they will be able to cool down easier. Of course what they don't mention is that a PBR is going to use a gaseous coolant like CO2 or He, and for that coolant to be useful it must be at a higher temperature than conventional PWR's are run at. What's the big deal about this? Well if the pressure vessel ruptures and exposes the PBR to the environment (many PBR's are not planning containment structures because they believe they are so safe) and temperature rises high enough, both hydrogen gas will develop due to airborne H20 and the graphite will burn if a pebble has defects. Lets not forget Windscale and Chernobyl on the effects of what a graphite fire in a reactor can do. If this occured it would be catastrophic. And before you say defects are unlikely, a rupture of a pressure vessel causing a loss of coolant casuality would be a violent event, as well as a hydrogen fire.
One thing I do think about PBR's is this: they are extremely safe reactors if they have both natural circ. air cooling and a containment structure pressurized with N2 gas.
You said: "The truth is that the better designs of forty years ago could have made safe nuclear power. The CANDU heavy water system is genuinely fail-safe. The coolant doubles as the moderator. That means if you loose one you loose the other and the reaction is halted."
This shows the naivety of some people who are not nuclear scientists or reactor operators regrarding nuclear power. Let me give you a quick lesson.
A reactor can be in several operational states: shutdown, starting up, at power, or shutting down. During startup the reactor will in a state known as supercritical. This means that for every neutron that causes fission in a uranium atom, more than 1 will cause fission in others. This allows reactor power to increase. Once desired power is attained the reactor will again be made critical (where there is a 1 to 1 ratio). When you want to shut down the reactor you make it subcritical. All of this can be controlled by control rods (among other things).
Chernobyl blew up because they had an accident that made the reactor very very supercritical. Power increased until the core exploded, shutting it down.
Now here's the shocker: TMI-2 was shut down when it partially melted down. Control rods were fully inserted. This means that the fission reactons for the most part had stopped (though they would still be occuring at trillionths the rate that they occured while critical). So fission was not generating any heat.
So what partially melted and reorganized the core? Decay heat. When fission occurs fission fragments are the result. These fragments fall away from the line of stability, hence rapidly beta- decay. Obviously this is governed by thier half-lives and the resulting fission products from any fission are pretty much random (though there are statistical proportions). This means some products will have short half-lives, others long, etc. And most products will probably go through many beta and perhaps alpha decays before reaching a stable point. This means that decay heat will be greatest right after shutdown, but will decrease over time.
This is why TMI-2 partially melted down. The reactor was critical, it was shut down, but the decay heat wasn't removed, so the reactor melted. It could happen to CANDU just as easily if they lost the ability to remove decay heat (which is why loss of coolant or loss of pressure control casualities in nuclear plants are big casualities).
You said: "Today there are vastly better designs, like the pebble bed reactor that MIT and others have been looking at."
There is no design that magics away decay heat. Sorry.
"The incoming also creates a small amount of 'heavy water' in the oceans. The creation process I've been told is forever as long as the sun shines, and has long ago, as in billions of years, reached an equalibrium point."
Wrong. In the Big Bang about 90% of all matter formed hydrogen-1, about 10% formed helium-4, and about 0.15% formed hydrogen-2 (deuterium). This value has been confirmed in theory and observations of very old stars. In any given star, it will preferably use deuterium vice hydrogen-2 as a fuel due to the lower energy requirement. This leads to a deficient deuterium spectra when older stars are observed. Once the first stars supernova'd (known as population I stars), the remnants of the star (which only had elements up to roughly iron since that is all that fusion can produce exothermically, higher is endothermic) was ejected at incredible speeds (up to 0.3 c in some cases). This ejecta sometimes collided with interstellar gasses with such force that it transmuted the elements up to uranium rarely. Later this gas formed a population II star, and then a population III star, in our case the solar system. There is no deuterium production in the earth, and it is at the ~0.15% level naturally since large stars that supernova rarely eject burnt fuel, just their outer layers. But the deuterium in the universe is constantly decreasing. Neutron absorption reactions in nuclear reactors can occasionally produce it, but that is the only way that I know if its production.
"The one item I can't drag up from memory is the byproducts of its fusion"
D + D -> He-3 + neutron + lotsa energy (~50% chance)
D + D -> T (H-3) + proton + lotsa energy (~50% chance)
D + D -> He-4 + energy (rarely, less than 1%)
"Maybe its time some of the people playing with this gave us a progress report?"
ITER is expected to break even in a couple of years.
You said: "I'm curious -- why?
Laws the prevent public disclosure always bother me, so I'd like to know."
In the Atomic Energy Act of 1954, Title 1 Chapter 12 (warning--big pdf) Control of Information, certain data such reactor designs, nuclear weapons designs, etc. are designated as Restricted Data. While you might think much of this wouldn't apply to a nuclear reactor you have to remember that civil nuclear reactors produce a small amount of plutonium and therefore also fall under any of the weapons restrictions in that chapter. Certain exemptions exist as listed in section 144 but they are difficult to get (requires Presidential approval). This basically makes everything about the technology of a nuclear power plant classified--hence radiation levels will also fall under this guidance. The NRC issues accident reports that declassify much data in the case of accidents or incidents because they feel it is good for public review. Of course they have section 144 approval to do so.
You said: "sorry, 2R/yr is the administrative limit. That is, if you get above 2R/yr the radiation safety officer has to work with you to alter your work pratices to decrease your anual dose. At the same time, it is true that you can have 5 R years."
Administrative limits are different from legal limits. For example, I have an administrative limit a fraction of the legal limit and a local control limit that is a fraction of that (though extensions that allow up to my administrative limit are allowed). If certain work permits and waivers are signed, I can go up to the full 3 rem/qtr or 5 rem/yr (but they are difficult to get). In casualities I can go up even higher depending upon whether equipment or lives are at stake.
The purpose of these limits is to follow the ALARA (as low as reasonably attainable) campaign. If I was to work in a radiation area of 5 mrem/hr and had a local limit remaining of perhaps 10 mrem (hypothetically--obviously this is very low to be considering doing any high radiation work), I should probably leave the area to check my dose at about an hour (having used up about 5 mrem) or when my self-indicating dosimeter reads 5 mrem. If the job is so complex that it requires more hours, additional shielding and cycling other personnel through would prevent any one person from exceeding their local control limit. If I had exceeded my 10 mrem of local control limit left, I would be blocked from additional radiation work until I could get an extension to my local limit.
You said: " You do realize that Three Mile Island was the single lamest nuclear "disaster" in history, right? Standing with my hand on the reactor, I would get the same amount of radiation from said reactor in one second as I get from the rest of the environment in one second. Compare to smoking, which (on average) quadrouples your radiation dose."
No. This is not true.
You could not do that for a small plant, and TMI-2 (anniversary is on the 28th btw), was a big plant (~3GW thermal). The Atomic Energy Act pretty much makes it impossible for me to give you any real numbers for the radiation levels outside the reactor pressure vessel shutdown or critical (though they may be published somewhere), I can tell you that it is not background. Civil nuclear plants typically start up, operate for 18 months at full power, shutdown to refuel and perform maintenance, and then repeat. Since TMI-2 was in the operating stage when its accident occured, there was a significant amount of fission products in the reactor core at the time of the accident. If you are standing next to the reactor core you do not have the full amount of radiation shielding that the general public has, so the radiation dose will be much higher. Also considering that some fission products escaped from the fuel and circulated through the coolant (of which some was released into the containment structure due to the pressure relief which set of the radiation alarms during the casuality), there will be alot of radiation in the general area not coming from the reactor vessel (which again will be significantly higher than background).
You said: " Yeah, potasium iodide, they are saying it keeps radiation out of your system for X amount of dollars, like this: http://www.nukepills.com/"
Potasium iodide doesn't 'get the radiation out of your system'. Please understand that radiation is the transmittal of energy through EM-wave or various particles (betas, alphas, neutrons). Radiation may pass through your body (perhaps doing harm) but it won't stay. Contamination is some radioactive substance that emits radiation governed by its half-life. If you drive by the a site that has alot of contamination you will get some radiation dose. As long as you don't ingest any of the contamination you will not get a dose when you leave.
The purpose of potassium iodide is to minimize the dose to your thyroid. One characteristic radionuclide from nuclear reactors and nuclear weapons is radioactive iodine (typically I-129 and I-131). Your thyroid can absorb a certain amount of iodine before it become saturated. If you use iodine pills, your thyroid will absorb a non-radioactive nuclide. This means that when you ingest radioactive iodine following a casuality, little of it will be absorbed into the thyroid, reducing the dose to the thyroid. Please note though, that the thyroid isn't the only organ that can kill you if it gets exposed to a significant amount of radiation. Its just the only one that there is an effective preventive measure for. If you are in the area of radioactive fallout, it will increase your chances of survival slightly, but it won't make you a radiation-resistant superman.
You said: " Wait a second! she is showing readings of less than 1 mR/hour. Power plant workers can work in 1 mR/hour for the entire year and not exceed NRC's strict 2 R/year limit. In otherwords, this is nothing. Parent poster doesn't know what he is talking about."
The NRC limit (see 10 C.F.R.) is 3 rem per quarter, and 5 rem per year. A rem is a weighted roetgen (R). The weighting factors are used because while a roetgen measures the energy deposited, a rem measures the physical damage (exposure versus dose). An example of a weighting factor is a gamma will have a factor of 1, while a fast neutron may have a factor of 20. So a 1 mR/hr exposure rate will give you 1 mrem/hr for gammas, and 20 mrem/hr for fast neutrons.
You said: "For example, the last paragraph about the kinetic energy of neutrons and whether you want fast or slow neutrons for a bomb or reactor is complete bullshit. A given nucleus has an optimum range of energy for neutron absorption, whether that nucleus is in a bomb or a reactor."
The microscopic cross section for absorption varies depending upon energy. But a nuclear bomb will not work with slow neutrons. The reason is very simple: neutrons created from fission are fast neutrons, so in order for them to become slow neutrons they must slow down by hitting a moderating substance. Slowing down takes time, hence, there is time for the bomb to transfer thermal energy and expand. This will destroy the critical geometry and make the bomb fissible vice boom. This is exactly the reason that discouraged early atomic bomb pioneers.
You said: "Further, breeding and/or refining nuclear fuel is not an exact process -- you're going to get quanties of other elements and isotopes according to the amount of fission, neutron capture and impurities in the original material -- the analysis will look at things like strontium, gadolinium, other fission byproducts and their isotopic ratios."
When you seperate plutonium from a uranium breeder or uranium from a thorium breeder reactor, it is a chemical process. One substance precipitates out of the pot and the other doesn't. You can get extremely precise results doing this. Please reread my post if you don't understand the difficulties in determining fission products.
You said: " I don't know if they can id specific weapons, but can't they already identify the reactor of origin for the nuclear materials used?"
The nuclides currently of interest in making a nuclear weapon are U-233, U-235 and Pu-239. U-233 can be made from neutron absorption of Th-232 (and subsequent double B- decay), U-235 occurs about 0.7% as natural U, and Pu-239 can be made by neutron absorption of 238 (and susequent double B- decay). The reason these nuclides are of interest is that if one of them absorbs a neutron, due to the quirks of physics, it now has enough energy for the nucleus to break apart without requiring any kinetic energy from the neutron. This is not true for most other common radionuclides.
So, if the bomb used U-233, it came from a thorium breeder reactor, U-235 came from some type of seperation plant (which requires advanced materials--tends to indicate a fully industrialized country), and Pu-239 would come from a uranium breeder reactor. Since U-233 and Pu-239 would be chemically seperated from the rest of their respective reactors' fuel, you aren't really going to get any good design information about their breeder reactors that created the U-233 or Pu-239. A U-235 bomb is the only one that you can really tell based on environmental impurities or irregularities in the U-234, U-235, and U-238 concentrations where the U was mined.
So how can you tell if the bomb was created with U-233, U-235, or Pu-239? Well, there is a statistical distribution of fission products created during fission of any fisionable nuclide. This distribution will vary from nuclide to nuclide. Each of these radionuclides will have a half-life (and branching ratios) as it decays to various radionuclides. If you know when the bomb detonated, you should be able to determine its type by the radionuclides left over at the point of detonation, right? Not exactly, for 2 reasons. First, some radionuclides are gaseous (once cooled to ambient temperature) prior to a decay and solid afterwards or vice versa, so environmental factors have to be taken into account (or just measuring radionuclides that will be solid at all points in their decay chains). Second, and most important, a nuclear bomb has lots of neutrons flying around. Depending upon the size of the bomb, the tamper, they type (atomic bomb, thermonuclear bomb, etc.), --basically the design--the concentration of neutrons in time for the bomb will vary. Whats important about this is not that all the fissionable material will be used up--thats the point of the bomb--but that the fission fragments will also be exposed to a neutron flux and transmuted.
What does this mean? Based on the fallout you can determine what the fissionable material is and the design of the bomb within your mathematical models.
Finally one point that I think needs pointing out: U-233, U-235, and Pu-239 are selected because they require no kinetic energy of a neutron hitting them to cause fission. Thats useful for a nuclear reactor where you want to control the fission rate, but in a nuclear bomb you have to use neutrons that are travelling very very fast; therefore, there will be a significant kinetic energy imparted upon an absorbing nucleus that one of these fast neutrons hits. Meaning: other nuclides (other than U-233, U-235, and Pu-239) could potentially be used in an advanced (but probably very large) nuclear bomb.
You said: "The cleanup after a fail safe event would be difficult and expensive because of its design, but the design also meant that a meltdown was just about impossible."
You realize that TMI-2 was shutdown when the fuel actually started melting, right? Even when you shutdown a nuclear reactor there will be some decay heat that decreases based on the different half-lives of fission products. If you are unable to remove the decay heat the reactor complex *will* fail, like TMI-2 on 28 March 1979.
You said: " How does the moon have military value? I'm no expert, but doesn't it take like six days to go up there? Not to mention the costs. From a military perspective, wouldn't a base in orbit around earth be more practical?"
Its like a man on a hill versus a man downslope. On the moon you have the ability to see every point on the Earth in time, but the 'dark side' (of course its not always dark) of the moon is never seen from Earth. It would be possible to stockpile weapons on the 'dark side' and then move them to a suitable base on the other side to attack the Earth. Additionally, if you are trying to defend the dark side, there is a very narrow cone-ring that you'd have to survey. But on the Moon you could easily attack any point on the Earth with a gigantic area that they'd have to defend against. And, of course, I haven't even started to talk about gravitational advantages.
You said: "The PC adventure market is mostly dead. No reason to go into reasons why, but who in their right mind would fund a game in a dead market? Sometimes a game comes along that can surprise everybody, but not that often."
Funny thing. You could have substituted adventure for RPG six years ago. Now you can't swing a dead cat around without hitting someone who is talking about their RPG characters or the RPG that they just bought or are playing, etc. The release of Baldur's Gate and its sequels, in my opinion, completely revived the market (though some might argue it was Everquest). The point I'm trying to make is that while the adventure market may be dead for now, if the right game comes around and it inspires people, the adventure market could come back in a flurry. Some company might get rich off of it (look at Bioware), but they won't get rich if they cancel the games.
You said: " Has it occurred to anyone that the reason the X Prize hasn't been won yet is becuase of the size of the prize? I mean, if I'm going to invest (and have others invest in ME) I think there needs to be a reasonable expectation of a return on that investment. 5, 10, 20 mil just doesn't seem to be enough to me."
This is only part of the reason. I think the bigger part is that the 2 week time between launch and subsequent relaunch is too short. Not even the space shuttle could qualify to win the X-prize with that restrictive of a time-table. I think the team that will win the X-prize will not win it with innovative launch technologies (it will probably be very similar to the 'booster pack' that the Space Shuttle uses) but with a rapidly replacable heat shield (one that won't take months to repair unlike the Space Shuttle's tiles).
You said: "Sure it can--you must not be aware of the advances in adaptive optics. There's a reason that the next-generation space telescope isn't designed for visible-light observations--advances in ground-based technology have overtaken the advantages of a space-based platform."
If a photon is absorbed by the atmosphere, it doesn't matter how large your telescope is or how advanced the adaptive optics are, you still won't see that photon. Space based telescopes always will be able to see that photon, that is why they are continuing to be developed.
You said: " The suits are actually nowhere near sterile. . . . taking enough of those chemicals to sterilize the suit everytime you go out could get both very heavy AND very expensive."
It is probably not that important to worry about not contaminating the Martian environment because it is believed that the unshielded UV radiation has created superoxides in the oxygen bearing Martian minerals. This would be lethal to any organisms, and this is the main reason it is believed there is no life on the surface of Mars. It could be argued that organisms could be picked up in the wind and carried far across the planet, but those organisms would be killed due to superoxides in the iron-heavy airborne Martian dust (its really too small to call sand). The main area where we would have to be careful is while digging, and then only in that particular local area. I would reckon to guess that a couple of hours in the Martian environment (being pelted with superoxide laden dust) would be as effective at killing terrestrial organisms as the sterilizing chemicals that could be brought onboard.
You said: "On Mars, with the presence of gravity, this bulky, massive suit would just be plain useless. Instead, a more sleek body suit might be prefered. Something like a scuba suit here on earth, ribbed with heating and cooling and bio-sensors, and instead of zipping or snapping or locking, make it skintight and put on simply by crawling in. Put on a sterile helmet and air supply."
There are a couple of reasons I don't think this would work.
(1) Since Mars has no method of shielding UV radiation, the chemistry in the soils has become very reactive, so that it is believed that contact with the soil would cause chemical burns. A 'breathable' suit would allow injury.
(2) Martian air pressure is less than 1% of what it is on Earth. What this means is that any exposed water will rapidly evaporate into the air if it doesn't have a chance to freeze first (and then it will probably sublimate). This may be an undesired condition for your skin.
(3) I think you underestimated the coldness of Mars. Air temperatures typically range from -20 to -90 C. The surface rocks are typically warmer in the day and colder at night, and rocks under the surface are typicically colder than surface rocks. This means that your suit must be able to able to heat across at least a 140 C difference (and you can't say the low specific heat of the low pressure air will act as a great insulator because you must also take into account that the astronaut may want to sit down). This will take some thick tubing and insulation.
You said: "Just to play a devil's advocate: what business do we have throwing our limited resources to other planets when we have so many problems already down here?"
I can answer that with a simple quote from Larry Niven: The dinosaurs went extinct because they didn't have a space program.
Its a silly quote but its very true. The probability of humanity being destroyed or anhillating itself will drop dramatically once we have a self-sustaining colony on an extraterrestial object. Its like insurance for humanity in a way.
Mars Rover Sample Return (MRSR) has been in development since the 1980's. Initially the Pathfinder program, which eventually spawned the Pathfinder mission, was designed to demonstrate the technologies for the MRSR. MRSR is classic vaporware. It has gone through several complete revisions including one that had a 1100 pound rover and a cost of $10 - $13 billion. MRSR if it ever launches will probably take place after the Mars Science Laboratory mission (if it ever launches). While it sounds like a cool idea to bring back rocks to give intense scientific analysis, I think it is more practical on science earned per dollar cost to invest other technologies such as a rover or lander that can drill far beneath the surface for samples, multiple advance seismic detectors, or rovers with ground penetrating radar. Many of these mission could be done for the same cost and a fraction of the failure probability of MRSR.
You said: "I think that the problems with Spirit and Opportunity might show we need to take it at a cautios pace before sending folks out there. Its been pointed out that these rovers took 10's of G's just to get there and land, and thats gotta be rough. Most pilots and astronauts to this point have seen about 10G's worst case, and for very short periods of time."
Your comparison is not valid because you are assuming that the same design requirements apply to a manned mission and an unmanned mission, and that the same implementation will be used. You realize that the first shots we took at the moon were unmanned machines with a camera that rammed the surface of the moon. You could make the argument that humans couldn't take the 1000s of G's of force imparted when colliding with the surface of the Moon. Of course, this is missing the point that a manned spacecraft that will land on the Moon (or Mars) will be of different design than a robotic mission.
You also said "One of the largest concerns about space travel is radiation exposure."
There are only 3 things you can do about radiation: time/distance/shielding. You can minimize the time of the exposure by flying a fast rocket. Since the primary source of radiation in the Solar System is the Sun, you can't really get far enough away to make it safe for the distance aspect. Finally you can beef up your shielding. It should be noted that if your rocket is long and faces away from the Sun with the persons in the cone of the rocket, you will have a significant amount of shielding just from the rocket materials (at least from the Sun). This would require orientating the rocket to face away from the Sun after all of your thrust for a particular stage of the mission has been imparted.
There is no current plans for a nuclear propelled Mars spacecraft. There is a plan for the Jupiter Icy Moons Orbiter (JIMO). This spacecraft will use a nuclear reactor coupled with an ion engine. The nuclear reactor assembly makes electricity and the ion engine uses it to propel the spacecraft with the scarce propellant that it brings with the spacecraft. Note that this is very much unlike the direct nuclear propulsion idea of using a propellant in the nuclear reactor as coolant and venting it to space after it is heated by the reactor. This second idea will produce alot of thrust for a very short time (as propellant is rapidly depleted) compared to the ion engine producing little thrust but for a very long time.
Since neither idea requires that the nuclear reactor ever start up prior to enterring space, there will be very little radioactive fission products in the reactor core. What this means is that the only really radioactive item in the core at launch (the stuff that can go into the atmosphere if the launch fails) is uranium. Since uranium has a long half life (7e8 years for U-235, and greater than 1e9 years for U-238), the cooresponding radioactivity will be that much less.
Note that JIMO will be the second US nuclear reactor placed in space (the first in 1965).
You said: "We don't know what happened before the Big Bang, and we will almost certainly never know. It's quite possible the question makes no sense, as time itself may be an artifact of the Big Bang"
Correct. Time and space was *defined* by the Big Bang. Just like the x- and y- dimensions don't make sense in 3-D space without the z-dimension, space-time makes no sense without the time dimension. To a beam of light, there is no difference between a light-second of distance and a second of time.