Envisioning the world of 2100

Discussion in 'Science and Technology' started by RAMA, Aug 9, 2012.

  1. Deckerd

    Deckerd Fleet Arse Premium Member

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    I've noticed that Mars completely ignores all the really hard questions and only goes for the really easy ones.
     
  2. Silvercrest

    Silvercrest Rear Admiral Rear Admiral

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    Maybe we should ask him about the "giant pyramid to space" thing.
     
  3. publiusr

    publiusr Rear Admiral Rear Admiral

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    An opinion that you don't share isn't 'spam--its an opinion.

    Big is sustainable, as we saw with 100= shuttle flights with not all that interest--because the STS was a LEO only system--but it was a defacto HLV in terms of mass to orbit--that that proves me correct.

    In terms of future tech--al we need do is look to the past--and support such systems as opposed to sniping at them from the interwebs

    Some projects to look at
    http://www.wired.com/wiredscience/2012/09/project-hyreus-1993/

    Now in terms of depots: Lee P. Scherer told Culbertson that the LOSS might not be needed, and that his office viewed neither the Nuclear Shuttle nor the LOSS propellant depot “as clear requirements.”

    This is what the illusion of cost-saving reusability destroyed--a quote:

    It is one of the most damning indictments of numerous short-sighted administrations, whether Democrat or Republican and whether influenced by external influences or not, to have effectively cut us off from deep-space exploration for half a century and eliminated dreams of the Moon and Mars for two generations of children.

    http://www.americaspace.org/?p=25013

    What SLS does is to reverse this:

    http://www.americaspace.org/?p=25146
    http://www.thespacereview.com/article/2154/1

    Not thinking big as we used to is the problem.

    Here is the problem with commercial space that folks seem to worship here. Real experts understand the need for heavy lift. Now if you want to keep selling NASA lots of smaller rockets--you argue for leaky depots.

    Another quote to prove my point:

    The twist with “commercial space” as it has taken shape is that the companies involved are saying that they must have government money in advance of performance to develop their product, while yet maintaining their right to conduct that product development according to their own concepts and standards. Nonetheless, the government must buy their product when it is available, and – oh by the way – is not allowed to develop its own product, because it will compete unfairly with “commercial” offerings.

    It is this posture that I find so offensive. If I pay you to do something for me, I want you to do what I want done, not what you want to do. I further want you to do it in the manner in which I want it done, not as you may happen to want it done. That is what I expect for the money I provide – just as I would if, say, I engage your company to build a custom home for me. If you do not choose to do what I ask, as I ask it to be done, that is okay. In that circumstance, however, I am not required to buy your product. I can seek another provider who will agree to do as I ask.

    But this quid pro quo, which would apply exactly in the case of a commercial contract for a custom home, apparently does not apply to a commercial contract for a custom spacecraft. NASA is forced to provide development money for a product whose design it cannot influence, and then to buy the product when it is finished, regardless of what responsible agency engineers might deem to be appropriate. The only outcome of such behavior that can possibly occur is that a technical, operational, or business failure will occur – and NASA will be held accountable for the failure, because public money was expended.

    So, the U.S. government is the 80% majority investor in SpaceX – and this is prior to the $400+ million CCICap award. But, the government does not own the design or the product when it is complete; it does not own even 80% of it. What NASA “owns” is the right to buy a seat at market price. The only real change from the classic “prime contract” seems to be that a largely different set of contractors is performing the work, which is done primarily with public funds but without government supervision. The working definition of “commercial” seems to be “not built by an established contractor working to government specifications”. I have only one question: can I get that deal?

    Some questions

    So even as Obama’s campaign releases a press statement extolling the virtues of Orion and SLS, his folks at NASA are still trying to kill these programs. As to his comments about SpaceX, I guess Griffin feels strongly about its poor track record because he was the one who led NASA when SpaceX won its COTS contract. Griffin was the one who cut SpaceX it’s first big check of $277.8M. With both SpaceX and Orbital Sciences years behind schedule and each over $118M over budget, I can see why he’s upset. Worse, unlike Constellation, which had an excuse in that it was short-changed for years, not once did not SpaceX or OSC receive their promised funding on time. So one is left wondering what their excuse is. Maybe someone from the NewSpace community could answer that question?


    More


    What is indisputable is that an HLV mission architecture is much better understood in terms of risk, technique, and planning, thanks to Apollo, than any other. And that means while a HLV mission guesstimate will be off in cost and time, it will not be nearly so much as for similar guesstimates of other architectures deeply studied but never tried. For example, lunar landing studies conducted in the late 50′s pegged the cost at between $1.5-2B. Apollo came in on-budget only because Webb added an arbitrary 40% to NASA’s best-guess estimate for Apollo.
    An HLV architecture certainly doesn’t exclude using ISS or SEP. But it does mean that lunar missions can be conducted absent the use of ISS, SEP, or anything else. that flexibility seems attractive.
    Its obvious that you feel the non-HLV architecture is the best way forward in BEO human spaceflight. And your unhappiness with Griffin’s decision 8 years ago comes through.
    For my part, since HLV-based architectures are better understood and we currently have an HLV in development, my inclination is to keep working on what we have. I’m not going to let the perfect be the enemy of the possible and oppose something currently underway.
    So, I guess we’ll have to agree to disagree.
     
    Last edited: Sep 14, 2012
  4. Deckerd

    Deckerd Fleet Arse Premium Member

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    I really don't want to nitpick but anything within our solar system is not deep space. The Voyagers are beginning to brush deep space.
     
  5. gturner

    gturner Admiral

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    The Shuttle was barely sustainable, and only by sucking up most of NASA's budget. It should've been retired by the late 1980's, but they couldn't afford to replace a system that was working, and due to the very low flight rates none of the Shuttles were near the end of their operational lives, which was supposed to be pretty short.

    One problem with SLS is that it's the same as a host of mid-1970's Shuttle-derived cargo designs. It's not reusable and the architecture doesn't offer any way to make it reusable, so the same people who built external tanks for the Shuttle will be building modified external tanks that will be thrown away, along with the either RS-25E or RS-68 engines, which are very expensive.

    It's an example of NASA not innovating, nor driving the technology in new directions, like coming up with cheap expendable liquid engines, or liquid strap-ons with propellant cross-feed, or reusable first stages that land vertically, or any of the other approaches private firms are pursuing. The projected flight rate of the SLS is going to be less than the Shuttle, depending on whether they design a payload for it.
     
  6. Mars

    Mars Commander Red Shirt

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    So tell me why can't you run a nuclear reactor for 5000 years? I hear nuclear fuel isn't that bulky, so I'm sure a 5000 year supply of Uranium could be stored aboard the ship, the ion drive would be needed only to bring the ship up to crusing speed, crusing speed would be about 0.1% of the speed of light to get to Alpha Centauri in 5000 years, that is 300 km/sec. If the starship accelerates at 1 mm per second squared, it would take 9.51 years to reach 300 km/sec, and another 9.51 years to slow down from it leaving about 4980 years of cruising, all the nuclear reactor would be used for then is sustaining the L5 habitat for all the plants and animals to be brought on the trip. There would be many generations of plants and animals in the interior hab, such that their would be an ancient forest growing in it by the time the ship arrived at its destination. The AI's job would be to sustain that ecosystem for the entire length of the voyage.
     
  7. Mars

    Mars Commander Red Shirt

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    The AI can slow down his consciousness so he won't get bored, if he experiences time at a rate of 100 seconds to his 1 second, then the voyage duration will seem to last only 50 years to him. He'll watch the animals zip across the meadows and through the forest at incredible speed, each day will pass every 14.4 minutes, he can watch the trees and the grass grow, watch the programmed seasonal cycles, for every 1 of his years, 100 years will pass on the ship, and if there is any trouble or maintenance problems, he will speed up his consciousness to deal with it.
     
  8. Mars

    Mars Commander Red Shirt

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    The problem is that it may not be left alone by the billions of other humans and sentient AIs that are also inhabiting the system, and if something were to destroy humanity, the ship might get caught up in it. There would be insufficient isolation if it stayed in the Solar System, if it is lost in the depths of interstellar space, it might be forgotten about. I figure if you give the human race another 5000 years and it does not do itself in, then the human race should be fairly safe, and their might even be a welcoming committee waiting their arrival at Alpha Centauri, but insurance policies are in case the worst happens, if the worst doesn't happen then there should be humans awaiting their arrival at Alpha Centauri.

    Because the AI itself doing the tending won't itself evolve, it will experience time at a 100:1 ratio for most of the voyage, so the trip will seem to take 50 years for it, there won't be any competing more sophisticated AIs for it to worry about, as it will be just as isolated as the humans will be when they arrive. The Ai will miss about 1000 generations of subsequent AI programs if civilization lasts that long and if not, it will represent the hope for the continued human future.

    How can you know that the human race will survive for the next 5000 years? I think the greatest danger is that of self destruction, not as asteroid strike or a supernova, to survive whatever calamity wipes out the human race, a part of it will have to be very far away, so the rest of humanity trying to destroy itself will not concern itself with that. You know what nuclear war is right, or runaway nanotech or AIs taking over, or humans uploading into machines and then something happening to those machines so they no longer function, or some kind of fantastic war being fought. Use your imagination, its best to be far away from whatever may occur in order to be safe.

    Well an isolated starship is not going to be building much of anything, probably be doing self maintenance and that is it, its harder to get billions of human beings and control them all so they don't build AIs, because for each one it may prove advantageous to build one, but taken together they may threaten humanity by their existance. Humans may become too technology dependent and atrophy to nothingness. the humans arriving at the system will efffectively be late 21st century humans with late 21st century technology, so they start as square one.

    Its not going to work, because the one who violates the treaty will always be at an immediate advantage.

    A lot more can go wrong with a community of billions of humans than with an isolated starship with frozen embryos traveling the void between the stars, very little is likely to happen during that almost 5000 year dormant cruise. Back on Earth and the solar System, billions of humans and AIs will be inventing dangerous new technologies we can't even anticipate, the isolated starship won't be a part of that, and the Solar System won't concern itself with them.
     
  9. gturner

    gturner Admiral

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    Ahem. You're saying that on a Trek board.

    1) The ship could be struck by a piece of interstellar debris
    2) The AI could get bored and start playing with the stored DNA, combining it with spider DNA to create mutant monsters.
    3) The ship could be colonized by space spiders, who mate with the mutant human/spider people
    4) The ship could be boarded by a Ferengi raiding party, who get eaten by the hybrid spiders
    ....
    3187) The ship could travel through a wormhole and end up back at Earth, dumping human-Ferengi-Romulan-Horta mutant space spiders with Borg implants and telekinetic power back on Earth.
     
  10. Mars

    Mars Commander Red Shirt

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    But we're talking real world starship not Star Trek. The most likely thing to happen is getting struck by space debris, and with thick shielding and a relative velocity of 300 km/sec, the ship will likely survive and repair the damage. The Ai basically goes to sleep, so it won't get board, that is the thing about computers, is they can turn themselves off and a timer can wake them again, they don't have to experience time second by second like we do. The ship will be traveling forward in time about as much as it travels in space, getting across those 5000 years of time will be its main purpose, Alpha Centauri is just a destination to separate themselves from the rest of humanity and whatever may go wrong there.
     
  11. gturner

    gturner Admiral

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    Well, the one snag in your plan is that the AI isn't actually needed for anything. Running a fission reactor doesn't need an AI, and doesn't even need a computer. An analog circuit, even a mechanical mechanism, can do it. Waking people up would just take a clock. Dodging debris just takes a vintage radar system and steering control running like the inverse of a missile seeker head (the original Sidewinder used only seven vacuum tubes to track, intercept, and kill). If you can freeze human embryos, then you can freeze anything else, so you don't need to maintain any type of ecosystem. It's a cargo barge with a star tracker, a radar, and an engine, and that doens't take much more sophistication to run than our Voyager probes from the 1970's.

    I also forgot to mention threat #1615: Space pirates from Earth who board the ship, kill off all the male embryos, and set their cryochambers to wake them up on the planet when all the female embryos are turning 18 so they can live on a planet of women.
     
  12. Crazy Eddie

    Crazy Eddie Vice Admiral Admiral

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    Assuming that theory has any validity, the simplest solution is to move the fuck out of yellowstone.
     
  13. gturner

    gturner Admiral

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    ^ But if you are in Yellowstone, make sure your webcam is streaming online video of screaming crowds before you take off futily running for your life.
     
  14. Crazy Eddie

    Crazy Eddie Vice Admiral Admiral

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    A mountain of hyperlinks to forum posts on other websites that have almost nothing to do with what we're talking about isn't an opinion, it's spam.

    Does it? Because, last time I checked, the STS is no longer operational and its replacement won't be ready before the end of the decade.

    Actually, we DO think big the way we used to, which is exactly the problem. It was THINKING BIG that gave us the shuttle program, and thinking even bigger that cut the shuttle's capabilities in half. It was the marathon of Big Thoughts in the 70s that led to optimistic projections about the shuttle's launch costs, about the kinds of missions it would carry out, about the new era of space exploration it would open up by carrying huge payloads into space and directly servicing them with qualified crews and later ferrying truckloads of passengers into orbital factories and space labs.

    And what was the result? Big thinking effectively cost us our first and orbiting launch platform when the shuttle mission failed to replace Apollo in a timely fashion. Big thinking resulted in a transport system that flew half as often as planned for ten times the cost, and later on filling only one in ten of its original mission roles for safety and political reasons. And when the shuttle program came to an end, history repeated itself: NASA has spent so many years trying to develop the Next Big Thing that they currently lack even the rudimentary spaceflight capabilities of early '60s. They cannot even put a crew into orbit, let alone service and maintain the space station. The next ten American spacecraft to fly anywhere at all will be built and operated by private operators with their pathetic "small change" operations.

    Any prudent business manager knows that "Thinking Big" is not something you do when you're just starting out, when you've got nothing to fall back on and no way to take up the slack if your Big Idea turns into a crapshoot. The Senate Launch System, in that regard, isn't a future launch system, it's a technological gambit, betting on the ability of a group of aerospace contractors to resurrect a 1960s rocket engine, a 1970s mission profile and combine all of those with a 1980s launch system which they now have to completely refurbish to achieve just over twice the original performance with half the budget they had when these things were originally developed. It would be a pretty sweet payoff if the SLS actually flies on time and on schedule... but what exactly does NASA plan to do if it blows up on the launch pad?

    If you were in any way concerned about the opinions of real experts you wouldn't be spamming unsourced essays from the nasaspaceflight.com forum.
     
  15. sojourner

    sojourner Admiral Admiral

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    You do realize that if it blows you'd have to move out to the fucking moon to avoid the catastrophe it would cause. It's an ELE.
     
  16. Crazy Eddie

    Crazy Eddie Vice Admiral Admiral

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    Because running at full power, a typical fuel rod will only last for 20 (25 if you're lucky) before it decays to the point of no longer producing useable heat and subsequently becoming a serious radiation hazard. And that's before you take into account neutron breakdown of shielding materials and the piping of the heat exchangers, which over time become brittle and have to be replaced considerably more often. You would essentially have to overhaul the entire reactor every ten years of continued operation, replacing the fuel rods every other overhaul. That is no easy task, even for a machine.

    In other words, your robots will have to completely rebuild the entire reactor two hundred and fifty times before the end of the voyage. God help you if you've got multiple reactors on board.

    Which goes to the overall point of this being a fundamentally impractical endeavor: that's a LOT of new capabilities being developed for a space craft that doesn't actually accomplish any concrete goal for anyone. Your stated goal is to ensure the survival of the human race 5000 years in the future, yet the sheer massive amount of resources that would be needed for a project this ambitious could be more efficiently used to eradicate world hunger, terraform Mars and tap the methane lakes of Titan to provide the world with an inexhaustible energy supply. It's a highly expensive and complicated solution to a problem that may or may not even exist.

    And you know this how?

    Neither will your generation ship if the AIs decide to chase after it. Or, for that matter, if the pilot AI gets an email from Earth containing the Cyberdyne Manifesto and decides to turn around and head back.

    Right, because PUTTING AN AI ON THE GENERATION SHIP is isolation enough.:lol:

    Because in the collected sum of mankind's knowledge about itself, its world, the solar system that contains the world and the immediate vicinity of our stellar neighborhood, there is no reason whatsoever to believe that it WON'T.

    More importantly -- and more relevantly to this thread -- I, like most human beings, don't give a damn one way or the other what might happen five thousand years from now. This is a thread about the world of 2100, less than a century into the future, at a time when my son will be watching his grandchildren go on to take meaningful careers.

    So if I'm to worry about the future at all, it'll be whether or not humanity is going to survive for the next FIFTY years. Is a generation ship on a 5000 year voyage a good way to insure that? No? Then why the hell would I want to spend money building one?


    On the other hand, it's relatively easy to control the six or seven thousand people on the entire planet who are even remotely smart enough to attempt to build an AI. We ALREADY do this with nuclear non-proliferation.

    On the other hand, you don't have a shred of evidence that the emergence of humanlike AI is even possible, let alone inevitable, let alone that any negative consequence would follow for humanity if it was.

    Until the next biggest country bombs him back into the stone age for violating the treaty.:mallory:

    Which is trivially true. The problem with this statement is that just about anything that can go seriously wrong on a space ship will usually result in the destruction of that space ship. With a population of 7 billion, a global-scale catastrophe could annihilate 99% of the human race and that would still leave more survivors than most countries have people.
     
    Last edited: Sep 15, 2012
  17. Crazy Eddie

    Crazy Eddie Vice Admiral Admiral

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    Which the Earth has experienced MANY times before, and yet is somehow still habitable. I'm not saying it wouldn't thoroughly suck. I'm saying it would not cause the extinction of the human race (just a massive and traumatic thinning of our numbers).

    OTOH, relocating to the moon doesn't sound like such a bad idea, all things considered. By 2100, I'd be surprised if it wasn't a serious alternative.
     
  18. Mars

    Mars Commander Red Shirt

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    Ah, but you forget, in space no longer usable fuel rods can be tossed overboard and never seen again, you don't need to store them anywhere or worry about their radiation.

    Well the nuclear power plant will only be at full power for 20 years out of the 5000 year voyage, for the rest of the voyage, it will only be used to provide light and heat for the habitat. There is no other power source available in interstellar space until the discovery of fusion.

    If humans can do it, a machine can do it, machines will probably already be doing most of this stuff for nuclear reactors anyway.

    So it seems to me to be more than equal to the taske performed by a calculator brain, you'd need an AI to oversee things, as your not going to get a human crew to do this for 5000 years, and pushing the ship to faster speeds has other problems. I'd say compared to building a starship that can reach speeds of up to 10% of the speed of light, building a slow starship like this would be easy, even when these things are taken into consideration. For the price of one speedy starship, you could probably build 100 of the slow ones.

    But slow starships are relatively cheap to build, this one would be the size of an O'Neill habitat, and not much more expensive to build, it can house 10,000 people when fully occupied, and an ion drive would accelerate it up to 300 km/sec and then slow it down again at the end of the journey, this is not much in the realm of starships, certainly teraforming Mars would be more expensive than this.

    As for World hunger, AIs alone could solve this problem, AI's could grow the food, AIs could do all the work, the rest is just a matter of redistribution. If we can get enough AIs to outnumber the human population, the starving millions need not even work for their food. I don't think there is any chance of the human race dying of starvation, maybe gluttony perhaps.

    I do perhaps think that maybe humans need to work to stay healthy, having machines do everything for them may pose a long term risk to their survival, which is why establishing a distant colony of humans is important, and isolation from the rest of humanity is also important.

    Machines would be in the same peril from obsolescence as humans. I think the event would be more like a forest fire, chances are it wouldn't spend much effort looking for remote spaceships in interstellar space, anyway being far away from the conflagration would be better than being right in it.

    Well this ship can certainly be launched by 2100, that is it can be built in that time frame with that time frame's technology, so it is an appropriate subject. Maybe you don't care if the human race perishes but I do, and I'm examining what technologies in the late 21st century might be available to save it.

    Both 2100 and 5000 years is beyond my expected life span, so I worry about them equally, because I don't expect to personally live in the year 2100, so I remove myself from immediate consideration, it is the rest of humanity, those that will come after me that I am concerned about, since I both won't live in the year 2100 or 7100, I am not concerned more about one than the other, they are of equal concern to me as it is about the future of the human race.

    Why does one buy life insurance, this is life insurance for the human race, I think it is worth some effort and expense.

    I hate to tell you this, but its not working, North Korea has acquired the nuclear bomb and Iran is acquiring it, and shunning them, or not trading with them is not going to stop them, the only way to control the entire planet is with a world government, and that's another fate which I wish to avoid, that of the human race being controlled and turned into drones, Ala "the Borg". Humans need to spread out over time and space so they don't get turned into an ant colony. A world government and trying to control us all puts all our eggs in one basket, if all our decisions get made at the top of government, then the wrong decisions could wipe us out!

    Its hard to predict the unpredictable, AIs will be quite clever, they'll be agents of change, you can't predict what that change will be or what that change will do, the more change there is the greater the risk to the human race. So we have to spread the human race out over time and space to prevent us all from getting caught in one of our mistakes.

    And we're back to starting a nuclear war aren't we.
    Its not the numbers but how far they are spread out that matters. If you can pack one billion human beings within the radius of one nuclear bomb blast, then they all die if one goes off, It is the limited scope of humanity on one planet that is the danger. The thing about spaceships, especially this one, is if it gets destroyed, no one dies, it is simply that no one gets born afterwards. One can have multiple spaceships, and you limit your chance of having one all-consuming disaster that destroys us all.
     
  19. gturner

    gturner Admiral

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    And that's why your ship will get boarded for a "health and safety inspection." :lol:

    A molten salt reactor is probably going to be better than a conventional nuclear reactor, for a host of reasons.

    1) A conventional reactor runs at very high operating pressures, requiring a heavy containment vessel, yet the containment vessel has to open to allow replacement of the fuel rods. That's very heavy and complicated.

    A molten salt reactor can operate at atmospheric pressure, so the reactor vessel itself doesn't need to contain high pressures.

    2) A conventional reactor has all the short half-life highly radioactive breakdown products trapped in the fuel rods, which not only causes problems with fuel poisoning, but the issue of a massive release of radiation during a melt-down.

    Molten salt reactors allow the seperation of breakdown products from the fuel during operation because they boil out of the liquid fuel, making it easy to vent them somewhere else for storage, if even venting them overboard as a gas.

    3) Having the reaction products boil out as a gas also eliminates most of the problems with reactor poisoning, an issue primarily with xenon-135, which has a 9 hour half-life and a huge neutron capture cross section, potentially sucking up so many neutrons that the reactor won't restart.

    Reactor poisoning isn't much of an issue unless you have to rapidly cycle the ship's power levels for maneuvering to avoid space objects, but if you might have to do that, then designing to avoid poisoning is critical.

    Naval powerplants use highly enriched uranium (instead of very low enriched uranium like commercial reactors) because they have to guarantee full power operation for combat maneuvers regardless of the output power levels over the previous few hours.

    But going that route means you've massively increased the cost of the fuel, and created further handling problems because it's much, much more fissionable than commercial fuel.

    4) Conventional solid fuel rods will need to be reprocessed, which is technically difficult.

    If you toss them overboard, you're throwing away 97% of your potential fuel, which means you have to store over thirty times as much initial fuel on board.

    The fuel rods, obviously, can't be stored too close together or you could risk a chain reaction, especially if a moderator is introduced (such as from a broken water pipe). So each future fuel rod has a shielding or storage space overhead.

    Unnecessarily upping the mass and space requirements for your fuel storage by perhaps several hundred times isn't a good design, and the ship will have to be able to reprocess fuel anyway, because if it can't, it will one day run out of fuel without the ability to manufacture any more no matter how much uranium the crew can dig up.

    5) If the molten salt reactor uses thorium, which is extremely likely, then you not only can reprocess the fuel on the fly, as part of the normal reaction cycle, but you can store tons of thorium as a giant lump, because it won't support a nuclear chain reaction no matter how pure it is. Thorium is also 100% fertile, so it can all be burned up. With the uranium cycle, you've generally got a lot of excess U-238 to deal with.

    6) Molten salt reactors can run at much higher temperatures, making them more thermodynamically efficient. That means more available power to the drive system for a given thermal output.

    On Earth, where the heat rejection is limited by outside ambient temperature, they could hit roughly 50% efficiency in a single fluid design. Water cooled uranium reactors run at about 35% efficiency.

    In deep space, both reactors could have their efficiency impoved by further stages using lighter gases with lower boiling points, but the molten salt reactor would retain the advantage.

    7) Molten salt reactors have a much higher specific power density, which is the energy output per mass. Conventional nuclear reactors work well in ships, which ran pretty well with coal-fired steam piston engines, but molten salt reactors were first designed to power an Air Force bomber. In aerospace applications, that's an advantage that's hard to ignore.

    8) Conventional reactors have to be shut down for long periods to replace the fuel rods. That means you have to have multiple reactors to guarantee that power will always be available to keep the ship from freezing.

    Molten salt reactors can circulate the fuel in and out as part of normal operations, so they never actually need to shut down. They can also be shut down, the fuel drained, and then refilled and restarted up to full power in just a few hours, as opposed to weeks or months with a conventional reactor.

    9) Since their reactor vessels doesn't have to hold high pressures, they are thin and lightweight, which means they are vastly easier to store, move, or fabricate, and multiple vessels could be carried for inflight swapping if neutron embrittlement becomes an issue.

    The reactor shielding (the room's walls) doesn't have to be structural, so it never has to be swapped.

    So neutron embrittlement is at least easier to cope with in a molten salt reactor that has to run for centuries, because fabricating a very thick, high pressure vessel is always difficult, or requires carrying a whole lot of extra steel.

    10) Thorium is more abundant than uranium, and doesn't require enrichment, so any human colony using thorium just needs to mine it, instead of trying to build an isotope seperation facility.

    Canadian CANDU reactors don't require fuel enrichment, but they do require a source of deuterium, which they extract from seawater. Though not technically difficult, it does require processing about 6,000 times as much water as would otherwise be required.

    And if the destination solar system is much older (or derived from older source materials) the U-235/U-238 ratio will be lower, possibly preventing even a CANDU from running without some level of fuel enrichment.

    ****

    A final note is that from an engine standpoint, you've got the initial and final acceleration phases (which burn fuel), and your coast phase where you keep the ship from freezing (which burns fuel). Once you've got hard numbers for the power requirements of those phases, you'd optimize for the minimal total energy consumed during the flight. If the deep-space heating and lighting is a huge demand and delta V isn't that expensive, you'd accelerate more to shorten the trip (100 years of lighting takes 50 times less fuel than 5000 years of lighting).
     
  20. publiusr

    publiusr Rear Admiral Rear Admiral

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    Mar 22, 2010
    Because, last time I checked, the STS is no longer operational and its replacement won't be ready before the end of the decade.

    And its enemies would love to kill it thereby wasting money when they should be supporting it.

    It was THINKING BIG that gave us the shuttle program...effectively cost us our first and orbiting launch platform when the shuttle mission failed to replace Apollo.

    Apollo was thinking big. STS was thinking reusable.

    Any prudent business manager knows that "Thinking Big" is not something you do when you're just starting out

    We are not just starting out--and how is that starting out when folks want to kill it and not give it a chance

    It would be a pretty sweet payoff if the SLS actually flies on time and on schedule... but what exactly does NASA plan to do if it blows up on the launch pad?

    What does NASA doe when any rocket blows up? Good grief--you're just being difficult.

    If you were in any way concerned about the opinions of real experts you wouldn't be spamming unsourced essays from the nasaspaceflight.com forum.

    The piece was from Covault, BTW. Of Av Week and space, and the folks he had on there are hardly unknowns

    So Griffin--who wrote AIAA texts is unsourced. A man on Augustine who trashed HLVs, gave us the Roton.

    Pot, Kettle

    And for those of you who think this isn't relavent--what do you think launches heavy reactors--Delta IIs? Get the ride first--the reactor later.