Kevin Jacobson

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A fission powered propulsion system

My idea for a fission powered rocket would work like this. You have a tank of pressurized hydrogen of any type. In a separate tank, are salts of Uranium 235. When released a designated chamber of the rocket, the uranium is bombarded by neutrons from neutron guns. Neutron guns aren't science fiction. For this purpose, all you would need is Neptunium 237, a five sided lead box, and a sheet of aluminum replacing the missing side of the lead box. the Neptunium gives of alpha rays which would react with the atoms in the aluminum to create a beam of neutrons. The area inside the box would have to be a vacuum to ensure no alpha rays are absorbed. An array of these neutron guns would aline the inside of the chamber. The neutron bombardment would soon fission the uranium salts right after they left the separate chamber of the rocket and release a huge amount heat that would transform the Hydrogen flowing from the other chamber into a plasma one it came into contact with it. Using fuel like this would require very little of it to provide large amounts of thrust. The plasma would then be accelerated by electromagnetic coils. The electromagnetic field would also serve to protect the inside of the chamber. I believe that this kind of propulsion would get us to mars in a matter of weeks. Although, if my idea were to ever end up being revolutionary, it would likely end up like project Orion or project Daedalus. So, to explain it simply, two chambers are side by side, one with the flow of hydrogen gas and the other with the stream of Uranium 235 salts being bombarded by neutrons. The flow time of the Uranium 235 in it's own rocket chamber would be timed out so it would fission right when it came into contact with the Hydrogen, thus producing plasma .

  • Jun 18 2012: How is your plan not nuclear thermal? If it doesn't have a nuclear chain reaction, what else can it be?

    Simple/dumb objects will probably be launched into orbit using a rail gun. But it will probalby have a limited level of precision for sites beyond cis-lunar space. Which will mean that rockets will be needed. Before I get too deep into a design discussion, what is usually the first question to be asked is what types of missions do you anticipate this rocket being used for?
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      Jun 19 2012: My design isn't nuclear thermal because it doesn't use a small reactor to heat up a fuel source.

      My spacecraft would likely be used for fast interplanetary missions. It would never enter a planets atmosphere for, as I've already stated, the radiological threat. It could be used for long missions to the Kuiper belt or Oort cloud for mining purposes. I guess I'll go into design. The crew area would consist of a medical area, an entertainment area since more than a week in space can have bad effects on an astronauts brain, a control room, sleeping area, and a liquid nutrients storage area so that there doesn't have to be a green house on board. There would be a small array of RTG's to power standard equipment and a large capacitor bank out side the ship to power the coils in the nuclear engines. There would be a large, retractable shield in the front of the spacecraft to protect from solar storms. There would be small ion thrusters on the side of the craft for direction changing(these would be seldom used). The chassis of the craft would consist of a layer of stainless steel, a layer of graphite mesh, another layer of stainless steel, a layer of extra leaded paint on the inside and that would be covered up with a layer of thick polyethylene which is actually a great radiation absorber.
      • Jun 19 2012: I focused so much on our conversation that I finally just scrolled down to view the rest of the page which answers my questions. I agree with Krisztián Pintér on the nuclear physics. Well most of it. He3 might open new possibilities with respect to fusion. I could imagine a hybrid fusion-ion system might be possible, but it would need more research.

        Part of the beauty of being interested in space at this point is that there are unlimited possibilities, and you have a lot of freedom to imagine what is possible.
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          Jun 19 2012: Fusion as a whole needs a lot more research, so before a HE3 fusion engine comes along, we will need revolution in space flight before that time comes.
  • Jun 15 2012: As someone interested in space development (putting real factories in space), I can tell you that we will probably just begin to have an operation that will pay for itself when you become my age (mid-30's; or 10-20 years out). After that, there will be a lot of interest in expanding the robotic exploration and mapping of interplanetary space, of installing the first permanent science stations in orbit (supported by the space economy), on the Moon and Mars, and the start of serious planning efforts for orbital space colonies.

    During this time, there might be some research related to He3-based fusion energy and propulsion, ion propulsion, and solar sails. If all you ever do beyond this point is focus on that, you might get in on that effort. Use the Khan Academy to gain mastery in math (to a modern level). If we build factories on the Moon, we're going to need to reinvent our entire industrial system, and there will probably be a lot of jobs in this area. Likewise for zero-g manufacturing. If you become an ISRU expert, you might be able to play a lead role. My generation will be the one that lay the economic foundation for our space civilization and if we're lucky maybe build part of the frame. Your generation will build the frame and if you're lucky some of the guts.

    Even though you're 13, I'd strongly recommend you to do whatever you can to raise about $1,500 for yourself and a chaperone to attend the International Space Development Conference (ISDC), hosted by the National Space Society, in San Diego on May 22-27, 2013. You might have an opportunity to meet Freeman Dyson and Buzz Aldrin in person. Yes they're still alive and they're nice people. Consider joining the National Association of Rocketry, the Students for the Exploration and Development of Space (SEDS), and possibly the Geological Society of America (just keep a space focus). Also explore student internships available to high school students to get into good colleges.
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      Jun 15 2012: Well, I wasn't expecting that. Regardless, I love the ideas you presented to me. Only problem is, the only way for me to make money around here is to get a paper route which would only get me around 500$ a year.BTW, as you stated in one of your comments, I often find myself thinking about a base on the Moon or Mars. I wish I had a friend that was as passionate about space exploration as I am. Most of my friends are popularity freaks whose area of interest is "Call of Duty" or "Halo". All of the other people I know that have some real academic talent still look at me like I'm crazy when I talk about space exploration.
      • Jun 15 2012: There's a lot an entrepreneurial teenager can do. Don't be afraid to consider mowing lawns, raking leaves, or shovelling driveways. Weekly contracts are probably best (10 per week x $20... it can add up quickly!!!). If you earn more than you need, consider getting a Lego MindStorms Kit or a powerful telescope. Work with one of your parents to put together a flyer, and then just plaster the neighborhood with them. Don't be afraid to talk to your science teacher and see if you can have a school fundraiser. In that way the school might apply for STEM outreach grants and you can possibly bring a friend or two along. Going that route could substantially drop the cost.

        I'm only encouraging you. After seeing what these conferences are about, I would have loved to have gone to one back when I was 13.
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          Jun 15 2012: I will definitely give some of these ideas a go. I might as well start now.
      • Jun 15 2012: The only thing I'd add is to make sure that you talk to your parents. Hopefully they already know that you're interested in space. If you're gung-ho about doing this, do a little homework (visit the ISDC site, figure out the cost of the hotel and flight, and give yourself a little spending money), then make a plan, crunch the numbers, and show your parents what your goals are. Also don't be afraid to dream a little and have secondary goals (maybe getting science/engineering tools or instruments, or start saving up for a car -- your driving years are coming up fast!!!). Ask them for help with flyers or with talking to neighbors (tell them that you're raising money for a trip), and maybe set up a savings account to keep your earnings in. If you're smart enough to talk about fission propulsion, you might just surprise yourself with what you're really capable of!

        If you have contracts with potential homeowners, your parents will need to get involved to make it enforceable. But also understand that if they do that and you don't follow through, they'll be on the hook to fulfill those contracts. On the plus side, if you have any friends or siblings, they might be able to share the work with you. On the down side, don't over-work. Have as much fun in your teen years as you can. When it comes to goals, limits are just as important as aiming high. Let me know how it turns out.
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          Jun 15 2012: There's a few things I don't understand. How do you join some of the groups you talked about and what do you mean when you talk about homeowner contracts?
      • Jun 16 2012: ISDC 2013 -
        NSS -
        SEDS -
        NAR -
        GSA -
        JA -

        A homeowner is someone who owns and lives in a house. Your target customer is someone who owns their house, who has a yard they need to take care of, and who is working/too busy to do it themselves.

        Ask your parents about the different types of contracts (most adults know) and the basics of what goes into them. Talk to the local chamber of commerce (, tell them that you want to start a business, you might get free legal advice or services and they might help you find customers. Your parents are going to need to talk to the local government and police to see if there are any laws you need to be aware of. They're also going to need to fill out taxes at the end of the year. Have your parents help clear up any red tape so that you can just focus on the important things in actually doing work and getting paid for it.
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          Jun 16 2012: Thanks for advice but couldn't I just post the flyers around the neighborhood and simply get paid strait up cash rather than talk to the local government?
      • Jun 16 2012: Ideally you shouldn't have to think about this at all. Have your parents do that. The local government might have rules in how to dispose of waste. It will probably take less than an 10 minutes to ask if there's anything you need to be aware of when it comes to getting paid for working on other's peoples' yards. You gotta learn sometime but learning what the government's rules are is part of doing business. Since you live in a small town, there more likely won't be any restrictive rules, but you need to make sure. If you show up in person, don't be afraid to ask the government workers if they need service or know anyone who does. Talking to people is always cheaper than making flyers. But that works too.
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          Jun 16 2012: Thanks for the information, this will be very helpful. In your opinion, are any online ways of making money trustworthy?
      • Jun 16 2012: Part of the global economy is online. To make money online, you'll need know a few computer programming languages and have the right set of tools. I'd recommend at a minimum HTML/CSS and the LAMP environment (Linux, Apache, MySQL, and PHP). As far as equipment goes, you'll want at least two computers, one to run a dedicated Linux Ubuntu Desktop and the other to run a dedicated Linux Ubuntu Server. On a Windows PC, you'll need to buy Adobe Creative Suite 5, which includes Photoshop, Flash, and Dreamweaver. If you're going to have an online business, you'll need to buy a professional version which isn't cheap ($900>). On Linux Ubuntu, you can download clones that have similar capabilities for free (there are nearly 50,000 free programs). You could also download programs that can help you with school. There's a lot of info on these things on YouTube.
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          Jun 16 2012: I think I'd rather stick with mowing lawns. It would be a lot easier and cheaper to do so. If I spent $900, I presume it would take me a while to make that money back. Also, back to my fission propulsion idea, is it possible to actually contact NASA about such things and get a patent for things like this?
      • Jun 16 2012: Mowing lawns will be a good start. It's pretty simple, it won't consume your attention, and it gives you enough free time to enjoy your childhood.

        You can patent anything that has never been patented before. This doesn't mean it has to work. A patent will only be good for about 20 years and after that it can enter into the public domain. I'd recommend testing out the concept first before patenting it and at least checking to make sure that Uranium salt is fissionable.

        A problem with fission propulsion is the Outer Space Treaty of 1967. It's the most important of all space treaties. One of the things that the OST '67 says is that nations are not allowed to have weapons of mass destruction in space, which is how fission propulsion is defined. This treaty is ultimately what killed Project Orion. While there is talk about replacing the treaty with a new one since it also prohibits private enterprise, it's unlikely that the WMD prohibition will change.

        In the meantime, keep your ideas coming! Consider joining NAR and gain experience launching rockets. It might be a good way of find other people in your area that share your interests.
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          Jun 17 2012: NASA uses nuclear thermal rockets and those aren't prohibited. My design wouldn't use enough energy ate a time to even cause a nuclear explosion. I don't think this would count as a weapon of mass destruction. Another reason that Project Orion died out was because Ted Taylor, who was Americas lead atomic bomb designer, saw that these atom bombs for the Orion vessel would be mini and he thought that if any intel got out about these mini nuclear devises, a terrorist would take advantage of that information. So, he ended up quitting Project Orion.
      • Jun 18 2012: Being that nuclear thermal rockets have never flown before, I see why people are unfamiliar with them. Since your design wouldn't create a fission chain reaction (explosion), it's basically a thermal rocket. I don't know what problems NERVA or other nuclear thermal rockets have, but I'd imagine that free neutrons that make everything radioactive would be a major one. It's a common problem with all nuclear reactors.

        If you'd really like a challenge, think about designing a rocket that incorporates material readily available on the Moon. Once we have lunar industries in place, it could be engine that drives the space economy that exists beyond cis-lunar space.
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          Jun 18 2012: Well, it's not exactly a nuclear thermal rocket, but I'm sure you already know how they work so I won't explain. You could also use Thorium instead if Uranium as a main fuel source and there is a lot of thorium on the moon, though I'm not sure exactly how much, there is enough to cover around a quarter the lunar surface. Thorium is also 3 times more abundant than Uranium on Earth, so thorium might actually be a better main fuel source. Specifically Thorium 232. About the thermal rockets, I don't think the exhaust is radioactive, its just that if the rocket fails and explodes, its like a mini Chernobyl so to speak. I personally think that some sort of large, reusable rail gun could be used to launch things into space as a cheaper solution to rockets.
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    Jun 14 2012: no offense here, but if you want to design a rocket, it is good to understand physics first

    hydrogen can not be liquefied by pressure, only if cooled. commercial hydrogen canisters contain gas.

    salts won't dissolve in liquid hydrogen, as it is apolar. they surely won't dissolve in gas.

    you need a huge neutron flux to hit most of the uranium atoms, and split them. such a neutron source is not known to man, and would destroy structural materials.

    as you explained, such a plasma would melt everything unless contained in magnetic field. nowhere in your proposal it is explained how do we get energy for that.

    ps: i just looked at your profile to see that you are 13. in that case, the initial sentence of my comment is inappropriate, and should be replaced with this:

    still much to learn, you have, young skywalker! but keep up the good work, you walk on the right path.
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      Jun 14 2012: Nothing like a little constructive criticism. Anyways, I don't mean to argue, but that kind of neutron flux may be achievable with a nuclear reactor since it was proposed in the nuclear salt-water idea(which operates on a similar principle as my idea, but would be less efficient). Instead of mixing the salts with the hydrogen(which that idea is obliterated) couldn't you just have a separate source for the uranium salts. The uranium 235 could just be released into the tank along side the hydrogen. Since you seem to dwarf me in terms of intelligence, I will ad some of your ideas to my proposal.
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        Jun 14 2012: question. what advantages hydrogen has? it could be water. you can make plasma out of water as well. and it does solve uranium salts. plus can be stored easily, and dirt cheap.

        however, the fission part is still problematic. in reactors, the chain reaction makes it suitable. you have to provide a small small fraction of the neutrons, just to jump start the reaction. then fission neutrons keep the reaction going. the problem is that you need to store the fuel subcritical, and suddenly make it near-critical when needed. yet another problem is keeping it together till the plasma phase. heat will throw the mixture apart well before it reaches the necessary like 100 thousand degrees temperature to get a good plasma. in a nuclear bomb, implosion does the job, and in a nuclear plant, we don't have such high temperatures. this is a technical problem i don't know the solution for.

        yet another problem is directing the plasma backward. you need a good power source to do that, and what would that be? a nuclear plant is hundreds of tons. keep in mind that the very goal of a rocket is to provide trust and being as light as possible. starting off with a hundred ton power plant is not a good idea, unless you can make super huge trust. i don't know the physics of it. what you need to figure out is basically how much energy we need to deflect charged particles.

        are you aware of the tsiolkovsky rocket equation?

        ah, and about intelligence. don't be so sure of that. i have a BSc degree in chemical engineering, and had 25 more years to read stuff. i certainly didn't come up with rocket concepts at age 13.
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          Jun 14 2012: Though some of the problems you have made me aware of I have no answer for, I can answer some. The advantage to hydrogen is that it is the most common element in the universe and can be readily extracted from water and other sources. The power source would be a capacitor bank with thousands of magnetized thin sheets of copper. The wiring would be made of silver since it is the most conductive metal known. If I were to build this, I would stick with the neutron gun idea since they don't produce radioactive waste, don't require electricity and work at full power for 2,144,000 years, which is the half life of Neptunium 237. My title may have been a bit misleading. This would be a spacecraft, not a rocket, constructed in space or lifted into space by large chemical rockets. I don't know if this is right, but couldn't the uranium be stored stable, launched into the chamber by a high speed, rotating coil tube, go from stable to sub critical to critical until it fissions. I'm sure this can be done with just neutron bombardment. By the time the fuel heats up enough to were it would separate, it would likely already be a low temperature plasma which could still be controlled by an electromagnetic field. The flow of the fuel through the chamber would have to be timed correctly for wanted results, but you could use a trial and error technique using different time lengths to see which one would work.I like to think of Tim Harford's god complex speech in this situation. This could be simulated on a supercomputer. Since this spacecraft would be launched in space, weight wouldn't be as much of a problem(other than the cost which is 10,000 dollars a pound). Cost would be the antagonist of this project.
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        Jun 14 2012: look, this non-chained neutron-induced fission won't work, but you know what? you are not a rocket scientist yet, so you can just play with such concepts at will, wink :)

        however, some new corrections:

        if you have a capacitor bank so powerful that it can hold significant amount of energy, the whole nuclear plasma thing is unnecessary. you can just as well use some sort of advanced ion engine, ionizing with laser or electric arc. the task is to store high density energy, so if you solved it, there are no more problems.

        fission produces radioactive byproducts. it does not matter how you achieve fission, uranium splits in an unpredictable way, resulting in different isotopes, many of them active. in addition, such powerful neutron beam activates nonactive matter as well.

        i figured that it would be a deep space device. i would not want such a thing take off in my city :) but it is still a rocket, in the sense that it is a reaction engine, the engine of a spacecraft.

        if you are so much interested in space tech, i suggest to study the different proposed futuristic rocket designs, they are quite fun to read about. btw did you know that the spaceship in the movie avatar (the ISV venture star) is an unusually realistic spaceship concept? it is based on another conceptual work of charles pellegrino. probably don't work either, but lot of neat ideas in there
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          Jun 14 2012: Thanks for all your input. You really changed my idea about how this whole thing would pan out if it were to become true. In response to some of your statements, this would be launched in space or launched from ground by chemical rockets so you wouldn't have to worry about Cesium or Plutonium raining down when you wake up :) In fact, this would probably be constructed outside were most satellites orbit. Maybe even on the Moon in the future. BTW, the spaceship on avatar uses a mix of a fusion propulsion(which is possible) system AND a fission powered propulsion system. Last but not least, Ion engines use somewhat rare noble gasses and produce small amounts of thrust. However, ion rocket designs would be perfect for low gravity conditions such as missions to the moons of Jupiter. I think in the future, however, we will use powerful propulsion systems to accelerate spacecraft and solar sails to finish the trek between planets and then the same process again.
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        Jun 15 2012: yet more notes:

        no, avatar spaceship uses combo fusion and annihilation. fission is not good enough for interstellar. neither fusion btw. they are not enough energy dense. the only candidate is annihilation.

        ion engines today are such, but there is no theoretical limit on their thrust. if you can pack energy in a spacecraft, ion engines, and some other electromagnetic propulsions are available. the problem is storing energy.
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          Jun 15 2012: Seeing how long it might take even an anti-matter engine to reach Proxima Centauri, which is only about 4.5 light years away and our closest star, I wonder how many years in the future we will have warp drive technology or wormhole technology. In theory, these things are possible.
  • Jun 14 2012: You should sell these ideas to the Iranian government.
  • Jun 14 2012: There is a lot of public fear regarding fission rockets because of radioactive reactant waste byproducts. Governments fear fission rockets because they incorporate technologies that can be weaponized, i.e. suitcase bombs. At the end of the day when you run a cost-benefit analysis, prohibiting their development is probably the right decision.
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      Jun 14 2012: This design wouldn't use the suitcase sized atomic bombs like Project Orion would. It would just use salts of Uranium 235, which I presume would be kept under the highest security possible. A spacecraft that uses this kind of fuel would either be constructed in space or by lifted into space by booster rockets to avoid any radiological threat from the exhaust which would indeed contain Plutonium. Besides, nuclear propulsion is the only way humanity can ever effectively colonize the solar system.
      • Jun 14 2012: You seem to think of nuclear propulsion using a similar set up as chemical propulsion, where you have a fuel and an oxidizer. In this case you're treating U235 salts as a fuel and the hydrogen as the oxidizer. The problem is nuclear reactions do not use oxidizers. Ignoring for the moment that U235 salts will probably not create sustainable reactions, if hypothetically there was a fission reaction in the reaction chamber, it would quickly chase through the fuel lines into the entire storage tank and consume the whole supply (nuclear explosion). While your U235 salts might use discrete packets, it depends on feeding them into an ongoing fission reaction at a sustainable rate, which happens too fast. Project Orion prevents this problem by containing explosions in small discrete packets. It doesn't use a reaction chamber but an ablative reaction plate. In the end, it creates more problems than it solves.
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          Jun 14 2012: The problem with an Orion type craft is that the specific impulses can kill the crew unless you have a dampening device, the pusher plate is worn down after continuous use and a lot of explosive power is lost with a pusher plate because a lot of the explosive energy is dispersed out into space. You would be better of with a pusher "bowl" design rather than a pusher plate. As well as that, if information was ever leaked on miniature atom bombs, a terrorist would take advantage of such info. BTW, the hydrogen is required to have full power from the rocket. You couldn't just have the Uranium salts(which would be delivered in specific packages) because you wouldn't get much thrust. This type of propulsion wouldn't require much fuel to provide a large amount of thrust. Nuclear pulse drives, even though they can accelerate a craft to large speeds, are quite wasteful and would cost quite a bit to provide all the nukes they would need. My idea also uses electromagnetic coils which would accelerate the plasma and also protect the rocket chamber, unlike a pusher plate.
      • Jun 15 2012: When I was 13, I too was interested in space propulsion, travel, and colonization. I had a good friend that shared my interest, and we'd bounce ideas back and forth. I still look back fondly at that time as the bright supernova year of my life. Even more than 20 year later, I'm still interested.

        Uranium naturally occur as 99.3% U238 and about 0.7% U235. Even if you shot a stream of U235 packets, it wouldn't normally explode into a fission reaction. There are a few documentaries on Project Orion. Freeman Dyson mentions maintaing a constant rate of force to simulate gravity.