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About farmerben

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    Sr. Spacecraft Engineer

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  1. Error! I see a thread with an interesting scientific question, then first post immediately shifts to a fictional FTL thing. Spacescifi, I like you and I like your contributions. But this style of thread creation is slightly offensive.
  2. True that. A 2-3 diameter cyclotron has sufficient energy. Maybe if you had dozens of them surrounding a reactor then you would have something. Nobody to my knowledge has tried to mass produce proton accelerators for the price of TVs. Anyhow alpha-beryllium neutron sources are an easier way to get neutrons. And still to this day the most inexpensive fission reactor is the RBMK 1000. If we position a reactor in the right spot, we could harvest high energy protons. Imagine a reactor target with 1000 cathode ray tubes surrounding it. The cathode ray tubes would deposit electrons on our target while becoming positively charged themselves.
  3. Using bleach to disinfect drinking water is actually a thing. Here are instruction from the US EPA
  4. I think muons are more likely to initiate fusion if you get one to replace an electron in the ground state of H22 There are fast muons raining down on us all the time, we just need more slow ones. Maybe a giant airship full of deuterium gas could get some. The Van Allen belts have plenty of high energy protons. We just need to concentrate the current. A giant magnetic field like a torus could pinch the protons into higher concentration. Or we could beam electrons at a target giving it a negative charge and allow it to pull in protons that way. If we are talking about compressing Uranium or Thorium into supercritical densities, I don't know if that is possible. Plutonium has several different density states, and the transition from one to the other can go from subcritical to supercritical. I believe that transition could be achieved by hitting plutonium with a hammer. Other metals like iron can change structure by hitting them with hammers, but they barely change density at all. Is that what we are talking about? Using lasers or magnets to hammer solid metals into super densities? I'd like to see more evidence that this phenomenon is a thing.
  5. Carlo Rubbia at CERN has done decades of research using proton beam spallation to drive subcritical reactors. This technology is spectacular all it needs is inexpensive high energy proton beams. Or a seat in the Van Allen belts. There is an economical device to accelerate electrons using a so called laser wakefield. If proton acceleration could be achieved on a similar scale, then beam driven subcritical reactors would be a reality.
  6. Huh? I'm sure someone in your group argued that directly overhead was about 90 degrees from the sun. And your argument for a very acute angle is??? Many years ago, on a vacation with my family, I derived the general case for how far you can see over the ocean, based on lines tangent to a circle. I won't derive it again right now, but I can tell you several variables are squared or square-rooted so the approximation you made is not accurate. IIRC standing 6' above sea level lets you see about 4 miles. Hotel balconies let you see 10-20 miles. At long ranges you really see mostly things above the horizon like the crest of a wave and the crest of the next wave beyond it, without seeing any surface in between.
  7. The US government is already dredging the lower Mississippi in sufficient quantity to fill 2000 acres of polders every year. From what I can see the mud being reclaimed gives us much less value than it could. My idea is bring firewood grade timber to the dredging polders. Assemble crude wooden formworks above the water level and set them on fire enough to lightly char, but not fully burn them. Then discharge the river material into the wooden formworks. We allow mud to overflow the formworks permanently burying them. Vehicles driving on top will compress the soil and fill in cavities. This will build mounds spaced out in the Mississippi delta. The charred wood will absorb nitrates and phosphates, and lock them for a very long time. The carbon will be immobilized for millennia. The higher altitude mounds absorb the impact of hurricanes better. There will still be plenty of wetland, but higher ground interspersed enriches biodiversity and human use. How does the engineering math work out? That mostly depends on how much labor is required to collect the wood and get it to small ports anywhere on the river. And how much labor goes into the form work for the mounds. It costs very little to carry 1000 tons of wood on a single barge down the river. Say out standard mound site is 10 acres, and we work on about 100 mound sites at a time. Then one barge worth of wood is enough to build up more than a foot around the perimeter on a site, with plenty extra to burn or bury randomly in the middle. How much forest is that? We can probably get 5 tons of scrap wood per acre consistent with sustainable thinning practices. So 200 acres of forest thinned to load one barge one time. Essentially we are feeding 20 acres worth of excess vegetative scrap per 1 acre of elevated reclaimed land. Where the living matter continuously renews while the buried stuff is immobilized. There are a lot of questions still to consider of economic, social, and political importance. I'm looking at it first and foremost in terms of the waste streams and externalities we currently generate, and looking for better places to put them. Like it or not, we live in an era when too many of the young people are under-employed and dependent on others. You know what they do? By day they ride around on ATV's looking for mud puddles and steep embankments tearing up as much forest as possible. At night they set fires, take drugs, and yell at each other. That's fine, it's a free country. But could they please do something useful and not be so annoying.
  8. Meanwhile the Army and Navy may get ramjets of their own. As a US taxpayer, I have no problem shooting million dollar bullets like popcorn. As long as our NATO allies give billions of dollars of research grants to companies as old as my long dead grandparents.
  9. Scintillators are more complex than I had realized as well. I was under the impression that they worked off X-rays and gamma rays, but that is probably because the detectors I am familiar with are shielded to reduce noise. They seem to be directly stimulated by high energy electrons and protons as well. In the case of neutrons and heavy ions I'm not so sure how they work. Some of them are using liquid or gas scintillators to slow down neutrons until they decay, others use neutron absorbers like lithium and boron to bring other elements in the crystal into an excited state. I did find an interesting article about how the LHC must calibrate and maintain their scintillators because the high energy hadrons cause spallation and fission events in their detection crystals degrading them over time. They are using rare earth elements in their crystals though. There are plenty of lighter salts not as prone to this sort of damage. Noble gasses and ionic salts can stand up to radiation pummeling in Jovian belts. I doubt if organic materials could survive very long. A metallic sail could tank some of the damage, I had envisioned it's main role as a collector.
  10. What limits will there be to the scale of such a device? I'm not aware of any important limits on the size of the tube, volume of lasing medium, etc. One of the limits is damage to the transparent aperture, which could be greater in this environment due to all the extra radiation. But it seems to me the scintillator pumping mechanism could scale to high energies better than a pump based on electrical currents. Both require active cooling at high energies. In the scintillator example all that power is evenly distributed over a large surface. A stellaser using the solar corona for a gain medium could potentially use an empty hole for an aperture and thus scale to higher energies than any type of laser that tries to contain gas with a transparent window.
  11. That Federov article reminded me of a really good Arthur C Clarke story. To my surprise the wiki page for that story actually mentions Federov.
  12. I was thinking about how to harness the radiation of Planetary magnetic fields to power lasers. A lot of pages on the web use the buzzwords I was searching for but none answered my questions. In the Jovian magnetic field it is possible to swing through very intense belts of high energy proton and alpha particles. I metallic sail passing through the belt will have a shower of gamma and x-rays coming out the other side. A scintillator crystal catches many of these high energy photons and emits violet photons instead. I am not sure if the peak wavelengths of any scintillator crystal match exactly that of any known lasing gas. If it is possible to adjust those wavelengths by 30 nm or so, using some extra material then a perfect match could be achieved. My understanding of lasers needs checked. I have in mind a tube coated with scintillator crystal. Gamma rays enter constantly from all sides. The walls of the tube give off violet light. Is it the case that incoherent violet light in a tube will, through interaction with lasing gas and two mirrors on the ends of the tube, create coherent violet laser light?
  13. A suborbital projectile is somehow propelled toward a target in Leo (~125 km altitude) at 500g. It closes this distance in less than 7 seconds, but lets go with 7s if we are not taking the shortest path. The target maneuvering at 2g can alter its position relative to expected position by about 1/2 a kilometer. The missile needs about 0.4s or 6% of its total to anticipate and respond to the most basic evasive maneuver. Assuming the missile has finite propulsion, then the target will be much safer at long range. If infinite propellant, not so much. But the time the evasion can waste certainly increases with more range. Which evasive maneuvers are the most effective? If you were the pilot of the target spacecraft what would you do? I'm going to use maximum rotational thrusters in the plane perpendicular to the distance vector of the incoming projectile, and fire the main engines with maximum possible thrust at first. Then introduce some randomness the closer the projectile comes. So halfway to impact I might choose numbers between 90%-100% of maximum possible primary thrust, without significantly changing my direction of angular acceleration. Only in the final second or so would I do something like fire retrorockets. Is it reasonable to spin a 1000 ton man shipped in half a second? If the ship can do less than one spin, I would not change the direction of angular acceleration at all. If it can do multiple spins from rest in that period of time, then it probably is a good idea to wobble. A zig zag maneuver covers more distance than a spin maneuver, so for a very large spacecraft its advantages increase. But for the generic case I think a spiral with just a bit of randomness is better. What do you think?
  14. I'm really enjoying the discussion about changing the fuel injectors so that a rocket engine can run with multiple fuels. Two plates that rotate can provide many configurations of holes. The original post implied you want to fill an empty methane tank with liquid hydrogen, and you are concerned about left over vapors. The vacuum of space can clear out vapors, but maybe we don't want to that. The methane will mostly become a frozen solid in liquid hydrogen, so you have to deal with chunks. A tiny trace of hydrogen in methane fuel will probably not have any serious effect.
  15. Many people believe they can seed clouds with silver. But a man from Utah told me "rain follows the strontium"