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wumpus

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Everything posted by wumpus

  1. I worked for a company that made drones in the early 90s (unfortunately they were out of business before drones really took off), and they made one of their prototypes out of kevlar. Thing once ran into a tree (they were fixed wing "aircraft", not quadcopters) and only the propeller (and possibly engine) was damaged. On the other hand, cutting the fabric was so hard (even with the special shears) that they weren't interested in making more. I have to wonder if you can laser-cut those things... So kevlar isn't as tough as steel. But if you have to accelerate the mass to orbit, you might prefer kevlar.
  2. Detonation of gasoline/oxygen mixtures in cars is not unknown, and common enough to have a name: "knock". Granted, if your engine starts knocking you pull off, turn the engine off, and have it towed to a mechanic (that much knock may well destroy your engine before it gets there). So getting the energy the engine was designed for in a shockwave is rarely instantly fatal. I'm not even sure if nitroglycerin has more energy than properly mixed gas/oxygen (nitromethane does, or at least at mixtures that fit in the same sized engine). High explosives typically don't have as much energy, just the ability to easily lose it all at once. And while I haven't worked out the math, at least one thread here was reasonably convincing that the main point of Orion wasn't to capture all the *energy* of the explosion, but the *momentum* of the explosion (well, the momentum of the material hitting the plate). Momentum is the key to rocketry, and Freeman Dyson and co took advantage of that.
  3. As far as I know, that was why they initially believed that the radiation and various isotopes would not return to Earth: nearly all the explosions happened when it was sufficiently sideways to miss the Earth. Unfortunately, if you aren't near the poles the magnetosphere can typically grab them and bring them back. No idea what the initial blasts were supposed to be, I'd just assume they were dialed back to survivable levels.
  4. But your Isp is effectively infinite. So when you see claims that "reactionless engines" are impossible, that isn't true. Just that all known reactionless engines have really low thrust. Of course, your Isp wouldn't really be infinite. There is a theoretical loss in mass (E/c2) just to produce the energy that produces the photons.
  5. Same as on Earth, the air would follow the ground, with a certain small amount of "constant wind" counter to rotation. So anything dropped would be slowly grabbed by the wind as it got closer and closer to "ground". No idea if anyone has determined how to deal with such airflow in an O'Neil cylinder (they were talking about them long before computer simulations were feasible). I suspect that width and baffles would be key to such construction.
  6. I've heard it pushed it back at least a year. But using the Apollo1 design plus Apollo1 schedule, the most likely landing scenario involves lithobraking.
  7. Toxic and likely explosive. Plus, low gravity planets would "quickly" (at least by geological time) lose their atmosphere. The atmosphere would have to be brought by settlers and not expected to last (I'd assume mass nuclear alchemy creation of oxygen). Pretty much the only way you will get winged humans. And menances from Earth.
  8. In the original Star Trek series (1960s), at least one of the episodes having a space battle with the Romulans was based on a US/Japanese submarine battle (from googling, I'm guessing "The Balance of Terror"). I don't think steering against a medium made much of a difference. The main issue in the battle was using sensors to try to detect the enemy (presumably sound with submarines, Sci-Fi sensors [presumably resembling electromagnetic sensors] in Star Trek). But yes, Star Wars was basically fairy tales with semi-modern fighter pilots. Not science fiction at all.
  9. Escape Dynamics (2010-2015) was pitching this system. You might want to look into their ads/whitepapers/claims. I think they were using microwaves for any test/prototypes.
  10. McNamara was not known for his ability to determine the effects of the wars/course of said wars he started/entered. Generally speaking, while I wouldn't be terribly surprised if significant numbers of people survived a nuclear war (even living in belligerent/nuked states), I'd strongly expect that the world economy and technological base would quickly fall to below Renaissance levels. It takes a lot of tech to run modern resource extraction (all the easy stuff was typically extracted well before 1900) and losing major key bits of modern tech would probably just see the whole thing collapse.
  11. The heart of Skylon is a system to cool incoming air (indirectly with LOH later used as fuel). With anti-matter, such cooling really isn't necessary (although it would certainly help efficiency). I'd recommend going straight to a SCRAMJET, although getting the thing started becomes an issue (which SABRE avoids by using compressors). But the real point of "if you have temperature limits you almost certainly have fuel limits", and the problems you are asking about simply don't exist in a world with easily available antimatter and interstellar travel. They are "technologies that no longer need improvement", quite possibly from centuries back (and whatever improvements they have is next to inconceivable as they are optimizing for things we can only guess about). If you want to show off your knowledge of thermal limits, interstellar space isn't the place for it. You'd need something set roughly in the 21st century. Although I'm pretty sure trying to use less than .1m2 of radiator per MW of power will require unobtanium (with near perfect themal conductivity, radiation, and a melting point over 4000K).
  12. Last I heard (some astronaut trying to explain rocket science to non-nerds), SSME was pretty much at the melting point already and regeneratively cooled with the LOH. And of course radiators aren't going to work in orbit. But the bigger question is why you couldn't just accelerate to orbital velocity within the atmosphere. Normal SCRAMJETs are next to impossible at that speed, but the only issue antimatter has is where the stuff will first hit matter. Edit: please don't make a Convert-o-tron that produces energy. It really needs to require (at least) 2mc2 energy per "m" of antimatter produced. Violating the conservation of energy makes Harry Potter look like hard sci-fi.
  13. More like (low) 4 digit Isp for orbital insertion while in vacuum, assuming you are just heating up liquid hydrogen and spitting it out like a nuclear thermal rocket. You won't need to cool a reactor, but you still need to keep the throat/nozzle from melting and that keeps the exhaust temperature not much higher than the SSMEs (which was mostly water, so it had a much lower Ve). If you don't need that type of thrust (you aren't in danger of falling back into a gravity well), you can probably easily hit 5 digit Isp (just don't expect to get 1g burns to generate that nice artificial gravity). But yeah. Torchship. If you are using arbitrarily small antimatter explosions, why bother with heated chemicals? While you might have a pusher plate you still want to have the thing run in thousands of bombs per second (possibly higher. But even then I doubt you could hide the noise). But launching/landing would still almost certainly use antimatter SCRAMJETS. I'd assume that an Orion would never attempt to land, and that antimatter SCRAMJETS would be used on shuttles to/from the Orion. Hoverslamming a SCRAMJET is an exersize for the reader, so I suspect that such craft would include Shuttle-like wings (I hate the shuttle's wings, but antimatter fixes virtually all rocket issues).
  14. Why do you care about antimatter scaling? With fission bombs you need at least critical mass, so mass efficiency scales up sharply after some minimum critical mass and eventually falls down as the bomb simply blows itself faster than it can split more nuclei. Antimatter doesn't care about scaling: you throw "m" amount of antimatter in a non-vacuum chamber and you get 2mc2 energy. You might as well make a simple rocket (assuming that you can evenly stream antimatter out of your containment device. But I can't imagine the containment device is remotely more difficult/complicated than accumulating the anti-matter. There's no need for (low frequency) pulsed rocketry with antimatter. If the blast emits radioactive fallout (like Orion) it makes a lot of sense to launch from Antarctica. Then PETA is likely more concerned with the penguins. But I doubt that Orion-like difficulties would happen with such a device.
  15. Nobody seems interested in scaling up current ion engines. I really haven't looked into deeply the issues of why, but field strength and density (especially density) play a huge part. Lab facility sized fusion will likely be the minimum size for fusion plants for the duration of the century. And even then I'd suspect that they are using >1T fields (but probably still single digit). A great example is the worlds most "powerful sustained magnet" (45T). It is 32mm wide (the magnetic bore), requires 35 tons of plumbing, and 30MW of power to work(note that 33T of that isn't going through superconducting wires, probably the reason for a lot of the power and cooling). Not something I'd try to put into orbit. https://nationalmaglab.org/about/around-the-lab/meet-the-magnets/meet-the-45-tesla-hybrid-magnet
  16. From memory, aligning the iron atoms (in solids) gives you at most 1 Telsa of field (iron amplifying a magnetic field). I can't imagine a significant advantage in going to liquid. And while superconductors have specific magnetic field limits, they also have specific current limits as well. So if you need cheap or efficient magnetic fields you face stark limits as well while building a superconducting magnetic field. Note that I suspect that this is more "the future" than any massive magnetic field (outside of fusion reactors). Simply scale up your magnets to give you the force needed at reasonable fields and don't bother with multiple Tesla fields (some rare earth magnets go a bit higher than 1T, but not that much).
  17. Starship is still hoverslamming (probably more hover than slam in crewed flight). No tires needed. As far a I know, passenger jets are pretty much pushing the limit of tire technology (although such manufacturers are quite silent about anything in their field so who really knows what those limits might be).
  18. Media reports (so take with an appropriate salty lake) implied that the pusher is simply stronger than humans. Once the pilot and copilot were too tired from fighting the pusher, you get an abrupt dive when the pusher takes over. This is a massive economic/political can of worms. The key spec to the 737-MAX was that it "flew the same as a 737" and didn't require any additional training. Including such a "throttle/disconnect" is to put a lie to that spec and leave Boeing on the hook for all training of pilots for this "new" aircraft. They absolutely will do everything they can to keep that from happening. Which implies that there might be a problem with the 737MAX not acting similar to a "real" 737 since the engines are in the "wrong place". One thing that might not be clear is just how rigorous FAA-controlled software development is. As far as I know (which is out-of-date second-hand information), a coding error (to the spec) is next to impossible. Any software error almost has to be part of the specification which implies deep issues that will take a very long time to fix (if only due to all the regulation and testing, and when this is done in parallel to plane development it shouldn't create huge delays). Is it true that an actual coding bug would be a scandal on par with crashing two aircraft? My take is that it is likely not so difficult to adjust the MCAS to work correctly on the 737MAX (and include all the sensors by default). I'm guessing that the delay is that all such quickly implemented measures require significant (by a cost standpoint) levels of training for pilots. There's also the additional issue of just how much stink this has made and what it will take to get pilots (and passengers) to fly a 737MAX once the grounding has been lifted. But lack of any word of a fix strongly hints that Boeing isn't happy with potential fixes (although it may well be that while Boeing would happily leak such information against the FAA's whims, the FAA isn't in control of the grounding. China (and Europe) matter a lot more world-wide and few trust the FAA in this matter).
  19. They aren't the same at all, or at least Starship is not falling into the same traps. Shuttle: attached horizontally, wings for lift, re-enters nose-first (airplane style). External fuel tank, burns fuel (H2) from sea level. Starship: attached vertically, wings to maintain orientation, re-enters belly first (skydiver style). Internal fuel tank, burns fuel (CH4) from staging. The last bit might be seen as problematic depending on the cost of the fuel tank and how many missions you are flying. But wing mass was a huge part of shuttle's orbital mass issue (although the "return a keyhole from orbit" was probably the worst. And it looks like anything Starship can bring to orbit it can probably return), and presumably avoided on Starship. Also Starship won't be directly damaged by any debris from the booster stage (short of an explosion). Also the re-entry style should make for significant visual differences as Starship has a traditional (for rockets) pointy nosecone while Shuttle and X-37 have blunt noses. If and only if SpaceX decides to abandon the "skydiver" landing system (and possibly retrothrusting as well). And never mind the computers, think of the poor tire engineers.
  20. These equation are neatly solved without an atmosphere. With an atmosphere it essentially requires simulation and numerical methods. I'd simply use a stock "x m/s of delta-v needed to get through the atmosphere" and add it to the previously calculated values. There really isn't an end to the rabbit hole of aerodynamics.
  21. Any idea how much boiloff you get from just the LOX? I'm fairly surprised they didn't just go straight to hypergolics, but zero-boiloff for LOX probably isn't that hard (especially if the work for Weber is available).
  22. Improved metallurgy? Can you design ambidextrous scissors? I don't expect scissor design to change much.
  23. One thing to remember before talking about "space McDonalds" is that McDonalds has always been a real estate company with a side business of selling hamburgers on said real estate. I'm not sure what real estate in space they intend to monopolize.
  24. Do you really want to deal with SCUBA equipment all the time? Although I think breathable liquids exist, I doubt anyone has long term data on their use. I'm fairly surprised astronauts haven't taken to strapping on wings: I'm guessing that current spacecraft/spacestations are sufficiently small that simply grabbing a handle and pulling yourself is easier.
  25. Ions are the way to go if you want to break the rocket equation (you can bring temperature stable [non-boiloff] fuels via engines with four-digit ISPs). For lunar purposes, I'd assume that ions would be largely considered as practice for Mars and beyond, as it takes "a zillion days" to reach escape velocity (mostly spiraling out to the Moon and then using the Moon to switch to an elliptical "orbit" into escape velocity) then a similar amount of time to get where you are going as a chemical rocket. To get funding, anyone committed to a "Lunar Gateway Outpost" should accept that such a thing makes a lot more sense if it contains fuel delivered via ions. Just don't expect to launch an ion and get there before 2024, they are for more patient astronauts.
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