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Everything posted by sevenperforce

  1. Multimodal nuclear engines are a pretty good deal, actually. The coolant loops you already need in order to run safely as a nuclear thermal rocket can be repurposed to provide electricity without much additional weight.
  2. Nuclear engines are mostly a problem for takeoff from Earth. Expelling radioactive propellant into the atmosphere, even if it is nearly harmless, isn't something people are happy about. For interplanetary transfers, or for landing on other worlds, people won't care as much about the use of nuclear engines. The average layperson wouldn't have the first clue about the difference between an NTR and an RTG. Also, launches from Earth wouldn't be very common. This is, after all, a long-term, extended-persistence interplanetary transfer vehicle capable of supporting a large crew for a long time. The initial launch would be followed by a series of missions to other worlds, returning to low Earth orbit to refuel and take on more supplies, but "dry dock" on earth wouldn't happen very often. Much easier to treat the ship like an orbiting space station and simply ferry up and down using capsules. It would definitely be more economical to refuel, even using inefficient chemical rockets, because this contains its own engines, tankage, and hab. This ship would be able to support a large crew for a long time, drop them on another planet, and then come back. Hard to beat that. Another option (not pictured) would be to attach a cluster of ion engines with their own fuel tanks, either passing through the open center of the ship or in a toroidal ring mated underneath. The ion engines would run off the nuclear reactors, which would continuously expel small amounts of coolant in order to keep from overheating. The internal fuel tanks would still end up partially depleted by the end of the burn, since the reactors would be using propellant as their coolant, but you could develop an extremely high delta V. This eliminates some of the major problems with using ion engines for interplanetary transfer (the high power requirements of ion engines typically result in either extremely low thrust, extremely large solar panels, or extremely large radiators and coolant loops with nuclear-thermal designs). Plus, you arrive with enough propellant to still use your engines the normal way. In theory, this ship could mate to any number of additional cargo containers, pods, or fuel reserves. Big, overpowered engines are a large initial investment, but they pay great dividends. Especially because a moon shot ends up being as simple as flying to the moon, landing, taking off, and coming back.
  3. Obviously the radshield is also the aerobrake heatshield.... =P
  4. Not superluminal, but damn if it ain't pretty. Of course I'm always also a sucker for the fastest ship in the 'verse.
  5. You can equip the ancient civilization with whatever industries are necessary in order to build the rocket, but you only have your own lifetime to do it in. Which means you'll need to limit yourself to stuff which can be done rapidly, without a lot of precursors and development and construction time. Basically stuff where manpower is your limiting variable...because that's where ancient civilizations have the edge.
  6. Errr...yes. The fuel tanks serve as the shielding; when the fuel tanks are depleted, shielding isn't as great, which is why you definitely want to refuel quickly. But it wouldn't be too bad; you could always enter a portion of the ship with additional shielding temporarily. See below -- I linked a mockup. Well, speak of the devil....
  7. If you're going to build an actual spaceship -- a craft you can take to another planet as easily as a pirate could sail across the Mediterranean -- there are a few things to keep in mind. Gravity. You're going to need artificial gravity if you want to be able to manage long trips, so you'll need to either have a spinning hab, or you'll need to spin the whole ship. Power. You need high-thrust engines to get on and off of planets, high-impulse engines to make your transfer burns propellant-efficient, and energy to run your ship in transit. Trimodal nuclear thermal engines are your only real choice (a trimodal NTR has three modes: high-impulse, where low-density propellant is heated and ejected by the nuclear core, high-thrust, where LOX is injected into the propellant stream to increase thrust at the expense of impulse, and thermal-electric, where the circulation of coolant generates electricity). Shielding. Your hab needs to be shielded from both solar radiation and the nuclear radiation of your engine(s). Volume. You need a large internal volume to carry an enormous amount of fuel if you're going to be able to make a transfer, land, take off again, and head back. Granted, you'd use in-orbit refueling wherever possible, but you need the flexibility to make a round-trip to unvisited worlds. Surface area. Although you need a large volume, you also need a form factor with a blunt-body surface area, allowing re-entry heating to be as minimal as possible. Further, large surface area will help with radiating heat away in space. Finally, a lifting-body shape will make launch and re-entry a bit nicer. What, then, is the optimal shape and configuration? Here you go. Yep, it's a flying saucer. The hab is located in the center column and is a single floor, preventing any unpleasant gravity gradients. Because the center is open, it allows windows to be embedded in the ceiling, which will feel more natural. The hab is far more "open" overall than most designs, while still being well-protected from radiation and micrometeoroid strikes due to its location in the center of the ship. It will feel very natural to have the sky "up" and the ground "down". The hab is shielded by wrapping the ship's tankage completely around it. The triangular cross-section maximizes internal volume while also having the optimal shielding profile. Obviously, the entire ship rotates. The ship is powered by six small nuclear reactors, feeding three linear exhaust nozzles: Each of the three exhaust nozzles is capable of running on a single reactor, so you still have maneuverability even if you need to scram one or two of your reactors. The coolant cyclers and generators are also in this area. Only minimal shielding is necessary, due to the placement of the large internal tanks. For on-orbit burns, the three nozzles all fire together, providing moderate thrust even at the highest operating impulse: During any such burn, there will be a slight misalignment of the apparent gravitational field, but it will likely be no more disorienting than standing on a train while it starts to move. It is also likely that in most cases, the ship will only "spin up" after its transfer injection burns, relieving this issue entirely. Takeoff and landing use the same orientation as on-orbit burns, but with the injection of liquid hydrogen or another oxidizer to dramatically increase thrust at the expense of specific impulse: During takeoff, however, maintaining this thrust orientation would make drag losses altogether unmanageable. For this reason, the nozzles are able to change orientation in order to thrust backward during in-atmosphere climbs (for reaching orbit from Terra, Mars, etc.): Because the "flying saucer" shape is one of the only shapes which is capable of achieving reasonable lift in subsonic, supersonic, and hypersonic flight, this allows for the higher-specific-impulse burn to be used (when applicable) to achieve orbital velocities. Obviously, on worlds without atmospheres, liftoff would be purely vertical without any intermediate horizontally-oriented burn stage. Re-entry uses the large blunt surface area underneath to dissipate heat passively (although active cooling could be used, in principle): Passengers are seated in the upper ring during takeoff and landing, both for gravitational orientation and for safety reasons. Launch abort escape would be achieved either through individual ejection seats or through the ejection of the entire upper ring using built-in thrusters. It is possible that the upper ring could also be configured to serve as an ejectable lifeboat in the case of an on-orbit accident. \ Attitude control could be achieved either by vectoring the thrusters, or by venting coolant. Placing the heavy engines at the outside isn't ideal, but given that this is going to be designed with enough structural integrity for powered landing, it shouldn't prove too problematic. The hab would have nearly 8500 square feet of floor space under artificial gravity, with more than 30 times the pressurized volume of the Space Shuttle crew cabin. I'm estimating a nominal dry weight of 1200 tonnes. The body encloses enough space for 9800 cubic meters of tankage; using a dense propellant like hydrazine, this corresponds to 9,900 metric tonnes of fuel. With pebble-bed reactors giving a specific impulse of around 520 seconds, you get a lovely 11 km/s of dV. Enough to reach orbit as SSTO (if you use LOX-injection augmentation). Also enough to fly to the moon, land, take off, and come back. Now to build the damn thing...
  8. Well, the heat from the hab can be eliminated by depressurizing the tankage; no heat sink without a heat transfer medium. And you'd probably want to use something with better boil-off properties, like hydrazine or ammonia or liquid methane (if you can get the latter two to disassociate). Trimodal engines inject LOX just after the chokepoint to augment thrust at the expense of specific impulse; you'd use these for takeoff and then refuel with something lower-density for orbital transfer.
  9. What kind of ISP could a dry ice cannon develop, theoretically? Would it be able to use a converging/diverging nozzle and achieve supersonic exhaust velocities? A high-thrust design would be set up so that the hot water was also the propellant. I was originally thinking specifically of chemical rockets based on combustion rather than something like phase change, but this is quite interesting.
  10. Unless, of course, you can use the negative mass ring to generate artificial gravity.
  11. You almost want to stick with fins for guidance and merely put two fused RCS rockets in the nose to knock it into a gravity turn and then into a circularization burn.
  12. Oh, the taper on the casing must have worked well. I made nice little legs for my Bic rocket but it didn't ever develop thrust.... I would add "must be a chemical rocket" just to make things exciting.
  13. Alright, here's an idea for you. Using only items you have in your home right now, try to build a rocket capable of lifting off vertically under its own power. If you happen to have actual rocket parts laying around, you cannot use them. Improvisation only. Now, if you aren't at home, or don't feel like building it, you could also suggest plans for how to go about building it, using what you know you have at home. I tried the other day, using a pen, the pen cap for a diverging nozzle, and hairspray. Either the rocket was to fuel rich or the choke point was too large, because it burned merrily until the whole thing melted, but never budged.
  14. Indeed. Honestly the scholars and alchemists and astronomers are only going to get in your way. I would recommend going straight to the military-industrial complex of the day. "Screw those nerds; give me three legions and let's build a gorram starboat!"
  15. Yeah, launch would be tricky. Come to think of it, simply wrapping the tank all the way around a central hab and making the whole thing hella large, with the tank following a triangular contour to serve as a radshield, would probably be a better idea. Make the whole thing a flying saucer with a hole in the center. Probably the best way to get a really insanely high tankage volume while still having a decent aerodynamic cross-section. If you could get people past their insane fear of all things nuclear, then it could launch under its own power, though it would need to be refueled as soon as it reached orbit.
  16. Yeah, the chemistry is very much going to be a case of going a long way from really basic raw materials.
  17. How do we not have materials of known quality available? We know where stuff was mined.
  18. I'm not saying it wouldn't be a large undertaking, only that the necessary information would all be provided at the outset.
  19. Indeed, but I'm not sure how one couldn't compensate for this by going back in time with an iPad full of everything we know about practical metallurgy.
  20. A very good point. Well, yes, you can take back a chemist/chemical engineer in the form of an iPad and a solar-powered charger, with all the chemical engineering information you could ever want. I hadn't considered Nordic countries...did they have enough manpower? The thing that worries me about spin stabilization is the issue of tolerances. If you're going to spin-stabilize, you need near-perfect radial axisymmetry. That was easy with Vanguard, but since we're going to be nailing together potentially-uneven sheets of primitive steel, spin stabilization could cause it to rip itself apart pretty quickly. Compressed-air nose thrusters coupled to a gyroscope using permanent-magnetic couplings could probably do the trick. Yeah, turbopumps are going to be a non-starter at pretty much any point in antiquity. I wonder if a ceramic exhaust bell might work...or perhaps a steel exhaust bell with an inner ceramic coating/plate.
  21. For a large, extended-persistence interplanetary transport capable of making transfers to multiple worlds, I think you need to account for the possibility of landing...if not on a large world, then at least on smaller moons. So you would want to have your engines passing through your center of mass. I like this layout: The habitable portion of the ship is a central rounded cylinder, surrounded by a circumferential fuel tank to provide general radiation shielding. The ship has two wings, each containing very large tank reservoirs. They serve as shields for the reactors. It has two bimodal or trimodal reactors, one on each wingtip, along with the main NTR thrusters which can be rotated. To provide artificial gravity, the thrusters are pointed in opposite directions (one up, one down) and fired, causing the entire ship to rotate.
  22. I wouldn't be so sure about selling genetic modification short. Granted, gene modification is not as simple as dial-a-microbe, but it is pretty powerful. It's powerful because the range of extreme conditions under which how "wild" bacteria can survive is simply huge. Besides, you can splice genes in from different kingdoms, or create genetically modified fungi, or certain types of algae, or any other range of possible creatures. Earth's biodiversity is just simply gigantic as it is. All you really need is to identify one biologically-active potential reaction, and then you can combine different species or even different kingdoms to create the chain you want. I'm thinking of something like a symbiotic yeast-bacteria colony...
  23. Extending the nautical comparison...everything we have built so far has basically been a collection of rafts. The space station is essentially a bunch of rafts chained together just off the shoreline. The Shuttle, I suppose, qualifies as more than a raft. Maybe it is the counterpart to a small Coast Guard patrol boat? This is true. Which is why building something that can actually qualify as a spaceship would be cool. Perhaps a spaceship is something that can move under its own power and host permanent occupants?
  24. Then again, if you just spam people toward Mars, you end up with an obligation to support them, which will get the job done faster.
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