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sevenperforce

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Everything posted by sevenperforce

  1. This is an Earth SSTO, not a Kerbal SSTO. I know it's not easy.
  2. If you're building an SSTO spacecraft intended to make maximum use of air augmentation, using a single engine cluster from liftoff to orbit, what are some of the pros and cons of the best fuel combinations? The way I see it, fuel density is going to be fairly important because you want your SSTO to be fairly compact, and deep cryogens probably should be avoided to save tank weight because you can't drop the tanks. You'll also want something that can react at least a little with atmospheric air so that you can run fuel-rich from Mach 0.7 up to Mach 4 or so and get a little airbreathing assist. And you can't sacrifice too much ISP because air-augmentation is going to run out when your velocity equals your actual exhaust velocity, and at that point you're still depending on the same engine for orbital insertion. But if your primary working maas from launch to Mach 10+ is going to be diatomic nitrogen and diatomic oxygen, should you use a low-molecular weight fuel or something with really high heat capacity? Air augmentation is about delivering as much thermal energy to an airstream as possible, which is different from the usual vacuum rocket optimization parameters. What fuel will have optimal mixing in a duct? Would it be feasible/advantageous to use a triprop design, with a denser oxidizer for takeoff and max air augmentation and cryolox for the upper portion of the flight? Any thoughts/analysis would be appreciated.
  3. If I recall correctly, earth is just on the edge of being able to sustain a stable orbit in Jupiter's Trojan points. It would not be stable in Saturn's.
  4. In theory, a shield could be placed at the front of your projectile which ablated readily and shed gas in a sheath around your projectile to cancel compressive and form drag. If you don't want to bother with an engine to circularize, simply place a 10-mile-long space station in orbit with a large maglev track on it, then build an alectromagnetic launcher on the surface to fire your payload up and outside of the atmosphere such that it intersects the front of the space station as it passes overhead. Then the orbiting space station can maglev the projectile/payload up to orbital velocity.
  5. How large of a body could stably orbit the moon? The Russians had showy stuff like the first satellite and first manned mission, but the US was first to get some of the really technically important stuff like first EVA, first orbital rendezvous, and other stuff that set them up for the moon shot.
  6. Ah, yes, I forgot there were 12. Those robots weren't very anthropomorphic, but they were quite capable...I find it hard to believe they would not have been able to at least assess basic habitability.
  7. I only watched it once, but IIRC the explanation had something to do with how only very simple signals could be sent back through the wormhole. A probe wouldn't be able to send back a large data stream, and presumably they couldn't trust a probe to make a full evaluation of all the criteria for habitability and send back a yes/no signal. So they sacrificed three astronauts instead. Of course, the fact that they have artificially intelligent talking walking robots that could almost certainly make as good or better an assessment as a human kinda clashes with this explanation. Plus, they landed on all three worlds anyway, so what was the point?
  8. Exactly -- fewer failure modes, shorter turnaround time. I think this form factor can manage SSTO...it's got maximum internal volume, minimal ascent cross-section, and maximum re-entry cross-section. I don't like the idea of landing a crew module tail-first, which is why I had the notion for a tail-first suicide burn followed by a controlled nose-down to horizontal attitude on the forward SuperDraco-style thrusters. Extensible landing legs are all that would be required; once down, the ground crew can easily put wheels under the legs. A primary advantage of the forward removable crew module with really powerful thrusters is that it offers unparalleled abort capabilities. Catastrophic launch abort? No problem; the thrusters blast you away from the exploding orbiter and then land propulsively well clear of the fireball. Meteor or debris strike in orbit that renders the orbiter unsuitable for re-entry (e.g, Columbia scenario)? Again, no problem; the crew module can detach and re-enter alone, using its underbelly shielding to aerobrake (ablatively, but at this point reuse is no longer the main concern) and touch down again on its thrusters. And autonomous-return FH-style liquid-fueled boosters would be preferred to SRBs, but that's beside the point.
  9. With the high number of heat-resistant surfaces, re-entry should be easy. Yeah, it has a high aerodynamic load so that means heavier construction, but enhanced thrust should make up for it. Bigger wings for what? It's not a lifting body.
  10. Neutrons have a magnetic moment, so a rotating magnetic field can almost certainly be configured to align them. Deflection by the appropriate nuclei is close enough to reflection to work, I think.
  11. A vertical tail-first landing is inherently unstable and egress is made highly difficult, which is why I'm aiming for a horizontal-attitude tail-first landing. I didn't realize about the tank-switching thing...someone might need to design a constant-flow system. Anyway, let's see here...next-Gen Shuttle, Take II. Yes, it looks unlike anything we've ever launched. And it will definitely do SSTO. The engines (not shown) are linear aerospikes, mounted on the sidewalls of the center body and the inside of the cowlings. Main fuel tanks are held in the cowlings. The engines on the central body point down and back; the engines on the cowlings point up and back. There's an additional ring of aerospike engines around the inner cowling at the rear which point backward. Takeoff and landing are both in a horizontal attitude. The engines mounted on the central sidewalls fire at full throttle, pulling air down over the upper fuselage and mixing inside the cowling before being ejected downward through the bottom of the cowling. RCS thrusters at the front of the fuselage (also not shown) fire to compensate for the slight forward push, and the spaceship rises vertically. Once the ascent begins, the ship starts to nose up and all engines are ignited simultaneously. The engines on the bottom of the inner cowling suck air in from below and thrust it backward, while the engines on the upper sidewalls of the central body suck air in from above and thrust it backward. This produces a highly-compressed vortex flow through the two openings at the back. As the ship accelerates, ram effect begins to contribute, as shockwaves entering the cowling are focused, heated by the side-mounted engines, and ejected out the back in a ramrocket configuration. Due to the open cowling, the airflow is dramatically higher than for any ducted rocket ever conceived, allowing the craft to reach hypersonic speeds with only a fraction of the normal fuel costs. The transition to hypersonic speeds marks the end of air-augmented advantages, so this is timed to coincide with around 100 km of altitude. At this point, the side-mounted engines are throttled down to reduce acceleration and the rear engines provide the remaining orbital insertion burn. Re-entry is a dream due to the high number of surface areas with which to dissipate heat. The side-mounted thrusters fire on approach to kill terminal velocity and make a soft touchdown on extensible landing legs. For higher cargo requirements, launch can be vertically-positioned with strap-on boosters.
  12. What if you filled a cylinder with uranium, lithium, and deuterium, then spun it up centrifuge-style? The uranium would migrate outward and the lighter elements would migrate inward. Eventually, the uranium would reach a high enough density to go critical, producing radiation pressure on the lighter elements in the center, ultimately causing them to fuse. I think.
  13. The reason I was going to suggest the tail-first retro burn was because the main propulsive engines are going to do a massively better job of slowing the ship down than hypergolic RCS engines, and with a lower propellant weight cost. I am trying to hammer out a design for an air-augmented engine that would be able to use the same engines to thrust vertically as horizontally without vectoring. How is a drop-in fuel tank different from an internal fuel tank? And if I recall correctly, the Shuttle was retrofit to accommodate Shuttle-Centaur, not the other way around.
  14. Ah, I see. Well, in that case I like the self-pressurizing lithium-hydride-saltwater approach, with fuel fission. Or we could go for something more exotic...like a gas-core centrifugal self-pumping neutron laser. Talk about a torchship.... EDIT: Here's what I mean. The entire thing is made of a neutron-reflective material, except for the hole at one end, which is plugged with a neutron-transparent material. You pump it full of uranium in whatever gaseous state you can manage. The casing has a magnetic charge, so you can spin it up by simply applying an external field. Once it starts spinning fast enough (clockwise, mind you), the gaseous uranium reaches sufficient density in the deep outer channels to go critical. This produces heat and pressure in those channels, pushing them in the direction of rotation and accelerating the reaction. High-energy neutrons produced by the reaction are aligned by the internal magnetic field of the rotating centrifuge and either bounce off the reflector at one end or pass through the neutron-transparent plug at the other end to escape. Effective exhaust velocity: 20,000 km/s.
  15. It seemed to be suggested that the Hermes lacked any further maneuvering fuel and would not be able to successfully return to Earth if it burned any more propellant.
  16. Supersonic retrop prop at what point in the sequence? I was thinking basically SuperDracos for hypergolic OMS/RCS. Docking port not illustrated; probably on top of the crew cabin or something. The reason I was going to have a separate cargo bay was to allow for Shuttle-like operation in the specific cases where it would be needed -- for example, if you need to deliver a payload along with the crew members to install/operate it, or if you are doing a moon landing and need to bring along time-sensitive cargo. Of course, you'd need to have quite a few strap-on boosters in those cases, but that's part of the plan anyway. You couldn't really put a payload fairing at the top per se. You'd need to replace the entire crew cabin with a payload module that would open to release the payload and then self-seal to protect the rest of the orbiter during re-entry. That puts tighter constraints on your payload dimensions than an internal centrally-located cargo bay. Fitting an entire rocket upper stage with its payload into the cargo bay of the Shuttle was a bad idea, I agree, but a drop-in fuel tank could be specifically designed for the orbiter without much difficulty, I think. And why would adding an external back-mounted tank be a problem if the engines can handle lifting it? The Shuttle's external tank fed through the heat shields.
  17. What about using something like ethane as the working fluid? Liquid at room temperature, plenty of hydrogen, not too much carbon.
  18. 53 tonnes to LEO, 20 tonnes to GTO, 16 tonnes to LLO, and 8 tonnes to LMO. If I remember correctly. Although those numbers are based on a Falcon Heavy comprising three Falcon 9v1.1 boosters rather then the larger, enhanced Full Thrust version. And whether the boosters are reused or not also factors in. Odd, it does, although I had never seen those before. I chose that shape because I wanted to maximize internal volume and re-entry cross-section but also maintain a small ascent cross-section to avoid excessive drag and aerodynamic loading. I also wanted the option of a crew module with the same basic shape for launch abort reasons. I need to run the numbers to see how close to SSTO this would get in its various configurations. Yeah, I mentioned above that the RCS/OMS system is based on a hypergolic SuperDraco-style engine. You're right, though; linear aerospike engines can be used quite easily for pitch control during ascent but a horizontally-oriented vertical landing would probably be asking too much. And gimballing conventional engines by 90 degrees is out of the question. I am just wary of the weight cost of adding more thrusters for landing alone. I have a design knocking around in my head that would allow the ascent engines to be used for horizontally-oriented takeoff and landing, which is pretty much the ultimate spaceship fantasy, but it is air-augmented. Heh. I'll run the numbers on that too, just for kicks. Using a HLV for crew transport is a pretty big waste, I agree, but using completely separate systems instead of recombining components to fit each individual mission is a big waste as well. That's why I rather like the idea of a cargo shuttle with a removable crew module, so it can take crew up SSTO by putting an internal tank in its payload bay OR be configured for heavy lift by swapping out the crew module for additional tankage and slapping on some reusable boosters.
  19. Errrr...why? Assuming that we're thinking about the same engine, there's no need to capture the exhaust. Irradiated hydrogen is not dangerous. An NSWR, on the other hand, is just about impossible to test. I'm still curious to know whether the uranium-core, lithium-hydride-propellant NTR would be feasible. To the fissile/fissionable question: fissionable material is stuff like depleted uranium; fissile material is stuff like enriched uranium. Fissile material can form a critical mass; fissionable material cannot. They made bomb tampers out of non-fissile but still-fissionable material because that was a good way to increase yield without requiring more costly and dangerous fissile mass. Even though the non-fissile tamper could not go critical on its own, the neutron flux from the fissile core going critical would trigger fission in the tamper, dramatically boosting yield. This was most commonly used with thermonuclear weapons, and allowed the same basic primary and secondary to allow for a large range of variable yields based on tamper material. All this is moot, of course, because I'm pretty sure there has never been a treaty about forbidding fissile or fissionable material in space; just a treaty banning nuclear weapons in space.
  20. If you really want a replacement for the Shuttle, something that can put payloads into space regularly and be completely reusable...well, here you go. 41 meters high, 20 meters wide, 10 meters deep. Payload bay is the same size as the Shuttle Orbiter's, but the lack of control surfaces allows surrounding space to be used for additional fuel. The engine is a truncated aerospike: The high-thrust aerospike engines provide optimal thrust and Isp respective to altitude. Optional/detachable cabin: The crew cabin module has about half as much space as the Shuttle Orbiter but three times the space of the Dragon V2. It fits into the main body and is equipped with multiple high-thrust hypergolic engines which also act as the OMS and RCS system. These allow the crew cabin to eject during launch abort. For crew transfer only, the payload bay is fitted with an additional internal tank and a disposable strap-on tank, allowing SSTO with the loss of the external tank alone. For unmanned flights, the crew cabin module is replaced with an autonomous control module with an auxiliary fuel tank but the same hypergolic engines. For manned flights including payload, or for higher-dV unmanned missions, 2-4 strap-on FH-style boosters are attached with propellant crossfeed; these detach at fairly low speed to return autonomously. Re-entry will be...exciting. The aerospike already has to be able to handle very high heat fluxes and will probably already be actively cooled, so the orbiter enters tail-first and upside down to burn off most of its speed, with active use of the RCS system for stabilization. As soon as enough speed has dropped off, the orbiter begins to rotate forward, exposing more and more of its underside. The lower speed at this point means that the heat shield on its underside can be constructed of a lightweight, non-ablative, lower-performing, highly reusable material rather than requiring the tiles that the Shuttle used. Active RCS stabilization continues as speed decreases, ultimately entering a low-L/D gliding flight: The orbiter does not make a very good glider and cannot manage a level approach, which is all the better because it doesn't have heavy landing gear. Instead, the RCS system returns the craft to a high angle of attack, and the aerospike engines are ignited, killing terminal velocity in a near-suicide burn. Then, the RCS system reduces power, allowing the angle of attack to drop until the orbiter is horizontal, and both the RCS system and the aerospike engines in combination fire to lower the orbiter to the ground: If the aerospike cannot be directed downward enough to execute such a landing, then additional RCS thrusters can be incorporated in the aft portion of the orbiter. Ambitious? Perhaps...but it seems like the best possible combination of geometry to allow for the capabilities of the shuttle with next-generation technology. The amount of hypergolic fuel, internal fuel, and the number of strap-on boosters can be adapted to each mission. By using in-orbit staging and/or refueling, the orbiter could easily manage a lunar transfer. Depending on the fuel capacity of the crew cabin, it could manage a landing on its own on hypergolics, or lunar-orbit refueling could allow the entire orbiter to make the descent to the lunar surface and return to refuel and make the transfer to LEO again. The ability to take off and land vertically in a horizontal attitude reduces the instabilities and risks of vertical landings and allows far simpler crew egress.
  21. Dang. Even with autonomous "catch", atmospheric rendezvous seems like a logistics nightmare.
  22. Well, I guess it comes down to the math at some point. Given a core hab large enough for interplanetary transfers with ntr engines, does it cost more to bring a separate lander with a separate hab and a separate engine and separate tankage sufficient for powered descent and ascent, or to just strengthen your landing legs and bring along extra fuel? The other option, I suppose, is something like Interstellar's lander that docks into the hab and provides it with propulsion, etc.
  23. I don't much like the idea of ejecting engines and tossing them and hoping they land someplace that's not too dangerous. Is it feasible to equip them with an expandable heat shield large enough to double as parachute/impact cushion? I suppose if you're already in orbit it costs only very negligible dv to aim for a particular region, but that's not exactly a recipe for pinpoint accuracy, and landing is going to be a major shock. I'm a little curious about the feasibility of using a non-cylindrical reusable single stage with two or maybe four strap-on boosters and propellant crossfeed. Something fairly alien in appearance, like an isoceles-triangular hyperboloid lifting body with an elliptic cross-section. The boosters would all strap on to one side, perhaps with a gap in between them for a raised payload bay. Double linear aerospike on the orbiter, but running the same fuel as the boosters, obviously. If you really wanted to get creative, it could even glide in to kill velocity and then descend vertically on overengineered SuperDraco OMS engines. That way you don't have to directly factor in extra weight for landing gear or wings, but you still get the advantage of gliding return, lowered terminal velocity, and propulsive landing. Even better, you land in a horizontal attitude. I'll see about doing a mockup tomorrow. And the bit about spacecraft vs spaceships was a bit of hyperbole on my part.
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