wumpus

[quote name='Shpaget']If it's a physically large bow, it doesn't need to be particularly strong. [/QUOTE] I've never heard of a bow too long to hold, but it should work if you allow the entire thing to pivot (preferably past the point the arrow stops accelerating). I'd only expect to see such a thing in a caste (presumably permanently attached to a murder hole), but I've never heard of such a thing. Any clues to the existence of one?

[quote name='Shpaget']This: [URL]https://www.youtube.com/watch?v=BLuI118nhzc[/URL][/QUOTE] Just how many pound draw do you need to fire an arrow at orbital velocity? You aren't going to hit the Earth from ISS with any bow pulled by mortal man (ignoring slow, slow air resistance).

V2s (and many sounding rockets) made propulsive landings. Ok, maybe they relied almost entirely on lithobraking (except for the V2s in London, which used explosive braking). Come to think of it, did any V2s use air bursts? That presumably involved considerable braking (followed obviously by considerable breaking of both the rocket and parts of London).

DeltaV is a measurement of an entire rocket (boosters and payload). You can't claim the human is just the fuel and work out deltaV from that. You can say that a [highly skilled athlete] can get to 4 m/s by jumping. Or you can build a "rocket" that would be the equivalent of a command chair and ion thruster. You could then work out how much deltaV the human could produce if all the electricity for the ion thruster can from a "command chair" with "spinning class" cycle wheel used to generate electricity. The big catch is that you still need to define when the human stops. Max output in a single day? Max output without additional feeding (cut the xenon, you won't need much)? DeltaV just doesn't work well for this type of thing. With enough food, water, and air the limits become the life support and xenon supplies, not the human (well there is the lifespan). Stop watching the Matrix. That was dumb and you should forget it.

[quote name='Aghanim']I But good luck have fun printing the wires and the power IGBTs necessary to drive it[/QUOTE] But you would still needs IGBTs and wires for a brushless. And induction is typically preferred for cars anyway (I still think a large brushless in the rear and an induction up front makes more sense).

retracted and redundant.

[quote name='Nibb31']How exactly do you print bearings, copper coils and rare earth magnets?[/QUOTE] [N.B. I never suggested printing electric motors, nor expect any printer being designed now to use such a method.] The coils would presumably be constructed the way any other printed circuit board (or flexstrip*, which would make much more sense). Presumably, at some point we will need pick and place machines on (super high end) 3d printers. Printing some of the bearing track, polishing some of the bearing track, adding the bearings, and then closing the bearing track might make sense [note: I am an EE. I have absolutely no idea how much a problem the unpolished part of the track would be. I fully understand it could kill the whole point of having a bearing. On a similar note, the idea of building a robotic arm capable of picking up a rare-earth magnet just boggles the mind (extra fields in your motors/servos. Noise as all your lines move through its B-field. How hard could it be?). Can you "3d print" ceramics? After seeing a story about fusion reactors using high temperature super conductors** (values of high meaning liquid nitrogen), I was wondering if you could whip up a motor based on "doping" a chemically appropriate ceramic cylinder with lines of superconductors (much like a silicon chip is "doped"). My guess is that this can only be considered "printing" in the same way an Intel i7 is "printed" by Intel, but it would still be infinitely cool (or at least LN2 cool). * Engineer has a problem connecting two boards/components. Engineer uses flexstrip. Engineer has two problems. ** [URL]http://spectrum.ieee.org/energy/nuclear/three-alternative-fusion-projects-that-are-making-progress[/URL]

[quote name='adsii1970']I read somewhere that NASA/JPL had done a feasibility study and decided that in the event of a catastrophic failure, the goal would be to dock with the ISS, use a Soyuz capsule for extraction of critically injured crew, but jettison the orbiter and allow gravity to run its course. [/QUOTE] I'm pretty sure that the inclination of the last Columbia flight wasn't anywhere near the ISS*. There was simply no way to get there. I also didn't seriously expect NASA to have a rescue shuttle ready. I was merely pointing out that once they had a ballpark figure of the cost the whole idea would be abandoned (especially since the first failure had no chance of rescue, they probably assumed the next wouldn't either). source - Strictly from my own lousy memory, an aside of one of Scott Manley's videos.

Less morbid answer. KE=1/2(mv**2) PE=mgv so KE at launch (the delta-V) is entirely converted to PE at apogee 1/2(mv[SUP]2[/SUP])=mgh v[SUP]2[/SUP]=2gh delta-v=square_root(2gh) so for a 1m vertical leap (serious jumpers like Micheal Jordan or Karch Kiraly in their primes. And for all I know they might still pull close to that off). delta-v=root(2*9.8)=~4.4m/s

Wouldn't a better comparison be Space Ship One? They not only landed a rocket that went into space, but to get the X-prize they had to: Do it manned. Do it twice (with a quick turnaround). Do it completely commercial (of course, so did Blue Origin).

[quote name='adsii1970']There's another important lesson here. NASA knew from nearly the beginning of the STS program that the falling insulation posed a considerable risk to the leading edge of the shuttle's wings. [/QUOTE] Two question about this whole debacle: Is there any mention about the cost of having an entire shuttle "gassed up and ready to go"? You don't (I hope) have to perform all the maintanence (pretty much a full shuttle rebuild) of a launch, but all the costs involved in a launch need to be paid (i.e. all operations required from sticking the shuttle on the pad to T-3 days). If you look at the economics behind the falcon, you will note a huge cost not involving the cost of the rocket: my guess is that a shuttle on the pad would eat most of those costs (at shuttle prices). Isn't the whole issue with heating tiles peculiar to the Columbia? My understanding was that was why it was "retired" in the first place. Columbia required reseating huge amounts of tiles every flight, while Challenger and later units had a solid heat shield. Simply protecting for this one narrow failure would likely leave way too many dangers for the shuttle fleet (a handy shuttle certainly wouldn't have helped Challenger).

The most obvious difference is that the fletchings won't work in space (i.e. the vacuum outside a spaceship, but the would work in the ISS). Expect the arrow to tumble while maintaining the exact trajectory it launched with. Second, the longer the range the weirder it gets: Point blank range: no change (but don't expect it to penetrate any target due to the tumbling effect). Normal range: Your "archery" isn't arching. No matter what the range (ignoring curvature of orbit), you are still at point blank. Orbital range: your trajectory is supposed to be heading out to a different orbit and will return (more or less) after every orbit. The return point should move further and further behind due to the slightly longer orbit. I suspect that air resistance on something as light as an arrow would have a greater effect, but have no idea how to calculate that.

Don't Soyuz capsules contain a shotgun? "Slug throwers" still tend to be ideal, especially if mass needs to be considered and siberian brown bears tend to be in the landing zones.

[quote name='Jovus']Not gonna happen. It's even less economically feasible now than it was the first time.[/QUOTE] That implies that ~20 passengers now don't have as much money as ~100 passengers of the 1960s-1990s. A completely unbelievable idea. Look at the market for yachts. While they lose to yachts by the complete failure of being practical, they win by being very, very, fast and very, very, expensive. Actually, what boggles my mind is that the rich haven't abandoned fancy cars en masse and moved to aircraft. Probably too much trouble to learn to fly.

You would probably need much better computer assistance than presently available. You would have to align everything exactly right just before the moment of docking, then dock. Every additional attempt would require the same docking pattern (no "just keep getting closer"). It could be done, but the timing requirements would be difficult. If you can dock Abyssal Lurker style (feet only, or spacebar only), you can likely dock on an outer wheel. I can't.

We call the coelacanth a "living fossil" even though it has been subject to as much evolutionary pressure as anything else (don't check whatever the coelacanth equivalent to an immune system is). It might not be too odd to call a small hominid population a relic when compared to an ~8,000,000,000 sized population. As far as I know, there is only one sample of [COLOR=#333333]Homo floresiensis known. It is pretty much impossible to know that until you find enough samples in one place.[/COLOR]

The ability to produce prototypes, update, and produce another is astonishing. The ability to produce molds for "real production" is probably the biggest draw. There is also the idea of printing connectors for off the shelf carbon fiber (or composite, fiberglass, or even PVC) tubes. Here is a similar link for "printing" the custom parts for a titanium bicycle (read: thousands of dollars) with a few grams of custom parts: [URL]http://www.bicycles.net.au/2014/08/future-3d-print-own-titanium-bicycle/[/URL] Note that it might even work better to 3d print the connectors onto the tubes instead of connecting three or more connectors and welding them in place. Obviously once you get about half your tubes together, you can't fit more than one tube into each connector once it is in place. Don't expect much of a revolution from just this. You have been able to buy a custom welded aluminum frame such as above, complete with some sort of body for less than the price of a car (assembly of the whole thing extra$$$): google "kit cars" for examples. It [I]might [/I]be possible to build a strong frame this way, then print some sort of skeleton that fitted to the frame to support the "body" (as seen by outside people) presumably directly connecting some sort of cut flatish off the shelf composite panel for the body. 3D printing would be most important for the iterated design needed to find a way to get the whole thing to work together, then presumably for the molds that hold the off the shelf parts together. A more interesting idea is a "rapid prototyped/manufactured" airplane. You can buy cars and bikes relatively cheap. Airplanes are another story. There are additional advantages to competent mechanics without the proper (A&R?) licensing: apparently the "manufacturer" can perform maintenance on the aircraft with significantly less paperwork/licenses*. This changes the costs considerably. * I am not a lawyer and this is not legal advice.

[quote name='ZooNamedGames']He's referring to stock... [/QUOTE] Yes, but since the first page covered how to fix his shuttle (do what both the actual* shuttle did and get pulled into space by the SRBs). And I'm still impressed by how big an issue that scaling Kerbin down by a factor of 10 really is (and how Squad makes it seamless). I figured they left out an obvious fix for jets/turbofans (other than the issue of being ripped to shreds once they exceed maximum air velocity), because spaceplanes are cool and fun to make, but the problems appear deeper than that. The answer why *stock* KSP makes it easier to fly spaceplanes than shuttles is that jet engines can reach nearly orbital velocity on Kerbin, but not Earth. The reason that jet engines are not scaled down is that they would need to be scaled down by a factor of 10 or so, and then wouldn't lift off at all (I'm assuming that the throttle is linear to thrust: swapping weasly for jumbo jets on the mallard *just* barely got the plane off the runway, but left me scrambling for every m/s for the next several kms, and never seemed to get above 100m/s *or* 50m of altitude). The scaling KSP uses to make orbiting easier and faster has some weird side effects, and one of them is that spaceplanes are easy. Shuttles, on the other hand don't make much more sense on Kerbin than they did on Earth (even though refurbishing the whole thing isn't required). Why a factor of 10? My understanding is that air resistance at minimal speeds is linear. Once you hit turbulence (bicycle speeds) it goes quadratic. Over the speed of sound it goes to cubic powers. So to halve the speed you need to lower the power by a factor of eight (rounded to 10, and half probably isn't nearly enough). While this is suspiciously similar to horsepower vs. speed on wheels, it gets there by different means. * For Soviet values of shuttle, I think it was hauled into space by liquid boosters. The shuttle's on-board engines (presumably had some if only for circularization), were even less important.

Just out of curiousity, how familiar is the OP with E.E."doc" Smith? Did the "doc" qualify? Can OP write better space opera than "doc"? Then there is the simple existence issue with space opera. How can it exist in a world where relativity holds (bonus points for allowing both faster than C travel and causality violations which means Trek passes...)? How does a ship limited by current means and the rocket equation have a prayer of interstellar (pretty much a requirement of space opera) travel. Not "space opera", but questionable licensing: Gravity: Fail. Haven't seen it, but the failures should be obvious before loading KSP. Interstellar: Passes basic KSP knowledge, but anyone familiar with the gravity needed for that type of time dilation (presumably including Scott Manley, but not me) can point out that the delta-V approaches infinity. The Martian: Pass? Need to see it, but haven't heard any failures.

If the "problem" is that Shuttles are harder than spaceplanes (or at least jet-based SSTOs), then the "solution" is to download the real solar system mod[collection]/overhaul. You can find all sorts of reasons why the shuttle was a bad idea over in the science forums, but the reason that there aren't a lot of spaceplane SSTOs on Earth is that Kerbin has an orbital velocity close to the speed jet engines can produce. Earth's is waaaay more than that.

[quote name='I_Killed_Jeb']the main issue with a wright flyer replica is that it flew by wing warping, not ailerons, so we can never make a true replica =([/QUOTE] That and as roarke points out, it needed a 25mph headwind or so to take off. One way to "cheat" is to use a much longer rail: since the Flyer was only powered by propeller, it would eventually make up the 25mph difference (although I have no data on the friction of the rail. The Flyer had quite a bit more power than they thought they needed, so there is a good chance to overcome that friction).

[quote name='K^2']You do realize that people who have made that site have already made an image version of it, right?[/QUOTE] Depends. Do you mean they decode the image for you or you simply feed the random number generator to your image browser. If the later, you could claim they already have a movie version as well. We had a movie version in the twentieth century. We called it "static" and sometimes saw it on TV. You might still hear the audio parts sometime.

[quote name='Armchair Rocket Scientist']Is there ANY jurisdiction where jet or rocket engines are street legal? I think a few people have built pulsejet vehicles, but they're generally either something small like a shopping cart or they only actually run the jets at a track. The noise generated by running a jet engine on a public road might well incapacitate other drivers. But yeah, think about how road-worthy a top fuel dragster is. This vehicle is less useful in every way. I should qualify that: I mean impractical for the application the articles say it's meant for. A rocket-powered vehicle is definitely practical for breaking the land-speed record, which is this vehicle's only intended application. On the other hand, this: [URL]http://www.gizmag.com/vv-plane-vtol-cargo-ducted-fans/33296/[/URL] is an impractical concept. It has four clusters of EDF units (inherently less efficient than larger propellers), the rendering has ridiculous spindly engine mounts which couldn't withstand the weight of the engines, let alone 30+ tonnes of thrust, and the company makes an implausible claim that it would be cost-competitive with trucks when they don't even have a working small-scale prototype to base things on. There is a difference between "bogged down in development" and "nonexistent product which anyone with a basic grasp of physics, let alone an engineer, can tell you won't work as promised."[/QUOTE] Odd that you should bring up top fuel dragsters. My understanding is that most jet and rocket propelled "cars" function as drag racers and typically exhibition as such, often as part of the show of top fuel racing. Richard Hammond's (of Top Gear fame) near-death crash was in a jet powered drag racer. They might be too rare and too fast for standard drag racing, but that is more or less what they do. My guess is that all easily available jets are built for subsonic travel (F-4 jets are typically beyond your shady arms dealers) and it is easier to develop a faster rocket than a jet (a big reason why you don't see jets in lower stages of "rockets". A one-off rocket is hugely cheaper [relatively only] to design/build).

Not sure about the mass of the other "fuels", but plain water won't give a higher ISP than hydrogen and oxygen. The reason is that both work by heating water vapor as hot as they can and then using that energy as exhaust velocity. Last I heard, not only did NTRs use lower temperatures than chemical rockets, the chemical rockets were limited by their temperature. No known metalurgy could handle higher temperatures. Obviously, there are densities between hydrogen and water, but expect it to be hard to match chemical ISPs with non-hydrogen NTRs. Having a NTR come apart would be bad. First, assuming you still have RCS thrusters, max thrust away from the radioactive material flying in formation with you (it presumably failed well out of any atmosphere and will stay in motion...). Hopefully you can get far enough away (note that if the radioactive bits are flying away sideways that isn't much better. You have shielding facing back and much less shielding to the sides). After that, you aren't going home (at least not on your own). Possible rescue missions. From start of Earth-Mars transfer but before Mars capture burn: probably the easiest rescue. Ship will be coming "back" to Earth's orbit (around the Sun). Rescue ship launches to a highly eccentric orbit around the Sun along the orbit. Flight might take months, but delta-V issues won't be much worse than the Moon. You will get in your Dragon (or Orion) capsule and you will be thankful. From start of Mars capture but not completing it: Nasty case. All the problems and delta-v needed to get to Mars in the first place, without the Obereth effect to help in capture. If the ship winds up in Mar's orbit (around the Sun, but not orbiting Mars) I'm not even sure this is possible (without exorbitant delta-v. We simply can't do exorbitant delta-v). From leaving Mars but not landing on Earth: life support failure and certain death. It might work in KSP, but only as long as you don't have life support mods. Pretty much any of these rescues will take months (or years) and only work if you use the mission's food/air/water to live. If you already used them, you die. Note that ignoring even life-support issues, if your plan included aerocapture back at Earth that means this is your last burn. In other words you won't even get a course close to Earth until the very last seconds of the burn. Plot a rescue ship going almost all the way to Mars orbit and then doing a rendezvous without Obereth. Maybe you might get the two transfer orbits to sync up like the first case, but I doubt it. Probably no way you could scrape up the delta-v for this one. But yes, this is typically better than most chemical rocket failure modes. Apollo 13 was unbelievably lucky to survive long enough to tell Houston they had a problem (a chemical fuel tank exploded. Luckily it wasn't hypergolic ("just" hydrogen and oxygen) and didn't ignite). [stan Love Astronautsplains Rocket Science (and why Mars is hard). Includes claim about current rockets hitting maximum ISP for water vapor]

I'd have a hard time believing that rooftop solar is any less constant across the grid than any issues with a non-constant grid. You certainly would need to spin up other generators to meet the changing load, but that will happen on any grid. My point was that natural gas is presently ideal for meeting just about any power need not effectively "paid for" via infrastructure. No batteries needed (until serious overbuilding occurs). As far as wind power, I've heard suggestions of running chemical plants when excess power was available, but it doesn't seem so likely (see costs of chemical plants). I think there was a PR attempt at such (it was hydrogen, which screams "greenwashing") in Germany. Germany has both a serious chemical engineering background an a recent (5 years ago?) issue with overbuilt wind power, but didn't seem to take this idea seriously. You would think aluminum [nicknamed "frozen electricity"] production would be ideal for excess electricity.