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> This is a technology which could transform space travel and see craft lifting silently off from launchpads Not with 12 millinewtons per kilowatt! In space, s
by dvh 6y ago
> This is a technology which could transform space travel and see craft lifting silently off from launchpads
Not with 12 millinewtons per kilowatt! In space, sure but not from launchpad.
- ashtonkem 6y agoSure, but that’s true of ion propulsion too. It’s pretty common for you to use different motors at different stages of flight; even liquid motors usually have different bell designs for different altitudes. If the emdrive works (if!), then you’d just bolt one on top of a regular rocket.
- Justsignedup 6y agoIf it works then we can just throw up a nuclear reactor into space and a small amount of nuclear fuel will create a continuous thrust which in space matters. Can lead to a spaceship that gets shuttled to which just ferries ships between planets.
- ben_w 6y agoIf we could put a nuclear reactor in space large enough for this to be useful, we could use the reactor to boil water and get vastly more thrust. Or run an ion drive and get more thrust. Or just let the fission fragments out the back and get more thrust. What this would be useful for is (by no coincidence) also the exact reason why it is considered crank science: you could use it to build a perpetual motion machine because it violates conservation of energy/momentum laws.
- jiofih 6y agoThe trick is not requiring propellant. You can’t carry 90 years worth of water or gas. The Dawn spacecraft launched to Ceres in 2007 used up 425kg of Xenon for only eleven days of thrust for its ion engine.
- ben_w 6y agoIf you let the fission fragments out the back of the reactor you get more thrust than this. (Even if the EmDrive worked).
- jiofih 6y agoYou still need tons of fuel for that, in the order of tens of tons per year travelled - unrealistic for travel outside our solar system. Thrust doesn’t really matter at that time scale.
- ben_w 6y agoThe fuel is the reactor fuel. Literally the fission products of the uranium/plutonium in your reactor, from where the power you want to use for the EmDrive comes from, would beat this. If the EmDrive actually worked, the correct use is to violate conservation of energy and momentum, not as a straightforward substitute for the engines we have now.
- doctor_eval 6y agoBut isn’t it consuming energy? Where is that kilowatt going?
- bjo590 6y agoSome napkin math. How long would it take a nuclear powered EmDrive to push a fully loaded semitrailer from 0m/s to the speed of the interntional space station? The maximum mass for a semi-truck fully loaded is 36000kg. The EmDrive generates 12millinewtons per kw. 1n = 1kg*(1m/s^2). Leo ~=7.66km/s^. A nuclear reactor produces ~1gw. We would need 275760000N to accelerate a semi truck to leo speeds. A nuclear powered EmDrive would take ~265 days to push a semi truck to low earth orbit speeds. The escape velocity of Earth's orbit is 11.19 km/s, and if you were going to take humans on the trip you'd need much more cargo than 36000kg. Granted, you wouldn't have to move the craft from 11.19km/s to 0km/s and then 0km/s to 11.19 km/s every time you entered and left orbit, but it would be a slow ride regardless.
- short_sells_poo 6y agoI think we can't ignore the weight of the nuclear reactor though - we are not lifting just the truck, the reactor has to carry it's own weight. And a 1GW reactor will dwarf the 36t payload I think.
- raducu 6y agoPlease, stop with the 12millinewtons -- if the effect is real, the cavity can be made orders of magnitude more efficient. But it is 99.9999% not going to work at all, the emDrive would just be a cheat at space travel. Something that can transform energy into momentum without shooting stuff back is the Holy Grail of space travel -- after a warp drive.
- imtringued 6y agoIon thrusters already do this though. Even with conventional rockets once you're in space finding new fuel shouldn't be a big deal. It's just a matter of building the infrastructure. Right now leaving earth is still the biggest problem.
- elcritch 6y agoYah that'll only require a few gigawatts. Or terrawatts? But if there is an unknown effect hopefully we can figure it out and refine it. Like with blackbody radiation it might be only incidentally overlapping a new effect.
- jsjohnst 6y agoFalcon 9’s engines combined produce ~7,500,000,000 millinewtons of force (at sea level) per SpaceX’s website (converted from their figure of 1.7M lb/foot of force). So doing some napkin math with the article’s 12mN/kW, that’s close to a terawatt. For reference, I think worldwide electrical power generation capacity is around 10x that. edit: made the math more explicit due to child comments and fixed spelling error
- deleted 6y ago[deleted]
- DaiPlusPlus 6y ago7,500,000,000 millinewtons = 7.500 Meganewtons 1 Watt = 1 Newton-meter/second You're missing some values.
- tremon 6y agoThe missing value would be the 12mN/kW that the top post opened with. Getting 7.5 MN output thrust with that conversion ratio requires 625GW of input power.
- deleted 6y ago[deleted]
- jsjohnst 6y agoExactly! To belabor the point further, the Falcon Heavy would be around 2 terawatts and the Saturn V would be around 3 terawatts by comparison.
- 6y ago
- m463 6y agowhat if the launchpads are... in space! :)
- namrog84 6y agoThen it'd probably be called a space port or something instead of a launchpad?
- Udik 6y ago> 12 millinewtons per kilowatt Just out of curiosity, where is all the rest of the energy going?
- trhway 6y agoyou seems to be conflating thrust(momentum) and energy a bit - linear on speed vs. quadratic on speed in classic case. It is very similar to photon drive - a lot of energy carried away by the photons while they generate too little thrust. If there is a genuine effect, and as EmDrive generates more thrust than photon drive for the same energy, it would mean that EmDrive does eject some small mass at large speeds (kind of like super ion thruster) - whether it is some mass chipped from the EmDrive (i'd bet it is the case) and/or created using the spent energy (say some smaller mass boson interaction with some field which looks less probable to me) - that we don't know yet.
- jjcm 6y ago> whether it is some mass chipped from the EmDrive (i'd bet it is the case) This would make sense of the standard design, but doesn't seem to make sense for the photon loop described in the article. The photon loop seems to be an entirely closed system.
- red75prime 6y agoThat's easy. It mostly goes into heat. Eddy current heating of the copper tube should be the largest part. Wires, waveguides, a microwave generator aren't 100% efficient too. Small part of energy is lost as electromagnetic radiation. What's mysterious is where the energy and the impulse are going if thrust is real. We can point the drive in such a way that it slows rotation of the earth, so the earth's rotational energy and angular impulse are decreasing. Where should they be going? I don't know.
- csunbird 6y agoObligatory xkcd: https://xkcd.com/1404/ https://xkcd.com/1404/
- treespace88 6y agoWith a cold fusion reactor attached, with some gravity shielding it should be viable.
- Rebelgecko 6y agoWhat is gravity shielding?
- neurostimulant 6y agoFirst you shield your spacecraft with a gravity shielding device so it's not affected by earth gravity anymore. Then, even an emdrive's tiny propulsion output should be able to push your spacecraft all the way to space, powered with a clean cold fusion reactor. It's all imaginary though, but a man can dream...
- OldHand2018 6y agoHmm, I'm not so sure. Once the gravity shield is invented, any reasonably strong human should be able to just throw the satellite into orbit. Why spend money installing an emdrive?
- dilyevsky 6y agoWhy not just teleport to where you want to be?
- ed25519FUUU 6y agoI was thinking rocket roller skates.
- Aeolun 6y agoWouldn’t that much energy melt whatever you are bouncing it around in?
- deleted 6y ago[deleted]
- raducu 6y agoIf the effect is real, my understanding is the force could be increased by many, many orders of magbitude by using a superconducting cavity.