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Re:The EmDrive just won't die by dvh on Sunday September 13, 2020 @11:42AM (#24461524)
> 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.

Re:The EmDrive just won't die by treespace88 on Sunday September 13, 2020 @05:08PM (#24463961)
With a cold fusion reactor attached, with some gravity shielding it should be viable.
Re:The EmDrive just won't die by dilyevsky on Sunday September 13, 2020 @08:01PM (#24465037)
Why not just teleport to where you want to be?
Re:The EmDrive just won't die by ed25519FUUU on Monday September 14, 2020 @01:19AM (#24467026)
I was thinking rocket roller skates.
Re:The EmDrive just won't die by Aeolun on Sunday September 13, 2020 @08:09PM (#24465106)
Wouldn’t that much energy melt whatever you are bouncing it around in?
Re:The EmDrive just won't die by Rebelgecko on Sunday September 13, 2020 @07:15PM (#24464740)
What is gravity shielding?
Re:The EmDrive just won't die by neurostimulant on Sunday September 13, 2020 @09:17PM (#24465639)
First 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...
Re:The EmDrive just won't die by OldHand2018 on Monday September 14, 2020 @10:05AM (#24470276)
Hmm, 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?
Re:The EmDrive just won't die by elcritch on Sunday September 13, 2020 @12:35PM (#24461990)
Yah 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.
Re:The EmDrive just won't die by jsjohnst on Sunday September 13, 2020 @05:07PM (#24463951)
Falcon 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

Re:The EmDrive just won't die by robocat on Sunday September 13, 2020 @06:25PM (#24464444)
I think your calculations must be out.

The work achieved (lifting some tons of rocket) is orders of magnitude less work than the power extracted from falling water (hydro, thousands of tons per second).

And the heat output of burning hydrocarbons and nuclear reactions worldwide were concentrated into a few rocket nozzles, that would be rather mind boggling!

Re:The EmDrive just won't die by ouid on Sunday September 13, 2020 @07:40PM (#24464886)
For the record, the saturn V rockets operated at 120GW. Which is also close to a terawatt.
Re:The EmDrive just won't die by jsjohnst on Sunday September 13, 2020 @06:39PM (#24464528)
Read the two comments (one I replied to and the one it relied to) for context. My comment wasn’t intended to be free standing on its own.
Re:The EmDrive just won't die by Aeolun on Sunday September 13, 2020 @08:10PM (#24465122)
If you don’t need all the falcon’s fuel, you don’t need nearly as much thrust either.
Re:The EmDrive just won't die by anamexis on Sunday September 13, 2020 @08:21PM (#24465223)
Sure, just something that can generate a terawatt of power.
Re:The EmDrive just won't die by jsjohnst on Sunday September 13, 2020 @09:43PM (#24465858)
Cold fusion maybe?
Re:The EmDrive just won't die by SteveNuts on Sunday September 13, 2020 @10:18PM (#24466100)
Does Adobe even still support that?
Re:The EmDrive just won't die by jsjohnst on Sunday September 13, 2020 @11:02PM (#24466330)
Re:The EmDrive just won't die by DaiPlusPlus on Sunday September 13, 2020 @06:17PM (#24464391)
7,500,000,000 millinewtons = 7.500 Meganewtons

1 Watt = 1 Newton-meter/second

You're missing some values.

Re:The EmDrive just won't die by tremon on Sunday September 13, 2020 @06:36PM (#24464514)
The 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.
Re:The EmDrive just won't die by jsjohnst on Sunday September 13, 2020 @06:54PM (#24464619)
Exactly! To belabor the point further, the Falcon Heavy would be around 2 terawatts and the Saturn V would be around 3 terawatts by comparison.
Re:The EmDrive just won't die by moron4hire on Sunday September 13, 2020 @06:42PM (#24464540)
Maybe it will require 1.21 gigawatts and travel through time.
Re:The EmDrive just won't die by Udik on Sunday September 13, 2020 @03:41PM (#24463359)
> 12 millinewtons per kilowatt

Just out of curiosity, where is all the rest of the energy going?

Re:The EmDrive just won't die by red75prime on Sunday September 13, 2020 @06:35PM (#24464509)
That'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.

Re:The EmDrive just won't die by trhway on Sunday September 13, 2020 @04:09PM (#24463576)
you 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.

Re:The EmDrive just won't die by jjcm on Sunday September 13, 2020 @04:30PM (#24463736)
> 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.

Re:The EmDrive just won't die by raducu on Tuesday September 15, 2020 @03:17PM (#24485524)
If the effect is real, my understanding is the force could be increased by many, many orders of magbitude by using a superconducting cavity.
Re:The EmDrive just won't die by ashtonkem on Sunday September 13, 2020 @12:02PM (#24461689)
Sure, 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.
Re:The EmDrive just won't die by IshKebab on Sunday September 13, 2020 @12:13PM (#24461793)
I think you didn't read the second half of the sentence he quoted.
Re:The EmDrive just won't die by ashtonkem on Sunday September 13, 2020 @12:17PM (#24461834)
I was in fact agreeing that it won’t work from the launchpad, but stating that that’s no big deal.
Re:The EmDrive just won't die by IshKebab on Sunday September 13, 2020 @01:02PM (#24462230)
Oh right. He wasn't suggesting that it was a big deal.
Re:The EmDrive just won't die by csunbird on Sunday September 13, 2020 @04:22PM (#24463677)
Obligatory xkcd: https://xkcd.com/1404/
Re:The EmDrive just won't die by Justsignedup on Sunday September 13, 2020 @12:30PM (#24461948)
If 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.
Re:The EmDrive just won't die by bjo590 on Sunday September 13, 2020 @04:32PM (#24463753)
Some 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.

Re:The EmDrive just won't die by short_sells_poo on Sunday September 13, 2020 @06:14PM (#24464374)
I 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.
Re:The EmDrive just won't die by raducu on Tuesday September 15, 2020 @03:22PM (#24485596)
Please, 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.

Re:The EmDrive just won't die by ben_w on Sunday September 13, 2020 @04:13PM (#24463602)
If 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.

Re:The EmDrive just won't die by jiofih on Sunday September 13, 2020 @04:41PM (#24463809)
The 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.
Re:The EmDrive just won't die by ben_w on Sunday September 13, 2020 @05:36PM (#24464133)
If you let the fission fragments out the back of the reactor you get more thrust than this. (Even if the EmDrive worked).
Re:The EmDrive just won't die by jiofih on Monday September 14, 2020 @03:27AM (#24467716)
You 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.
Re:The EmDrive just won't die by ben_w on Monday September 14, 2020 @04:17AM (#24467950)
The 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.

Re:The EmDrive just won't die by Aeolun on Sunday September 13, 2020 @08:14PM (#24465155)
If we can turn mass into energy, why can’t we turn energy into mass?
Re:The EmDrive just won't die by ben_w on Monday September 14, 2020 @04:20AM (#24467964)
You can, we’ve been doing that for ages. What’s the rest of your question?
Re:The EmDrive just won't die by doctor_eval on Sunday September 13, 2020 @05:59PM (#24464281)
But isn’t it consuming energy? Where is that kilowatt going?
Re:The EmDrive just won't die by ben_w on Sunday September 13, 2020 @07:02PM (#24464663)
What is the “it” here?

EmDrive looks like an accounting error to me, not something that actually works. Any energy it expends turns into heat, radiating in a predictable but not necessarily isotropic way. This radiation carries momentum, but much less than the EmDrive claims to be capable of.

A rocket or ion drive? The energy goes into the kinetic and gravitational potential of the exhaust.

(Aside: kilowatts are power, not energy).

Re:The EmDrive just won't die by imtringued on Monday September 14, 2020 @04:10AM (#24467915)
Ion 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.
Re:The EmDrive just won't die by m463 on Sunday September 13, 2020 @12:36PM (#24461997)
what if the launchpads are... in space! :)
Re:The EmDrive just won't die by namrog84 on Sunday September 13, 2020 @04:41PM (#24463806)
Then it'd probably be called a space port or something instead of a launchpad?