Skip to comments.NASA Confirms The Plausibility of Reactionless Drives??!!
Posted on 08/01/2014 4:13:21 PM PDT by servo1969
Let me geek out on you (I love science) and explain to you the science (I love science) and why this had previously been confined to the pages of science fiction (I am a nerd; and oh Dear Sweet Bunsen-Burner Lighting Lord, do I love science).
So it's a pretty firmly established principle that every act causes, and requires, an equal and opposite reaction.
If I understand this right (did I mention I love science?), this means that any space vessel will have to carry with it an enormous amount of reaction mass.
You can't -- we think, or thought -- just push energy out the backside of a spaceship and make it go voom. (Voom is a term that we who love science use.)
You have to actually impart momentum to physical mass -- a gas, for example. You spurt the gas out of the back of the spaceship. The gas is going backwards quickly, which makes the spaceship go forwards.
Without actually ejecting mass in the opposite direction you want the spaceship to go, we think -- or thought (those of us who think about science because, oh right, we love it) -- you have no propulsion at all.
So this means that the various spaceships you see in movies are all wrong. (All wrong is a scientific term.) A real spaceship should have tremendously large tanks of reaction mass, which it uses in flight to propel it. The proportion of "tank" to actual ship should be enormous -- the actual ship part of the ship would be tiny.
Basically a real spaceship would be an enormous series of gigantic tanks, with a tiny little cockpit/living space somewhere on it like a pimple. (Pimples are small oil-filled sacs in the epidermis -- That's science!)
Not only does this look goofy, thus destroying our dreams of sleek spaceships, but it imposes considerable, considerable engineering challenges on spaceship design, as the ship would be something like 90% reaction mass.
You'd have to carry around that much mass-- and when you tried to propel yourself, you'd have to accelerate that much mass, and of course all that mass doesn't wish to be propelled and will resist you. (We call that resistance-of-mass-to-acceleration "inertia" -- now there's some deep Science for ya.)
All told, it would be so, so much easier if we were disburdened of this very inconvenient law that only a mass being ejected from the rear of the ship could propel the ship forward.
This is why science fiction often postulates "reactionless drives." The term describes a hypothetical, fanciful drive system which does not require mass to be ejected from the ship, but instead just pumps out energy.
Or something. Writers are rarely detailed about it because it's just silly.
This is -- or was -- widely believed to be simply impossible and a very silly, if nonetheless pleasing, background conceit of science fiction.
Or science fantasy, really, when you take into account a reactionless drive is physically (or should I say physics-ally) impossible. (Did you see that? That was a science joke.)
But is it impossible?
Short answer: Yes, it's impossible.
Long answer: But maybe not.
Nasa is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on. Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion.
British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.
[A] US scientist, Guido Fetta, has built his own propellant-less microwave thruster, and managed to persuade Nasa to test it out. The test results were presented on July 30 at the 50th Joint Propulsion Conference in Cleveland, Ohio. Astonishingly enough, they are positive.
Now I gotta tell you: Frankly, I think this is all an error, and it will soon be disproven. I think there's some artifact going on here, something no one is checking.
I think it is true, and will remain true, that you have to shoot propellant out your rear to go forward.
But this does have one nice effect:
You can now read science fiction stories postulating reactionless drives and consider them plausible, rather than fantasy.
Until they disprove it all.
Thanks to various members of the blog's I Love Science/I am a Nerd team, @conarticritic, @rdbrewer4, and @comradearthur.
The ion drive will predate warp drive
Newton Law of Motion #1 violated
Either that or Second Law of Thermodynics violated.
Other than that: perfect like cold fusion in Ytah
Okay, step away from the keyboard, sir.
Slinky also makes a wonderful toy
Another Muslim invention!
hell, anybody who’s ever scraped out a jeffries tube knows that...
People used to mock Robert Goddard with his ‘loony’ ideas about spaceflight. You’d think people would be more open to new ideas but it seems things never change.
If microwave propulsion is proven to work despite defying previously accepted orthodoxies about physics then it simply means there need to be new orthodoxies about physics.
I believe it is possible, does not violate the laws of motion or thermodynamics, and is relatively straight forward. Does that make me a barking moonbat?
“Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.”
It would be interesting to see exactly how this guys “relativity-based theory” works. After all, relativistically, the microwave energy is equivalent to mass, but you should still need to shoot a whole lot of microwaves out the back of the ship in order to generate any forward thrust.
Just bouncing microwaves around in a box would seem to achieve nothing. One impact on one side might move the box infintesimally forward, but the reflection hitting another side would then impart momentum in another direction, and in the aggregate, it should all negate and result in no motion at all.
The only way I can conceive of this working is if you could direct the microwave impacts to only hit the front side of the box. This would require catching any reflecting photons and redirecting them back at the front side, without letting them strike any other surface to impart their momentum. Some sort of non-physical system, like a magnetic containment field, might do the trick, but I have a feeling that there is a “catch” I am not thinking of that would make even that solution not work.
As soon as they said, convert electricity, I stopped.
Where does the electricity come from? At best perfect nuclear conversion of mass to energy.
Try running the numbers for a machine to get to say 90% light. It is 100,000 fuel to payload ratio. Then there is slowing down and return.
It would be awesome if it is true. Humans would literally OWN the solar system. Probably not beyond it for a long time though.
“If microwave propulsion is proven to work despite defying previously accepted orthodoxies about physics then it simply means there need to be new orthodoxies about physics.”
But the science is settled! There is a consensus! What are you, some kind of denier??
Fire the wave motion gun!
from my viewing/reading of that anime... they told us how to make the propulsion system and humans devised the way to make a weapon from it
and then they will pooh-pooh the next idea
Like an Ion engine it probably takes forever to build up speed
Vendome, you are the only one I know that can find a space bar while still in orbit.
If I had a long enough extension cord, I could fly my microwave oven to the moon!
No, it makes you correct. The author of this blog-post is confused.
The law of conservation of momentum in three dimensions only holds approximately, because classical physics is only an approximation. In relativistic physics, conservation of momentum hold exactly, and is four dimensional. The fourth component of momentum is energy, and the laws of conservation of energy and conservation of momentum are one law in relativity.
In Lorentz invariant terms: pμpμ = m2. [in a system of units where ħ = c = 1.]
In practical units and more familiar terms: ]
As long as you can convert some mass -- usually binding energy from a chemical or nuclear bond -- into momentum/energy, you don't need "reactive mass." The article has been wrong since 1906.
There is nothing new here. Please move along.
I stopped reading after “NASA a major player in spaceflight” then realized it must be fiction
Ah, I found some “meat” about how the drive works, and it seems to work basically how I speculated it might. It directs the photons to impact one side more than the other, but instead of using a containment system, it relies on a relativistic effect to achieve this:
“The device uses a magnetron producing microwaves directed inside a specially shaped, fully enclosed tapering high Q resonant cavity whose area is greater at one end, upon which radiation pressure would act differently due to a relativistic effect caused by the action of group velocity in different frames of reference.”
“Roger Shawyer’s idea is to try to design a microwave cavity as a conical frustum in such a manner that forces due to radiation pressure on one side are greater than the other.
Cullen showed the propagation rate of electromagnetic waves in space (group velocity) and the resulting force it exerts can be varied depending on the geometry of a waveguide within which it travels. The increasing confinement of a narrowing waveguide (convergent) leads to a widening wavelength and a decrease of the group velocity (lower momentum transfer). Conversely, a widening waveguide (divergent) leads to a narrowing wavelength and an increase of the group velocity (higher momentum transfer).
Shawyer states that if the electromagnetic wave travelling in a tapered waveguide is bounced between two reflectors, with a large group velocity difference at the end surfaces, the force difference resulting from the radiation pressure difference will give a resultant thrust to the waveguide linking the two reflectors, in the direction of the larger surface.”
Jesus, if this works, it is genius. Using simple geometry of the cavity to force the waves to transform their momentum into wavelength in order to control the direction of thrust. That’s a sublime solution if ever I’ve seen one.
The science behind it is not new and has been known for over 100 years. See post #14.
I think the novel part here is what they are converting to achieve the effect. They set the photons oscillating in a chamber which forces the wavelengths to change as the photon goes from one end to the other. This alters the group velocity of the photons, which changes the radiation pressure as the photons strike each end of the cavity.
So the conversion seems to be between the forward group velocity and the lateral oscillation, which is immaterial as it pertains to the desired effect of the drive. The photons don’t lose any energy before hitting the other side, they are just reconfigured so that they will impart energy less efficiently before they hit that side.
My engineering education thoughts, exactly!
Baby steps. We haven’t even invented the wheel when it comes to space flight but there are a lot a lot of interesting technologies that are off the table for political and financial reasons.
The Orion drive could get us to the nearest stars within a matter of a few decades but cost trillions of dollars not to mention launching a crapload of nuclear bombs into orbit.
Project Deadelus was another interesting concept for getting to the nearest stars in a few decades.
In any case, baby steps are cool as long as they’re steps forward. I’m thinking moon base, Mars base, asteroid mining to printing large ships in space with ores mined from asteroids.
That all depends on scale of the drive. These demonstration models probably wouldn’t budge a Prius, but if you have a big enough magnetron and nuclear reactor to power it, the acceleration should be much greater.
EXACTLY! Thank You!!!
Everything Robert Goddard was completely theoretically possible. And had been understood, theoretically, for a couple of hundred years.
It's pretty clear that most of the Wiki article was actually written by the inventor of the drive, who does not really address his critics, and who did not originate the theory himself [whihc may or may not be applicable to his drive.]
A better example would be the Wright Brothers. There actually was some theoretical debate about whether heavier than air flight was possible.
They actually pushed the boundaries of science and practically invented the science of aerodynamics.
Yeah, these kind of comments, like the well-known claim that Bumble Bee flight “violates the laws of aerodynamics” drive me nuts. The Chinese had rockets as far back as the 7th century, and rockets have been used in warfare for nearly a thousand years. Nobody thought Goddard’s ideas were kooky in the least.
Among the interesting facts from the paper: The measured thrust was only about 0.0001 ounces. They put the device in a vacuum chamber, but never bothered to actually test it in a vacuum. Most significantly, they build a "null" device, intentionally built to not produce any thrust, but that also appeared to show thrust. This is a strong indication that there is a systematic measurement error in their setup.
Clarke’s Three Laws are three “laws” of prediction formulated by the British writer Arthur C. Clarke. They are:
1.) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2.)The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
3.)Any sufficiently advanced technology is indistinguishable from magic.
Nothing is “impossible”, there’s only stuff we haven’t tried yet....
Really nuclear power has been used in powering satellites for decades but are low powered reactors in the 10 top 500 kWatt range.
The problem that will have to be dealt with for a nuclear power plant to power such an engine is waste heat. The small size of the past and present space reactors made the waste heat easy enough to deal with.
The only method of disposing of waste heat in space is radiant heat. Some sort of enormous heat radiator will have to be developed.
I’ve always wondered if instead of requiring a large reactive mass by pushing, instead we tried to pull and push. What I mean by this is have a collector up front that pulls in light, particles, background radiation energy like a vacuum... it could be partially or wholly passive and then funnel it through a nozzle on the back end.
This should create a positive force in the forward direction though incremental energy pressure differential, but it would have the potential of limiting or eliminating the mass required to be carried for fuel.
There may also be a means of attraction through gravimetric force if willing to add significant mass to the vessel to increase attraction of particles - diverting them from the mass and aft of the vessel.
I see from some of the latter posts the geometric ideas in this proposal and see a similarity with lift on wings.
Captain, the tribble with troubles (hic) is they drank all me scotch.
Ah, Space Battleship Yamato...
I always regret that the non-technically leaning readers will miss the significance of that statement.
This is an example of true classic science. An essential part of true science demands a second step; try to devise ways to explain or disprove the original theory.
I’m not a physicist, but what if you had two microwave emitters mounted opposite sides of a box pointing to a front panel and emitting opposite waves. each wave would bounce towards the other emitter and get cancelled... but the bounce point would receive the energy.
if that worked, then just have loads of paired emitters on the inner walls to increase the force on the front wall.
I believe this would eliminate the opposite reaction when the bounced waves would normally hit the back wall, nullifying the forward momentum. if so, then the forward momentum would allow for as much ‘thrust’ as the energy you have to create the microwaves.
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