Em drive...

[Lo.M]

Also known as: Radio frequency resonant cavity thruster.

It is a device concept that claims to be a spacecraft propeller. It is intended to generate momentum by reflecting the microwaves internally in the device, violating the moment conservation law and other laws of physics.

It was introduced in 2001 by Roger Shawyer.

https://en.m.wikipedia.org/wiki/EmDrive

To give you an idea: Down ion thrusters produced almost 30 times more impulse for the same amount of electricity than the Em drive.

Edited March 24, 2021 by Lo.M

[Gargamel]

We already have a pretty sizable thread on this topic, although IIRC, it's been thoroughly debunked.  

We won't merge them as that thread isn't very recent, and yours has a poll. 

[Lo.M]

Just now, Gargamel said:

We already have a pretty sizable thread on this topic, although IIRC, it's been thoroughly debunked.  

We won't merge them as that thread isn't very recent, and yours has a poll. 

Ok

 

2 minutes ago, Gargamel said:

although IIRC, it's been thoroughly debunked.  

Yes

[cubinator]

If it had any chance of being what it says it is, somebody would have launched one into space and accelerated a spacecraft with it by now.

[SpaceFace545]

I have zero background in physics and my best understanding of it is from an honors chemistry class but, I think it is possible for this too work. It just kinda makes sense if you think about it.

[kerbiloid]

Spoiler

"Em... Drive!"

 

[sevenperforce]

2 hours ago, SpaceFace545 said:

I have zero background in physics and my best understanding of it is from an honors chemistry class but, I think it is possible for this too work. It just kinda makes sense if you think about it.

I have a degree in physics, I'm a published scientist, and I will sit here and tell you quite clearly that it is not possible for this to work.

There are a lot of things which make intuitive sense that simply don't work.

[SpaceFace545]

23 minutes ago, sevenperforce said:

I have a degree in physics, I'm a published scientist, and I will sit here and tell you quite clearly that it is not possible for this to work.

There are a lot of things which make intuitive sense that simply don't work.

makes sense

[sh1pman]

8 minutes ago, sevenperforce said:

I have a degree in physics, I'm a published scientist, and I will sit here and tell you quite clearly that it is not possible for this to work.

There are a lot of things which make intuitive sense that simply don't work.

As a published chemist, have to agree. Well, not that my degree matters much in this case, but I guess a background in science gives an instinctive idea of what’s plausible and what’s total BS. Extraordinary claims have to be backed by extraordinary evidence, which would be something like sending a smallsat to the Moon using nothing but emdrive. But if I were a grant reviewer, I wouldn’t give any public money to such a project.

[Lo.M]

1 hour ago, sevenperforce said:

I have a degree in physics, I'm a published scientist, and I will sit here and tell you quite clearly that it is not possible for this to work.

There are a lot of things which make intuitive sense that simply don't work.

As an student environmental engineer I have to agree with you.

Edited March 24, 2021 by Lo.M

[Spaceman.Spiff]

1 hour ago, sevenperforce said:

I have a degree in physics, I'm a published scientist, and I will sit here and tell you quite clearly that it is not possible for this to work.

There are a lot of things which make intuitive sense that simply don't work.

As a high schooler in Biology, I have to agree with you. 

Also, Scott Manley did some good videos on this topic.

 

[magnemoe]

It was magnetic interaction who I suspected as the probable error. 

Now they should try with docking ports. It works in KSP

In short if you set the magnetic attraction on one docking port to max and the other to 0, have them facing each other on the same craft you get trust, an distance like 4 structural panels works best. 

[munlander1]

The EM drive has been debunked https://www.grenzwissenschaft-aktuell.de/latest-emdrive-tests-at-dresden-university-shows-impossible-engine-does-not-develop-any-thrust20210321/

[sevenperforce]

1 hour ago, munlander1 said:

The EM drive has been debunked https://www.grenzwissenschaft-aktuell.de/latest-emdrive-tests-at-dresden-university-shows-impossible-engine-does-not-develop-any-thrust20210321/

Love it.

This bit cannot be understated:

His theory (…we limit ourselves here to the laboratory standard and not to his astronomical claims), as well as the experiments cited by him are excluded by 4 orders of magnitude.

With both the EmDrive and the LemDrive, we have achieved a measurement accuracy that is below the photon pressure. That is, even if one of these concepts worked, it would be more effective simply to use a laser beam as a drive.

Obviously proponents can still try to claim they "did it wrong" but any claim that NASA's tests support the EM Drive can no longer be maintained.

[munlander1]

“With both the EmDrive and the LemDrive, we have achieved a measurement accuracy that is below the photon pressure. That is, even if one of these concepts worked, it would be more effective simply to use a laser beam as a drive.”

My understanding of that quote is that the accuracy of their measurements was greater than the photon pressure generated by the Em drive and since they detected no significant force above that, if the EM drive did actually provide thrust, it is so small a laser would provide more force. Is that correct?

[sevenperforce]

5 minutes ago, munlander1 said:

“With both the EmDrive and the LemDrive, we have achieved a measurement accuracy that is below the photon pressure. That is, even if one of these concepts worked, it would be more effective simply to use a laser beam as a drive.”

My understanding of that quote is that the accuracy of their measurements was greater than the photon pressure generated by the Em drive and since they detected no significant force above that, if the EM drive did actually provide thrust, it is so small a laser would provide more force. Is that correct?

I don't believe the EmDrive generates any total photon pressure, but that the LemDrive (the one that uses a laser resonator) does generate photon pressure. 

I think what they're saying, though, is that their measurement accuracy was greater than the amount of photon pressure which would be produced if you used the same amount of energy to directly power a photon drive.

In other words, suppose you were trying to operate the EmDrive at 50 W. A photon drive operated at 50 W would produce a thrust of 1.67e-7 N. They are saying that they have ruled out any thrust for the EmDrive to well below 1.67e-7N.

For the LemDrive, which is expected to generate photon pressure but claimed to produce additional thrust, they're saying the difference between the photon pressure it is expected to generate and its actual thrust is lower than 1.67e-7N.

So yeah, in either case a laser pointer would do better.

[StrandedonEarth]

New testing has shown it works 100 x better than a photon drive!!!!

Spoiler

NOT!!!!! April Fool’s!

 

[StrandedonEarth]

On 3/24/2021 at 1:54 AM, magnemoe said:

It was magnetic interaction who I suspected as the probable error. 

Yes, as I understood it at the time, the thrust that the developer claimed was measured was actually being generated by an electromagnetic interaction with the cables supplying power.

And while I certainly understand that it is simply impossible within the known laws of physics, one can always hope to find a new law, principle, effect, or particle of physics that allows for a reactionless (propellant-less) drive (aka "space drive") which would be the holy grail of vacuum propulsion. But extraordinary claims require extraordinary proof/evidence, which is not found in this case.

Edited April 2, 2021 by StrandedonEarth
clarity

[Lo.M]

8 hours ago, munlander1 said:

The EM drive has been debunked https://www.grenzwissenschaft-aktuell.de/latest-emdrive-tests-at-dresden-university-shows-impossible-engine-does-not-develop-any-thrust20210321/

Yes

[kerbiloid]

Did they try a wheel of EmDrives?

Spoiler

If it rotates, they work.

[magnemoe]

4 hours ago, StrandedonEarth said:

Yes, as I understood it at the time, the thrust that the developer claimed was measured was actually being generated by an electromagnetic interaction with the cables supplying power.

And while I certainly understand that it is simply impossible within the known laws of physics, one can always hope to find a new law, principle, effect, or particle of physics that allows for a reactionless (propellant-less) drive (aka "space drive") which would be the holy grail of vacuum propulsion. But extraordinary claims require extraordinary proof/evidence, which is not found in this case.

Yes it was worth looking into as an low cost project. 
The main physical law an pure reaction less drive like KSP kraken drives breaks is that they are perpetuum mobiles. 
How? well put an em drive on an beam in an vacuum chamber and start it up, as acceleration of an reaction less drive is constant with an power input its RPM will increase say 1 rpm / minute. 
Kinetic energy is mass*velocity^2 and this hold true for rotating objects too.
At some rotation energy increase will be higher than the power input, keep going for some time then use an generator bleed off the rotation increase and you can then extract more power than you put into the reaction less drive. 
This kind of break physic. 

Rockets have an constant accelration as they accelerate the reaction mass with them, other systems does not have an constant acceleration with constant energy input. 
An cars acceleration will slow down as it goes faster and breaking distance increase with velocity^2

 

 

[Lo.M]

----- > In a Comprehensive new Test, the EmDrive Fails to Generate any Thrust - Universe Today

[wumpus]

On 3/23/2021 at 2:24 PM, Lo.M said:

To give you an idea: Down ion thrusters produced almost 30 times more impulse for the same amount of electricity than the Em drive.

Well, the real ratio of Dawn ion thrust vs Em drive is infinite.

On the other hand, a blue* LED will do exactly what the Em drive claimed to do: put energy in and get momentum out, without using any propellant outside of the energy you put in your device.  Just don't expect to get within a factor of 30 of Dawn.  If you wanted to scale Dawn up, consider accelerating the ions in something more like a cyclotron.  Thanks to relativity, your "delta momentum" is just the force of thrust (F=dp/dt): this doesn't really change as you approach c.

* blue chosen because I think the equations scale better with more momentum per Joule of light with shorter wavelength.  In practice you would pick whatever put out the most light per Watt.  Don't forget to make your heat sinks direct most of the black  body radiation in the same direction as your propulsive light source, as they will produce a significant percentage of your momentum.

Edited April 5, 2021 by wumpus
botched the corrected F=ma equation. In my defense, I was taught "F=ma"

[kerbiloid]

An idea.
"Arduino EmDrive".
and
"Superprecise Arduino EmDrive Thrust Indicator"