Cannae/EmDrive

[shynung]

3 hours ago, K^2 said:

Take typical interplanetary ion densities. Take "engine" cross-section of 1m² orbiting the Sun. You can use solar wind speeds as reference for how much matter passes through your engine. Now boost all of that matter to 0.1c, which is well above the upper limit for EMDrive given Power/Thrust ratio. Look at the trust you get.

I'll save you a Google search. Solar Wind is 3amu/cm³ at 500m/s. Now you just have to do the math.

I'll take it.

One amu is 1.67377e-27 kg. 3 amu is 5.02131e-27 kg. If there are that much mass for 1 cm³, than 1 m³ of the stuff masses 5.02131e-21 kg. I'll round it up to 5e-27 kg.

Starting velocity is 500 m/s away from the sun, final velocity is 30e6 m/s. Assuming the velocity change happens in one second, and the spacecraft is thrusting away from the sun from a standstill (which means starting velocity is -500 m/s), that's an acceleration of 30e6 + 500 m/s².

F = ma , so the thrust produced is 5e-27 * (30e6 + 500) = 1.5e-19 Newtons.

Did I get it?

[kunok]

23 hours ago, K^2 said:

I can totally buy momentum transfer at short, but not microscopic range, resulting in thrust from whatever ions are still floating in the chamber, something evaporated from the chamber, or perhaps even from the equipment used to measure the thrust.

What I don't buy is virtual particle transfer of momentum over long scale. And by that I mean anything beyond a few centimeters at the most.

If this is the principle of operation, it's still exciting, because it's really new. But useless in most operations that the EMDrive is being advertised for. If it happens to be a way to get thrust from surrounding ions, this could be a good system to keep small satellites, perhaps even cubes, in LEO orbit almost indefinitely. Which is something. But it wouldn't make it a practical deep-space drive, unless there is a way to convert it into a conventional, albeit potentially more efficient ion drive.

Well, this can be useful in the surroundings of any body with atmosphere? It would be important to determine which is the lower density of gas needed to be practical. Free DeltaV if you have lots of electricity and you're close to a atmosphere is still a huge improvement.

Free low orbit keeping and orbital inclination changes, it would be awesome. Getting a little more free push from flybys, or fuel-less rcs, this can be so good.

 

But I really don't think it works.

[K^2]

On 3/9/2016 at 7:21 AM, shynung said:

Did I get it?

Yup. Do you see now why I simply dismissed this as an option? Unless you can figure out how to turn these into giant, almost weightless sales, it's just not usable.

You can improve the situation using a magnetic scoop, of course, but you end up with the same considerations with drag that ultimately buried the Bussard ramjet.

[Bill Phil]

If mass is related to energy, then expelling energy should be equal to expelling a mass of equivalent energy, right? That's how photon rockets work, afaik. But then again, they're very impractical. 

Even so, could photon rockets be related to the EmDrive? My guess is no, but I've got no idea in this area.

[K^2]

2 hours ago, Bill Phil said:

If mass is related to energy, then expelling energy should be equal to expelling a mass of equivalent energy, right? That's how photon rockets work, afaik. But then again, they're very impractical. 

Even so, could photon rockets be related to the EmDrive? My guess is no, but I've got no idea in this area.

Photons have no rest mass, which is why they are difficult to push from. You need 300MW of power to generate 1N of thrust with a photon drive. EMDrive is measured to do at least 10 times better, which means that it pushes from something that does have rest mass.

[Bill Phil]

32 minutes ago, K^2 said:

Photons have no rest mass, which is why they are difficult to push from. You need 300MW of power to generate 1N of thrust with a photon drive. EMDrive is measured to do at least 10 times better, which means that it pushes from something that does have rest mass.

Interesting...

If we ignore the scientific issues, what could this bring to propulsion technology?

[K^2]

8 minutes ago, Bill Phil said:

If we ignore the scientific issues, what could this bring to propulsion technology?

You mean, if it works as described in most optimistic claims, with no requirements for a medium or stored propellant? Setting aside the fact that we'd probably have to burn all the physics textbooks written since, oh, late 19th century, the impact would be primarily on unmanned exploration. The net thrust is still pretty low, but it adds up over time if you don't have to bring any extra mass with you. So deep space probes, perhaps even some interstellar ones would be possible. It'd be quite handy in studying outer Solar System as well.

If it works as described in every way except not needing propellant - that is, there is some sort of a leak it utilizes to get thrust - it can still be useful as a type of ion thruster that has better TWR than most other designs we've considered, as well as pretty good power-efficiency. Still great for Solar System exploration, but not quite there for interstellar. The biggest win for this outcome is that it doesn't break known physics, so we'd just have to account for phenomenon.

Finally, the most likely possibility is that we'll find a glaring source of error, and this whole thing will be put to rest.

[Bill Phil]

Can you elaborate on why it defies physics?

@K^2

[K^2]

Because it gains momentum at a rate that doesn't match the loss of energy. So it either generates off-the-shell exhaust, which is impossible, or it doesn't conserve momentum, which is even more impossible.

If it interacts with some medium to produce this thrust, then it merely becomes very improbable.

[RainDreamer]

Propulsion with no reaction mass would breaks quite a few laws of physics. That is like, warp drive level of tech.

[K^2]

23 minutes ago, RainDreamer said:

Propulsion with no reaction mass would breaks quite a few laws of physics. That is like, warp drive level of tech.

Warp drive can't generate a measurable force, which is how it gets around that limitation. EMDrive actually generates thrust, so it can't qualify even for that loophole.

[Rakaydos]

50 minutes ago, K^2 said:

Because it gains momentum at a rate that doesn't match the loss of energy. So it either generates off-the-shell exhaust, which is impossible, or it doesn't conserve momentum, which is even more impossible.

If it interacts with some medium to produce this thrust, then it merely becomes very improbable.

Off the Shell exhaust? You said it's impossible, but what does it even mean?

[PB666]

1 hour ago, K^2 said:

Because it gains momentum at a rate that doesn't match the loss of energy. So it either generates off-the-shell exhaust, which is impossible, or it doesn't conserve momentum, which is even more impossible.

If it interacts with some medium to produce this thrust, then it merely becomes very improbable.

One thing that I have to add, there is a possibility that it causes a twist of quantum length.

How this would work is that as a vehicle travels through its media it has an axial crosssectional area. This limits all momentum shifts to all atoms that lie in areas and 10-8 meters on either side, the way we currently view quantum mechanics they should not be able to push-off of atoms outside of this moment of crosssectional area.

So one minor violation of current physics is that if the devices 'warps' the outerbounds of quantum length then it could push off things further away, so lets say it increases the interaction range by 100 meters, if the device has a profile of 0.1 meter then it could increase force 1000000 fold over. In this sense if the device could be made very compact, it could be very useful for nanosatellites, its cheap it only requires hv.

But here again we run into the same problem with solar electric thrust based craft (including ION drive), you can put mass in a three dimensional volume but this drive needs to be spread across an area so its relative effectiveness drops by K*mass^1.5.  It would not be useful from transporting anything heavy.

A couple of uses

- a small device could be placed on every space craft to move them to a graveyard, moon intercept or decay orbit.
- it could be set to pick up space junk.

The primary drawback

I have to repeat though what I said in previous threads. There are two basic types of fuels - chemical/nuclear which are capable of creating their own work that applies to thrust, and detached energy - reaction mass systems (and we can add a true EM drive). The second generates very high ISP but with a disproportionately large input and loss of power.

The more you accelerate the reaction mass, the higher proportion of energetic power is lost to that reaction mass. This is not a problem if you have a really great source of power, but our current solar panel (structural and area per KW as 1 au) is not there, and nuclear requires alot of cooling. Again with really small craft this is not to much of a problem.

We can think of the Cannae drive as an Ion drive (using either ablated or external ions) that has a ISPv of 3 x 10^7 m/s (ISPg = 3000000). It takes a whopping amount of hv to create any useful amount of thrust. Therefore if we argue that its twisting quantum length over [arms stretched wide range] then - ok- but then were is the power supply?

acceleration  =  2 * efficiency * power / ISPv * mass

IMHO we should not even concern ourselves with whether Cannae works the way some think it does, the primary concern in deep space travel is power/mass generation. Even if it works they way they say it does, and I believe it approximates that which has been detailed, its not a perpetual motion machine, and it cannot generate any additional power for thrust. Therefore if we add a stringent power requirement Cannae is all but useless.

 

 

Edited March 14, 2016 by PB666

[Bill Phil]

1 hour ago, K^2 said:

Because it gains momentum at a rate that doesn't match the loss of energy. So it either generates off-the-shell exhaust, which is impossible, or it doesn't conserve momentum, which is even more impossible.

If it interacts with some medium to produce this thrust, then it merely becomes very improbable.

The best I can tell is that it's based on "vacuum pressure", whatever that means. No confirmation, of course. 

[PB666]

53 minutes ago, Bill Phil said:

The best I can tell is that it's based on "vacuum pressure", whatever that means. No confirmation, of course. 

Vacuum energy is basically virtual particles, read the link I provided a few days back to the thread, virtual particles can act, but there is a limitation upon the distance.

 

[Streetwind]

3 hours ago, Bill Phil said:

Interesting...

If we ignore the scientific issues, what could this bring to propulsion technology?

One of the lead scientists involved in quantum thruster research at Eagleworks estimated between 0.1 N/kW and 0.4 N/kW for this technology. Compare to contemporary ion engines, which do 0.05 N/kW at 2,000s Isp, or 0.01 N/kW at 19,000s Isp.

In other words, it's fairly straightforward - imagine an ion drive that gets ten to twenty times the thrust per power input, mounted on a spacecraft that doesn't need to dedicate mass toward storing fuel. That's among the best case scenarios as of today's rough estimations. IF it works as a hypothetical quantum thruster, of course, and not as something else.

The world is certainly holding their fingers crossed

 

Edited March 14, 2016 by Streetwind

[FreeThinker]

Could it be that Em Drives are a form of Lorenz Effect Propulsion which use Earth Magnetic Field to generate thrust?

It that is the case, we could create more effective Lorence propulsion method using high power magnetic fields

Someone had the same idea and found a ingenious way to use this to turn it into a orbital propellar which could lift a craft into space. Now the only thing we need are powerfull ligh reactors or transmitted power grid ...

Edited March 14, 2016 by FreeThinker

[PB666]

4 hours ago, FreeThinker said:

Could it be that Em Drives are a form of Lorenz Effect Propulsion which use Earth Magnetic Field to generate thrust?

It that is the case, we could create more effective Lorence propulsion method using high power magnetic fields

Someone had the same idea and found a ingenious way to use this to turn it into a orbital propellar which could lift a craft into space. Now the only thing we need are powerfull ligh reactors or transmitted power grid ...

1. Nope this has already been ruled out in the latest set of experiments

2. regarding 2 posts above, its not likely that the power efficiency is 0.1 N/kW and 0.4 N/kW, in fact, whoever said this don't believe anything he/she says.

 

[K^2]

8 hours ago, Rakaydos said:

Off the Shell exhaust? You said it's impossible, but what does it even mean?

Once you throw in momentum, the famous "E = mc²" becomes E² = p²c² + (mc²)². Physicists often use "natural units", where c = 1. So this becomes E² = p² + m². If you graph the three components of momentum p and the mass m together, all allowed values form a hypersphere of radius E. This is called the Mass Shell.

There is a fundamental reason for this shell's existence. Only propagators that are on the mass shell preserve amplitude. Translated to what it means for the particle, in order for a particle to propagate freely in space over a "large" distance, it must be "on the shell". Off-the-shell propagators are a mark of virtual particles. They do not satisfy the above equation, but neither can they propagate freely. They have to be absorbed after a very short jump. Typically, we are talking about distances between atoms or less.

Because of this, no matter what Quantum weirdness is happening within a particular drive, if we step back a little, and draw an imaginary boundary around our space craft, everything leaving the spacecraft must satisfy the mass shell equation. This is why Quantum Thruster is possible, but it must produce an exhaust that's on the shell somewhere downrange. And this leads right back to conservation of momentum and energy.

If the net exhaust from the drive has m = 0, then we have a trivial E = pc. That's 300MW per 1N of thrust. Mind, even a drive that achieves precisely that would be fantastic, because we have no idea how to build anything close to 100% efficient photon drive. It wouldn't be immediately useful, but we'll find a use for it in the future.

If mass of the exhaust is not zero, then the spacecraft is shedding that mass. Whether it's doing so directly, like a conventional rocket or an ion drive, or converts energy into mass doesn't matter. Because in craft's own frame of reference, any energy it has on board contributes to its total mass. E = mc². So regardless of mechanism, the best we can have is an equivalent of a really efficient ion drive.

7 hours ago, Bill Phil said:

The best I can tell is that it's based on "vacuum pressure", whatever that means. No confirmation, of course. 

That doesn't work, either. Vacuum is a medium. You can push from it, but like with any medium, the only way to do that is to excite the medium. Even if you are swimming in a pool and push from water, from perspective of field mechanics, what you are doing is creating all kinds of quasiparticles in the water which you use as a form of exhaust.

Now, you can do that with vacuum. But all of the excitations in vacuum follow the shell rules above. You still need a minimum of 300MW per 1N of thrust if you didn't bring any propellant on board.

[PB666]

2 hours ago, K^2 said:

They have to be absorbed after a very short jump. Typically, we are talking about distances between atoms or less.
 

To be precise, a hydrogen atom is hypothetically 40 picometers in diameter. Planks length is 1.616199(97)×10⁻³⁵. However, the paper demostrates that virtual particles can act over distances about 10 times the size of a hydrogen atom. So planck's length is not really a constraint. In fact I suspect is has alot to do with how gravity is manifest (inertia) in the our current universe, there has been yet to be found a useful meaning of planck's length other than it is the smallest length that might ever be seen. Double special relativity holds that the length is constant.

Again given the difference were quantum momentum transfers can occur and the universal lengthstick I suspect that the virtual transfers have multiparametric components. We shall have to see.

Are you yet ready to see this drive in space?

[PB666]

I think, I may be wrong but electron density is key. Copper for instance face center cube. 1s2 2s2 2p6 3s2 3p6 3d10 4s1

* ss ss pp pp pp ss pp pp pp dd dd dd dd dd s

http://winter.group.shef.ac.uk/orbitron/AOs/4s/wave-fn.html

The wave density function for 4s is shown here, the wave function extends much further than maximal electron density.

Then we get into assumption, the surface electrons on the appartus would be radicals of a sort, particularly in oxygen, and more than likely the surface layer would be sulfate, oxide, hydroxide. So basically the surface shell is going to be the distance from the copper + whatever atoms are bound on the surface layer and their electrons. On top of this then we have the low probability density functions of these ionic components and potentially radicals that might exist.

So we actually can, in considering electron dynamics get pretty far away from copper atoms on the surface, I would say maybe 5 Angstrom (500 picometer).

 

[FreeThinker]

Here is an interesting interview with the original Developer of the EM-Drive

 

Edited March 18, 2016 by FreeThinker

[FreeThinker]

One thing as a mod developer I would realy like to be answered is how does the Em-Drive scale with Power and Size. Will there be an upper limit? will it come down to surface area? Is posible to achieve TWR higher than than 1?

What about stacking multiple EM- Drives together, will they interfere? Can they be build inside a vessel? Can they be miniaturized into Thrusters?.

[Scotius]

Smallest model of Emdrive i've seen on video was about the size of coffee cup. Allegedly superconducting model can achieve TWR>1. Allegedly (since it is supposed to be reactionless drive) it can be built inside a ship.

[kunok]

We don't really have idea if it really works less how will be it's characteristics.

Still I really will like to have an engine mod to a type of engines that works only close to at atmosphere or when in an atmospheric low pressure, the way @K^2 proposed. It can be interesting from a gameplay view, a total different approach.