Mach Effect Thrusters: Humanity to the Stars

[Zeiss Ikon]

There's a semi-famous quote found on atomicrockets.com: "Friends don't let friends write reactionless drives."  This is because a reactionless drive overthrows "the tyranny of the rocket equation."  Given enough energy and time, a reactionless drive can reach relativistic velocity with a relatively small ship, one that isn't 99.99999999% reaction mass.  Singleships become a possibility -- starships crewed by a single person.  Interstellar exploration and colonization is limited only by the relativistic speed limit and the availability of a suitably powerful and durable energy source: you can go in less than a human lifetime aboard the ship (assuming you find a way to shield against space junk at relative velocity of .9 c or higher), but if you come back you'll be centuries or millennia in the future.

That quote may need to be retracted soon.  Humanity apparently already has a reactionless thruster that has been shown to work, has a theoretical basis that holds up to peer review, and appears to be scalable to a level that would, at the minimum, support generation type colony ships traveling at above .1 c and probes traveling at .4 c.

This article, despite being headed with photo of a test article of an EM drive that hasn't be conclusively demonstrated to produce thrust, details a different design of partially mechanical thruster that depends on something called the Mach Effect, in which a mass that is both changing velocity and changing energy (the latter, for instance, due to changing electrical charge) changes (inertial) mass.  Given this (long predicted by theory and well tested, by this point) phenomenon, one need merely "push while the mass is heavy, and pull while it's light" at a reasonably high frequency to obtain a time averaged net thrust.  Even if your individual drive units only give net thrust of a few millinewtons (at present, 2 mN is the tested value), the fact they don't throw mass overboard means they can, if run for long enough, accelerate a large ship to arbitrary rapidity (rapidity is a linear measure of internal-apparent velocity, taking Lorentz contractions into account -- unlike velocity, which is limited to the speed of light, rapidity can be arbitrarily large).

Whether it will make sense to launch generation ships to plant colonies will depend on a lot of factors -- whether we can confirm habitable planets at interstellar distances, and how rapidly we expect travel rates to increase (and especially if we believe a warp-based FTL is possible) -- but the capability to do so may exist before the end of this century.  Or sufficient scaling of Mach effect thrusters may become like hydrogen fusion -- ten to twenty years away for the past half century.  I suspect we'll know before there are enough people living on Mars to fill a small town.

Edit to add: No, this isn't an April Fool, either.  I just found it today, but the article linked is dated from last October.

Edited April 1, 2018 by Zeiss Ikon
Address possible concern

[p1t1o]

Any links to the peer-reviewed abstracts?

Edited April 1, 2018 by p1t1o

[YNM]

IMO "Reactionless" doesn't imply no traditional propellant. A car sliding down a hill is reactionless if that's enforced to the strictest limits.

The rather large question with such energy-expending but not mass-expending (traditional sense) thrusters/drives is that "how do they point the energy". The spinning rotor of a helicopter makes (almost) no movement at all for the helicopter, until it is directed - and both expends energy.

So yeah, while engineers would probably don't care much on how it really works in the first place as long as enough info are given for it's usage, we still need to know what happened (or happening).

Edited April 2, 2018 by YNM

[DerekL1963]

Well, the article isn't entirely wrong...  they did get a NASA contract.   But NIAC contracts are kind of like DARPA, small investments in "out there" concepts that may or may not be valid and may or may not yield usable technology in the future.

https://www.nasa.gov/press-release/nasa-invests-in-shapeshifters-biobots-other-visionary-technology
https://www.nasa.gov/directorates/spacetech/niac/2018_Phase_I_Phase_II/Mach_Effect_for_In_Space_Propulsion_Interstellar_Mission

Or, to put it another way, the article Zeiss links to is just wee bit...  well, the polite term is incredibly optimistic.

[wumpus]

While it is likely that the em-drive is bunk, that doesn't mean that massless (or asymptotically massless) thrusters are impossible.

You can easily create momentum bearing objects from pure energy and fling them out your exhaust port: an LED does this very well.  There are known to be hard limits on the thrust an em-drive can produce without breaking *more* physical laws (such as energy conservation).  It is quite possible that this is the limit (although probably for perfectly efficient light sources of arbitrary low wavelength, not real LEDs).

You can build an ion drive with arbitrary Isp out of a synchrotron.  I'd assume that both the thrust and the efficiency aren't remotely serious for interplanetary use, but they might be reconsidered for interstellar uses.  Just change the Ve in the rocket equation to p/m_r and solve for the relativistic momentum (m_r meaning rest mass).

At this point I suspect the limiting factor is energy, not the tyrannical rocket equation, and I'm not sufficiently familiar with the energy problems of interstellar craft (the rocket equation essentially forbids them).  One thing to remember: if your output is sufficiently inefficient you might wind up getting more thrust from intelligently designed cooling panels (that emit sufficiently high frequency EM in the right direction).

 

[Zeiss Ikon]

1 hour ago, p1t1o said:

Any links to the peer-reviewed abstracts?

This kind of link?  https://www.sciencedirect.com/science/article/pii/S0094576517308111

Quote

Abstract

The Mach-Effect thruster is a propellantless propulsion concept that has been in development by J.F. Woodward for more than two decades. It consists of a piezo stack that produces mass fluctuations, which in turn can lead to net time-averaged thrusts. So far, thrust predictions had to use an efficiency factor to explain some two orders of magnitude discrepancy between model and observations. Here, a detailed 1D analytical model is presented that takes piezo material parameters and geometry dimensions into account leading to correct thrust predictions in line with experimental measurements. Scaling laws can now be derived to improve thrust range and efficiency. An important difference in this study is that only the mechanical power developed by the piezo stack is considered to be responsible for the mass fluctuations, whereas prior works focused on the electrical energy into the system. This may explain why some previous designs did not work as expected. The good match between this new mathematical formulation and experiments should boost confidence in the Mach effect thruster concept to stimulate further developments.

BTW, I appear to have misread or misremembered the thrust levels tha thave been replicated; it's 2 microNewton not 2 mN.

[Steel]

1 hour ago, Zeiss Ikon said:

That quote may need to be retracted soon.  Humanity apparently already has a reactionless thruster that has been shown to work, has a theoretical basis that holds up to peer review, and appears to be scalable to a level that would, at the minimum, support generation type colony ships traveling at above .1 c and probes traveling at .4 c.

"has been shown to work" is a strong statement. From what I've read, METs are in the same sort of shape as EM drives. Some people report seeing small thrusts, others report measuring no measurable thrust at all, several tests conclude that external factors and interference is likely to be skewing the results.

[magnemoe]

2 hours ago, Steel said:

"has been shown to work" is a strong statement. From what I've read, METs are in the same sort of shape as EM drives. Some people report seeing small thrusts, others report measuring no measurable thrust at all, several tests conclude that external factors and interference is likely to be skewing the results.

Two ways to test it, one is to ramp up power 2-3 order of magnitude to get better data, other is to test it in space. If orbital period increase you have an deal. 
3rd way who look like is the one selected is to increase performance. 
However even an em-drive of current performance would be very useful for stuff like satellite station keeping and reaction wheel bleed of. 
Not only because no fuel use but because of simplicity, 

[magnemoe]

2 hours ago, wumpus said:

While it is likely that the em-drive is bunk, that doesn't mean that massless (or asymptotically massless) thrusters are impossible.

You can easily create momentum bearing objects from pure energy and fling them out your exhaust port: an LED does this very well.  There are known to be hard limits on the thrust an em-drive can produce without breaking *more* physical laws (such as energy conservation).  It is quite possible that this is the limit (although probably for perfectly efficient light sources of arbitrary low wavelength, not real LEDs).

You can build an ion drive with arbitrary Isp out of a synchrotron.  I'd assume that both the thrust and the efficiency aren't remotely serious for interplanetary use, but they might be reconsidered for interstellar uses.  Just change the Ve in the rocket equation to p/m_r and solve for the relativistic momentum (m_r meaning rest mass).

At this point I suspect the limiting factor is energy, not the tyrannical rocket equation, and I'm not sufficiently familiar with the energy problems of interstellar craft (the rocket equation essentially forbids them).  One thing to remember: if your output is sufficiently inefficient you might wind up getting more thrust from intelligently designed cooling panels (that emit sufficiently high frequency EM in the right direction).

 

Photon drives works but not very well  Solar sails is a bit better
You can get an in practice reactionless drive interacting with an magnetic field. don't work so well in earth orbit but should work well on Jupiter. 
It however has an limit in that the energy you use to brake into orbit has to be equal to the kinetic energy you kill. 
This is also nothing new, same is true for accelerating and braking an car, acceleration will tapper of even on an dragster not only because air resistance but because you kinetic energy increase v^2. 

Otherwise physic has an serious problem, you can turn an em drive into an perpetuum mobile pretty easy: flywheel in an vacuum chamber, add em-drives to it, spin it up and turn on the drives.
it takes very modest rpm to have them move so fast you can generate serious power with an 10 meter flywheel. 
In space this is very easy. 

My guess is that if it work its energy limited, and yes energy requirements for 0.1C is idiotic high, still an good em-drive and some breeder reactors for power should work. 
On the gripping hand Fermi paradox suddenly get very bleak, we should get some interstellar colonies asap.  

[Bill Phil]

Well, Q thrusters can do it, as can photon rockets. They just create tiny amounts of thrust for massive energy expenditure, and aren't reaction-less. Even this system described isn't reaction-less. Reactions are happening, just of a different sort.

[wumpus]

7 hours ago, magnemoe said:

Photon drives works but not very well  Solar sails is a bit better
You can get an in practice reactionless drive interacting with an magnetic field. don't work so well in earth orbit but should work well on Jupiter. 

Both of these require you to remain near a star or planet, and you will exceed escape velocity .00001% of your way to relativistic speed.  Drifting between stars under constant acceleration leaves you with fewer choices.

[K^2]

12 hours ago, Zeiss Ikon said:

"push while the mass is heavy, and pull while it's light"

Nope, can't be done under modern Field Theory. The problem is that stress-energy tensor is the gauge charge of the local symmetries of space-time, which means there is an associated conserved flow. To put plainly, you can't just increase energy/mass of an object. That energy has to flow towards or away in a continuous manner, and the flow itself has inertia according to the energy/mass it carries.

Because people's brains tend to swell and overheat when trying to reason about mechanics of quantum fields, there is a fantastic simplification here. The conserved current acts just like any other current. Even a liquid flow. So lets forget all about relativity and quantum mechanics. Try to build a classical propulsion system where you change the mass of the oscillating object. Lets say, a bucket of water. We'll pump water in, push the bucket away, pump water out, and pull the bucket back in.

Wait, that can't possibly work! But why? Because the water flowing into/out of the bucket is the thing that carries mass. As it flows through whatever plumbing back towards you so that you can fill the bucket again, it cancels out all the thrust you may have generated.

A relativistic "thruster" on the same principle suffers from exactly the same problem. The energy that flows into the charged particle before you push it away has to flow out at the far end. Then that energy has to flow back to the front end, presumably, as electrical current. And that electrical current will have exactly the same momentum as what you got out of the push in the first place, because it's exactly the same amount of energy just sloshing about inside your "thruster".

Now, just like in the classical sense, you can chose to abandon that water. If you can fill the bucket from a store, and simply expel the water in the back before pulling bucket in, you will get net thrust. But it will be exactly the same net thrust as if you just expelled the water out the back. If you don't reclaim energy in the relativistic version, with charges, the energy is expelled in the only way massless energy can exist, as photons. So you ended up building a photon drive. Best case scenario, 300MW per 1N of thrust, but odds are, it will actually be extremely inefficient, and you'll get a lot less thrust than that.

[PB666]

It really doesnt matter, when the thrust is P/30MW instead of a P/300MW it roughly means that the drive is ten times less useless than a photon drive. Since the are no 30MW power supplies in space to tap into, and the frictional,force exceeds the force that could be imparted using power from solar panels . . . . . .roughly two useless curiousities. 

Edited April 4, 2018 by PB666

[Nuke]

oooh megadrive thread!

[FreeThinker]

@Zeiss Ikon @SpaceMouse  and I have been working on a Mach Effect Engine drive for KSPIE. Spacemouse has made double fully rotatable engine model of the Mach Effect Engine. The idea is to fit a vessel with at least 2 engines, allowing it to make any maneuvers in space while keeping the vessel in the direction of travel

There is any interesting video on the topic of using the Mach Effect drive for interstellar travel

Now we need help converting the equation found Mach Effect thruster Model pdf into a usefull formula which I can use to calculate thrust given electric input power, engine capacity and speed of the vessel. Any help would be appreciated.

Edited May 5, 2018 by FreeThinker

[Nuke]

they said they wanted to use a phased array of small thrusters. i have a hunch that if the drive works, you could do the thruster as a mems device, throw the hardware for the phased array right no the die next to the thruster and build a full array on a pcb plane, which then can be stacked into a block, place the whole thing on a fully articulated gimbal platform and produce thrust in any direction. i also dont think it works as an electric -> kinetic transducer as most reactionless drives claim to be. woodward was claiming f1 level performance from an engine that could run on existing space power systems. you are really just powering a vibrator and keeping it in tune to the natural mass fluctuations of the universe. the universe is essentially your reaction mass. of course extraordinary claims, etc.

Edited May 6, 2018 by Nuke

[kerbiloid]

Yesterday I've read that pdf document, aligned the formulas and the given data in their logical sequence, into an odt.
Looks like everything required for the calculation is there, nothing is omitted (except Young Modulus of stainless steel, which can be taken from a book).

But there are several strange things.

1. They use "angular frequency" w.
They use it in harmonic oscillation formulas like sin(wt+p/2), so I guess it already includes 2p.
As I thought before, w = 2pf, where f is a "just frequency".
But on page 10 they say literally: "with a  frequency f = 2pw", still substituting w in the sines.
That's strange.

2. On page 16 they calculate electrical capacity of the scheme, substituting the length of a single piezo disc.
And never multiply it by the disc number (though at page 6 they say that the discs are "electrically connected in parallel", so I guess their capacities should be summarized).
If I calculate this capacity, it's 1.8 nF (i.e. exactly 1/8 of total capacity of all 8 discs used in the plant).
But at page 18 they say that total capacity is 14 nF, i.e. they multiply it by 8 but never mention this in formulas.

3. They never show intermediate or given values (used voltage, frequency, numerous coefficients). 
All intermediate formulas look simple and logical, their results look quite sane.
But the formulas for thrust and power either require arbitrary values (such as voltage and frequency) which are unknown, or give results other than in pdf if substitute V and w in those rare cases when they are given.
From ~25% to orders of magnitude (when they are ~V^2..4 and w^4..6 and you don't have proper data to substitute, that's nothing strange.).

4. There are three different formulas for thrust.
Two of them are F~w⁴ and one is F~w⁶.
As the w would be selected from the resonance series (page 21) which depend on the mass and geometry, this probably makes the calculation result highly volatile.
Authors know about this and mention the 4-vs-6 somewhere (can't find again at the moment), but this is enough good approximation for exactly this plant.
Also they say that the system parameters will significantly vary if (scale the system).

All three formulas give rather differing results in general case, and if you put them aside to each other, reduce the same coefficients, and find out that they require enough strange looking coefficients to be more or less equal

5. On page 18 they give formulas for effective power and and power loss.
According to that, the loss is ~4% of the effective power. So, is the oscillating electromechanical system 96% effective?

So, I'm afraid this pdf gives not very much in sense of a real scale engine calculation.

(I can upload my odt, but unlikely it will add something)

Edited May 7, 2018 by kerbiloid

[Nuke]

one thing that's always bugged me is how do they know what the mass of the universe is doing at any given time and how would this occur in any predictable and therefore exploitable way? im assuming it has something to do with gravity waves, any chaotic signal would have well defined harmonics. i think in one of their ssi videos they called it a 'transient' (i presume they mean something in their signals that shouldnt be there, or has not been accounted for) and it was one of their points of interest, a manifestation of the mach effect perhaps.

 

i still have some serious doubts though, given that their lab looks smaller than my bathroom and that so many other people giving talks at the ssi conferences seemed like total quacks (all the mach effect people shooting things down left and right). was kind of a big red flag for me. other people are starting to build their own mach thrusters. the guy on hack-a-day doing the baby em drive has switched to mach thrusters. it does seem that many of the 3rd party tests come from the same devices being tested in other labs. so it would be interesting to see a new device get tested. also seemed like the only progress they made in the last year or so was looking at new materials to replace the rather self destructive pzt discs. the more thrust mantra still remains (and franlky thats a good thing for anyone building reactionless drives, get us results outside of the noise threshold for a change).

[KSK]

On 5/6/2018 at 12:30 PM, Nuke said:

i also dont think it works as an electric -> kinetic transducer as most reactionless drives claim to be. woodward was claiming f1 level performance from an engine that could run on existing space power systems. you are really just powering a vibrator and keeping it in tune to the natural mass fluctuations of the universe. the universe is essentially your reaction mass. of course extraordinary claims, etc.

You see, eventually your music  the beat from your space drive will help put an end to war and poverty. It will align the planets and bring them into universal harmony, allowing meaningful contact with all forms of life, from extraterrestrial beings to common household pets. And... it's excellent for dancing.

[Nuke]

2 hours ago, KSK said:

You see, eventually your music  the beat from your space drive will help put an end to war and poverty. It will align the planets and bring them into universal harmony, allowing meaningful contact with all forms of life, from extraterrestrial beings to common household pets. And... it's excellent for dancing.

i was thinking invading the aliens and taking all their stuff. but we can listen to reign in blood while were doing it. 

[K^2]

Flippin' finally. This goes for both EM Drive and Mach-Effect Thruster. Physics 2:0 Sci-Fi.

 

[Scotius]

There is always Q-Thruster yet

[K^2]

They all have the same problem. They don't consider the entire stress-energy flow. Best analogy that should appeal to everyone here, it's like trying to understand lift without considering how air flows away from the wing.

Now, I'm not saying that it's definitely absolutely impossible to generate thrust without exhaust. There are two loopholes in conservation of momentum that I'm aware of, and there could, of course, be more.

1) It's not strictly necessary for an object that has momentum to be moving. So in principle, a linear gyro does not violate conservation laws, and in vicinity of a massive body, a linear gyro is just as good as reactionless drive. Not to mention that linear gyro allows for generation of artificial gravity on a ship, which is all kinds of nifty. Unfortunately, conditions under which you have excess momentum in the system not associated with movement of center of mass are scarce, and building a device that can function as a linear gyro is definitely an unsolved problem.

2) Mössbauer Effect allows for recoil-free transfer of momentum in a periodic lattice. If our universe happens to have large scale periodic structure, such as if the universe has T³ topology ("doughnut" shaped universe), then momentum is technically quasi-momentum, and reactionless drives are at least theoretically possible. I can tell you significantly less about how one of these would work than I could tell you about building a practical warp drive, but it's one of these "doesn't contradict basic physics" things.

 

Every time people talk about reactionless drive, I allow for a tiny possibility that somebody accidentally stumbles onto one of these loopholes. But there is absolutely no doubt that it'd be entirely by accident for the kind of explanations we've been seeing for EMD, QT, and MET. You'd have the same chance of accidentally inventing reactionless drive by playing with magnets or literally trying to pull yourself up by your own hair.

In terms of anything like a forecast, if we ever break free from tyranny of rocket equation, the most likely candidates are linear gyros and sub-light warp, likely working together. A ship equipped with both can take off and land on planets, establish or break orbit, and go anywhere within Sol in a matter of hours, all within comfort of 1g for all on board and without requiring enormous amounts of energy. And we're not going to get there with the help of crackpots playing with resonance chambers. It would be through a lot of very clever applications of field theory, involving some paradigm shifts in how we interpret the math, and an absurd amount of computational power. We're honestly making progress on warp. Just not something anyone should be expecting anything from for many decades.

[Nuke]

the development of high precision thrust balances is the interesting part. we kind of know where the gotchas are now. i cant believe they didnt think of the earth's magnetic field, because thats on of the first 'didja check' things i was thinking of. i guess its time to test all the things and let the cull begin.

Edited May 23, 2018 by Nuke

[sevenperforce]

A compact resonance chamber that can produce thrust effects equivalent to an electromagnetic tether would be hella useful, even if it wasn't truly reactionless. LEO-to-GEO-and-back space tugs that never have to be refueled? Sign me up!