Quantum vacuum plasma thrusters as starship propulsion?

[Pyotor Gagarin]

Something about quantum vacuum plasma thrusters seems a little too good to be true.

Unlimited propellant.

One whole Newton from only 3kW.

Nevertheless, It looks like NASA's "Eagleworks" lab has been taking some interest in this concept over the last four years.

So could Q-thrusters eventually take a place alongside Bussard Ramjets, and Antimatter Pion drives as a favored hypothetical method of starship propulsion? Could they surpass these to become a real technology? Or are they headed nowhere fast? Please share your thoughts and predictions.

[EatThePath]

Until it's been verified to hell and back, I will always distrust reaction-less thrusters and put them in the bad science category. I don't know enough quantum to debunk this myself, but it hits the right notes to get red flagged.

[Pyotor Gagarin]

Until it's been verified to hell and back, I will always distrust reaction-less thrusters and put them in the bad science category. I don't know enough quantum to debunk this myself, but it hits the right notes to get red flagged.

Note: Q-thrusters are not reaction-less. They would push against quantum vacuum plasma instead of using onboard propellant. Still a far fetched idea, but apparently not breaking Newton's third law.

[EatThePath]

So what happens to the momentum when those virtual particles wink back out of existence? If it just vanishes, then the drive is breaking conservation of momentum, isn't it?

[Fractal_UK]

So what happens to the momentum when those virtual particles wink back out of existence? If it just vanishes, then the drive is breaking conservation of momentum, isn't it?

Remember that the quantum vacuum is not empty, it does not even have an average energy of zero. There is some non-zero energy associated with the quantum vacuum at all points in space (though quite how much is a big problem in physics as quantum theory suggests that this energy might be enormous but observations suggest it is probably tiny), either way, no matter how small it is this energy has some associated mass which means that if one can influence it then such an engine would not violate the conservation of momentum.

[Jokurr]

Interesting stuff, this is the first I've heard of it. A crazy high specific impulse and a thrust level that beats ion engines by a considerable margin. If it turns into a reality that could have profound implications.

[K^2]

Keep in mind that a quantum plasma drive has maximum theoretical efficiency of a photon drive. I believe, the only theoretical advantage is better TWR. Still, you need ridiculous amounts of energy to obtain any useful thrust.

[NovaSilisko]

Well, the Dawn spacecraft's ion engines produce on the order of tens of millinewtons and consume several kW of power, this on the other hand produces a whole newton (already more than the majority of ion engines), from 3 kW (in theory, of course!)

But it's still probably the most promising propulsion system under development, I think. It's come much farther than a lot of concepts of this nature in that prototypes are actively being developed.

[K^2]

Anything over 10μN at 3kW would violate conservation of momentum. Same deal with specific impulse over 3x10⁹. I don't know if miscalculation is on the part of the researchers or if whoever wrote the article messed up orders of magnitude, but these numbers are wrong.

P.S. It might be that the researchers computed thrust based on mass of electromagnetic vacuum, but you cannot use that for propulsion. That's a fairly important consequence of the field theory.

P.P.S. I really should expand on that point, probably, but I'm not sure how to do so in simple terms. Basically, it's a matter of having access to a finite spectrum due to the whole thing being localized in space and time. Yeah, you can take a fluctuation in electromagnetic vacuum and push off of it. But if you only do this locally, all you produce is waves. Specifically, electromagnetic waves. Light. Your rocket's "exhaust" has zero rest mass, and so you are limited to performance of a photon drive.

Edited May 29, 2013 by K^2

[Rune]

Anything over 10μN at 3kW would violate conservation of momentum. Same deal with specific impulse over 3x10⁹. I don't know if miscalculation is on the part of the researchers or if whoever wrote the article messed up orders of magnitude, but these numbers are wrong.

P.S. It might be that the researchers computed thrust based on mass of electromagnetic vacuum, but you cannot use that for propulsion. That's a fairly important consequence of the field theory.

P.P.S. I really should expand on that point, probably, but I'm not sure how to do so in simple terms. Basically, it's a matter of having access to a finite spectrum due to the whole thing being localized in space and time. Yeah, you can take a fluctuation in electromagnetic vacuum and push off of it. But if you only do this locally, all you produce is waves. Specifically, electromagnetic waves. Light. Your rocket's "exhaust" has zero rest mass, and so you are limited to performance of a photon drive.

Uhh... that explains some things a bit. But, I must confess, I still don't get the whole thing at anything close to the level where I can comment on its feasibility. Still, my automatic response to seemingly reactionless drives is always "something smells fishy".

So what you are saying is that it would boil down to a photon drive? Then the effective isp would depend on your powerplant, I guess. And a big powerplant that would be, nothing like 3kw/N, that's a few orders of magnitude off.

Also, a google search tells me this is another name for a Mach Effect drive. I've always been very skeptic of that. But it reiterates the 3kw/N system thrust ratio. I'm a bit baffled.

Rune. The thrust thing is very weird. Wouldn't such a high T/W electric thruster be a breeze to demonstrate?

[magnemoe]

Its a bit fishy and probably don't work, however its an high risk/ high payoff project who is pretty inexpensive to test so they test it.

[Baughn]

The test results look good, anyway. Not 3kW/N, but good enough to be useful if it's real and not environmental. It's definitely good enough to test.

But! This is KSP. It'd make a good addition to KSP Interstellar or a similar high-tech mod, I think, as an endgame ion engine equivalent; nice power sink, no reaction mass needed but not suitable for landings or takeoff except perhaps on Minmus.

[TheGatesofLogic]

Until it's been verified to hell and back, I will always distrust reaction-less thrusters and put them in the bad science category. I don't know enough quantum to debunk this myself, but it hits the right notes to get red flagged.

Q-Thrusters technically aren't even reactionless, but this is:

http://www.emdrive.com/yang-juan-paper-2012.pdf

Special relativity makes everything better

[Scotius]

The test results look good, anyway. Not 3kW/N, but good enough to be useful if it's real and not environmental. It's definitely good enough to test.

But! This is KSP. It'd make a good addition to KSP Interstellar or a similar high-tech mod, I think, as an endgame ion engine equivalent; nice power sink, no reaction mass needed but not suitable for landings or takeoff except perhaps on Minmus.

Quantum Thruster is already in KSPI It's high on the Tech Tree - hogs a lot of power, but allows for building ships with incredible amounts of dV. Scott Manley featured it in his KSPI series. Look it up.

[K^2]

There is some bad science behind Quantum Thrusters that resulted in them appearing to be over-unity efficient. From perspective of field theory, a good Quantum Thruster is just a very efficient photon drive. In other words, you need roughly 300kW of power per 1N of thrust. Which might actually turn out to be the best photon drive we can build, but without a matter-antimatter reactor, it's not sufficiently efficient to be of any use.

If your power source is nuclear, your best bet is ion drives. You'll get better maximum dV for amount of fuel/propellant you bring.

[KASASpace]

If I recall correctly, they meant for the Q-thruster to be a form of RCS.

[K^2]

If I recall correctly, they meant for the Q-thruster to be a form of RCS.

That would just be silly.

[KASASpace]

That would just be silly.

1 Newton of Thrust is more suited to maneuvering than full scale propulsion, especially if it doesn't need a nuclear reactor to get that thrust.

It is Wikipedia, but it says it all (1 Newton and all):

http://en.wikipedia.org/wiki/Quantum_vacuum_plasma_thruster

[K^2]

1 Newton of Thrust is more suited to maneuvering than full scale propulsion, especially if it doesn't need a nuclear reactor to get that thrust.

It is Wikipedia, but it says it all (1 Newton and all):

http://en.wikipedia.org/wiki/Quantum_vacuum_plasma_thruster

Contrary to that page's claims, it takes 300kW of power to generate that 1N of thrust. In other words, with modern reactors, even an arcjet is going to make for a more efficient RCS.

[Guest]

Not "more efficient", stronger maybe, but remember that we're talking photon drives. Nothing can be more efficient than a photon drive if we go by the traditional definition (since it doesn't throw away any mass). That said, using a photon thruster as RCS would still be a terrible waste, since they sit idle most of the time. As such, an RCS thruster needs to be light, efficiency is a secondary concern.

[Streetwind]

As far as I gathered then, this quantum thruster would be analogous to a an electric propeller for atmospheric flight. An electric propeller plane carries and expends no propellant whatsoever; it just uses electricity to spin the rotor, which pushes against something (in this case the atmosphere). The quantum thruster would push against something as well, so it's not reactionless. Still, it's kind of hard to imagine that this thing is actually workable, especially with those performance numbers. This is not something you can point at and say "yeah, I can see this working if they manage to figure out how to build it". This is more along the lines of "yeah, pics or it didn't happen". Just look at all the hubbub around the Woodward effect: it's closely related, and despite repeated claims for "experimental verification" still remains vaporware after decades. None of the alleged results have been verified by actual credible sources.

In the near term, other forms are far more realistic and interesting. For RCS, you can just take pulsed plasma thrusters. Isp in the neighborhood of 1,400s is "only" four to five times that of chemical RCS, but these things are tiny, uncomplicated, dirt cheap and do 1N on less than 90W of power. Yes, not kW, just W. These things are among the oldest forms of electric propulsion and have been flown many times. Even cubesats can utilize these kinds of thrusters despite only having a solar panel the size of a hand or two.

EDIT: woops, derped a unit conversion. The PPT actually does require kW, not W. (They're still being considered for cubesats, just with less thrust than I thought.)

Edited April 14, 2014 by Streetwind

[K^2]

Not "more efficient", stronger maybe, but remember that we're talking photon drives. Nothing can be more efficient than a photon drive if we go by the traditional definition (since it doesn't throw away any mass). That said, using a photon thruster as RCS would still be a terrible waste, since they sit idle most of the time. As such, an RCS thruster needs to be light, efficiency is a secondary concern.

You are forgetting mass of the reactor fuel you have to power the drive. If you have matter-antimatter reactor, yes, nothing is more efficient than a photon drive. But if you are using a nuclear reactor, you are stuck with a lot of dead weight. There is the used up uranium mass, the mass of moderators, and the mass of the reactor itself. You don't use it as propellant mass, but it adds to mass of the rocket. As a result, if you consider effective exhaust velocity, instead of c of the photon drive, you end up with a tiny fraction. In fact, a photon drive with a modern nuclear reactor yields something in the 3km/s - 30km/s range. I'd have to do some math to pin-point it better. This makes arcjets competitive at the worst, but I'm pretty sure they'll turn out to be better once I put in all of the numbers.

As far as I gathered then, this quantum thruster would be analogous to a an electric propeller for atmospheric flight. An electric propeller plane carries and expends no propellant whatsoever; it just uses electricity to spin the rotor, which pushes against something (in this case the atmosphere). The quantum thruster would push against something as well, so it's not reactionless. Still, it's kind of hard to imagine that this thing is actually workable, especially with those performance numbers.

It pushes against the fields. Predominantly, electromagnetic field. Naturally, whatever carries away momentum is the excitation in the relevant fields, carrying the momentum. Which brings us right back to it being a photon drive. So yeah, performance numbers are bogus.

[DaveofDefeat]

So whats a photon drive and how is it different from a flashlight?

[K^2]

A flashlight can work as a photon drive. Just not a terribly efficient one. Basically, any drive where recoil is carried away by electromagnetic radiation is a type of a photon drive.

[KASASpace]

Contrary to that page's claims, it takes 300kW of power to generate that 1N of thrust. In other words, with modern reactors, even an arcjet is going to make for a more efficient RCS.

You do realize that the entire point of the Q-thruster is to be a small thruster, right?

That said, the team that actually discovered their viability mentioned they would be useful as RCS.

It is not silly, it is a smart way of using it, as it only costs electricity, so less mass is used in RCS fuel.