Quantum vacuum plasma thrusters as starship propulsion?

[Nuke]

most electric thrusters are quite small. its the power supply thats big and heavy.

[KASASpace]

most electric thrusters are quite small. its the power supply thats big and heavy.

Yes it is.

However, as an RCS this would excel, mainly because the gains you get over not using any fuel, so an array of large solar panels (admittedly, the ISS produces less power.....) could be built, storing it in capacitors or flywheels to be used later on (when behind a planet, or very far away).

Of course, that means you have to bring capacitors and such, but you get more Delta-V than typical RCS systems.

[Nuke]

yea but then the solar panels and their structural trusses are heavy. batteries are heavy, rtgs are heavy, nuclear reactors are heavy. there is no way around the problem. you want a supply to give you the most electrical power with the least weight.

also a thruster is a thruster no matter if you point it front back or sideways. in ksp i have been known of using ion engines for steering using exotic action groupings. ive also done orbital transfers purely on rcs power. im quite fond of thruster arrangements that serve both purposes.

[CaptainArchmage]

It doesn’t violate the laws of physics. It is propellantless but not “reactionlessâ€Â. Additionally, the power use of 500W-3kW says one of these could be tested from a standard electrical outlet in the wall ( which couldn’t possibly go wrong ). The thrust is low but may actually be better than most ion engines in real life, so as long as a suitable power source exists it could be a better choice than many other engines. Again because of the low thrust, you will still need some way to get this into orbit.

[K^2]

Yes it is.

However, as an RCS this would excel, mainly because the gains you get over not using any fuel, so an array of large solar panels (admittedly, the ISS produces less power.....) could be built, storing it in capacitors or flywheels to be used later on (when behind a planet, or very far away).

Of course, that means you have to bring capacitors and such, but you get more Delta-V than typical RCS systems.

You can reduce the size of your power supply, add the propellant for an arcjet or similar electric thruster, and still have a lighter system with more delta-V than you could ever get out of Quantum Thruster. The idea of using Q-Thruster as RCS is stupid. It can only occur to people who don't understand enough field theory to know that it can't outperform a photon drive, and that believe in the absurd 3kW/N figure.

[Rakaydos]

You can reduce the size of your power supply, add the propellant for an arcjet or similar electric thruster, and still have a lighter system with more delta-V than you could ever get out of Quantum Thruster. The idea of using Q-Thruster as RCS is stupid. It can only occur to people who don't understand enough field theory to know that it can't outperform a photon drive, and that believe in the absurd 3kW/N figure.

Why do you need a full newton for stationkeeping maneuvers? even as, say, a 75% efficet photon drive, it's still a good choice for long duration missions, because it "burns" continuously to counter orbital decay without ever needing to refuel.

[KASASpace]

You can reduce the size of your power supply, add the propellant for an arcjet or similar electric thruster, and still have a lighter system with more delta-V than you could ever get out of Quantum Thruster. The idea of using Q-Thruster as RCS is stupid. It can only occur to people who don't understand enough field theory to know that it can't outperform a photon drive, and that believe in the absurd 3kW/N figure.

What? I was basing it off of 300kW/N!

It is no where near stupid. Some people will inevitably fail to realize such things, however.

Now, 1 Newton of thrust is more like station-keeping thruster and maneuvering thruster, heck, the Apollo Command module's RCS produced 444.82216 Newtons of thrust, so clearly it cannot be practically used for much beyond station keeping and similar tasks as Ion engines.

[KASASpace]

yea but then the solar panels and their structural trusses are heavy. batteries are heavy, rtgs are heavy, nuclear reactors are heavy. there is no way around the problem. you want a supply to give you the most electrical power with the least weight.

also a thruster is a thruster no matter if you point it front back or sideways. in ksp i have been known of using ion engines for steering using exotic action groupings. ive also done orbital transfers purely on rcs power. im quite fond of thruster arrangements that serve both purposes.

Yeah, they are. Everything is heavy, but it provides similar advantages as Ion Engines, minus propellant, and much more power required.

[K^2]

Yeah, they are. Everything is heavy, but it provides similar advantages as Ion Engines, minus propellant, and much more power required.

Ion thruster will require about 100x less power. To generate 300kW of power, your ship will need about 3,000 square meters of solar panels. That's about the size of a football field. For 1N of thrust. With an arcjet, you can get the same 1N of thrust from 5kW. Just 50 square meters. Now, which do you prefer to carry with you on your ship? Propellant, or a football field worth of solar panels?

[Alchemist]

Anybody who considers solar powered photon drive should remember 2 words: solar sail.

1) A solar sail to produce the same trust would be much lighter

2) light pressure on the solar panels would still produce more thrust than your drive (and that's not accounting for solar wind). Even if used as attitude RCS, it's may be difficult to ensure it overcomes probable torque from these sources

[shynung]

Anybody who considers solar powered photon drive should remember 2 words: solar sail.

There is a limitation. Solar (or photon) sails use photons emitted by a remote source of energy (e.g. Sun). Once said spacecraft goes into interstellar space, they cease to be useful.

[K^2]

So do solar panels. And yeah. A solar sail is going to be 5-10 times more efficient for the same area. They are a bit more difficult to position for maneuvering, though.

At any rate, I only used solar panels as an example. A 300kW power source of any kind is going to be huge and heavy. And it's going to be way more efficient to bring a much smaller power source and propellant for absolutely any mission.

[KASASpace]

Ion thruster will require about 100x less power. To generate 300kW of power, your ship will need about 3,000 square meters of solar panels. That's about the size of a football field. For 1N of thrust. With an arcjet, you can get the same 1N of thrust from 5kW. Just 50 square meters. Now, which do you prefer to carry with you on your ship? Propellant, or a football field worth of solar panels?

It depends more on how do you get it to space:

By launching,

or orbital construction.

Personally, I would want the "football field" because when a micrometeorite hits the Arcjet's power source, it can easily lose the majority of its power.

And, also, you forget a few simple things:

Power can be stored,

and you can use the same power for twice the thrust and do it in about half the time.

[Nuke]

energy storage always comes with losses. you dont get out what you put in. batteries self-discharge over time and are subject to all kinds of effects that make using them for long term energy storage rather inefficient. i had some packs for my r/c heli that didnt even survive the winter, even with periodic maintenance chargings. youve mentioned capacitors, these are nice for short term buffering, or when you need to store up energy from a low power source to be discharged quickly. but their self discharge characteristics are worse than batteries. they have a very low internal resistance (all components have resistance), which gives them high discharge rates but this also speeds up their self discharge rates.

[K^2]

It depends more on how do you get it to space:

By launching,

or orbital construction.

No, it doesn't. Because we are talking about total delta-V you can get. And you can get smaller, cheaper ship with higher delta-V using electrostatic thrusters already than you could ever with Quantum Thrusters.

Again, it's physically impossible to build Quantum Thrusters that are more efficient than ion drives, unless you master matter-antimatter energy production. It's not an engineering issue. It's a simple mathematical fact.

Personally, I would want the "football field" because when a micrometeorite hits the Arcjet's power source, it can easily lose the majority of its power.

You do understand that odds of impact scale with size, right?

And, also, you forget a few simple things:

Power can be stored,

and you can use the same power for twice the thrust and do it in about half the time.

Oh, really? Why don't you look up energy density of modern batteries. You'll get more delta-V with chemical fuel than batteries. Don't even need to get fancy here.

[Alchemist]

That's the ultimate weakness of photon drives (unless your fuel is antimatter): with any finite power source electric drive with some propellant will give much more delta v for the same mass (and for specific power source there could exist even more efficient engines). While with almost unlimited energy of solar panels you get something not only weaker than the solar sail of the same mass, but even weaker than than light pressure on its own solar panels. The same goes for any ultralelativistic particle accelerators as well - ISP means nothing if you carry a very heavy power source that quickly runs out or can't support any useful thrust.

Unfortunately, I don't see how a propellantless drive could have useful levels of power and thrust without violating energy and momentum conservation. Unless we find something to interact with in the deep space (something more solid than the quantum vacuum), but that would be completely another story.

Edited April 15, 2014 by Alchemist

[KASASpace]

No, it doesn't. Because we are talking about total delta-V you can get. And you can get smaller, cheaper ship with higher delta-V using electrostatic thrusters already than you could ever with Quantum Thrusters.

Again, it's physically impossible to build Quantum Thrusters that are more efficient than ion drives, unless you master matter-antimatter energy production. It's not an engineering issue. It's a simple mathematical fact.

REALLY? REALLY?

Okay, you just gave me the smoking gun, sir.

A propulsion method that only uses electricity will, as long as it gets power, have as much Delta-V as you need.

You do understand that odds of impact scale with size, right?

Odds of impact don't matter in space, because no matter what you will get hit, even the smallest of satellites get hit with space debris.

Oh, really? Why don't you look up energy density of modern batteries. You'll get more delta-V with chemical fuel than batteries. Don't even need to get fancy here.

Oh, so you don't understand how when you double the thrust, you get the same Dv out of a burn when it's half the time?

[andrewas]

The best specific energy I can find for a battery is something under 1MJ/Kg. A Q-thruster producing 9.81N at 300KW/1N would drain that battery in 0.34 seconds. That could be considered the effective ISP of the system.

Tell me again how storing energy is in any way helpful for q-thruster performance?

And there are no really exciting battery technologies on the horizon. Lithium/sulfur may double the performance if they can get it to work, which they've been trying since the 60s, but doubling a tiny number still gives you a tiny number. We need orders of magnitude improvement to make battery powered Q-thrusters even remotely viable.

No, Q-thrusters, if they have any application at all with current energy generation technology, will be used in deep space missions where they can fire continuously. They do better in the inner system where solar power is plentiful, cutting down the mass of solar panels needed to run them. I still don't think they'll work out for any real mission, its better to carry a few hundred KG of propellant for an ion engine than a huge solar panel for a Q-thruster. And the ability to run forever doesn't help as much as you think, nobody wants an engine which forces you to extend an already multi-year mission so the engine can deliver the required dV. And solar panels degrade over time, so even if you have infinite patience the dV from a solar Q-thruster is finite.

[K^2]

REALLY? REALLY?

Okay, you just gave me the smoking gun, sir.

A propulsion method that only uses electricity will, as long as it gets power, have as much Delta-V as you need.

Except, no such sources exist. Top of the line modern solar panels will produce up to 300W/m² in direct sun light and have mass of about 1kg/m². They'll last two decades at the most. So we have 1μN/kg for 20 years on a photon drive. That's 630m/s of delta-V maximum. That's it. 630m/s. In the entire life of the craft. And to achieve that, you'll need to carry 1,000T for every 1N of thrust. I could do better with model rocket engines out of the store.

Again, the only way that a photon drive makes sense is with matter-antimatter reactor. If your reactor has less than 100% mass-to-energy conversion, you are better off with ion drive of some sort. Always.

And the best mass-to-energy ratio we have is nuclear reactors. These can do less than 0.1%, and it's still way, way better than chemical sources or even "renewable" energy, such as solar.

Odds of impact don't matter in space, because no matter what you will get hit, even the smallest of satellites get hit with space debris.

And a larger array will get hit that much more frequently, causing failure of that many more cells. You aren't winning anything with larger arrays.

Oh, so you don't understand how when you double the thrust, you get the same Dv out of a burn when it's half the time?

If you double the thrust, but more than double the mass of the ship with batteries, it doesn't give you extra delta-v.

[KASASpace]

Except, no such sources exist. Top of the line modern solar panels will produce up to 300W/m² in direct sun light and have mass of about 1kg/m². They'll last two decades at the most. So we have 1μN/kg for 20 years on a photon drive. That's 630m/s of delta-V maximum. That's it. 630m/s. In the entire life of the craft. And to achieve that, you'll need to carry 1,000T for every 1N of thrust. I could do better with model rocket engines out of the store.

Again, the only way that a photon drive makes sense is with matter-antimatter reactor. If your reactor has less than 100% mass-to-energy conversion, you are better off with ion drive of some sort. Always.

And the best mass-to-energy ratio we have is nuclear reactors. These can do less than 0.1%, and it's still way, way better than chemical sources or even "renewable" energy, such as solar.

Yet, there is energy all around us. Everywhere in many forms. Dark Energy, kinetic energy, potential energy, zero point energy, the list goes on. Now, we can't tackle zero point energy or dark energy, but who knows? By the time the Q-thruster is used en mass, we may have the know-how and understanding to do so.

And a larger array will get hit that much more frequently, causing failure of that many more cells. You aren't winning anything with larger arrays.

Hit more frequently, yes, but less likely to get a fatal hit right off the bat.

Mir's solar arrays lost 40% of their power output over a decade, and it had way less solar cell area than the ISS, yet the ISS manages to stay better...

If you double the thrust, but more than double the mass of the ship with batteries, it doesn't give you extra delta-v.

Did I say more Dv, no, I said the same. And I never said get "more batteries," those things are horribly inefficient.

Probably flywheels, much more efficient.

[K^2]

Yet, there is energy all around us. Everywhere in many forms. Dark Energy, kinetic energy, potential energy, zero point energy, the list goes on. Now, we can't tackle zero point energy or dark energy, but who knows? By the time the Q-thruster is used en mass, we may have the know-how and understanding to do so.

You really have no idea what these words mean.

Hit more frequently, yes, but less likely to get a fatal hit right off the bat.

Mir's solar arrays lost 40% of their power output over a decade, and it had way less solar cell area than the ISS, yet the ISS manages to stay better...

And more than a decade of research into solar arrays had nothing to do with it? I know for a fact that ISS arrays are much better at continuing to work after a micro-asteroid impact.

Did I say more Dv, no, I said the same. And I never said get "more batteries," those things are horribly inefficient.

Probably flywheels, much more efficient.

Flywheels are only slightly better than best batteries. And as I've said above, photon drive doesn't make sense even with nuclear reactors. Again, unless your batteries are matter-antimatter storage, this isn't going to help.

[KASASpace]

You really have no idea what these words mean.

If that's what you immediately think, than neither do you.

And more than a decade of research into solar arrays had nothing to do with it? I know for a fact that ISS arrays are much better at continuing to work after a micro-asteroid impact.

That's kind of my point.

Flywheels are only slightly better than best batteries. And as I've said above, photon drive doesn't make sense even with nuclear reactors. Again, unless your batteries are matter-antimatter storage, this isn't going to help.

"Only slightly better"

yet a BUS was able to use one and managed to drive around, with limited recharges. A battery of similar size would never have been able to help.

Plus, you can generate power in more than one way. For example, using peltier tiles, and the already built in cooling system would allow for power generation via heat difference.

Edited April 16, 2014 by KASASpace

[K^2]

A flywheel of mass m spinning with surface velocity v has total energy mv²/4. Maximum surface velocity for a steel flywheel is a little over 300m/s regardless of diameter. So a flywheel can only store about 25kJ/kg. Modern Li-poly battery holds more than 500kJ/kg. In other words, a modern battery is more than 20x better than a flywheel at storing energy. That's why you see a lot of remote controlled airplanes with batteries and none with flywheels. Oh, and there are commercial busses that run on batteries.

Please, stop arguing by posting various nonsense, when you don't know the physics or math to back it up. You really don't have any idea what you're talking about.

[Alchemist]

Yet, there is energy all around us. Everywhere in many forms. Dark Energy, kinetic energy, potential energy, zero point energy, the list goes on. Now, we can't tackle zero point energy or dark energy, but who knows? By the time the Q-thruster is used en mass, we may have the know-how and understanding to do so.

And there also is the second law of thermodynamics. Any idea on how to harvest Maxwell's demon?

[Rakaydos]

Any idea on how to harvest Maxwell's demon?

That one has actually been solved... Two compartments separated by a diode-like divider that does not allow excited particles to pass. On one side of the divider, there is a laser to excite particles, while negligibly increasing their temperature. A pressure differential builds, without a temperature differential. Opening the divider allows the particles to expand into a partial vacuume, lowering the tenperature of the excited gas by significantly more than the energy gained from electron excitation.