Hydrogen-Hadron engine

[JMBuilder]

I have an interesting idea. It involves taking a concept design and combining it with existing technology used in an unorthodox fashion.

A special intake would take in the thin amount of Hydrogen in space, sending it to two Hadron colliders. The Hydrogen particles would be accelerated and collided to produce antimatter, which would instantly annihilate, creating large amounts of force directed through a nozzle to produce thrust.

Any thoughts?

[Kinglet]

I have an interesting idea. It involves taking a concept design and combining it with existing technology used in an unorthodox fashion.

A special intake would take in the thin amount of Hydrogen in space, sending it to two Hadron colliders. The Hydrogen particles would be accelerated and collided to produce antimatter, which would instantly annihilate, creating large amounts of force directed through a nozzle to produce thrust.

Any thoughts?

Sadly, that is completely impossible. The amount of antimatter generated by hadron colliders is insanely small. The force would be too small to produce thrust.

[Horn Brain]

Not to mention that the second step (colliding hydrogen to make antimatter and annihilating it) is the equivalent of hooking up a pump to a water wheel to pump water from the bottom of the wheel to the top...

Just point the high speed hydrogen out the back. Why bother turning something with directional momentum into randomly-sprayed gamma rays that you now have to somehow absorb and convert to thrust again?

This is basically a bussard ramjet. Here, go read: Wiki

[Tarrow]

A special intake would take in the thin amount of Hydrogen in space, sending it to two Hadron colliders.

At the current rate of production from the LHC, it'd take in the region of 100 million years to produce one gram of antimatter.

Also requires 120 MW of power to run the collider, so you'd be hauling a fairly hefty nuclear power station with ya.

Horn Brain is right, it'd be massively more efficient to just accelerate the collected gas directly. Or ignore the collider setup and just feed the collected gas through the power station for mega-NERVA action.

[Kryten]

It takes more energy to produce antimatter than you can get from annihilation of that antimatter-at least twice as much, as the process also produces equal amounts of matter.

[rpayne88]

Also, the LHC is 29km in diameter. Good luck getting that into orbit without breaking the bank.

[Nuke]

what about accelerating the hadrons to near c and throwing them out the back of the ship. that would give you insane isp, but miniscule thrust.

[Luis]

An ion drive, in other words. Except with a very low density source of reaction mass.

[K^2]

An ion drive, in other words. Except with a very low density source of reaction mass.

You can get decent density by using a Bussard scoop. But it isn't a new idea.

[Nuke]

An ion drive, in other words. Except with a very low density source of reaction mass.

and an exhaust velocity very close to c. does the mass increase from relativistic speed of those particles effect the rocket equation at all?

[K^2]

and an exhaust velocity very close to c. does the mass increase from relativistic speed of those particles effect the rocket equation at all?

Depends on your choice of frame. But you are looking at some added complexity either way.

For the "conventional rocket", the easiest thing to do is work out fuel consumption for constant acceleration in rocket's frame, then integrate over constant proper acceleration in map frame to get actual delta-v or delta-proper-v, depending on what you are looking for. You also have to keep in mind that the way delta-v is added is using relativistic addition formula. If you want, I can track down or re-derive the correct formulation of rocket formula for relativistic speeds.

If you scoop up propellant from interstellar medium, however, things might be a bit more complicated. I haven't really worked that out, but the way I'd attack this problem is still from the rocket's frame. So I'd treat the medium as incoming at relativistic speeds and work out energy consumption required to accelerate it.

[JMBuilder]

What about an accelerator firing electrons at a gold target? Large amounts of Positrons can be created that way.

[Spica]

Remember though, the mass of an electron/positron is less than 1/1700 of the mass of a proton. That means that you can have a LOT of electrons, but they will weigh practically nothing. I once saw a video by Vsauce saying that the entire mass of the electrons making up the data in the internet is something like 50 grams.

[JMBuilder]

The point isn't the weight. It's the release of energy to produce thrust.

[Kryten]

But energy isn't released. Again, producing antimatter tales more energy than you can possibly get out of the antimatter.

[maccollo]

The point isn't the weight. It's the release of energy to produce thrust.

So you are better of just releasing the accelerated particles at near the speed of light in a single direction. At that point it's all kinetic energy.

If you collide the particles to generate antimatter you convert that kinetic energy into matter and anti matter, which then gets converted into radiation, which you must then somehow turn into thrust.

[ZetaX]

It takes more energy to produce antimatter than you can get from annihilation of that antimatter-at least twice as much, as the process also produces equal amounts of matter.

While the premise is correct, the conclusion is wrong. Annihilation of the antimatter also consumes that equal mass of matter again, making it even.

[JMBuilder]

So... Antimatter annihilation wouldn't produce thrust?

[maccollo]

So... Antimatter annihilation wouldn't produce thrust?

It will create pure radiation. Gamma radiation in fact, which tends to go straight through stuff, and it's omnidirectional.

But the idea of a large particle accelerator as an engine with an ISP close to C is a sort of cool idea. You just need a power source of godlike efficiency to make it practical.

Edited January 3, 2014 by maccollo

[JMBuilder]

I'm trying to think of an engine that requires ONLY electricity to function. The hydrogen in space is the best candidate for fuel... But then what?

[Kryten]

Since photons have momentum, you can get thrust simply by shining a light out of the back of your ship.

[K^2]

I'm trying to think of an engine that requires ONLY electricity to function. The hydrogen in space is the best candidate for fuel... But then what?

You use linacs to accelerate said hydrogen to get thrust, as people have already implied.

Since photons have momentum, you can get thrust simply by shining a light out of the back of your ship.

Which does have potential to have best I_SP, but you basically have to have matter/anti-matter reactor to get that. Otherwise, having some sort of reaction mass is going to make a huge difference in efficiency. Even interstellar hydrogen is better than nothing.

[78stonewobble]

You use linacs to accelerate said hydrogen to get thrust, as people have already implied.

Which does have potential to have best I_SP, but you basically have to have matter/anti-matter reactor to get that. Otherwise, having some sort of reaction mass is going to make a huge difference in efficiency. Even interstellar hydrogen is better than nothing.

Sooooo wouldn't the "optimal" approach be to somehow create our reaction mass along the way?

Think star trek replicator.

Offcourse the fuel to make the energy to make the reaction mass (fuel) and all the inefficiencies in doing that will probably render the point moot, but still...

[K^2]

Sooooo wouldn't the "optimal" approach be to somehow create our reaction mass along the way?

No, because it doesn't help you any. Creating matter takes up energy, so you'll have the same net efficiency.

Say, you have exactly 1kg * c² of energy. Your first option is to focus that energy into a beam of light. That will get you exactly 1kg * c of impulse. Your other option is to convert some part of it into matter, and use the rest to accelerate matter. Suppose, you created some quantity m of matter. That leaves you with (1kg - m) * c² of energy to accelerate it. The total energy of that matter, once you accelerate it, is going to be γmc², which still has to be equal to total energy you started with, 1kg * c². So γm = 1kg. On the other hand, the impulse you are going to get is γmc, and with γm = 1kg, that's the same 1kg * c of impulse that you'd get with light.

So it really comes down to which one you can do more efficiently. Convert energy to light or convert it to matter and accelerate it. In practice, converting energy to matter tends to be inefficient, so you are better off with a photon drive.

Now, if you happen to have that mass already sitting around, then you are cooking with gas.

[78stonewobble]

No, because it doesn't help you any. Creating matter takes up energy, so you'll have the same net efficiency.

Say, you have exactly 1kg * c² of energy. Your first option is to focus that energy into a beam of light. That will get you exactly 1kg * c of impulse. Your other option is to convert some part of it into matter, and use the rest to accelerate matter. Suppose, you created some quantity m of matter. That leaves you with (1kg - m) * c² of energy to accelerate it. The total energy of that matter, once you accelerate it, is going to be γmc², which still has to be equal to total energy you started with, 1kg * c². So γm = 1kg. On the other hand, the impulse you are going to get is γmc, and with γm = 1kg, that's the same 1kg * c of impulse that you'd get with light.

So it really comes down to which one you can do more efficiently. Convert energy to light or convert it to matter and accelerate it. In practice, converting energy to matter tends to be inefficient, so you are better off with a photon drive.

Now, if you happen to have that mass already sitting around, then you are cooking with gas.

Yeah, it gets you nowhere in practicality.

I was thinking more along the lines of variations of existing concepts. Gathering the reaction mass and fuel as you go (ramscoop) and beamed energy concept (solar, laser, microwave whatever). To the point of having the ship itself consist of nothing more than payload and a structure that gets energized in such a way that it uses interstellar matter as it's reaction mass.

A sort of antaenna that receives/absorbs directed energy and uses it to create a magenetic field to gather fuel and accelerate it.

Offcourse subject to the same problems as any other project of beamed energy (dispersion at distance) and ramscoops (drag).