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Posted (edited)

[Moderator's note:  Much of the content here, including this OP, was split off from another thread where it was off-topic. That thread is about the recent Rosatom rocket engine failure.  This thread is about Cheif Operation Director's idea for a perpetual-momentum machine that violates the laws of physics.]

On 8/9/2019 at 9:18 PM, Nothalogh said:

 That's exactly how Open Cycle NTRs work

On 8/9/2019 at 9:18 PM, KeranoKerman said:

That’s how they work, with liquid hydrogen 

On 8/9/2019 at 9:18 PM, Ultimate Steve said:

Yes, that is usually how nuclear engines work. Open cycle, you basically flow the fuel straight through the reactor, closed cycle, you have heat transfer devices that heat the fuel indirectly. Closed cycle is safer, but open cycle is more efficient. This way you can get specific impulses of around 1000, plus or minus some, depending on how far you push it.

 

Yes but it is inefficient and you are still restricted by fuel. If the ruskies could find a way to harness the air and create propulsion without actual expelling the gas they have a winning system,

Edited by Cheif Operations Director

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1 minute ago, Cheif Operations Director said:

harness the air and create propulsion without actual expelling the gas

So a nuclear thermal jet engine

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What if they just "sucked" the air back in after expelling it. 

Just now, Nothalogh said:

So a nuclear thermal jet engine

still expels the air for thrust right?

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1 minute ago, Cheif Operations Director said:

Yes but it is inefficient and you are still restricted by fuel. If the ruskies could find a way to harness the air and create propulsion without actual expelling the gas they have a winning system,

You can still get really good efficiency with closed cycle.

Harnessing the air, that's a nuclear jet engine, and the USSR actually flew a nuclear jet engine powered aircraft once. Uses no propellant other than the nuclear fuel. Unfortunately it was open cycle though.

Just now, Cheif Operations Director said:

What if they just "sucked" the air back in after expelling it. 

still expels the air for thrust right?

Yes.

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Just now, Cheif Operations Director said:

What if they just "sucked" the air back in after expelling it. 

Well, then it wouldn't really go anywhere, and neither would the heat, this would end very badly

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Just now, Nothalogh said:

Well, then it wouldn't really go anywhere, and neither would the heat, this would end very badly

It would create thrust then you use the exhaust fumes back into the engine re-heating it you would not use any fuel other than the nuclear reactor. I mean if you can harness the nuclear reactor to create thrust then you are in business. 

I should clarify by harness I mean do not use extra fuel via explusion. Rather just use the nuclear reactor. 

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3 minutes ago, Cheif Operations Director said:


 

It would create thrust then you use the exhaust fumes back into the engine re-heating it you would not use any fuel other than the nuclear reactor. I mean if you can harness the nuclear reactor to create thrust then you are in business. 

You're proposing to recapture the turbine exhaust of a nuclear thermojet, recondense it to liquid state, and cycle it through the the reactor again?

 

That's called a whole nuclear power plant, and those are quite heavy

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1 minute ago, Nothalogh said:

You're proposing to recapture the turbine exhaust of a nuclear thermojet, recondense it to liquid state, and cycle it through the the reactor again?

 

That's called a whole nuclear power plant, and those are quite heavy

Sure but you can have thrust for 30 years straight. I mean imagine if voyager was accelerating for 30 years straight

Also nuclear submarines do it

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5 minutes ago, Cheif Operations Director said:


 

It would create thrust then you use the exhaust fumes back into the engine re-heating it you would not use any fuel other than the nuclear reactor. I mean if you can harness the nuclear reactor to create thrust then you are in business. 

I should clarify by harness I mean do not use extra fuel via explusion. Rather just use the nuclear reactor. 

So you take in air and don't expel it? Then what's the air for?

In order to create thrust, you need to throw something backwards (unless you are talking about solar sails or something). Planes throw air backwards, boats throw water backwards, cars "throw" the road backwards (you don't notice because Earth is so huge), rockets throw exhaust backwards, etc.

The same rule holds true for nuclear, you need to throw something backwards, be it hydrogen or air.

Now, you can get creative, though. You can use the fission fragments from the reaction as your throw backwards material. This is called a fission fragment rocket and can get efficiencies of over 100,000 seconds. However it is also not good as you are basically spewing nuclear waste everywhere directly. I believe it is also fairly low thrust.

You can also go Orion style and blow up nukes behind you to push you forwards. That's also not a good idea in most cases.

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Just now, Ultimate Steve said:

you take in air and don't expel it? Then what's the air for?

You re-capture the air and then recycle it. This allows you to covert heat into mechanical force.

1 minute ago, Ultimate Steve said:

The same rule holds true for nuclear, you need to throw something backwards, be it hydrogen or ai

exactly

why waste the propellant?

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Just now, Cheif Operations Director said:

You re-capture the air and then recycle it. This allows you to covert heat into mechanical force.

So you heat up air, expel it, capture it again, and repeat? I'm not sure if I'm getting what you're saying. What exactly would the air then power?

3 minutes ago, Cheif Operations Director said:

exactly

why waste the propellant?

If you catch the propellant you just expelled, you get no net force.

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Just now, Ultimate Steve said:

So you heat up air, expel it, capture it again, and repeat? I'm not sure if I'm getting what you're saying. What exactly would the air then power?

Ok, You put the rocket engine in the center of the craft (no this is not a rocket pendulum) then you fire the engine propelling you forward. THEN you recapture the expelled air and put it into a condenser at the end of the rocket. Then pump it forward back into the reactor. to be expelled again. If have large enough condensers you can do it and get a net positive thrust. Since all of the gas/liquid is recycles you could integrate it with the rest of the vehicle for heating and cooling nessicary parts of it. Once the engine is running to throttle down you turn off the reactor. Since the craft is built around this design you can fly your science probe on full thrust for YEARS. 

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1 minute ago, Cheif Operations Director said:

Ok, You put the rocket engine in the center of the craft (no this is not a rocket pendulum) then you fire the engine propelling you forward. THEN you recapture the expelled air and put it into a condenser at the end of the rocket. Then pump it forward back into the reactor. to be expelled again. If have large enough condensers you can do it and get a net positive thrust. Since all of the gas/liquid is recycles you could integrate it with the rest of the vehicle for heating and cooling nessicary parts of it. Once the engine is running to throttle down you turn off the reactor. Since the craft is built around this design you can fly your science probe on full thrust for YEARS. 

There is no reaction mass going backwards, then. The force of the engine would be exactly undone by the force the exhaust imparts on the catcher/condenser and you would get no net force. Sort of like how it takes the same amount of energy to accelerate something as it does to decelerate something. unless there is something I am missing.

 

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8 minutes ago, Cheif Operations Director said:

Ok, You put the rocket engine in the center of the craft (no this is not a rocket pendulum) then you fire the engine propelling you forward. THEN you recapture the expelled air and put it into a condenser at the end of the rocket. Then pump it forward back into the reactor. to be expelled again. If have large enough condensers you can do it and get a net positive thrust. Since all of the gas/liquid is recycles you could integrate it with the rest of the vehicle for heating and cooling nessicary parts of it. Once the engine is running to throttle down you turn off the reactor. Since the craft is built around this design you can fly your science probe on full thrust for YEARS. 

That literally will not work.

53 minutes ago, Nothalogh said:

I forget, who are our resident nuclear rocketry experts?

**cough**

They could be doing an experimental low-thrust, high-efficiency RTG-based rocket. Direct-pass RTG radioionization of the working fluid in a heat exchanger; use the heat exchanger to drive a dynamo for an accelerating magnetic nozzle.

But probably just an NTR. If it has any appreciable thrust, definitely an NTR.

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1 minute ago, Ultimate Steve said:

There is no reaction mass going backwards, then. The force of the engine would be exactly undone by the force the exhaust imparts on the catcher/condenser and you would get no net force. Sort of like how it takes the same amount of energy to accelerate something as it does to decelerate something. unless there is something I am missing.

 

 

1 minute ago, sevenperforce said:

That literally will not work.

 

Ok fair enough, I am being an idiot. However just an idea what if the fuel was magnetic and you used magents to slow it down in one directing and pull it in another. then you may have a net positive thrust?

Im still using the nuclear reactor btw

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Just now, Cheif Operations Director said:

Ok fair enough, I am being an idiot. However just an idea what if the fuel was magnetic and you used magents to slow it down in one directing and pull it in another. then you may have a net positive thrust?

Then the impulse would be imparted back to the magnets. Zero net thrust.

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Posted (edited)
15 minutes ago, Cheif Operations Director said:

Ok, You put the rocket engine in the center of the craft (no this is not a rocket pendulum) then you fire the engine propelling you forward. THEN you recapture the expelled air and put it into a condenser at the end of the rocket. Then pump it forward back into the reactor. to be expelled again.

Conservation of momentum dude. Crackpots have been trying to get designs like this accepted for years, and it always comes down to that old principle. No mass expelled from the system, no net thrust.

 

2 minutes ago, Cheif Operations Director said:

what if the fuel was magnetic and you used magents to slow it down in one directing and pull it in another. then you may have a net positive thrust?

Doesn't matter how you try to cheat physics, it works just as badly.

 

Edited by steve_v

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Just now, Cheif Operations Director said:

What?

Because you basically built a circular loop of cable, and are thermally propelling it around in a circle.

On the upside, it might work as a gyroscope

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1 minute ago, Cheif Operations Director said:

What?

The magnets are attached to the craft, no? If those magnets accelerate (or decelerate) the reaction mass to recapture it, an equal force is applied to the magnets themselves and hence the craft, exactly balancing the system. No net thrust.

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When you slow something down using a magnet, the force goes to the magnet. Like if you had a piece of iron and a magnet, not only would the iron be pulled towards the magnet, the magnet would be pulled towards the iron.

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1 minute ago, Nothalogh said:

Because you basically built a circular loop of cable, and are thermally propelling it around in a circle.

On the upside, it might work as a gyroscope

put the magnets at an angle, or just forget the accelerate part so it is at a 90 angle from the exhaust.
 

Just now, steve_v said:

The magnets are attached to the craft, no? If those magnets accelerate (or decelerate) the reaction mass to recapture it, an equal force is applied to the magnets themselves and hence the craft, exactly balancing the system. No net thrust.

Ok? So put those magnets in a postion where it will help with de-acclerating the fuel.

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Just now, Cheif Operations Director said:

put the magnets at an angle, or just forget the accelerate part so it is at a 90 angle from the exhaust.
 

You have a loop of mass, going around in a circle.

Enjoy your gyroscope

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1 minute ago, Ultimate Steve said:

When you slow something down using a magnet, the force goes to the magnet. Like if you had a piece of iron and a magnet, not only would the iron be pulled towards the magnet, the magnet would be pulled towards the iron.

exactly. If those magnets are pushing away from eachother and they are at a 90 angle the magnetic fuel would get slowed and the magents would get push toward the side of the craft or the tail. 

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2 minutes ago, Cheif Operations Director said:

put the magnets at an angle, or just forget the accelerate part so it is at a 90 angle from the exhaust.

Equal and opposite reaction, remember?

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