Antimatter Propulsion.. From Earth To Mars Only Requires Milligrams?!

[farmerben]

External combustion can be very efficient in terms of energy, it just tends have a lot of mass and volume.  Stationary power plants, and still some cargo ships use steam turbines.  

Many locomotives are hybrid electric.  Electric drive, (external) diesel generators.  

I wonder if you could trickle a tiny amount of antimatter into an RTG like case and get a steady few kilowatts of electric power?

[kerbiloid]

It could be frozen in a normal matter matrix, to make the atomic motion slow, and the contacts between the particles rare.

So, it will be slowly annihilating and releasing heat, but to prevent its warming from that heat, the whole thing should be enormously huge, and at the same time having low overall energy production rate.

[Terwin]

16 hours ago, Spacescifi said:

I meant efficiency with the thrust to weight ratio. Detonating a nuclear or antimatter bomb requires less mass/weight than exhausting enough propellant to gain the equivalent amount of thrust if you just detonated the bomb.

By the time you reach the TWR of the bomb with a rocket your engine will either melt or you have some type of nuclear saltwater rocket shenanigans going on that are teetering at the edge of blowing up your vessel in a catastrophic explosion the whole time.

Um, no.

Consider a regeneratively cooled rocket nozzle.

It is able to withstand great temperatures and a lot of well-controlled pressure coming in an easy to predict way.

 

Now design something that can withstand highly variable temperatures and pressures with the ability to change rapidly, both in intensity and direction, with much tighter weight restrictions because it can only harness a fraction of the energy it is being battered with, as most of it is pushing the wrong way.  Note: temperatures and pressures can get much higher than the nozzle interacts with.

 

You are suggesting that it is easier to design and build a mobile structure to resist tornadoes than it is to build a stationary, reinforced wind-break that only needs to survive 1% of the wind-speed of a tornado, from one direction.

 

For the same energy release, a rocket is always better than external combustion.  Always.

Thermal antimatter will always be more efficient in both TWR and ISP than any sort of external combustion antimatter.

*  If your materials can withstand a temperature of X, then running your thermal antimatter at (x-safety margin) will always equal or beat being far enough away form an explosion so that it cools down to (x-safety margin) as you will, at best, get the same result, but only by benefitting from a small fraction of your fuel and reaction mass.

*  Anything you can do to get a better result from your am-pusher plate, can also be done to get the same benefits(or more) in a thermal rocket.

*  A rocket gets to benefit from roughly 100% of the pressure from the heated reaction mass, while any sort of pusher-plate will, at best, get less than half of the pressure from an external combustion event(because to get any more, it would need to be inside your reaction chamber, even 50% would require half of the event be inside of a chamber of some sort, but much of that would be laterally focused and thus lost), usually only a small fraction of 1% because being any closer means your vessel gets vaporized by the explosion if you make it large enough to be a useful external reaction.

 

[Spacescifi]

2 hours ago, Terwin said:

Um, no.

Consider a regeneratively cooled rocket nozzle.

It is able to withstand great temperatures and a lot of well-controlled pressure coming in an easy to predict way.

 

Now design something that can withstand highly variable temperatures and pressures with the ability to change rapidly, both in intensity and direction, with much tighter weight restrictions because it can only harness a fraction of the energy it is being battered with, as most of it is pushing the wrong way.  Note: temperatures and pressures can get much higher than the nozzle interacts with.

 

You are suggesting that it is easier to design and build a mobile structure to resist tornadoes than it is to build a stationary, reinforced wind-break that only needs to survive 1% of the wind-speed of a tornado, from one direction.

 

For the same energy release, a rocket is always better than external combustion.  Always.

Thermal antimatter will always be more efficient in both TWR and ISP than any sort of external combustion antimatter.

*  If your materials can withstand a temperature of X, then running your thermal antimatter at (x-safety margin) will always equal or beat being far enough away form an explosion so that it cools down to (x-safety margin) as you will, at best, get the same result, but only by benefitting from a small fraction of your fuel and reaction mass.

*  Anything you can do to get a better result from your am-pusher plate, can also be done to get the same benefits(or more) in a thermal rocket.

*  A rocket gets to benefit from roughly 100% of the pressure from the heated reaction mass, while any sort of pusher-plate will, at best, get less than half of the pressure from an external combustion event(because to get any more, it would need to be inside your reaction chamber, even 50% would require half of the event be inside of a chamber of some sort, but much of that would be laterally focused and thus lost), usually only a small fraction of 1% because being any closer means your vessel gets vaporized by the explosion if you make it large enough to be a useful external reaction.

 

 

My point is you cannot have the same TWR as external pulse propulsion using rocketry.

For all the mass required for rocketry (most of it being propellant), and the engine waste heat being a factor, you won't be able to ever have the TWR of nuke or antimatter external pulse propulsion, unless you try something dangerous like NSWR.

[kerbiloid]

12 hours ago, Terwin said:

Consider a regeneratively cooled rocket nozzle.

It is able to withstand great temperatures and a lot of well-controlled pressure coming in an easy to predict way.

1. To cool it, you need a coolant fluid, pumped through pipes to the radiators.
Liquid fluids vaporise at much lower temperatures than metals melt. They are out of scope.
Gaseous fluids, like H or Xe, are limited with ionization temperature (just ~10 kK). But the pipes anyway limit this with 1.5 kK.
So, no coolant can provide the chamber equilibrium temperature higher than several kK.

2. The radiators also limit the heat flow, as Luminosity ~ T⁴.
Even if use droplet cooling with liquid radiator "panels" in electromagnetic field, the droplet temperature is anyway limited by the droplet metal boiling point, so still several kK.

All of this means that the chamber structure can withstand only 1..2 kK equilibrium temperature, which makes the total power of the non-Orion engines pathetic, regardless of their efficacy percentage.

The immaterial chamber of Orion isn't limited with any material properties at all. It can be kilometers in size, limited only by the plasma jet angle.
Or almost unlimited if use two-stage charges, consisting of far part with an X-ray laser powered by a meganuke, detonated at hundreds kilometers behind, and passive close part, receiving the hit of the X-ray beam and forming the plasma jet out of its material and the beamed energy.

Edited March 16 by kerbiloid

[magnemoe]

On 3/15/2024 at 1:34 PM, kerbiloid said:

It could be frozen in a normal matter matrix, to make the atomic motion slow, and the contacts between the particles rare.

So, it will be slowly annihilating and releasing heat, but to prevent its warming from that heat, the whole thing should be enormously huge, and at the same time having low overall energy production rate.

https://schlockmercenary.fandom.com/wiki/Antimatter Do not let near fire or cosmic rays, you need enough normal matter so an random cosmic ray don't cause an chain reaction, this probably bring energy density down towards nuclear bombs. 
In schlockmercenary they use this for smaller weapons down to hand grenades who you can not do with nukes. 
I still think that an solar storm would be an problem, in schlockmercenary radiation weapons should work well to cock off antimatter in fullerene 

[Terwin]

On 3/15/2024 at 4:44 PM, Spacescifi said:

My point is you cannot have the same TWR as external pulse propulsion using rocketry.

For all the mass required for rocketry (most of it being propellant), and the engine waste heat being a factor, you won't be able to ever have the TWR of nuke or antimatter external pulse propulsion, unless you try something dangerous like NSWR.

I would appreciate you explaining the physics of this to me, because everything I know about rocketry says that antimatter pulse is stupidly wasteful and inefficient compared to thermal antimatter rocketry, for both ISP and TWR.

Are you assuming that pulse propulsion does not need reaction mass?  Nuclear pulse requires a tungsten plug to work as the reaction mass that hits the pusher-plate, and antimatter pulse would also require a large amount of reaction mass to throw against the pusher-plate, much of which would miss and be wasted, along with > 90% of the energy in the antimatter explosion, much like nuclear pulse.  The only difference is that a nuculear pulse is  ~ 1,000,000 times as energy dense as chemical reactions, letting you get 100 times the push with only 0.1% of the efficiency.  (antimatter pulse does *not* have this advantage over antimatter thermal, because they both have the same energy density)

[Spacescifi]

43 minutes ago, Terwin said:

I would appreciate you explaining the physics of this to me, because everything I know about rocketry says that antimatter pulse is stupidly wasteful and inefficient compared to thermal antimatter rocketry, for both ISP and TWR.

Are you assuming that pulse propulsion does not need reaction mass?  Nuclear pulse requires a tungsten plug to work as the reaction mass that hits the pusher-plate, and antimatter pulse would also require a large amount of reaction mass to throw against the pusher-plate, much of which would miss and be wasted, along with > 90% of the energy in the antimatter explosion, much like nuclear pulse.  The only difference is that a nuculear pulse is  ~ 1,000,000 times as energy dense as chemical reactions, letting you get 100 times the push with only 0.1% of the efficiency.  (antimatter pulse does *not* have this advantage over antimatter thermal, because they both have the same energy density)

 

Again it is a heat and safefy issue with the rocket. A rocket is more or less a directed explosion.

Despite the fact that antimatter requires bomb mass, to try to replicate the same feat using regenerative cooling on a rocket nozzle I presume would require more propellant mass expended than if you just detonated an AM bomb orion style against the pusher plate.

Reason being you have to carry away the heat.

Whereas with Orion you do not have a heat problem nearly as much because of distance and the pusher plate.

You can also detonate higher and higher energy yield bombs without increasing your pusher plate equipped ship's mass to cope with it.

Whereas your energy yield of your rocket exhaust is capped by however much it's reaction chamber can take.

Mini-mag is like the limits of rocketry and Orion mixed into one.

A magnetic nozzle being propelled by external pulse propulsion.

In fact the main form of propellant you lose on an Orion pusher plate is the sacrificial oil used to absorb the plasma every time it hits the plate.

[Piscator]

4 hours ago, Spacescifi said:

In fact the main form of propellant you lose on an Orion pusher plate is the sacrificial oil used to absorb the plasma every time it hits the plate.

In fact, the main form of propellant you lose is the bombs. Which, as has been pointed out, are used very inefficiently.

[kerbiloid]

If compare the pusher plate and nukes total mass to the enormous kilometers-wide structures or negligible thrust of its alternatives, then Orion is super-efficient.

It combines small size, low mass, and short burn time.

[Terwin]

13 hours ago, Spacescifi said:

 

Again it is a heat and safefy issue with the rocket. A rocket is more or less a directed explosion.

Not at all, a rocket is a controlled conflagration(just like a lighter, gas stove, gas water heater, fire place, coal power plant, etc.).  There is research into continuous detonation engines, but it is very difficult to maintain the continuous detonation(but would greatly increase ISP)

 

13 hours ago, Spacescifi said:

Despite the fact that antimatter requires bomb mass, to try to replicate the same feat using regenerative cooling on a rocket nozzle I presume would require more propellant mass expended than if you just detonated an AM bomb orion style against the pusher plate.

Reason being you have to carry away the heat.

The reaction mass carries away the heat, and generating the heat to heat up the reaction mass is the entire reason you have the antimatter on board, this is a benefit, not a cost.

13 hours ago, Spacescifi said:

Whereas with Orion you do not have a heat problem nearly as much because of distance and the pusher plate.

Orion has much more of a heat problem than a rocket because the pusher plate absorbs some of the heat and you have no productive way to get rid of that heat, more over, the further you get form the explosion(and the heat) the worse you thrust and isp get.

The best option to manage for the heat for Orion that I have seen is to coat your pusher pate with some sort of liquid, cutting down on how much of your pusher plate gets vaporized with each bomb, but this is only a partial option as running the Orion continuously will still heat up the plate until it finally gets soft enough to get splattered by the next bomb.

13 hours ago, Spacescifi said:

You can also detonate higher and higher energy yield bombs without increasing your pusher plate equipped ship's mass to cope with it.

Whereas your energy yield of your rocket exhaust is capped by however much it's reaction chamber can take.

Nope, Unless you are using some sub-optimal configuration to avoid destroying your launch mount, you always use the same bomb, the largest you can safely use for propulsion.  This maximum safe size may go down as your pusher plate gets eroded, but it will never go up.  (moving the bomb further away has the same effect as using a smaller bomb, so using a larger bomb further away just wastes materials)

13 hours ago, Spacescifi said:

Mini-mag is like the limits of rocketry and Orion mixed into one.

A magnetic nozzle being propelled by external pulse propulsion.

In fact the main form of propellant you lose on an Orion pusher plate is the sacrificial oil used to absorb the plasma every time it hits the plate.

Sort of, as you will have the non-charged particles wearing away at your nozzle hardware, giving you the life-span limitations of Orion, combined with the massive energy requirements of an ion engine because you need to generate the magnetic fields to push away the charged particles(but much less efficient than an ion engine because the particles are much further way from the field), giving you the combined draw-backs of Orion and ion engines.

Edited March 17 by Terwin

[kerbiloid]

3 minutes ago, Terwin said:

Orion has much more of a heat problem than a rocket because the pusher plate absorbs some of the heat and you have no productive way to get rid of that heat, more over,

1. Orion receives just the part of total heat which is carried by the plasma jet. Most part of waste heat dissipates around the explosion point.

2. Orion works in pulse mode, unlike the continuous chemical or nuclear reaction engines, so it has ~0.5 s to emit some part of the absorbed heat.

3. Orion pusher plate is cooled by portions of coolant water, pumped through the plate internal structure/

3b. The Orion coolant water doesn't need a close cycle, it turns into steam and gets vented out right in situ.
Loss of water? No, a free attitude control, water-steam RCS, to hold the Orion on course during the engine work.

4. The Orion pusher plate is massive, unlike the nozzle lattice of permanukes and thin chalice of chemicals.
It has great heat capcity, so the waste heat is distributed uniformly.

5. The pusher plate is prevented from the direct tungsten plasma hit by the soft plasma cloud of former oil, sprinkled on the plate between the explosions.

6. The Orion thrust is great, unlike the puny permanuke nudging. The interplanetary jump acceleration takes less than hour. So, the Orion doesn't need heavy rad protection from permanently working megareactor, the crew can sit in a small room, protected from rear end.
Thus, it's more safe and efficient even from the radprotection and mass view.

17 minutes ago, Terwin said:

The best option to manage for the heat for Orion that I have seen is to coat your pusher pate with some sort of liquid, cutting down on how much of your pusher plate gets vaporized with each bomb

And this is a description of the coolant water and sprinkled oil.

18 minutes ago, Terwin said:

Nope, Unless you are using some sub-optimal configuration to avoid destroying your launch mount, you always use the same bomb, the largest you can safely use for propulsion.

From the very beginning the Orion was to use several yield in flight, from sub-kiloton in upper air (and, I guess, in the Martian de-orbiting), to several kiloton in vacuum, exploded at different distances.

By varying the yield and the frequency, it can vary its thrust.

21 minutes ago, Terwin said:

This maximum safe size may go down as your pusher plate gets eroded, but it will never go up.

It can go down instead.

21 minutes ago, Terwin said:

as you will have the non-charged particles wearing away at your nozzle hardware

The onboard reactor for the minimag Z-pincher can be using aneutronic B+H or N+H or C+H fusion, where the non-charged particles are generated at low rate, or even (B+H) be absent.

Though, I believe that the mini-mag is a temporary-to-never intermediate design, and the two-staged fusion X-ray laser charges, compressed to fusion by similar Z-pinchers (i.e. returning to the original idea with intermediate inert discs) can bring the thrust to interstellar ark values.

 

[magnemoe]

11 hours ago, Piscator said:

In fact, the main form of propellant you lose is the bombs. Which, as has been pointed out, are used very inefficiently.

Who is true for all engines, now orion pulse nuclear has an expensive fuel as in nuclear bombs, you could build them much cheaper if mass produced as pulse charges. 
Also back in the 50's they thought that an pure fusion bomb was not far away. Who was not true and an good fusion engine makes orion obsolete outside the very high trust regime as in moving asteroids or asteroid sized space stations fast. 

[kerbiloid]

6 hours ago, magnemoe said:

good fusion engine makes orion obsolete outside the very high trust regime

And that's the problem, as the high thrust means high energy production rate, and most part of this energy will be waste heat, heating the solid structure of the combustion chamber, regardless of physical principles of the energy production.
This means either appropriate size (tens meters) but low thrust, or high thrust but huge size (kilometers), as L ~ R²T⁴, so RT²=const.

As the T is limited with the construction (i.e. solid) material melting point, so R~sqrt(L), i.e. chamber size ~ sqrt(energy production rate, and thus thrust).

It's possible to actively cool the chamber, but as it happens in vacuum, the only way is to radiate the waste heat outside with radiator panels.
But first, the panels temperature is limited with melting point of the panel material, and boiling point of a droplet-based liquid cooling, i.e. in a ny case with 1.5 .. 2 kK.
And second, you should transfer the waste heat from the chamber to the radiator, so you need a coolant and pipes for it.
So, this is also limited with melting point of pipes, boiling point of liquid cooland or ionization point of gaseous one.

In any case, the active cooling system temperature is limited with ~2 kK, and this makes the low-thrust-vs-huge-heavy-chamber inevitable.

The only realistic, not handwaving, way to solve it, is to completely remove both combustion chamber and cooling system, by moving the reaction zone far outside from the ship, and directing the kinetic energy from the reaction zone towards the ship rear shield, aka pusher plate.
And that's what Orion is.

The propulsion nukes don't have to be full-featured weapons. They can be simplified, purposed only to interact with the ship drive.
Thus, they can widely use U-233 deuteride instead of plutonium, and be compressed by the Z-pinchers, like in minimag Orion.

The same can be replaced with fusionukes in the more future future.

[darthgently]

On 3/18/2024 at 12:36 AM, kerbiloid said:

And that's the problem, as the high thrust means high energy production rate, and most part of this energy will be waste heat, heating the solid structure of the combustion chamber, regardless of physical principles of the energy production.
This means either appropriate size (tens meters) but low thrust, or high thrust but huge size (kilometers), as L ~ R²T⁴, so RT²=const.

As the T is limited with the construction (i.e. solid) material melting point, so R~sqrt(L), i.e. chamber size ~ sqrt(energy production rate, and thus thrust).

It's possible to actively cool the chamber, but as it happens in vacuum, the only way is to radiate the waste heat outside with radiator panels.
But first, the panels temperature is limited with melting point of the panel material, and boiling point of a droplet-based liquid cooling, i.e. in a ny case with 1.5 .. 2 kK.
And second, you should transfer the waste heat from the chamber to the radiator, so you need a coolant and pipes for it.
So, this is also limited with melting point of pipes, boiling point of liquid cooland or ionization point of gaseous one.

In any case, the active cooling system temperature is limited with ~2 kK, and this makes the low-thrust-vs-huge-heavy-chamber inevitable.

The only realistic, not handwaving, way to solve it, is to completely remove both combustion chamber and cooling system, by moving the reaction zone far outside from the ship, and directing the kinetic energy from the reaction zone towards the ship rear shield, aka pusher plate.
And that's what Orion is.

The propulsion nukes don't have to be full-featured weapons. They can be simplified, purposed only to interact with the ship drive.
Thus, they can widely use U-233 deuteride instead of plutonium, and be compressed by the Z-pinchers, like in minimag Orion.

The same can be replaced with fusionukes in the more future future.

Would there be any advantage to the pusher plate being parabolic with the focal point being the reaction zone?  I'd think the angle of incidence of the explosion on the plate would make a difference, but would it be significant?

Edited March 22 by darthgently

[kerbiloid]

1 hour ago, darthgently said:

Would there be any advantage to the pusher plate being parabolic with the focal point being the reaction zone?

No, it would be problematic for its edge, as it the plasma cloud should expand radially and escape.

The jet angle is anyway tiny, several degrees.

Edited March 22 by kerbiloid

[Terwin]

2 hours ago, darthgently said:

Would there be any advantage to the pusher plate being parabolic with the focal point being the reaction zone?  I'd think the angle of incidence of the explosion on the plate would make a difference, but would it be significant?

If the compression wave hit the entire surface at the same time, that seems like it would make the impact have a shorter, sharper duration.  Considering that you are already needing a shock-absorber, that does not seem like a good change.

If the explosion is off center, having curved surfaces could also introduce lateral jiggle, potentially causing severe wear or even destruction of the shock-absorbing mechanic.

A flat surface where all forces striking and rebounding from it should only push you froward seems like a safer bet.

On the other hand, if you are close enough that you could cover a larger proportion of the shock-wave with less material by curving it, then it may be worth the extra engineering.

[kerbiloid]

Orion doesn't use shockwaves. It's a kinetic hit of a plasma jet. Shockwaves are parasite.