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Spacescifi

Laser assisted rocket launch and landing

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Posted (edited)

 

So this is the inverse of the nuclear thermal rocket idea. Instead of taking the hesvy reactor and radiation shielding with your rocket at launch, you keep all of that at a power station on earth.

NTR offer good but still weaker thrust than combustion chemical or solid booster rockets.

 

It seems to me that a nuclear laser beam heating up the rocket's fuel through heat exchangers is the best of both worlds with the least risk.

Since you still get your chemical LOX or methane rocket for high thrust, but this time a laser is increasing your ISP while you still get good thrust.

It is a win-win!

Scifi scenario: In an advanced setting with antimatter in use, one could drop antimatter pods into reentry from orbit, and then use lasers powered via the antimatter from the landed pods to actually increase a starship"s chemical rocket ISP as it lands and even when it launches.

 

To extend ISP even more air intake thermal laser boosted rockets. A thermal jet essentially.

 

Once out of antimatter laser pods you likely could not land as easily again, but it is still a nice advantage for a large vessel SSTO.

From my reading, any high ISP thermally powered rocket's efficiency scales up better than down, but the scaled up weight makes it all for naught at launch. That is why I favor laser beam to rocket heat exhanger material.

EDIT: The real problem is not so much power as it is material limitations. A hotter engine is great as it can increase a rocket's ISP and thrust, but too hot and your engine melts and you fall out of the sky.

So what are the most heat resistant materials known? Those would be what we make the engine out of and possibly the heat exchangers.

EDIT 2: Assuming we did have a material that could stand the heat of high efficiency thermal rocket engines, we would not need to play around with magnetic nozzles in space. Furthermore if the hull was plated with the same material it would make reentry an easier endeavor, not to mention that reentry heat exchange alone might boost a rocket's ISP for landing VTOL.

Your thoughts?

Edited by Spacescifi

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Idea is not new, some company wanted to use this to power an SSTO. Heat up the heat shield and use this to heat up air and later hydrogen for trust. 

They would need an series of beamed power stations, also getting airborne would be an issue but you could air drop it, perhaps even an powered trolley. 

In space you could even use sunlight although beamed power would be better and give good trust. 

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10 hours ago, Spacescifi said:

So what are the most heat resistant materials known? Those would be what we make the engine out of and possibly the heat exchangers.

Amorphous carbon is a possible candidate. This is very hard to make, but it could make for great nozzle material, lightweight armor resistant to both lasers and kinetics, a heatshield and a strong structural material. However, most work on it is theoretical, we don't have the technology to make it in quantity. You are, however, looking at a melting point of nearly 3000K (I'm not quite sure it truly melts, but that's another matter entirely), and very good mechanical properties. 

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Posted (edited)
48 minutes ago, Dragon01 said:

Amorphous carbon is a possible candidate. This is very hard to make, but it could make for great nozzle material, lightweight armor resistant to both lasers and kinetics, a heatshield and a strong structural material. However, most work on it is theoretical, we don't have the technology to make it in quantity. You are, however, looking at a melting point of nearly 3000K (I'm not quite sure it truly melts, but that's another matter entirely), and very good mechanical properties. 

So not good enough for metallic hydrogen, which has reaction chamber temperatures as high as 6000k.

I will say it again, we are not power limited, just material limited.

 

Where we should redouble our efforts is making super heat resistant materials.

If we can do that, SSTO's are quite viable, even with modern rocketry.

Since we could already do highwr pressures and temps, but our materials cannot take it.

 

 

That brings to mind, what other applications would a material that could withstand 8000k be good for besides rocketry?

Scifi is why I ask. I love to explore the logical conclusion of scifi tech capability that popular media scifi often ignores.

 

What do u think?

Edited by Spacescifi

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Except that "super heat resistant materials" are generally on order of amorphous carbon. You can't go much further with matter, because chemical bond energy is limited. Weird materials can only get you so much. 3000-4000K is the highest we are ever likely to go. Magnetic fields have no melting point, and as such are the way to go. 

If you could have unobtainium that can withstand 8000K, then you essentially have magnetic nozzles without the magnets. You could make liquid or even gas core nuclear power plants (not normal solid core ones, uranium has a melting point, too), which would be much more efficient. Basically, from thermodynamics standpoint, the hotter you can go, the better. Since we struggle against thermodynamics so much, anything that could help us there would be very useful indeed.

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On ‎8‎/‎10‎/‎2019 at 11:52 PM, Dragon01 said:

You could make liquid or even gas core nuclear power plants (not normal solid core ones, uranium has a melting point, too), which would be much more efficient.

Bruh...

 

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The problem with gas core reactors is that besides propulsion, they're usually more trouble than they're worth. Unobtainium plating that remained solid at 8000K would handily change that.

For terrestrial power plants, solid core thermal is sufficient. Gas core makes sense if your fuel supply is limited compared to your power needs (so that squeezing out thermodynamic efficiency matters a lot), of if high temperature is an end in itself, as in a rocket.

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5 minutes ago, Dragon01 said:

The problem with gas core reactors is that besides propulsion, they're usually more trouble than they're worth. Unobtainium plating that remained solid at 8000K would handily change that.

They may have a layer of cooling fluid between the walls and the reaction zone.

Also: http://up-ship.com/blog/?p=5353

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Yes, there's a lot of ideas, and it's possible to do if you really need it. That still doesn't make them very practical with current technology, there's simply no reason to go to all this trouble for a terrestrial power plant. 

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Posted (edited)
On 8/10/2019 at 1:52 PM, Dragon01 said:

Except that "super heat resistant materials" are generally on order of amorphous carbon. You can't go much further with matter, because chemical bond energy is limited. Weird materials can only get you so much. 3000-4000K is the highest we are ever likely to go. Magnetic fields have no melting point, and as such are the way to go. 

If you could have unobtainium that can withstand 8000K, then you essentially have magnetic nozzles without the magnets. You could make liquid or even gas core nuclear power plants (not normal solid core ones, uranium has a melting point, too), which would be much more efficient. Basically, from thermodynamics standpoint, the hotter you can go, the better. Since we struggle against thermodynamics so much, anything that could help us there would be very useful indeed.

 

 

8000k is good but we are not totally out of the woods yet.

It dawned on me that with 8000k heat tolerances, it almost matters not what propellant you use, you will get good boost. Since if metallic hydrogen creates over 6000k temp, running liquid hydrogen through an unobyanium reactor with 8000k tolerance at over 6000k I would hope would give similar thrust and ISP.

Right?

 

The real difficulty is size vs weight.

 

A smaller ship is easier to lift off and would probably reach a higher top speed with the same fission reactor made of unobtanium running at over 6000k (even though it tops out at over 8000k).

While a larger heavier ship would have a lower top speed and have a slower time lifting off.

Obviously there is a balance that must be struck between temperature, weight, and speed.

 

I think we can safely write off destroyer size/weight fission SSTO's even with my unobtanium. Since the heat required for lifting heavier loads just goes higher and higher.

 

Where the unobtanium would work is large shuttlecraft.

Big ships should just be Orion pusher plates, boosted by unobatinum fission rocket core rockets before using pulse detonation on the unobtanium plate.

Edited by Spacescifi

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Posted (edited)
5 hours ago, Spacescifi said:

I think we can safely write off destroyer size/weight fission SSTO's even with my unobtanium. Since the heat required for lifting heavier loads just goes higher and higher.

3F2BAB0740742345845768FDEBA8C6AEEFBA5588

This is an SSTO-rated frigate. What does it run on? A methane-fueled solid core NTR. No unobtainium needed. The engine is vacuum-optimized, so if you modify it with an altitude-compensating nozzle you may need to ship the missiles separately (SIM-1s are quite hefty, being basically SLBMs optimized for starship to starship warfare). You can make battleship-sized SSTO starships with solid-core NTRs.

Also, it's actually heavier than a destroyer of similar size. Most of its internal volume is taken up by methane tanks, and it has a lot of hull armor, as well.

Edited by Dragon01

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56 minutes ago, Dragon01 said:

3F2BAB0740742345845768FDEBA8C6AEEFBA5588

This is an SSTO-rated frigate. What does it run on? A methane-fueled solid core NTR. No unobtainium needed. The engine is vacuum-optimized, so if you modify it with an altitude-compensating nozzle you may need to ship the missiles separately (SIM-1s are quite hefty, being basically SLBMs optimized for starship to starship warfare). You can make battleship-sized SSTO starships with solid-core NTRs.

Also, it's actually heavier than a destroyer of similar size. Most of its internal volume is taken up by methane tanks, and it has a lot of hull armor, as well.

Those barrels are thicc. No inner anti-drone belt, tho?

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The barrels are thick because of what kind of stresses they endure. It's the case with everything except conventional guns. COADE probably doesn't model the optimal way of stiffening the barrels, but something of that sort is needed to reduce dispersion to acceptable levels. Yes, that means all the "space combat will take place at millions of kilometers" notions are BS, unless you count the missile exchange (which requires weighty missiles and is a crapshoot, anyway). The 12mm has power draw of a 1GW and engages at a little over 300km (mostly due to sheer muzzle velocity, which is 54km/s), but it fires 3.5g sand grains. The 17mm draws 120MW, and with 20 gram rounds going at 11km/s it's the heavy hitter that can get through hull armor. The idea is that the 12mm takes out guns (and radiators, if it can hit them) and the 17mm shreds the hull. And yes, they miss a lot. They have rate of fire to make up for that.

These railguns eat drones and missiles for breakfast, BTW. Due to aforementioned accuracy issues at long ranges, rates of fire are on order of 600000 RPM (100 microseconds between rounds). Anything that gets near will get hit at least once, and drones that can withstand hits from the 12mm aren't very practical, it turns out. Of course, it's not the only design philosophy possible in COADE, and this frigate is not the mightiest warship possible.

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If "all" you want is an Earth-based SSTO, you don't need unobtanium nozzles, anything that worked with a NTR should get similar efficiency with laser propulsion.  That said, Escape Dynamics (the company that tried for 5 years to do this and then went bankrupt) only managed about 500s.  You'll need hydrogen reaction mass, but the Isp should get high enough for SSTO.  Escape Dynamics' method of "laser propulsion" didn't involve "riding the laser", it instead heated the reaction mass, so propulsive landing (and hovering) should be possible (assuming your valve can withstand maximum temperature for hovering).

The lasers are the tricky part, and can be expected to be hid behind a security wall as the US Navy develops them.

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