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The Realistic Challenges Of BIG Nuclear Powered Space Lasers


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Forget the politcal angle for discussion and let us discuss the physical challenges.

Lens radius: Five meters wide 

Power:  Two nuclear reactors.


Challenges: Lasers are hardly the most efficient invention. They make a lot of waste heat, and that will need to be shed via radiator fins. That is overlooked I think when high yield repeat use space lasers are considered.


Main Question: What is the most powerful laser we could put in orbit on a spacecraft that we still wished to move under it's own thrust?

Bonus Question: What is it's effective burn range?  Given the 5 meter focusing lens?


That's the irony pf spacecraft,  the heavier the equipment inside a spacecraft the lower it's overall max thrust will be. Since heavy equiment has more inertial resistance to push against.


At some point your rad fins become so heavy that your EPIC space laser has so low thrust that it may as well be a station.

What is the sweet spot of spaceship weight where you can get as powerful a laser with nuclear power as we can expect with modern tech on a mobile spacecraft?

Would such a laser be suited well enough for asteroid mining or not?


This is not for scifi..just curious what our current limits truly are.

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38 minutes ago, Spacescifi said:

Five meters wide 

It's not BIG, it's tiny.

39 minutes ago, Spacescifi said:

Two nuclear reactors.

I was going to put three, but as you wish.
(Why two? Why three? Who knows...)

Also, a nuclear reactor is not very useful to power a pulse laser, it should recharge capacitors or regenerate fuel.
So, all known orbital lasers are chemical.

40 minutes ago, Spacescifi said:

What is the most powerful laser we could put in orbit on a spacecraft that we still wished to move under it's own thrust?

Any, but slowly.

41 minutes ago, Spacescifi said:

What is it's effective burn range?

To burn what? Gunpowder? Tungsten?

42 minutes ago, Spacescifi said:

the heavier the equipment inside a spacecraft the lower it's overall max thrust will be.

No correlation between the thrust and the cargo.

42 minutes ago, Spacescifi said:

At some point your rad fins become so heavy

Vacuum fins? It's in orbit.

45 minutes ago, Spacescifi said:

Would such a laser be suited well enough for asteroid mining or not?

No. We don't have asteroids in orbit.

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14 minutes ago, kerbiloid said:

It's not BIG, it's tiny.

I was going to put three, but as you wish.
(Why two? Why three? Who knows...)

Also, a nuclear reactor is not very useful to power a pulse laser, it should recharge capacitors or regenerate fuel.
So, all known orbital lasers are chemical.

Any, but slowly.

To burn what? Gunpowder? Tungsten?

No correlation between the thrust and the cargo.

Vacuum fins? It's in orbit.

No. We don't have asteroids in orbit.

 

What if we someday find a way to convert 99% of nuclear reactor power into a laser pulse?

Would still be too weak with two reactors? So that the best you could do is slowly scorchan asteroid?

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5 hours ago, Spacescifi said:

What if we someday find a way to convert 99% of nuclear reactor power into a laser pulse?

The nuclear reactor is a slow device.

A slow laser loses a lot of energy by the hot spot emission (proportional to T4) and is ineffective for destruction.

An effective laser is the pulse one, and it needs a lot of energy at once, it's a fast device.

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3 hours ago, kerbiloid said:

The nuclear reactor is a slow device.

A slow laser loses a lot of energy by the hot spot emission (proportional to T4) and is ineffective for destruction.

An effective laser is the pulse one, and it needs a lot of energy at once, it's a fast device.

 

I see. Thanks.

So I suppose the only thing a nuclear reactor could do to booste a chemical laser is heat up the chemicals prior to whatever reaction is used to power the laser.

The irony is that the chemical would probably have to be burned like propellant in the process...so not efficient.

 

With chem lasers do you actually run the risk of running out of chemical? Does it vape away or something?

EDIT: Answered. The USA airforce laser recirculates the chemical so it never runs out. Can fire so long it does not overheat. Virtually unlimited zapping.

 

Yet according to wikipedia other options besides chemical lasers are being sought:

Despite the performance advantages of chemical lasers, the Department of Defense stopped all development of chemical laser systems with the termination of the Airborne Laser Testbed in 2012. The desire for a "renewable" power source, i.e. not having to supply unusual chemicals like fluorine, deuterium, basic hydrogen-peroxide, or iodine, led the DoD to push for electrically pumped lasers such as diode pumped alkali lasers (DPALS).[18][failed verification]

Edited by Spacescifi
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21 minutes ago, Spacescifi said:

the only thing a nuclear reactor could do to booste a chemical laser is

nothing.

It can provide electricity and ion propulsion. Theoretically, recharge capacitors, but this is mostly in KSP mods.

22 minutes ago, Spacescifi said:

the chemical would probably have to be burned like propellant in the process.

It has to. A chemical laser sat will run out of fuel if not overheat.

24 minutes ago, Spacescifi said:

Does it vape away or something?

It gets exhausted sideways to prevent rotation impulse.

26 minutes ago, Spacescifi said:

led the DoD to push for electrically pumped lasers such as diode pumped alkali lasers (DPALS)

They had played KSP and want something like capacitors.

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37 minutes ago, kerbiloid said:

nothing.

It can provide electricity and ion propulsion. Theoretically, recharge capacitors, but this is mostly in KSP mods.

It has to. A chemical laser sat will run out of fuel if not overheat.

It gets exhausted sideways to prevent rotation impulse.

They had played KSP and want something like capacitors.

tenor.gif

Bravo! You just killed the scifi trope of space laser combat!

No lasers in Elite dangerous! No lasers in Children of a Dead Earth!

Since they would run out of chemical too soon and do too little damage in the process.

Granted, ED is total fiction...they probaby use sustained fusion to power their lasers ingame.

Children Of a Dead Earth does not have that to rely on, so they probably rely on free electron lasers or something non-chemical.

https://en.m.wikipedia.org/wiki/Free-electron_laser

https://www.google.com/amp/s/www.wired.com/2011/02/unexpectedly-navys-superlaser-blasts-away-a-record/amp

 

So there are yet other options afterall and will there likely be even more because...

tenor.gif

Edited by Spacescifi
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On 11/24/2020 at 2:21 AM, Spacescifi said:

 

What if we someday find a way to convert 99% of nuclear reactor power into a laser pulse?

Would still be too weak with two reactors? So that the best you could do is slowly scorchan asteroid?

How?  Most efficient way commonly used is heating a gas to spin a turbine.  That should top out near 66% efficiency or so.  Regardless, your radiators will have to emit nearly all energy generated by the reactor into blackbody radiation (less the emitted laser.  But that can't be a significant percentage).  As the lasers get powerful, the radiators get larger.  I'm sure I've quoted the calculations at you a few times.

On 11/24/2020 at 12:13 PM, Spacescifi said:

Bravo! You just killed the scifi trope of space laser combat!

No lasers in Elite dangerous! No lasers in Children of a Dead Earth!

Since they would run out of chemical too soon and do too little damage in the process.

Granted, ED is total fiction...they probaby use sustained fusion to power their lasers ingame.

Children Of a Dead Earth does not have that to rely on, so they probably rely on free electron lasers or something non-chemical.

https://en.m.wikipedia.org/wiki/Free-electron_laser

https://www.google.com/amp/s/www.wired.com/2011/02/unexpectedly-navys-superlaser-blasts-away-a-record/amp

None of these address the power source you'd need, nor the efficiency of the laser.  Even with fusion, you'll have such massive radiators that they would be obvious targets if you could attack them from three non-coplanar directions.

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5 hours ago, wumpus said:

How?  Most efficient way commonly used is heating a gas to spin a turbine.  That should top out near 66% efficiency or so.  Regardless, your radiators will have to emit nearly all energy generated by the reactor into blackbody radiation (less the emitted laser.  But that can't be a significant percentage).  As the lasers get powerful, the radiators get larger.  I'm sure I've quoted the calculations at you a few times.

None of these address the power source you'd need, nor the efficiency of the laser.  Even with fusion, you'll have such massive radiators that they would be obvious targets if you could attack them from three non-coplanar directions.

 

So you're point is that due to power inefficiency of lasers, they will never make much viable use for asteroid mining, and even less for space combat.

They are best used in factories on worlds with chemicals readily available to power it.

Might as well fly up to a space rock and pop out a drill and net to catch loose chunks while the mothership attaches itself with tethers and landing legs to the rock.

To not need radiators you would need perfect blackbody mirrors that reflect all your blackbody radiation out.

 

Interesting article:

https://physics.stackexchange.com/questions/369862/hot-blackbody-and-hot-mirror

 

With perfect 100% reflective blackbody mirrors, you probably won't need radiators. Just reflect heat away.

Edited by Spacescifi
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18 hours ago, Spacescifi said:

 

So you're point is that due to power inefficiency of lasers, they will never make much viable use for asteroid mining, and even less for space combat.

They are best used in factories on worlds with chemicals readily available to power it.

Might as well fly up to a space rock and pop out a drill and net to catch loose chunks while the mothership attaches itself with tethers and landing legs to the rock.

To not need radiators you would need perfect blackbody mirrors that reflect all your blackbody radiation out.

 

Interesting article:

https://physics.stackexchange.com/questions/369862/hot-blackbody-and-hot-mirror

 

With perfect 100% reflective blackbody mirrors, you probably won't need radiators. Just reflect heat away.

Nothing I said was about asteroid mining, unless you are worried about a claim jumper blasting you with a mining laser (might make a great bit of sci-fi, along the lines of a space western).  On the other hand, it may be far more efficient to simply focus solar power with a giant mylar mirror instead of building the laser.   My point was that the radiators are going to be a big target.  Others have pointed out just how impossible it is to focus a laser across interplanetary distances.

Blackbody mirrors *are* radiators.  Just perfect ones.  And "perfect" materials don't seem to mix with high energy (at least things like superconductors and similar large-scale quantum effects).  Note that if you had such a thing, it would also make an interstellar (maybe just for probes) drive (nearly infinite Isp).

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On 11/24/2020 at 2:05 AM, Nuke said:

im more of a bomb pumped x-ray laser kind of guy. you only get one shot, but you only need one shot. 

Wait, if the primary output of nuclear fission is x-rays, could a Zubrin NSWR "continuously" power a laser?

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1 hour ago, Nothalogh said:

Wait, if the primary output of nuclear fission is x-rays, could a Zubrin NSWR "continuously" power a laser?

 

I think you are on to something.

If military forces have tested lasers of this sort it is mos definitely classified, since if anything goes horribly wrong your entire laser facility goes up in a nuclear fireball.

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2 hours ago, Nothalogh said:

That's not a bug, it's a feature.

Depends on who you ask.

Zubrin? It's a worse case scenario bug. 

Dissenters? Feature.

Either way, it would be a high price to pay for having spaceship with Xasers (x-ray lasers).

 

Ha...perhaps that's why no one rich is willing to openly support NSWR lasers.

Nevermind all the radiation it creates.

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