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Laser powered rockets

Posted by: box - Thu May 23, 2013 2:41 pm
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Laser powered rockets 
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Space Walker
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Post Laser powered rockets   Posted on: Thu May 23, 2013 2:41 pm
The basic idea is having a large number of high power output lasers placed along the ascent path. The lasers all target the same object, it has a heat exchanger on the bottom that is used to heat the reaction mass /usually water/, the hot reaction mass is expelled at the back.

If I understood what I read correctly that's the basic concept.

Questions:
Is this a dumb idea? :)

Do we have heat exchanger technologies advanced enough to pull this off?

Am I correct in thinking that once we heat water to 2000 or so Kelvin it will mostly exist as separate hydrogen and oxygen atoms or molecules in this gas mixture assuming we continiously pump it with energy?

So if we heat up water with laser in a rocket type of setting, at some point the exhaust is not steam but a burning mixture of hydrogen and oxygen as it recombines into hot steam because it is no longer being heated by the laser.

So a normal LOX/Hydrogen rocket, and a laser heated water rocket have the same exhaust, a burning flame of hydrogen/oxygen?

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Post Re: Laser powered rockets   Posted on: Thu May 23, 2013 3:22 pm
Not a dumb idea, just one with a lot more detail technical problems than it's advocates like to admit.


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Post Re: Laser powered rockets   Posted on: Thu May 23, 2013 4:54 pm
The upshot (If you'll pardon the expression) is that you don't have to carry as much energy onboard, but you still have to carry the Reaction Mass. Water can just as easily be saturated with the energy to boil it (Like ANAS, or Ammonium Nitrate in Aqueous Solution, for instance) without adding significant mass, nor any more volume to require more Tank/s, and more fuel to lift the tanks...

Another problem is that in an atmosphere, you're losing a lot of energy to Heat. Even if you use frequencies (UV) that go right through the air without slowing down, you still have the emitter, which needs to be cooled, which requires energy... With traditional fuel systems (And monopropellant systems like ANAS, or Alluminum/LoX) the waste heat is automatically exchanged to the propellant to add more expansion, so it's less of a loss.

Were I to design something like this, as a Launcher, I'd probably make it an air breathing booster with something else for accelerating from launch altitude to orbital velocity. Give it an intake, a large black target inside the engine, and light it up from the ground. This would necessitate a vertical launch, since you have to keep it oriented to the LASER.

I wouldn't suggest putting them "In the path" because that means flying multiple emitters in 747s as part of the entire launch structure stretching up through the low-mid altitudes, with fuel for them, separate power supplies... If the plan is to conserve energy, and cost, this would multiply both, and add potential points of failure all along the launch trajectory, and even that will only get you so high before you have to switch to something else.

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Post Re: Laser powered rockets   Posted on: Fri May 24, 2013 3:55 am
One note- there's no need for a vertical launch, you can aim the laser. There already is a laser you could use: http://en.wikipedia.org/wiki/Tactical_High_Energy_Laser. Of course, it is not as noble a use as its original use, but that is neither here nor there.

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Post Re: Laser powered rockets   Posted on: Fri May 24, 2013 9:07 am
SuperShuki wrote:
One note- there's no need for a vertical launch, you can aim the laser. There already is a laser you could use: http://en.wikipedia.org/wiki/Tactical_High_Energy_Laser. Of course, it is not as noble a use as its original use, but that is neither here nor there.


But vertical launch ensure the least atmosphere for the laser beam to pass through, so less power losses.


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Post Re: Laser powered rockets   Posted on: Fri May 24, 2013 12:47 pm
SuperShuki wrote:
One note- there's no need for a vertical launch, you can aim the laser. There already is a laser you could use: http://en.wikipedia.org/wiki/Tactical_High_Energy_Laser. Of course, it is not as noble a use as its original use, but that is neither here nor there.
Of course you can aim the LASER, I wasn't debating that, but can the craft efficiently use it? And no, that one isn't even remotely the power level we're talking about. The ability to heat artillery shells until the blow up is nothing compared to how much energy it takes to lift even a kilogram to orbit. That cute little light would be entirely unsuitable.

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Post Re: Laser powered rockets   Posted on: Fri May 24, 2013 1:16 pm
Psiberzerker wrote:
SuperShuki wrote:
One note- there's no need for a vertical launch, you can aim the laser. There already is a laser you could use: http://en.wikipedia.org/wiki/Tactical_High_Energy_Laser. Of course, it is not as noble a use as its original use, but that is neither here nor there.
Of course you can aim the LASER, I wasn't debating that, but can the craft efficiently use it? And no, that one isn't even remotely the power level we're talking about. The ability to heat artillery shells until the blow up is nothing compared to how much energy it takes to lift even a kilogram to orbit. That cute little light would be entirely unsuitable.


Are you perturbed for some reason?

Of course, I was referring to the ability of the thing to aim itself. That technology is here. But you knew that didn't you? What brilliance!

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Post Re: Laser powered rockets   Posted on: Fri May 24, 2013 1:32 pm
SuperShuki wrote:
Of course, I was referring to the ability of the thing to aim itself. That technology is here. But you knew that didn't you? What brilliance!
That's not the only technical challenge, though, nor the reason why I suggested vertical launch. First, we need a powerful enough emitter, and that one ain't gonna do it. Next, we need to design a craft that's capable of absorbing the light, and turn it into usable energy for thrust. This is tricky, because we can't just have a mirror sticking out in the air-stream. You'd have to hit the target, and just the target, because any beam of that much energy would be enough to destroy the entire craft.

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Post Re: Laser powered rockets   Posted on: Fri May 24, 2013 1:52 pm
You could at least have laughed.

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Post Re: Laser powered rockets   Posted on: Sat May 25, 2013 1:26 am
I probably should have posted the pdf I read which details the concept a bit further and asesses key technologies available and costs of said technologies.

It isn't a single powerful laser, it is fields of tens or hundreds of small lasers all capable to target and follow a target that flies overhead.

The spacing of these stations is along the launch trajectory and the stations would "hand" over the target from one to the other as it passes over.

Probably the most crucial part that is missing is the interface that would absorb the energy from the lasers and transfers it into the reaction mass. LaserMotive have built and operated beamed powered systems but they operate on electricity, the interface is photovoltaics.

We have the laser technology, but what we don't have is the way to turn incoming megawatts or gigawatts of energy over a couple of square meters into thrust through the efficient heating and expelling of a propellant.

My main question was regarding this converter. Is some sort of a composite ceramic that absorbs and transfers heat very efficiently the solution? The outer surface will probably have to be flat, or slightly curved to make use of laser light coming at too high of an angle, but how do you use such a hot surface to heat a liquid or highpressure steam to 2000+ kelvin.

Is it just me or this sounds like a heatshield but instead of keeping the heat out, we want to transfer and direct it into the inside of the craft to do some work with it?

Also could 3d printing be a solution to creation composite ceramics with the right characteristics for this?

Another idea I just had. If you had such ceramic panels, and you had propellant on board, couldn't you use a reentry shield made partially of this and onboard propellant to slow down your craft faster during reentry and reduce the time it takes to bleed the orbital energy into the atmosphere?

Probably an another useless idea. :)

Though wouldn't that help with much heavier cargo where it would take too long to bleed orbital energy for the shields to withstand or the craft would get too deep into the atmosphere before bleeding off energy so the temperature would rise too high for the shield to withstand.

An active reentry system that recycles the orbital energy into useful deltaV. :)

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Post Re: Laser powered rockets   Posted on: Sat May 25, 2013 7:17 am
http://www.niac.usra.edu/files/studies/final_report/897Kare.pdf

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Post Re: Laser powered rockets   Posted on: Sat May 25, 2013 5:40 pm
Why does the laser have to hit the spaceship at all? Why can't you squirt out liquid water, evaporate that, and have the steam push the craft?

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Post Re: Laser powered rockets   Posted on: Sun May 26, 2013 4:18 pm
SuperShuki wrote:
Why does the laser have to hit the spaceship at all? Why can't you squirt out liquid water, evaporate that, and have the steam push the craft?

You're going to push water up to 100 miles altitude coherently, then use a laser to boil it externally, then somehow use this to push an aircraft by some application of physics I'm unaware of? I can't find anything right about this proposal.

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Post Re: Laser powered rockets   Posted on: Sun May 26, 2013 9:20 pm
shoot and hit a contact that is a photo cell designed for that frequency and EXTREME HEAT, establish TWO laser channels, to two panels, DUMP current up the beam, either through the evacuated plasma channel center as a electron beam, or by conducting up the plasma :D

"Plasma leads"

:D

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Post Re: Laser powered rockets   Posted on: Sun May 26, 2013 10:34 pm
Psiberzerker wrote:
SuperShuki wrote:
Why does the laser have to hit the spaceship at all? Why can't you squirt out liquid water, evaporate that, and have the steam push the craft?

You're going to push water up to 100 miles altitude coherently, then use a laser to boil it externally, then somehow use this to push an aircraft by some application of physics I'm unaware of? I can't find anything right about this proposal.


Well, if you can do the other stuff, why not this? (that's a rhetorical question)

By the way, is there anything left about this proposal?
:P

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