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Laser launched rockets


DusterBoy
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Re: Laser launched rockets

 

By scaling up' date=' I mean making it able to launch a manned vehicle.[/quote']

Might take a while. Minimum laser power for laser launch into orbit is on the order of 100 kW/kg (of payload), and reaching that lower limit is unlikely. There's something of a shortage of lasers capable of producing several hundred megawatts continually for multiple minutes.

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Re: Laser launched rockets

 

Might take a while. Minimum laser power for laser launch into orbit is on the order of 100 kW/kg (of payload)' date=' and reaching that lower limit is unlikely. There's something of a shortage of lasers capable of producing several hundred megawatts continually for multiple minutes.[/quote']

Then let's get a bunch that can deliver a pulse and recharge, ready to go again when their turn comes around.

 

In what context would this be the most efficient way to get something aloft? Honest question; I don't know the limits of the concept.

Biggest advantage is your power supply can stay on the ground. You can use, say, the energy of a nuclear reactor without having to lift a nuclear reactor. Much better than sitting on top of tons of high explosives and lighting a match.

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Re: Laser launched rockets

 

Stupid question... would this work if your source laser was mounted on the ship? Or would you just tear the laser mount off the back of the ship?
Are you talking about having the laser on the ship targeting another part of the ship, then no acceleration will happen.

 

However, you could use a laser as a thruster, where you use E = mc2 (and Momentum of light = E/c) to cause accelleration, you would required a very high power Power Source to make any decent acceleration

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Re: Laser launched rockets

 

And the Kzinti Lesson applies. The beam will be impressive in power and destructive capacity. As in, several orders of magnitude more than those little flashlights you were thinking of for armament.

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Re: Laser launched rockets

 

Yeah, you can scratch out a back-of-the-envelope calculation for photon rockets and end up with appalling numbers. For a vehicle the mass of the Space Shuttle, if you want enough thrust to accelerate you at 1 gee (which is enough to levitate you above the surface of the Earth; you need a little more thrust to lift you to orbit) your rocket power requirement is about 10^15 W.

 

FWIW, that power requirement exceeds the world electricity generation capacity in 2006 by a factor of several hundred.

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Re: Laser launched rockets

 

In what context would this be the most efficient way to get something aloft? Honest question; I don't know the limits of the concept.

 

In theory it should be Very good....you don't have to haul a metric b-load of fuel with you....just to burn it up. So the lift per KW is much better...

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Re: Laser launched rockets

 

Yeah, you can scratch out a back-of-the-envelope calculation for photon rockets and end up with appalling numbers. For a vehicle the mass of the Space Shuttle, if you want enough thrust to accelerate you at 1 gee (which is enough to levitate you above the surface of the Earth; you need a little more thrust to lift you to orbit) your rocket power requirement is about 10^15 W.

 

FWIW, that power requirement exceeds the world electricity generation capacity in 2006 by a factor of several hundred.

Is that based on light pressure alone, or using the laser to heat reaction mass?

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Re: Laser launched rockets

 

Is that based on light pressure alone' date=' or using the laser to heat reaction mass?[/quote']

 

you beat me to it. I have seen a couple of different concepts over the years, iirc.

 

Photon pressure- only good for small items or in Doc Smith level stuff (okay, Mote in God's Eye did use it with a solar Sail also, but...)

 

I seem to recall proposals that would heat air inside the chamber to expand it as a form of jet engine

also proposals to feed a "fuel source" into the chamber, and heat/ignite it with the laser.

 

I still prefer mass drivers for earth to orbit launch, or space elevators of course.

 

now from the Moon, maybe solar powered lasers could be used...

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Re: Laser launched rockets

 

Dean Ing had an interesting approach to Laser Propulsion in the book Big Lifters. Very good read by the way. Man Kzin wars see's some Laser Propulsion stuff in the beginning as well. Certainly some potential there.

 

~Rex

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Re: Laser launched rockets

 

My impression from the video (s -- I watched a couple of the related ones in English as well) is that the laser is focused by the shape of the underside of the craft to superheat the air flowing through the vents in the body, causing a rapid expansion of that air that pushes against the body of the craft and produces the thrust. This presents the practical use of the craft with two major problems:

 

1) The craft is limited to use where the density of air is great enough to provide the necessary thrust. So, no orbital lifting.

 

2) the laser must be directly underneath the craft, and lined up properly, or it will at best produce unbalanced thrust, which would drive it further, or completely, out of alignment with the laser, and back into gravity's persistent embrace. So, no flying on windy days. Or near the jet stream, if you can even fly that high.

 

It is an interesting technology, but it doesn't seem very useful.

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