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:hm: I'm very new to the Mars Society but I'd like to find out the fate of a propulsion technology that involved a material that explosively reacted to laser energy. It showed a lot of promise although I have never heard anything of it in a long time. A cylinder was coated with a very special (very expensive) material. The cylinder was rapidly rotated and a laser fired at the cylinder. An explosive reaction accelerated the cylinder. The beauty of this method was that it did not require fuel. Energy could be obtained via solar panels and then used to fire the lasers that would accelerate the craft. True, you would need conventional rockets to get to orbit but the trip to Mars would not require it.
As I said, I'm very new here but I would like to know if anything became of that technology. A craft powered in this manner could be, and would be, much lighter then one requiring fuel?
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I think you misunderstand that such a system doesn't need fuel. A better term than "fuel" is propellant, and that would be the stuff coating the rocket tube and burned off by the laser... unfortunatly, the mass of this stuff would still be quite large, though perhaps lower than regular chemical propellants. Such a setup would be fairly hard to do, and wouldn't have any easy way to reverse it for the return to Earth.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Thanks for the reply.
Actually, this material was not a propellant. It was some type of material that reacted to the laser, it did not burn or explode as propellant do. That was the beauty of it.
I do not recall how quickly it's reactive properties exhausted, that's one of the things I was curios about.
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You might be thinking of somthing that undergoes laser-induced ionization? In any event, it is still a reaction mass means of propulsion, so you will need to carry quite a bit with you. It is quite possible that it would be fairly efficent, though difficult to pull off and no return trip.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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That sounds more like it.
At the time that I saw the demonstration (program) it did not appear that much material was being consumed in the process. However, impossible to tell from what I had seen.
If the material was very efficient and went a long way then it would certainly open up a number of benefits for a trip to Mars. The mechanics of such a craft would be extremely simple as well compared to most of the alternatives.
Thanks for the info.
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Was the laser mounted on the spacecraft, or was it beamed in from somewhere else?
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There have been some tests with laser power craft. The projectile is a pound or so and looks similar to a flying saucer. A powerful laser is aimed at it and the back of the craft is shaped so as to focus the laser energy to a very small area. The propulsion is either carried out by explosively heating a piece of plastic or simply heating the air. It works but is terribly inneficient. There are similar approaches using microwaves that have more promise for being scaled up.
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There have been some tests with laser power craft. The projectile is a pound or so and looks similar to a flying saucer. A powerful laser is aimed at it and the back of the craft is shaped so as to focus the laser energy to a very small area. The propulsion is either carried out by explosively heating a piece of plastic or simply heating the air. It works but is terribly inneficient. There are similar approaches using microwaves that have more promise for being scaled up.
That is an Earth-LEO launch system that only works in the atmosphere. He seemed to be talking about an in-space propulsion system.
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Sounds to me like its some sort of laser ablation system, or a derivitve thereof. There are certain substances which will ionize when exposed to optical laser light, which could be useful for spaceflight. A higher-thrust/lower-Isp externally powerd ionization ion engine?
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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It is a piece of aluminum spun up to high velocties then the laser shines behind it, and the air explodes behind it. It then, theoretically accelerates to escape velocity. It has only climbed about 100 feet thus far in tests, and it was guided by wire.
Dr. Leik Myrabo is the person who is researching this. Go to:
[http://www.rpi.edu/dept/mane/deptweb/fa … yrabo.html]http://www.rpi.edu/dept/mane/deptweb/fa … yrabo.html
[http://www.cnn.com/SPECIALS/cold.war/ex … ite.sands/]http://www.cnn.com/SPECIAL....e.sands
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It will work, yes, but its still not very effective without a laser of extreme power, and then you have to find a way to keep it from melting... also, when operating outside the atmosphere, it will still require some kind of propellant gas to operate, which will cut into the payload substantially like any spacecraft.
There are plenty of operational complications for such a system too...
~Beam focusing/aiming over large distances
~Small spacecraft size, need for impractically large laser for even a modest launch
~No means of propulsion except away from the laser source, at least not one without a complicated, bulky, and probably dangerous mirror arrangement.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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The laser system has had some mild success. So far they've been able to get a 1 lb craft to about 200 feet. Exactly how they plan to get a deent mass to LEO is beyond me. The lase they used for that test wasa multiMEGAwatt beam. They don't get much bigger than that.
Plus, those big lasers are just insanely inefficient - 0.1% efficiency is really good in those circumstances.
On the other hand, microwave power transmission is not a bad idea. I read a paper - it might have even ome from Myrabo's group - that loked interesting. Microwave transmitter arrays can hit 70-80% efficiency and move huge amounts of energy. They basically posited an X-33 spaceplane with an H2 payload and a microwave reciever on the belly to heat that H2 up. By doing so, they were able to theoretically get enough energy to the craft to let it get to orbit with significant payload. (Isp was something crazy like 1700) The only problem was that in order to get away with a single microwave emitter array, the X-33 would have had to hit an acceleration of 25 G's near the end of the boost phase. Fine for cargo but no humans could survive that without serious injury.
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Would a particle beam work instead of a laser?
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Not really, those are pretty inefficent too, and it would be harder to extract useful heat energy from them without incinerating the vehicle.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Particle beams have three big problems. One - as GCNR mentioned, particle beams are even more inefficient to produce than lasers. Two - particle beams tend to be heavily scattered by air. Three - high energy particle beams are highly destructive, if they hit the target, you'll get all sorts of radiation damage.
Microwaves are the only real variant of this technology that looks practical with the technology we have available.
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I'd like to add an additional comment, just to clarify my initial idea.
The laser (or it looks like it would more appropraietly be a microwave) would be integral to the spacecraft. The solar panels would power the device. The microwave generator would essentially be a long boom extending out from the spacecraft (not a remote beam of energy). The boom would point back to the 'dish' of the spacecraft. The craft would blast itself around, hope you understand my meaning.
Accuracy would not be an issue. When you want to slow down you simply spin the ship around and 'blast' the reactive dish until you have slowed down to the desired speed.
Finally, my idea in regards to this technology was for the interplanetary trip. We could use any other technology to get out of Earth orbit. This technology would keep the craft very light.
For added safety we could have several dishes and several microwave generators on the craft for fault tolerance.
Thanks.
PLIND
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What you are talking about is what Sbird termed a Photonic drive... that is, the photons from the microwave source are the reaction mass/propellant for the system.
While this would be fairly efficent, you would need a gargantuan MW source and massive electricity to power it.
This system would be far far weaker thrust wise than even ion engines since photons deliver such low amounts of momentum. Somthing like this might help as a booster on an unmanned interstellar probe, but the thrust made would be much much too small to do anything practical with without the addition of another propellant (like hydrogen). If you did add a secondary propellant, then the efficency of the engine would plummet substantially because of the low temperature the gas could attain.
The VASIMR engine that Nasa has half-heartedly tinkerd with actually does use microwave energy to heat the hydrogen propellant in the engine, and it can do so with reasonable efficency and low-to-modest thrust, but requires massive amounts of energy.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Well this topic has been inactive for a while but the research has been pressing forward. There are obstacles to beam propulsion design for one in the ship materials and also with regards to the beam hitting the target vehicle acurately.
Regulatory agencies will need to develop ways to ensure stray beams don't fry passing airplanes or satellites passing overhead. And it will take $1 billion or $2 billion to build a system with enough oomph to lift one or two humans into orbit
Scientists shine a light on lasers in spaceflight
RPI gathers experts for symposium on "beamed energy propulsion"
http://www.timesunion.com/aspstories/st … yID=294101
Other topic related on newmars
Beamed Energy Propulsion
3rd International Symposium
http://www.newmars.com/cgi-bin....pulsion
Power Limits of Advanced Propulsion
http://www.newmars.com/cgi-bin....pulsion
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A particle beam would give more thrust in this case. Particles moving at high velocities then hitting stationary particles attached to the ship. All kinds of forces here including kinetic.
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