It would be a hell of a way
to light a barbeque
Raygun 747 missile-zapping test video released
The US Missile Defence Agency has released video of last week's test of the Airborne Laser Testbed (ALTB) - the huge, jumbo-jet-mounted laser cannon built to blast hostile ballistic missiles out of the sky as they boost upward from their launch sites. The ALTB was formerly known simply as the Airborne Laser (ABL), but has …
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Tuesday 16th February 2010 14:21 GMT lIsRT
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Apparently not - unless it's 100% reflective, some of it will be vaporised and the vapour will start to absorb the laser energy instead, then the energy just conducts as heat into the coating (which then disintegrates).
Or so I read.
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Wednesday 17th February 2010 12:04 GMT Michael H.F. Wilkinson
One might still
coat a missile with an ablation-type heat shield (think Apollo era). If it is also reflective (in the correct wavelength band) it will reflect part of the heat, but that by itself is apparently not enough. However, if you allow a thick shield to evaporate this has two effects: It carries the heat away from the missile effectively, and could create a cloud of droplets or particles which could scatter part of the laser energy. The vapour absorbing energy is not a problem as it will not conduct energy to the missile effectively.
Launching missiles in thick fog could help, but IR travels quite far through fog (would reduce range further though).
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Tuesday 16th February 2010 17:06 GMT Dapprman
It was completed and successfully tested
However there were strong objections to the disposal of the toxic waste produced. Apparently the residents of the northern towns actually felt it was safer to put up with the occasional missile (most land harmlessly) than have a large toxic waste dump near by - though this was before the big increase prior to the last major Israeli incursion of Gaza.
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Wednesday 17th February 2010 10:52 GMT Trevor Pott o_O
@Ammaross Danan
First off, "slapping a nuclear reactor in the back of a plane" would violate quite a few treaties, not to mention make eleventeen squillion NIMBYs explode.
Secondly, you could put the biggest power source you wanted on that plane, but power generation isn't the problem. (Power generation on something the size of a 747 isn’t a problem. The solid state array required for a megawatt-class laser isn’t that big, leaving plenty of room for old-fashioned fossil-fuel-based generators.)
Heat is the killer to this idea. A large portion of all the energy you are pumping out is converted to light, but not all...when you are talking megawatt class lasing, this is a terrific engineering problem. You have to sink that heat off your lasers, (and possibly your focusing mechanisms, I honestly don’t know the answer to that one,) conduct that heat to an appropriate radiator, and then radiate it away.
Big ass water-cooling system and/or heat pipes can help with some of that, but where do you dump the heat? Directly into the atmosphere isn't exactly an option. The air be a little thin where they be lasing, and the surface area required starts to boggle the mind. I am sure with enough time and effort the heat dissipation issue can be overcome, perhaps by recycling the waste heat into sub-generation, perhaps by using heat pumps to dump the heat as super-heated exhaust. This gets into the realm now of muchos big time maths, and a lot of trial-and-error.
Either way, we can cheerfully pack a megawatt+ worth of generation capacity onto a 747 without ever having to put fissionables into a position where they might be blown up in our atmosphere. Avoiding the scattering of fissionables everywhere helps keep the rate of exotic cancers down.
If you can come up with some neat ways to overcome the heat dissipation problems however, then DARPA would love to hear from you.
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Wednesday 17th February 2010 15:07 GMT Anonymous Coward
Quite a few defense analysts..
..over the last few years have clutched their crystal balls and opined that when it all kicks off, Israel will be involved.
They're mighty jumpy over there, a bunch of warlike right wingers running the military of a nuclear state- surrounded by countries which really are out to get them, paranoia aside. Hell of a situation- my money is on Israel nuking Iran or vice versa. It's not going to be good.
On the upside, if things get out of hand, living in London, I'll be a prime nuke target, and likely die nice and fast :)
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Thursday 18th February 2010 12:29 GMT John Smith 19
running some numbers
Heat could well be the long pole in this tent. The laser diode pumped lasers are pretty good on this at (IIRC) about 32% efficiency. I've no idea what chemical systems are. From memory HeNe is around 5%. The rest (68% or 95% depending on system) is heat. Chemcial systems were chosend for their (apparent) mechancial simplicity, not necessarily for there efficiency.
So a MW class laser has to dump somewhere between 2 and 19MW. To put that in perspective. 1MW/m^2 was the Apollo heat shield spec (which at 100W/cm^2 is also roughly the heat output of a modern CPU).
So you're looking at 2-19 square metres (205 Sq Ft) of heat dumping surface. Large but not impossible *provided* you have a heat sink to dump the heat into. It would not be the first time people have used the fuel for cooling. Likewise engine intake air (at 40kft) is also pretty cold If the efficency is <5% then you're proportionately in bigger trouble. Heat pipe cooled leading edges were proposed for the space shuttle (the top surface of the wing during re-entry is a *lot* cooled than the edge or windward sides) but an aircraft with a wing mounted radiator has not (AFAIK) flow since the 1930's.
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