Lasers!!

Exactly. That is why after viewing the movie in 1979, my military solution was instead of camo paint, a highly polished finish would protect from lasers. Might still work today with laser sights.

Obviously there does not exist a perfect reflector. Polished steel or chrome might reflect 85-90% of light. Aluminum and silver mirrors 90 - 95%.
Then there is the question of the lights wavelength, UV - Visible - IR. Consider that IF I had a Megawatt laser and hit your perfectly clean and polished Aluminium tank, perhaps something >5% would be absorbed. That's still 50,000 watts of energy IF IF IF all that energy made it through the atmosphere to the tank. Gasses like CO2 and water vapor absorb light as does particulate matter which can also reflect the beam. You can see an ordinary flashlight beam or searchlight beam in the sky because of this reflection by particulate matter.

Well it is not as simple as "brightly polished."

Take two sheets of aluminum. Paint one black and polish the other one to as much of a mirror-like shine as possible.

Which one gets hotter?

Answer: The brightly polished one gets hotter. What matters is how it absorbs Infra Red, and while polished aluminum looks reflective, in IR terms it is blacker than black is.

My high school physics teacher said that one day in the late 1930's his crew was sent to pick up a new, natural aluminum DC-3 from a desert location not far from the present day Las Vegas. Sitting in the Sun, they found the airplane was too hot to enter, walk up the aisle to the cockpit, and get the engines started. They had to wait until night (their Navy commander at the other end of the phone in San Diego refused to believe it was that hot).

So the frequency of the laser matters as does the characteristics of the target.

Aluminium is an excellent REFLECTOR of IR. A simple experiment: Take some nice shiny aluminium foil and hold it near your face. In a very short time you will FEEL the heat (IR) FROM your face (about 90% EMISSIVITY) being reflected back from the surface of the Aluminium. Note the thin Mylar emergency blankets are coated with REFLECTIVE aluminium. The same REFLECTIVE aluminium blankets are placed in attic spaces to REFLECT the IR being emitted from the hot roof before it can enter the living spaces below.
Heat control with aluminum foil is made possible by taking advantage of its low thermal emissivity and the low thermal conductivity of air. It is possible with layered foil and air to practically eliminate heat transfer by radiation and convection: a fact employed regularly by the NASA space program. In the space vehicle Columbia, ceramic tiles are embedded with aluminum bits which reflect heat before it can be absorbed. "Moon suits" are made of reflective foil surfaces surrounding trapped air for major temperature modification.
Note: IR spectrum is from 1mm to 700nm. IR-A is from 800 - 1400nm. IR-B is from 1400nm - 3micrometers



Also just as a reminder about your bodies ability to detect temperature:
1st even though they are shiny they still absorb some light (both visible and infrared).
2nd they have small heat capacity so they warm up fast even if the amount of heat they capture is not very large.
3rd (and most important) Your skin does not feel the temperature of the objects you touch (you have no nerve endings in the objects). Your skin feels its own temperature. When you touch a hot object heat moves into your skin warming it up giving you the sensation of warmth. Metals are good heat conductors so they allow heat to flow fast into your skin increasing the sensation of warmth. By the way, that's also the reason why metal will feel colder than wood in cold weather.

Military lasers are quite different than conventional lasers.

A mirror-finish surface will not reflect all of the energy delivered, especially with the X-ray or electro-magnetic based lasers.

GrauGeist said:

X-ray or electro-magnetic based lasers.

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A military X-ray laser is still a pipe dream. The problem is with the amounts of energy needed to produce X-ray photons. E = hf so high frequency radiation requires LOTS of energy. The first X-ray laser proposals required nuclear explosions to power them. Part of the Star Wars program. The newest free electron X-ray lasers show a lot of promise. The Linac Coherent Light Source (LCLS) being built at the Stanford Linear Accelerator Center. It will use the last kilometer of SLAC's linear accelerator to pump electrons to 4.5 to 14.3 GeV of energy, then pass the beam through 112 m of undulator magnets to generate hard X-ray pulses at 0.15 to 1.5 nm lasting 1 to 230 fs. That's fs or FEMTO (10^-15 seconds). Going to be tough to get that one into the battlefield.

As for an Electro-Magnetic based Laser that would include every laser in existence since all radiation is part of the E-M spectrum from radio-waves to gamma rays varying in frequency and wavelength. If you meant to say the ELECTROLASER then that is a device under development by a number of companies and the military. A laser is used first to ionize a path through the atmospheric and then an electrical discharge is sent down the ionized path. Essentially what happens during a lightning strike. Depending on the electrical discharge the device can stun or kill just like natural lightning. Against vehicles it can overload their electrical systems disabling the vehicle. It has even been proposed that fired from a aircraft flying in a thunderstorm the ionized beam could direct a lightning bolt to precise targets

Honestly, I could imagine somebody out there in some nation's defense department trying to figure out a way to place lasers on land & mobile bases with mirrors placed in space to allow beams to be bounced anywhere on Earth. This would be quite dangerous as it would allow a nation the ability to strike anywhere at the speed of light.

The Germans had an idea of taking a huge mirror which would be assembled in space, and maneuvered with thrusters to focus the sun down on a small spot. Except an idea like this wouldn't depend on the exact position of the sun: While blooming is a problem, they have worked ways around it to varying degrees.

Interestingly, at some point in the past (1970's to 1980's) the USSR had developed some kind of weapon (not sure if it was a laser or betatron) that could effectively use blooming deliberately. The idea is that it would produce a fast expanding explosion in the atmosphere.

And that said: No matter how I die it was murder. I would never purposefully kill myself, and I'm not into auto-erotic asphyxiation.

The German "Sun Gun" was arguably the most ambitious German wunderwaffe of the war. The plan, based on ideas described by physicists decades before, was to launch a massive reflector made of metallic sodium more than 5,000 miles into space and have it focus the sun's energy on a given city in order to set it ablaze.
While certainly devastating in concept there are, even today, massive engineering problems to overcome just getting the object into space and building it. Geosynchronous orbits are only over the equator so the mirror could not hover over London, for example, and would only pass over a city occasionally depending on its orbital path. Then consider the target such a large mirror would make.

The Rheotron invented by Max Steenbeck at Siemens-Schuckert in the 1930s had the ability to accelerate electrons to near light speeds. These high energy electrons could then be directed into various metal targets producing hard X-rays. These devices captured by the Americans in April 1945 were later called Betatrons after Beta particle radiation (electrons)
The German plan was to use this technology to create x-ray beam weapons. Beams of high energy X-rays would be directed against high flying bombers. The X-ray beams would interfere with the aircraft engines ignition forcing the planes drop to lower altitudes where they would be in range of German AA guns. Intense enough beams could even blind, injure, or kill the aircraft crews
However, these "death rays" were never finalized before invading American forces captured the prototypes in April, 1945.

Also recall that British Scientists/Engineers also were at work trying to design a Death Ray. In 1935 the Superintendent of the Radio Research Station, Robert Watson-Watt was assigned to advise the government on the practicality of producing a 'death ray'". Arnold F. Wilkins was assigned the task of calculating how much energy would be required to damage an aircraft, or its crew. Wilkins concluded that the concept was theoretically sound, but that the power requirements were beyond anything that modern technologies could produce. So, on February 4, 1935, the two reported back that there was simply no way for anyone to build a death ray.
HOWEVER, he remembered receiving notices from Post Office engineers that aircraft flying in the vicinity of BBC masts were causing disturbances to radio signals. What engineers referred to as the 'fluttering' effect. Wilkins theorized that it should be possible to develop an aircraft detection system by transmitting and receiving a re-radiated signal back from an incoming plane. In other words Britian would have the ability to detect incoming planes without actually having to visually see them. They called their system RDF or Radio Detection Finding. Americans would later rename it RADAR. Not a Death Ray but the nature of air warfare had changed forever

mikewint said:

The German "Sun Gun" was arguably the most ambitious German wunderwaffe of the war. The plan, based on ideas described by physicists decades before, was to launch a massive reflector made of metallic sodium more than 5,000 miles into space and have it focus the sun's energy on a given city in order to set it ablaze.

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I thought it had thrusters to position it...

While certainly devastating in concept there are, even today, massive engineering problems to overcome just getting the object into space and building it.

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Well yes, and no

1. Hoisting something that large in one fell swoop: Yeah, it would be ridiculously difficult.
2. Launching bits and pieces into space and assembling them while in orbit: Difficult, but do-able.

I'm not a fan of developing such a device: Just to be clear.

Zipper730 said:

Well yes, and no

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I don't believe anyone ever thought of a one piece operation.
This concave mirror, according to the German plans, was going to be 3.5 SQUARE MILES in area (9 sq km). The proposal also called for the mirror to be made of SODIUM metal with a melting point of 208F (97.8C). The sun facing side of the ISS easily reaches 250F (121C) and the dark side -250F (-157C). Think of what such temperatures would do to the sodium metal. In addition consider the expansion and contraction faced by such a large mirror and what it would do to the mirror's shape.
Yes you could easily move the mirror to face in any direction but such motion would face tremendous inertia both in starting and stopping the movement not to mention the stresses and strains placed upon the mirror as you start and stop the motion.
Next we face the focal point of the mirror. The mirror's curvature determines the point of focus. Depending on where on the Earth's surface you want the focal point to hit you would have to be able to adjust the mirror's curvature either nearer or further to reach the target.
Lastly think on how many meteors would strike such a large object. Even grains of sand can do considerable damage when they strike at 25,000 mph or more.
So yea, considerable engineering problems to over come