I am asking this question on behalf of my friend, with whom I frequently have intellectual (in her case) and pseudo-intellectual (in my case) email correspondence. She has posed the following question:
Assuming that the laser weapons in question emit light within the visible spectrum, and that the white coating would reflect all frequencies equally (not just in the ratios necessary for the human eye to perceive it as white), is this theoretically a viable defense?
Or in the case of the Misty spy satellite, using a cone-shaped balloon apparently works. You can read the patent details here.
I am not a physicist, but I should think that if it were white enough that would probably work. However, I am sure that in real life white things do not reflect all the light energy that impinges on them (they are all really a little bit greyish, I guess), so a sufficiently high energy laser would soon create enough heat to burn through the white coating.
Why settle for a white coating? A mirrored finish would do a much better job at reflecting light.
Theoretically, she’s correct.
Practically, it’s impossible to make a surface perfect enough. Any imperfections, down to the microscopic level, would be magnified by proportion to the amount of energy their being exposed to by the laser.
Say, theoretically, the spaceship only has 10m x 10m surface facing you, a very small surface area for a battleship. If there was only 1 sand-sized particle of imperfection in it, of not-perfect reflection, the entire armor would be rendered useless. Further, this problem is exacerbated by the fact that space isn’t actually empty. If any particles happened to be sitting on the armor, they’d absorb the heat from the laser, and likely melt into into the reflective shield causing an imperfection.
Yes, I’m nerdy. Yes, I’ve thought of this in the past. Yes, I’m damn proud of it.
ETA: So, that is to say, unless you’re assuming a perfect society which can build anything it can design, even in theory, and a society which has perfect deflection shields, then it’s practically impossible, although theoretically possible.
A white coating would scatter lasers. White is a product of scattering produced by multiple boundaries between particles and domains. If you take a white compound and make it into a single crystal, it will be transparent.
In terms of high energy laser weapons though, I suspect it is much more than an optics problem. Even an extremely good reflector will absorb some heat. That heat will change the coating, making it less reflecting. I don’t know what the reality of high energy laser weapons is though. Frankly, I think if you can get close enough to hit something effectively with a laser, your better off firing a bullet.
Lasers travel at the speed of light, you can hit something an indefinite distance away. If you had a hypothetical optic system, you could easily hit something on the moon from the surface of the Earth, with no regards to gravity whatsoever (we’ll ignore atmosphere, for the moment).
The possibilities are endless.
In reality, lasers aren’t perfectly collimated. The energy disperses.
But in a reality where a perfectly white ship can me made to scatter a laserbeam with no damage to the ship the technology should exist to make a laser perfectly collimated
I thought we were trying to talk about reality. White won’t be a perfect reflector. By it’s very nature, a white surface is flawed. That is what causes the scatter.
Even if you produce some magical perfectly reflecting surface you still have the issue of any atmosphere gases being heated by the laser so the surface gets burnt by heat before the laser hits and bounces. Heck, even the act of bouncing would cause heat all around. Perhaps enough to damage the surface enough for a second shot to penetrate.
Even if they are perfectly collimated to begin with, a laser has an inherent divergence angle that is a product of the frequency.
This often comes up with regard to the use of directed energy systems with anti-ballistic missiles; some proposals to protect missiles involve polishing the body, painting it with reflective paint, or spinning the missile. This misses the point in that the purpose of the laser isn’t to literally burn a hole through the skin of the missile but rather to deliver sufficient energy to heat the missile body causing the material to weaken and allow aerodynamic forces to exceed structural margins. With a powerful enough laser, any imperfection or slight absorption will invalidate any effort to protect the missile in this regard. Unfortunately for ABM advocates, however, it is basically impossible to deliver this amount of energy through the atmosphere for more than a few dozen miles owing to thermal blooming effects (energy is absorbed by the atmosphere, resulting in turbulence that causes optical distortion). This also only really works on uninsulated metallic thin-skinned liquid rockets; heavier solid rocket motors with metallic or composite bodies have a lot of thermal mass to absorb the incoming energy and (because they are generally launched from a silo) have a protective layer of cork or carbon-impregnated elastomer that will char and protect the underlying substrate, and so unless you managed to hit some unprotected vulnerability it won’t do much of anything for any reasonable action time of a laser.
You also need to consider that the most energetic lasers are going to be ultraviolet up to x-ray. Unless your paint is reflective to these wavelengths, it won’t help you to paint it white.
Stranger
Most weaponized lasers emit invisible infrared energy, such as the Navy’s MIRACL project, which used a deuterium fluoride chemical laser to produce a one megawatt infrared beam.
Even if you could make the body of the missile reflect enough of the energy to stay intact, what are the changes that your coating will survive the launch and subsequent reentry?
The thermal launch environment isn’t typically that aggressive; either (in the case of a solid motor) it lifts off and away from the pad or silo pretty quickly, or a ducting or flame diverter system is used to direct the plume away from the vehicle. The acoustic conditions (reflected shockwaves) and launch transients are usually more problematic, although obviously any impingement of the plume will deposit some residue that will stick to the surface and later absorb heat from a directed energy weapon. Silo-launched boosters typically have a thin layer of TPS to prevent any damage, and as discussed above, this would largely mitigate any reasonable directed energy weapon.
Modern ballistic missile systems don’t have the boost vehicle (BV) re-enter with the payload; instead, they separate stages as they burn out and then somewhere near apogee they deploy one or more re-entry vehicles (RV) that are typically concealed beneath a shroud prior to deployment. This helps to keep the RV more difficult to pin-point, and also allows for deployment of decoy RVs with the same mass and dynamics but no payload.
Stranger
White cars get pulled by laser radar (lydar) guns all the time.
That is, assuming you could predict your target’s movements for eight minutes with perfect or near-perfect accuracy. Good luck with that.
Lets assume a REALLY powerful laser.
Lets assume a highly reflective target.
Assume a small imperfection in on the target, like a small scratch or piece of dust.
If the laser is powerful enough for that to be a a problem for the target you have another possible problem.
If that same super powerful laser beam intercepts a piece of dust along its way to the target in the atmosphere, when it hits that piece of dust, the resulting explosion/thermal bloom is going to royally screw up the laser beam/path fairly quickly.
Chrome?
If the moon was as far away as the sun, maybe. Luckily, it’s not.
Lasers would also be better suited to attack vacuum enclosures on a planet surface at those distances, or even far greater ones (say, from the Earth to Io or Europa).