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Comment: Re:Fizz (Score 1) 116

by weilawei (#49741343) Attached to: Hydrogen-Powered Drone Can Fly For 4 Hours at a Time

Make a hollow propeller mounted on a pen tube, with a hole at each end of the prop (facing opposite directions, to drive the prop). Push pen tube through 2 liter bottle cap (loosely fitting in the hole), cut tube short, flare end to retain. Fill bottle with mentos and coke as usual and cap.

Might work, might not. Haven't tried it, but you could work out the bugs (bubbles?) pretty cheap.

Comment: Re:Is that even correct ? (Score 2) 185

by weilawei (#49719635) Attached to: Navy's New Laser Weapon: Hype Or Reality?

From your link:

Saturation attacks. Since a laser can attack only one target at a time, requires several seconds to disable it, and several more seconds to be redirected to the next target, a laser can disable only so many targets within a given period of time. This places an upper limit on the ability of an individual laser to deal with saturation attacks—attacks by multiple weapons that approach the ship simultaneously or within a few seconds of one another. This limitation can be mitigated by installing more than one laser on the ship, similar to how the Navy installs multiple CIWS systems on certain ships.

Hardened targets and countermeasures. Less-powerful lasers—that is, lasers with beam powers measured in kilowatts (kW) rather than megawatts (MW) 10 — can have less effectiveness against targets that incorporate shielding, ablative material, or highly reflective surfaces, or that rotate rapidly (so that the laser spot does not remain continuously on a single location on the target’s surface) or tumble.

Now, another reference:

In order to facilitate comparison with the findings of other authors we chose to express the threshold fluence in units of pulse energy per unit area . The multipulse damage threshold for molybdenum at 1064 nm reported by Zhou [29] of 1 J/cm^2 for 10 ns pulses is rather higher than the value of the order of 0.3 J/cm^2 we find. Similarly, we find that stainless steel gets damaged at about 0.2 J/cm^2, whereas the value of 2.3 J/cm^2 for 120 ns pulses at 1064 nm found by Leontyev [30] would lead us to expect a threshold of around 0.4 J/cm^2 for 5 ns pulses.

Also, you're severely overestimating the reflectivity of materials likely to be exposed to the atmosphere, especially in battle conditions. 70% would be nice. They also discuss that, as well as how much short pulses at short wavelengths reduce the reflectivity (up to around ~25% in nitrogen, which air is largely composed of).

Comment: Re: Responsibility lies with the Taxpayers (Score 1) 201

by weilawei (#49715525) Attached to: Baton Bob Receives $20,000 Settlement For Coerced Facebook Post

Shifting the burden onto the taxpayers only pushes the majority of them further into the hole as the potholes continue to go unfixed and their beater car gets the shit beat out of it. After all, there's not much budget left for the massive amount of roadwork...

You're welcome for the car.

Comment: Re: Hmm (Score 1) 149

You grossly misunderstand. You wouldn't surround it with something, but stick a rocket on it (possibly two, like a spinning wheel firework) and accelerate it in the direction it's already spinning. No washing machine required, and the technology is almost simple as possible: anchor + rocket.

As for iron, you'd need to exceed the tensile strength+gravity of the material to begin with, which is already going to require an object spinning enormously fast. I DID say it was probably not feasible. It was just an amusing thought. Perhaps you should learn to read and separate serious suggestions from facetious ones.

Also, a nuke is highly unlikely to simply "evaporate" a large body. You might succeed in creating a cloud of large debris though, as plenty of objects are loosely held together to begin with.

Comment: Re:Why not a type of Bola? (Score 1) 149

by weilawei (#49708943) Attached to: Ask Slashdot: Best Payloads For Asteroid Diverter/Killer Mission?

The object is likely spinning. I'd want to eliminate the tether, which is huge point of failure. While static loading isn't as big an issue, shock loading IS a big problem, and it's unlikely we'll be able to entirely prevent it, or it will be prohibitively expensive in terms of mass (fuel for burns to slowly load the tether). Either way, you'll need to match the spin (i.e., orbit around) the object in order to eliminate the relative motion.

Also, I have no idea how much force you would need to perturb the orbit sufficiently. If you were still spinning, you would only be able to fire the engines for a portion of your orbit. You might actually use that to stop the spin, and then drag it higher/lower in its orbit. In any event, you would need the required force to be less than the maximum static load on your tether multiplied by the fraction of the time you can actually burn the engines.

IANAAE (I am not an aerospace engineer). You probably shouldn't actually try anything I suggest.

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