Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror

Slashdot videos: Now with more Slashdot!

  • View

  • Discuss

  • Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

×

Comment: Not that simple (Score 1) 228

by fyngyrz (#49201149) Attached to: Laser Takes Out Truck Engine From a Mile Away

You are making a LOT of assumptions. All of these matter: Ability of the mirror to dissipate energy prior to ablation or meaningful distortion. Collimation of the beam. Reflectivity of the mirror at the laser frequency. Ability of the laser to stay on target, and for how long. Distance from the laser. Atmospheric clarity and particulate density. Atmospheric turbulence. Disruption from atmospheric heating.

It's just not as simple as you paint it.

Comment: Re:how much it took (Score 1) 228

by fyngyrz (#49201115) Attached to: Laser Takes Out Truck Engine From a Mile Away

CIWS targeting is, as the acronym hints, "close in." You should think of the distance between the shooter (of anything) and the target as a lever. A tiny pivot at one end of the lever (the weapon's aim) translates to a "much" larger motion at the end of the lever (the point of impact.) Tolerances that will work at 100 yards aren't anywhere near close enough to work at many miles, or hundreds of miles in the case of missiles not aimed particularly at you (so you can be sure they will get close enough to hit.)

Comment: Suitable defensive grid? (Score 1) 228

by fyngyrz (#49201075) Attached to: Laser Takes Out Truck Engine From a Mile Away

There are other issues. That truck was relatively close, between 1 and 2 miles ("more than a mile away"). To hit an ICBM at apogee, even it it goes right over you, you are going to have to spend a lot of energy on atmospheric heating, and you'll lose even more to atmospheric distortion. We're talking 300 to 700 times the distance, depending on exactly what "more than a mile away" actually means. But it is certain that 30 kw at the source will not equate to 30 kw at the target at those distances. So now the problem becomes more than "hit the target", it is also "stay on target for X time", and that assumes that enough energy can be delivered to overcome the missile skin's ability to dissipate it. Because if you can't do all those things, you can't hurt the missile.

Also, the odds of it going right over you kind of suck.

Comment: Re: how much it took (Score 2) 228

by fyngyrz (#49201029) Attached to: Laser Takes Out Truck Engine From a Mile Away

I"m pretty sure a regular mirror would not be employed.

But here's some hand-wavy math.

If a mirror reflects 99% of the light that hits it at the laser frequency (remember, there's only one frequency to be covered), and the light that hits it can heat proportional to 30 kw (however one figures that), then the mirror is absorbing a 300 watt equivalent and reflecting the rest unless the reflective surface fails.

If the reflective surface is highly heat conductive and the beam isn't all that tightly collimated, likely it won't flinch at all. Like any impact, the effect is all about how much energy you can shoehorn into the smallest possible area. If the beam is ~1/3 of an inch on target, then given 99% reflectivity, it's effectively 1 kw / square inch. If the beam is 1/30th of a square inch on target, it's 30 kw/square inch absorption after reflection. So it makes quite a difference. I think.

Anyone who works with lasers and mirrors, feel free to step in and correct or expand.

Comment: ...with remaining eye (Score 1) 228

by fyngyrz (#49200937) Attached to: Laser Takes Out Truck Engine From a Mile Away

1) is if the laser is in visible light or not. If you can't see the red dot source a mile off, you can't evade it.

Pretty sure if you "see the red dot a mile off", the location where your eye was is just the steaming, goo-surrounded beginning of a well-cauterized hole that completely transits your head. Assuming tight collimation. With a broader 30 kw beam, your head would explode (steam pressure), and with a really broad beam, you'd turn into a human crisp before you had time to think "Hey! Las..."

Comment: Re: Many are leaving ham radio too (Score 1) 135

You have the Part 15 and ISM services for that. You really can buy a microwave link that's metropolitan-distance and legal to use.

We lost much of our 440 capability to PAVE PAWS in California. Remember, Amateur Radio is not the primary service on many bands. The military is on 440.

Comment: Re:Many are leaving ham radio too (Score 1) 135

If you want that nearly infinite microwave spectrum, you have the Part 15 and ISM services. Absolutely nothing is stopping you. Power is not the issue with those frequencies, it's line of sight and Fresnel zones.

No, I absolutely do not have to prefix my words with anything. You do that by posting as an anonymous coward. I use my real name to indicate that I stand behind my words.

Comment: Re:LOL! (Score 1) 97

by creimer (#49198319) Attached to: Anthem Blocking Federal Auditor From Doing Vulnerability Scans

But there's no way I'd let them in my doors either.

Pray that you never get a federal job. OPM conducted my background investigation for a security clearance. My two-hour routine interview turned into a four-hour nitpicking interview. Being single and staying in the same studio apartment for nearly ten years was considered odd. Working a weekday job and a weekend job for a year, and having multiple overlapping contract jobs for several years, was odder. Not being able to remember every detail of every job I had to take since the Great Recession was oddest. When asked if you're going to commit terrorist acts against the U.S.A., always tell the truth.

+ - OCO2's 1st map of CO2 output->

Submitted by WindBourne
WindBourne (631190) writes "

This past summer, NASA launched its first satellite devoted to measuring atmospheric carbon dioxide, a heat-trapping gas that is driving global warming.

.... scientists with the space agency unveiled the first carbon maps obtained by the spacecraft, named the Orbiting Carbon Observatory-2, or OCO-2.

This map is little bit more than a month's worth of data.
Note that the large CO2 emissions in the southern hemisphere is due to Ag with a temporary burns, while the emissions in the north are basically at its lowest points. Also note the CO2 to the east of China over the Pacific."

Link to Original Source

Science is to computer science as hydrodynamics is to plumbing.

Working...