Just in case you haven’t heard, there’s a conspiracy theory out there which claims that the 2018 Camp Fire in California was deliberately started by a space-based solar power collection system.
For the record, I don’t believe this happened. But if we wanted to do so, could we?
I did a back-of-the-envelope calculation for an ideal blackbody absorber (the target) on a 20C day in quiescent sea-level air. Accounting for convective and radiative losses, and assuming a required ignition temperature of 260C, my estimate is that this could be achieved by hitting it with a radiative flux of 10,000-30,000 watts per square meter. In other words, about 10-30 times normal insolation, delivered continuously for…a while. This figure was a threshold value, so in theory you’d asymptotically approach ignition temperature after a very long time; if you want to speed things up, add more power. If your real target is not an ideal blackbody, you’ll need to compensate for that with…more power. For the sake of discussion, let’s say 50 kw/m^2 is required for a period of 30 seconds.
Does any technology exist to deliver this kind of intensity and tracking stability from orbit? About 20 years ago, we tried the opposite approach - blasting something in orbit using a ground-based laser - and didn’t do so good:
Amid much controversy in October 1997, MIRACL was tested against MSTI-3, a US Air Forcesatellite at the end of its original mission in orbit[5] at a distance of 432 km (268 mi).[6] MIRACL failed during the test and was damaged[7] and the Pentagon claimed mixed results for other portions of the test. A second, lower-powered chemical laser was able to temporarily blind the MSTI-3 sensors during the test.[8]
With a 1-megawatt laser, dispersing the beam over a 4.5x4.5 meter area would give you 50 kw/m^2, which by my math is just enough to start getting interesting. Making this happen from LEO would mean a path length of at least 120 miles, with a lot of atmospheric distortion along the way, and would require a tracking system that can keep targeting the same patch of tinder-dry forest for thirty seconds. If you had a MIRACL-type laser in orbit, could this be achieved?
From what I’ve heard from members of the United States House of Representatives, I believe it depends on the religious affiliation of the space laser in question.
I’m sure nobody here in this thread needs to wonder this, but why would a conspiracy group, well organised enough to put a powerful satellite laser into orbit, need to do that just to start a forest fire, when they could achieve the same result by sending a person with a box of matches, or a drone with fireworks on it? (saving multi-millions of their budget, which they could then spend on mind control or turning the frogs gay)
Because they wanted to sell the movie rights to their entire evil plan. Who would want to make a movie about a guy with a box of matches starting a forest fire?
It’s only feasible if you have a real genius, preferably one who is also very cool, develop your laser. It also helps if you aim the laser at a giant Jiffy Pop.
Using a laser in space to accomplish the same result as a careless smoker is the kind of thing Rube Goldberg would come up with…Waitaminute! Goldberg? It’s all starting to make sense now.
This is GQ. Despite the fact that this originated from a politician, please confine yourself to factual responses related to the scientific aspects of this.
THIS GOES FOR EVERYONE. SO FAR NONE OF THE SUBSEQUENT REMARKS ARE APPROPRIATE FOR GQ. THERE ARE OTHER FORUMS FOR JOKES OR POLITICAL REMARKS ABOUT THIS.
Laser beams begin to cause plasma breakdown in the atmosphere at energy densities of around one megajoule per cubic centimeter. This effect, called “blooming,” causes the laser to defocus and disperse energy into the surrounding air. Blooming can be more severe if there is fog, smoke, dust, rain, snow, smog, or foam in the air.
Techniques that may reduce these effects include:
Spreading the beam across a large, curved mirror that focuses the power on the target, to keep energy density en route too low for blooming to happen. This requires a large, very precise, fragile mirror, mounted somewhat like a searchlight, requiring bulky machinery to slew the mirror to aim the laser.
Using a phased array. For typical laser wavelengths, this method would require billions of micrometer-size antennae. There is currently no known way to implement these, though carbon nanotubes have been proposed. Phased arrays could theoretically also perform phase-conjugate amplification (see below). Phased arrays do not require mirrors or lenses, and can be made flat and thus do not require a turret-like system (as in “spread beam”) to be aimed, though range will suffer if the target is at extreme angles to the surface of the phased array.[72]
Using a phase-conjugate laser system. This method employs a “finder” or “guide” laser illuminating the target. Any mirror-like (“specular”) points on the target reflect light that is sensed by the weapon’s primary amplifier. The weapon then amplifies inverted waves, in a positive feedback loop, destroying the target, with shockwaves as the specular regions evaporate. This avoids blooming because the waves from the target pass through the blooming, and therefore show the most conductive optical path; this automatically corrects for the distortions caused by blooming. Experimental systems using this method usually use special chemicals to form a “phase-conjugate mirror”. In most systems, however, the mirror overheats dramatically at weapon-useful power levels.
Using a very short pulse that finishes before blooming interferes, but this requires a very high power laser to concentrate large amounts of energy in that pulse which doesn’t exist in a weaponized or easily weaponizable form as of January 2020.
Focusing multiple lasers of relatively low power on a single target. This is increasingly bulky as the total power of the system increases.
There’s some almost-relevant stuff here, although their goal is to keep the beam power low enough to avoid forest fires, not high enough to cause forest fires.
All lasers have an intrinsic divergence angle but of course when firing through any medium a certain amount of absorbance will occur, resulting the thermal blooming effects described above, which limits practical power delivery to target regardless of frequency.
One technical issue that has not been addressed is just the power generation and throughput required to achieve necessary power density and sustainment levels to get the target up to an ignition or decomposition temperature. Generating sufficient power requires a rapid exothermal process or the ability to store and then delivery energy quickly with some kind of supercapacitor system. All of this generates waste heat which a compact satellite could not reject efficiently.
For the Strategic Defense Initiative, nuclear pumped X-ray frequency lasers were proposed which was essentially a fission weapon pumping X-ray output into the lasing cavity, which has the obvious downside of detonating ‘radiation enhanced’ weapons in space. An alternative is the free electron laser where relativistic acceleration of electrons produces high frequency synchrotron radiation, but there will still be a large amount of waste heat produced which itself would probably destroy the laser and satellite unless it had a very larger cold temperature reservoir to reject the excess thermal energy. This would obviously limit the utility of such a device.
And this begs the question of why a secret cabal of people would use “***ish Space Lasers” to start fires when ordinary pyrotechnics are perfectly adequate for the purpose, whether lighting a fire in person, delivered remotely by drone, or hijacking the electrical power distribution system and somehow causing an overload. A better conspiracy theory would be a ***ish weather control system that is creating climate change-like effects, which has the advantage that nobody could debunk it because there is no possible way that it could feasibly work. If you’re going to go in on crazy, go all the way in.
LSLGuy, space-based power satellites theoretically deliver power on microwave frequencies with the energy sufficiently dispersed that it won’t cause excess heating, and require kilometers-wide array of receivers. The concept was really ginned up to justify orbital habitats promoted by Gerard K. O’Neill, and really doesn’t make sense in terms of the gains because for the cost you could just make larger ground-based solar arrays to collect the same mount of energy at lower cost, even given the reduction in solar insolence and day-night cycle. Solar power isn’t really adequate to power a high power laser unless you could somehow contrive to store a large amount of energy and then release it in a high power burst.
Solar power isn’t really adequate to power a high power laser unless you could somehow contrive to store a large amount of energy and then release it in a high power burst.
The atmospheric thermal bloom would be noticeable to any defense agency with IR early warning satellites. It wouldn’t look exactly like a launch but it might look like an energetic detonation, so very much in Space Force’s mission remit.
So the conspiracy would have to design a laser weapon capable of as-yet unattained energy density at range and working through its own atmospheric distortion, and also supress the activation and involvement of the National Command Authority, who would rightly become quite excited by what looks somewhat like nuclear airbursts.
I kind of feel like conspiracy theories are less about the conspirators actually believing the theory as it is about using the conspiracy to harness the power of angry gullible morons to achieve some goal.
