thebeave
Contributor
".
Does that bit of kookiness in her FB post defy the laws of science as we know them? Could a spacecraft in orbit around earth concentrate solar energy and beam it back to earth and start a wildfire? AFAIK, we do not have a spacecraft that could do that now, but it seems plausible that such a thing is within the law of physics, is it not? I used to be able to start a fire in my backyard with a $5 magnifying glass as a kid (not to mention cooking a few ants ). Unless someone can prove otherwise, it seems doable by a spacecraft IMHO. Do I think such spacecraft started the CA wildfires? 100% NO FUCKING WAY.
My quick thoughts on this question:
You could start a fire with your magnifying glass because you could concentrate the sunlight. This depends on the f-number of the lens; that is, the ratio of the focal length to the collecting area. The smaller the number the more concentration. Your magnifying glass was probably in the area of F/3 or lower — just a guess. To achieve a similar concentration from a few hundred miles up the collecting area would have to be at least dozens of miles in diameter.
I don’t know the cutoff f-number that can start a fire but I think we would notice a satellite that was many miles large in orbit around the Earth.
I used the magnifying glass story as just an example of one way solar energy can start a fire. I'm not necessarily suggesting that a giant glass lens is the only way to send a fire-starting energy beam down to earth. You could conceivably make a focused energy beam via other technologies.