ISTR reading some years ago about the Russian space agency’s plan to put a giant mirror into geosynchronous orbit. The mirror could reflect the rays of the sun onto northern Russian cities during the winter, thus providing extra daylight during the otehrwise short winter days.
Since I haven’t heard any more about it, I’m assuming the project was scrapped.
However, I’d like the City of Springfield to give it a try, as I’m rather sick of getting off work at 5:00 and it’s already dark. The Springfield metro area could use a little extra sunlight during the winter months. Putting aside the political implications (namely, giving 140,000 some-odd people extra daylight whether they want it or not) and the cost (billions), I’m curious as to whether or not this would work, and what (if any) harm it would do.
First, how big would this mirror have to be? The Springfield metro area is roughly 15 miles in diameter. I’m assuming a concave mirror would work better than a flat one.
Secondly, what harm would it do to the native flora and fauna? Would the local wildlife just be confused and thus have their mating cycles thrown off? Would the trees not shed their leaves properly? Finally, would all that reflected light appreciably warm up the area in question? Not that I’d mind-- average winter temperature in Springfield: pretty damn cold. If it did heat up the area, even a degree or two, would that mess up the ecosystem?
My guess is that a feasible space-mirror could, at most, give as much light as a quarter-moon, and probably not even that. The albedo of the full moon is, say, 12%, and assuming your mirror was nearly 100% efficient, and in geosynchronous orbit over Springfield (i.e. about nine-tenths closer than the moon) then… well, I dunno, but it would be pretty expensive.
The energy saved would never be enough to pay for the mirror itself and if you want more light at lower cost, you’re better off replacing all incandescent street lights with LEDs.
As for the environmental effects, artificial light has already screwed up the widdle birdies and whatnot so adding the equivalent of safety flare wouldn’t exactly destroy life as we know it.
Just WAGing, but… IF such a mirror is put in use: the city get´s more sun radiation, temperature in the local area rises, air heats and a local area low pressure system forms, thus “sucking” cold air from the surrondings, creating weather instability such as storms. You want to trade more daylight for miserable weather?
Well, one of the things the Russians thought that they’d be able to use it for was thawing out Siberia. Considering how bad Siberia’s weather is supposed to be, I don’t think a few extra storms would be noticed.
How big would that mirror be? If my math is right a mirror one kilometer in diameter would have a viewing angle of about 0.001 degrees. By comparison, the Moon has a viewing angle around 0.5 degrees.
If you want the reflection to be as bright as the full sun, then the apparent size of the mirror must be the same as the full sun, i.e 0.5 degrees. At geosynchronous orbit, that means approximately 230 mile in diameter. A network of smaller mirrors in lower orbit would be more practical.
If you just wanted to light up a city, really bright streetlamps would probably be even mora practical.
Hang on just a moment. I’m not a weatherman, but I seem to recall that when you heat a gas, the pressure tends to rise. Whether or not this is correct, this reflector is a hideously bad idea. We’ve already got a giant reflector up there, and it’s called the moon.
The apparent angular size of the sun is .009 radians according to this site. If the Russians want to put this in a high geosynchronous orbit, it would need to be at an orbital altitude of 35,790 km (according to this article on geosynch. orbits at wikipedia). That means that to appear to be the same size as the sun, it would need to be 322.11 kilometers in diameter. That means it would have an area of 81,489 square kilometers, or just under the area of Lake Superior.
Given current launch costs (I can’t get any reliable cites, but everyone agrees that it’s more than $5/gram) it seems like it would be prohibitively expensive even to put some imaginary, gossamer, perfectly reflective substance that weighs less than gold foil up there.
With such a huge & necessarily thin object up there, it would also be that much harder to keep it focused, especially with the solar wind pushing it different directions all day.
I think aluminized mylar can get above 80% easily, and be durable enough to last many years. OK so that’s less than 100%, but 0.8 solar should be bright enough for all intents and purposes.
By the way, since the mirror is so large and far away, the spot of light on the earth’s surface will be very fuzzy. The edge of the penumbra (so to speak) will be twice the size of the mirror. Only at the center do you get the full 0.8-solar brightness.
Using space mirrors is something that might happen frequently in the colonisation of inhospitable planets, should it ever be desirable to attempt such a thing;
You could have a swarm of them, lighting the planet from behind; this might be desirable if the whole planet is too cold, or perhaps if the planet rotates too slowly the mirrors could provide light with an earthlike diurnal rythym, while direct sunlight is blocked by a mirror.
As far as getting the material in orbit- the best way would be to grab a small carbonaceous asteroid, aand make it in space; there is also aluminium on the Moon, if you prefer home grown material.
Having said that, the Russian plan was hopelessly ambitious; you would be lucky to see any conceivable balloon that could be put in geostationary orbit by present day technology as anything more than a bright dot.
(Sometimes the solar panels of geostationary satellites flare to about magnetude +2, apparently; not as bright as an iridium flare, but visible)
[raises hand]
Even though I figured HeyHomie was referring to Springfield, IL, I still immediately thought of the Simpsons. “Mr. Burns isn’t going to stand for this…”
What were you planning to do with the mirror come good-old summertime? 'Cause, it seems to me that if it made things comfortable in the winter you gonna have one fine toasty Fourth of July.
You´re partially right, if you heat a closed bottle filled with air, the pressure inside will rise, because the air explands; but in an open environment as the athmosphere the air will simply expand and rise, lowering the local area pressure.