FCC approves giant mirror satellite designed to beam sunlight to Earth after dark

[PurpaFur]

Now we're talking! Far more useful to shade areas than to light them. I miles big shadow across most areas would significantly drop the temperature saving energy and people.

Seems to me, that someone had proposed just the opposite a few years ago. Believing the Earth was too hot; so throw some shade on certain areas.

The notion that shade can be cast from orbit is ridiculous. At 400 km altitude, an opaque disk would have to be about 3.7 km wide merely for its full shadow (umbra) to reach a point on Earth. Look up Umbra/Penumbra. Not to mention that a shade in LEO would not be able to direct its shadow like a reflector could direct light, so the shadow would rapidly move across the earth's surface, too fast to be useful at any one given location.

The alternative is to place such a shade at the Sun-Earth L1 point, but at that distance the shade would need to be roughly 14,000km wide just to fully cover the sun at any one point on earth. 27,000km wide would be needed to place the entire earth inside the shadow.

 

[Endymio]

The alternative is to place such a shade at the Sun-Earth L1 point, but at that distance the shade would need to be roughly 14,000km wide just to fully cover the sun at any one point on earth. 27,000km wide would be needed to place the entire earth inside the shadow.

Physicist Greg Benford actually proposed this some 20 years ago: a gigantic spinning fresnel lens at L1. It would only need to be the size you calculate if you wished to block sunlight entirely -- for cooling, he suggested a disk 1000 km across (but only a few millimeters thick), which would reduce solar insolation by a couple of percent, for an estimated cost of around $10B ... far less than the trillions being spent on 'green energy' projects globally.

Of course, such cooling is necessary only if warming gets out of hand. Since the first IPCC report, the estimates of maximum warming have been repeatedly reduced, and the mild amount of warming we're likely to experience over the next 50 years will be far more positive than negative.