In the 1984 update to his epochal 1962 book, Profiles of the Future, Arthur C. Clarke had a chapter titled "Cosmic Engineering", with a couple of paragraphs in which he explored the idea of orbiting mirrors (they're on page 232-233 of my battered paperback, if you have the same edition):

The idea of ‘orbiting mirrors’ was suggested by Hermann Oberth as long ago as 1925. He pointed out that reflectors miles wide could be made from very small amounts of material such as films of metallic sodium. (Today, aluminized Mylar would be a good candidate.) Something like this might even have happened back in the 1960s. There was a time when the Pentagon seriously considered abolishing night in Vietnam. Only a few Saturn Vs, it was calculated, would be necessary to do the job…

(Elipses for dramatic effect in original.) Beyond providing illumination a war zone, there are other obvious benefits to erecting an orbiting mirror, Clarke wrote:

More constructively, orbiting mirrors might greatly increase agricultural yields (24-hour-day crop growing), alleviate climatic extremes by pumping heat into cold areas, perhaps even direct movement of rain clouds and establish a form of weather control. These would be great benefits; but as usual, there would be a price to pay.

Imagine the combined howls of the anti-war and then-nascent environmental left if there actually was a giant mirror orbited over Vietnam, and the hue and cry of the latter group still to come, if and when an orbiting mirror is ever deployed purely for agricultural or climatic purposes.

But the Associated Press is cheerfully reporting on a negative image version of an orbiting mirror, as it explores combating some of the more apocalyptic envirodoom scenarios--or with a name the "Solar Umbrella", maybe it's more akin to a plot dreamed up by Batman's arch-villain, The Penguin:

For far-out concepts, it's hard to beat Roger Angel's.

Last fall, the University of Arizona astronomer proposed what he called a "sun shade." It would be a cloud of small Frisbee-like spaceships that go between Earth and the sun and act as an umbrella, reducing heat from the sun.

"It really is just like turning down the knob by 2 percent of what's coming from the sun," he said.

The science for the ships, the rocketry to launch them, and the materials to make the shade are all doable, Angel said.

These nearly flat discs would each weigh less than an ounce and measure about a yard wide with three tab-like "ears" that are controllers sticking out just a few inches.

About 800,000 of these would be stacked into each rocket launch. It would take 16 trillion of them — that's a million million — so there would be 20 million launches of rockets. All told, Angel figures 20 million tons of material to make the discs that together form the solar umbrella.

And then there's the cost: at least $4 trillion over 30 years, probably more.

"I compare it with sending men to Mars.I think they're both projects on the same scale," Angel said. "Given the danger to Earth, I think this project might warrant some fraction of the consideration of sending people to Mars."

Close the global umbrellas--prevent global darkening!

(Via Newsbusters.)