Afterword

The idea of using space-based mirrors to modify Earth’s climate goes back to the visionary German-Hungarian thinker Hermann Oberth. In his book The Road to Space Travel (1929), Oberth suggested using huge orbiting mirrors to reflect sunlight to the Earth, to prevent frosts, control winds, and to make the polar regions habitable. In 1966 the U.S. Department of Defense studied the idea for rather different purposes, as a way to light up the Vietnamese jungles at night.

Not surprisingly Oberth’s idea appealed to the Russians, much of whose territory is at high latitudes—and who had a deep and ancient fascination with the sun (chapter 42). They actually tested a space mirror in 1993, when a twenty-meter disk of aluminized plastic was unfolded in Earth orbit. Cosmonauts aboard the Mir space station saw a spot of reflected light pass over the surface of Earth, and observers in Canada and Europe reportedly saw a flash of light as the beam passed over them.

Meanwhile in the 1970s the German-born American space engineer Krafft Ehricke made an intensive study of the uses of what he called “space light technology” (see Acta Astronautica 6, page 1515, 1979). In the context of mitigating global warming, the idea of using space mirrors to deflect light from an overheating Earth was revived by American energy analysts as recently as 2002 (see Science 298, page 981).

But much more ambitious uses of space light technology have been explored. Space light is by far the most abundant energy flow in the solar system—and it is free, for whatever purpose we choose. We could stave off the next Ice Age, we could shield Venus to make it habitable, we could warm up Mars—and for how to sail on space light, see “The Wind from the Sun” (available in Clarke’s collected stories, Gollancz, 2000).