Tuesday, October 28, 2008
The Russians have done this experimentally with a satellite named Znamya.
FOR A FEW MINUTES LAST FEBRUARY,(in 1993) THE MOON HAD A RIVAL: A 66-foot-wide mirror of aluminum-coated plastic orbiting 220 miles above Earth. Before sailing over to the planet's sunny side, the mirror reflected a beam of sunlight that swept east from France to Belarus. The Russian scientists and engineers who launched the mirror claimed that the experiment--the first of its kind--was a success. An array of much larger mirrors, they say, could be used as a light source in remote areas like Siberia.
The mirror, called Znamya ("banner"), was just a few thousandths of an inch thick and weighted just over nine pounds. It was carried into space furled inside a drum stowed in a Progress supply vehicle. When the vehicle docked with the Russian space station Mir, cosmonauts from Mir maneuvered the drum into position just inside the docking port of the Progress pulled away from the space station, the mirror unwrapped around a central, spinning axle extending from the drum. Once unfurled, it looked a little like a flat umbrella.
For the six minutes during which ground crews kept it positioned to catch the sun's rays, Znamya shone a two-and-a-half-mile-wide beam of sunlight about as bright as a full moon down to a predawn Europe. The cosmonauts said they could see a faint circle of light racing over Earth's surface at 17,000 miles per hour. Although clouds covered much of Europe that morning, a few ground observers reported seeing a flash of light as the beam swept by.
Their next satellite failed to deploy properly & the programme was halted.
To do this as a permanent development would clearly require that we have a serious permanent presence in space able to deploy these things at a higher altitude & presumably at geosynchronous orbit if it is intended to permanently light one neighbourhood.
A two-and-a-half-mile-wide beam as strong as the full Moon isn't environment changing but for 9 pounds of tinfoil 66 feet wide it is impressive. The potential is obviously there to make some currently undesirable property pretty attractive.
Before somebody gets environmentalist about the global warming effect the cross sectional area of the Earth is 50 million square miles so you would need thousands of much larger mirrors to even increase sunlight across the Earth by 0.1% & if, centuries from now, we did, the same sort of tinfoil could be used for orbital shades. Such shades have also been suggested for solving catastrophic global warming & while that is perfectly possible I would rather get some evidence it actually happening before "solving" it.