2 a handheld collapsible source of shade [syn: parasol]
something to keep the sun off
A space sunshade can be described as an umbrella that diverts some of the suns rays, stopping them from hitting the earth and heating the planet, thus preventing global warming.
It would be composed of 16 trillion small glass disks at an altitude of 1.5 million kilometers, otherwise known as the L1 Orbit. A sunshade that blocks 2% of the sunlight, reflecting it off into space, would be enough to halt global warming, giving us ample time to cut our emissions back on earth. The catch is that such a sunshade would have a diameter of 1800 km: it would cost tens of trillions of dollars to get the disks into space. It has been proposed that this would be accomplished most easily with a large railgun or coilgun which fires a capsule containing a million 1-gram shades into space.
Even so, it would still take years to launch enough of the disks into orbit before they have any effect. Thus, if using this technology should become essential, enough time would be needed to implement it.
Roger Angel presented the idea for the Sunshade at the National Academy of Sciences in April, 2006 and won a NASA Institute for Advanced Concepts grant for further research in July, 2006. His team members working on the grant are David Miller of the Massachusetts Institute of Technology, Nick Woolf of UA's Steward Observatory, and NASA Ames Research Center Director S. Pete Worden.
Creating a sunshade in space is so expensive that even its developer has stated: "The sunshade is no substitute for developing renewable energy, the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that. But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out."