The Japanese Institute of Space Astronautical Science has tested a ‘ reflective polyimide resin only 0.0075 millimetres thick’ in space, deploying two sails at an altitude of 150 kilometers (93 miles) and 170 kilometers (106 miles). This article in New Scientist provides the details, noting that this is the first time a solar sail has ever been deployed in space (I assume they mean the first ‘free-flying’ solar sail, since Russia’s Znamya space mirror tested deployment technologies on February 4, 1993). The Planetary Society’s Cosmos 1 sail would have been the first space-based deployment of a free-flying sail, but the sail was destroyed in 2001 along with its booster rocket. The second test for Cosmos 1 may occur as early as this year. Deployment of thin films in space is dicey stuff, as a later Znamya experiment made all too clear in February of 1999. Attempting to spin the sail, engineers controlling the Progress supply ship to which it was attached accidentally extended an antenna, against which the foil became immediately entangled. Both Znamya and the Progress spacecraft were destroyed in Earth’s atmosphere the next day.