Excellent question, the article called it a solar sail but only mentioned its drag properties. I kept wondering why you would need a solar sail to keep something in orbit...?
"NanoSail-D will remain closer to home. "Our mission is to circle Earth and investigate the possibility of using solar sails as a tool to de-orbit old satellites and space junk," explains Alhorn. "As the sail orbits our planet, it skims the top of our atmosphere and experiences aerodynamic drag. Eventually, this brings it down.""
It is a lightweight, inexpensive, spaceship-deployable sheet. Currently it is being used as a drag parachute, but it could just as easily be used as a sail.
