Sail Technology

Space exploration is limited to the technology we can use. Few years ago NASA proposed a project The Terrestrial Planet Finder. The TPF was a collection of satellite telescopes 'linked' together, it would increase the apparent aperture size to improve the resolution of what we can observe. However, this project's budget was through the roof because of how heavy the launch will be. Over in Europe the European Space Agency has researched a way to remove old satellites that finished their missions already. The traditional method of retrieving satellites is to have sufficient fuel to fly it back, this method would increase the weight of the satellite. With the new sail technology, it lowers the cost and mass needed to return satellites. By opening the Deorbit Sail the drag will pull the spacecraft out of orbit and back to earth. This makes it possible to upgrade and reuse old satellites. This kind of research are small steps to sending bigger satellites and systems of satellites that will maximize resolution. 

http://www.esa.int/Our_Activities/Space_Engineering/Clean_Space/Tacking_sails_to_a_satellite