§ 3.4.2 Interorbital Lightsails
Like wind, sunlight exerts pressure. This pressure is so "light", or gentle, that humans don't feel it. However, in orbital space, if you make a large sail out of thin aluminum reflective material, you can go places without any propellant, merely using the pressure of the sun. However, you need to control your sails so that you go where you want to go.
Going away from the Sun, you tilt the sail at an angle of approximately 35 degrees, since achieving a higher orbit is a combination of being pushed away from the sun and picking up angular momentum (orbital speed at the moment). You can go in towards the sun, too, by pointing your sails at an angle so that you slow down your orbital speed in order for the sun's (or Earth's) gravity to pull you inward. Thus, you have flexibility in maneuvering, assuming you have well designed sails.
Notably, going straight out from the Sun is not useful for achieving into a higher orbit, and just makes your orbit more elliptical, passing back through the point where it was when the sail was deployed. The component of force which increases angular momentum is what produces useful changes to orbital parameters.
Light sails are perhaps better known as "solar sails". However, the phrase "solar sails" is often confused with "solar cells", two very different technologies. This is compounded by different international accents. Indeed, within the USA, my southern accent confuses people in the northeast US on this phrase. Both phrases are used in the literature, and I use the minority phrase "light sail".
The following links give information on Light Sails:
U3P has a nice layman's explanation of the concept of solar sailing as well as its scientific history, on their beautiful Solar Sails website, which also includes animations, images, specific papers and more web links. Also covers Znamya, the Russian in-space solar sail experiments. Multiple language translations. (U3P means Union for the Promotion of Photonic Propulsion.)
Benjamin Diedrich's Solar Sails page, which includes a great list of web links, books, articles & reports, and people, as well as explanations of the concepts (though not most basic).
In addition to the Russian Znamya effort, commercial lightsails could come sooner than expected if the InterWorld Transport's Commercial Solar Sailing R&D Project is commercially successful. This is a serious hardware project.
Manfred Leipold has a Solar Sail page at the German Aerospace Center (DLR) The DLR has investigated the feasibility of solar sail technology and assessed several deep-space mission scenarios utilizing solar sail propulsion over the last 5 years. Recently, a feasibility study on a low-cost solar sail technology demonstration mission in Earth orbit was conducted cooperatively by DLR and NASA/JPL (Jet Propulsion Laboratory). Currently, a breadboard model of a fully deployable sail structure is being developed for ground demonstration purposes and testing on a co-funding basis between DLR and ESA.
A UKSEDS (U.K. Students for the Exploration and Development of Space) page entitled The Microlight Solar Sail talks of past and potential student projects. (SEDS is Students for Exploration and Development of Space.)
The physics of solar sailing is also discussed in a page by Christopher Neufeld (Canada).