The NASA Pathfinder

The NASA Pathfinder is a solar powered aircraft. It is one of the first unmanned aircrafts, and is made to perform atmospheric research. It was developed by the ERAST program in the early 1980's, but has been modified to what is now known as the NASA Pathfinder Plus.

 Pics cr: NASA

For more info:
http://en.wikipedia.org/wiki/NASA_Pathfinder

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-034-DFRC.html#.U2b3e_ldV1Y