Misty. That's the codename for one of the most advanced spy satellites up there. Launched in a 1990 military mission of space shuttle Atlantis, Misty is hidden by something really weird: A balloon.
As you can see in the image, Misty uses a conical reflective balloon. Little is known about how it works but in theory this design—which is patented by Teledyne Industries, who did the design for the US government—can both deflect ground lasers, radar waves, and hide it from the plain eye. [GWU via This Is Rocket Science]