The into says it all.

    The year was 1987 as NASA launched the last of America's deep space probes. In a freak mishap that freezes his life-support systems, Captain William "Buck" Rogers was thrown into an orbit which returned Buck Rogers to Earth... 500 years later.

    He is susequently revived in the year 2491 by the malevolent forces of the Draconian (interstellar) Empire. He discovers that the Empire has plans to conquer Earth and escapes. When he is close to Earth he encounters the Earth Defense Force and is taken into custody.

    Soon after, it is revealed to him that he is 500 years in the future. The world he lived in was devastated relatively soon after he left in a nuclear holocaust. (I guess that that's why the intro says 'the last of America's deep space probes').

    Buck is shocked by this turn of events, but slowly builds a life working with the Earth Defense Directorate, who have the technology to explore the universe as well as defend Earth.