Buck Rogers: Have we met before?
Brigadier Gordon: I don't think so captain, we're from different times.
When Brigadier Gordon saves Buck and introduces himself, Buck asks if they have met. Gordon tells him that they are from different times.
This is a reference to the fact that before playing Brigadier Gordon here, he (action star Larry "Buster" Crabbe) played Buck Rogers in both the classic black-and-white 1939 and more recent 1977 movies, both entitled Buck Rogers.
Crabbe also played related comic strip space hero Flash Gordon in 1936's Flash Gordon, 1938's Flash Gordon's Trip to Mars, and 1940's Flash Gordon Conquers the Universe.
It is a popular practice to bring the original actor of a character back to play another (usually older) character in a remake as an inside joke.