YouTube user ‘damewse’ knows that NASA is “the most fascinating, adventurous, epic institution ever devised by human beings” and he also knows their media ‘sucks’. So he made some unofficial commercials for them. Well done, sir. The voice is none other than Carl Sagan.
The original clip (but without the footage added in by damewse) is by Michael Marantz and can be found here (Narrative taken from Sagan’s “Pale Blue Dot”): Earth: The Pale Blue Dot.