Every schoolfilly has heard of the Federation - the tall, mysterious, magicless beings from another world, who visit only rarely and briefly; waiting, they say, for 'stable planetary political unity'.
This is the story of when they first visited Equestria; of early contact between the Princesses and the Federation. It is also the tale of how Princess Luna, with some help from the House of Sparkle, managed the first fully Equestrian warp jump; and of how Spike became the first dragon in space.
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Additional note: There is an alternate ending for this story, which can be found over here. It follows on directly after the chapter titled Further Communications (and there is a note in the author's notes for that chapter to that effect, with another link).
The reasons for the split are contained in the comments to this story. (Note: Said reasons contain spoilers)