When a remarkable spell summons a human mind into the body of a unicorn filly, Princess Twilight Sparkle does the only thing she can think of: Take on an apprentice.
Applejack and Pinkie have barely seen each other since Applejack's parents died. Pinkie is willing to do anything to get some time where she can help her only friend... and that friend will do anything to never leave the Acres again.
Humanity's space exploration ultimately took the form of billions of identical probes, capable of building anything (including astronauts themselves) upon arrival at their destinations. One lands in Equestria. Things go downhill from there.