This is awesome, thanks for the github link! I wonder what service is providing the data -- the lack of back-end in the repo and need for Web Workers makes me think it's something external. A brief tour of the source makes me think that the clue would be somewhere in satellites.js, but that is a doozy of a file.

The site downloads orbit data from the static file http://stuffin.space/TLE.json, which in turn is updated daily using the http://space-track.org API.

Looks like it's an internal JSON file (http://stuffin.space/TLE.json) representing the TLEs for each orbit (https://en.wikipedia.org/wiki/Two-line_element_set).