To not conflict with multiple LICENSE aggreements (e.g. code undser MIT, illustrations under CC), using external repository, so illustrations could be replaced/removed easier, with lower impact to intellectual property owners.
SpaceX
is a trademark of Space Exploration Technologies Corp.
and
here it is used only to refer original author of derived illustrations.
See more information in https://www.spacex.com/trademark/
This repositoruy is using illustrations from https://www.flickr.com/photos/spacex,
which are under Attribution-NonCommercial 2.0 Generic
(CC BY-NC 2.0
) license.