music/space.ogg - Mid-Air Machine - Creative Commons Attribution-ShareAlike
backgrounds/galaxy.png - NASA - Public Domain
sprites/ss.png - Pixabay - Pixabay License
sprites/css.png - Pixabay - Pixabay License
sprites/sat.png - NASA - Public Domain
sprites/asteroid.png - NASA - Public Domain
sprites/radio.png - NASA and Page Asgardius - Public Domain
backgrounds/supernova.png - NASA/JPL-Caltech - Public Domain
sprites/iss.png - ESA/NASA - Creative Commons Attribution-ShareAlike 3.0 IGO