It says Space Exploration, so I assume they mean the mod, not the Space Age DLC. The mod was designed to be much harder than the DLC, and among the new challenges were periodic meteor strikes and Coronal Mass Ejections, big lasers from space that could burn down whole forests and badly wreck your bases and outposts. Space Age lacks those features.

I remember you needed a defense cannon to deal with the meteors, though only in a certain range around the cannon, and a big, ridiculously power-hungry planetary shield... thing? to stop the CMEs.