Wube hired the creator of that mod to develop this expansion, and he says that they are nothing alike (except for the “going to space” part).[0]

[0] https://factorio.com/blog/post/fff-373

Fun fact for those that didn't know. The dev's hired the author Earendel to come convert said mod into a full DLC. It's interesting seeing how the different dynamics of making a polished and widely playable DLC changes what does and doesn't make the cut from mod -> DLC. I hope some of Earendel's love of secrets do make it.

Is it harder than Sea Block? That's the one that was finally too much for me to finish, after doing other big ones like Bobs Mods, AngelBob, Pyanodon, etc. I've got a Sea Block attempt with hundreds of hours in it, my largest base ever, before I fell off. If Space Exploration is more complex I'm a little afraid of it.

Much easier than seablock. But it's a chore. The end game is a grind instead of a challenge like sesblock