I might be wrong, but Lucian of Samosata (2nd century AD) was probably the very first writer to ever describe contact with 'alien' species, interplanetary travel, as well as the Roman version of space battles in his "True History".

hi! not discouraging other responses, but you can get started on these (also, I have a feeling I'm missing something recent of substance, so if anyone remembers, pls link it here thx!)

• What do people from past centuries say about man ever walking on the moon? - a link to a comment on Lucien; 1638 John Wilkins

• At what point in time did we realize that exploration of space could be a real possibility? How much did we actually know about space before actually being able to go there physically or sending a probe? What was the very first thing sent into space? - 13th c Zakariya al-Qazwini; 1752 Voltaire; mid-late 19th c scifi & science

related posts that may be of tangential interest

• When did we first know the properties of space? - 17th c

• When did we discover that there is no breathable air on the moon?

• Before the launch of the first satellites, how did scientists know that there was no gravity/oxygen in space?

• Before Americans sent a man to the moon in 1969, what did people believe was on the moon? Did they believe it was inhabited by anything? Did they believe the composition of the moon was different (e.g. moon made of cheese)?

• What did the world think about "walking in space" before humans actually went there? Were there any popular but crazy predictions?

• in 1924 if you mentioned to someone (someone from the Anglo sphere) the words either “spaceship” or “space- alien” do you think it's likely (more than 50-50) that you would have had to explain the concept to them before going on?