kosmoŝipo

Read it and you have it. Kosmo plus ŝipo, with the linking -o- kept because kosmŝipo would be unsayable. That is the whole word. Nobody had to teach you kosmoŝipo; you were taught kosmo at rank 1,382 and ŝipo at 324, and the compound falls out. English needed a new word, German built Raumschiff the same way Esperanto did, and this is the argument for an agglutinative language in one line. The compounding article has the rule for when the -o- stays.

Kosmo is bigger than space. Greek kosmos means the world as an ordered whole, which is why it is also the root of kosmetiko - cosmetics put a face in order. In Esperanto kosmo covers both the cosmos as everything there is and outer space as the place rockets go, so kosmoŝipo is unambiguous but kosma needs a moment: kosma radiado is cosmic radiation, kosma vojaĝo is spaceflight.

The science-fiction shelf. Sciencfikcio at rank 2,477 is the genre, raketo at 2,836 the rocket, eksterterano at 2,855 the alien - literally an outside-earth-one, and one of the most satisfying words the affix system produces. Add planedo at 1,036 and kosmonaŭto for the crew, and you can read a pulp novel. Esperanto has a genuine science-fiction tradition, and it is a friendlier way into original literature than the poetry is.