A pretty well-done mod that will allow you to fly into space and start exploring it! This is an incredible mod called Galacticraft. Now you will be able to create a rocket from scratch and fly to the Moon or even Mars.
Space mod for Minecraft 1.12.2 (Galacticraft)
The mod is quite global and has many new blocks, technologies, as well as interesting items. Your rocket will need fuel, which you will also need to craft manually. To fly to the moon you need to prepare extremely responsibly.
When you get into space, you yourself will understand how incredible this journey will be for any player. Upon landing, you will find yourself in a completely different world, where gravity is different and there is nothing alive.