This question is about attaining the technology required to build a spaceship. The asserted duplicate question assumes that technology already exists.
In order to build a spaceship, you need to:
- Form steel with machine tools.
- Ditto aluminum.
- And titanium.
- Smelt iron from ore and add precise amounts of carbon to make steel.
- Smelt titanium from ore.
- Electrically split aluminum from bauxite ore.
- Refine chromium,vanadium and all the other trace minerals needed for steel.
- Mine the iron ore.
- Ditto titanium ore.
- Ditto bauxite.
- Mining operations are incredibly complex.
- The mining operations, as well as the smelters, forges, machine shops, etc, all need energy -- lots of energy -- which is mined/pumped from the ground.
- And electricity.
- And a way to generate lots of electricity.
- And transmit it thousands of miles.
- None of that technology burst forth whole from our brains. It all took many centuries -- even millennia -- of development.
- And all requires fire.
- And the ability to move and lift staggering amounts of stuff across vast distances.
- Members of your species have to transmit all this information to others (remembering that oral tradition cultures have not developed spacecraft).
- Which means some form of writing.
How do you do that when:
- your species has no legs,
- water attenuates light, and
- water extinguishes fire, and
- there's no evolutionary advantage to hands underwater (otherwise, some species would have developed them)?