This Is Done After You Build Your Rocket -
(Make Sure You Don't Click Auto-Launch!)
Go To A Body Of Water And Look For Some Swimming Fish.
- You Can Mine These Fish!
Right Click (On Pc) To Mine Fish Close To Shore.
Once The Rocket Is Finished -
Click On Your Silo And A "Cargo" Slot Has Appeared, Put The Fish Into This Slot.
Achievement Pops When The Fish Hits Orbit.
Good Luck!