>>12378670On the face of it you may imagine that a rocket's tanks are just metal tubes, but they're metal tubes in the same way a rocket engine is 'just' some plumbing. A huge amount of engineering effort is used to produce vehicle structures that have good wet-dry mass fractions (ie the mass of propellant they hold is much greater than the mass of the actual vessels) that can still hold up to the forces involved in launching vehicles into space.
This problem is actually HARDER for smaller rockets, and gets easier with bigger rockets, because with bigger rockets the thickness of material necessary to achieve a good wet-dry mass ratio is still thick enough to easily work with, but as you shrink the rocket down you eventually end up needing to somehow manufacture shit out of 1/4 mm aluminum and it just becomes very impractical.
For example, Starship uses ~5mm steel sheet metal if I remember correctly, and is 9m wide. A Starship-style vehicle scaled to 36 meters in diameter would be made of steel plate 2 cm thick, or about 3/4 inch. Building shit out of 3/4 inch steel is very easy, because of how stiff the stuff is at human-hand scale. However, going the other way, if you tried to scale Starship down and make a vehicle the size of Electron at 1.2m diameter, you'd need to work with material a bit over half a millimeter thick, which would be easy to accidentally bend and ruin just by holding it wrong with your hands.
