About 230 years ago, molten lead that rained from the sky—historically something to avoid at all costs—became a clever new way to manufacture an important commodity: shotgun ammo.

Precisely round pellets fly straighter, but casting each in its own 1/8-inch mold isn’t exactly mass production. In space, making them would be easy. In zero gravity, surface tension pulls any liquid into a sphere, the shape with the least surface area for a given volume.