You need to construct a sphere that is strong enough withstand 1 atmosphere of pressure but also lighter than the weight of the air being displaced. In a sci-f

You need to construct a sphere that is strong enough withstand 1 atmosphere of pressure but also lighter than the weight of the air being displaced. In a sci-fi book you would construct your unobtanium shell in space and use them to splash down heavier payload to earth. But the material needed is probably still magic. I think Reynolds also had smelting in space, where molten metal would be turned into a huge volume of froth using some lighter than air gas. The 'burgs' of metal foam could then gently float down to earth.