Over water seems rather reasonable considering what we can do with cable laying ships. Whatever method is used to get it up in the air, it'll need to be safely

Over water seems rather reasonable considering what we can do with cable laying ships. Whatever method is used to get it up in the air, it'll need to be safely reversible. Over water bringing it down is much easier. And you'll have to bring it down for repairs. Every five minutes it will do a full loop.. Iron is fairly ductile, but those stresses will add up. And wikipedia says the kinetic energy involved is close to a small nuclear bomb. Back of the envelope math suggests the iron cylinder would be very thin. It will wear out sooner or later. My guess is that Musk's big breakthrough is for a cheap and reversible deployment system. I'm double checking my numbers now (and reading the original papers) but the entire contraption might weight a lot less than we are implicitly assuming. Like, light enough that a single large plane/blimp could support the entire cable/sheath system. And a small fleet of planes could safely tow the cable through the sky. Or a fleet of blimps could support the entire cable while it was stopped for maintenance. (Both would need a large number of well trained pilots, it would make the skycrane maneuver look simple.) edit: The original paper talks about a ribbon 5cm wide and 7.6mm thick weighing 15.6 Gg. I dropped a kilo in the back of the envelope calculations. So it would need at least 100 very large aircraft to hold up. Still feasible, but more than a little crazy.