I'm guessing the learnings from project loon are in play here. (loon proved that alphabet could 'fly' balloons around with no fuel just by adjusting the altitud

I'm guessing the learnings from project loon are in play here. (loon proved that alphabet could 'fly' balloons around with no fuel just by adjusting the altitude, ostensibly as lower-than-space comms relays) If you can move bulk from anywhere to anywhere with (almost) no fuel you are on to a sure winner. iirc the 12 largest ships on the planet produce as much co2 as all the cars.