Start-ups in the mobile infrastructure market are rare, but US firm Altaeros says it has a new approach to the difficult economics of rural 5G build-out. The company has pioneered a variation on the increasingly popular approach of using balloons or ‘stratellites’ to support rural coverage. Its SuperTower platform uses small airships, called aerostats, to raise cellular radio equipment 800 feet into the air, in place of building a mast. This reduces the cost of deploying and operating a rural network by about 60%, says the company, because one aerostat can do the work of about 15 cell towers. The aerostats are not free-moving balloons, however, but are tethered, with power and cables running along those tethers. The start-up’s CEO…