The Tanzanian islands of Zanzibar and Pemba are about to become a test site for a mobile internet network its creators hope will not just revolutionize lives there, but possibly across sub-Saharan Africa and beyond. Only around 20% of Tanzanians use the internet, according to the World Bank. UK company World Mobile is launching a hybrid network using aerostats — that it says will provide near-blanket coverage across the islands. Two solar-powered, helium-filled balloons will float 300 meters above land and have a broadcast range of around 70 kilometers, using 3G and 4G frequencies to deliver their signal. The balloons can survive winds of up to 150 kilometers per hour and stay airborne for up to 14 days before descending for refilling. In the few hours of downtime, other aerostats will be airborne, ensuring users are never without service, says the company.