Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

10 Platform one Autumn 2015 | Unmanned Systems Technology Facebook’s Connectivity Lab is to start testing its autonomous base station aircraft to deliver internet access to remote areas. The Aquila UAV has a 50 m wingspan, which is covered entirely with solar cells to provide power, but weighs less than 500 kg (without the payload), and tests with it are due to begin by the end of 2015. The technology was developed by a team from Ascenta in the UK, which Facebook acquired in 2014. Aquila differs from previous Ascenta designs such as Zephyr in that it will be launched via helium balloon. It will be lifted into position at an altitude of 65,000 ft, well above commercial airspace, and stay aloft for up to 90 days. This addresses one of the challenges for Google’s balloon-based internet access Project Loon, which has to keep the balloons at a particular location. Aquila will achieve the same thing with an autopilot that keeps the craft circling in a 3 km radius above a fixed point. A data link to the ground will be provided by a free-space optical (FSO) system that uses a 1550 nm laser and indium gallium arsenide (InGaAs) receiver. Facebook claims to have achieved data rates of up to 10 Gbit/s but hasn’t said over what distance, as absorption from the atmosphere would reduce this over long distances. Although most FSO systems operate at 1 Gbit/s, ground- based 10 Gbit/s FSO systems were launched in 2008 with a range of up to 850 m, and companies such as MRV Communications hold key patents on low-power FSO technology. The network architecture proposed by Facebook is also new. This has one craft holding its station above the downlink location, with lateral data links to other, secondary Aquila craft using the same FSO technology. This would allow the secondary craft to be further away, as there is less signal absorption at such high altitudes. Each secondary craft could provide internet access over a 50 km radius, and this could solve the problem of extending coverage across wide areas. The data link between the secondary craft could then also be used to provide a mesh network, where each craft forwards data to a neighbour, again allowing a way to extend the coverage. Facebook has not specified the radio technology it sees being used for internet access by the population on the ground, but expects Aquila to be used by telecoms operators. This would see 3G or 4G cellular base stations as the payload in the secondary craft rather than wi-fi. Google is also testing UAV base stations and FSO systems after its acquisition of Titan Aerospace (See UST , issue 1). Facebook updates UAV status Airborne base stations The proposed architecture is new, with one craft holding its station above the downlink and with lateral data links to other, secondary craft The Aquila will be launched at high altitude from a helium balloon then circle about a fixed point