There are multiple control and networking systems connected together with a CAN bus (for controller area network, used in cars). It sounds like 4-5 ARM cores total: two Linux systems ("unfortunately" two) and one realtime controller in the main payload, and a failsafe controller up on top of the balloon (which controls helium release and parachute deployment). The controllers are designed to recover from being reset very quickly, since resetting is used as a kind of universal problem solver (sensor issues, cosmic rays flipping bits, etc.).
The stratospheric daily temperature swing (30°C down to -80°C) causes difficulties, so the electronics are in styrofoam boxes about 3cm thick, and a heating system keeps the electronics warm and the batteries warmer. The rough altitude is 20km, but it sounds like they cover about a 5km height range, I think connected to the daily cycle somehow too.
The solar panel provides 100W in full sunlight. It is mounted directly under the transparent balloon (which reduces the amount of energy by 20-25%). The batteries hold about "ten laptop" batteries' worth.
There are three vertically mounted omnidirectional antennas for balloon-to-balloon communication, and one downward facing antenna. The downward one has a 90° cone angle, and is designed so that the signal strength is even across the 40km diameter ground area. 2.4GHz and 5.8GHz, one for balloon-to-balloon and one for ground (I think 2.4GHz is ground).
The communication protocol is custom, to account for the large distances and to coordinate the ground systems so they don't transmit at the same time (since they can't see each other). The system basically acts as a VPN between end users and the ground station (upstream ISP), and traffic inside the VPN is encrypted separately as well. Currently upload and download speeds are symmetric (they don't really know what the speed will end up being, but roughly the same as 3G).
The eventual goal is commercial internet access to parts of the world that can't get it other ways, but there are no concrete plans for how that will work yet, since they expect to go through many more iterations of prototypes first. Commercial use will necessarily involve large fleets of balloons to provide continuous coverage (even if they end up covering more are each), since they move quite a lot. The balloons measure atmospheric conditions themselves and are coordinated from the ground.
Edit: I forgot to mention that there is a standard aircraft transponder (yellow and black cables in first picture), and the corners of the ~1.7m square solar panel have strobe lights to meet air codes.
The protocol uses time division multiplexing to solve the hidden node problem (https://en.wikipedia.org/wiki/Hidden_node_problem) where two nodes can be transmitting at the same time causing a collision.
They also mentioned that they didn't tilt the solar panel to follow the sun for reduced complexity, cost, weight and the risk of failure of a servo system.
They don't know what the speeds will be but 'as fast as 3G' was the marketing line.
To me it seemed like this project still had some large hurdles to viability but it was cool none the less.
Edit: that should have said 8m high
There are multiple control and networking systems connected together with a CAN bus (for controller area network, used in cars). It sounds like 4-5 ARM cores total: two Linux systems ("unfortunately" two) and one realtime controller in the main payload, and a failsafe controller up on top of the balloon (which controls helium release and parachute deployment). The controllers are designed to recover from being reset very quickly, since resetting is used as a kind of universal problem solver (sensor issues, cosmic rays flipping bits, etc.).
The stratospheric daily temperature swing (30°C down to -80°C) causes difficulties, so the electronics are in styrofoam boxes about 3cm thick, and a heating system keeps the electronics warm and the batteries warmer. The rough altitude is 20km, but it sounds like they cover about a 5km height range, I think connected to the daily cycle somehow too.
The solar panel provides 100W in full sunlight. It is mounted directly under the transparent balloon (which reduces the amount of energy by 20-25%). The batteries hold about "ten laptop" batteries' worth.
There are three vertically mounted omnidirectional antennas for balloon-to-balloon communication, and one downward facing antenna. The downward one has a 90° cone angle, and is designed so that the signal strength is even across the 40km diameter ground area. 2.4GHz and 5.8GHz, one for balloon-to-balloon and one for ground (I think 2.4GHz is ground).
The communication protocol is custom, to account for the large distances and to coordinate the ground systems so they don't transmit at the same time (since they can't see each other). The system basically acts as a VPN between end users and the ground station (upstream ISP), and traffic inside the VPN is encrypted separately as well. Currently upload and download speeds are symmetric (they don't really know what the speed will end up being, but roughly the same as 3G).
The eventual goal is commercial internet access to parts of the world that can't get it other ways, but there are no concrete plans for how that will work yet, since they expect to go through many more iterations of prototypes first. Commercial use will necessarily involve large fleets of balloons to provide continuous coverage (even if they end up covering more are each), since they move quite a lot. The balloons measure atmospheric conditions themselves and are coordinated from the ground.
Edit: I forgot to mention that there is a standard aircraft transponder (yellow and black cables in first picture), and the corners of the ~1.7m square solar panel have strobe lights to meet air codes.