Balloons like these can reach up to 40 km in altitude, where the low pressure lets the helium stretch the balloon more and more until it bursts. Then, the payload falls back to the ground under a parachute, hopefully not too far from where it took off.
To make sure the payload can be received, most balloons transmit their telemetry (position, altitude and readings) to one or multiple ground stations through a radio link. That’s where it gets fun.
Balloons usually climb up to 30-40 km, and can drift quite a bit due to winds. Depending on the conditions, it’s not impossible for payload to be more than 200 km from the receiver, which makes reliable transmissions challenging.
The range of a transmitter-receiver couple depends on a few factors: the shape of both antennae, the transmission power and the line-of-sight.
In the USA, the amateur radio license allows you to transmit from airborne stations (which is exactly what the balloon is). This allows the use of fairly powerful transmitter (up to 5 watts).
In the UK, we don’t have such luck. A few frequency bands are considered license-exempt and can be used airborne, as long as a certain power limit of 10 mW is not reached. Because of the low power, long-distance communications require good antennae, and a data format that is not too vulnerable to noise, or at least provides a way to correct errors.
In most High-Altitude Balloon projects, the payload is made one of two ways: either a custom circuit board is designed for a specific mission, or low-cost boards (Beaglebone, Raspberry Pi, Arduino) is used with custom software running the data collection and transmission.
This goes against what is done for example on most satellites: save for high-profile missions where everything needs to be controlled, most satellites today are based on buses: the manufacturer sells a series of standard platforms that host radio communications, power and control systems, and provide an interface for the client’s payload to tap into those systems.
For the project, I’d like to work on communications, applied to low-cost systems (High-Altitude Balloons, maybe nano satellites simulations). The project would be split in two parts:
Design a modular flight computer based on low-cost computers (Raspberry Pi for example) that would provide power and communications to instruments. Any payload that follows the specification could be connected to the bus with as little work as possible.
Design the radio system used by the bus to transmit arbitrary data packets received from each instrument to the ground. Because of the limitations of license-exempt transmitters in the UK, it would have to work even with low-power radio links, which means low bandwidth: it will need to be efficient in speed and size of packets, and reasonably error-tolerant.