Transmitters are at the heart of Icarus and are being specially developed for this project. They need to be small so that they don’t impede the animals wearing them. They need to be able to withstand cold, heat, moisture and dust. And they need to maintain enough power to transmit their data by radio – over months or years – to a receiver station located up to 600 kilometres away in space – currently on board the International Space Station. The Icarus transmitters, which have a GPS function, weigh a mere five grams each and are barely bigger than a euro cent coin. The transmitters consist of a plastic housing, a lithium-ion battery, an application-specific radio module and a basic module for controlling the transmitter’s functions and sensors: accelerometer, magnetometer, temperature, humidity, and pressure sensor as well as a GPS module which calculates an exact location to a few metres. The battery supplies the power for taking the measurements and transferring the data. The solar cell on the surface recharges the battery. The transmitter has two antennas, one 200mm long for radio transmission, and one 50mm long for the GPS receiver.

The International Space Station (ISS) acts as a receiver station until Icarus has its own satellites. The ISS circumnavigates the Earth at an altitude of around 400 kilometres and thus flies at a comparatively low orbital altitude. This makes it suitable for the minimum transmission power of the Icarus transmitters. The researchers can thereby keep the energy consumption of the transmitters at a low level.