Receivers in space
Satellites are expensive. For a project that still needs to be tested in practice, the Icarus researchers are therefore initially reverting to a more cost-effective alternative. The International Space Station (ISS) will act 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.
In spring 2018, astronauts will install the Icarus modules on the ISS. They will consist of three reception antennae, each measuring up to two metres in length, and one transmission antenna, which will be installed on the outside of the ISS. The Icarus transmitter on the ground will receive both configuration commands and the precise path data to calculate the next contact window via the transmitting antenna. The data transmitted to the receivers on the ISS is then transferred via the space station's communication system to the Russian control centre in Moscow and from there it is redistributed to the Icarus user data centre and the scientists.
Icarus's electronic data processing module will be installed in the space station's pressurised cabin. It is responsible for decoding the weak signals received simultaneously from the mini-transmitters via the receiver antennae and for separating the various data streams from one another.
The ISS orbits the Earth 16 times a day; in doing so, its path shifts by 2,500 kilometres to the west each time. The receiver antennae receive signals from an area measuring 90 by 900 kilometres. As a result, they cover about 80 percent of the Earth's surface between the 55th parallel north and 55th parallel south.
At higher latitudes, in favourable conditions, one transmitter can be read out up to four times a day, but as a rule it is done just once a day. Closer to the Equator, for example in Africa and in Central and South America, gaps emerge that can only be bridged after two to three days. Icarus's own satellites will also facilitate the daily reading of transmitters. Furthermore, when working with the ISS, Icarus will not initially be able to cover the biologically important areas in Canada or Siberia. With satellites, the regions of scientific interest above the 55th parallel in Europe, Asia and North America will become accessible.