At 22:20 GMT today, ESA will launch its European Data Relay Satellite, EDRS-A as a hosted payload on the Eutelsat-9B satellite on a Proton rocket from Baikonur, Kazakhstan. Dubbed as the “Space Data Highway” it will be positioned in the Geostationary orbit and will use cutting edge laser technology to communicate with Sentinel 1 and 2 satellites which are in low earth orbit. It will later be joined by EDRS-B and between them they will provide near realtime data from the Sentinel satellites to any ground station within the view of these two relay satellites. By relaying the data the system will cut down the delay between data acquisition and delivery to the intended users. This will be very useful in situations of disaster and emergency.
The idea is not new. In an article in Radio Electronics of 1945, Arthur Clarke proposed the idea of geostationary satellites. Three such satellites could cover the earth with inter-satellite links between the three to make the connectivity truly global. He had very ‘optimistically’ predicted that this could be realised in 50 to 100 years. Geostationary satellites became operational by the 1960s and inter satellite data links became a fact with the US Tracking and Data Relay Satellites, TDRS in 1983. This illustrates the speed at which technology is developing.
EDRS is operationalising satellite to satellite laser communications. This is a tremendous technological achievement. Laser beams, unlike radio beams are highly collimated and therefore the transmitter and receiver have to be on stable platforms. Satellites in space have to therefore achieve a level of stabilisation which pushes the envelope. The beam must track the LEO satellites precisely. For the LEO satellites the requirement is to provide a stable link as it moves rapidly in the field of view of EDRS.
The use of laser beams enables very high data rates, typically 1.8Gbps between satellites. The downlink to ground stations will be 600Mbps on Ka band. The technology of laser transmission from satellites to earth is not yet practical due to health hazards and due to attenuation in weather conditions.
Once operational, the system will be a major step forward in data transmission surpassing the TDRS system and bringing to reality Arthur Clarke’s idea many many years before 2045.
