Europe is building a potentially revolutionary space-based telecommunication system that will allow the transmission of vast amounts of data via laser links across huge distances and enabling the immediate download of imagery from Earth-observing satellites.
The first node of the European Space Data Relay System (EDRS) - dubbed the Space Data Highway - was launched on 29 January 2016 and has since reached its position in the geostationary orbit at 9 degrees east longitude.
The cutting-edge technology is hosted on the Eutelsat-9B broadcasting satellite and is the first of its kind to be deployed in space.
The EDRS-A payload, weighing 53 kilograms and the size of a microwave oven, will link with a similar system on low Earth-orbit Sentinel satellites, enabling the transmission of up to 1.8 gigabits of data per second (Gbps).
“A regular teleconnection you can have at home usually provides 20Mbps,” said Michael Witting, EDRS Project Manager at the European Space Agency (ESA), which has developed the system jointly with Airbus Defence and Space.
“The EDRS is about 90 times more than that. In terms of what is available in space, the American Tracking and Data Relay Satellite System (TDRSS) uses a similar architecture, relaying data through satellites, but they are using conventional radio frequency links, which means the data rate is at about 300Mbps, which is six times lower than what EDRS provides.”
Currently, data from Earth-observing satellites could only be downloaded when spacecraft passed over one of its ground stations. In the case of the Sentinel satellites, part of the European Copernicus Earth observation programme, this results in a delay of around 100 minutes before the images reach the ground.
“Sometimes we need the data very quickly and very urgently on the ground,” Witting said. “In situations like flooding where you have aid troops on the ground, in earthquake scenarios like what happened in Nepal, to monitor oil spills which move very quickly on the ocean – you can’t usually wait two hours because the oil spill would have moved. Or for navigating through moving ice flows in the Arctic region.”
The powerful laser links of the space data highway enable an Earth-monitoring satellite like Sentinel, orbiting at some 700km above the planet’s surface, to beam the data to the relay node at 36,000km above the Earth. Located in the geostationary orbit above a fixed spot on the Earth, the terminal has a constant view of a ground station and can send data down to the ground with zero delay.
“It was a real challenge to get this working,” Witting said. “You have two satellites communicating and talking to each other over a distance of 45,000 kilometres both moving at the speed of 28,000km/h. You have to point at an object that is really far away and moving extremely fast and you still have to be able to hit it and track it all the time.”
The ability to communicate in real time across vast distances is only one of the advantages of moving to the optical spectrum. While there are hundreds of users competing for the use of the radio spectrum, the optical spectrum is currently completely empty. That means there is no risk of interference and also no need for complicated coordination. The laser signal, Witting said, is also virtually impossible to jam or eavesdrop on.
“When you use a laser to communicate between two points, it’s really point-to-point communication. If you want to listen in to it, you would have to fly with a third satellite in between the two satellites which are communicating. The same goes for jamming the signal, you can’t really jam the signal,” he said.
In future, the engineers will raise the bandwidth of the system beyond the current 1.8Gbps.
“It’s only for this first project that we are using something which we know works for sure, but there is potential for even higher bandwidth,” said Witting.
If all goes as planned, first data from the Sentinel satellites could be transmitted via the EDRS laser terminal on Eutelsat-9B by the end of April. Commercial operations are set to begin this summer with the Copernicus programme being the first user planned.
In future, the space laser links could be used to control drones or download their data and to improve communications with the International Space Station.
A second satellite will be launched next year, which will extend the coverage, capacity and redundancy of the system. A third node is being considered for possible deployment in 2020 that could provide coverage over the Asia-Pacific region.