The first satellite of the European Data Relay System (EDRS) is set to launch from Baikonur cosmodrome in Kazakhstan tonight with its laser node payload, which aims to make the transfer of Earth imaging data from satellites to ground stations about 90 times faster than your typical earthly internet connection and drastically cut down delays.
“You can imagine if it’s almost 100 times the speed of a normal internet connection at home, you can transmit phenomenal amounts of data in very short periods of time,” said Michael Witting, project manager for EDRS at the European Space Agency.
At the moment, most Earth imaging satellites are placed in low Earth orbit and transmit the data they collect to stations on the ground. But a satellite can only make contact when it’s over the relevant ground station, which can often mean gaps of 90 minutes between communications and a limited time slot to transfer the data.
The EDRS-A node will be launched on the Eutelsat-9B satellite into geostationary orbit—much higher up at around 36,000 km—and so has a wider view of the planet. Witting said it could transmit data to a ground centre “between 50 percent and in the best case 100 percent of the time.”
This could be particularly useful for satellites with applications that are hindered by latency, such as Earth observation satellites that are used to inform on-the-ground disaster relief efforts. “Anything from disasters at sea, oil spills, earthquakes, tsunamis, natural disasters like flooding and so forth where you have on the ground forces to help, time is of the essence,” said Witting. “It makes a difference if you get the message after 15 minutes or if it takes one and a half hours.”
ESA has partnered on the project with French company Airbus Defence and Space, which will operate the service. Airbus will offer the high-speed data transfer as a commercial service, but the first two customers are ESA satellites Sentinel-1 and Sentinel-2, which both carry out Earth observation.
EDRS works by collecting data from the lower satellite over an optical (laser) link and then bouncing it back down to the ground station. The laser terminal, developed by German company Tesat, is the first of its kind and has a much higher bit rate than the radio links typically used by satellites.
"It’s more or less akin to standing in Europe and taking a laser beam or a torch and pointing at a coin in New York, across the Atlantic."
“Just to give you a comparison, the data rate that we have on the optical link in space is up to 1.8 gigabits per second,” said Witting. “If you imagine you have an internet connection at home, it’s typically today 20 megabits or so.” (And that’s a generous estimate of your average internet speed.)
The main challenge of the system is connecting the satellites over such a great distance—depending on where each is in its orbit, we’re talking up to 45,000 km between the two. That means that operators need to know where each satellite is in relation to the other with great accuracy, and the satellites’ laser terminals need to be able to target the laser beam with great precision. Witting said that “it’s more or less akin to standing in Europe and taking a laser beam or a torch and pointing at a coin in New York, across the Atlantic.”
One design feature that helps keep a steady link is the fact that the EDRS laser terminal is fixed away from the main satellite body, to stop it being disturbed by any vibrations.
EDRS-A will launch tonight around 22:20 GMT and is expected to be in service for its first Sentinel customers in May. A second satellite, EDRS-C, is planned to launch in mid-2017. Witting said it is much the same as EDRS-A, except that it will not include a radio frequency connection as well as the laser link (this was included on EDRS-A at the request of potential customers). The second satellite will add capacity to the system, as each can only relay data from one other satellite at a time, as well as adding greater geographical coverage and acting as a redundancy if one suffers and outage.
Ultimately, ESA hopes to add more to the system to create a worldwide space data highway it calls GlobeNet.