ESA satellites will now ease SOS senders’ fears by assuring help is on the way

24 Jan 2020

Model Galileo satellite at the system’s control centre at Oberpfaffenhofen, Germany. Image: ESA

ESA’s Galileo satellites will now try to ease the fears of those sending SOS messages across the world by letting them know they’re not shouting into a void.

When anyone with an emergency beacon in remote parts of the world transmits an SOS message, one of 24 European Space Agency (ESA) Galileo satellites can pick the message up and send it to search and rescue services. But in the middle of a stressful situation – and with time possibly running out – those in distress have no idea whether someone on the other end has picked up the message.

However, that’s about to change as the ESA announced that it has switched on a new ‘return link’ system for the Galileo satellites with the Cospas-Sarsat search and rescue package.

ESA’s Galileo principal search and rescue engineer, Igor Stojkovic, explained that anyone in trouble would now receive solid confirmation that responders have heard their message and know where they are.

“For anyone in a tough situation, such knowledge could make a big difference,” he said.

Founded by Canada, France, Russia and the US in 1979, Cospas-Sarsat began with payloads on low-orbiting satellites, whose rapid orbital motion allows doppler ranging of distress signals to pinpoint their location.

However, this only gave a limited field of view, while higher geostationary satellites were put outside of doppler ranging. At an altitude of more than 23,000km, the Galileo satellites have the benefits of both worlds, boosting signal detection time from four hours to less than five minutes, with the ability to pinpoint a distress call down to 1km.

The Cospas-Sarsat satellite repeaters are aided by a trio of ground stations at the corners of Europe, known as Medium-Earth Orbit Local User Terminals (MEOLUTs), based in Norway’s Spitsbergen island, Cyprus and the Canary Islands, and coordinated from Toulouse in France. A fourth station on La Réunion in the Indian Ocean is currently under development.

The Galileo satellites relay distress messages to the MEOLUTs, which are then sent to local search and rescue services.

“The switching on of the return link service was enabled by a thorough test campaign carried out by ESA, with the support of the Global Navigation Satellite System Agency and CNES (the French space agency),” Stojkovic said. “We needed to be sure the service remains reliable even with multiple distress calls being replied to at once.”

Colm Gorey was a senior journalist with Silicon Republic