The first switch-on of a Galileo search and rescue package shows it to be working well. Its activation begins a major expansion of the space-based Cospas-Sarsat network, which brings help to air and sea vessels in distress.

The second pair of Europe's Galileo navigation satellites - launched together on 12 October 2012 - are the first of the constellation to host SAR search and rescue repeaters. These can pick up UHF signals from emergency beacons aboard ships and aircraft or carried by individuals, then pass them on to local authorities for rescue.

Once the satellites reached their 23.222 km-altitude orbits, a rigorous test campaign began. The turn of the SAR repeater aboard the third Galileo satellite came on 17 January.

ESA's Galileo SAR engineer, Igor Stojkovic, said at this stage, the main objective is to check the repeater has not been damaged by the launch. The first day was a matter of turning the repeater on and checking its temperature and power profiles were as predicted. The following day involved sending a signal to the repeater using the UHF antenna at ESA's Redu Centre in Belgium, then picking up the reply from the ESA L-band antenna.

Redu's antenna is 20 metres in diameter, so the shape of the relayed signal was captured in great detail, out of all proportion to surrounding noise. ESA can precisely measure its power, the time the relay took and so on, Stojkovic added.

More detailed system testing will follow, to completely prove this new type of SAR payload in orbit.

This international system has been taking the search out of search and rescue for more than three decades, saving some 31,000 lives along the way.

Cospas is a Russian acronym for 'Space System for the Search of Vessels in Distress', with Sarsat standing for 'Search and Rescue Satellite-Aided Tracking'. Ground stations - known as Local User Terminals - pinpoint the source of distress calls using signals relayed by participating satellites, then alert local authorities.