An Emergency Position Indicating Radio Beacon (EPIRB). This type of radio distres beacon is carried on ships. If the transponder is activated, either deliberately, or in the case of an accident where the transponder becomes submerged, automatically, the beacon's position is accurately pinpointed by a satellite in orbit. This type of satellite-aided tracking system has greatly facilitated marine search and rescue misions. It has been particularly vital for saving lives in ocean yacht racing accidents. The system is known as SARSAT (Search and Rescue Satellite-Aided Tracking System).
© Science Museum / Science & Society Picture Library