Cosmos 1555 was a Soviet navigation satellite launched from the Baikonur cosmodrome aboard a Proton rocket. It was a test flight of the Glonass system, flown to test the components and equipment of the space navigation system established in order to locate the Soviet Union's civil aircraft and its merchant and fishing vessels. Three satellites were launched by a single carrier rocket. Glonass was the equivalent of the US GPS (Global Positioning System).