The Cosmonauts Sea was named in 1962 by the Soviet Antarctic Expedition in honor of the world's first cosmonauts and the beginning of manned space exploration era. The name first appeared as a Russian proposal to the International Hydrographic Organization. The 10th edition World Atlas (2014, United States' National Geographic Society) and the 12th edition of the Times Atlas of the World do not use the name. But Soviet and Russian-issued state maps do, as do the maps in Wikipedia.

More Info: en.wikipedia.org