Engineers working on a Vela Nuclear Detection Satellite (NDS). This satellite, designed and built by TRW Systems at Redondo Beach, California, USA, was one of two scheduled for launch in tandem in early 1967. The Vela satellites were developed by the USA to monitor compliance with the 1963 Limited Test Ban Treaty (LTBT) by the Soviet Union. The LTBT is a treaty prohibiting all test detonations of nuclear weapons except underground. Photographed in 1967.