By: David Rilley-Harris, Curator, DITSONG: National Museum of Military History (DNMMH)   Vela satellites prior to launch (Picture: National Security Archive. https://nsarchive.gwu.edu/briefing-book/nuclear-vault/2019-09-22/vela-flash-forty-years-ago).   In 1963, numerous countries signed or acceded to the Partial Test Ban Treaty (PTBT), including the USA, USSR, South Africa, and Israel.

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