Christina Pushkin was a Soviet physician. She was born in 1940. On 10 November 1963, as she and Grigori Kalashnikov were headed for the Baikonur Cosmodrome in a jeep, they were both shot. Their corpses were then completely destroyed in a time-bomb explosion.
After her death, Peri Brown, the Sixth Doctor having taken her identification papers while inspecting their corpses, assumed Pushkin's identity, and took her place at the Cosmodrome in helping return Vostok 7 to Earth. (AUDIO: 1963: The Space Race)