During the height of the US/Soviet space race, Soviet scientist invested heavily into research of suborbital and orbital flights with dogs. Their main goal was to find out whether or nor human flight was feasible, and for that purpose they launched more than 25 dogs to various high altitude missions.
Process in witch they choose the suitable dogs for space mission vas very rigorous. They tested many types and species of dogs, and finally they decided that a suitable test subject must have several key traits. Trough training dog must be accustomed to severe gravitational stress (they rode them in centrifuges, and simulated launch conditions with powerful rocket sleds), they must be able to stand in one confined place for very long time (they trained them in small boxes, leaving them inside for up to 20 days) and willing to feed them self with nutritious jelly-like protein based food. After those tests Soviet scientist decided that perfect candidates were small female dogs. They had better temperament in small enclosed spaces and were better suited for the equipment witch gathered their urine and feces.
First sub-orbital flight with dogs Dezik and Tsygan happened on July 22, 1951. These space dogs survived after reaching altitude of 110 kilometers. In the following five years 14 dog missions were carried by the Soviet R-1 class rocket (copy of the World War II German rocket V-2).Most notable dogs from that time were Smelaya and Bolik who both managed to run away from the training facilities just days before the launch, but they were found just in time to launch on their separate missions. Between 1957 and 1960 flights were carried on a new and improved R-2A and R-5 rockets witch managed to carry dogs to the altitude of 200 km and 400km, respectively. Notable dogs from that period of time were Otvazhnaya (made five successful flights), Albina and Tsyganka (fist dogs who successfully tested detachable capsule witch separated from main rocket at altitude of 85km).
In 1957 Soviet scientist set their sights to the high Earth orbit. On November 3, 1957 they launched Sputnik 2 who carried dog Laika - first living creature who reached earth orbit. Official reports stated that Laika lived in orbit until she ran out her oxygen supply, but in 2002 it was found out that she died just few hours after launch from overheating. After that famous mission Soviets launched dogs Belka and Strelka on a 1 day mission in 1960. Both dogs and several other animals on board (40 mice, 2 rats and various plants) successfully returned to the Earth. Few other notable dogs from that period of time were Pchyolka and Mushka (they spend a day in space but they died on re-entry), Chernushka, Zvyozdochka (selected for final test flight before the launch of Yuri Gagarin’s first manned mission to space), Veterok and Ugolyok (who both survived the 1966’s 22 day mission in space, longest one until the Skylab 2 become operational in 1973).