Sputnik 6, two dogs launched 1960

 

Pchyolka and Mushka

Pchyolka and Mushka Stamp

Sputnik 6 (also known as Korabi-Sputnik 3), launched December 1, 1960, carried two dogs into space, Pchyolka and Mushka.  The flight lasted a day before the capsule "deorbited" ahead of schedule.  During re-entry, the engine failed to cut off properly and allowed the spacecraft fuel to be depleted.  As a result, the capsule re-entered on a trajectory that might have allowed it to land in a foreign territory.  Instead of saving the dogs, the Soviets activated the self-destruct mechanism rather than letting the capsule fall into the hands of a foreign power.  Both dogs were killed.