It was never a secret that Laika, the first living creature into orbit, died during her mission. The secret was how she died.
Laika, a stray mutt from the streets of Moscow, was aboard Sputnik 2 when it blasted off in November 1957. The mission was an astonishing success for the Soviet Union, which had just one month earlier become the first country to send a satellite into space. Not only did they manage to launch a second satellite while the Americans were still scrambling to launch their first, but the Soviets also put the first living creature into orbit. The news wasn't so good for Laika, though: Shortly after launch the Soviets announced she would not return from her pioneering mission. For decades, they insisted she died painlessly several days after the launch.
It wasn't until a 2002 presentation by Dr. Dimitri Malashenkov of the Institute for Biological Problems in Moscow that the world learned the truth — and it was grim. As it turns out, very little about the process was painless for Laika. To prepare her for the tight quarters aboard Sputnik2, she had been crammed in increasingly smaller cages for 15 to 20 days at a time. Once aboard, she was chained she couldn't turn around. And although the craft was equipped with a cooling fan, a carbon dioxide absorber and an oxygen generator for Laika, the intensity of spaceflight proved to be too much. She died from overheating and stress a mere five to seven hours into the mission [source: Whitehouse].