Laika The Space Dog

Laika (Russian: Лайка; c. 1954 – 3 November 1957) was a Soviet space dog which became one of the first animals in space, and the first animal to orbit the Earth. ... Laika died within hours from overheating, possibly caused by a failure of the central R-7 sustainer to separate from the payload.

Little was known about the impact of spaceflight on living creatures at the time of Laika's mission, and the technology to de-orbit had not yet been developed, so Laika's survival was never expected.