Laika (Russian: Лайка, literally meaning "Barker") was a Soviet space dog (c. 1954–November 3, 1957) who became the first animal to orbit the Earth and the first orbital death. The technology to deorbit had not yet been developed, so there was no expectation for survival. Little was known about the impact of spaceflight on living things at the time Laika's mission was launched. Some scientists believed humans would be unable to survive the launch or the conditions of outer space, so engineers viewed flights by non-human animals as a necessary precursor to human missions. Laika, a stray, originally named Kudryavka (Russian: Кудрявка Little Curly), underwent training with two other dogs, and was eventually chosen as the occupant of the Soviet spacecraft Sputnik 2 that was launched into outer space on November 3, 1957.

Laika likely died within hours after launch from overheating, possibly due to a failure of the central R-7 sustainer to separate from the payload. The true cause and time of her death was not made public until 2002; instead, it was widely reported that she died when her oxygen ran out, or (as the Soviets initially insisted) she was euthanised prior to oxygen depletion. However, the experiment proved that a living passenger could survive being launched into orbit and endure weightlessness. It paved the way for human spaceflight and provided scientists with some of the first data on how living organisms react to spaceflight environments. On April 11, 2008, Russian officials unveiled a monument to Laika. A small monument in her honor was built near the military research facility in Moscow which prepared Laika's flight to space. It features a dog standing on top of a rocket.

Laika, one of the Russian space dogs, was the first living passenger in orbit when she flew on Sputnik 2 (3 November 1957). No provisions were made for her return, and she died in orbit within hours from stress and overheating.

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• Work with animals is a source of suffering to all of us. We treat them like babies who cannot speak. The more time passes, the more I’m sorry about it. We shouldn’t have done it. We did not learn enough from the mission to justify the death of the dog.
  • Oleg Gazenko, one of the scientists who trained Laika (speaking in 1998).

• Prayers were said for the dog and people were asked to observe a minute's silence each day 'with special thoughts for her early and safe return to Earth'.
  • Daily Herald newspaper (November 1957)

• That does not raise my apprehension, not one iota.
  • President Eisenhower's comments on the military significance of the Soviet Space Agency sending a living passenger into orbit. (3 November 1957)