Laika was a Soviet space dog that became the first animal
Animals in space
Animals in space originally only served to test the survivability of spaceflight, before manned space missions were attempted. Later, animals were also flown to investigate various biological processes and the effects microgravity and space flight might have on them...

 to orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

 the Earth – as well as the first animal to die in orbit.

As little was known about the impact of spaceflight
Spaceflight is the act of travelling into or through outer space. Spaceflight can occur with spacecraft which may, or may not, have humans on board. Examples of human spaceflight include the Russian Soyuz program, the U.S. Space shuttle program, as well as the ongoing International Space Station...

 on living creatures at the time of Laika's mission, and the technology to de-orbit had not yet been developed, there was no expectation of Laika's survival. 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.
Unanswered Questions

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|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)