After the surprise public impact of Sputnik 1, the satellite and launch teams were called back from vacation and in one month assembled Sputnik 2 (using equipment already developed for dog sounding rocket flights). The spacecraft, which remained attached to the upper stage, carried the dog Laika. No recovery was possible, and the dog perished in orbit due to higher-than-expected temperatures.
The life-support system and the consumables were designed for a 7-day flight. Control of the internal atmosphere was provided by a carbon dioxide absorbing device, an oxygen generator, an oxygen regulator, and a fan that activated when the cabin temperature went above 15 deg C. Food and water were ejected by tube directly into the stomach in jelly form, and wastes were removed by another implanted tube. Restraints kept Laika from moving far -- she could not even turn around. Her electrocardiogram, and data on respiration rate and maximum arterial pressure, were radioed to the ground when over the Soviet Union. Some kind of device (a crude television monitor?) allowed her movements in the cabin to be seen.
Three dogs -- Albina, Laika and Mushka -- were involved in flight preparations. Albina was the back-up dog, and had survived earlier sounding rocket flights into space. Mushka was the stand-in for tests. All the dogs had been trained to survive in small cages in preparation for the flight. Laika was sealed into her cramped cabin four days before launch.
Despite her ordeal on the ground she survived the launch and her heart rate returned to normal after a time. She had proven that an animal could survive in sustained spaceflight. But in practice the environmental control system was not up to the task. Telemetry showed that temperature and humidity increased relentlessly. By the fourth orbit none of the physiological sensors were returning data -- Laika had evidently died. This fact was not revealed until the 21st Century.