I've heard that there was a problem in the cooling system on sputnik 2. But, was it an engineering error? Obviously a dog cannot survive such harsh conditions. Did the engineering team overlook this issue?
After reaching orbit the nose cone was jettisoned successfully but the Blok A core did not separate as planned. This inhibited the operation of the thermal control system. Additionally some of the thermal insulation tore loose so the interior temperatures reached 40 C. It is believed Laika survived for only about two days instead of the planned ten because of the heat.
The mission was a suicide mission for the dog from the get-go, she was never intended to survive. Her quick death was because of the above mentioned malfunction.