Sensory deprivation is the blocking of the senses, such as placing someone in a tank, filled with water and the person is blindfolded and their hearing is blocked, as well.

Short term deprivation can heighten senses, whereas long time deprivation can result in hallucinations.

Sensory deprivation, or Restricted Environmental Stimulation Therapy (REST), is a technique by which sensory input (sound, light, smell, etc.) is minimized. This practice encourages an extremely deep level of relaxation.

In connection with manned space flight.

they produce altered state of consciousness

No, he is trapped in a sensory deprivation tank which give the illusion of being dead.