How do you know if a part of your body is dead from infection?

Loss of any and all feeling, loss of most if not all movement, turns black or purple.

during longer space exploration trips, crewmembers may develop vision impairment risks and short-term cardiac atrophy or a decrease in the size, strength, weight, and activity of the heart during space flight because they can experience microgravity. in addition, the long-term medical condition is loss of bone mineral density and radiation exposure.