After an Astronaut completes a space mission, lasting from one week to six months, they are transported from a weightless environment to normal gravity. Re-adapting to Earth’s gravity is hard because their muscles and bones have weakened, and the heart has to work much harder to pump blood around the body. Astronauts returning back in a spacecraft have to be helped out by rescue staff, and they are carried to waiting helicopters for the first part of their journey home. Some feel lightheaded, some may faint, while others may also have trouble standing up, walking, turning corners and keeping a sense of balance. If they close their eyes, they are likely to fall over. Even sleeping can be difficult.