Examples from literature

• A major challenge for astronauts is the low-gravity, or micro-gravity environment, which means they must re-learn how to move the body. 
• Although scientists have learned how to solve these problems through exercise, diet, and medicines, astronauts who spend long periods of time in micro-gravity conditions still find they are very weak when they return to Earth’s higher gravity. 
• Astronauts often sleep tied into special beds so they do not hurt themselves while they are unconscious. 
• Gold is used to protect astronauts from the brightness and heat of the sun. 
• Many early achievements were Russian, such as the first rocket to orbit the Earth (1957), the first astronaut (Yuri Gagarin, 1961), and the first woman in space (Valentina Tereshkova, 1963). 
• Mars One began the selection of the astronauts in 2013. 
• Polyakov’s experiences showed that astronauts could spend long periods of time in space without suffering long-term problems, although there are still questions about whether humans could live for many years in this kind of environment. 
• To prepare themselves for this environment, astronauts spend months training underwater. 
• When astronauts go to space, they float due to the lack of gravity.