They need air and an atmospheric pressurized environment.
They have to check up that the instruments are all in working order.
Project Gemini and Project Apollo had astronauts practice piloting and working in space.
effects and accommodations
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Having neutral buoyancy underwater simulates the weightlessness the astronauts will experience in space.
Ensure all systems are working correctly.
Living and working quarters for astronauts in space are usually located in the pressurized modules of the spacecraft, such as the International Space Station (ISS). These modules provide the necessary environment for crew members to eat, sleep, work, and conduct experiments while in space.
NASSS
Astronauts use a variety of instruments for scientific experiments, repairs, and maintenance while in space. Some common instruments include cameras for photography and video recording, robotic arms for handling equipment, and scientific instruments for conducting experiments in biology, physics, and materials science. Additionally, astronauts use specialized tools for spacewalks to repair and maintain the spacecraft.
Astronauts use instruments that are designed to travel in space and withstand extreme temperatures. Some of these kinds of instruments include a pistol grip tool, a robot crane, safety tethers, and a trace gas analyzer.
Space suits: to protect astronauts from extreme temperatures, micrometeoroids, and provide oxygen. Extravehicular Mobility Units (EMUs): for spacewalks to enable astronauts to move and work outside the spacecraft. Tether systems: to keep astronauts connected to the spacecraft while working in space.
The International Space Station normally has a crew of three or four, and while they rotate, most astronauts do not get to live on the space station. As of Feb. 2010 the number is now up to 6.