The space shuttle carries Human and other modules that are required to carry out various experiments out there in space ,International Space Station(ISS).
The Crew of seven or six with all the necessary things including Food,Communication Equipments,for living will stay for seven days,and while they are ready to return those who stayed there for last six months conducting several experiments and research will be coming and in substitute to them those who went will be stayed there..
The various parts of Orbiter,Cockpit Deck,Fuel Tank,Observation Window,Cargo Bay,Heat shield,Maneuvering Engine..etc..all of this each one is important and they recheck the conditions and the status while they return to earth.
