Space shuttle. Artist's impression of a Space Shuttle in orbit over the Earth. The payload bay doors are opened once the Shuttle has reached orbit. This is because the doors have radiators which allow heat from the Shuttle to dissipate into space, keeping the craft cool. Inside the payload bay here is a Spacelab module, shown here in cut-away with astronauts inside. In the rear of the bay are several small scientific instruments. In this configuration, the Shuttle could stay in orbit for 8 to 9 days. Longer missions require additional oxygen and nitrogen tanks; Shuttles thus converted may stay in orbit for up to 16 days.