All of the OrbiterÕs on-board systems need electricity in order to run. This electricity is generated by three fuel cells located under the payload bay. The cells use cryogenic hydrogen and oxygen as their fuel. These liquid fuels are also stored under the payload bay.

When they come into contact with each other in the fuel cell, the liquid hydrogen and oxygen react to make electricity and water. The electric power system (EPS), distributes the electricity generated by the fuel cells throughout the ship. It powers everything from the lights to the OrbiterÕs avionics systems. The water flows through tubes and cools down the crew compartmentÕs air circulation system to make sure it doesnÕt get too hot inside the cabin. The water is also used by the crew for drinking, cooking, and washing.