English: The third and final main engine has been installed on Space Shuttle Discovery at NASA's Kennedy Space Center in Florida. The engines will provide part of the driving force for the Space Shuttle on its Return to Flight mission to the International Space Station. 'Behind me, what we're seeing today is the installation of the third engine on the Discovery vehicle. That's a major milestone for NASA on Return to Flight.' Among the three engines, one is making its fifth space flight, one is making its third, and one is flying for the very first time on the mission, which is targeted for May's launch planning window. Weighing in at just over 7,000 pounds each, the Space Shuttle Main Engines are the largest reusable liquid rocket engines in the world. During liftoff, they use up more than half a million gallons of fuel and generate as much energy as 23 Hoover Dams. The Boeing Company's Rocketdyne Propulsion and Power Division builds the engines for NASA. 'We're very proud to accomplish that milestone for NASA, which is going to lead us on Return to Flight, and we'll be very proud to be there.' Returning the Space Shuttle to flight is the first step in NASA's Vision for Space Exploration, which calls for man to return to the Moon, then on to Mars and beyond.