A booster rocket is a type of rocket used to increase the speed and altitude of a spacecraft. The most commonly used booster rockets are the ATLAS and Agena, both of which are five-letter words. The ATLAS rocket was developed by the United States in the 1950s and was used for a variety of missions, including the first manned spaceflight. The Agena rocket was developed by the United States in the 1960s and was used for a variety of missions, including the Gemini program. Both rockets were used to launch satellites and other spacecraft into orbit.