The Space Shuttle Discovery was the third of five reusable NASA orbiters, logging 39 launches and landings between 1984 and 2011—the most flights of any spacecraft in history. Perhaps its greatest accomplishment was the April 25, 1990 deployment of the Hubble Space Telescope ("HST") which revolutionized astronomy and astrophysics, particularly our understanding of the age and expansion of the universe. With characteristics of a rocket (for vertical launch) and a glider aircraft (for landings), space shuttles were the workhorses of America's space program at the turn of the 21st Century, and were critical to the construction and maintenance of the ISS (International Space Station).