The Hubble Space Telescope (HST) Servicing Mission 3B is currently the best example of NASA's ability to maintain, repair, and improve satellites in orbit. Actually, the genesis of this mission occurred more than 30 years ago. In the late 1960s and early 1970s, during the early development phase of the space shuttle, NASA was experiencing a 20–30% failure rate of its satellites due to either launch vehicle or satellite problems. Designers at NASA's Goddard Space Flight Center realized that a modular spacecraft could be repaired or serviced in orbit by spacewalking astronauts, so they developed an astronaut-friendly modular spacecraft concept that could be serviced by an extravehicular-activity (EVA) crew from the space shuttle. This concept featured ease of integration and testing during ground processing, and it proved to be less expensive and more reliable than competing “throwaway” concepts, in which equipment in space is discarded when it is no longer operable.