The dramatic success of NASA’s astrophysics science program over the past 20 years has resulted from a series of assets in space ranging from Small Explorers to Observatory-Class
missions. NASA’s Observatory-Class missions, such as the Chandra X-ray Observatory (CXO), the Hubble Space Telescope (HST), and the Spitzer Space Telescope (SST), form the
cornerstone of this program by providing all researchers, regardless of institutional affiliation, a spectrum of science opportunities across programs large and small. These observatories stand out in their breadth of capabilities and consequent diversity of high impact science, their reach within the scientific community, and their proven ability to inspire the nation. Each mission was
designed to address specific scientific imperatives recognized by past Decadal Survey Committees, whether it was to refine the extragalactic distance scale, examine galaxies as they were in the distant past, determine the relationship between black holes and quasars, observe the
ultimate fate of stars in their death throes, or reveal heavily obscured regions of star-formation. These were ambitious goals, as are those envisioned for future Observatory-Class missions, such as the James Webb Space Telescope (JWST)
