NASA calls Lyman Spitzer Jr., (1914-1997) one of the 20th century's greatest scientists. The longtime Princeton astrophysicist lobbied for a large space telescope as early as 1946, work that culminated in the launch of the Hubble Space Telescope in 1990. After Spitzer's death in 1997, NASA continued to develop the Great Observatories Program, a group of four space-based telescopes each observing the universe in a different kind of light. The final telescope was launched in 2003, and NASA named this new space-flyer the Spitzer Space Telescope in honor of the visionary scientist.