Between 1990 and 2003, NASA scientists launched a series of technologically advanced telescopes into space. Dubbed the Great Observatories, these four astronomical telescopes were designed to observe areas of space with equipment that could monitor the range of frequencies on the electromagnetic spectrum.
The first of those telescopes, the Hubble Space Telescope, is perhaps the most famous of the bunch. (The other three are the Compton Gamma Ray Observatory, the Chandra X-ray Observatory and the Spitzer Space Telescope.) For one thing, it alone among the group can be actively maintained in space by astronauts.
