The Hubble Space Telescope (HST) is one of the most important instruments in the history of astronomy. Launched in 1990, the Hubble orbits the Earth at an altitude of approximately 589 km. Although the idea of a space telescope was originally conceived in 1946, it took 44 years of technical struggles and budget problems before one was actually put into operation. Hubble is part of NASA's Great Observatories program, which includes the Chandra X-ray Observatory, the Spitzer Space Telescope, and the Compton Gamma Ray Observatory.
The Hubble Space Telescope is probably most famous for its picture known as the Hubble Ultra Deep Field, which shows extremely faint galaxies billions of light years away. It is the most distant and sensitive optical image ever taken. The Hubble Ultra Deep Field is considered on par with The Blue Marble as among the most famous space photographs ever taken.
There are numerous advantages to putting a telescope above the Earth's atmosphere. For one, the atmospheric twinkle effect is gone. Secondly, there is no background light being reflected off air particles, where interferes with taking optical images.
Weighing in at 11,110 kg (24,250 lb), Hubble circles the Earth every 96–97 minutes, orbiting at a speed of 7,500 m/s (16,800 mph). The bandwidths of light it can image are optical, ultraviolet, and near-infrared. For ultraviolet, it is a unique telescope, because UV rays are almost completely blocked by our ozone layer. Although they can cause cancer to human beings, UV rays provide important information about various astronomical objects. Hubble images the relevant portions of sky and sends the information down to control centers on Earth through high-bandwidth radio communications.
The advantages of space telescopes over ground telescopes was first advanced by Lyman Spitzer in 1946, who is considered the "father" of the Space Telescope. His paper Astronomical advantages of an extra-terrestrial observator pointed out the improvements in angular resolution and optical bandwidth that a space telescope would have. This led to the proposal being funded by NASA. Today, images from the Hubble Space Telescope are among NASA's finest PR and education tools.