Hubble Space Telescope
The first of NASA's four Great Observatories. Astronauts aboard space shuttle Discovery deployed Hubble Space Telescope on April 25, 1990. It was the first big telescope designed to escape the blurring effects of Earth's atmosphere, allowing it to see the universe more clearly than any other telescope. Its observations showed that the universe is about 13.7 billion years old. They also provided some of the first evidence of "dark energy" -- a force that's causing the universe to expand faster as it ages. Several repair and refurbishing missions by shuttle astronauts have kept the telescope going and vastly improved its scientific capabilities. It is expected to continue operating until around 2015.