The Space Shuttle was a partially reusable low Earth orbital spacecraft system that was operated from 1981 to 2011 by the U. S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program name was Space Transportation System (STS), taken from a 1969 plan for a system of reusable spacecraft of which it was the only item funded for development. The first of four orbital test flights occurred in 1981, leading to operational flights beginning in 1982. In addition to the prototype whose completion was cancelled, five complete Shuttle systems were built and used on a total of 135 missions from 1981 to 2011, launched from the Kennedy Space Center (KSC) in Florida. Operational missions launched numerous satellites, interplanetary probes, and the Hubble Space Telescope (HST); conducted science experiments in orbit; and participated in construction and servicing of the International Space Station. The Shuttle fleet’s total mission time was 1322 days, 19 hours, 21 minutes and 23 seconds.
Dr. Porco believes that the icy moon, with its underground liquid sea of water, organics, as well as an energy source, may potentially host life similar to that found in analogous environments on Earth. The March 2012 images of Cassini's "tiger stripes" revealed that these cracks widen and narrow, as was suspected from pictures taken previously. The fissures also change over time more frequently than was originally thought. The two opposite sides of the fissures move laterally relative to one another. This is analogous to the way two banks of the San Andreas Fault can move forward and back, as well as in opposite directions. The greatest slipping and sliding happens when Enceladus is closest to Saturn--as scientists expected. Despite this oddball moon's many exotic attributes, it actually sports one of the most Earth-like surfaces in our Solar System. Titan may also experience volcanic activity, but its volcanoes would erupt with different ingredients than the molten-rock lava that shoots out from the volcanoes of Earth. In dramatic contrast to what occurs on our own planet, Titan's volcanoes erupt icy water "lava" (cryovolcanism). Titan's entire alien surface has been sculpted by gushing methane and ethane, which carves river channels, and fills its enormous great lakes with liquid natural gas. There are over 100 moons dancing around the eight major planets of our Sun's family. Most of them are small, frozen, icy objects, harboring only a relatively scanty amount of rocky material, that circle around the quartet of giant gaseous planets that dwell in the outer, frigid realm of our Solar System--far from the comforting warmth and brilliance of our Star. The quartet of majestic, giant denizens of our outer Solar System--Jupiter, Saturn, Uranus, and Neptune--are enveloped with gaseous atmospheres, and orbited by a multitude of dancing, sparkling moons and moonlets. In marked contrast, the inner region of our Solar System--where our Earth dwells--is almost bereft of moons. Of the quartet of relatively petite, rocky "terrestrial" planets--Mercury, Venus, Earth, and Mars--only Earth is circled by a large Moon. Mercury and Venus are moonless, and Mars is orbited by a duo of tiny, lumpy, potato-shaped moons, Phobos and Deimos. Phobos and Deimos are probably escaped asteroids, born in the Main Asteroid Belt between Mars and Jupiter, that were captured by the gravitational embrace of the Red Planet long ago.