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. Beneath The Icy Crust Of Enceladus. The research paper written by scientists with the Cassini mission, published in the journal Science, suggests the presence of hydrogen gas. Hydrogen gas, that could potentially provide a chemical energy source for life, is pouring into the subsurface ocean of Enceladus from hydrothermal activity on the seafloor of this bewitching, distant moon-world. A moon is a natural body that is in orbit around a planet, and it is kept in place by both the host planet's gravity and the gravity of the moon itself. Some planets possess orbiting moons; some do not. There are several theories explaining how Earth's Moon came to be. At this point, the favored model is termed the giant impact theory, often playfully called the Big Whack or Big Splash theory by astronomers when they are in a humorous frame of mind. These funny nicknames were derived from the central tenet of the theory, which is that a Mars-sized body, named Theia, smacked into the primordial Earth billions of years ago. The collision caused part of our planet's crust to be hurled violently into space. Some of this shattered, somersaulting debris was snared into Earth-orbit, where it formed a host of moonlets that were ultimately pulled together by gravity to evolve into our Moon.