Launched as GRAIL A and GRAIL B in September 2011, the probes were renamed Ebb and Flow by schoolchildren in Montana. The probes operated in almost circular orbit near the lunar poles at an altitude of approximately 34 miles, until their mission came to an end in December 2012. The distance between the twin probes altered a bit as they soared over areas of lesser and greater gravity that were caused by visible topological features on the Moon's surface, such as impact craters and mountains--as well as by masses that were secreted beneath the lunar surface.
Dr. Porco further believes that Enceladus's orbit could have been much more eccentric in the past. The greater the eccentricity, the greater the tidal squeezing, and the resulting structural variations produce heat. In this case, the heat would have been saved inside the icy moon, melting some of the ice to replenish the liquid water sea. Dr. Porco continued to explain that "(T)he tidal flexing occurring now is not enough to account for all the heat presently coming out of Enceladus. One way out of this dilemma is to assume that some of the heat observed today was generated and stored internally in the past... (N)ow that the orbit's eccentricity has lessened, the heat emanating from the interior is a combination of heat produced today and in the past."
When President John F. Kennedy stated in 1960's that the US will go to the moon in less than a decade, most people were extremely skeptical. The reason for this stemmed from the fact that USSR had shown more accomplishments in the space race after the launch of Sputnik, which was the world's first satellite. Naturally, the skepticism was unfounded, since the US put all of its efforts in to the Moon program as billions of dollars were put in to it. The development of the Saturn rocket as well as the development of the Apollo lunar module took less than a decade, since the whole heart and soul of the American public was put into the Lunar program. Even the various tragedies such as the loss of Astronauts in the Apollo fire tragedy didn't deter the public. As a result, 1969 was an important year in the human history as mankind stepped into Lunar soil for the first time. Sadly, the program was discontinued and since the 1970's, no man has even stepped into the Lunar soil ever again.