NASA\'s Juno mission to Jupiter has successfully changed its orbit in preparation for a 2016 arrival at the giant gas planet, the space agency says. In performing its first deep-space maneuver, the spacecraft initiated the first of two planned firings of its main engine to refine the spacecraft\'s trajectory, setting the stage for a gravity assist from a flyby of Earth Oct 9, 2013, that will send it on its way for arrival at Jupiter July 4, 2016, NASA Jet Propulsion Laboratory in Pasadena, Calif., said Thursday. The engine was fired for 29 minutes, 39 seconds, changing the spacecraft\'s velocity by about 770 mph, JPL said. \"This first and successful main engine burn is the payoff for a lot of hard work and planning by the operations team,\" JPL Juno Project Manager Rick Nybakken said. The burn occurred when Juno was more than 300 million miles away from Earth. A second one is planned for Sept. 4. \"We still have the Earth flyby and another 1.4 billion miles and four years to go to get to Jupiter,\" said Scott Bolton, Juno\'s principal investigator at the Southwest Research Institute in San Antonio. Juno was launched Aug. 5, 2011.