NASA launched the Juno spacecraft on its way to Jupiter in August of 2011. The spacecraft is due to reach Jupiter on July 4, 2016. In order for the spacecraft to reach the velocity needed to make it to Jupiter by 2016 NASA scientists put Juno into a looping orbit that would use the Earth's gravity to slingshot the spacecraft to 16,330 mph.
Yesterday Juno was supposed to have completed the second of two critical main engine firings to adjust the spacecraft's course and place it on the property trajectory to pass 310 miles above the Earth on October 9, 2013. That October flyby will complete Juno's first elliptical orbit around the sun. Juno performed the first "deep space maneuver" requiring the firing of its main engine last Thursday on August 30.
That firing required the engine to be active for 29 minutes and 39 seconds changing the spacecraft velocity by about 770 mph. The firing also consumed 829 pounds of fuel. The reason the critical second firing of the main engine was delayed this week had to do with an unexpectedly high propellant pressure within the spacecraft propulsion system. The spacecraft controllers decided to delay the burn to give them an extra 10 days to examine the pressure increase and consider options to mitigate any potential catastrophe.
The second main engine firing has been rescheduled to September 14 and will not affect the mission. Juno will eventually reach a speed of 160,000 mph, making it the fastest man-made object ever, before slowing down to enter orbit around Jupiter. When Juno arrives at Jupiter in 2016 its main engine will fire for 30 minutes placing it into a 107 day capture orbit around Jupiter. The goal of the Juno mission is to investigate Jupiter's origins, interior structure, atmospheric dynamics, and polar magnetosphere.