Twenty-four months since its launch from Cape Canaveral Air Force Station, Fla., NASA’s Juno mission officially passed the halfway point in a five-year journey to Jupiter yesterday (Monday). The spacecraft—which will examine the structure and composition of the Solar System’s largest planet and search for clues about its formation from a unique polar orbit—reached the milestone at 8:25 a.m. EDT (5:25 a.m. PDT) on 12 August.
“Juno’s odometer just clicked over to 9.464 Astronomical Units,” said Principal Investigator Scott Bolton of the Southwest Research Institute in San Antonio, Texas. “The team is looking forward, preparing for the day we enter orbit around the most massive planet in our Solar System.”
To put that in perspective, a single Astronomical Unit—equivalent to about 93 million miles—represents the mean distance between Earth and the Sun. By this yardstick, Juno’s accomplishment means that it has traveled 879,733,760 miles since its 5 August 2011 launch. At the time it hit the halfway point, it was approximately 34.46 million miles from Earth, following a convoluted trajectory which will see it perform a close flyby of our Home Planet on 9 October 2013 to receive a gravity-assisted boost toward Jupiter.
“Juno will come within 347 miles of Earth,” said Project Manager Rick Nybakken of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “The Earth flyby will give Juno a kick in the pants, boosting its velocity by 16,330 mph. From there, it’s ‘Next stop, Jupiter.’”
Upon arrival at the planet on 4 July 2016, Juno will spend a little more than one Earth-year completing 33 orbits of Jupiter, from pole to pole. Each orbit will take approximately 11 Earth-days to complete and will describe a highly elongated path, reaching a close point of 2,672 miles and extending far beyond the orbit of Jupiter’s outermost “Galilean” moon, Callisto. This type of orbit will help Juno to avoid long-duration contact with the giant planet’s harsh radiation belts, which have the potential to damage its electronics and—for the first time on a Jupiter-bound mission—its electricity-generating solar arrays.
Its eight on-board instruments will probe the mysterious world’s thick cloud cover and are expected to uncover new findings about its origins, structure, atmosphere, and magnetosphere. The mission will study Jupiter’s deep winds, which are known to blow at up to 384 mph, and will utilize infrared and microwave sensors to measure internal thermal radiation. Juno will be intentionally deorbited into the Jovian atmosphere in October 2017 to eliminate the possibility of a collision and contamination of any of Jupiter’s moons. Like Juno’s mythological namesake—the wily goddess Juno, wife of Jupiter, the king of the gods in the ancient Roman pantheon—the spacecraft will peer through the planet’s gaseous mask and uncover details about its true nature.
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