The spacecraft launched on August 5, 2011 to start its six year mission, culminating in a Jupiter arrival in 2016. The probe's trajectory included a flyby of Earth designed to conserve fuel. Unlike previous missions to the outer Solar System, Juno's energy will come only from solar panels, despite the relative dimness of the Sun at Jupiter's orbit.
|Juno's trajectory from launch in 2011 to arrival at Jupiter in 2016.|
In 2012, Juno executed several deep-space-maneuvers that prepared the probe for its flyby of Earth. Next, in October 2013, Juno completed its Earth flyby, assuming a trajectory directly toward Jupiter.
On July 4, 2016, the spacecraft executed an engine burn that inserted it into orbit around Jupiter. The probe assumed a highly elliptical orbit that took it past the north and south poles of Jupiter with every revolution.
The image above shows Juno's orbits around Jupiter over time, beginning with the orbital insertion on July 4.
This image, Juno's first acquired from orbit, shows the gas giant as well as three of the four Galilean moons, Io, Europa, and Ganymede (from left to right).
After its initial insertion burn, the Juno spacecraft spent over two months completing an elongated orbit that took it far away from the Solar System's largest planet. The first of 37 science flyby took place on August 27 and brought Juno over the north pole of Jupiter, capturing the first ever image of this polar region (see below).
The polar region is very different in appearance than the midlatitudes and equatorial region of Jupiter. The latter regions have characteristic colored bands of red, white, and orange, as well as prominent storm features. The poles are bluer, and lack these storm features. Juno's initial orbit was 53.4 days in duration. At its second closest approach to Jupiter on October 19, a maneuver was planned that would reduce the orbit to 14 days. However, the spacecraft entered safe mode just before the flyby when the onboard computer found conditions to be awry and neither data collection nor orbital maneuvering occurred on the 19th. Juno was later found to be functioning normally.
After two more successful flybys on December 11, 2016 and February 2, 2017, mission directors decided to not risk the reduction maneuver and maintain Juno in its 53-day orbit indefinitely. The main impediment to the function of the probe was the radiation belts near Jupiter's poles, which would gradually deteriorate Juno's functioning with every flyby. Since this radiation is only significant at closest approach, the longer orbit will not prevent the spacecraft from making the planned number of flybys. However, it did reduce their frequency by a factor of almost 4. Originally, 33 total orbits were planned in less than 1.5 years. The adapted budget plan covered only 12 orbits through July 2018, a span of two years.
Nevertheless, valuable data and images continued to pour in. The image below is a color-enhanced view of Jupiter's south pole, highlighting the massive swirling storms circling the pole.
Juno will hopefully provide further information concerning the formation and evolution of Jupiter, specifically about its interior, about which little is known.
Sources: https://www.missionjuno.swri.edu/news/juno_spacecraft_in_orbit_around_mighty_jupiter, https://www.nasa.gov/feature/jpl/nasa-s-juno-spacecraft-sends-first-in-orbit-view, http://www.nytimes.com/2016/07/05/science/juno-enters-jupiters-orbit-capping-5-year-voyage.html?_r=0, https://www.nasa.gov/feature/jpl/jupiter-s-north-pole-unlike-anything-encountered-in-solar-system, https://www.nasaspaceflight.com/2016/09/juno-closest-approach-jupiter-readies-for-primary-science-mission/, https://www.nasa.gov/press-release/nasa-s-juno-mission-to-remain-in-current-orbit-at-jupiter