Juno is a NASA space probe orbiting the planet Jupiter. Built by Lockheed Martin and operated by NASA Jet Propulsion Laboratory, the spacecraft was launched from Cape Canaveral Air Force Station on August 5, 2011, 16:25:00 UTC, as part of the New Frontiers program. Juno entered a polar orbit of Jupiter on July 5, 2016, 03:53:00 UTC, to begin a scientific investigation of the planet. After completing its mission, Juno was originally planned to be intentionally deorbited into Jupiter's atmosphere, but has since been approved to continue orbiting until contact is lost with the spacecraft.Mission to Jupiter: Juno, JPL: "Now in its extended mission, Juno will continue its investigation of the solar system's largest planet through September 2025, or until the spacecraft's end of life." It will continue to explore Jupiter to study Jovian rings and the inner moons area, which is not well explored; this phase will also include close flybys of the moons Thebe, Amalthea, Adrastea, and Metis.
Juno mission is to measure Jupiter's composition, gravitational field, magnetic field, and polar magnetosphere. It also searches for clues about how the planet formed, including whether it has a rocky core, the amount of water present within the deep atmosphere, mass distribution, and its deep winds, which can reach speeds up to .
Juno is the second spacecraft to orbit Jupiter, after the RTG-powered Galileo orbiter, which orbited from 1995 to 2003. Unlike all earlier spacecraft sent to the outer Solar System and beyond—which used radioisotope thermoelectric generators for power—Juno is powered by solar panels, more commonly used by satellites orbiting Earth and working in the inner Solar System. Accordingly, Juno required the three largest solar panel wings ever deployed on a planetary probe (at the time of launching). These play an integral role in stabilizing the spacecraft as well as generating power.
As of August 6, 2026, Juno remained operational and in contact with Earth through the NASA Deep Space Network.
Naming
A NASA compilation of mission names and acronyms referred to the mission by the backronym Jupiter Near-polar Orbiter. However the project itself has consistently described it as a name with mythological associations and not an acronym. The spacecraft's current name is in reference to the Roman goddess Juno. Juno is sometimes called the New Frontiers 2 as the second mission in the New Frontiers program, but is not to be confused with New Horizons 2, a proposed but unselected New Frontiers mission.
Overview
Juno was selected on June 1, 2005, as the next New Frontiers mission after New Horizons. The desire for a Jupiter probe was strong in the years prior to this, but there had not been any approved missions. The Discovery Program had passed over the somewhat similar but more limited Interior Structure and Internal Dynamical Evolution of Jupiter (INSIDE Jupiter) proposal, and the turn-of-the-century era Europa Orbiter was canceled in 2002. The flagship-level Europa Jupiter System Mission was in the works in the early 2000s, but funding issues resulted in it evolving into ESA's Jupiter Icy Moons Explorer.
Juno completed a five-year cruise to Jupiter, arriving on July 5, 2016. The spacecraft traveled a total distance of roughly to reach Jupiter. The spacecraft was designed to orbit Jupiter 37 times over the course of its mission. This was originally planned to take 20 months.
Juno trajectory used a gravity assist speed boost from Earth, accomplished by an Earth flyby in October 2013, two years after its launch on August 5, 2011. The spacecraft performed an orbit insertion burn to slow it enough to allow capture. It was expected to make three 53-day orbits before performing another burn on December 11, 2016, that would bring it into a 14-day polar orbit called the Science Orbit. Because of a suspected problem in Juno main engine, the burn scheduled on December 11, 2016, was cancelled and Juno remained in its 53-day orbit until the first Ganymede encounter of its Extended Mission. This extended mission began with a flyby of Ganymede on June 7, 2021. Subsequent flybys of Europa and then Io decreased the orbital period to 33 days by February 2024.
During the science mission, infrared and microwave instruments will measure the thermal radiation emanating from deep within Jupiter's atmosphere. These observations will complement previous studies of its composition by assessing the abundance and distribution of water, and therefore oxygen. This data will provide insight into Jupiter's origins. Juno will also investigate the convection that drives natural circulation patterns in Jupiter's atmosphere. Other instruments aboard Juno will gather data about its gravitational field and polar magnetosphere. The Juno mission was planned to conclude in February 2018 after completing 37 orbits of Jupiter, but now has been commissioned through 2025 to do a further 42 additional orbits of Jupiter as well as close flybys of Ganymede, Europa and Io. The probe was then intended to be deorbited and burnt up in Jupiter's outer atmosphere to avoid any possibility of impact and biological contamination of one of its moons.
Flight trajectory
Launch Juno was launched atop an Atlas V (551 configuration) at Cape Canaveral Air Force Station (CCAFS), Florida on August 5, 2011, 16:25:00 UTC. The Atlas V (AV-029) used a Russian-built RD-180 main engine, powered by kerosene and liquid oxygen. The main engine ignited and underwent checkout then, 3.8 seconds later, the five strap-on solid rocket boosters (SRBs) ignited. Following the SRB burnout, about 93 seconds into the flight, two of the spent boosters fell away from the vehicle, followed 1.5 seconds later by the remaining three. When heating levels had dropped below predetermined limits, the payload fairing that protected Juno during launch and transit through the thickest part of the atmosphere separated, about 3 minutes 24 seconds into the flight. The Atlas V main engine cut off 4 minutes 26 seconds after liftoff. Sixteen seconds later, the Centaur second stage ignited, and it burned for about 6 minutes, putting the satellite into an initial parking orbit. The vehicle coasted for about 30 minutes, and then the Centaur was reignited for a second firing of 9 minutes, placing the spacecraft on an Earth escape trajectory in a heliocentric orbit.
Prior to separation, the Centaur stage used onboard reaction engines to spin Juno up to 1.4 r.p.m. About 54 minutes after launch, the spacecraft separated from the Centaur and began to extend its solar panels. Following the full deployment and locking of the solar panels, Juno batteries began to recharge. Deployment of the solar panels reduced Juno spin rate by two-thirds. The probe is spun to ensure stability during the voyage and so that all instruments on the probe are able to observe Jupiter.Juno Mission Profile & Timeline
The voyage to Jupiter took five years, and included two orbital maneuvers in August and September 2012 and a flyby of the Earth on October 9, 2013. When it reached the Jovian system, Juno had traveled approximately .
Deep space maneuvers and flyby of the Earth
After traveling for about a year in an elliptical heliocentric orbit, Juno performed two deep space maneuvers (DSMs), firing its engine twice near aphelion (beyond the orbit of Mars) to change its orbit and return to pass by the Earth at a distance of 559 kilometers in October 2013. The combination of the DSMs and the resulting Earth flyby helped Juno slingshot itself toward the Jovian system in a maneuver called a gravity assist. The spacecraft received a boost in speed of more than , and it was set on a course to Jupiter. The flyby was also used as a rehearsal for the Juno science team to test some instruments and practice certain procedures before the arrival at Jupiter.
Insertion into Jovian orbit Jupiter's gravity accelerated the approaching spacecraft to around . On July 5, 2016, between 03:18 and 03:53 UTC Earth-received time, an insertion burn lasting 2,102 seconds decelerated Juno by and changed its trajectory from a hyperbolic flyby to an elliptical, polar orbit with a period of about 53.5 days. The spacecraft successfully entered Jovian orbit on July 5, 2016, at 03:53 UTC.
Orbit and environment
Juno highly elliptical initial polar orbit takes it within of the planet and out to , far beyond Callisto's orbit. An eccentricity-reducing burn, called the Period Reduction Maneuver, was planned that would drop the probe into a much shorter 14 day science orbit. Originally, Juno was expected to complete 37 orbits over 20 months before the end of its mission. Due to problems with helium valves that are important during main engine burns, mission managers announced on February 17, 2017, that Juno would remain in its original 53-day orbit, since the chance of an engine misfire putting the spacecraft into a bad orbit was too high. Juno completed only 12 science orbits before the end of its budgeted mission plan, ending July 2018. In June 2018, NASA extended the mission through July 2021.
The orbits were carefully planned in order to minimize contact with Jupiter's dense radiation belts, which can damage spacecraft electronics and solar panels, by exploiting a gap in the radiation envelope near the planet, passing through a region of minimal radiation. The Juno Radiation Vault, with 1-centimeter-thick titanium walls (three times as thick as the Galileo spacecraft body's), also aids in protecting Juno electronics by reducing the incoming radiation by a factor of 800. Despite the intense radiation, JunoCam and the Jovian Infrared Auroral Mapper (JIRAM) were designed to endure at least eight orbits, while the Microwave Radiometer (MWR) was made to endure at least eleven orbits. All instruments are operational as of perijove 71. Although the flux of electrons close to Jupiter is about ten times as high as it is around Jupiter's moon Europa, Juno will still receive a lower total dose of radiation in its polar orbit (20 Mrad through end of mission) than the Galileo orbiter received in its equatorial orbit. Galileo subsystems were damaged by radiation during its mission, including an LED in its data recording system.
Orbital operations
The spacecraft completed its first flyby of Jupiter (perijove 1) on August 26, 2016, and captured the first images of the planet's north pole.
On October 14, 2016, days prior to perijove 2 and the planned Period Reduction Maneuver, telemetry showed that some of Juno helium valves were not opening properly. On October 18, 2016, some 13 hours before its second close approach to Jupiter, Juno entered into safe mode, an operational mode engaged when its onboard computer encounters unexpected conditions. The spacecraft powered down all non-critical systems and reoriented itself to face the Sun to gather the most power. Due to this, no science operations were conducted during perijove 2.
On December 11, 2016, the spacecraft completed perijove 3, with all but one instrument operating and returning data. One instrument, JIRAM, was off pending a flight software update. Perijove 4 occurred on February 2, 2017, with all instruments operating. Perijove 5 occurred on March 27, 2017. Perijove 6 took place on May 19, 2017.
Although the mission's lifetime is inherently limited by radiation exposure, almost all of this dose was planned to be acquired during the perijoves. , the 53.4 day orbit was planned to be maintained through July 2018 for a total of twelve science-gathering perijoves. At the end of this prime mission, the project was planned to go through a science review process by NASA's Planetary Science Division to determine if it will receive funding for an extended mission. In June 2018, NASA extended the mission operations plan to July 2021.
Extended missions