An artist's concept of Juno at Jupiter
|Major contractors||Lockheed Martin Corporation|
|Launch date||12:25:00, August 5, 2011 (EDT) (16:25:00 UTC)
elapsed: 1 year, 9 months, and 18 days
|Launch vehicle||Atlas V 551 (AV-029)|
|Launch site||SLC-41, Cape Canaveral, Florida|
|Mission duration||6 Earth years (cruise: 5 years, science: 1 year)|
|Satellite of||Jupiter (planned)|
|Orbital insertion date||August 2016|
|Mass||3,625 kilograms (7,990 lb)|
|Batteries||Two 55 amp-hour Lithium-Ion|
|Periapsis||4,300 kilometers (2,700 mi)|
|Main instruments||Microwave radiometer, Jovian Infrared Auroral Mapper, Advanced Stellar Compass, Jovian Auroral Distribution Experiment, Jovian Energetic Particle Detector Instrument, Radio and Plasma Wave Sensor, Ultraviolet Imaging Spectrograph, JunoCam|
|Imaging resolution||(JunoCam) 15 km/pixel|
|Transponders||4 (2 X-band, 2 Ka-band)|
Juno is a NASA New Frontiers mission to the planet Jupiter. Juno was launched from Cape Canaveral Air Force Station on August 5, 2011. The spacecraft is to be placed in a polar orbit to study the planet's composition, gravity field, magnetic field, and polar magnetosphere. Juno will also search for clues about how Jupiter formed, including whether the planet has a rocky core, the amount of water present within the deep atmosphere, and how the planet's mass is distributed. It will also study Jupiter's deep winds, which can reach speeds of 618 kilometers per hour (384 mph).
The spacecraft's name comes from Greco-Roman mythology. The god Jupiter drew a veil of clouds around himself to hide his mischief, but his wife, the goddess Juno, was able to peer through the clouds and see Jupiter's true nature.
Mission summary 
Juno requires a five-year cruise to Jupiter, arriving around July 4, 2016. The spacecraft will travel roughly over a total distance of 2.8 billion kilometers (18.7 AU; 1.74 billion miles). The spacecraft will orbit Jupiter 33 times during one Earth year. Juno's trajectory will use a gravity assist speed boost from Earth, accomplished through an Earth flyby two years (October 2013) after its August 5, 2011 launch. In 2016, the spacecraft will perform an orbit insertion burn to slow the spacecraft enough to allow capture into an 11-day polar orbit. Once Juno enters into its orbit, infrared and microwave instruments will begin to measure the thermal radiation emanating from deep within Jupiter's atmosphere. These observations will complement previous studies of the planet's composition by assessing the abundance and distribution of water, and therefore oxygen. While filling missing pieces of the puzzle of Jupiter's composition, these data will also provide insight into the planet's origins. Juno will also investigate the convection that drives general circulation patterns in Jupiter's atmosphere. Meanwhile, other instruments aboard Juno will gather data about the planet's gravitational field and polar magnetosphere. The Juno mission is set to conclude in October 2017, after completing 33 orbits around Jupiter, when the probe will be de-orbited to crash into Jupiter so as to avoid any possibility of it impacting its moons.
Scott Bolton of the Southwest Research Institute in San Antonio, Texas is the principal investigator and is responsible for all aspects of the mission. The Jet Propulsion Laboratory in California manages the mission and Lockheed Martin Corporation is responsible for the spacecraft development and construction. The mission is being carried out with the participation of several institutional partners. Co-investigators include Toby Owen of the University of Hawaii, Andy Ingersol of California Institute of Technology, Fran Bagenal of the University of Colorado at Boulder, and Candy Hansen of the Planetary Science Institute. Jack Connerney of the Goddard Space Flight Center served as instrument lead.
Launch timeline 
The Atlas V (AV-029) Russian-designed RD-180 main engine, powered by kerosene and liquid oxygen, was started and underwent checkout 3.8 seconds prior to the ignition of five strap-on solid rocket boosters (SRBs). Following SRB burnout, approximately 1 minute 33 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 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. 16 seconds later, the Centaur second stage ignited and burned for approximately 6 minutes, putting the satellite into an initial parking orbit.
The vehicle coasted for approximately 30 minutes, and then the Centaur was re-ignited for a second firing of 9 minutes, putting the spacecraft on an Earth escape trajectory.
Prior to separation the Centaur stage used onboard reaction engines to spin Juno up to 1.4 RPM. 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's batteries began to recharge. Successful deployment of the solar panels reduced Juno's 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.
Scientific objectives 
The Juno spacecraft's suite of science instruments will:
- Determine the ratio of oxygen to hydrogen, effectively measuring the abundance of water in Jupiter, which will help distinguish among prevailing theories linking the gas giant's formation to the Solar System.
- Obtain a better estimate of Jupiter's core mass, which will also help distinguish among prevailing theories linking the gas giant's formation to the Solar System.
- Precisely map Jupiter's gravity to assess the distribution of mass in Jupiter's interior, including properties of the planet's structure and dynamics.
- Precisely map Jupiter's magnetic field to assess the origin and structure of the field and how deep in Jupiter the magnetic field is created. This experiment also will help scientists understand the fundamental physics of dynamo theory.
- Map the variation in atmospheric composition, temperature, structure, cloud opacity and dynamics to pressures far greater than 100 bars (10 MPa; 1450 pound/sq inch) at all latitudes.
- Characterize and explore the three-dimensional structure of Jupiter's polar magnetosphere and its auroras.
This type of orbit helps the craft avoid any long term contact with Jupiter's radiation belts, which can cause damage to spacecraft electronics and solar panels. The "Juno Radiation Vault", with 1 cm thick titanium walls, will also aid in protecting and shielding Juno's electronics. The spacecraft is planned to complete at least 33 polar orbits, each taking from eleven to fourteen days.
Scientific instruments 
||The primary goal of the radiometer is to probe the deep atmosphere of Jupiter at radio wavelengths ranging from 1.3 cm to 50 cm using six separate radiometers to measure the planet's thermal emissions.
||The primary goal of JIRAM is to probe the upper layers of Jupiter's atmosphere down to pressures of 5–7 bars (72–102 pound/square inch) at infrared wavelengths in the 2–5 μm interval using an imager and a spectrometer.|
||The magnetic field investigation has three goals: mapping of the magnetic field, determining the dynamics of Jupiter's interior, and determination of the three-dimensional structure of the polar magnetosphere. The magnetometer experiment consists of the Flux Gate Magnetometer (FGM), which will measure the strength and direction of the magnetic field lines, and the Advanced Stellar Compass (ASC), which will monitor the orientation of the magnetometer sensors.
||The Gravity Science Investigation will probe the mass properties of Jupiter by using the communication subsystem to perform Doppler tracking. Gravity Science is a distributed instrument. It includes the X-Band and Ka-Band transponders on the spacecraft and the 34-meter Deep Space Network antenna at Goldstone, California.
||JADE will resolve the plasma structure of the Jovian aurora by measuring the angular, energy and compositional distributions of particles in the polar magnetosphere of Jupiter.
||JEDI will measure the energy and angular distribution of hydrogen, helium, oxygen, sulfur and other ions in the polar magnetosphere of Jupiter.
||This instrument will identify the regions of auroral currents that define Jovian radio emissions and acceleration of the auroral particles by measuring the radio and plasma spectra in the auroral region.
||UVS will record the wavelength, position and arrival time of detected ultraviolet photons during the time when the spectrograph slit views Jupiter during each turn of the spacecraft. Using a 1024 × 256 micro channel plate (MCP) detector, it will provide spectral images of the UV auroral emissions in the polar magnetosphere.
||A visible light camera/telescope, included in the payload to facilitate education and public outreach. It will operate for only seven orbits around Jupiter because of the planet's damaging radiation and magnetic field.|
Solar panels 
Juno is the first mission to Jupiter using solar panels instead of the radioisotope thermoelectric generators (RTGs) used by Pioneer 10, Pioneer 11, the Voyager program, Cassini–Huygens, and the Galileo orbiter. Once in orbit around Jupiter, Juno will receive 4% as much sunlight as we do on Earth, but advances made in both solar cell technology and efficiency over the past several decades makes it economically feasible to use solar panels of practical size to provide power at a distance of 5 AU from the Sun.
The Juno spacecraft uses three solar arrays symmetrically arranged around the spacecraft, which were stowed against the sides of the spacecraft for launch. Shortly after the spacecraft cleared Earth's atmosphere the arrays were deployed. Two of the arrays have four hinged segments each, and the third array has three segments with a magnetometer in place of the fourth segment. Each panel or array is 2.7 meters (8.9 ft), by 8.9 meters (29 ft) long, the biggest on any NASA deep-space probe. One of the panels is slightly narrower than the others; this is to facilitate their stowage for launch. These smaller panels are 2.091 meters (6.86 ft) wide. The total area of the arrays is 60 square meters (650 sq ft). If the arrays were optimized to operate at Earth, they would produce 12 to 14 kilowatts of power. Only 486 W will be generated when Juno arrives at Jupiter, declining to 420 W as radiation degrades the cells. The solar panels will remain in sunlight continuously from launch through to the end of the mission, except for short periods during the operation of the main engine.
A central power distribution and drive unit monitors the power that is generated by the solar arrays, distributes it to instruments, heaters and experiment sensors as well as batteries that are charged when excess power is available. Two 55 amp-hour lithium-ion batteries will provide power to the vehicle when it passes through eclipse. Those batteries will be able to withstand the radiation environment of Jupiter.
Juno's telecommunication systems have more in common with New Horizons than with Cassini–Huygens spacecraft. Juno supports tone fault signalling for cruise mode operations, but it is expected to be used less often. Communications are via the 70 m antennae of the Deep Space Network (DSN) utilizing an X-band direct link. The Command & Data processing of the Juno spacecraft includes a flight computer capable of providing ~50 Mbit/s of instrument throughput. Gravity science subsystems use X-band and Ka-band doppler tracking and autoranging.
Propulsion system 
Juno uses a bipropellant Leros-1b main engine, manufactured by AMPAC-ISP in Westcott, UK. It uses hydrazine and nitrogen tetroxide for propulsion and provides a thrust of 645 newtons. It is fixed to the spacecraft body and is used for major burns. The engine bell is enclosed in a debris shield. Juno utilizes a monopropellant reaction control system (RCS) consisting of twelve jets that are mounted on four rocket engine modules. These thrusters are used for control of the vehicle’s orientation and to perform trajectory correction maneuvers.
Galileo's plaque and LEGO figurines 
Juno carries a plaque to Jupiter dedicated to Galileo Galilei. The plaque was provided by the Italian Space Agency and measures 2.8 by 2 inches (7.1 by 5.1 cm). It is made of flight-grade aluminum and weighs 6 grams (0.21 oz). The plaque depicts a portrait of Galileo and a text in Galileo's own hand, penned in January 1610, while observing what would later be known to be the Galilean moons. The text translates as:
On the 11th it was in this formation, and the star closest to Jupiter was half the size than the other and very close to the other so that during the previous nights all of the three observed stars looked of the same dimension and among them equally afar; so that it is evident that around Jupiter there are three moving stars invisible till this time to everyone.
The spacecraft also carries three LEGO figurines representing Galileo, the Roman god Jupiter and his wife Juno. In Roman mythology, Jupiter drew a veil of clouds around himself to hide his mischief. From Mount Olympus, Juno was able to look into the clouds and reveal her husband's real nature. Juno holds a magnifying glass as a sign for searching for the truth and her husband holds a lightning bolt. The third LEGO crew member, Galileo Galilei, has his telescope with him on the journey.
Although most LEGO toys are made of plastic, LEGO made these figures of aluminum to endure the extreme conditions of space flight.
Juno was originally proposed at a cost of approximately US$700 million (FY03) for a June 2009 launch. NASA budgetary restrictions resulted in postponement until August 2011, and a launch on board an Atlas V rocket in the 551 configuration. As of June 2011[update], the mission was projected to cost $1.1 billion over its life.
See also 
- Moons of Jupiter
- Atmosphere of Jupiter
- Comet Shoemaker–Levy 9
- Exploration of Jupiter
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|Wikimedia Commons has media related to: Juno|
- Official website on NASA.gov
- Juno mission web site on South West Research Institute
- Juno Mission Profile by NASA's Solar System Exploration
- NASA Selects New Frontiers Concept Study: Juno Mission to Jupiter at NASA Jet Propulsion Laboratory
- The Juno Mission to Jupiter at Space.com
- NASA 360 New Worlds New Discoveries 1/2. Retrieved June 30, 2011.