Juno Spacecraft

Juno was carefully designed to meet the tough challenges in flying a mission to Jupiter: weak sunlight, extreme temperatures and deadly radiation. The spacecraft is covered in thermal blankets to protect it from the extreme environment of space. All of the most-sensitive electronics are placed inside an armored vault to shield them from Jupiter’s deadly radiation.

OVERVIEW

Communication
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  COMMUNICATIONS SYSTEM
  How does Juno communicate with Earth when it is hundreds of millions of miles away?
  
  Communication SYSTEM
  
  Juno keeps in touch with Earth via a sophisticated two-way radio and antennas that link to NASA’s Deep Space Network. Because the spacecraft will travel so far from Earth, it can’t be steered in real time by mission controllers. A signal sent from Earth would take about 45 minutes to reach Jupiter, and it would take another 45 minutes to receive the spacecraft’s reply. This is why Juno (and other spacecraft that operate at great distances) must be able to carry out tasks automatically, following lists of instructions from Earth, and reporting its current status and the data gathered by its science instruments. For example, if Juno encounters a problem and enters the standby condition known as safe mode, the spacecraft will automatically reposition itself so that the solar arrays are pointed at the sun, and then wait for instructions from Earth.
  
  The spacecraft has five antennas, including the largest and primary communication antenna, known as the high-gain antenna. Four other antennas can be used as backups, or when the main antenna is pointed away from Earth, for certain science operations and navigation maneuvers.
  
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  The five different antennae that comprise Juno's communication system
  
  HIGH-GAIN ANTENNA (HGA)
  The high-gain antenna (named for the gain achieved though its narrowly focused beam, sits on top of the electronics vault. This 2.5-meter (8-foot) -wide, saucer-shaped radio antenna is Juno’s main communications link with Earth. It will be the primary antenna used during Juno’s time at Jupiter. The HGA has the strongest signal of the spacecraft’s five antennas, which enables Juno to transmit data at a much higher rate than the others. The antenna will transmit less power than a 40-watt light bulb, yet this will be sufficient to carry all the results from the scientific instruments, plus information about the spacecraft’s health and safety. Juno’s HGA is protected from heat produced by the sun’s harsh light with insulating blankets when it is in the inner solar system.
  In addition to its communications role, the HGA also functions as part of Juno’s Gravity Science system. Like a laser, the antenna requires extremely accurate pointing because it sends and receives radio signals in the form of a tight beam.
  
  MEDIUM-GAIN ANTENNA (MGA)
  The medium-gain antenna is one of two small antennas located next to Juno’s high-gain antenna. It has a wider field of view than the HGA so it doesn’t have to be pointed quite as precisely at the Earth to transmit and receive signals, but its signal is not as powerful. The MGA will be used during the cruise phase of the mission at times when it would be difficult to keep the high-gain antenna locked onto Earth while pointing the solar arrays more or less toward the sun.
  The MGA is the antenna that the spacecraft will most often switch to if it enters safe mode because of a problem.
  
  LOW-GAIN ANTENNAS (LGA)
  The two low-gain antennas have a wider field of view than the MGA, meaning they require less precise pointing to communicate with Earth. They have relatively weak signal strengths, so they can send data only at low rates. The fore LGA, on top of the spacecraft, is pointed in the same direction as the HGA and MGA; the aft LGA is on the bottom of the spacecraft and points in the opposite direction. Juno may use this antenna instead of the MGA sometimes if it enters safe mode.
  
  TOROIDAL LOW-GAIN ANTENNA (TLGA)
  The toroidal low-gain antenna fills in the gap between the low-gain antennas by sending its signal out of the sides of the spacecraft. This antenna comes in handy during maneuvers when the other antennas must be pointed far away from Earth. Juno will rely on its TLGA during a couple of critical moments: the Deep Space Maneuvers, which adjust the spacecraft’s path on the way to Jupiter, and the Jupiter Orbit Insertion burn that will be executed upon arrival at the giant planet.
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  Deep Space Network
  A global array of giant radio dishes allows NASA to communicate with spacecraft across the solar system.
  
  Deep Space Network
  
  To keep in touch with Juno, ground controllers use the giant radio antennas of NASA’s Deep Space Network, or DSN. The DSN antennas are 70-meter and 34-meter (230-foot and 112-foot) -wide dishes located at three sites around the world: California, USA; Madrid, Spain; and Canberra, Australia. The DSN sites are positioned around the globe so that, as Earth rotates, the entire solar system is in view of at least one of the antennas. The DSN and Juno’s High Gain Antenna also work in concert to serve as the main components of Juno’s Gravity Science investigation.
Data Handling
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  Computing and Data Handling
  How does an unmanned spacecraft interpret information?
  
  Computing and Data Handling
  
  The Juno “brain and central nervous system” is called the C&DH, for Command and Data Handling subsystem. The C&DH controls the functions of the spacecraft, collects and organizes the data from the science instruments, checks on the health and safety of the spacecraft, and controls the transmission of data back to Mission Control. Juno’s brains are powerful enough to protect it from most malfunctions by putting the spacecraft into a safe mode if engineering sensors identify an anomaly, and waiting for further instruction from Earth. Amazingly, this computer is very simple – less powerful than your typical laptop computer, and doesn’t use much power
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  Fault Protection
  What if Juno's systems malfunction?
  
  Fault Protection
Design + Structure
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  Spacecraft Design
  Learn more about Juno’s design and structure.
  
  Spacecraft Design
  
  Juno’s main body is made of an advanced carbon composite material in a honeycomb structure. The spacecraft has a hexagonal shape, with three large solar arrays symmetrically placed around the hexagon. Most of the science instruments are between the solar arrays, with their sensors attached to Juno’s main deck. The instruments’ electronics are housed inside Juno’s titanium vault, atop the main deck, which provides the base for Juno’s main antenna. Beneath the main deck reside the propellant tanks and Juno’s rocket engine that’s used for maneuvers and orbit insertion.
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  Firsts
  Juno does a few things no spacecraft has done before.
  Firsts
  The Juno mission benefits from three important firsts:
  Juno is the first spacecraft to go into orbit around the poles of one of the gas giant planets of the outer solar system.
  It is the first solar powered spacecraft to visit the outer solar system.
  The spacecraft is the first to carry a specially designed vault to shield its sensitive electronics from dangerous radiation in space.
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  Protecting Juno
  What precautions must be taken to protect a spacecraft on a journey to Jupiter?
  
  Protecting Juno
  
  Space is a harsh and unforgiving environment. Impacts from micrometeors could cause grave damage to an unprotected spacecraft. Temperatures tend to be scorching hot or extremely cold, without any air to circulate in order to keep a spacecraft from overheating or freezing. Juno faces an especially tough challenge from the intense belts of charged particle radiation that surround Jupiter. To meet these threats, engineers protect the robotic explorer with a shiny skin of insulation and a unique protective shield for its electronics.
  
  The shiny blankets on Juno’s exterior protect the spacecraft from micrometeoroid strikes and act as insulation. The material also helps electricity to flow over the spacecraft in the charged environment around Jupiter – electrons that can’t flow build up as an electric charge, which can be unleashed as a dangerous spark. Juno’s shiny skin is its best defense against these threats.
Propulsion
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  Why Does Juno Rotate?
  In space it’s easier to spin than not spin.
  
  Why Does Juno Rotate?
  
  In space, there’s nothing to anchor objects in place, so a spacecraft will tend to spin unless it can maintain its orientation with some kind of engineered system. Juno rotates like a giant gyroscope or spinning top because once it is set in motion at the beginning of its mission, it will continue rotating in a very stable and predictable way for the rest of its lifetime.
  
  With very little to perturb its spinning motion in space, Juno’s controllers on Earth can be confident that the spacecraft’s antennas, solar arrays and science instruments are pointing in the direction they are supposed to. Mission controllers can adjust Juno’s orientation when needed by commanding the spacecraft to fire any of its 12 thrusters. The three solar arrays can also change their tilt by a small amount to help balance Juno’s spin, much like a person uses outstretched arms to remain steady on a balance beam.
  
  The thrusters also can be used to adjust the rate at which Juno spins. The faster the spacecraft spins, the more stable it becomes. This is especially important during the engine burn that will place Juno into orbit around Jupiter.
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  Propulsion and Onboard Rockets
  How do we steer Juno as it travels to Jupiter?
  
  Propulsion and Onboard Rockets
  
  Juno has six large propellant tanks that feed its main rocket engine and thrusters. The main engine is used for important maneuvers on the way to Jupiter and later to slow the craft down when it reaches its destination and allow the planet's gravity to capture the spacecraft into orbit. This is what allows Juno to become a satellite of Jupiter.
  
  The thrusters are used to point Juno in preferred directions, both to collect science and change its orientation between pointing directly toward the sun (to collect maximum solar energy) and toward Earth (to send data down and receive commands).
  
  The propellants Juno uses are hydrazine and nitrogen tetroxide, two common types of liquid rocket propellant for spacecraft. Juno's main engine uses both propellants to produce thrust, while the thrusters use only hydrazine.
Radiation
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  Radiation
  How does radiation affect the Juno mission?
  
  HOW MUCHRADIATION?
  
  HOW MUCH RADIATION?
  
  Juno is going into one of the harshest regions in the solar system – Jupiter’s radiation belts. Sure, Jupiter’s radiation is bad, but how bad can it really be? Outside the vault the spacecraft is expected to receive the equivalent of more than 100-million dental x-rays. Inside the vault, Juno’s hardware will be exposed to radiation equivalent to only 120-thousand dental x-rays, so the vault creates a radiation environment about 800 times less intense. This is similar to the radiation levels experienced by spacecraft that orbit a planet we have much more experience with – Mars.
  
  THE RADIATION VAULT
  
  The vault was designed into the spacecraft to shield Juno’s sensitive electronics. Much like metallic lead protected Superman from Kryptonite, the titanium vault on Juno blocks the high-energy particles surrounding Jupiter from damaging Juno’s electronic brains. The titanium walls essentially absorb the electrons and protons – that move at nearly the speed of light – and protect the spacecraft’s instruments and solid-state electronics. The vault must be thermally controlled via the use of specially designed vents that block radiation but let heat pass.
  
  DESIGNING THE VAULT
  
  Juno’s radiation vault is the first of its kind, so it was designed from the ground up. The vault is essentially a titanium box, and the electronics’ boxes that control each of Juno’s instruments and systems are attached to those walls. Juno’s engineers had to determine how to regulate the temperature within the vault because all of the electronics there create heat, like a home computer or stereo. And since there would be no opportunity to adjust the size of the vault if the electronics did not fit, the exact sizes for all the components had to be determined far in advance.
Solar Arrays
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  How Do We Power a 6-Year Journey?
  Juno doesn’t burn fuel to power its instruments, so where does the energy come from?
  
  WHY SOLARPOWER?
  
  HOW DO WE POWER A 6-YEAR JOURNEY?
  
  Jupiter’s orbit is five times farther from the sun than Earth’s location, so the giant planet receives about 25 times less sunlight than Earth. Juno is the first solar-powered spacecraft designed to operate at such a great distance from the sun, thus its solar panels are quite large to generate sufficient power.
  
  The Juno orbit and spacecraft orientation have been carefully designed so that Juno’s solar panels face the Sun most of the time (except during engine burns). Therefore, the solar panels are illuminated by the sun for the entire mission. This means the spacecraft has continuous access to its power source. Juno only passes into eclipse once after launch, for a few minutes following the Earth flyby in 2013.
  
  HOW DO SOLAR CELLS WORK?
  
  A solar cell converts sunlight into electricity. Materials within the cell have special properties that cause electrons to flow from them when struck by light. Flowing electrons are what we call electricity. Not all of the energy of the sunlight is converted to electricity – some of the light is reflected and some is turned into heat. The more light a solar cell converts into electricity, the more efficient the cell. Juno’s very efficient solar arrays benefit from many advances in solar cell technology achieved over the past 20 years.
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  Solar Arrays
  Juno uses revolutionary solar technology.
  
  Solar Arrays
  
  Three large solar arrays provide the power needed to operate everything. Because the sunlight intensity at Jupiter is only 1/25th that at Earth, the arrays are “super-sized” to ensure that enough power is produced to operate the spacecraft. The solar arrays have 18,000 solar cells that convert the sun’s energy into electricity through the photovoltaic effect. Jupiter’s extremely cold temperatures (-300° Fahrenheit) and intense radiation fields (equivalent to 20 million chest x-rays) required specialized testing and design. At Earth, the arrays produce over 2,000 watts of power (enough to power a large microwave oven), but at Jupiter they produce only 420 watts. This is a small amount of power, to be sure, but Juno is designed to be extremely energy efficient.
  
  The panels extend outward from Juno’s hexagonal body giving the overall spacecraft a span of more than 20 meters (78 feet). One of the arrays is modified to hold the magnetometer experiment. The magnetometer needs to be far away from the spacecraft to ensure that it measures Jupiter’s magnetic field and not Juno’s magnetic field. Before launch, the solar panels will be folded into hinged segments so the spacecraft can fit within the fairing (or nose cone) of the Atlas V rocket.
  
  Juno’s solar arrays are also used to help balance the spacecraft’s rotation. Following a maneuver to adjust Juno’s course or the angle of its tilt, the spacecraft may wobble a bit, like a top. The arrays can be tilted up or down a small amount to reduce this wobble, similar to the way that an ice skater raises his or her arms in order to spin fast and perfectly straight. This use of the solar arrays allows mission controllers on Earth to adjust the precise pointing of the spacecraft’s saucer-shaped main antenna.

INSTRUMENTS

Gravity Science
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  Gravity Science
  Bill Folkner explains how understanding Jupiter’s inner structure depends on measuring changes in its gravitational field.
  
  Gravity Science
  
  The Gravity Science experiment will enable Juno to measure Jupiter’s gravitational field and reveal the planet’s internal structure. Juno will see how the material inside Jupiter churns and flows and determine whether the planet harbors a dense core at the center. Variations in Jupiter’s inner structure will have tiny effects on its gravitational field, which ever so slightly alters Juno’s orbit. The closer Juno gets to Jupiter, the more pronounced the displacements are. These subtle shifts in Juno’s motion cause equally subtle shifts in the frequency of a radio signal received from and sent back to Earth. Known as the Doppler effect, it’s the same type of frequency shift that happens when the pitch of an ambulance’s siren increases when speeding toward you and decreases when speeding away from you. To measure these tiny shifts, Juno’s telecommunication system is equipped with a radio transponder that operates in the X band, which are radio signals with a wavelength of three centimeters. The transponder detects signals sent from NASA’s Deep Space Network on Earth and immediately sends a signal in return. The small changes in the signal’s frequency tell us how much Juno has shifted due to variations in Jupiter’s gravity. For added accuracy, the telecommunication system also has a Ka-band translator system, which does a similar job but at radio wavelengths of one centimeter. One of the Deep Space Network’s antennas, located in Goldstone, California, has been fitted to send and receive signals at both radio bands. An instrument called the Advanced Water Vapor Radio- meter helps to isolate the signal from interference caused by Earth’s atmosphere. Dr. John Anderson of the Jet Propulsion Laboratory (JPL) leads the Gravity Science team. Mr. Anthony Mittskus leads the Telecom Subsystem, which is produced by JPL. The Italian Space Agency contributed the Ka-band translator system.
JADE
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  JADE
  Dave McComas describes the set of instruments charged with detecting the electrons and ions that produce Jupiter’s aurora.
  
  JADE
  
  The Jovian Auroral Distributions Experiment (JADE) will work with some of Juno’s other instruments to identify the particles and processes that produce Jupiter’s stunning auroras. It will also help create a three-dimensional map of the planet’s magnetosphere. JADE consists of an electronics box shared by four sensors: three will detect the electrons that surround the spacecraft and the fourth will identify positively charged hydrogen, helium, oxygen and sulfur ions. These sulfur ions are ejected from the volcanoes on Jupiter’s moon Io. When Juno flies directly over auroras, JADE will be able to observe the light show, resolving structures as small as 50 kilometers (30 miles) in size. Considering that the auroras can stretch for tens of thousands of kilometers around the pole, JADE will be able to discern a lot of detail. JADE will also measure the particles that fly out from Jupiter’s poles, spiraling along as they’re guided by the magnetic field. Dr. David McComas of the Southwest Research Institute (SwRI) leads the JADE instrument team. JADE is provided by SwRI.
JEDI
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  JEDI
  Barry Mauk explains how measuring high energy particles will help us understand the processes behind Jupiter’s rotationally dominated magnetosphere.
  
  JEDI
  
  The Jupiter Energetic Particle Detector Instrument (JEDI) will measure the energetic particles that stream through space and study how they interact with Jupiter’s magnetic field. These electrically charged particles – consisting of electrons and ions – follow the influence of the magnetic field. Many of them are channeled by the field toward Jupiter’s poles, where they crash into the atmosphere and create brilliant auroras. JEDI will determine the amount of energy the particles carry, their type and the direction in which they’re zipping around. Working with Juno’s other instruments designed to study the magnetosphere – the bubble created by Jupiter’s magnetic field – JEDI will help us under- stand how the planet produces the auroras. JEDI will also examine the processes by which the magnetic field interacts with the particles to dump energy into the planet’s atmosphere. Dr. Barry Mauk of the Johns Hopkins University Applied Physics Laboratory (APL) leads the JEDI team. The instrument is provided by APL.
JIRAM
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  JIRAM
  JIRAM will provide a visual and thermal view of Jupiter’s aurora.
  
  JIRAM
  
  The Jovian Infrared Auroral Mapper (JIRAM) will study Jupiter’s atmosphere in and around the auroras, learning more about the interactions between the auroras, the magnetic field and the magnetosphere. JIRAM will be able to probe the atmosphere down to 50 to 70 kilometers (30 to 45 miles) below the cloud tops, where the pressure is five to seven times greater than at Earth’s sea level. JIRAM consists of a camera and spectrometer, which splits light into its component wavelengths, like a prism. The camera will take pictures in infrared light, which is heat radiation with wavelengths of two to five microns (millionths of a meter) – three to seven times longer than visible wavelengths. In particular, the instrument will snap photos of auroras at a wavelength of 3.4 microns – the wavelength of light emitted by excited hydrogen ions in the polar regions. Methane in the atmosphere absorbs light at this same wavelength, darkening the atmosphere behind the auroras. In front of a darkened background, the auroras stand out even more brightly. The instrument will also try to learn about the structure and origin of voids in Jupiter’s atmosphere called hot spots. These spots – like the one the Galileo probe happened to have dropped into in 1995 – are windows into the depths of Jupiter’s atmosphere. By measuring the heat radiating from Jupiter’s atmosphere, JIRAM can determine how water- containing clouds circulate under the surface. It turns out that this sort of motion – called convection, in which hot gas rises and cool gas sinks – reveals the amount of water in these clouds. Certain gases in the atmosphere – methane, water, ammonia and phosphine, in particular – absorb certain wavelengths of infrared light. When the spectrometer measures the infrared rainbow emitted by Jupiter, the wavelengths of light absorbed by those gases would be missing. The missing wavelengths indicate the chemical composition of the atmosphere. JIRAM was developed by the Italian National Institute for Astrophysics and funded by the Italian Space Agency.
JUNO CAM
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  Juno Cam
  Where is the best place to photograph Jupiter? Junocam will let the public help decide.
  
  Juno Cam
  
  Designed to capture remarkable pictures of Jupiter’s cloud tops, Juno’s color, visible-light camera – called JunoCam – will see what you would see if you were an astronaut orbiting Jupiter. As Juno’s eyes, it will provide a wide view, helping to provide context for the spacecraft’s other instruments.
  
  Because Juno rotates a couple of times per minute, its images would smear if it were to try to take a complete picture at once. Instead, it is a "push-broom imager," taking thin strips of an image at the same rate that the spacecraft spins. JunoCam then stitches the strips together to form the full picture.
  
  JunoCam takes images only during closest approach – about 5,000 kilometers (3,100 miles) above the cloud tops – when it gets the best vantage point possible. Taking pictures with a resolution of up to 25 kilometers (16 miles) per pixel, the wide-angle camera will provide incredible new views of Jupiter’s atmosphere.
  
  Eventually, the high-energy particles surrounding Jupiter will destroy JunoCam’s electronics. But the camera is designed to last for at least seven orbits – enough time to take plenty of pictures.
  
  JunoCam’s hardware is based on a descent camera that was developed for Curiosity, the Mars rover slated to launch later this year. Some of its software was originally developed for the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft. JunoCam is provided by Malin Space Science Systems.
  
  JunoCamis provided by Malin Space Science Systems.
Magnetometer
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  MAPPING THE MAGNETOSPHERE
  What does Jupiter’s magnetopshere look like? Jack Connerney tells us how we will find out.
  
  Magnetometer
  
  Using its magnetometer (MAG), Juno will create an extremely accurate and detailed three-dimensional map of Jupiter’s magnetic field. This unprecedented study will allow us to understand Jupiter’s internal structure and how the magnetic field is generated by the dynamo action inside – the churning of electrically charged material deep below the surface. MAG will also monitor the field for long-term variations, called secular variations, during the entire mission. Measurements of these variations, in combination with the map, will help us determine the depth of the dynamo region. Because Jupiter lacks a crust or continents that complicate the picture, Juno’s observations could be the most detailed ever of a planetary dynamo. Electrical currents can align themselves with the magnetic field, and these so-called Birkeland currents help drive the brilliant auroras around Jupiter’s poles. To better understand the auroras, MAG will measure these currents. MAG 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. Juno’s other instruments have their own small magnetic fields, and to avoid contamination, the MAG sensors sit as far from the rest of the spacecraft as possible. They are mounted on the magnetometer boom that sticks out from one of Juno’s solar arrays. As an extra precaution, there are two sets of MAG sensors – one 10 meters (33 feet) from the center of the spacecraft and one 12 meters (39 feet) from the center. By comparing measurements from both sensors, mission scientists can remove any contamination from the data. Dr. Jack Connerney of the NASA Goddard Space Flight Center (GSFC) leads the Magnetic Field Investigation. The FGM is provided by GSFC and the ASC is provided by Danish Technical University.
Microwave Radiometer
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  Microwave Radiometer
  Measuring thermal radiation will help us create a 3D picture of Jupiter’s atmospheric structure.
  
  Microwave Radiometer
  
  Juno will use the Microwave Radiometer (MWR) instrument to be the first spacecraft to probe inside Jupiter, learning about its structure and chemical composition. To see what’s under the cloud tops, the MWR will measure the radiation emitted from inside the planet. The clouds radiate in all frequencies of the radio, microwave and infrared ranges. But only microwave frequencies can make it out through the thick clouds. The depth from which the radiation can escape depends on frequency, so by measuring different frequencies of microwave radiation, the MWR can study different layers of Jupiter’s interior. The MWR consists of six radiometers designed to measure the microwaves coming from six cloud levels. The levels range from the cloud tops, where the pressure is the same as that on Earth, down to a depth of hundreds of miles, where the pressure is a thousand times greater. The deepest layers will reveal Jupiter’s water content, which is key to understanding how Jupiter formed. The MWR will also allow us to determine how far down atmospheric features, such as the cloud bands and the Great Red Spot, extend. Each of the six radiometers has an antenna, and all six antennas are located on two sides of Juno’s hexagonal body. Each antenna is connected by a cable to a receiver, which sits in the instrument vault on top of the spacecraft. Dr. Michael Janssen of the Jet Propulsion Laboratory (JPL) leads the MWR instrument team. JPL provided the MWR sub-system components, including the antennas and receivers.
UVS
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  SEEING IN UV
  Randy Gladstone explains how seeing Jupiter’s auroras in UV helps us understand Jupiter’s upper atmosphere and the particles that cause the aurora.
  
  UVS
  
  The Ultraviolet Imaging Spectrograph (UVS) will take pictures of Jupiter’s auroras in ultraviolet light. Working with Juno’s JADE and JEDI instruments, which measure the particles that create the auroras, UVS will help us understand the relationship between the auroras, the streaming particles and the magnetosphere as a whole. The Hubble Space Telescope took some impressive images of Jupiter’s auroras, but Juno will get an even better view – looking directly down on them over the north and south poles. UVS includes a scan mirror for targeting specific auroral features. UVS is sensitive to both extreme and far-ultraviolet light, within a wavelength range of 70 to 205 nanometers (billionths of a meter). In comparison, visible light has wavelengths that range from 400 to 700 nanometers. Dr. Randy Gladstone of Southwest Research Institute (SwRI) leads the UVS team. SwRI provided the UVS instrument. CSL/BELSPO (Belgium) contributed the scan mirror.
WAVES
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  READING THE WAVES
  What do radio waves tell us about Jupiter’s electric fields and magnetic fluctuations?
  
  WAVES
  
  The Waves instrument will measure radio and plasma waves in Jupiter’s magnetosphere, helping us understand the interactions between the magnetic field, the atmosphere and the magnetosphere. Waves will also pay particular attention to activity associated with auroras.
  
  The magnetosphere, an enormous bubble created by Jupiter’s magnetic field, traps plasma – an electrically charged gas. Activity and other features in the plasma trigger waves that only an instrument like Waves can detect. The plasma fills the magnetosphere. Because plasma conducts electricity, it behaves like a giant circuit, connecting one region with another. Activity in one end of the magnetosphere can therefore be felt somewhere else, allowing Juno to monitor the entire magnetosphere.
  
  Radio and plasma waves surround all the outer planets, so previous missions that have explored the gas giants were equipped with similar instruments. J Juno's Waves instrument consists of two sensors; one detects the electric component of radio and plasma waves while the other is sensitive to just the magnetic component of plasma waves. The first sensor, called an electric dipole antenna, is a V-shaped antenna, four meters from tip to tip -- similar to the rabbit-ear antennas that were once common on TVs. The magnetic antenna -- called a magnetic search coil -- consists of a coil of fine wire wrapped 10,000 times around a 15- centimeter-long core. The search coil measures magnetic fluctuations in the audio frequency range.
  
  Dr. William Kurth of the University of Iowa leads the Waves team, and the University of Iowa provides the instrument.