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Juno--The New Jupiter Probe

written by: •edited by: RC Davison•updated: 8/31/2011

On August 5, Juno began a five year flight to Jupiter. On arrival, it will spend a year making measurements of the gas giant’s magnetic, gravity and radiation fields. It will measure the water in the atmosphere and other atmospheric components. The goal—is our theory of planet formation correct?

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    Destination Jupiter!

    12:25 PM EDT, August 5, 2011:

    The five SRBs (solid rocket boosters) on the giant ATLAS V Launch Vehicle ignite and the flight of NASA’s new Jupiter probe began.

    Juno, named after the Roman god for Jupiter’s wife, will spend five years en route to the gas giant. Once there it will take up station in orbit around Jupiter for a year to make the most detailed measurements of the Jovian environment ever. When its mission is over, it will plunge into the planet’s thick atmosphere, still sending back data until it burns up or is crushed by atmospheric pressure.

    Juno was launched by a launch vehicle (LV) developed and built not by NASA but by a commercial consortium consisting of Boeing Aircraft and Lockheed Martin Aircraft. The consortium is called the United Launch Alliance (ULA). The ATLAS V is the largest, most powerful LV currently available. Ironically, it uses Russian engines in its first stage to generate 800,000 pounds of thrust. The five SRBs add another 300,000 plus pounds of thrust.Juno on Way 

    The second stage is an upgraded NASA design—the LH2 powered Centaur. This commercial combo sent Juno on its way.

    Juno is a four ton, 11.5 ft tall spacecraft. It is unique for a trip to an outer planet because it will be solar powered. All other craft sent beyond Mars have used atomic power (radioisotope thermoelectric generators) because solar energy was too weak 400,000 miles out. But solar technology has come a long way this century. Juno’s solar panels can generate 450 watts at Jupiter, plenty for the spacecraft’s energy efficient instruments.Juno at Jupiter with Solar Panels Unfurled 

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    A Long and Winding Road

    But Juno’s journey has hardly begun. It has escaped Earth’s gravity, but it has not escaped the Sun’s pull. To do that, it must gain much more speed than its LV could give it. The way to gain that is with a gravity slingshot, or boost. In other words, Juno must use the gravitational energy of another planet to speed itself up and slingshot itself on the 400,000 mile trek to Jupiter.

    And, what better planet to do that with than the home world from which it came?

    About a year after launch, Juno will cross Mars’ orbit and begin to fall back towards its home planet. It will pick up speed during that fall which will take another year and a couple of months. As it whips around Earth in October of 2013, travelling near escape velocity again--25,000 mph, Mother Earth will give it an additional 16,300 mph boost and send it on its way to Jupiter. That leg will take three more years.Juno Misson Profile 

    As the spacecraft approaches Jupiter in 2016, the tremendous gravitational pull of the giant speeds up the robot to almost 100,000 mph. To achieve orbit, it must slow down by firing onboard rockets. In fact, 2/3 of the spacecraft’s four ton weight is made up of propellants for this maneuver and the Deep Space Maneuvers (DSM) required during the flight.

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    Operation Jove

    Juno will go into a polar orbit around the gas giant. Jupiter’s radiation and magnetic fields are so intense the spacecraft must avoid them as best possible. A polar orbit does that. On its 33rd revolution around the planet, it will dip down to within 3300 miles of the cloud tops at the poles, swinging back high into space over the equator where the radiation is greatest.

    Juno will seek to find out how much water is in Jupiter’s atmosphere. It will measure the compostion, temperature, cloud motions and other properties of the atmosphere, and measure the planet's gravity fields. This should help us understand Jupiter's composition.

    Juno also will study the magnetic field that create Jupiter's auroras. This should give us a better understanding of how its tremendous magnetic field interacts with its atmosphere.Jupiter's Aurora 

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    The Instrumentation

    These measurements will be conducted with eight extremely sensitive instruments.

    • Gravity Science
      Two transponders operating on different frequencies (Ka- and X-band) will detect signals sent from NASA's Deep Space Network on Earth and immediately send signals in return. Small changes in the signal's frequencies (as they are received on Earth) provide data on how much Juno's velocity has been modified due to local variations in Jupiter's gravity.

    • Magnetometer (MAG)
      Juno features a flux gate type magnetometer to measure the strength and direction of Jupiter's magnetic field lines.

    • Microwave Radiometer (MWR)
      The Microwave Radiometer will probe beneath Jupiter's cloud tops to a depth as great as 1,000 atmospheres -- about 342 miles (550 kilometers) below the visible cloud tops.

    • Jupiter Energetic Particle Detector Instrument (JEDI)
      The Jupiter Energetic Particle Detector Instrument will measure the energetic particles that stream through space and study how they interact with Jupiter's magnetic field.

    • Jovian Auroral Distributions Experiment (JADE)
      The Jovian Auroral Distributions Experiment will identify the particles and processes that produce Jupiter's stunning auroras.

    • Waves
      The Waves instrument will measure radio and plasma waves in Jupiter's magnetosphere.

    • Ultraviolet Imaging Spectrograph (UVS)
      The Ultraviolet Imaging Spectrograph will take pictures of Jupiter's auroras in ultraviolet light.

    • Jovian Infrared Auroral Mapper (JIRAM)
      JIRAM will be able to probe the atmosphere down to 30 to 45 miles (50 to 70 kilometers) below the cloud tops, where the pressure is five to seven times greater than on Earth at sea level. Juno Instruments 

    Juno also carries a camera, Called JunoCam, but it is not a part of the scientific instrumentation. It is onboard to send back pictures of Jupiter for public use. And it is not expected to survive long in Jupiter’s radiation fields. Its life expectancy is eight days.

    The scientific instrumentation on the other hand is highly shielded by a centimeter thick titanium box around all the sensitive electronics.Juno Radiation Shield 

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    Spinning Around Jupiter

    Juno has another aspect that is unique. Rather than using control rockets for stabilization, it is spin-stabilized. This accomplishes two goals. It of course stabilizes the spacecraft both on its journey and during its 33 orbits of Jupiter. It also eliminates the need to put the instruments on a scan platform to point them in different directions. Gravity and atmospheric observations are obtained through orientation of the spacecraft's spin plane. All other experiments utilize ride-along pointing and work in either one or both orientations. This saves considerable weight.

    On its five-year journey, Juno will spin at two rpm. Once in orbit around Jupiter, NASA's new Jupiter probe will slow to one rpm.

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