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Music

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Magnetic fields have been
a curiosity for thousands
of years.

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And so of course we know
now that magnetic fields are

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generated by what's called
dynamo action,

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the convective motion of an
electrically conducting fluid.

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Even though we can map the
Earth's magnetic field with

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extraordinary accuracy, with
satellites in orbit about
the Earth,

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the one thing we can't do
is see clearly through all the

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crustal magnetization that
is right beneath our feet.

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Jupiter is a gaseous planet,
hydrogen, helium, there is no

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magnetized crust that obscures
our view of the dynamo
deep below.

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So the exciting part about the
Jupiter mission is that

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we'll be able to image, for the
first time, the magnetic field
on the

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dynamo's surface in a way that
would never ever be possible
on Earth.

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Jupiter's also the planet
with the largest magnetic field.

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Its magnetosphere is huge.

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If you were to look up into the
night sky, and if you could see

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the outline of its
magnetosphere, which you can't,

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it would be about the
size of the Moon in the sky.

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It's a very, very
large magnetosphere.

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In fact, in the Voyager program
we learned that the
magnetic tail,

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the part of the magnetosphere
that is drawn away

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from the Sun, extends all the
way out to the orbit of Saturn

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and in all likelihood beyond.

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It's a very large
feature in our solar system.

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It's a pity we can't see it.

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Juno's the fastest spacecraft
ever to venture into the outer
solar system.

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It's the first to orbit pole to
pole about Jupiter,

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and it's the most heavily
shielded spacecraft that
we've ever launched.

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The mission is designed to
basically wrap Jupiter in a

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dense net of observations
completely covering a sphere.

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So to do that we need a polar
orbit, one that passes over the

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north pole, along a line of
longitude, and over the
south pole.

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And we do this over the
thirty-seven orbits of the

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nominal mission, and by the
time we're done we've got orbits

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separated in longitude by about
every twelve degrees,

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so we completely cover the
sphere.

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A magnetometer is, uh, it's
best to think of it as a
fancy compass.

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Unlike a compass that just
records the direction of the

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magnetic field, our instrument
tells you both what direction

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the field is in and
what the magnitude is.

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And we can measure that very,
very accurately, to a hundred
parts per million.

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Juno's magnetometer is another
in a long line of magnetometers

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built here at the Goddard Space
Flight Center, following designs

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developed by Mario
Acuña years ago.

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Our instrument is between one
and two orders of magnitude more

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accurate than anything
that's flown to Jupiter before.

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And of course part of that is
the result of the star cameras

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that we're able to fly with
our sensors, so that we can

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determine the absolute
orientation in space of
these sensors.

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If we did not know the
orientation of the sensor

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as well as we can determine it
with the star cameras,

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we would lose accuracy in the
vector measurement.

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So we carry four star cameras
with our two magnetometer
sensors.

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These have to be held in the
same orientation with respect to

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each other under very extreme
environmental conditions.

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So we designed what we call
the magnetometer optical bench.

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It's a special structure, about
a square foot in size,

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that is made of a carbon silicon
carbide material, almost
impossible to machine,

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but once it's fabricated and the
sensors are assembled, they act
as one.

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And that's one of the reasons
why we can achieve much higher

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accuracy than has ever
been attempted before.

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We hope to learn more about how
a magnetic field is generated

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by dynamo action deep in
a planet's interior.

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For me, the great excitement is
the opportunity to look down

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and get the first clear,
unobstructed view of what the

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magnetic field looks like on the
surface of a dynamo where
it's generated.

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It's always incredible to be the
first person in the world to
see anything.

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We stand to be the first to
be able to look down upon
the dynamo

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and see it clearly for
the first time.

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Satellite beeping