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[Music throughout]

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Most space telescopes,

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from NASA's Hubble to Webb, 

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use components called reaction wheels

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 to change where they are pointing.

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The reaction wheels are basically
flywheels driven by electric motors.

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They spin to store angular momentum.

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By slowing or speeding the rotation
of a given wheel

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a computer can precisely adjust
how the spacecraft points

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in one plane.

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With three wheels set at
specific angles,

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a satellite can control its pitch,

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roll, 

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and yaw, 

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and then hold that position
without any change.

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NASA's Nancy Grace Roman
Space Telescope

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has six reaction wheels,

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rather than the necessary three, 

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to give it more angular momentum for faster pointing,

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as well as complete redundancy

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should any one wheel fail.

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Each of Roman's wheels is 18 inches across,

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weighs roughly 45 pounds,

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and spins up to 4000 rpm.

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As long as the solar cells
provide them with electricity,

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the reaction wheels can keep Roman
perfectly pointed at the stars.