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[Emily Beckman] Once the fuel
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runs out, there is no more mission.
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You have to decommission.
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So the fuel is very important
for the spacecraft.
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It can only last as long as the fuel.
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[Title: Moving Roman - Propulsion]
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[Narrator] Telescopes like NASA's
Nancy Grace Roman Space
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Telescope move and point
using two methods.
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There are reaction wheels
to turn the spacecraft with precision
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and then hold it steady.
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And then there are thrusters
that use propellant for large motions
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to push the spacecraft into its correct
orbit and maintain that orbit.
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All which require fuel.
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Before entering the large clean room,
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the propulsion tanks were assembled
in a smaller lab.
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[Emily Beckman] So right now we're looking
at the propulsion system for the Roman
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Space Telescope.
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Today
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we put our last tank on the propulsion
support frame.
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The propulsion support frame is the frame
that's supporting everything.
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[Narrator] The four tanks seen here
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were each carefully lifted individually.
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The deck that supports them
gets positioned below that tank.
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These four tanks
fuel a series of 24 thrusters
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with two different sizes.
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[Emily Beckman] On the sides.
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We have all of the engines,
so we have four sets up top.
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Those are our upper ACS’s.
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We have four sets at the bottom.
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Those are our lower ACS engines.
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And then at the bottom over here,
those big triangle pods,
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those are all of our Delta V engines.
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So those will do our big maneuvers.
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[Narrator] With the tanks in position.
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They're ready for integration
into the telescope spacecraft bus,
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which happens in NASA's
largest clean room.
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Now, thrusters use conservation
of momentum, ignited
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fuel creates expanding gas,
which exits the engines in one direction.
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And the observatory moves
in the opposite direction.
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The thrusters are so efficient
in the vacuum of space
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that they can be surprisingly small
to move
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the 18 thousand pound spacecraft.
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This is all it needs.
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With the thrusters
on the outside of Roman,
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the propellant tanks will sit
within the observatory central cylinder
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close to their teammates,
the reaction wheels.
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When the reaction wheels
get to their maximum speed,
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they have to be slowed down again.
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The thrusters fire to balance
the angular momentum change
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so that the spacecraft doesn't
turn as the wheels slow.
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Since fuel is limited,
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it usually determines
the lifespan of distant
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spacecraft.
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Luckily, the telescope can also point
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only using electricity.
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But how reaction wheels work.
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That's another story.