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♪

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Hello. I'm Lacy Thompson.

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I serve as a
news chief here

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at NASA's
Stennis Space Center

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near Bay St.
Louis, Mississippi.

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I'm standing
not too far from

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the Fred Haise Test Stand.

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This is where NASA tests
RS-25 engines to help

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power the SLS or Space
Launch System rocket

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on Artemis missions
back to the Moon,

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as we prepare for
future journeys to Mars.

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I'm joined by one of
our NASA test engineers

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and test conductors,
Derek Zacher.

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Derek has agreed to answer
some of the questions

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we've received
during recent

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livestream broadcasts
of RS-25 tests.

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Derek, thank
you for joining.

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Happy to be here.

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Before we get on
to the questions,

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I'd like to ask you
to share a little bit

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about yourself and how
you became a test engineer

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and conductor here
at NASA Stennis.

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All right.

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Well, got into, interested
in aerospace as a child.

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I was more interested
in the jet engines

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and aircraft than I
was rockets and space.

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I went to school
down at Embry Riddle,

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down in Daytona Beach,
and that was close enough

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to Kennedy that I was
able to go down and see a

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bunch of launches and got
really excited about it.

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Had an opportunity
to come down here

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to Stennis working
for Orbital Sciences

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on their Antares program.

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And then, when, after
our first launch there,

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I was able to get a
job here at NASA working

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with the team here on the
stand testing the RS-25.

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Thank you, Derek.

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We're so
glad you're part

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of the NASA
Stennis family.

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Now let's get on
to the questions.

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And the first question
relates to an upcoming

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RS-25 test on the
Fred Haise Test Stand.

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Somebody wants to
know what the engine

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being tested is for,
whether it's a

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new engine or a heritage
space shuttle engine.

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All right.

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This engine here
is made up,

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manufactured of
all new components.

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It's part of our
certification test series.

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What we did was
we're, we have about

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12 engines left
that are going to

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work through
Artemis II through IV.

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And now, then we
have to utilize

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new manufactured engines.

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So we are using
new techniques

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for manufacturing, new
materials that either

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weren't available
at the time when this,

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when these
engines were first

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manufactured or weren't
suitable for the reusable

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aspects of the space
shuttle main engine.

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So these tests are to
verify that those changes

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don't impact the
performance of the engine,

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that it's still, it's
suitable to meet our needs

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and is still
reliable to get

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our astronauts
safely into orbit.

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And those new engines
are being produced by the

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lead engines contractor
Aerojet Rocketdyne,

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is that correct?

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Yes, sir. Correct.

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They are being, all
the components are

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manufactured out at their
facility in California,

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and then they are
shipped here to Stennis,

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where they are
assembled and then

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brought out to the
stand to be tested.

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And after we are finished
testing them, when we get

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to the flight
engines after testing,

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they will be sent down to
Michoud Flight Facility

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outside of New Orleans,
where they will be

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integrated into the
next SLS core stage.

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Well, thank you, Derek.

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Let's get onto
the next question.

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And somebody
wants to know

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what weather conditions
permit a test.

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For instance, can you test
during a thunderstorm?

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All right.

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We could test pretty
much any time.

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There are activities
prior to the test

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that require our
personnel to be outside

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doing setups
and inspections.

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Obviously, they
can't be outside

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during a
thunderstorm for those.

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We have a lightning
detection system

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at our facility that will
alert us if there are

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lightning strikes within
5 to 10 miles.

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And in those situations,

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our people
can't go outside.

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Down here in Mississippi,
we're lucky that most of

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the time the weather comes
here in the afternoon,

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and the mornings
are pretty clear.

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So when we know weather's
coming in, in the

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afternoon, we'll try to
pull all of the setups

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and all of the
inspections forward

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in the count to try to
get them out of the way

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before the
weather comes in.

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We have backup generators
that provide power,

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that in the event that we
have a lightning strike

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that knocks out
commercial power,

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we'll still have power
to run all of our systems.

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And then in the event
that in the last

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couple of minutes
before a test,

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we, when we're
trying to do our

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final inspections,
if we can't send people

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outside to do those,
most of the areas

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that we need to look
at have adequate coverage

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via a video
camera that we can do

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with inspection that way.

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At the end of
the day, though,

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what it comes down to
is if the test director

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feels that it is a, the
risk level has elevated

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to such a level that
it's not acceptable,

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he can choose to
scrub the test.

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Well, that's great
information, Derrick.

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Thank you.

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Now, the next
question is how loud

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and powerful are
these RS-25 tests?

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For instance, will they
set off nearby car alarms?

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All right, well, these
are pretty loud tests.

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We don't allow too many
people outside of enclo...

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enclosed structures
close to the stand.

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But anybody
within about 200 yards

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or so is wearing hearing protection because

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it's above our
acceptable limits.

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I have never
heard of a car alarm

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going off out here.

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But on that
note, you know,

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we're a pretty
secure area out here.

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So most people don't
even lock their cars

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when they're out here.

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So it probably doesn't.

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They're probably
not even armed.

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Now, I have heard
some friends that live,

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you know, 15, 20
miles away from here.

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They're telling me that
when the clouds are low

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and the weather is just
right, they can actually

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hear us from, you know,
15, 20 miles away.

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So it is pretty loud.

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Thanks, Derrick.

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And of course, if the
car alarm went off,

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you probably
wouldn't hear it

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over the
sound of the test.

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Probably not.

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So, so the next
question we have is

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how much thrust does
the RS-25 engine produce?

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Alright, the
RS-25 engine produces

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470,000 pounds of thrust.

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That's vacuum rated.

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So that's at altitude,

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that's at 100% of
the rated power level.

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Now, on the Fred Haise
stand in preparation

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for Artemis missions, we
are testing these engines

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to 113% of its
rated power level,

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and at that power,
at that setting

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it produces approximately 530,000 pounds of thrust.

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To give you a
little bit of idea,

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of perspective here,

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that's about 15 times
the combined thrust

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of the two engines
on an F-22 fighter.

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Thanks, Derek.

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Now, speaking
about the thrust,

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someone wants to
know how hot and fast

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is the engine
plume during a test.

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All right.

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The gas coming out of
the nozzle of the engine

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is at about 6,000
degrees Fahrenheit.

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It's moving at about 4,
a little over 14,000

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feet per second or over
9,000 miles per hour.

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The heat is so much
that we use about

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230 to 240,000 gallons
per minute of water

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in our deflector to
cool it and to keep the,

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the, the engine from
damaging our facility.

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Thanks, Derrick.

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Now, some folks that
have watched the,

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the engine test during the
livestream, they've asked

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what produces
that cone of light

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you see right beneath
the engine nozzle?

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Alright, that cone
of light is called

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a shock diamond or
sometimes referred to

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as a mach diamond.

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What causes that is
that when we're testing

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at sea level here,
the engine nozzle

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is a little over expanded

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because it's
optimized for at altitude.

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What that causes is the
the pressure of the plume

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coming out of the
nozzle is slightly lower

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than the atmospheric
pressure around it.

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So as the atmospheric
pressure interacts

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with the plume,
it compresses it

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and straightens
it back out.

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And instead of letting
it continue to expand,

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this actually causes
the velocities to reduce

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and the
temperatures to increase.

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So right at that point
where that diamond is,

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the temperatures are
actually starting to

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ignite any residual fuel
that's in the plume, and

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that's why it's visible
in that, in that area.

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If you watch, depending
on what videos you see

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as you're watching it,

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you'll see that
diamond moving

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in relation to the
exit plane of the nozzle.

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And when that moves,
that's when we

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are changing the power
level of the engine.

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So the closer
it is to the engine,

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the lower our
power level is.

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Thanks, Derek.

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That shows us that physics
can sometimes be beautiful

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because that is a
lovely mach diamond

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to look at during a test.

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Yes, sir, it is.

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Now, the next question
we have is how much fuel

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is used during a
typical RS-25 hot fire.

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All right, Lacy,

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our propellant consumption
on a typical test varies

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based off of our
power level settings.

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So what our
profile is looking at

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and also the duration.

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Typically for a
normal profile,

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we're looking at about
6,500 gallons per minute

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of liquid oxygen and
about 14,000 gallons

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per minute of
liquid hydrogen.

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Our typical test is
approximately 500 seconds.

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Sometimes what you'll see
us go a little longer,

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like our last
test was 630 seconds,

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but we'll typically use
about 55,000 gallons

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of liquid oxygen and
about 140,000 gallons

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of liquid hydrogen during
a normal 500 second test.

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We use an additional 8,000
gallons approximately

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of liquid oxygen to chill
in our transfer line,

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our run ducts and the
engine prior to test,

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and we'll use about
another 6 or 7,000 gallons

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of LH or liquid
hydrogen to do the same

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on the fuel
side of the system.

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Our run tanks aren't large
enough to accomplish this.

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So what we'll do
is we'll top off

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our fuel tanks
prior to test.

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But then again our, but
our even, even with that,

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our LOX tank is
only 40,000 gallons

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and our LH tank is
only 100,000 gallons.

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So we need to top off
those tanks during tests

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from our barges
that you see

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docked at the
side of the stands.

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We'll have separate people
that operate those that,

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those transfers
to keep their,

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00:13:13,959 --> 00:13:15,194
keep the test conductor

254
00:13:15,261 --> 00:13:18,230
free from having
to worry about that.

255
00:13:18,297 --> 00:13:22,201
So, we use a lot
more than what you think

256
00:13:22,268 --> 00:13:24,203
just for what the
engine's consuming.

257
00:13:24,270 --> 00:13:27,406
But we've managed
to make it work.

258
00:13:27,473 --> 00:13:28,340
Thanks, Derek.

259
00:13:28,407 --> 00:13:30,376
Now we have a final
question for the day.

260
00:13:30,442 --> 00:13:32,211
And most people, as
they watch the test,

261
00:13:32,278 --> 00:13:34,813
they notice the,
the large white cloud

262
00:13:34,880 --> 00:13:36,615
exiting the test stand.

263
00:13:36,682 --> 00:13:37,983
And somebody
wants to know,

264
00:13:38,050 --> 00:13:41,487
is that plume,
is that cloud safe?

265
00:13:41,554 --> 00:13:43,856
Yes, that cloud is safe.

266
00:13:43,923 --> 00:13:46,792
It is primarily
water vapor.

267
00:13:46,859 --> 00:13:50,229
So with the RS-25 engine
operating on liquid oxygen

268
00:13:50,296 --> 00:13:52,531
and liquid hydrogen,
when you combine

269
00:13:52,598 --> 00:13:55,534
those two elements,
you get water.

270
00:13:55,601 --> 00:13:57,937
So you get water in
a vaporized state,

271
00:13:58,003 --> 00:14:00,906
and then you mix that
with the 200,000 gallons

272
00:14:00,973 --> 00:14:02,741
of water that's
coming down the deflector

273
00:14:02,808 --> 00:14:07,646
that is being vaporized
by that hot plume,

274
00:14:07,713 --> 00:14:09,081
and that's why
the cloud is so big.

275
00:14:09,148 --> 00:14:13,619
It is almost
all water vapor,

276
00:14:13,686 --> 00:14:16,322
you know, and
it's perfectly safe.

277
00:14:16,388 --> 00:14:18,824
As it cools, as it
rises in the atmosphere

278
00:14:18,891 --> 00:14:20,993
and cools, it'll
actually start raining,

279
00:14:21,060 --> 00:14:23,195
and we get a
localized rain event

280
00:14:23,262 --> 00:14:25,364
right here on
the facility.

281
00:14:25,431 --> 00:14:27,833
And it's perfectly
fine if it get,

282
00:14:27,900 --> 00:14:30,569
if that
water gets on you.

283
00:14:30,636 --> 00:14:32,905
Well, thank you for
joining us today, Derek.

284
00:14:32,972 --> 00:14:34,073
And that's all
the time we have

285
00:14:34,139 --> 00:14:35,975
for questions
on this broadcast.

286
00:14:36,041 --> 00:14:38,244
But if you have questions,
we invite you to send them

287
00:14:38,310 --> 00:14:41,780
in so we can answer them
on a future livestream.

288
00:14:41,847 --> 00:14:44,216
There is an email address
on the screen now,

289
00:14:44,283 --> 00:14:45,517
and we'll be
sharing that also

290
00:14:45,584 --> 00:14:47,886
during our livestream
that's upcoming.

291
00:14:47,953 --> 00:14:51,290
We're approaching an
RS-25 test right now.

292
00:14:51,357 --> 00:14:52,791
We thank you
for joining us.

293
00:14:52,858 --> 00:14:56,295
Now, let's get ready to
shake, rattle and roar.

294
00:15:23,989 --> 00:23:48,527
(engine rumbling)