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Hello. I'm Lacy Thompson.
I serve as a news chief here
at NASA's Stennis Space Center
near Bay St. Louis, Mississippi.
I'm standing not too far from
the Fred Haise Test Stand.
This is where NASA tests RS-25 engines to help
power the SLS or Space Launch System rocket
on Artemis missions back to the Moon,
as we prepare for future journeys to Mars.
I'm joined by one of our NASA test engineers
and test conductors, Derek Zacher.
Derek has agreed to answer some of the questions
we've received during recent
livestream broadcasts of RS-25 tests.
Derek, thank you for joining.
Happy to be here.
Before we get on to the questions,
I'd like to ask you to share a little bit
about yourself and how you became a test engineer
and conductor here at NASA Stennis.
All right.
Well, got into, interested in aerospace as a child.
I was more interested in the jet engines
and aircraft than I was rockets and space.
I went to school down at Embry Riddle,
down in Daytona Beach, and that was close enough
to Kennedy that I was able to go down and see a
bunch of launches and got really excited about it.
Had an opportunity to come down here
to Stennis working for Orbital Sciences
on their Antares program.
And then, when, after our first launch there,
I was able to get a job here at NASA working
with the team here on the stand testing the RS-25.
Thank you, Derek.
We're so glad you're part
of the NASA Stennis family.
Now let's get on to the questions.
And the first question relates to an upcoming
RS-25 test on the Fred Haise Test Stand.
Somebody wants to know what the engine
being tested is for, whether it's a
new engine or a heritage space shuttle engine.
All right.
This engine here is made up,
manufactured of all new components.
It's part of our certification test series.
What we did was we're, we have about
12 engines left that are going to
work through Artemis II through IV.
And now, then we have to utilize
new manufactured engines.
So we are using new techniques
for manufacturing, new materials that either
weren't available at the time when this,
when these engines were first
manufactured or weren't suitable for the reusable
aspects of the space shuttle main engine.
So these tests are to verify that those changes
don't impact the performance of the engine,
that it's still, it's suitable to meet our needs
and is still reliable to get
our astronauts safely into orbit.
And those new engines are being produced by the
lead engines contractor Aerojet Rocketdyne,
is that correct?
Yes, sir. Correct.
They are being, all the components are
manufactured out at their facility in California,
and then they are shipped here to Stennis,
where they are assembled and then
brought out to the stand to be tested.
And after we are finished testing them, when we get
to the flight engines after testing,
they will be sent down to Michoud Flight Facility
outside of New Orleans, where they will be
integrated into the next SLS core stage.
Well, thank you, Derek.
Let's get onto the next question.
And somebody wants to know
what weather conditions permit a test.
For instance, can you test during a thunderstorm?
All right.
We could test pretty much any time.
There are activities prior to the test
that require our personnel to be outside
doing setups and inspections.
Obviously, they can't be outside
during a thunderstorm for those.
We have a lightning detection system
at our facility that will alert us if there are
lightning strikes within 5 to 10 miles.
And in those situations,
our people can't go outside.
Down here in Mississippi, we're lucky that most of
the time the weather comes here in the afternoon,
and the mornings are pretty clear.
So when we know weather's coming in, in the
afternoon, we'll try to pull all of the setups
and all of the inspections forward
in the count to try to get them out of the way
before the weather comes in.
We have backup generators that provide power,
that in the event that we have a lightning strike
that knocks out commercial power,
we'll still have power to run all of our systems.
And then in the event that in the last
couple of minutes before a test,
we, when we're trying to do our
final inspections, if we can't send people
outside to do those, most of the areas
that we need to look at have adequate coverage
via a video camera that we can do
with inspection that way.
At the end of the day, though,
what it comes down to is if the test director
feels that it is a, the risk level has elevated
to such a level that it's not acceptable,
he can choose to scrub the test.
Well, that's great information, Derrick.
Thank you.
Now, the next question is how loud
and powerful are these RS-25 tests?
For instance, will they set off nearby car alarms?
All right, well, these are pretty loud tests.
We don't allow too many people outside of enclo...
enclosed structures close to the stand.
But anybody within about 200 yards
or so is wearing hearing protection because
it's above our acceptable limits.
I have never heard of a car alarm
going off out here.
But on that note, you know,
we're a pretty secure area out here.
So most people don't even lock their cars
when they're out here.
So it probably doesn't.
They're probably not even armed.
Now, I have heard some friends that live,
you know, 15, 20 miles away from here.
They're telling me that when the clouds are low
and the weather is just right, they can actually
hear us from, you know, 15, 20 miles away.
So it is pretty loud.
Thanks, Derrick.
And of course, if the car alarm went off,
you probably wouldn't hear it
over the sound of the test.
Probably not.
So, so the next question we have is
how much thrust does the RS-25 engine produce?
Alright, the RS-25 engine produces
470,000 pounds of thrust.
That's vacuum rated.
So that's at altitude,
that's at 100% of the rated power level.
Now, on the Fred Haise stand in preparation
for Artemis missions, we are testing these engines
to 113% of its rated power level,
and at that power, at that setting
it produces approximately 530,000 pounds of thrust.
To give you a little bit of idea,
of perspective here,
that's about 15 times the combined thrust
of the two engines on an F-22 fighter.
Thanks, Derek.
Now, speaking about the thrust,
someone wants to know how hot and fast
is the engine plume during a test.
All right.
The gas coming out of the nozzle of the engine
is at about 6,000 degrees Fahrenheit.
It's moving at about 4, a little over 14,000
feet per second or over 9,000 miles per hour.
The heat is so much that we use about
230 to 240,000 gallons per minute of water
in our deflector to cool it and to keep the,
the, the engine from damaging our facility.
Thanks, Derrick.
Now, some folks that have watched the,
the engine test during the livestream, they've asked
what produces that cone of light
you see right beneath the engine nozzle?
Alright, that cone of light is called
a shock diamond or sometimes referred to
as a mach diamond.
What causes that is that when we're testing
at sea level here, the engine nozzle
is a little over expanded
because it's optimized for at altitude.
What that causes is the the pressure of the plume
coming out of the nozzle is slightly lower
than the atmospheric pressure around it.
So as the atmospheric pressure interacts
with the plume, it compresses it
and straightens it back out.
And instead of letting it continue to expand,
this actually causes the velocities to reduce
and the temperatures to increase.
So right at that point where that diamond is,
the temperatures are actually starting to
ignite any residual fuel that's in the plume, and
that's why it's visible in that, in that area.
If you watch, depending on what videos you see
as you're watching it,
you'll see that diamond moving
in relation to the exit plane of the nozzle.
And when that moves, that's when we
are changing the power level of the engine.
So the closer it is to the engine,
the lower our power level is.
Thanks, Derek.
That shows us that physics can sometimes be beautiful
because that is a lovely mach diamond
to look at during a test.
Yes, sir, it is.
Now, the next question we have is how much fuel
is used during a typical RS-25 hot fire.
All right, Lacy,
our propellant consumption on a typical test varies
based off of our power level settings.
So what our profile is looking at
and also the duration.
Typically for a normal profile,
we're looking at about 6,500 gallons per minute
of liquid oxygen and about 14,000 gallons
per minute of liquid hydrogen.
Our typical test is approximately 500 seconds.
Sometimes what you'll see us go a little longer,
like our last test was 630 seconds,
but we'll typically use about 55,000 gallons
of liquid oxygen and about 140,000 gallons
of liquid hydrogen during a normal 500 second test.
We use an additional 8,000 gallons approximately
of liquid oxygen to chill in our transfer line,
our run ducts and the engine prior to test,
and we'll use about another 6 or 7,000 gallons
of LH or liquid hydrogen to do the same
on the fuel side of the system.
Our run tanks aren't large enough to accomplish this.
So what we'll do is we'll top off
our fuel tanks prior to test.
But then again our, but our even, even with that,
our LOX tank is only 40,000 gallons
and our LH tank is only 100,000 gallons.
So we need to top off those tanks during tests
from our barges that you see
docked at the side of the stands.
We'll have separate people that operate those that,
those transfers to keep their,
keep the test conductor
free from having to worry about that.
So, we use a lot more than what you think
just for what the engine's consuming.
But we've managed to make it work.
Thanks, Derek.
Now we have a final question for the day.
And most people, as they watch the test,
they notice the, the large white cloud
exiting the test stand.
And somebody wants to know,
is that plume, is that cloud safe?
Yes, that cloud is safe.
It is primarily water vapor.
So with the RS-25 engine operating on liquid oxygen
and liquid hydrogen, when you combine
those two elements, you get water.
So you get water in a vaporized state,
and then you mix that with the 200,000 gallons
of water that's coming down the deflector
that is being vaporized by that hot plume,
and that's why the cloud is so big.
It is almost all water vapor,
you know, and it's perfectly safe.
As it cools, as it rises in the atmosphere
and cools, it'll actually start raining,
and we get a localized rain event
right here on the facility.
And it's perfectly fine if it get,
if that water gets on you.
Well, thank you for joining us today, Derek.
And that's all the time we have
for questions on this broadcast.
But if you have questions, we invite you to send them
in so we can answer them on a future livestream.
There is an email address on the screen now,
and we'll be sharing that also
during our livestream that's upcoming.
We're approaching an RS-25 test right now.
We thank you for joining us.
Now, let's get ready to shake, rattle and roar.
(engine rumbling)