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Hi, I'm Chris and this is NASA Now.
[ Sounds of Fireworks ]
Have you ever watched fireworks and noticed
that you see the flash before you hear the sound?
You have probably heard that light travels faster than sound
but how fast does sound travel, and how does sound travel
through the atmosphere?
We'll talk with a NASA expert
who will help us crack the sound barrier question.
That's ahead, first here's what's happening at NASA Now.
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Supersonic aircraft flying over a special test area
of Edwards Air Force Base
in California are making quite a racket to help crack
down on noise pollution.
NASA Dryden Research Center is collecting and analyzing data
on sonic booms for a special project called SCAMP,
or Superboom Caustic Analysis and Measurement Program.
The research will be used by scientist and engineers
to design low-boom supersonic aircraft
that will create less noise pollution.
This is all part of NASA's green aviation initiative
to develop commercial and military aircraft
that are faster and more efficient
with less impact on the environment.
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Now let's take a look at the past.
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October 14, 1947, world-renowned test pilot Capt.
Chuck Yeager does what no human has done before.
Yeager breaks the sound barrier piloting the XS-1 test vehicle;
which means he is the first person ever to fly faster
than the speed of sound.
The speed of sound in air at sea level is right
around 761 miles per hour, or 1225 kilometers per hour.
The speed of sound varies depending
on altitude and temperature.
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Imagine traveling almost 23 times faster than the speed
of sound, approximately 17,500 miles per hour,
or 28,163 kilometers an hour.
That's the speed necessary for a spacecraft
to enter into low earth orbit.
So how did NASA's shuttle fleet, during its 30 years of missions,
safely return 789 astronauts and cosmonauts back to Earth?
To help us answer this question we caught up with Guidance,
Navigation and Flight Controls Engineer George Hatcher
at Kennedy Space Center.
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When you separate from the International Space Station,
and when you're docked with it,
both of you are still going 25 times faster
than a speeding bullet coming out of a rifle barrel.
Because we've given this vehicle 17,500 miles per hour worth
of momentum just to get it into orbit so that it can match
up with the International Space Station.
All of that kinetic energy has
to be dissipated before we can fly it like an airplane.
Because we need to get it down to say for instance Mach 5,
which is the threshold of hypersonic flight,
before we can start nosing over and flying like an airplane.
We fly belly first because it presents the largest area
possible to maximize the drag
so that we can slow down with efficiency.
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The speed of sound is essentially how long does it
take for one molecule of air to bounce into another one,
so that information in the form
of pressure waves can propagate throughout the air?
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When the vehicle moves 25 times faster than the air can talk
to itself, when this molecule gets hit the next one doesn't
even know the shuttle is coming.
It doesn't have time for that molecule to bounce
into the other one before the shuttle has barreled through it.
It in fact, hits the molecule so hard that it dissociates them.
There's enough energy, kinetic energy,
of the vehicle hitting the atmosphere
that the electrons are ripped clean of their nuclei.
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When you tear electrons off of their nuclei,
you end up with a fourth state of matter, which we call plasma.
Plasma, in nature, really only exists on the sun.
So if you can imagine how hot the sun is,
that can give you an idea of the environment
that the shuttle sees on the way back in the atmosphere.
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The reason that we have all these tiles on the bottom
of the vehicle and the reason
that they must withstand temperatures of hundreds
of degrees is because now you start
to impact the upper atmosphere
and even though it's very sparse,
the molecules are very far apart,
the vehicle is doing what we call mach 25, 25 times faster
than the speed of sound.
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When we start flying like a plane,
it's flying faster than an SR-71.
[ Boom Boom ]
Twin sonic booms heralding Atlantis' arrival.
It's flying faster than the cruising speed of a spy plane
that can go from LA to New York in under an hour.
This is the reason that when you watch that map as it screams in,
it can enter the atmosphere over the Pacific and in a matter
of minutes land in Florida.
So, we're talking many, many times faster than any kind
of passenger jet that you would travel on.
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Did you know that you don't need a plane or space shuttle
to break the sound barrier?
The crack of a whip is produced when a section
of the whip moves faster than the speed of sound
and creates a sonic boom, which is measured
in pounds per square foot of overpressure.
Overpressure is the amount of the increase
above the normal atmospheric pressure that surrounds us.
Normal air pressure at sea level is right
around 14.7 pounds per square inch.
Now you know.
Now it's time to check out what's up.
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Fall is in the air and that means we are likely
to see the Orionid meteor shower.
Every year around the same time,
the Orionid meteor shower averages
around 13 meteors per hour from October 18th to the 26th.
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Teachers, now you can bring the thrill
of speed into your classroom.
Check out this new lesson.
Coming this year to the Virtual Campus is a new lesson called
Linear Equations: NASA Connect - Breaking Barriers.
Your students will try their hand at designing
and testing a balloon X-1 rocket model.
For more information visit the NASA Explorer Schools Virtual
Campus and look in the lesson library.
Well that's it for NASA Now.
Join us next time when we see there's more to the moon
than just a lot of dust.
We'll see you then on NASA Now.
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NASA Now comes to you from the Virtual Campus
at NASA Explorer Schools.