[Background Music]
NASA studies how space vehicles perform as
they enter the atmosphere of planets by using
specialized research facilities.
One of these is the Hypervelocity Free-Flight Facility
at Ames Research Center at Moffet Field, California.
Researchers use scale models of space vehicles
that are not much larger in diameter than
a penny.
The models are propelled up to 20 times the
speed of sound through a 75 foot long test section
to simulate atmospheric entry.
The test section can be filled with air or
CO2, at low pressure simulating in high
altitude.
Planetary probe enters the atmosphere at much higher speeds than can be replicated by using 
a conventional gun to propel the models.
In the 1960s, NASA addressed this by developing a Hydrogen propelled gun technology called
"2 Staged Light Gas Gun."
Models can be fired at velocities up to 8
kilometers per second or about 1800 miles
per hour.
The models come in a variety of shapes, so they are encased in sleeves called "sabots"
to ensure consistent fit in the barrel of the gun.
The facility is ready for the test. [gun fires]
The sabot separates allowing the model to
fly down the range [pop sound]
In this test, the model is fired through a
partial sheet to give it an oscillation and
we observe its flight in slow motion through
the 16 measurement stations. The shockwave
just in front of the model is very hot--thousands of degrees.
Each test takes only a hundredth of a second.
