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One method for measuring the velocity
of the impacting projectile uses two laser curtains positioned a short distance
uprange of the target. Electronics attached to the laser system can detect
disruptions in the uprange and downrange beams as the projectile passes through
them. Since we know the distance between the curtains and and the elapsed
time between the disruptions between the two laser beams, we can calculate the projectile
velocity.
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We can also measure projectile velocity
using light detectors, since light is generally emitted during a hypervelocity
impact event. Light is emitted when the projectile impacts the target, but it
is also emitted when the sabot pieces impact the sabot stripper uprange. Again,
we know the distance and the time between these two light emissions, so we can
calculate a velocity.
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High speed cameras can also be used
to measure velocity. In addition they can be used to verify projectile integrity prior
to impact. Since the camera records an exact framing rate for a given
test, we know the time interval between frames. Using calibrated reference points,
we can measure the distance a projectile travels from one frame to the next. The velocity
can be quickly calculated. The cameras can also be used to measure other velocities,
like the velocity of various parts of the debris cloud, or of ejecta. We have more
information on the high speed cameras.
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Launching a projectile at hypervlocities
is such an energetic event, that occasionally the projectile breaks up during the
launch. Flash X-Rays are therefore used to verify the integrity of the projectile
for each shot. Flash x-rays are also used to map the propagation of the debris cloud
as it travels inside an opaque target. The HITF light gas gun has 3 x-ray heads. One
100 kV head perpendicular to the flight range which will verify projectile integrity
prior to impact, and two 300 kV heads in the target chamber which will scan the target
during impact.
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