In early August North Korea threatened
to launch four intermediate-range
ballistic missiles to a point about 30
or 40 kilometers off the coast of Guam.
Tom, could you walk us through how US
missile defense systems would respond if
such a launch was detected 
So if that happens, the United States 
would first detect the missiles heat signatures
with satellites such as the Defense Support
Program, or the newer space-based
infrared system. Those satellites would then
cue terrestrial radars such as the TPY-2 
x-band radars in Japan and South Korea
which track the missiles with greater precision.
The threat missiles would be within
the radar field of view for
perhaps five or six minutes.
Aegis BMD ships might also be in
position to track the missiles flight.
The trajectory of the missiles headed
from North Korea to Guam would take them
over the southern part of Japan
they’d fly just south of Hiroshima and 
at that point they'd be at an altitude of
about 700 kilometers. So Tom, if the U.S.
determined that these missiles were
actually a threat to Guam, what systems
would be called upon to respond?
If the U.S. determines the missiles to be a
potential threat, we might try to shoot
them down using various missile defense
interceptors. This might include the
sea-launched standard missile-3, launched
from an Arleigh Burke-class destroyer, or
a land-based THAAD battery based in Guam
or some combination of the two.
Both systems have an excellent test record
but neither has been used in an operational
context against a ballistic missile
fired in anger. And all of this
would happen within a relatively short
period of time. So North Korea said it
would take about 17 minutes time of flight 
to reach Guam, others have said it could
take as little as 14 minutes
of course it depends on the specific
trajectory used - a more lofted trajectory
would take longer and rise to a higher
altitude in space while a more shallow
trajectory would take a bit less time
and stay at a lower altitude
so an intercept attempt with an Aegis
standard missile would be outside the atmosphere
close to its apogee, during its mid-course,
or during its downward descent
with the THAAD system. So all of this
provides an interesting case study into
how such a scenario could unfold and the
way U.S. missile defense systems are
designed to protect against such threats.
Right, this is the kind of threat that
we've seen coming for a long time, this
is why the systems are located where
they are, the radars and the interceptors,
but we hope we don't have to use them.
To learn more about both the
threat missiles from North Korea and
the various missile defense systems
check out missilethreat.csis.org
