New Study: Missile Defense Not Feasible

This is the ninth

study of technical concerns relevant to public policy issues released
by the society, and the first one done in over 15 years. The
eighth
study in 1987 focused on the
science and technology
of “directed energy weapons”, at the time one of the leading contenders
for strategic defense funding. It had a significant impact in redirecting
funding from the proposed laser and particle beam weapons to the more
realistic “kinetic” missile interceptors that are now undergoing testing.

Previous APS studies dealt generally with
energy
policy
and nuclear reactor
safety, in response to the energy crisis
of the 1970’s and the accident at Three Mile Island. As a nonprofit
membership organization, with members who work in universities
and research institutions and in the nuclear and defense industries,
and with the history of physicists developing
remarkable
innova
tions
in the conduct of warfare, while at the same time promoting peace,
APS studies are known for their factual, objective,
and nonpartisan analyses.

Boost
Phase Intercept involves destroying hostile missiles while they are still
in their boost phase, rising through the atmosphere on rocket power.
There are a number of obvious advantages to destroying missiles
at this point, rather than the current
midcourse
defense strategy that underlies the
National Missile Defense
program. During boost phase, the target is a large, hot, booster that is
moving relatively slowly, not a fast-moving small, cool, warhead. By
midcourse, there are a number of simple defense strategies, such as
use of decoys, that greatly reduce the chances of a successful
intervention.

There are two well-known disadvantages of boost phase interception, though, both
related to the need for very rapid reaction. An ICBM is in boost phase
for at most 4-5 minutes, vs. the 20-30 minutes the warheads spend in flight
on the way to their targets. So we need to be certain in a very
short period of time that what we are targetting is in fact
a hostile ICBM, and not
an
innocent target. Secondly, the short opportunity time means the
counter-missiles must be positioned sufficiently close to the
ICBM launch site that they can actually reach their target within minutes.
That means deployment not on our territory, but in the neighborhood
of the hostile nation. It could be done with air or sea-launched missiles,
but a better option seems to be ground-based deployment in a manner
similar to the current plans for
ground-based
midcourse defense, located closer to hostile territory.

The new
APS
study, relying on material in the open literature and basic principles of
rocket propulsion, signal detection, and laser beam propagation, casts
considerable doubt on the practicality of even this, the most promising
missile defense strategy. The conclusions of the study are:

1. Boost-phase defense against intercontinental ballistic missiles (ICBMs) hinges on
   the burn time of the attacking missile and the speed of the defending interceptor
   rocket. Defense of the entire United States against liquid-propellant ICBMs, such as
   those deployed early by the Soviet Union and the People’s Republic of China (China),
   launched from countries such as the Democratic People’s Republic of Korea (North
   Korea) and Iran, may be technically feasible using terrestrial (land-, sea-, or air-
   based) interceptors. However, the interceptor rockets would have to be substantially
   faster (and therefore necessarily larger) than those usually proposed in order to reach
   the ICBMs in time from international waters or neighboring countries willing to host
   the interceptors. The system would also require the capability to cope with at least
   the simplest of countermeasures.

2. Boost-phase defense of the entire United States against solid-propellant ICBMs,
   which have shorter burn times than liquid-propellant ICBMs, is unlikely to be practical
   when all factors are considered, no matter where or how interceptors are based.
   Even with optimistic assumptions, a terrestrial-based system would require very large
   interceptors with extremely high speeds and accelerations to defeat a solid-propellant
   ICBM launched from even a small country such as North Korea. Even such high-
   performance interceptors could not defend against solid-propellant ICBMs launched
   from Iran, because they could not be based close enough to disable the missiles
   before they deployed their munitions.

3. If interceptor rockets were based in space, their coverage would not be constrained
   by geography, but they would confront the same time constraints and engagement
   uncertainties as terrestrial-based interceptors. Consequently, their kill vehicles (the
   final homing stage of the interceptors) would have to be similar in size to those of
   terrestrial-based interceptors. With the technology we judge could become available
   within the next 15 years, defending against a single ICBM would require a thousand
   or more interceptors for a system having the lowest possible mass and providing
   realistic decision time. Deploying such a system would require at least a five- to
   tenfold increase over current U.S. space-launch rates.

4. The Airborne Laser now under development could have some capability against liquid-
   propellant missiles, but it would be ineffective against solid-propellant ICBMs, which
   are more heat-resistant.

5. The existing U.S. Navy Aegis system, using an interceptor rocket similar to the
   Standard Missile 2, should be capable of defending against short- or medium-range
   missiles launched from ships, barges, or other platforms off U.S. coasts. However,
   interceptor rockets would have to be positioned within a few tens of kilometers of
   the launch location of the attacking missile.

6. A key problem inherent in boost-phase defense is munitions shortfall: although a
   successful intercept would prevent munitions from reaching their target, it could
   cause live nuclear, chemical, or biological munitions to fall on populated areas short
   of the target, in the United States or other countries. Timing intercepts accurately
   enough to avoid this problem would be difficult.

Meanwhile, testing (and spending) continues under the current US
missile defense
strategy.