June 2019, ScientificAmerican.com 65PENELOPE BREESEGetty ImagesMARCH 23, 1983
President Ronald Reagan announces
the nation will start an expanded R&D
program for missile defense, called the
Strategic Defense Initiative, or SDI.MAY 1972
U.S. and Soviet Union
sign the Anti-Ballistic
Missile Treaty, limiting
defense technology.JANUARY 29, 1991
In place of the SDI, President George H. W. Bush announces
the Global Protection Against Limited Strikes (GPALS) system
to counter unauthorized, accidental or limited attacks.
JULY 31, 1991
Presidents Bush and Mikhail Gorbachev
of the former Soviet Union sign START I, reducing
arsenals to 6,000 deployed warheads on each side.THE
TROUBLED
PAST OF
MISSILE
DEFENSE
The U.S. has struggled
to make effective long-
range missile inter-
ceptors, including the
Ground-based Mid-
course Defense system,
and diplomatic
ap proaches have
often been undercut.
Ground-based Midcourse
Defense (GMD) System Tests
Success Failureenter the atmosphere and drop toward their targets in the termi-
nal flight phase, which lasts only a few minutes.
Defense efforts have focused on the midcourse period be-
cause it lasts much longer than the boost phase, and by inter-
cepting at long distances from the targets, the system can defend
much larger areas than it could at the terminal stage. The earliest
interceptors carried their own nuclear weapons to blow up the
incoming warhead. But in the late 1970s development began on
prototype interceptors that carried a nonexplosive “kill vehicle.”
Onboard sensors were supposed to guide the vehicle into the in-
coming warhead during its midcourse phase. At a collision speed
of 10 kilometers per second, the kinetic energy per mass is more
than 10 times the energy released by a similar amount of high ex-
plosives, so such impacts could destroy warheads in a direct hit
and avoid the use of a nuclear detonation for defense. This “hit to
kill” method requires sophisticated technology. The kill vehicles
must be guided to within centimeters of a precise target point on
the incoming missile warhead.
Bush’s plan was to get a system into the field quickly and
then improve it. In September 2004 the administration stated
that the system had achieved a “limited deployment option,”
which meant it could be turned on and used if necessary. Only
five interceptors were in place the day of that announcement.
Today the GMD comprises space-based sensors, terrestrial ra-
dars, 44 interceptors based in Alaska and California, and facilities
and personnel to control operations. The Department of Defense’s
current plan is to increase the number of interceptors to 64 by
2023 and possibly add more soon thereafter to reach a total of 100.HOLES IN THE DEFENSE
thE push to dEploy this system, however, has produced serious
shortcomings, and the GMD has yet to demonstrate a usefulmilitary capability. The roots of the problems lie both in the
shortcuts the government took to move the program forward
and in the technical complexity of missile defense.
In 2002 Bush’s dod exempted the program from the Penta-
gon’s traditional “fly before you buy” oversight rules, intended to
make sure major defense systems and equipment work well be-
fore the nation has to depend on them. Under those rules, the
GMD system would need to meet criteria for technical maturity
and effectiveness and to undergo demanding operational tests to
ensure that it worked as required under real-world conditions
before being put in the field. But Bush’s exemption meant that
prototype interceptors for research and development—by defini-
tion not intended for the real world—could be used in urgent sit-
uations. While faster, this approach permits the use of unreliable
or poorly tested equipment.
In 2014—10 years after the limited deployment announce-
ment—all GMD interceptors in the field were put there before
the Pentagon had conducted a single successful intercept test of
their design, according to reviews by the dod and Congress. Ide-
ally, a rigorous engineering process identifies problems early
and allows them to be fixed before deployment. But with the
GMD system, failed intercept tests revealed design flaws that re-
quired expensive retrofits of dozens of interceptors already in si-
los. Because the interceptors were being fielded as they were be-
ing tested, hardware and software components and designs vary
from interceptor to interceptor, making it difficult to use the
performance of one to predict that of another or to resolve prob-
lems across the entire fleet.
GMD interceptors have destroyed their targets in just more
than half the 19 intercept tests conducted. The record is not im-
proving with time. Six of the 11 tests since 2004 have failed to de-
stroy their target. Of the most recent six tests, three have failed.1980 1990