Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 30
2
U.S. Boost-Phase Defense
BACKGROUND
One of the primary perceived benefits of boost-phase defense is the ability to
shoot down a missile during its powered phase, when it presents a bright plume
signature and before it disperses its payload and countermeasures, thereby clearly
identifying the target to be destroyed. This potential to overcome the midcourse
discrimination problem has been among the reasons for interest in the pursuit of
boost-phase defense.
The difficulty is that the boost-phase interceptor (BPI) has to be within range
of a point at which it can intercept the target when launch occurs and must be able
to respond with a very short action time. This turns out to be much easier said
than done. Since the time from detection of a hostile launch until it completes
boost is often as little as a minute and, even for slower burning liquid-fueled
intercontinental ballistic missiles (ICBMs) is unlikely to exceed 250 sec, any
boost-phase intercept—accomplished kinetically or by directed energy—must
be launched after detection from a platform that is within the range and action
time of the interceptor, essentially intercepting before “booster cut-off” of the
hostile missile.
While it sounds like a good idea, boost-phase defense presents a unique set
of challenges. For starters, whether a solid or liquid rocket motor is used to pro-
pel the hostile missile, the boost-phase timeline is very short. In a gross sense,
the intercept process must first determine if the launch in fact is a hostile missile
and, if it is, determine its trajectory. Then the vehicle providing the “kill” func-
tion—known as the kill vehicle (KV)—must acquire and shoot at the target. Here,
detection range and kill range capability must be considered.
Ground- and ship-based, manned and unmanned aircraft as well as space-
30
OCR for page 31
U.S. BOOST-PHASE DEFENSE 31
based interceptor platforms have all been proposed, but either the interceptor
platform has to be so close to the threat launch point as to be vulnerable to attack
itself, or the velocity of the intercepting projectile has to be very great. The latter
is one reason for the interest in using directed-energy (speed of light) weapons
for boost-phase interecept.
Today’s proposed boost-phase systems originated in the Strategic Defense
Initiative era’s research programs. In more recent years, considerable effort has
been expended in the development of an in-flight directed-energy platform—a
heavily modified Boeing 747-400F airplane. Another option is destroying mis-
siles on their launch pads prior to a suspected launch; this could have grave politi-
cal consequences should an “innocent” missile be destroyed on the pad.
While boost-phase defense has been advocated as the most efficient way to
deal with fractionated payloads and exoatmospheric (midcourse) penetration aids,
it is extremely sensitive to assumptions about threat booster characteristics. Over
time, boost-phase defense tends to be renamed ascent-phase defense when the
kinematic realities set in. In fact, ascent-phase defense is code for engagement in
the postboost or early midcourse phases of flight.
The limitations and complications of a surface-based boost-phase defense lie
primarily in the concepts of operations (CONOPS), policy, time, and geography.
Since the timelines for engagement in the boost-phase are extremely short, the
on-site commander must have authorization from the National Command Author-
ity to launch an interceptor immediately after a threat missile has been detected. 1
Also, access must be gained to countries adjacent to the threat country in order
to position a boost-phase system close enough, and at the correct geometries, to
successfully engage the threat missile. Finally, boost-phase systems are only ef-
fective against countries that do not have large enough landmasses to allow them
to launch missiles from deep within their territory.
The airborne laser is designed to deliver energy at the speed of light to per-
form the boost-phase intercept mission. Space-based lasers were also pursued in
the past. Virtually no fly-out time is involved, and the beam agility is a function
only of how fast the pointing optics can be repositioned. While laser weapons
sound like the obvious answer, the energy that a laser can deliver on a target is
limited by the power available and the aperture of the device. Atmospheric effects
disturb the beam. Much has been accomplished in advancing the pointing and
tracking capabilities and the adaptive optics to maintain beam quality, but some
fundamental limitations remain.
1
Even if the weapons release delay is assumed to be zero, the range limits make boost-phase
defense infeasible.
OCR for page 32
32 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
PROPOSED SYSTEMS
The recently redirected airborne laser (ABL) program was one of two boost-
phase systems under development. While the ABL program came from more
than 2 decades of military laser development, it could not provide an operation-
ally useful boost-phase capability, partly because the inherent range limitations
of the atmospheric propagation meant that the Boeing 747-400F would need to
operate in hostile airspace. An alternative approach has been to develop a kinetic
kill vehicle (KKV) for boost-phase defense by harnessing the successful invest-
ments the United States has made over the past several decades for the purpose
of midcourse defense, although a KKV for this purpose would have to be much
more agile than a KKV for midcourse defense. The Kinetic Energy Interceptor
(KEI) program was undertaken for that reason. In principle, boost-phase kinetic
interceptors could be launched from land-, sea-, air-, or space-based platforms.
However, the efficacy of such interceptors is uncertain. In the following section
the committee provides additional information on the U.S. boost-phase systems
examined in this report, as called for in the congressional tasking. Specifically, the
KEI and ABL programs and other existing boost-phase technology demonstration
programs are first described and then analyzed.
Kinetic Energy Interceptor
The KEI program was initiated in 2002 by the Missile Defense Agency
(MDA) based on a recommendation by the Defense Science Board that a boost-
phase intercept capability be developed with higher average velocity (high v bo
and high acceleration) missiles to enhance ballistic missile defense and as an
alternative to the ABL program.2 The Office of the Under Secretary of Defense
for Policy also found that a boost-phase intercept capability was required for af-
fordability reasons. Furthermore, the ABM Treaty had recently been abrogated,
making it possible to develop and deploy such a system. MDA developed a
capabilities-based Request for Proposal for a transportable, ground-based boost-
phase interceptor system and presented it to industry in December 2002.
The KEI program was originally funded as a $4.6 billion (in then-year dol-
lars), 8-year development and test boost-phase system using a modified SM-3
seeker and an Exoatmospheric Kill Vehicle Divert and Attitude Control System
(EKV DACS) for the KV. Immediately after the contract had been awarded, how-
ever, the funding for KEI was significantly reduced and government requirements
were added. The mission was expanded in 2004 to include not only boost-phase
intercepts but also ascent-phase (prior to countermeasure deployment) and mid-
course intercepts.
The KEI program was terminated in 2009, just before a planned booster
2
Sean Collins, Missile Defense Agency, “Kinetic Energy Interceptor (KEI) Briefing to the National
Academy of Sciences,” presentation to the committee, January 14, 2010.
OCR for page 33
U.S. BOOST-PHASE DEFENSE 33
flight test. According to MDA, the threat had evolved to the point where the
expected capability of the KEI system was inconsistent with the strategy for
countering rogue nation threats.3 It is also possible that extremely high costs and
delays played a role in termination of the program. By that time, the KEI program
had experienced mission changes coupled with technical difficulties, which led
to cost growth. The projected cost to complete the contract almost doubled, from
$4.6 billion to $8.9 billion (also in then-year dollars). In addition, the develop-
ment schedule, originally 5.5 years, was projected to take 14-16 years to com-
plete. Over the course of the program, the average unit cost of a KEI interceptor
had also increased, from $25 million to over $50 million (in then-year dollars).
Prior to termination of the program, the mitigation of technical issues had delayed
the first prototype booster flight test date (established in 2007) by over a year.
As shown in Figure 2-1, the KEI system consisted of a BMC2 component, a
mobile launcher, and an interceptor all up round. KEI had no organic sensors but
had direct access to overhead IR sensors and indirect access to other overhead
national asset capabilities and to BMD system ground sensors when available.
The KEI fire unit consisted of redundant BMC2 systems that received sen-
sor input, calculated the fire control solution, and communicated with the inter-
ceptor before and during flight. The mobile transporter erector launcher (TEL)
transported and launched one round per launcher. It was transportable by C-17
or C-5A aircraft. The interceptor component was a 40-inch diameter, two-stage
solid rocket. It carried a third-stage rocket motor (TSRM) in the payload that
was used when additional velocity was required. The KV was a derivative of the
SM-3 (two-color seeker) and the EKV DACS. It would have been capable in the
boost, ascent, and midcourse intercept regions.
The CONOPS for the KEI system was very much the same as the CONOPS
for tactical air and missile defense systems currently employed by the U.S. Army
and the U.S. Navy. The land-based system was mobile and transportable by U.S.
Air Force aircraft. The CONOPS called for KEI batteries to be garrisoned at
continental United States (CONUS) locations until needed for national defense
or defense of an allied country. A fire unit consisting of command and control
units and 10 missile launchers with their associated transport vehicles would be
transported to the theater of operations. The fire unit would move to its combat
position and be emplaced. Emplacement time was estimated at approximately 3
hr. The fire unit commander would receive his rules of engagement (ROE) from
his higher headquarters, which during expected periods of combat would require
“Weapons Free” (authorization to fire). Upon launch of a threat missile, overhead
sensors would detect and report the launch directly to the KEI fire unit. The KEI
command and control system would evaluate the threat, classify it, and launch a
KEI interceptor at a predicted intercept point in space. Continuous updates would
be provided to the interceptor based on overhead sensor data.
3
Ibid.
OCR for page 34
34
FIGURE 2-1 KEI system integration. BMDS, ballistic missile defense system; CNIP, C2BMC network interface processor; JNIC, Joint National
Integration Center; ROE, rules of engagement. SOURCE: Craig van Schilfgaarde, David Theisen, Steve Rowland, and Guy Reynard, Northrop
Grumman Corporation, “An Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives:
Northrop Grumman Perspective,” presentation to the committee, July 13, 2010. Courtesy of Northrop Grumman Corporation.
OCR for page 35
U.S. BOOST-PHASE DEFENSE 35
Airborne Laser
The ABL program was planned to provide a boost-phase defense capabil-
ity against a range of missile threats. This is no longer a program of record for
the MDA but has been downgraded to a research program called the Airborne
Laser Test Bed (ALTB), an advanced program for the directed-energy research
program. For the purposes of this report, ABL is referred to as if it could provide
an operational defense capability; where appropriate, the differences between the
original ABL and the present ALTB are noted.
The attractiveness of using directed-energy weapons, notably lasers, for
boost-phase defense arises out of their potential to deliver a lethal dose of damage
to a target at the velocity of light from long distances. The fundamental properties
on which the choice of the laser depends include the wavelength, power output,
efficiency of conversion of the primary energy into laser energy, and, of course,
size and weight.
So, in principle, the laser is ideal for boost-phase intercept since it is able
to project a large amount of power at the speed of light over several hundred ki-
lometers onto a modest-sized (~1 m) spot. To capitalize on these benefits, MDA
established the ABL program, which was proposed to consist of a large airframe
(a modified Boeing 747-400F airplane) carrying a multimegawatt laser, known
as the high-energy laser (HEL). The HEL beam is directed onto the boosting
missile body for several seconds. During that time sufficient energy per unit area
(fluence) is delivered to cause enough heating to result in mechanical failure of
the missile body itself, thus disabling it and preventing the payload from reach-
ing its target. The advantage of this system is that it delivers a lethal fluence to
the threat missile in a matter of seconds from a great distance. Because the laser
beam travels at the speed of light, the distance from which the threat can be
intercepted is not limited by the flight time of a rocket interceptor. Rather, the
range is limited by the fluence required, the laser power, and the ability to focus
the beam onto the target at low elevation angles through the atmosphere. The
ability to focus depends on the laser beam quality and issues of light propagation
in the atmosphere itself. The beam propagation limitations are complex and are
provided in the classified annex (Appendix J).4
Figure 2-2 displays key parts of the ABL system aboard the Boeing 747-
400F. HELs are located in the body of the airframe, and the beam exits the plane
at the nose, directed by a large (1.5-m-diameter) movable mirror in a turret. 5 The
beam may be directed anywhere within a sphere with a cone cut out in the back-
ward and forward directions with respect to the line of flight. The mirror rotates
4
David K. Barton, Roger Falcone, Daniel Kleppner, Frederick K. Lamb, Ming K. Lau, Harvey L.
Lynch, David Moncton, et al., 2004. Report of the American Physical Society Study Group on Boost-
Phase Intercept Systems for National Missile Defense: Scientific and Technical Issues, American
Physical Society, College Park, Md., October 5.
5
Ibid., p. S299.
OCR for page 36
36 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
FIGURE 2-2 Cutaway of the ABL system showing its key parts. SOURCE: Col Laurence
Dobrot, USAF, Missile Defense Agency, “Airborne-Laser System Program Office: Pre-
sentation to the National Academy of Sciences,” presentation to the committee, January
14, 2010.
within the turret so that the beam may be directed by up to about 120 deg from
the line of flight.6 The turret rotates so that any angle around the line of flight
may be chosen.
The ABL must be on station near the location from which the threat missiles
would be launched. One or more ABLs would orbit in figure 8-like patterns in
that vicinity. Such patterns allow an advantageous side-on view of the potential
threat all of the time except when the airframe must turn at the end of the 8;
however, a side-on or head-on attitude is always maintained by choosing the
correct direction of circulation in the 8. The ABL would fly at an altitude of ap-
proximately 12 km in order to minimize the amount of atmosphere through which
the beam must travel. For redundancy and for dealing with multiple launches, two
ABLs would cover one threat area. Such redundancy would be necessary during
refueling operations to avoid gaps in coverage.
The ABL would operate autonomously to identify threats by means of on-
board IR sensors that detect the exhaust plume of the boosting missile. With
knowledge of the location of the threat, the tracking illuminator laser (TILL)
is activated to acquire the target, determine the exact aim point desired using
the image of the nose, and provide illumination for first-order adaptive optics
(AO) corrections. (Astronomers have used AO to at least partially cancel out
atmospheric disturbances.) The beacon illuminator laser (BILL) places its beam
6
Ibid., p. S339.
OCR for page 37
U.S. BOOST-PHASE DEFENSE 37
on the missile body, and that image provides the higher order correction infor-
mation. Finally, the chemical oxygen-iodine laser (COIL) is activated with the
HEL focused on the target for long enough to deliver the fluence required to
induce mechanical failure of the missile. Mechanical failure results from heating
a metal sufficiently to weaken it. It is not necessary to melt the metal to weaken
it considerably. The failure itself may come from rupture due to pressure inside
the container or from a loss of strength to resist the axial forces of acceleration
of the boosting missile. There will probably be a clear optical signature of the
mechanical failure to confirm the intercept. The signature may be an explosion
or very erratic flight of the booster.
It is unlikely that the defense will know when a threat missile is likely to be
launched. Therefore, the ABLs must be able to remain on station for extended
periods. Providing continuous coverage will require in-flight refueling and a
handoff to other airframes to relieve the crew or provide other maintenance for
the airframe or its systems.
Other
Space-Based Interceptors
One problem of surface-based (i.e., on land, at sea, or in the air) KKVs is
their access to the threat missile. There is a limit on how far a KKV can be based
from the intercept point (not the launch point); this limit depends on the fly-out
time of the interceptor and the burn time of the threat. A country that is large
enough can deliver an array of missile threats that are not vulnerable to surface-
based intercept in their boost phase. There may be political constraints on basing
interceptors outside enemy territory, in neighboring countries. One way to avoid
the geographic constraints suffered by surface-based interceptors is to base them
in space, on platforms that carry one or several such interceptors. The enemy
may thereby be denied all locations within the latitudes of the orbits. This is the
attractive feature of space-based interceptors (SBIs).
At this time there is no program of record within MDA for SBIs. This report
noted large differences in the size estimates of Lawrence Livermore National
Laboratory’s (LLNL’s) KV and that of the more conservative estimate found in
the 2004 American Physical Society (APS) report previously noted. The com-
mittee’s assessment of these differences and their validity are discussed in the
classified annex (Appendix J). In short, the committee believes the LLNL KV
was much lighter because it had much less divert velocity propulsion, apparently
because it separated from the booster first stage much later than did the APS KV
design. The committee believes the sizing methodology used in the APS report
OCR for page 38
38 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
is more realistic.7 In addition, MDA canceled the Space Test Bed program in its
2010 budget. Moreover,
in previous budgets, MDA had established the Space Test Bed to explore con-
cepts for and to conduct research to support potential deployment of boost-phase
intercept defenses in space. In the 2009 budget, MDA had planned to spend
about $300 million for that research, and the Congressional Budget Office’s
(CBO’s) projection of DOD’s plans, based on the 2009 future years defense plan
(FYDP), incorporated the assumption that an operational space based interceptor
system would be developed and fielded.8
The SBI platforms would be placed in multiple rings of satellites, with multi-
ple satellites per ring.9 The orbits are inclined with respect to Earth’s equator, and
the maximum latitude that the SBIs can cover is a little larger than the inclination
angle. Such a constellation of satellites results in nonuniform coverage of the
ground, where “coverage” means the number of satellites that are within range
to deliver an SBI to a threat missile within the time window. Generally speaking,
one wants to have at least one SBI within range, but it may be desirable to have
more than one for redundancy or to deal with raids. There is substantially better
coverage (i.e., more satellites within range) for latitudes near the orbit inclination
angle and poorer coverage at low latitudes. However, coverage at latitudes above
the orbit inclination rapidly drops to zero above the latitude of the inclination of
the orbit.
Airborne-Based Interceptors
Recently, ABIs, also known as airborne hit to kills (AHTKs), have been
reconsidered and show some potential applications in certain conflict scenarios.
The primary difficulty with ABIs, like all other proposed kinetic boost-phase
systems, is the need to be close enough (within about 50 km) to the target so
that an interceptor with a given speed and a KKV of sufficient agility can reach
and successfully home in on the accelerating booster before the boost phase
ends. ABI programs have existed in the past, but today only a few low-end
ABI systems based on existing interceptors remain on the drawing boards—for
example, the network-centric airborne defense element (NCADE), based on a
modified advanced medium-range air-to-air missile (AMRAAM) missile, and
7
Ibid.
8
Congressional Budget Office. 2004. Alternatives for Boost-Phase Missile Defense, Washington,
D.C., July.
9
The critical number for coverage is the average number of satellites within range, and that is well
characterized by the product of the number of rings times the number of satellites per ring. The trade-
off between the number of rings and the number of satellites per ring for a fixed product is slowly
varying. In addition, the satellites were assumed to have a service life of about 7 years and the disposal
of expired platforms is not taken into account.
OCR for page 39
U.S. BOOST-PHASE DEFENSE 39
the air-launched hit-to-kill (ALHK) program, based on an air-launched version
of the PAC-3 missile. These systems might be able to intercept boosting targets
at very short range, but they rely primarily on aerodynamic forces for divert
and, consequently, cannot intercept accelerating targets above approximately
30 km in altitude, where most of the boost phase occurs, especially for missiles
with ranges beyond 1,000 km. Hence, they cannot provide a robust boost-phase
intercept capability.
ANALYSIS
Overview
A boost-phase defense system is one that presumably avoids the midcourse
countermeasure problem, provided the system can intercept the hostile missile’s
burning booster rocket with its bright exhaust plume before the hostile missile
reaches its desired velocity and deploys its payload. If such a boost-phase defense
system can achieve that end within the extremely short engagement window
available, it can protect a large area against launches from a specific locale. In
principle, boost-phase intercept is technically feasible and appears attractive. To
take an extreme example, a soldier with a 50-caliber machine gun or handheld
rocket launcher 300 yards from a missile launch pad could easily destroy that
missile as soon as it lifts off its launch pad. This is so for three reasons: (1) the
soldier can see the hostile missile as soon as it emerges from its launcher; (2) the
speed and acceleration of the hostile missile at that time are very low compared
to the fly-out velocity of the soldier’s firepower; and (3) the hostile missile’s mo-
tion at that time is tracked by the soldier’s eyes and is predictable. For the same
reasons, an Aegis SM-2 Block IV antiair missile can shoot down a short-range
ship-launched Scud-type theater missile during boost if the Aegis ship is down-
range within 50 km of the launch.
Unfortunately, trying to intercept a hostile booster rocket (solid or liquid
propellant) from a significant distance dramatically turns the tables. For one
thing, there is not much time between knowledge of where the hostile missile is
directed and the time available for the interceptor to reach out to hit the target at
a militarily useful range. This is compounded by the fact that the hostile missile is
traveling at about the same velocity as the interceptor and its acceleration is less
predictable. Even so, it is possible to guide a suitably maneuverable interceptor
in order to hit a hostile thrusting booster, assuming the interceptor can get there
in time.
As noted in Chapter 1, the committee had access to classified information
provided by the Missile Defense Agency on its programs of record; however, the
committee chose to develop a set of notional threat missiles, notional interceptor
designs, and notional sensors to explore the basic physical limitations of missile
defense system performance, with the understanding that a public report was
OCR for page 40
40 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
not only requested by Congress but also helps improve public understanding of
ballistic missile defense issues. The following analysis is based, in large part, on
notional data developed by the committee and is stated as such throughout this
chapter. While boost-phase defense has been advocated as the most efficient way
to deal with fractionated payloads and exoatmospheric (midcourse) penetration
aids, such systems are extremely vulnerable depending on threat booster charac-
teristics and operational considerations. The committee’s analysis of boost-phase
defense concludes that it could be technically possible in some instances but
operationally and economically impractical for almost all missions.
Time, Range, and Technical Constraints:
Iran and North Korea as Examples
As previously noted, the committee’s analysis focused on assessing U.S.
boost-phase defense systems against ballistic missile threats from Iran and North
Korea. Figure 2-3 illustrates the dilemma for all boost-phase defense systems
(i.e., the pressing intercept timelines for both solid and liquid threat booster
rockets) and specifically displays this dilemma for what most boost-phase defense
advocates would call the less onerous of the two ballistic missile defense prob-
lems—that is, defense against ICBMs launched from North Korea). Moreover,
advocates for boost-phase defense would argue that because of North Korea’s
relatively small size and proximity to a coastal boundary, Aegis ships along with
military aircraft could get fairly close to the threat boost trajectories in order
to minimize the reach required. In Figure 2-3, it is assumed that the threat was
detected at an altitude above the cloud cover, which we would assume to be 30
sec after launch of a notional solid-propellant missile and 45 sec after launch of
a notional liquid-propellant missile.
In understanding the challenges of boost-phase defense of the U.S. homeland
and Canada, it is helpful to begin by looking at the ground tracks of trajectories
on the rotating Earth from launch to impact and where an ICBM payload lands as
a function of where its boost is terminated. Figure 2-4 shows the ground tracks of
ICBMs launched from Iran and North Korea to reach the United States. 10
While it is convenient to describe missile performance in a standard way,
that is, on a nonrotating Earth basis—it is important, particularly for longer range
threats, to consider rotating Earth effects. This is important both for assessing
what territory is at risk for a given threat missile performance and for looking
at the ability to engage such threats during their boost or early midcourse phase
of flight. While there are additional second-order Earth effects—such as Earth’s
oblateness (nonspherical shape) and local gravity variations—which must be
considered in accurate targeting, these are not of importance for this discussion.
10
Figures 2-4 to 2-8 and Figures 2-11 to 2-16 were generated from the committee’s analysis using
Google Earth. © 2011 Google, Map Data©2011 Tele Atlas.
OCR for page 62
62 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
Countering Early Deployment of Chemical or Biological Submunitions in
Theater Conflicts
Chemical or biological submunitions deployed immediately after boost phase
are a low-technology threat that could saturate terminal and exoatmospheric de-
fenses at shorter missile ranges. Because such weapons are area dispersed and do
not require precise delivery, it is not far fetched to contemplate that if each is en-
capsulated in an ablative material such as silicone rubber to survive reentry, they
could be deployed immediately after boost phase. While not a game changer on
the battlefield, such weapons require the donning of protective gear, which would
impede and disrupt combat operations. Such weapons are far more disruptive to
civilian targets. The latter threat has been studied and found practicable when the
short-range reentry heating is modest and the means for thermal protection does
not need to be sophisticated. In such a case, the submunitions cannot carry and
do not require individual guidance and control systems but simply are ejected at
low dispersal velocity.
Only boost-phase intercept, prelaunch attack, or midcourse sterilization of
the threat volume would be able to counter this type of threat. It is one scenario
in which intercepting a hostile missile in its boost phase of flight might be effica-
cious. Specifically, carried by multimission aircraft as part of their ordnance load
and having as their primary mission the destruction of a missile launch capability
or other ground target, such airborne boost-phase interceptors could, once air
superiority had been established, engage any weapons that were able to launch
in an adversary’s airspace. Alternatively, some form of volume kill—sweeping
or sterilizing the threat volume after the payload has been deployed—might be
used. The sooner this could be done after submunition dispersal, the smaller the
volume that would have to be swept but the more vulnerable the sweeper platform
would be. Unfortunately, there is no effective volume kill capability other than
the detonation of a nuclear weapon.
Countering Ship-Based Theater Ballistic Missiles Launched with Early
Deployed Submunitions Against CONUS, Deployed Forces, U.S. Allies,
Partners, or Host Nations
Some observers consider the possibility of attacks by short-range ballistic
missiles launched from ships near U.S. (or allied) shores to be a very serious po-
tential threat. Transfers of older liquid-fueled theater ballistic missiles (TBMs) to
nonstate actors have already been reported. Ship-launched TBMs with chemical
or biological submunition payloads from rogue or nonstate actors aimed at large
U.S. coastal population centers would have no immediate return address. While
the prospect of a nonstate actor getting nuclear material (at least enough for a
dirty bomb) cannot be excluded, a simpler chemical or biological attack could do
substantial damage and might be an attractive option for such an actor.
Because the launch point for such a threat would, by definition, be relatively
OCR for page 63
U.S. BOOST-PHASE DEFENSE 63
close to U.S. territory, boost-phase intercept could be practical. Existing SM-2
Block IV air defense interceptors launched from within 50 km of the ship launch-
ing the threat could engage such shorter range threats during boost phase, within
the atmosphere. In addition, CONUS-based tactical aircraft carrying weapons if
developed for theater boost-phase intercept could be scrambled to fly CAP either
over any suspicious ship that evaded detection before reaching a threatening
range or until an Aegis ship arrived. For example, a fighter aircraft interceptor
platform equipped with an appropriate acquisition sensor and perhaps a modi-
fied AMRAAM could be first on the scene for that mission if no Aegis ship was
within 50 km.
These are not likely to be large-scale threats that warrant the development
of a special system to counter them, and modified existing assets could probably
play that defensive role at least for the coastal threat. Specifically, Aegis ships
with some SM-2 Block IV interceptors that can shadow suspect ships closely
enough to engage any launch in its boost phase, followed by a counterbattery
strike on the ship itself, could be deployed on both coasts.
Countering Long-Range Missiles Launched from North Korea Toward Hawaii
or the Mid-Pacific
There is a case in which the relative geographical location of a threat coun-
try and its potential target would allow boost-phase interceptors to be stationed
routinely in positions from which boost-phase intercept would be feasible. This
case is the long-range threat trajectory from North Korea to Hawaii or other mid-
Pacific islands.22 Here, three conditions would need to be met for such a boost-
phase intercept to occur: (1) the threat would be coming toward the interceptor
launch platform (an Aegis ship in international waters, say) so the geometry is at
a favorable angle; (2) the boost-phase timelines would be long enough to allow a
boost-phase engagement in that unique geometry; and (3) an SM-3 sized intercep-
tor would have sufficient reach within a rational timeline, it would be externally
cued, and its KV would have the necessary additional agility.
It has been suggested by some that a capability exists for the essentially
instantaneous detection of a missile launch from its silo or launch pad, which
would allow earlier commit of a boost-phase interceptor and thereby somewhat
extend its range. Of course, very early detection would buy many seconds more
of additional fly-out time for interceptors than would waiting for sensor data
(from a space-based infrared system (SBIRS)). Here, the idea would be to fire an
interceptor toward a nominal point in the fly-out corridor as soon as a launch is
detected and to update the interceptor during its powered flight, when better data
22
The “long-range” condition reflects that some potentially significant targets, like U.S. bases on
Guam or the Japanese homeland, are so close to North Korea that a ballistic missile aimed at them
would have too short a burn time (and too low a burnout altitude) for a boost-phase intercept to be
feasible from an Aegis inteceptor on board a ship in the Sea of Japan.
OCR for page 64
64 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
are available, diverting it to a better-predicted intercept point—with an interven-
ing coast, if needed—before igniting a third stage. Boost-phase engagement firing
doctrine calls for the interceptor to be used this way to divert during its powered
flight in order to reduce the divert velocity and acceleration requirement for
the kill vehicle to deal with; however, it does not commit interceptors until the
threat’s heading can be estimated.23
Testing of Boost-Phase Defense Systems: Results to Date and Outlook
The committee was tasked to assess the past and planned test programs’
value in demonstrating feasibility and the cost-effective utility of the KEI and
ABL programs. While the cancellation of KEI and the realignment of the ABL
program to an R&D test bed (with which decisions the committee concurs) have
made this assessment somewhat moot, the committee has observations about
both.
Kinetic Energy Interceptor
The KEI program was terminated after cost and schedule problems delayed
flight testing of the vehicle. Both stages of the booster had been ground tested
and were deemed ready for flight test, and simulations using some actual tactical
warning and attack assessment (TWAA) elements were conducted with the battle
management architecture.
That said, the committee believes the foregoing analysis illustrates that no
matter how successful tests might one day have been, the system would have
had negligible utility as a boost-phase system because it cannot be based close
enough to adversaries’ fly-out corridors to engage either long- or short-range mis-
siles without being vulnerable to attack. Neither KEI nor any version of SM-3
that will fit on existing launchers has enough reach to have military utility as a
boost-phase defense.
The committee agrees with the decision to cancel the KEI program as such,
but the booster rocket motors could, with some modifications, be used as part of
a more effective Ground-Based Missile Defense (GMD) system. The committee
returns to this subject—a recommended evolution of the GMD—in Chapter 5 of
this report.
Airborne Laser
Several tests have been conducted with mixed results for one reason or an-
other. None of the problems have been fundamental to successful operation of
23
The committee also shows that it is counterproductive to commit an intercept earlier than the
timelines shown in Figure 2-3 even if the launch can be detected immediately (see classified annex,
Appendix H).
OCR for page 65
U.S. BOOST-PHASE DEFENSE 65
the laser or its beam conditioning and control. Several target missiles have been
destroyed, but all the tests have been at ranges too short to have any military
utility for boost-phase defense. The limitations of the ABL are due to the need to
sight at low elevation angles through the atmosphere, which fundamentally limits
the standoff range for boost-phase engagements. No amount of future testing is
likely to change that limitation.
Accordingly, the committee concurs with the DOT&E report, which con-
cludes that the ABL has no operational utility for missile defense for a variety of
reasons, not the least of which is the illogic of placing such an expensive asset in
harm’s way because of that range limitation.24 The committee found no reason
to believe that ABL could ever be an effective boost-phase defense system, and
it believes that the reversion of the ABL to a research and development test bed
was a sound decision.
There are logical applications that were identified by the Defense Science
Board in an unclassified report that do not entail such short reaction times, going
in harm’s way, endurance on station, or atmospheric problems at low elevation
angles.25 Specifically, the single existing ABL could serve as an emergency anti-
satellite (ASAT) device. The aircraft could on its own timeline be positioned to
deposit energy on a spacecraft for dwell times limited only by its entire operating
time at very high angles of elevation without going anywhere near an adversary’s
air defenses. Advanced high-powered solid-state or hybrid lasers could be tested
on board as well.
FINDINGS
Terrestrial-Based Boost-Phase Defense
Major Finding 1: While technically possible in principle, boost-phase missile
defense—whether kinetic or directed energy, and whether based on land, sea,
air, or in space—is not practical or feasible for any of the missions that the com-
mittee was asked to consider. This is due to the impracticalities associated with
space-based boost-phase missile defense (addressed in Major Finding 2), along
with geographical limits on where terrestrial (nonspace) interceptors would have
to be placed and the timeline within which such interceptors must function in
order to defend the intended targets.
• Intercept must take place not just before burnout of the threat booster
but also before it reaches a velocity that can threaten any area to be protected.
24
DOD Office of Testing and Evaluation. 2010. “Airborne Laser (ABL) Assessment of Operational
Effectiveness, Suitability, and Survivability,” January.
25
Defense Science Board. 2001. Defense Science Board Task Force on High Energy Laser Weapon
Applications. Office of Under Secretary of Defense for Acquisition, Technology, and Logistics,
Washington, D.C., June.
OCR for page 66
66 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
Because of the short burn times of even long-range ballistic missile boosters, the
interceptor launch platform cannot for its own survivability be so close to the ter-
ritory of an adversary as to be vulnerable to the adversary’s perimeter defenses,
but it must be close enough to the boost trajectory so that the interceptor can reach
the threat missile before it reaches its desired velocity.
• Surface-based boost-phase interceptors are not feasible against a large
country like Iran for missiles of any kind unless the interceptor platforms are
based in the southern Caspian Sea. While it has been suggested that unmanned
stealthy aircraft could loiter inside or close to the borders of an adversary, the
committee does not believe it to be a feasible approach against a country with
an effective air defense like Russian S-300 SAMs, in the face of which stealth
aircraft will have a limited time of invulnerability as they maintain station in an
environment with a high-density air defense sensor.
Range Limits
In practice, the operational limits on both kinetic and laser interceptor ranges
necessitate that boost-phase defense platforms be located near likely launch sites
(or, more precisely, near possible intercept points). Locations that meet the re-
quirements are available only in certain limited circumstances—a relatively small
threat nation and good access to areas near it over international waters or friendly
territory and outside the range of its air defenses.
For kinetic interceptors, range is limited by the short duration of powered
flight for ballistic missiles—approximately 180-250 sec for ICBMs (although
some liquid-fueled types may have longer boost times) and approximately 60-180
sec for short-, medium-, and intermediate-range ballistic missiles.
Boost-phase defense of allies or deployed forces against shorter than inter-
continental range attacks requires even closer stationing than for longer range
threats, because shorter boost times and lower altitudes at burnout—which are
the determinants of the windows for boost-phase intercept and of the proximity
requirement for both kinetic and laser intercept—are even more demanding.
Only in highly favorable geographic situations, e.g., trajectories from North Ko-
rea to Hawaii and some other Pacific Ocean targets, is it likely that boost-phase
interceptor platforms could be located so as to overcome the time, distance, and
altitude constraints.
Despite their essentially unlimited speed of “flight,” the use of lasers as the
kill mechanism does not avoid the requirement for relatively close-in stationing
of the interceptor platform. Lasers operate at the speed of light, but they are range
limited because laser power deteriorates with distance from the target. Moreover,
although the laser beam reaches the target at the speed of light, it must dwell
on the target for several seconds to deposit sufficient energy on the booster to
destroy it. The altitude of the target at thrust termination and of the platform for
the interceptor also contribute to loss of power on the target, limiting effective
OCR for page 67
U.S. BOOST-PHASE DEFENSE 67
ABL range. The dwell time relative to the short duration of an engagement also
limits the raid handling capability of any laser ballistic missile defense system.
The net effect of these time, altitude, and range constraints is that both ki-
netic and laser boost-phase interceptors must be ready to engage from within a
few hundred kilometers of the intercept point. As a practical matter, the intercep-
tor platforms must be ready to engage on or over international waters or friendly
land areas. (It is sometimes claimed that stealth UAVs armed with boost-phase
interceptors could operate in an adversary’s air space. However stealth is ex-
tremely difficult to maintain for platforms loitering for long periods in airspace
under surveillance by a reasonably capable air defense.)
Decision Time and Command and Control
Missile defense operates within the established military chain of command
and employs systems of control and authorization that are consistent with stan-
dard operational practices that have withstood the test of time and suit real-world
considerations.
In standard U.S. practice, weapons release authority is reserved for the higher
command echelons, indeed ultimately for the President as commander in chief
of the armed forces. Reliable and redundant communication links tie the release
authority to the personnel in immediate control of the weapons system in ques-
tion. However, it is equally a principle of the command and control system that
requirements for higher-level authorization should not be so inflexible as to delay
action to the point of ineffectiveness. Rules of engagement—which can change
as threat conditions change—are guidelines for action, including when time or
other considerations make seeking higher authority infeasible.
The special circumstances of missile defense—the potential of a missile at-
tack to do massive damage, the ramifications of mistakenly destroying a foreign
nation’s space launch vehicle (or even a routine developmental test missile), the
possibility of creating space debris (or debris or even weapons falling to Earth),
the compressed timelines and heavy reliance on sensor data—make it difficult to
strike the appropriate balance between higher level—ultimately Presidential—
control and sufficiently rapid response.
These problems arise for any missile defense. The flight time for an ICBM
attacking the United States from Iran would be only about 40 minutes, and all
other flight times can be shorter. The time needed to detect and characterize a
threatening launch—probably on the order of 1 min—and the time needed to
conduct the intercept after weapon release—on the order of 15-17 min for mid-
course intercept—leave a window of only a few minutes for requesting release
authority, for the decision maker to consider and make the decision, and for that
decision to be communicated to personnel who control the interceptor system.
The problem is challenging enough for midcourse intercept, where the win-
dow for engagement would be a few tens of minutes. Even more daunting would
OCR for page 68
68 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
be the authorization of a boost-phase intercept, for which there would be virtu-
ally no time because the interceptor would have to begin the engagement within
seconds of the sensors reporting that a hostile launch had occurred.
The short boost period not only imposes limits (far more significant for ki-
netic than for laser-kill systems) on the time available for the intercept itself, it
also means—for either laser or kinetic kill—that there be very rapid detection of
the launch; its classification as threatening; tracking; decision and release author-
ity to engage; and execution of release with all of these in addition to whatever
time is needed for the engagement itself. Accomplishing this in the time available
is a formidable operational challenge.
The short time for intercept raises an important policy question. To allow
boost-phase interceptors to be fired within a few tens of seconds of detection of
the launch of the attacking missiles, authority to engage would have to be del-
egated to the military personnel with immediate control of the system. Indeed, in
practice, the “decision” to intercept would need to be made largely by a computer
program, with human input essentially limited to confirming that the system ap-
pears to be functioning properly. Accordingly, civilian and higher level military
authority would have to be exercised by determining the rules of engagement
that were embodied in the computer program rather than in real time during an
actual attack.
Other Issues
A significant technical limitation of boost-phase intercept, in addition to
those presented by the short powered flight of the target, arises from the fact
that ballistic missiles are accelerating nonuniformly during powered flight, not
to mention almost discontinuously at staging events. This further complicates
predicting the target’s future location, which for kinetic-kill intercepts increases
the divert requirements for the kinetic-kill vehicle. Also, the target is accelerating
rapidly, which means that the interceptor must have a comparable acceleration
capability. As a result, kinetic-kill vehicles designed for midcourse intercepts
will have limited boost phase intercept capability even if one assumes they are
stationed within range of the intercept point. These requirements for boost-phase
kinetic kill can be met technically, but they add to the weight and complexity of
boost-phase intercept systems.
A further technical and operational issue for boost-phase intercepts is that
even a successful intercept has the “shortfall” problem—that is, the potential not
just for fragments of engines, fuel tanks, and the like but also for an intact and
armed nuclear weapon to fall on friendly or neutral territory. Moreover, it is a
misconception that a boost-phase intercept could cause threat missile debris to
fall on the country of origin. In short, it is physically impossible for this to happen
unless the interceptor is based in the country of origin and is close enough to the
threat launch point to intercept the threat in the atmosphere.
OCR for page 69
U.S. BOOST-PHASE DEFENSE 69
Indeed, by the time of intercept, which would take place relatively late in
powered flight and well above the atmosphere, the reentry vehicle (RV) would
already have been given sufficient velocity to continue on a trajectory that could
extend into the original target area, or at least into friendly or neutral territory, and
produce a nuclear detonation on impact. In principle, a kinetic-kill boost-phase
interceptor could be aimed so as to impact the RV containing the warhead (as
contrasted to the booster itself), but ensuring such impact would be challenging,
because of uncertainties about the position of the RV relative to the hot rocket
exhaust, which is guiding the interceptor. A laser kill mechanism, even if properly
aimed, would probably not be powerful enough to destroy a warhead carried on
an RV hardened to survive reentry. It might, however, be possible to count on
midcourse defense to deal with RVs that “escape” from a boost-phase intercept.
It can therefore also be concluded that none of these measures to mitigate “short-
fall” are likely to be effective, and that the consequences of a nuclear detonation
on land “caused” by a U.S. intercept would be so severe that a boost-phase system
must constrain intercepts to windows that minimize the risk of an RV falling on
land. Such a constraint would, however, add another significant limitation to the
already extremely tight window for intercept.
Finally, boost-phase intercepts are not immune from countermeasures, in-
cluding hardening to reduce the booster’s vulnerability to lasers, spoofing precur-
sor launches, and the like. Iran has conducted tests in which several missiles of
various types were launched nearly simultaneously. A nation could seek to defeat
a boost-phase defense by launching several decoy boosters at the same time as
the actual missile in the hope of confusing, or even overwhelming, the defense’s
sensors and data processors. Even more sophisticated countermeasures can be
postulated—for example, fractionated upper stages—though typically they come
at a price to the offense in terms of complexity and reduction in volume available
for the weapons payload.26
Overall Evaluation
As a practical matter, however, these other potential disadvantages would be
dwarfed by the fact that both kinetic and laser interceptors would have to be on
platforms relatively close to the targets. Even leaving aside how such proximity
would expose the interceptor platforms to attack, this range-determined constraint
makes boost-phase intercept operationally infeasible, because, except in a few
cases, it would not be realistic to count on a boost-phase intercept platform being
close enough to effect intercept.
• In particular, Iran is too large geographically (and its northern neighbors
26
Additional discussion on decoys and countermeasures is provided in the classified annex (Ap-
pendix J).
OCR for page 70
70 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
too unlikely to consent to U.S. boost-phase intercept overflights or basing) to
make boost-phase operationally feasible, even against liquid-propellant ICBMs.
• By contrast to Iran, the small size of North Korea and its long coastlines
mean that boost-phase intercept for ICBMs is not ruled out by geography, as long
as North Korea sticks to liquid-propellant engines, and a large enough interceptor
such as KEI could be based at sea, as explained below.
• In general, boost-phase intercept systems are more feasible the longer the
boost time of the target missile. Therefore, they tend to be more feasible against
liquid-propellant missiles than solid-propellant missiles, owing to the longer
boost times associated with the former. However, it would be imprudent to justify
boost-phase intercept development based on its potential against liquid-propellant
missiles when solid-propellant missiles are an obvious countermeasure; such a
system could become obsolete as soon as it is deployed. In fact, the deployment
of a boost-phase intercept system would likely stimulate the development of
solid-propellant systems if they were not already being pursued for other reasons
(e.g., solid-propellant missiles are more suitable for mobile deployment and
hence can survive better against air attack). For example, Iran already has tested a
two-stage solid-propellant medium-range ballistic missile (MRBM). Boost-phase
intercept deployment against liquid-propellant missiles would be justified only if
a hostile country does not, or cannot, deploy solid-propellant ICBM technology,
as was the case for the former Soviet Union for almost 40 years. So far, there is
no sign that North Korea is working on solid-propellant rockets for longer range
missiles, but it could shift toward solid propellant, possibly with assistance from
Iran, with which it has significant cooperation. The question becomes, Should
the United States invest in a boost-phase system with some capability against
liquid-fuel North Korean ICBMs if that country might shift to solid-fuel rockets
before or soon after the system becomes operational?
• There may be specialized cases in which boost-phase defense is feasible
because either the threat must come toward the platforms or the platforms can be
placed close enough to the threat and in an adequately benign environment. For
example, a boost-phase intercept might be workable if the threat is North Korean
medium- or long-range missiles heading toward U.S. bases in the western Pacific
and therefore flying toward the Sea of Japan, on or over which boost-phase in-
tercept platforms could be stationed. In this situation, and comparable situations
elsewhere, the platform proximity problem is manageable, because the threat is
coming toward the interceptor.
Space-Based Boost-Phase Defense
Major Finding 2: While space basing for boost-phase defense would in principle
solve the problems of geographical limits that make surface-based boost-phase
intercept impractical, the size and cost of such a constellation system is extremely
OCR for page 71
U.S. BOOST-PHASE DEFENSE 71
high and very sensitive to the timeline in which interceptors must be launched.
As a result it is susceptible to countermeasures such as salvo launches that either
delay and reduce its coverage or squander space-based intercepts.
• In principle, a constellation of satellites equipped with boost-phase
interceptors could be configured so as always to be geographically in range for
an intercept. The number of satellites required depends, in part, on the burn time
and altitude of the threat missiles. Shorter powered flights of solid-fueled threat
missiles require many more satellites for coverage. Shorter range missiles with
their shorter burn times and lower burnout altitudes cannot be engaged by space-
based boost-phase intercepts.
• The total life-cycle cost of placing and sustaining the constellation in
orbit is at least an order of magnitude greater than that of any other alternative
and impractical for that reason alone.
Overall Evaluation
Space-basing for boost-phase intercept would, in theory, solve the problems
of proximity that make surface- and air-based boost-phase interceptors generally
impractical. In principle, a constellation of satellites equipped with boost-phase
interceptors could be configured so as always to be geographically in range for an
intercept. The number of satellites required would depend in part on what threats
are to be defended against. Shorter powered flight times for the threat missiles
would require more satellites for coverage.
A space-based system would have to overcome objections (and, arguably,
legal obstacles) to “weapons in space.” More important, a space-based system
would be vulnerable to the sort of primitive ASAT device that a country capable
of deploying an ICBM would probably be able to develop.
The most powerful objection to a space-based system, however, is the total
acquisition cost (both initial and replacement satellite costs plus launch costs) for
the large number of satellites needed for continuous coverage of potential threat
launch locations because of the relative motion of satellites in orbit to Earth
below (see Appendix J in the classified annex). Some 700 satellites would be
required for defense against liquid-fueled ICBMs and some IRBMs, with some
residual capability against solid-fueled ICBMs. For confident defense against
solid-fuel ICBMs, as many as 1,600 to 2,000 satellites would be needed. The
total life-cycle cost of developing, building, launching into orbit, and maintain-
ing in orbit, even an austere and limited-capability network of 650 satellites, for
example, would be approximately $300 billion (in FY 2010 dollars). The cost
for greater capability would be correspondingly greater. From an annual acquisi-
tion cost perspective, these relatively high costs over the time frame estimated
to provide operational space-basing for boost-phase interceptors would probably
prove unaffordable.
OCR for page 72
72 MAKING SENSE OF BALLISTIC MISSILE DEFENSE
Airborne-based interceptors (ABIs) have been proposed for boost-phase
defense and possibly for terminal defense. All near-term systems on which the
committee was briefed have very limited boost-phase capability (intercept ranges
on the order of 50 km). The limited ranges of which a system would be capable
do not allow boost-phase intercepts from outside the territory of even a small
country such as North Korea. Such a system would be viable only if the aircraft
could fly CAP for extended periods of time over enemy territory after air su-
premacy had been achieved.
