Responding to the Emerging Threat of Chinese DF-21D (CSS-5 MOD 4) Anti-Ship Ballistic

Missiles in the Near-Space Environment

LTC Wallace E. Steinbrecher, GA ARNG

Joint Forces Staff College

AJPME 11-07B

March 1, 2011

Faculty Advisor: LTC Larry Dotson

Biography

Lieutenant Colonel Wallace Steinbrecher is the Commander of the 170th

Military Police

Battalion with headquarters in Decatur, Georgia. He concurrently serves as the Executive

Officer for the Pre-Mobilization Training and Assistance Element with headquarters at Fort

Stewart, Georgia. He was commissioned in 1990 through the Officer Candidate School at Fort

Benning, Georgia. He began his Army career in 1982.

He received his B.S. (Criminal Justice) from Armstrong State University in Savannah,

Georgia, his M.S. (Administration of Justice) from Andrew Jackson University of Montgomery,

Alabama, and is a second-year law student at the Concord School of Law.

He is married to the former Tamra Jean Tebo of South Bend, Indiana, and has two

daughters ages 21 and 19.

THE ORIGINAL VERSION OF THIS PAPER WAS WRITTEN TO SATISFY WRITING REQUIREMENTS OF THE

JOINT FORCES STAFF COLLEGE (JFSC). THE CONTENTS OF THIS PAPER DO NOT NECESSARILY REFLECT

THE OFFICIAL POLICY OF THE U.S. GOVERNMENT, THE DEPARTMENT OF DEFENSE, OR ANY OF ITS

AGENCIES.

1

Thesis

The Chinese are preparing to operationally deploy a new variant of ballistic missiles

specifically aimed at US aircraft carriers. This system can acquire, track, and engage at ranges

greater than 1000 miles.

In the near-term, the US has existing technologies that can be quickly modified to counter

this threat in the near-space (less than 60 miles in altitude) environment. In the long-term,

developing technologies can be used to defeat this threat at all points during the flight envelope.

Defining the Threat

Historically, U.S. aircraft carriers and their associated carrier strike groups (CSGs) have

operated relatively freely under an air defense umbrella and an anti-submarine screening force.

These screening and defense forces provide a stand-off distance that exceeds the range of

conventional anti-ship missiles such as the French-made Exocet with a range of 70 km (MM38)

or 180 km (MM48) (Friedman 1994, 109). One technology that threatens the U.S. carrier fleet in

the Pacific is a variant of the Chinese DF-21/CSS-5 solid propellant medium range ballistic

missile (MRBM). This system has a range of over 2000 km and travels at a speed of Mach 10

(approximately 7612 mph) making it extremely difficult for some shipboard Close in Weapons

Systems (CIWS) to acquire, track and engage successfully. Since the warhead is arriving at the

end of a ballistic arc instead of a flat trajectory as would a conventional ASM, CIWS would be

challenged with a target arriving at an angle anywhere from 20 degrees at long range to 45

degrees at shorter range (Hobgood et al. 2009, 5). If this weapons system were coupled with the

growing Chinese system of space-based and land-based sensors, the integrated system could

acquire, track, and engage targets at over-the-horizon distances exceeding 1000 miles. When

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such integration is achieved, this system could significantly restrict U.S. naval operations during

a crisis in the Taiwan Straits and could threaten US assets in Okinawa and mainland Japan.

Ballistic Missile Flight Envelope

Most research and development into ballistic missile defense has concentrated on

countering strategic weapons such as intercontinental ballistic missiles (ICBMs) and was

centered on kinetic (direct strike) kills. While the DF-21 exhibits a flight envelope like any other

ballistic missile during most of its flight, its ability to maneuver during the terminal phase

enormously makes present kinetic anti-ballistic missile (ABM) systems unsuitable. The primary

difficulty in defending against a ballistic missile is the number of calculations necessary to strike

one object moving at hypersonic speeds with another object moving at hypersonic speeds.

Modern digital computers have moved the solution closer to reality. The US Missile Defense

Agency (MDA) divides a ballistic missile flight into 4 main phases:

Boost Phase

The missile boost phase is only from one to five minutes. It is the best time to track the

missile because it is bright and hot. The missile defense interceptors and sensors must be

within close proximity to the launch, which is not always possible. This is the most

desirable interception phase because it destroys the missile early in flight at its most

vulnerable point and the debris will typically fall on the launching nations' territory.

Ascent Phase

This is the phase after powered flight but before the apogee. It is significantly less

challenging than boost phase intercepts, less costly, minimizes the potential impact of

debris and reduces the number of interceptors required to defeat a raid of missiles.

Midcourse Phase

This phase begins after booster burns out and begins coasting in space. This phase can

last as long as 20 minutes. Any debris remaining will burn up as it enters the atmosphere.

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Terminal Phase

This phase is the last chance to intercept the warhead. This contains the least-desirable

Interception Point (IP) because there is little room for error and the interception will

probably occur close to the defended target.

Missiles are vulnerable to attack at any phase, but especially so during the launch and the boost

and ascent portion of the midcourse phase.

Prior to launch, if the location of the launcher is known, a strike on it and the associated

support equipment would stop the launch (known as “kill the archer, not the arrow”). However,

killing the archer requires precision-guided munitions (PGMs) systems located at relatively close

range to a known target location, along with associated spaceborne or airborne sensor platforms.

In the case of the DF-21, the use of transportable erectable launchers (TELs) dispenses with the

Figure 1: Typical ballistic missile flight envelope. Some systems are

capable of departing from a ballistic path during the descent phase and

can maneuver upon reentry (From Missile Defense 101: ICBM

Fundamentals 2007, 9).

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need to launch from prepared sites, further complicating the ability to employ “kill the archer”

techniques.

During the boost portion of the flight envelope the missile is easy to acquire since the

exhaust plume is extremely bright to IR sensors. Since the missile and warhead are mated during

this phase and are traveling in a more-or-less vertical manner, the target aspect is largest during

this phase, improving the probability of the kill system acquiring the target. Also during this

phase the missile is traveling through a region of maximum dynamic pressure (max Q) during

which time the airframe stresses are at a maximum value.1 If engaged with a kinetic system

during this phase, a hit anywhere on the missile would be sufficient to cause it to fail.

The midcourse phase of the flight consists of ascending and descending portions. During

the ascending portion, the missile completes staging (if a multi-stage system) and final velocity

is achieved (max ∆ v). The missile is no longer under powered flight and is coasting

(decelerating) to the apex of its ballistic arc (apogee). At apogee, the missile’s velocity is

instantaneously 0. If the payload vehicle is not independently maneuverable, it will begin to

freefall (accelerating) in a mathematically-defined ballistic trajectory just as an artillery round

would fall (this assumes a homogenous atmosphere).

During the midcourse phase, the missile is vulnerable to attack at several points. Once

the missile’s engine reaches burnout, velocity will continue to rise initially as the missile is

entering a region of the atmosphere where drag is decreasing, but will then begin to slow until

reaching apogee when the instantaneous velocity is 0, essentially becoming a stationary target.

Space dynamics are well understood, so as long as the missile is acquired, its subsequent ballistic

1 Considering the definition of dynamic pressure: q = ρ v² / 2, where q is the aerodynamic pressure, ρ (rho) is the air

density and v is the vehicle speed.

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behavior (up to apogee) is reduced to a trajectory calculation. The trajectory calculation remains

valid for the descending portion of the trajectory if the payload vehicle is not independently

maneuverable. The intercept solution becomes much more complex if the missile carries a

maneuverable reentry vehicle. The reentry path can be calculated only as a probability whose

boundaries are determined by the amount of reaction control system (RCS) propellant carried on

board and/or the limits of the flight control surfaces.

Again, just like a ballistic artillery round, these payloads will have a point of impact error

in both range and deflection (defined as Circular Error Probable, or CEP). In order to reduce

CEP to the absolute minimum, a missile can deliver maneuverable reentry vehicles. These

payload vehicles have either an active target acquisition system on-board (radar, IR, video) or

can receive guidance corrections from an external sensor system (spaceborne sensors, over-the-

horizon radar, AWACS). Once the guidance corrections are calculated, either on-board or

Launch site

Apogee (∆v=0)

Point to vary trajectory in mid-

segment

Point of impact

assuming a pure

ballistic trajectory

Point of impact

assuming mid-segment

guidance correction

Terminal guidance

corrections applied

Point of impact

with terminal

guidance

corrections

applied

X X’ X”

Figure 2: The ability to intercept a missile at X’ and X” represents a capability gap in existing U.S.

systems (From Erickson and Yang, 2009).

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externally, the payload vehicle’s guidance computer system uses RCS thrusters while in the

vacuum of space and/or a system of moveable control surfaces while in the sensible atmosphere

to change its trajectory.

While there are systems in the US inventory that are capable of intercepting simple, non-

maneuvering ballistic threats during the descent or terminal portion of the midcourse phase, there

are no systems that have proven effective against maneuvering reentry vehicles during the

terminal phase. At present, there is no comprehensive, integrated system capable of defeating a

ballistic missile threat during all points of the flight envelope.

Existing Capabilities to Address the Threat

Current US Ballistic Missile Defense Systems (BMDS) are based on a layered defense

model. Each part of the system (both kinetic and sensor) are designed to acquire and attack an

incoming missile at specific phases of the missile’s flight envelope. Some examples of current

and near-term weapons systems and sensor systems are shown in Table 1.

System Name Phase Function

Weapon System

Kinetic Energy Interceptor (KEI) Boost Intercept

Airborne Laser (ABL) Boost Intercept

Standard Missile (SM-3) Block 1A Midcourse Intercept

Patriot Advanced Capability-3 (PAC-3)

Midcourse Intercept

SM-2 Block IVA (SM-T) Terminal Intercept

Terminal High Altitude Area Defense (THAAD)

Terminal Intercept

Arrow Weapons System Terminal Intercept

Sensors Cobra Dane Radar Boost/Midcourse Detection/Tracking

Cobra Judy Radar Boost/Midcourse Detection/Tracking

Upgraded Early Warning Radar Boost/Midcourse Detection/Tracking

AN/TPY-2 (Forward Base Mode) Boost/Midcourse Detection/Tracking

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Sea Based X-Band Radar (SBX) Midcourse Detection/Tracking

AN/SPY-1 Midcourse Detection/Tracking

AN/TPY-2 (THAAD Mode) Terminal Detection/Tracking

Green Pine Radar Terminal Detection/Tracking

PAC-3 Radar Terminal Detection/Tracking

Space Tracking and Surveillance System (STSS)

All Detection/Tracking

Space-Based Infrared System (SBIRS) All Detection/Tracking

These current systems rely on a network of remote and on-board sensors to acquire, track

and maneuver to intercept a ballistic threat. The Chinese DF-21 system has been designed to

exploit shortcomings in the currently fielded systems. Using the example threat of a DF-21

system coupled with a fully-integrated sensor system, the missile could be traveling in excess of

Mach 10 and could maneuver during the terminal portion of the flight, altering its aimpoint and

ultimately forcing the current family of BMDS to estimate a false trajectory (Hobgood et al.

2009, 17). As there are systems that can engage a DF-21 during the flight envelope from launch

to midcourse, this report concentrates on an intercept during the terminal phase.

Terminal Phase Intercept

The terminal phase is very short and begins once the missile reenters the sensible

atmosphere. It is during this phase that the remains of the booster vehicle and any deployed

decoys begin to burn up, leaving the hardened reentry vehicle. This phase is the final

opportunity to make an intercept before the warhead reaches its target. A terminal phase

intercept is the most difficult and most undesirable type of intercept. The computing power

necessary to target a maneuvering vehicle during this phase is tremendous and the warhead will

likely be near its intended target when (if) it is intercepted.

Table 1: Existing Ballistic Missile Defense Systems (From Hobgood et al., 2009).

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The warhead of a ballistic missile can contain one or multiple reentry vehicles

(warheads). Typically, these warheads are ballistic (free-falling) and their accuracy is totally

dependent on calculations made before launch. By contrast, the DF-21 system will employ a

maneuverable reentry vehicle that can calculate and command course corrections to a target such

as a ship whose position has changed since launch.

A Proposed System

All of the weapons systems illustrated in Table 1, with the exception of the Airborne

Laser (ABL), require the intercepting vehicle to maneuver in close proximity to the inbound

warhead to produce a kinetic kill. As stated, the use of maneuverable reentry vehicles during the

terminal phase enormously complicates the intercept solution. What is needed is a way to

engage the inbound warhead(s) during the terminal phase without having to calculate a precise

intercept trajectory. The desired point of attack for this proposed system is the DF-21’s terminal

guidance system.

One common feature of all maneuverable reentry vehicles is that they possess some sort

of terminal guidance system, whether on-board through a guidance computer or remotely

through a data/telemetry link. Early ballistic missiles such as the V-1 and V-2 of WWII used a

clockwork mechanism for guidance, but most systems since that time rely on an electronic

system (Neufeld 1995, 73).

Electronic systems are susceptible to attack through a mechanism known as an

Electromagnetic Pulse (EMP). In simplest terms, an EMP is a dramatic spike in induced current

through an electronic system that can physically damage it on the component level. Subjecting

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the guidance system to the effects of a strong EMP will render it nonoperational, thus destroying

the missile’s ability to maneuver to the target during the terminal phase.

The advantage of an anti-ballistic missile (ABM) armed with an EMP warhead is that it

does not have to impact with the incoming missile, so a precise trajectory calculation is not

required. The EMP burst radius is a direct function of the electromagnetic power delivered at the

instant of warhead detonation. Simply stated, more power = larger kill radius. A general

discussion of EMP is found in Appendix A and a technical discussion of the means to generate a

non-nuclear EMP can be found in Appendix B.

One of the obstacles to employment of EMP weapons in the past has been the weight of

the capacitors used to charge the EMP device. The introduction of lightweight ultracapacitors

has made it possible to equip current generation ABMs such as the PAC-3 or SM-2 block IV

with effective EMP warheads. A technical discussion of the capabilities of ultracapacitors is

found in Appendix B.

The proposed system envisions the mating of an EMP warhead to a Navy Standard

Missile-3 (SM-3), or an Army Patriot Advanced Capability-3 (PAC-3) missile providing both

land and sea-based capabilities. Flight guidance would be provided by existing AN/TPY-2 radar

systems operating in THAAD mode or by the PAC-3 fire control radar.

The SM-3 is the Navy’s current midcourse ballistic missile interceptor. The SM-3 block

IB features enhanced capabilities and would be the desired candidate for fitting with an EMP

warhead. The block IB design includes an advanced, two-color, infrared seeker for

discriminating targets at greater range. In addition, the missile is outfitted with a Throttleable

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Divert and Attitude Control System (TDACS) that provides the warhead with greater agility,

making it ideal for use against a maneuverable target (Hobgood et al. 2009, 57).

The Patriot Advanced Capability-3 (PAC-3) is the newest iteration of the Patriot missile,

using kinetic kill technology to intercept and destroy tactical ballistic missiles. It is initially

guided by the PAC-3 Fire Control Radar, but receives terminal guidance from an on-board

seeker. The seeker could be reconfigured to act as a proximity detection device to initiate the

flux generator firing cycle.

Figure 3: SM-3 (Naval) Concept Architecture

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Summary

Future adversaries could have the means to render ineffective

much of our current ability to project military power overseas. (A)ttacks

with ballistic and cruise missiles could deny or delay U.S. military access

to overseas bases, airfields and ports… New approaches for projecting

power must be developed to meet these threats.

-Quadrennial Defense Review Report, 30 SEP 2001

With the DF-21, China may have found an effective way of countering the military might

of the United States in the Taiwan Straits. The limitations of current U.S. legacy ABM systems

create both a strategic and tactical vulnerability that must be aggressively addressed in order for

the U.S. to remain relevant in the Far East. The technologies exist to reliably counter the DF-21

Figure 4: PAC-3 (Surface) Concept Architecture

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and the similar systems that will undoubtedly follow it, what remains is the integration of those

technologies into a functioning ABM system.

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Appendix A

Electromagnetic Pulse (EMP)

One familiar example of an EMP is a lightning stroke that causes house lights to dim,

flicker, or to go out for a short period. The lightning stroke induces a brief transient of high

current in the power lines which act as antennas. This current spike will cause overcurrent safety

devices (fuses, fusible links, etc.) to “trip out” in order to protect devices connected to the line.

Power lines are engineered to routinely accept such induced surges and the protection devices

reset quickly.

Using an EMP weapon as a way to “blind” an enemy’s electronics grew out of an

analysis of a nuclear weapon test. The Sandia National Laboratory conducted a study of early

nuclear test EMP effects. Its 1989 report stated “(i)n July 1962, a 1.44 megaton US nuclear test

in space, 400 kilometers (250 mi) above the mid-Pacific Ocean, called Starfish Prime,

demonstrated to nuclear scientists that the magnitude and effects of a high altitude nuclear

explosion were much larger than had been previously calculated. Starfish Prime also made those

effects known to the public by causing electrical damage in Hawaii, about 1445 kilometers

(898 mi) away from the detonation point, knocking out about 300 streetlights, setting off

numerous burglar alarms and damaging a telephone company microwave link.” (Vittitoe 1989).

The mechanism of damage to an electronic system by an EMP event is the fast risetime

associated with the current surge. Electronic systems are engineered to “see” a gradual rise in

signal level, and can even recover from an overcurrent event if the risetime-to-peak current is

slow enough. However, as Figure 3 shows, an EMP overcurrent event rises from baseline to

peak (Imax

) almost instantaneously. Protection devices such as inrush current limiters, fuses, and

14

crowbar circuits cannot react fast enough, so the overcurrent propagates throughout the circuit,

destroying it.

Solid-state devices used in guidance systems such as t

Transistors and integrated circuits are especially susceptible to damage from an EMP

event, due to their low current handling capabilities. Since there is also a magnetic field

associated with an EMP event, magnetic storage media used for trajectory calculations such as

erasable programmable memories (EPROMs) and computer hard drives can also be corrupted.

As an aside, obsolete electronics technologies such as vacuum tubes are generally immune from

EMP events since their current handling capacity is magnitudes greater than solid-state devices.

Likewise, older media storage devices such as rope-core memories (such as used in the Apollo

Guidance System) are resistant to induced magnetic fields (Hall 1996).

Imax C

u

r

r

e

n

t

Time

Baseline current

Figure 3. A current spike. Note the almost vertical risetime.

15

Appendix B

Generating the Electromagnetic Pulse

Until fairly recently, EMP generation has been associated with a nuclear detonation, but

there are non-nuclear ways of generating an EMP2. The concept of non-nuclear EMP was

studied as far back as 1960, when it was postulated that explosive compression of an initial

magnetic flux-containing structure, such as a charged helical coil, would generate an EMP on the

order of 109

J (1,000,000,000, or 1 billion joules of energy3) (Fowler et al. 1975, 2). Such a

device is known as an Explosive Magnetic Flux Compression Generator, or more simply, a Flux

Compression Generator.

To understand how a flux generator works, a basic knowledge of electrical and magnetic

forces is required. Although there are other structures that will work, it is easiest to illustrate

using a helical coil as the flux-containing structure. If a coil is charged with electrical energy

from a source of current, either a capacitor bank or a battery, a magnetic field (flux) is generated.

If an explosive charge is placed so that the conducting surface containing the flux (here, the coil

structure) is driven by the explosive wave front, the result is an electromagnetic pulse delivered

to a load coil (antenna).

2 An EMP generated by a nuclear event is a complex multi-part pulse consisting of the E1 (fast pulse), E2

(intermediate pulse), and E3 (slow pulse). A non-nuclear EMP is not so complex, but at close ranges the mechanism

of damage is the same. The difference in pulse types is due to the fact that nuclear events yield energies on the order

of one million times greater than a chemical energy yield of the same weight. 3 A Joule is defined as the energy expended in passing an electric current of one ampere through a resistance of one

ohm for one second.

16

Figure 4. A flux compression generator at rest. Borrowing terms from motor and generator

construction, the helical coil is referred to as a solenoid and the casing surrounding the explosive

charge is called an armature. Other non-moving parts of the structure are called stators.

Figure 5. A flux compression generator at initiation. The detonation is timed so that the explosion

wavefront opens the capacitor bank input at or near peak current. The wavefront propagates down the

coil, “driving” the conductors through the magnetic field. The load switch opens and the pulse is

delivered to the load coil.

17

Since non-nuclear EMPs are local in their effects, it is not necessary for the system to

actually impact the incoming missile. While the mechanisms for generating a non-nuclear EMP

are understood, there are several practical issues associated with delivering a workable system in

an anti-ballistic missile (ABM) configuration. Chief among these issues is the weight associated

with the warhead’s initial energy source,

Initial Energy Sources and Weight Reduction

The initial energy charge for the conductors of the generator can come from any of

several different sources. Options include capacitor banks, inductive stores, and battery banks

(Fowler et al., 11). This discussion is limited to a consideration of capacitor banks.

Typical high-energy density capacitors store energy at about 150 J/kg. Thus, to reach an

initial energy of 1 megajoule (106 J,) the initial charge capacitor bank alone would weigh

approximately 6666 kg. By way of comparison, a Sprint ABM missile from the 1970’s weighed

3500 kg, complete with a 1 kiloton W-66 nuclear warhead (Parsch, 2002). Rocket engines are

notoriously inefficient, having to lift their own fuel as well as their payload. While rocket

engines exist that can boost such a payload, a lighter solution is needed.

One possible solution is the Electric Double-Layer Capacitor (EDLC) or ultracapacitor.

The energy density of EDLCs is on the order of hundreds of times greater than standard paste-

filled electrolytic capacitors of the same mass. Thus, a 1 megajoule capacitor bank made of

EDLCs could weigh as little as 7 kg. The EDLC also has a fast discharge time due to its low

internal resistance. Conventional capacitor discharge times are reduced as capacitance is

decreased; with an EDLC, high capacitance values and fast discharge times are both possible

(Fowler et. al, 12).

18

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