Nuclear Explosions in Space: The Threat of EMP (Electromagnetic Pulse)

NUCLEAR EXPLOSIONS IN SPACE: THE THREAT OF EMP (ELECTROMAGNETIC PULSE) MINI BRIEF NUMBER MB82221 AUTHOR: George N. Chatham Science Policy Research Division THE LIBRARY OF CONGRESS CONGRESSIONAL RESEARCH SERVICE MAJOR ISSUES SYSTEM DATE ORIGINATED 03/02/82 DATE UPDATED 12/15/83 FOR ADDITIONAL INFORMATION CALL 287-5700 1216 CRS- 1 I S S U E DEFINITION A high-altitude nuclear explosion produces electrons which may be c a u g h t by t h e Earth's magnetic field a n d convert their energy i n t o radio waves. The n e t effect i s a microsecond burst of i n t e n s e , broad frequency r a d i o wave Although EMP e n e r g y , Which i s o n e form of a n Electromagnetic P u l s e or EMP. d o e s n o t threaten living things, i t can disrupt or destroy unprotected solid s t a t e e l e c t r o n i c s , including those used i r a d i o and telephone services, computers and computer magnetic memory b a n k s , aircraft instrumentation and f l i g h t controls, ignition and control modu1e.s in a u t o m o b i l e s , protective devices Which sustain electric power distribution in t h e United S t a t e s , and satellites and their ground stations. At i s s u e i s the vulnerability o f the Nation and the measures that can be implemented to minimize the d a m a g e t h a t c a n b e caused by EMP. BACKGROUND History T h e high-altitude EMP was f i r s t encountered during nuclear testing over Johnson Island i n t h e Pacific i n 1958. D u r i n g this test p e r i o d , 1 9 5 8 - 1 9 6 3 , EMP was not a threat to the relatively primitive vacuum tube electronics nor to t h e electromechanical relays o f telephone systems. It w a s regarded a s a mystery and a n "interference." In 1 9 6 2 the Rand Corporation i n California published a n explanation of how the pulse w a s generated along with its approximate magnitude. Electronic vulnerability to t h e EMP emerged i n t h e next decade with the electronic revolution which began in the early 1960s. T h e vacuum tube era gave way to solid s t a t e electronics. Only milliwatts of power could perform electronic tasks which required watts using t h e older technology. As efficiency r o s e , sensitivity to transient surges of current a l s o rose. T h e solid state circuitry, a l m o s t universal by 1 9 7 0 , proved to be a thousand to a million times a s easily damaged by an E M P a s the older vacuum tube technology. T h e growth of understanding within the military establishment of EMP effects a s well a s the problems of EMP countermeasures i s revealed i n the history of the Safeguard antiballistic missile (ABM), a system of r a d a r s , c o m p u t e r s , and nuclear-armed interceptor missiles to have been d e p l o y e d a t twelve sites a c r o s s t h e United S t a t e s starting i n the early 1970s. As an understanding of EMP developed i n the military, protective measures cost i n the ("hardening") and EMP simulation equipment became a major Safeguard project. Although the missiles and ground c o n t r o l s y s t e m s were hardened, the possibility w a s recognized t h a t t h e e ~ p 1 0 ~ i O nf r o m the Safeguard or S o v i e t nuclear warhead might isolate t h e sPte from all communication. Essential links to NORAD (the North American D e f e n s e Command) and N O R A D v s l i n k s to the P r e s i d e n t could b e t e r m i n a t e d by the pulse. The extent to which Safeguard might impair the overall defensive capability remained a d e b a t e throughout t h e l i f e of the project (1969-1976). Ironically, the threat posed by Safeguard w a s significantly reduced by the May 1 9 7 2 anti-ballistic missile treaty with t h e ' Soviet Union. T h e treaty CRS- 2 MB82221 UPDATE-12/15/83 permitted t w o ABM s i t e s ; a 1 9 7 4 protocol to t h e treaty reduced that number to A s i n g l e Safeguard base became operational in April 1 9 7 5 but closed i n one. February 1 9 7 6 , primarily d u e to concern that the utility of a single ABM site could be nullified by t h e growing S o v i e t missile force. Concern over the l o s s of communications to EMP remained. Solid s t a t e electronics initiated several trends i n the early 1 9 6 0 s which began to accelerate a n d still continue to do s o today. Circuitry i s n o w more Compact by six or seven orders of magnitude compared to vacuum tube technology. Power consumption has decreased by a similar. amount. T h e cost of circuitry has a l s o decreased by f i v e t o six orders of magnitude. This combination of f a c t o r s has led to a geometric growth of tasks and capabilities. Small electronic c h i p s n o w control a n d monitor vehicle engines, provide instrument displays, and provide $20.00 pocket calculators t h e mathematical power t h a t would h a v e c o s t over a million dollars i n the l a t e 1950s. They c o n t r o l and program factory m a c h i n e s , h o m e kitchen equipment, toys and games. Along with this revolution their sensitivity t o transient charges of electricity h a s risen i n about the s a m e proportion. Modern circuitry i s a b o u t a million times a s easily destroyed by a n EMP a s the older vacuum tube systems. T h i s sensitivity may be expected to rise steadily along with growth of the r o l e played by electronics. T h e EMP Phenomenon T h e gamma ray flash from a high-altitude nuclear explosion produces a spherical w a v e front. T h e portion of this sphere expanding toward t h e Earth impacts t h e upper a t m o s p h e r e tearing l o o s e a heavy c h a r g e of electrons. The f r e e electrons a r e immediately captured by the Earth's magnetic field. They dissipate their velocity by spinning around t h e magnetic field l i n e s , converting their energy i n t o radio waves. The--net e f f e c t i s a microsecond burst of i n t e n s e , broad frequency radio wave energy, which i s o n e form of a n Electromagnetic P u l s e o r EMP. Since t h e EMP contains a broad spectrum of f r e q u e n c i e s , a n electrical conductor o f a n y length c a n serve a s a n antenna. T h e heaviest jolt i s received from the electrical service lines. H o w e v e r , wiring internal to electronic equipment a l s o receives a n d conducts t h e s u r g e directly i n t o t h e circuitry. T h e disruptive capability of t h e EMP i s due more to i t s s h a p e than to t h e total energy i t contains. T h e duration of the pulse i s a b o u t a millionth of a second (a microsecond) but the peak power density i s nearly i n s t a n t a n e o u s -- a f e w billionths of a second (about 10 nanoseconds). T h e t o t a l energy received from a nominal one-megaton burst a b o v e t h e a t m o s p h e r e i s small a b o u t half a joule per square meter. T h e peak power - - d e n s i t y , however, T h e onset of t h e peak power density i s reaches 6 megawatts per square meter. a hundred t i m e s more rapid than t h a t of lightning. AS a c o n s e q u e n c e , conventional lightning s u r g e protective devices a r e n o t effective against t h e EMP. -- Any electrical conductor may serve a s a n antenna f o r t h e pulse, even short lengths of internal wire. All electronic circuitry more advanced than that using vacuum tubes may be affected by the pulse. T h i s may include all communication networks, transmitters a n d receivers, and a l l telephone systems except those i n which g l a s s fiber has been substituted for wire. Computers CRS- 3 MB82221 UPDATE-12/15/83 may be destroyed a n d magnetic tapes and discs erased. Machines a n d vehicles which employ electronic modules in their operation would be disabled. Electronic instruments such a s a i r c r a f t NAVCOM a n d f l i g n t control systems may be destroyed. Satellites exposed to the expanding spherical wave f r o n t of gamma and x-rays could a l s o r e c e i v e a crippling or destructive EMP. T h e radiation could f r e e electrons from the metal skin of the s a t e l l i t e , creating a n electric charge. T h e intensity of the charge could reach a million volts per meter. T h e electronic payload would then r e c e i v e large induced c u r r e n t s , not EMP o r unlike a lightning strike. T h i s effect i s called a system-generated SGEMP. Protection or hardening against SGEMP presents a problem which is not entirely solved. E v e n a double walled satellite would not be i m m u n e to a pulse strong enough to induce a charge i n the i n n e r shell. A single nuclear warhead could Conceivably disable a l l satellites n o t shielded by the Earth. T h i s would include s y n c h r o n o u s , a s well a s l o w a l t i t u d e civil and military satellites. Defensive systems such a s laser battle stations and o f f e n s i v e s y s t e m s such a s k i l l e r satellites o r enroute missiles could a l s o be disabled or damaged by the SGEMP. T h e E f f e c t of EMP A nuclear explosion 1 5 0 miles a b o v e the geographic center of the country i s t o o distant to i n f l i c t direct damage or threaten life. H o w e v e r , a t this a l t i t u d e , the expanding sphere of gamma radiation would excite a l e n s shaped segment of the upper atmosphere several thousand square miles in area. The resulting EMP would cover most of the United States. Large-scale power blackouts could occur. P o w e r plants could automatically shut down a s the pulse triggered fault sensors. T h e power distribution grid would then be imbalanced causing many more generating facilities to s h u t d o w n i n response to s u r g e s and overloads. However, with n o a d d i t i o n a l EMP's, power distribution could be restored i n a matter of hours o r a day. More serious would be the destruction of electronic circuitry. On l i n e equipment would r e c e i v e t h e EMP through the electrical service connection. New equipment i n s t o r e s or warehouses would r e c e i v e the pulse through w i r e l e a d s which would s e r v e a s antennae. In brief the main effects of t h e EMP would be t e m p o r a r y , large-scale power l o s s e s followed by longer-duration communications effects. Computer dependent banking f u n c t i o n s , a i r f l e e t o p e r a t i o n s , and s u r f a c e transportation s y s t e m s could a l l b e affected. T h e r e a r e concerns that d e f e n s i v e and retaliatory capability a s well a s the operation . o f military communication systems could a l s o be disrupted. Protection from t h e EMP T h e word "harden," borrowed from the military, has'come to mean "protect." For example, a computer which has been "hardened" i s shielded o r o t h e r w i s e protected against t h e EMP. Protection from the pulse i s s i m p l e in principle. C o n d u c t o r s such a s power cables or a n t e n n a l e a d s may be fitted with surge a r r e s t o r s or filters designed specifically for the fast r i s e t i m e of the pulse. Other than t h i s , the equipment may be either encased i n metal (a CRS- 4 MB82221 UPDATE-12/15/83 Faraday Shield) or simply taken d e e p underground. New e q u i p m e n t , s t o r e s , a n d spares could b e protected by t h e use of a continuous metal c o v e r i n g , possibly a f o i l , applied a s part of t h e packaging process. S o m e protection for large open networks such a s electrical power a n d telephone g r i d s could be achieved by replacing the systems n o w i n u s e with underground networks or by protecing the networks a b o v e ground. Such procedures a r e generally considered too costly for practical consideration. Advancing technology may eventually reduce t h e EMP a s a threat to the telephone a s copper conductors a r e replaced by o p t i c a l fibers. However, optical f i b e r systems have terminals and repeaters which must a l s o b e hardened. Military hardening began in aircraft strategically i m p o r t a n t i n conducting a retaliatory strike or serving a s a n a e r i a l command post. This includes most aircraft i n the Strategic Air Command. Unhardened aircraft in which t h e pilot's i n p u t to the control surfaces i s electronic ("fly-by-wirew) may be disabled by t h e EMP, but there a r e only a f e w of these. Further hardening i s n o w underway to protect surface installations and military communication networks. Continuity of electric power i n missile launching f a c i l i t i e s i s being assured by the installation of f u e l c e l l s a s well a s auxiliary generators. Optical fiber cables are replacing conventional telephone networks for l o c a l communication. Information o n the hardening s t a t u s of long distance military communication networks i s n o t available. Since t o t a l hardening of civil and military resources against EMP i s not possible, d e c i s i o n s on protection must weigh threat a s s e s s m e n t , c o s t , a n d consequences. In the c a s e of the military, t h e deterrent value of a n i m m u n e retaliatory f o r c e i s a l s o a consideration. Issues 1. T h e n u m b e r of space-capable l a u n c h e r s increases with time and some may become commercially available during this decade. Can a threat a s s e s s m e n t be made of t h e prospect of a hostile nation or g r o u p inflicting a n EMP i n the manner of a terrorist blow, not a s a n opening t o war? 2. Should governing bodies be encouraged to protect their o w n computer capabilities a n d magnetically recorded data? Should f i n a n c i a l institutions and communication .networks? 3. S h o u l d systems of protective developed a n d their use encouraged? packaging for electronic goods be 4. Should industrial a n d public educational programs be initiated which encourage hardening of electronic circuitry i n vehicles, factory equipment and possibly i n t h e home? 5. When a power plant generator i s s t a r t e d , it will n o t produce current until a n o u t s i d e electrical source i s applied to i n i t i a t e the f o r m a t i o n of i t s magnetic field. Once formed the generator sustains i t s own field. This means that i n a total shut d o w n , the plant remains off-line until electricity can be brought i n from a n o t h e r plant o r generator. H a v e utilities made adequate provision to reduce down time in the event of widespread total shut-downs (such a s by keeping small auxiliary generators on hand)? CRS- 5 MB82221 UPDATE-12/15/83 6. Should the replacement of copper telephone lines with cables of optical fiber, at least over trunk l i n e s , be encouraged or somehow accelerated? 7. To what extent should orbiting equipment, civil a s , w e l l a s military, be protected against SGEMP? ADDITIONAL REFERENCE SOURCES Broad, W. J. Nuclear pulse (I) awakening to the chaos factor. Science, May 2 9 , 1981: 10009. ----- . Nuclear pulse (11) ensuring the delivery of the doomsday signal. Science, June 5 , 1981: 1116. ----- . Nuclear pulse (111) playing a wild card. June 1 2 , 1981: 1248. Raloff, J. EMP: a sleeping electronic dragon. news, May 9 , 1981: 300. Lemer, E. J. Electromagnetic pulses: IEEE s p e c t r u m , May 1981: 41. Science, Science potential crippler; Longmire, C. L. On the electromagnetic pulse produced by nuclear explosions. IEEE transactions on electromagnetic compatibiiity, v. EMC-20, no. 1 , Feb. 1978: 3. U.S. Dept. of Energy. Feasibility of isolating vulnerable equipment of the electric power s y s t e ~ .from sources of EMP. 1978. Glasstone, Samuel and Philip Dolan. T h e effects of nuclear weapons. Chapter 1 1 , the electromagnetic pulse and its effects: 514-540. Third edition. Washington, U.S. Govt. Print. Off., 1977.