chapter 10 command, control, and communications … · chapter 10.–command, control, and...

Chapter 10

COMMAND, CONTROL, ANDCOMMUNICATIONS (C3)

Chapter 10.– COMMAND, CONTROL,AND COMMUNICATIONS

Page

Overview. . . . . . . . . . . . . . . . . . .277Technical Aspects of Strategic C3 . . . . . . . . . . . . . . .278

Communications Links. . . . . . . . . . . . . . . . . . . . . . . . . . . . .278Vulnerabilities of Communications Systems, . . . . . . . . . . . .281Command and Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......283

C Functions for MX Basing. . . . . . . . . .284Preattack Functions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .,......284Transattack and Postattack Functions. ., . . . . .285

C ) SystemsforMX Basing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . ...........285f3aselineMPS System . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., ....286MPS 13 asing With LoADS ABM System. ......,. . . . . . . . . . . . . .......,289Launch UnderAttack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ....290Small Submarines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...290AirMobileMX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...293

Overviewof Radio Communications. . . . . . . . . . . . . . . . . . . . . . . . . . . . ...294RadioWavePropagation . . . . . . . . . . . . . . . .,..,. 294Disruption of Radio Communications Due to Nuclear Detonations ............296

T A B L ETable No.

34. Radio Communications Bands. . . . . . . . . . . . . . . . . . . . . . . . . .......,.279

124125126127128129130,131132.133.134,135.136137

138139140

F I G U R E SFigure No

Communicat ions System for Basel ine MPS System (Transattack) . . . ,286Possible Additions to Baseline MPS Communications System (Transattack). 288Communicat ions System for Basel ine MPSSystem (Postattack) . . . . .288Possible Additions to Baseline MPS Communications System (Post attack). .289Preattack C) System for Small Submarines . . . . . . . . . . . . ....291Transattack C’ System for Small Submarines . . . . . . . . . . . . . . . . .......292PostattackC’ System for Smal l Submarines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293T r a n s a t t a c k A i r M o b i l e M X C o m m u n i c a t i o n s S y s t e m . . 2 9 4Physical Paths of RadioWaves .. . . . . . . . . . . . . . . . . ...295Electromagnetic Transmission Ranges at Different Frequencies . . . .295Over-the-Horizon Radio Transmission . . . . . . . . ..296Geometry of Aircraft Direct Path Communications.. . . . . . . . . .. ....296Geometry of Satellite Communications . . . ...297Electromagnetic Pulse Ground Coverage for High-AltitudeNuclear Explosion . . . . .................................................................................. . . . . . . ..297Origin of Electromagnetic Pulse From High-Altitude-Nuclear Explosion. . .298Atmospheric Radio Propagation at Different Frequencies. . . ........... 299Radio Propagation Paths Before and After High-Altitude-Nuclear Explosion 299

Chapter 10

COMMAND, CONTROL, ANDCOMMUNICATIONS (C’)

OVERVIEW

A missile force that physically survives an at-tack is of no use if the means to command theforce do not survive as well. Reliable com-mand, control, and communications (C3, pro-nounced “C-cubed”), impervious to Soviet at-tempts at disruption, are needed if command-ers are to assess the status of an MX force,retarget the missiles if desired, and transmitlaunch commands. There is a wide variety oftechnical possibilities for wartime communica-tions and just as wide a range of means to dis-rupt and impede them. The nature of the dis-ruption suffered by the U.S. C3 system in war-time would depend on the amount of damagedone to communications installations them-selves and on the extent of disturbance of theatmosphere due to nuclear explosions. Thoughsome disruption would inevitably result re-gardless of the nature of the Soviet attack, themost stressing circumstance would result froma deliberate Soviet attempt to deny U.S. com-manders the means to control and executetheir forces.

It will be apparent that no single communi-cations link can be made absolutely surviv-able, but disruption can be made difficult,time-consuming, provocative, and costly ofSoviet resources. Multiple links can also beprovided, subject to different failure modes,and provision can be made for reconstitutingsome links if the primary system is destroyed.

The actual functions that a C3 system sup-porting an MX force must fulfill depend tosome extent on doctrine for the force’s use. Ata minimum, the communications system mustbe consistent with the operations of the force(e.g., must not compromise missile location inmultiple protective shelter (MPS) basing orsubmarine location in submarine basing) andmust permit one-way communication of shortlaunch commands (Emergency Action Mes-sages— EAMs) from commanders to the mis-

siles to order execution of preplanned optionsof the Single Integrated operational Plan(SIOP). In addition, it could be desirable forthe C3 system to support prompt response tolaunch commands (“responsiveness”), flexibleor ad-hoc retargeting outside of the SIOP, andtwo-way communications so that the forcescould report their status to commanders andconfirm execution of orders. Last, if the forceexpected attrition in an attack, it could be de-sirable for the surviving missiles to be able toredistribute targets among themselves so thatthe highest priority targets were always cov-ered by surviving missiles. For a given basingmode, the hardware to carry out these func-tions, and the functions themselves, can differsubstantially from the preattack or peacetimeperiod to the transattack and postattackperiods.

OTA has sought to prescribe a technicallyfeasible C3 system that satisfies these criteriafor each of the principal basing modes. Inmany cases the system described differs sub-stantially from those that are available to U.Sforces today. Obviously, providing these sys-tems would involve some cost, but with the ex-ception of launch under attack, in no case is C3

a cost driver for the basing mode as a whole.Some elements of these C3 systems would fur-thermore support other strategic and conven-tional forces, so their costs should perhaps notbe assigned entirely to the MX basing mission.

There are distinct and important differencesfrom basing mode to basing mode regardingboth the technical means to support effectiveC 3 and potential vulnerabilities. In each case itappears that with adequate funding and effort,acceptable technical solutions are available,though it would be extremely difficult to pro-vide a C3 system survivable against any and allcontingencies. Direct comparisons are diffi-cult, but on balance OTA can see no clear rea-

277

278 ● MX Missile Basing

son for preference among the basing modes on in concrete terms the functions desired from athe basis of C3. C 3 system supporting MX basing. The next sec-

tion describes the C3 systems for the basingThe next section discusses the technical as- modes and describes how they might function

pects of strategic C’ in general terms, including before and after attack. The last section con-available means of communication and their tains a technical overview of radio communi-vulnerabilities. The following section lays out cations.

TECHNICAL ASPECTS OF STRATEGIC C3

Communications Links

The communication of information betweentwo points requires an intervening communica-tions link. For instance, a telephone micro-phone converts acoustic signals (i.e., a humanvoice) into electrical signals, and the earphoneconverts the electrical signal back into sound.The lines over which the signal travels betweenthe phones is referred to as the communi-cations link. By bouncing radio waves off theionosphere, it is possible to communicate oververy great distances. in the case of this type ofcommunications, the path over which the ra-dio wave travels is the communications link.At very high radio frequencies, radio waves arenot reflected by the ionosphere. In order toachieve long-range communications in thiscase, it is necessary to transmit the signal to asatellite that then retransmits it back to Earth.The channel established through the satellite iscalled the communications link. This seeming-ly expensive and complex method of radiocommunications is valuable for two reasons:

1 . Sate l l i te commun icat ions l i nk s can

2

achieve high data rates relative to radiocommunications that require reflectionfrom the upper atmosphere.Satellite links, if they are not destroyed,are extremely reliable, since communica-tions capabilities do not change with thefIuctuating conditions in the upper atmos-phere.

The time it takes to transmit a message of agiven length over a communications link isdetermined by the data rate of the link. Anymessage, whether transmitted by voice, tele-type, or picture, can be expressed as a se-

quence of “on or off” signals called bits. Thedata rate is the number of bits per second thatcan be transmitted over a particular link. Tel-etype rates are typically a few hundred bits persecond. Since each sequence of five to sevenbits would be enough to represent a letter ofthe alphabet, and since on the average thereare five letters per word of the English lan-guage, a 300 bit-per-second teletype link couldcarry 8 to 12 words per second. Voice com-munications require data rates of several thou-sand bits per second. High-frequency satellitelinks can transmit data at hundreds of millionsof bits per second. These data rates could sup-port tens of thousands of separate voice chan-nels. A particularly important type of messagein the case of strategic C’ is the EAM. Thesemessages, ordering a strike by U.S. strategicforces, could be preformatted and might con-sist of a small number of bits, since even a for-mat with a small number of bits would lead toa large number of possible messages thatcould have the same format. For instance, ifEAMs consisted of 20 bits, then more than amillion different messages with the same for-mat could be created. EAMs can therefore bevery short messages and can be transmitted ina short time even by links with relatively lowdata rates. Much more information wouldhave to be transmitted to order a strike thatwas not among the preplanned options. A highdata-rate link would be required to transmitsuch long messages in a short time.

Land lines

Landlines consist either of wires that con-duct electricity or of glass fibers (i.e,. fiber-optic) through which light can be guided.

Ch. 10—Command, Control, and Communications (C3) . 279

Both types of Iandlines can be used for ex-tremely high data-rate communications andare therefore very useful for communicatingwith land-based strategic weapons systems,The communications Iinks and nodes associ-ated with Iandlines, however, are vulnerable tophysical destruction in war and are subject todisruption or destruction by electromagneticpulse (EMP) generated by high-altitude nuclearbursts. Landlines might therefore only be ofuse before an attack on a land-based strategicweapons system.

Radio Links

Radio communication bands are, by conven-tion, referred to by acronyms. Since theseacronyms are commonly used in discussions ofcommunications systems, they are summa-rized in table 34.

VLF/LF

Very low frequency (VLF) and low frequency(LF) radio signals are useful for reliable com-munication over very large distances. A power-ful VLF/LF station can be received over dis-tances of many thousands of miles, even ifthere are nuclear detonations in the upper at-mosphere. VLF/LF signals penetrate seawaterwell enough to make communications possiblewith submarines and, at a cost in data rate, canbe made resistant to jamming. VLF/LF radiohas two important drawbacks: the antennas re-quired for transmission and reception must bevery large and are therefore susceptible tophysical destruction, and the data rates that

are possible with VLF/LF are low. However, air-planes are able to trail large antennas in flightand transmit suff ic ient ly powerful VLF/LFradio waves to permit long-range communi-cations. Airplanes can communicate withground stations, other aircraft, and submergedsubmarines in this way.

M F

Medium frequency (MF) radio links are high-

er frequency than VLF/LF radio links and canbe used to transmit information at higher ratesthan is possible with VLF/LF. (The reason forthis and other features of radio propagation isdiscussed in the Overview of Radio Communi-cations section. ) MF radio is in the same bandof frequencies as AM radio broadcasting. LikeAM radio, MF signals do not, under normalconditions, propagate much further than thelength of a metropolitan area, though at nightskywave propagation can lead to longer range.MF is a reliable means for moderate data-ratetransmissions over short distances. Since theradio signals at these frequencies do not travelvery far, they are generally (but not always) dif-ficult to jam from great distances. Distancesover which communications at these frequen-cies can generally be affected are 40 to 50miles between ground stations and 100 to 150miles between an airplane and a ground sta-tion.

H F

H i g h f r e q u e n c y ( H F ) ( “ s h o r t w a v e ” ) r a d i os i g n a l s a r e e x t r e m e l y u s e f u l f o r l o n g - r a n g e

Table 34.—Radio Communications Bands

Name of Range Frequency Range* Wavelength Range

Extremely low frequency ELF .3-3 KHz 1,000-100 kmVery low frequency VLF 3-30 KHz 100-10 kmLow frequency LF 30-300 Kfiz 10-1 kmMedium frequency MF 300-3,000 KHz 1,000-100 mHigh frequency HF 3-30 MHz 100-10 mVery high frequency VHF 30-300 MHz 10-1 mUltra high frequency UHF 300-3,000 MHz 100-10 cmSuper high frequency SHF 3-30 GHz 10- 1 cmExtremely high frequency EHF 30-300 GHz 1 -.1 cm

“Hertz = cycle per second, KHz= KiloHertz = 1,000 cycles per second, MHz= MegaHertz = 1,000 KHz,GHz = GigaHertz = 1,000 MHz.

tm = meter= 328 feet, km= kilometer= 1,000 meters= .6212 miles, cm = 01 meters= 394 inches.

.


moderately high data-rate communications. Incontrast to VLF/LF radio systems, HF equip-ment and antenna systems are compact and donot require large amounts of power. A seriousproblem with HF band communications is thatthey are easily disrupted by nuclear detona-tions in the upper atmosphere, and can be“blacked out” over very large distances forperiods of hours. Another problem with HFcommunications is the possibil ity of usingdirection finders to determine the location ofthe transmitter well enough to attack it. Apossible further problem with HF is that thenumber of usable frequency bands is limited.Many users trying simultaneously to use HFcould jam one another.

In spite of these drawbacks, the upper at-mosphere would recover electrically severaltens of hours after nuclear detonations oc-curred and would then be able to support thelong-range transmission of HF. For this reason,HF would be useful for an indefinite periodafter a nuclear attack for high-data-rate com-munications even if other communicationslinks were destroyed.

Today’s fielded HF systems require manualtuning, introducing some unreliability even inday-to-day peacetime communications. Micro-processor-tuned HF systems resulting fromtechnology improvements would make HFhighly reliable except in periods of significantblackout.

VHF

Very high frequency (VHF) waves are notstrongly reflected from the upper atmosphereand do not travel far over ground. VHF is theband at which FM radio broadcasts occur, andit is familiar to radio Iisteners that FM stationshave shorter range than AM stations. Very highdata rates are possible with VHF, and antennasand equipment can be made compact.

Long-range communications are possibleusing VHF by reflecting radio signals off theionized trails of meteors. Since it is necessaryto have a reflecting meteor trail in the rightlocation of the upper atmosphere to permitcommunications between two points beyond

the radio horizon, delays of a few minutescould occur before it would be possible totransmit a message using VHF. One possibleadvantage of VHF is that it might be possibleto communicate effectively by bouncing radiosignals off the bottom of the ionized regionformed by a high-altitude burst. Thus, VHFcommunications might actually be improved ifthe Soviets blacked out HF or UHF.

UHF

Ultrahigh frequency (UHF) is extremely use-ful for line-of-sight communications betweenaircraft. The data rates are high and the equip-ment is quite compact and low power. UHFcan be used to communicate to ground instal-lations from an aircraft at a distance of about200 miles and can be used to communicatebetween aircraft at distances between 300 and450 miles. For this reason, UHF could be usedto communicate between airborne commandposts and to transmit launch commands toland-based missiles.

It is possible to use direction-finding tech-niques to locate UHF transmitters and it is alsopossible to jam receivers This problem is un-likely to be serious for l ine-of-sight aircraftcommunications but it could be a problem forUHF links through satellites.

Satellite Communications (SATCOM)

UHF SATCOM

UHF sate l l i te l i nk s a re use fu l not on lybecause data rates can be very high, but alsobecause UHF antennas are not extremely di-rectional, so users do not have to have meansfor pointing antennas at satellites. A drawbackof UHF SATCOM links is that it is possible tojam the uplinks to the satellites from smallmobile jammers (ship or ground mobile) lo-cated anywhere in the satellite’s hemisphere ofview. A problem associated with the multi-di rect ional nature of UHF s ignals i s thatenough signal can be “seen” from other direc-tions that it is in principle possible to locateground-based UHF transmitters from space.Nuclear detonations in the upper atmospherecan also result in “blacking out” of UHF

Ch. 10—Command, Contro/, and Communications (C3) 281

signals for a few hours over regions of theEarth’s surface. These regions of blackoutwould have radii of tens to hundreds of miles.The United States now uses UHF SATCOM reg-uIarly for worldwide mi1itary communications.

UHF satellites could be launched from silosinto low orbit in wartime to reconstitute dis-rupted I inks.

SHF/EHF SATCOM

Super high frequency (SHF) and extremelyhigh frequency (EHF) satell ite l inks are ex-tremely useful for very high data rate, reliablecommunications. Because of the large band-width, such links are, at least for EHF, unjam-mable. Because the wavelengths are so short(on the order of fractions of a centimeter), it ispossible to have very highly collimated radiobeams that can be trained on the satellite. Inaddition, SHF/EHF antennas are sufficientlysmall (about 5 inches in diameter) that theycan be conveniently mounted on ground vehi-cles, aircraft, surface ships, and submarinemasts.

Since the SHF/EHF beam is so tightly col-limated, it is nearly impossible for a receiverthat is not in the beam to “see” the signal. Theonly way that the presence and location of anSHF/EHF transmitter could be detected wouldbe if the search receiver was itself in the beam.Thus, SHF/EHF satellite uplinks from forces inthe field, surface ships, and submarines wouldnot pose the risk of revealing the location ofthe transmitters.

A potential problem with SHF/EHF is an at-mospheric phenomenon called scintillation.Electron density fluctuations in the ionosheredue to high-altitude nuclear bursts could causethe beam to be bent as it propagated throughthem. This bending would result in fluctua-tions in the quality of reception at the receiver.It is believed that with suitable signal modula-tion scintillation would not be a problem at all.For EHF, scinti l lation would not last, in anyevent, for more than a few minutes after ahigh-altitude burst. Another minor problem isthat water absorbs EHF signals. However, amajor rainstorm would be required to impede

communications. Mist and clouds would notbe a problem.

LASER SATCOM

The high frequencies and directional natureof laser communication allow for extremelyhigh-data-rate, low power consumption, un-jammable l inks between satell ites and be-tween satellites and aircraft flying above theclouds. Communications between ground sta-tions and satell ites would not be feasiblebecause of the possibility of cloud cover. Evenin clear weather, such communications wouldcreate a visible pencil of l ight in the sky,revealing the location of the user. For thisreason laser SATCOM might endanger the co-vertness of submarines, surface ships, andmobile ground units.

Vulnerabilities ofCommunications Systems

Physical Destruction

One obvious way to attempt to deny com-munications capability to U.S. strategic forceswould be to physically destroy as many sus-ceptible elements of the system as possible.This destruction would include landlines, land-line switching stations, radio transmitter sta-tions (i.e., VLF/LF/MF, etc.), satellite up-and-down-link stations, and fixed command cen-ters

After an in i t ia l attack, i t could not beguaranteed that landline communicationswould exist with land-based forces or thatfixed VLF stations would be broadcasting tothe submarine forces. Only communicationslinks made possible with aircraft and satelliteswould necessarily still be intact.

Electromagnetic Pulse (EMP)

An effect of the detonation of nuclearweapons, both inside and outside the at-mosphere, that is less appreciated but still veryimportant is EMP. The case of a detonationoutside of the atmosphere is, however, themost relevant as a general problem for com-munications systems.

83-477 0 - 81 - 19


As explained in the Overview of Radio Com-munications section, a high-altitude nucleardetonation could generate a sudden electricfield over large regions of the United States ofup to 50,000 volts/meter. This intense electricfield could destroy or disrupt communicationsand electrical equipment of all types. Highquality assurance and testing are required toensure that components are properly sealedand protected if they are to survive the effectsof the EMP from high-altitude detonations.

Ionospher ic Disrupt ion

Another effect of h igh-al t i tude nucleardetonations i s ionospher ic dis rupt ion. Theelectron densities in the ionosphere would bechanged suddenly by the ionizing effects ofprompt gamma rays from the nuclear detona-tion and/or beta rays from fission decay prod-ucts. These effects could cause significantdegradations at those radio frequencies thatare reflected from (HF) or pass through (UHFSATCOM) the ionosphere.

Jamming

Jamming refers to the ability of a hostiletransmitter to drown out the signal being re-ceived. The susceptibility of a radio link tojamming depends on power, bandwidth, modu-lation technique, and antenna directivity. Ingeneral, jamming becomes more difficult asthe frequency of the transmission increases. Ifthe nature of potential wartime jamming canbe foreseen, it can be compensated by changesin modulation technique and increases inpower.

Ant i satellite (ASAT) Threats

There is considerable concern that the heavydependence of the U.S military on SATCOMwill make satellites the targets of attack. Themeans of attack could be direct-ascent in-terception, space mines, land-based lasers, oreven space-based lasers.

Several of the basing modes discussed in thisreport could make effective use of SATCOM.A highly reliable SATCOM system based ondeep-space millimeter-wave (E H F) communica-

tions has been proposed for military use andwould be very useful to support MX basing.The following discussion explains why there isconsiderable interest in such satelIites.

Though geosynchronous orbit would bemost convenient for such satellites operatingat EHF frequencies, it would perhaps be ad-visable to deploy them in h igher orbits .Geosynchronous orbit is that unique orbit22,300 miles from the Earth at which the or-bital period of satellites is equal to the rotationperiod of the Earth. Thus, satellites in geosyn-chronous orbits remain over the same point onthe Earth’s surface as both they and the Earthgo around. Because its position relative to theEarth’s surface would remain the same, userswould have a fixed point upon which to focustheir directional antennas. Because of its con-venience, however, geosynchronous orbit isquite crowded. It would therefore be possiblefor the Soviets to station a “space mine” near aU.S. communications satellite and answer inresponse to U.S protests that the mine was infact some other sort of satellite that it was con-venient to position in geosynchronous orbit.The United States would then not be in a posi-tion to assert that the Soviets had no businessthere, because it would be quite plausible thatthey did have legitimate purposes for position-ing a satellite in this unique, convenient orbit.

If on the other hand the U.S. satellites werein an orbit chosen more or less randomly fromamong the infinite number of possible alti-tudes, the United States would be in a betterposition to assert that the only possible pur-pose for a nearby Soviet satellite must be to in-terfere with that of the United States. TheUnited States might then just i fy on thesegrounds measures against such interference.

Satellites could also be threatened by directattack from a missile launched from the SovietUnion. However, the U.S. satellites could bepositioned high enough that it would takemany hours (18 or so) for an attacking vehicleto reach them. Furthermore, since the intercep-tor missiles required to reach high orbits wouldbe quite large, the Soviets would probably onlylaunch them from the Soviet Union. Most of

Ch. 10—Command, Control, and Communications . 283

the U.S. satellites would be on the other side ofthe Earth when the f i r s t interceptor waslaunched, and launch of other interceptorswould have to be staggered to intercept therest of the satellites as they “came around. ”Direct-ascent antisatellite attacks on high or-bits would therefore present a timing problemto the Soviets. The United States would cer-tainly be aware that the satellites were underattack hours before they were destroyed.

Last, land-based lasers could not deliver suf-ficient power to the orbits of interest (fivetimes geosynchronous or so, or half way to theMoon) to destroy the satellites.

A number of measures could be taken to en-sure the survival of these satell ites. For in-stance, they could be provided with sensors toallow them to determine when they were underattack, and they could maneuver to avoidhoming interceptors and deploy decoys orchaff to confuse homing sensors. Backupsatell ites at such distances from the Earthmight also be able to be hidden entirely by giv-ing them small optical, infrared, and radarsignatures. Dormant backup satellites mightbe hidden among a swarm of decoys andturned on when the primary satell ites en-countered interference. Last, backup satellites(probably using UHF instead of higher frequen-cies) couId be deployed on missiles in silos andlaunched into low orbits to replace the pri-maries. These reconstituted satell ites couldalso be attacked, but it would take time for theSoviets to acquire data on their orbits, evenassuming the United States allowed them un-hindered operation of the means to acquirethis data. Some of these techniques for satel-lite security are more effective than others.

Command and Control

This chapter deals for the most part with thecommunications aspect of C3. The commandand control functions for U.S. strategic forcesare outside the scope of this discussion, but itis necessary to specify how the commandstructure is linked to the communications sys-tem and thus to the forces.

Decisions regarding the use of U.S. strategicforces are in the hands of the National Com-mand Authorities (NCA), i.e., the President andSecretary of Defense or their successors. Themilitary provides a National Military Com-mand System to support NCA. This system con-sists of fixed command centers and survivablemobile command posts. The fixed ground cen-ters include the National Military CommandCenter in the Pentagon, an Alternate NationalMilitary Command Center at a rural site out-side Washington, D. C., the underground com-mand center at Strategic Air Command (SAC)headquarters at Of futt Air Force Base inOmaha, Nebr., and North American AerospaceDefense Command headquarters in CheyenneMountain, Colo.

Since the fixed ground centers could be de-stroyed early in a nuclear war, a fleet of sur-vivable Airborne National Command Posts isprovided for postattack command and control.The most important aircraft in this fleet is theE-4B (modified Boeing 747) National Emer-gency Airborne Command Post (NEACP, pro-nounced “kneecap”) available for Presidentialuse. In addition, there is a fleet of strip-alertaircraft at military bases throughout the coun-try, including command posts of the nuclearcommanders and the Post-Attack Commandand Control System (PACCS) fleet. This fleetcould establish a network of line-of-sight UHFcommunications from the Eastern to CentralUnited States within a short time after an at-tack. Finally, SAC maintains an EC-135 (modi-fied Boeing 707) command aircraft, called“Looking Glass,” on continuous ai rbornepatrol over the United States.

Ground-mobile command posts–disguisedas vans traveling the Nation’s highways toavoid being targeted — are also a possibility forsurvivable command posts.

In the descriptions that follow of possible C3

systems for each of the basing modes, it will beassumed that all force management functionsand launch commands originate with, or passthrough, the airborne or grounded NEACP, andthat NEACP is provided with the necessarycommunications systems to link them with theMX force.


C’ FUNCTIONS FOR MX BASING

This section outlines the functions desiredof an MX C3 system to support the variousaspects of U.S. Nuclear Weapons EmploymentPolicy. These policy aspects are associatedwith such terms as Basic Employment Policy,Flexible Response, Quick Reaction Hard-Tar-get Counterforce, Secure Reserve Force, andthe like, as derived from the public statementsof senior defense officials. This section trans-lates these notions into concrete functions re-quired of a C3 system for MX. The next sectionwill prescribe hardware capable of performingthese functions for each basing mode.

These functions, and most certainly themeans to accomplish them, differ among thepreattack, transattack, and postattack periods.For the purposes of this chapter, the trans-attack period is defined as the period of air-borne operation of certain C3 aircraft (N EACP,Ai rborne Launch Control Center (ALCC),TACAMO, etc.). The distinction between trans-attack and postattack as used here thereforeconcerns the hardware avai lable to ac-complish the C3 functions and not the func-tions themselves. Transattack and postattackfunctions will therefore be treated together.

Preattack Functions

Peacetime Operations

Peacetime communications are required forcommanders to assess continuously the statusand readiness of the MX force. Continuousone-way communications from commandersto the forces is an obvious requirement. Two-way communications — including from the mis-sile forces to commanders— is clearly impor-tant, though intermittent report-back (relevantfor the case of submarine basing) might beadequate.

Since the communications links have suf-fered no damage, the only impediment tomaintaining adequate peacetime communica-tions would be the requirement that the meansof communications should be consistent withthe operations of the force. Thus, the peace-time communications should not be of such a

nature as to compromise missile locations inthe case of MPS basing or defense unit loca-tions in the case of the MPS/LoADS (low alti-tude defense system) combination, nor betraythe locations of patrolling subs in small sub-marine basing.

Responsiveness

In the event that NCA ordered the launch ofthe MX missiles according to one of the pre-planned options of the SIOP before the forcehad suffered attack, all that would be requiredof the C3 system would be the capability totransmit a short, preformatted, encryptedmessage to the MX force. Since the messagewould be short, low-data-rate communicationswould suffice.

There could be a requirement that missilelaunch be accomplished rapidly after the deci-sion to launch was made. This could be thecase if a Soviet attack were believed imminentand it was thought desirable to strike Sovietforces before they could attack the UnitedStates or disperse from their home bases. Thisrequirement of responsiveness would seek tomake the time interval between disseminationof the EAM ordering launch and actual missilelaunch as short as possible. A portion, thoughnot necessari ly most, of this time intervalwould be comprised of the time it took for therelevant communications links to transmit theshort EAM to the MX force with low probabili-ty of error.

in order to strike certain hardened targetssuch as missile silos, it would also be desirableto be able to control the arrival times of RVS sothat detonation of one would not compromisethe effectiveness of others (“fratricide”). Suchtime-on-target control could be accomplishedby including in the EAM a reference time, rela-tive to which each missile would determine thearrival time required of its RVS in order to coor-dinate arrival with RVS from other missi les.The precise timing would be achieved by coor-dinating launch time, maneuvers of the mis-sile, and reentry angle.

Ch. 10—Command, Control, and Communications (C3) ● 285

In addition to short response time, it couldbe desirable for the MX force to be able tocommunicate back to the commanders in ashort time to confirm successful launch.

Ad-Hoc Retargeting Before Launch

Ad-hoc retargeting refers to the ability toconstruct attacks that are not among the pre-planned options of the SIOP. Such retargetingflexibil ity could involve either rearrangingtargets from the extensive target sets alreadystored in the MX missile launcher’s memory orreprogramming the missile with entirely newtarget sets. Both s i tuat ions would requiretransmission of larger amounts of data thancontained in the short EAM. In the latter case,the information would include target latitudesand longitudes (calculated in the proper coor-dinate system), reentry angle, timing, andfuzing.

Since large attack options would likely beincluded among the S IOP options, extensivead-hoc retargeting might be confined to a rela-tively small portion of the force, in which caseonly that portion need be in a position toreceive such high-data-rate communications.

The portion of the force retargeted wouldpresumably be required to report back receiptof the new targets, confirm them, and reportsuccessful launch.

Transattack and Postattack Functions

Prelaunch Damage Assessment andReoptimization Within the SIOP

In the event that the MX force suffered attri-tion in the attack, it might be desirable for thesurviving missiles to reallocate targets in sucha way that the highest priority targets con-tinued to be covered even if the missiles thatoriginally covered these targets were de-stroyed in the initial attack.

Commanders would presumably also wish toknow the extent of attrition and remainingtarget coverage.

Order for Launch of Preplanned Options

Dissemination of the EAM after an attackwould require that the surviving portion of theC 3 system support at least one-way low-data-rate messages. Report-back confirming suc-cessful launch would require two-way com-munications. It is not clear that the need forrapid response would always be as great in thepostattack period as in the preattack period.

Ad-Hoc Retargeting

Assignment of entirely new targets to the MXmissiles and confirmation of receipt would re-quire teletype data-rate two-way communica-tions.

C’ SYSTEMS FOR MX BASING MODES

In this section, the problems of providing ef-fect ive C3 for each of the principal basingmodes are discussed and technically feasiblesolutions identified. In many instances, the C3

system described for hypothetical future MXbasing modes differs substantially from C3 sys-tems supporting present strategic forces. Thesesystems would have to be acquired at somecost, though in no case (excluding launch un-der attack) is the C3 system a major cost driverfor the system as a whole. Moreover, some ofthe communications systems described wouldbe useful for other military missions in addi-tion to MX basing. OTA has only identified

feasible C3 systems and has not attempted tofind a “best” solution. Also, the systems havenot been subjected to the cost tradeoffs thatcould occur if a decision were made to deployone of them.

The baseline MPS system is in full-scaleengineering development and subject to cer-tain budgetary constraints. it is thereforenatural that the baseline system could be im-proved on (e.g., with regard to two-way Iong-haul communications) with additional funding.Since for the other basing modes similar fund-ing constraints have not been applied to the C3


-—

systems described here, feasible improvementsto the baseline MPS system—available atsome additional cost — are identified.

Baseline MPS System

Preattack

Peacetime MPS C3 operations would be ac-complished principally through the fiber-opticnetwork linking each shelter with the Opera-tional Control Center (OCC) and with othershelters. Each fiber cable would contain threelines (one for communications in each direc-tion and one spare) capable of 48 kilobit/sec-ond data rates. With such high data rates,launch orders and retargeting informationcould be transmitted in a very short time.Response time to an EAM would be driven byoperational procedures and by the severalminutes it would take the missile to emergefrom the shelter and erect.

PLU would be maintained by having the mis-siles and simulators transmit encrypted statusmessages with identical formats according touniform message protocols.

Transattack

The transattack period is defined in thischapter to comprise the period of airborneoperation of the ALCC and NEACP. One ALCCwould always be airborne in peacetime, withanother on strip alert. The in-flight enduranceof the ALCC would be about 14 hours, afterwhich communications would have to be ac-complished from the grounded aircraft to theMPS shelters.

The transattack C3 system for the baselineMPS system is shown in figure 124.

Communications between the ALCC andNEACP are relatively secure. Immediatelyafter the attack, however, the HF and UHFSATCOM could be disrupted, and it wouldtake some time to set up the UHF line-of-sightPACCS net.

Of the links from the ALCC to the shelter, HF( l ine-of-s ight) could be dis rupted by thenuclear environment, and MF represents acompromise between the better propagationof low frequencies through an ionized at-

Figure 124.–Communications System for Baseline MPS System (transattack)

SOURCE: Office of Technology Assessment.

Ch. 10—Command, Control, and Communications (C’) “ 287

mosphere and the higher data rates of high fre-quencies.

MF, which has short range, would be theonly means in the present baseline systemdesign by which the shelters could communi-cate with the ALCC to report their status.Transmission would be through the buried MFdipole antenna at each shelter. Taking into ac-count soil propagation losses, the effectiveradiated power from each shelter would beonly about 2 watts. The low power of the trans-mitter at each shelter would be multiplied bythe “simulcast” technique where each surviv-ing shelter that contained an MX rnissile wouldtransmit its status via MF. Other surviving shel-ters receiving this message would repeat thetransmission simultaneously with rebroadcastsby the original shelter. In this way, after manyrepetitions, all of the surviving shelters wouldbe t ransmitt ing, in sequence, the statusmessage of each individual shelter, with a totaleffective transmitting power of all the shelterstaken together.

Since only the shelters containing MX mis-siles would be transmitting in this period, theseemissions might reveal the locations of the sur-viving missi les if the Soviets could detectthem. However, the short range of ground-wave MF would preclude direction-finding byremote ground stations or ships, and iono-spheric absorption and refraction would pre-vent satellites from detecting and locating theemissions. Thus, this hypothetical threat toPLU may be impossible for the Soviets to capi-talize on. This security from detection is one ofthe reasons why MF communicat ion waschosen.

The simulcast would also be used to enablethe surviving missi les to redistribute targetsamong themselves in order to maintain cover-age of the highest priority targets. The missileswould be numbered I through 200, and foreach SIOP option there would be 200 targetsets, numbered 1 through 200 in priority order.Before the attack, missile #l would have targetset #l, missile #2 target set #2, and so on. Afterthe attack, missile #200 would listen on the MFsimulcast for a status message from missile ##1.

If missile #I did not report or reported that itwas unable to fire, missile #200 (if it survived)would assume target set M. If missile #2 hadnot survived, its target set would be assumedby missile #199 (if it survived), and so on.

Transattack two-way communications be-tween the ALCC and the missile force wouldrely exclusively upon the single MF I ink, SinceMF is short-range, the ALCC would have to ap-proach within 50 to 100 miles of the missilefield in order to receive the MF simulcast andassess the status of the force. There could beconcern for the effects upon the ALCC of dustand radiation lofted into the atmosphere bythe attack.

Th i svialingand/orshownW O U I d

situation could be improved by pro-HF transmitters (as well as receivers)SATCOM terminals at the shelters, asin figure 125. A UHF SATCOM terminalcost about $100,000, so SATCOM at

each shelter would cost about $500 miIIion.

Postattack

The postattack period, as defined for thepurpose of this discussion, would begin whenthe ai rborne command posts (ALCC andNEACP) were forced to land, either to refuel orfor extended grounded operations. The base-line C3 system for this period is shown in figure126. HF and MF skywave communicationscould be disrupted for hours or days after at-tack. The ground-wave communications wouldin any case be short range. The ALCC wouldhave to be within 50 to 100 miles of the shel-ters or it would be out of MF range. The Sovietswould not necessarily spare airfields this closeto the deployment area. There would thereforebe a need for long-haul two-way communica-tions from the grounded aircraft to the sheltersin the postattack period. This communicationwould be needed especially if the ALCC wereinoperable, and the grounded NEACP had tocommunicate with the MX force over thou-sands of miles.

Means to provide these two-way long-haulcommunications that are not part of the pres-ent baseline design are shown in figure 127.


Figure 125.—Possible Additions to Baseline MPS Communications System(transattack)

SOURCE: Office of Technology Assessment,

Figure 126.–Communications System for Baseline MPS System (postattack)

Shelter


Ch. 10—Command, Contro/, and Communications (C’) ● 289

Figure 127.—Possible Additions to Baseline MPS Communications System(postattack)

(ReconstitutableUHF SATCOM)

antenna

HF, MF ground network

SOURCE. Off Ice of Technology Assessment.

They include adaptive HF, ground-based HF orMF relays prol i ferated across the UnitedStates, satellite communications, and erect-able LF antennas.

MPS Basing with LoADS ABM System

The two principal C3 functions required ifLoADS were added to MPS basing would be:1 ) tactical warning of Soviet attack so that theLoADS defense units (DUS) could break out oftheir shelters and prepare to defend; and 2)communications to transmit a breakout orderand authorization to activate the nuclear-armed interceptors (“nuclear release”).

If the design goal providing for awakeningdormant electrical equipment in the DU andbreaking the radar and interceptor cannis-ter through the shelter roof within a very shortperiod of time could be achieved, warning of

Soviet attack would not be required until latein the flight of the Soviet ICBM reentry vehi-cles (RVS). Means to provide such late warning(within 15 minutes of impact) could includerocket-launched sensor probes, sensor aircraft,and ground-based radars, in addition to sat-ellites. Such warning sensors are discussed ex-tensively in chapter 4. Radars similar to theLoADS radars themselves could be positionedat the northern edges of the deployment area.The sensors could provide attack assessment ifsuch information were required to attempt tolimit degradation of defense effectiveness inthe face of a potential Soviet Shoot-Look-Shoot capability (see ch, 3). Without adequatewarning for breakout, the LoADS defensewould clearly be useless. If breakout occurredin peacetime as a result of error, the shel-ters containing the LoADS DUS would bedestroyed.

83-477 0 - 81 - 20


Though it might be feasible physically toactivate the defense in a short time, the proce-dures whereby commanders assessed the warn-ing information and ordered breakout and nu-clear release could in practice lengthen the re-ponse time considerably. In the present LoADScommand concept, breakout and nuclearrelease are effected by two distinct com-mands. The communications needed to sup-port timely activation of the defense would de-pend on who was authorized to order nuclearrelease. Offensive nuclear release must beordered by NCA. Whether authority for defen-sive nuclear release could be delegated to mil-itary commanders is unclear.

At the time the breakout and release orderswere given, detonations of Soviet SLBM RVScould already have occurred in the deploy-ment area and at other centers of the NationalMilitary Command System. MF injection fromthe ALCC might therefore be the only means totransmit the defense commands. If the ALCCoperating area were expanded by using longerrange communications (H F or VLF/LF) betweenthe ALCC and the shelters, the lower data ratescould lengthen the time it would take to trans-mit commands to the defense.

At present, uncertainties in the LoADS sys-tem architecture and unresolved operationalprocedures do not permit judgment on the fea-sibility of supporting the defense’s warningand breakout needs.

If a LoADS defense were added to a vertical-shelter MPS system, the radar and interceptorcannister would have to be emplaced in sepa-rate shelters. In this case it would probably benecessary to deploy a separate communica-tions network to support the rapid transfer ofdata from the radar to the interceptors in anengagement.

Launch Under Attack

Warning and communications systems tosupport reliance upon launch under attack arediscussed extensively in chapter 4. Since thesesystems would be the only “basing mode” tospeak of, considerable time, effort, and money

would presumably be spent assuring their relia-bility in the face of determined Soviet effortsat disruption. As discussed in chapter 4, itwouId be technically feasible to deploy a widevariety of warning sensors and communica-tions links to airborne command posts that,taken together, would be exceedingly difficultfor the Soviets to disrupt. Such disruptioncould furthermore be made time-consumingand provocative.

What cannot be determined on the basis oftechnology alone is whether information pro-vided by remote sensors would be adequate tosupport a decision of such weight as thelaunch of U.S. offensive weapons, whetherprocedures could be devised to guaranteetimely decisions by NCA, and whether (giventhe complex interaction of human beings andmachines operating against a short timeline) abound could be set and enforced upon theprobability of error resulting in catastrophe.

Small Submarines

Since seawater absorbs radio waves of allbut the lowest frequencies of the radio spec-trum, completely submerged submarines areconfined to low data-rate receive-only LF, VLF,and ELF communications. Two-way communi-cations and high data rates require puttingeither a mast antenna or a trailing buoy anten-na above the surface. While the buoy or mastantenna itself poses essentially no threat tosubmarine covertness, broadcasts at moderatefrequencies could reveal the locations of thesubmarines. E H F communications to surviv-able deep-space satellites such as have beenproposed for a wide variety of military com-munications missions would permit high data-rate communications from submarines to com-manders with essentially no risk to submarinecovertness. Present U.S. fleet ballistic missilesubmarines use a variety of classified meansfor report-back.

This section describes a technically feasibleC 3 system to support small submarine basingof MX. The system described differs somewhatfrom the C’ system that supports present sub-


marine forces and intends to provide the smallsubmarine force with some of the attributes ofa land-based missile force.

Preattack

SYSTEM DESCRIPTION

The preattack C ] system is shown128.

The land-based VLF transmitters

in figure

exist atpresent. The network provides worldwide cov-erage and would be more than adequate forthe small submarine deployment area. Thetransmitters have high power, adequate anti-jam capability, and can transmit an EAM tosubmerged submarines in an extremely shorttime. There is also a worldwide LF network.

The EHF satellites do not exist at present,but a similar satell ite (LES 8/9) has beendeployed with great success. EHF frequenciesare chosen because jamming them is virtuallyimpossible, submarines can communicate withvirtualIy no chance of betraying their loca-tions, data rates are high, and small (5 inch)mast antennas can be used. Such satellites indeep-space orbits could be made exceedingly

difficult for the Soviets to disrupt (see thediscussion of ASAT in the Technical Aspects ofStrategic C3 section).

PREATTACK FUNCTIONS

peacetime covert operations could be ac-complished in the same way as with the pres-ent submarine force copying VLF. The VLF net-work would also permit transmission of anEAM in an extremely short time. The SIOPwould contain a timing plan, keyed to a refer-ence time in the EAM, to allow the missiles tocoordinate their time-on-target. Depending onwhere it was in the deployment area, eachmissile would calculate a launch time, reentryangles, missile maneuvers, and bus deploy-ment to provide the required time-on-targetcoordination. Coverage and footprinting couldbe arranged by advance operational planning.

Ad-hoc targeting instructions for l imitednuclear options could be assigned to 10 to 12percent of the force that would be snorkelingat any given time. These submarines could becopying high data-rate SATCOM via their mastantennas. If a larger portion of the force wererequired for ad-hoc retargeting, the VLF net-

Figure 128.—Preattack C3 System for Small Submarines

SOURCE: Office of Technology Assessment


work could direct more submarines to erecttheir masts or deploy awash buoys to copyother communications.

Report-back could be arranged, at no addi-tional risk to the submarines, by having themtransmit status messages via EHF SATCOMwhenever they snorkeled. Classified means areused today for submarine report-back.

Transattack

SYSTEM DESCRIPTION

The transattack period is defined for the pur-poses of this chapter as the period whenNEACP and TACAMO are airborne. This periodwould normally be the first 12 to 14 hours afterattack plus additional periods if provisionwere made for extended operations. The trans-attack CJ system is shown in figure 129.

The land-based VLF antennas are assumeddestroyed in the attack, though this might notbe true of the antennas on the soil of other na-tions. The EHF satellites are assumed intact.

There are at present several TACAMO air-craft in the Atlantic and a few in the Pacific.

More Pacific TACAMOS are expected to sup-port Trident operations. These TACAMO air-craft will be EM P-hardened.

Both TACAMO and the E-4B NEACP wouldbe capable of transmitting an EAM directly tosubmerged submarines from their VLF trailingantennas <

TRANSATTACK FUNCTIONS

Prelaunch damage assessment and targetingreoptimization would be unnecessary for thesmall submarine force, since it would be ex-pected to be almost completely survivable.

EAM transmission could occur via VLF fromTACAMO or NEACP. When the submarineslost communications with the land-based VLFtransmitters, they would tune to TACAMO.

Ad-hoc retargeting would require high datarates and two-way communications, so VLFwould not be appropriate. A short-coded mes-sage via VLF ordering certain submarines tocome to depth and copy targeting instructionsvia E H F SATCOM would be a means to accom-plish ad-hoc retargeting the transattack period.

Figure 129.-Transattack C3 System for Small Submarines

SOURCE Office of Technology Assessment

Ch. 10—Command, Contro/, and Communications (C3) “ 293

Postattack

Two-way communications via EHF SATCOMcould be available in the postattack period,and HF and UHF SATCOM could be reconsti-tuted in this period as well. The postattack C3

system is shown in figure 130.

A i r Mob i le MX

Preattack

The principal preattack C3 requirements foran air mobile fleet would concern receipt oftimely warning messages to support the fleet’shigh alert posture. A wide variety of reliablewarning sensors, available at some cost, isdiscussed in chapters 4 and 6. The communi-cations I inks from these sensors to com-manders authorized to order dispersal of thefleet and from commanders to the alert air-bases would presumably be used before thecommunications system had suffered exten-sive damage.

The responsiveness of an air mobile force toa launch order wouId be limited to the time—perhaps 10 minutes or so– it would take the

aircraft to take off and cl imb to launchaltitude.

Transattack and Postattack

The C3 system to support the complex forcemanagement needs of the dispersed MX fleetwould require at least teletype data-rate com-munications between each missiIe-carrying air-craft and command aircraft. The aircraftwould be required to report their status, in-cluding remaining fuel supplies, and receivelaunch instructions. Targeting reoptimizationwould not be required if a substantial portionof the fleet survived the initial attack. The air-borne fleet could make use of a wide variety ofcommunications including UHF l ine-of-sight(including the PACCS fleet), adaptive HF,VLF/LF, and SATCOM, as shown in figure 131.The communications system itself would below risk, the principal C3 problems being asso-ciated with the need to manage the dispersedforce, assess its status, and ready it for launch.

The problems of making provision for endur-ance beyond the few hours of unrefueled flighttime are discussed extensively in chapter 6. If

Figure 130.—Postattack C3 System for Small Submarines

SOURCE: Off Ice of Technology Assessment


Figure 131 .—Transattack Air Mobile MX Communications System

PACCS


air f ie lds surv ived for reconst i tut ion, theywould have to be located, their status assessed(including local fallout levels), and landingaids provided in advance.

Last, providing for missile accuracy com-parable to land-based MX would require com-munications from Global Positioning Satellites(GPS) or a Ground Beacon System (GBS).

OVERVIEW OF RADIO COMMUNICATIONS

Radio Wave Propagation

This section discusses some of the character-istics of radio waves that are relevant to strate-gic communications systems.

Radio waves are electromagnetic disturb-ances that propagate with the speed of lightand, under certain conditions, can be bent, re-flected, and absorbed within different regionsof the upper atmosphere. The propagationcharacteristics of radio waves in the upper at-mosphere differ markedly for waves of differ-ent frequencies. Propagation can also changewith time of day, time of year, and sunspot ac-tivity. In addition high-altitude nuclear explo-sions can dramatically alter the propagationcharacteristics of radio waves within the at-mosphere. This circumstance has obvious andimportant implications for communicationssystems that may have to function reliably in anuclear environment.

Radio communications bands are, by con-vention, referred to by different names. Sincethe names of these bands are commonly usedin discussions of communications systems,they are summarized in table 34.

The rate at which a radio wave is able totransmit information is determined by its fre-quency (assuming there is no significant noise,fading, or other fluctuation effects mixed inthe signal). This rate can be thought of as thenumber of times per second (the unit of fre-quency is the Hertz; one Hertz is the same asone cycle per second) the signal can be turned“on” or “off” in order to create the sound of avoice or to t ransmit informat ion in otherforms. This “on-off” rate can never be greaterthan the frequency of the wave since the fre-quency of the wave is in fact the number oftimes per second that the wave itself is turned“on and of f.” A rough rule of thumb is that a

Ch. 10—Cornmand, Contro/, and Communications (C’) ● 295

radio signal can carry information at about 10percent the rate of its frequency. Thus, if low-fidelity voice communication requires thetransmission of a voice signal that has primaryfrequency components in the 1,000 to 2,000cycle per second range, then the radio wavemust have a frequency of at least 10,000 to2 0 , 0 0 0 Hertz . Th is means that the lowestusable frequencies for voice communicationslies in the upper end of the LF band. High-quality voice transmission would require thetransmission of voice components at frequen-cies of order 10,000 to 15,000 Hertz, thus re-quiring frequencies on the order of severalhundreds of kiloHertz. These frequencies lie inthe lower end of the MF band or broadcastband, where commercial AM radio stations arelicensed to operate. For situations that requireparticularly reliable signal reception and goodrejection of noise, much higher frequencies arepreferable, as is the case with high fidelitymusic transmissions that are transmitted in theVHF (FM radio) band. Still higher data ratesmay be required for transmitting enough in-formation to construct pictures rapidly in time,as is the case in television broadcasting. Televi-sion information rate requirements dictateradio f requencies in the VHF and UHF radiobands.

R a d i o w a v e s c a n b e r e c e i v e d b e t w e e nground stations over several different physical

paths If the stations are close enough togetherto have line-of-sight contact, they can receive“direct-wave” transmissions (see fig. 132). It is

also possible to use different layers of the up-per atmosphere to bend or reflect radio waves

back toward the surface of the Earth for over-the-hor izon recept ion (or for over- the-hor izonradars). Signals received over such paths are

called skywaves. Radio waves can also be re-flected from the surface of the Earth, to theionosphere, and back again toward the Earth.This phenomenon, which occurs mostly at low-er radio frequencies, can result in the radiowave being “guided” along the Earth’s surfacefor great distances. The radio waves are, in ef-fect, trapped by the boundaries of the iono-sphere and the Earth’s surface.

F igu re 133 shows a g raph o f t yp ica ldistances over which communications can be

Figure 132.—Physical Paths of Radio Waves


Figure 133.—Electromagnetic Transmission Rangesat Different Frequencies

Nightime skywave

2,000 -

10-4 10-’ 1 10’ 10’ 10’ 105 1 0

Frequency in megaHertz

SOURCE. Office of Technology Assessment

achieved between ground stations using com-monly available radio equipment. VLF signals(designated by an arrow at 10 KHz on thegraph) can be reliably received at distances ofmany thousands of miles because they are

296 ● MA Missile Basing

guided along the Earth’s surface by the bound-aries on the ionosphere and the ground (fig.134 shows the geometry of VLF over-the-horizon radio propagation). At higher frequen-cies encountered in the LF band, radio wavesbegin to suffer attenuation at the greaterdistances due to absorption. As a result ofthese effects, LF reception tends to be ofshorter range than that of VLF waves. At stillhigher frequencies, less and less of the radiowaves get redirected back to the Earth’s sur-face by the ionosphere and the range at whichradio transmissions can be received drops tothe line-of-sight distance. (For radio transmis-sions, line-of-sight distances are approximately40 miles. This distance is somewhat larger thanvisual Iine-of-sight distances. ]

Many communications applications requirehigh data rates in addition to long range andhigh reliability. High data-rate communicationmandates the use of high radio frequencies.Since high frequencies are either not reflectedor poorly reflected from the ionosphere, it isnecessary that the transmitter and receiverhave line of sight geometry if reliable com-munications are to be affected. One way of in-creasing the range of line-of-sight radio com-munications is to use airplanes.

Figure 135 illustrates schematically the ge-ometry for line-of-sight communications be-

Figure 134.— Over-the. Horizon Radio Transmission

❑

T r a n s m i t t e r Receiversite site


Figure 135.—Geometry of Aircraft DirectPath Communications


tween aircraft. As an airborne relay, line-of-sight transmission between aircraft can be af-fected over distances of approximately 400miles using the HF and UHF bands. The aircraftcan also communicate with ground installa-tions over distances of approximately 200miles at those same frequencies.

Another feature of aircraft communicationslinks is that they are constantly in motion andare therefore difficult to target from great dis-tances. For this reason, aircraft are particularlyuseful as survivable command posts, launchcontrol centers, and communications relays.

For still greater distances and high data-ratecommunications, satellites can be used as or-biting relays. The geometry of an orbitingsatellite relay is shown in figure 136. A par-ticularly convenient orbit used for long-range,high data-rate satellite communications is at adistance of 22,300 miles from the Earth. Satel-l ites in orbits that l ie in the plane of theEquator at that distance will always remainover the same point on the Earth’s surface. Forthis reason, many communications satellitesare put in such “geosynchronous” orbits.

Disruption of Radio CommunicationsDue to Nuclear Detonations

Electromagnetic Pulse

When a nuclear detonation occurs, a largenumber of gamma rays is emmitted by nucleiin fission and fusion reactions, resulting in aninitial “gamma flash” of extremely high inten-sity. If the nuclear weapon is detonated at analtitude above the sensible atmosphere, thegamma rays from the weapon can induce ex-tremely intense electromagnetic fields in thelayer of air between 15 and 25 miles altitude.

Ch. 10—Command, Control, and Communications (C3) . 297

Figure 136.—Geometry of Satellite Communications

Satellite

SOURCE. Off Ice of Technology Assessment

These electromagnetic fields will then prop-agate towards the surface of the Earth.

Nuclear-explosion-generated electromag-netic phenomena of this type are known asEMP effects. EMP fields are of great interestsince they are sufficiently intense to representa potential threat to the survivability of almostal I electronic equipment.

Figure 137 shows the area over which an in-tense electric field of 25,000 volts per meter ormore would be generated by a nuclear explo-sion of several hundreds of kilotons yield at analtitude of 190 miles. The area affected essen-tially covers the entire United States and partsof Canada and Mexico.

The size of the area that could be affectedby EMP is primarily determined by the heightof burst and is only very weakly dependent onthe yield. For example, the size of the affectedarea shown in figure 137 could be increased by60 percent if the detonation height were in-creased to an altitude of 300 miles. Thus,severe EMP effects are possible over very largeareas without the use of high-yield weapons.

Figure 137.-Electromagnetic Pulse GroundCoverage for High-Altitude-Nuclear Explosion

Peak electric field25,000 volts/meter or greater

Height of burst = 190 miles

SOURCE: Off Ice of Technology Assessment

The physical reason for the altitude depend-ence of EMP phenomena can be seen fromfigure 138. The tangent to the Earth from theburst point determines the maximum range atwhich the gamma rays can induce intense elec-tromagnetic fields. The gamma rays initiallygenerated by the exploding weapon deposittheir energy in a band of the atmosphere be-tween 15 and 25 miles altitude. The electro-magnetic field that reaches the surface of theEarth is generated within this band of at-mosphere. If the weapon is detonated at agreater height, the tangent will occur at agreater ground range from the surface zeropoint, and the extent of the gamma ray-in-duced band will also be greater.

During the initial period of a nuclear attack,intense electr ic f ie lds f rom high-alt i tude-nuclear detonations could cause severe dam-age to electronic equipment. PowerIines, radioantennas, metal conduits, and other conduct-ing surfaces would collect EMP energy likeantennas and destroy or disrupt the electricalequipment to which they were connected.Even equipment that had been carefully de-signed to survive the effects of EMP could betemporarily disrupted for a period after a high-


Figure 138.—Origin of Electromagnetic Pulse From High-Altitude-Nuclear Explosion


altitude nuclear detonation (for instance EMP-protected computers could be disrupted byloss of sections of memory or computation).

Ionospheric Disruption

Since the gamma rays from a high-altitudenuclear detonation can change the electrondensities in very large regions of the iono-sphere, the propagation characteristics ofradio waves may change dramatically. A resultof this change could be a “blackout” of radiocommunications.

Figure 139 shows the skywave paths of radiowaves of different frequencies. The D layer ofthe ionosphere is responsible for ref Iecting VLFand LF radio signals. Nuclear explosions in orabove the D layer would change ionizationlevels in the D layer. The effect of this changewould be to lower the altitude at which VLFand LF signals would be reflected from theionosphere. This effect could disrupt com-munications over long ranges, but it would beunlikely that VLF and LF communicat ionswould be blacked out by nuclear detonations.

MF radio propagation is normally limited togroundwaves because the MF radio waves getabsorbed in the D layer before they can reachthe upper layers and be reflected back to theEarth’s surface. At night, when the lack ofsunlight results in a drop in the ionization ofthe D layer, MF radio may propagate to fairlygreat distances (see the curve marked night-

time skywave transmission in fig. 133). For thisreason it is sometimes possible at night to pickup AM broadcasts from remote transmitters.Nuclear explosions in or above the D layercould blackout MF skywave communicationsfor hours near the point of detonation.

The HF band is used extensively for long-range communications. If conditions in theionosphere are such that H F waves are not ab-sorbed, HF waves will be bent back to Earthwhen they reach the E and F layers of the iono-sphere (see fig. 139). HF is particularly usefulfor long-range communications because its f re-quency is high enough that large amounts ofinformation can be transmitted and yet it islow enough that the ionosphere will bend itback to the surface of the Earth.

Nuclear detonations in or above the D layercould change ionization levels sufficiently tocause absorption of HF waves in the D layer.The changed ionization levels could also lowerthe altitude at which HF waves were reflectedfrom the ionosphere (see fig. 140). This changecould result in severely degraded HF communi-cations for periods of minutes to hours.

A nuclear burst at an altitude of approxi-mately zoo mi Ies wou Id be expected to disruptHF communications over the same area inwhich severe EMP would be experienced. Theblackout from such a detonation could last forhours.

—


I n bands above H F, most radio transmissions satellites were not attacked, communicationswould suffer varying degrees of degradation at these frequencies would probably not sufferthrough the ionosphere. However, provided severe degradation.

Figure 139.—Atmospheric Radio Propagation at Different Frequencies

... -n 1

I .[ ——. d . . -----*--*-——u) 240Pa>

-&..-”-–------ OD.- - - - J\=-

. -. .- -. -. . . . .

200 400 600 800 1000 1200

Approximate ground range in milesSOURCE Off Ice of Technology Assessment

Figure 140.— Radio Propagation Paths Before and After High-Altitude-Nuclear Explosion

Explosion induced Skywavebeforeionospheric absorptionnvnlncinn

Explosion induced 7 ‘,’ionospheric reflection ~,z _

//4

N ‘ 4’

/

\

\

\\

explosion

\

.

SOURCE Off Ice of Technology Assessment

chapter 10 command, control, and communications … · chapter 10.–command, control, and...

Documents