The Kiernan Reentry Measurements System on Kwajalein Atoll

K.R. Roth, M.E. Austin, D.J. Frediani, C.H. Knittel, and A.V,Mrstik

The Kiernan Reentry MeasurementsSystem on Kwajalein Atoll

The Kiernan Reentry Measurements System (KREMS),located on KwajaleinAtoll in thePacific, is the United States' most sophisticated and important research and development (R & D) radar site. Consisting of four one-of-a-kind instrumentation radars,KREMS has played a major role for the past 25 years in the collection ofdata associatedwith ICBM testing. Furthermore, it has served as an important space-surveillancefacility that provides an early U.S. view of many Soviet and Chinese satellite launches.Finally, the system is slated to playa key role in Strategic Defense Initiative (SDI)experiments.

Kwajalein Atoll, which rests 9° north of theequator and 3,500 km southwest of Hawaii, is anecklacelike strand of islands remotely locatedin the Pacific Ocean. Situated 7,000 km downrange from Vandenberg Air Force Base in California (Fig. I), Kwajalein is also the location ofthe Kiernah Reentry Measurements System(KREMS)-the United States' most sophisticated and important R&D radar site. KREMSincludes four unique, high-power, precisionradars:

ALTAIR (ARPA Long~Range Tracking andInstrunH~htationRadar),

TRADEX [Target Resolution and Discrimination Experiment),

ALCOR (ARPA-Lincoln C-Band ObservabIes Radar),

MMW (Millimeter Wave),

(See the box "Acronyms.") Figure 2, a recentaerigl photograph of Roi-Namur, the northernmost island ofthe atoll, shows the location ofthefour radars.

Lincoln Laboratory, under the sponsorship ofthe United States Army Kwajalein Atoll(USAKA), has been the scientific director ofKREMS since the radar system's inception in1959. (See the box "A Brief History ofKREMS.")In this capacity, the Laboratory's responsibilities include scheduling the system's operationto support various user requirements; verityingthe calibration of the sensors; and validating,

The Lincoln Laboratory JOlU1wl. Volume 2, Number 2 (1989)

reducing, and publishing the data collected. Inaddition, the Laboratory plans the upgrades,performs the systems engineering, and overseesthe implementation of modifications.

To assist the Laboratory, two contractors havebuilt the radars and are responsible for operating' maintaining, and modifying them. GEGovernment Electronic Systems Division (formerly a part of RCA Corp.) is responsible forTRADEX, ALCOR, and MMW, while GTE Government Systems Corp. (formerly Sylvania) isresponsible for ALTAIR.

KREMS's primary objective is to collect andrecord high-quality metric and signature radardata in support ofa wide variety ofuser requirements. (In the context ofthis article, metric datais information about a target's position andvelocity. Signature data is information regarding the scattering characteristics of a targeL)KREMS's broad scope of functions reflects thesystem's national-range status in the StrategicDefense Command. The radar system's functions support five areas:

(1) missile system development and operational testing;

(2) space surveillance, tracking, and objectidentification;

(3) discrimination research;

(4) ballistic-missile defense (BMD) component and system tests;

247

Roth et aI. - The Kiernan Reentry MeasurementsSystem on Kwajalein Atoll

.' ~

(b)

(e)

(c)

(d)

Fig. 1-(a) Map showing location of Kwajalein Atoll, which encircles the world's largest lagoon. (b) Roi-Namur Island. (c)Kwajalein Island. (d) Missile launch from Vandenberg Air Force Base in California. (e) Missile reentry at Kwajalein.

(5) scientific research.

The first support area involves collection ofdata on missile system components. Thesecomponents include reentry vehicles (RV),penetration aids such as decoys and metallicfoil chaff, and delivery systems such as postboost vehicles (PBV)-platforms used to carryand deploy RVs. KREMS provides these data to

248

the Air Force Ballistic Systems Division, theStrategic Air Command, and the Navy. The dataare used to evaluate systems as they evolvefrom the development stage through operational readiness.

The responsibilities of the second supportarea are detecting and tracking new foreignlaunches (NFL), imaging foreign and domestic

The Lincoln Laboratory Journal, Volume 2. Number 2 (1989)


Acronyms

AID analog to digital MMS Multistatic MeasurementSystemALCOR ARPA-Lincoln C-BandMillimeter WaveObsenrables Radar MMW

\ . ALTAIR ARPA Long-Range Tracking MIT multitarget trackerand Instrumentation Radar

NFL new foreign launchAOS Army Optical Station PACBAR Pacific BarrierARPA Advanced Research Projects PBV post-boost vehicleAgency

PPS pulses per secondARS ALTAIR Recording System

PRF pulse-repetition frequencyBMD ballistic-missile defense

Pacific Range Electromag-PRESSBWG beam waveguidenetic Signature Studies

CMOS complementary metal-oxideRADOT recording automatic digitalsemiconductor

optical trackerCPU central processing unit RC right circularCW continuous wave

RCS radar cross sectionDARPA Defense Advanced Research R&D research and development

Projects AgencyRF radio frequencydBsm decibels referred to 1 squareRLOS radar line of sightmeter

ERIS Exoatmospheric ReentryVe- rms root mean squarehicle Interceptor System RV reentry vehicle

FJB frequency jumped burst SATKA Surveillance, Acquisition.GBM ground-based measure- Track. and Kill Assessment

ments SOl Strategic Defense InitiativeHEOI High Endoatmospheric De- SIE SATRJ\Integrated

fense lnterceptor ExperimentsHOE Homing Overlay SIMPAR Simulate the Perimeter

Experiment Acquisition RadarICBM intercontinental ballistic SNR signal-to-noise ratio

missileSOl Space Object Identification

IF intermediate frequencySPADATS Space Detection and.

KCC KREMS Control Center Tracking SystemKDS Kwajalein Discrimination TRADEX Target Resolution and Dis-

" System crimination ExperimentKREMS Kiernan Reentry Measure- 1Wf traveling-wave tube

ments SystemUSARJ\ United States Army

LC left circular Kwajalein AtollLITE Laser Infrared Tracking USP Universal Signal Processor

Experiment

The Lincoln Laboratory Journal. Volume 2. Number 2 (1989) 249


near-earth satellites (the Space Object Identification, or SOl, program), tracking high-prioritynear-earth satellites, and tracking deep-spacesatellites (the Satellite Catalog Maintenanceprogram) for the U.S. Space Command Spacetrack System (Fig. 3). KREMS, a supporter oftheNASA Space Shuttle Program since the program's inception, also tracks shuttles and images payloads dUring deployment and subsequent orbit transfers.

The third support area, discrimination research, covers collection of data used to studyBMD signature phenomena. In this capacity,KREMS plays a major role in the national BMDdiscrimination research program by providingthe scientific community with the capability to

test candidate waveforms, signal-processingconcepts, and BMD algorithms. The U.S. BMDdatabase consists primarily of KREMS datagenerated dUring the past 25 years.

The fourth support area includes support ofBMD component and system tests. During the1970s, KREMS collected and recorded data forthe Safeguard system and System TechnologyRadar programs. More recently, the radar system collected and recorded data that characterized target vehicles, assessed interceptor missdistances, and analyzed postimpact debris forthe Homing Overlay Experiments (HOE) and theDelta experiments of the Strategic Defense Initiative (SOl). For SOl, KREMS also provided realtime metric data to support a series of Surveil-

. l

Fig. 2-Aerial view of the KREMS facility.

-.

250 The Lincoln Laboratory Journal. Volume 2. Number 2 (1989)

Roth et aI. - The Kiernan Reentry MeasurementsSystem on Kwqjalein Atoll

Fig. 3-KREMS's Spacetrack role.

lance, Acquisition, Track, and Kill Assessment(SATKA) Integrated Experiments (SIE). In thefuture, the evaluation of SOl component andsystem performance for the Exo-Reentry Intercept Subsystem (ERIS) and the HighEndo-Oefense Interceptor (HEDI) will requirefurther support from KREMS. A more extensivediscussion ofKREMS's role for SOl is containedin Ref. 1.

The fifth and final support area falls under thebroad category ofscientific research. To supportdifferent users studying various natural phenomena, KREMS has performed extensivemultifrequency sea-clutter backscatter measurements that help the Navy characterize andmodel the clutter environment. KREMS has alsogathered ionospheric scintillation and electrondensity profile data that help the Defense Nuclear Agency improve its ionospheric models. Inaddition, the radar system will assist NASA bygathering orbital-debris data not contained inthe Spacetrack catalog, a listing of satellitescurrently orbiting the Earth.

The Lincoln Laboratory Joumal. Volume 2. Number 2 (1989)

KREMS

KREMS comprises a diverse collection of radars that cover a broad frequency spectrum,from VHF through W-band. Figure 4 shows thecurrent operating bands of the four radars andTable 1 lists their basic parameters.

Except for MMW, all of the radars operate atpeak power levels in the megawatt range. Hightransmit powers and large antenna aperturesprovide the system sensitivities necessary toproduce the high signal-to-noise (SNR) datarequired to study radar Signature phenomena.The radars also have large instantaneous bandwidths. MMW, with its I,OOO-MHz bandwidth,achieves a resolution of approximately onequarter of a meter. In addition to the featuresshown in Table I, all of the four radars arecoherent in that they provide both radar-crosssection (ReS) amplitude and phase data. Thefour radars also operate at dual polarization in

which both the principal and orthogonal radarreturns are received simultaneously.

251


A Brief History of KREMS

Thirty years ago. the AdvancedResearch Projects Agency (ARPA)of the Department of Defenseneeded a site for conducting research on ballistic-missile defense. ARPA (which has sincebeen renamed DARPA) choseKwajalein because of the atoll'sgeography and strategic locationin the Pacific. Kwajalein, a member ofthe Republic ofthe MarshallIslands, is situated about 3.500kIn southwest of Hawaii and encircles the world's largest lagoon.The size and location ofthe lagoonmade it an ideal impact area forICBMs launched from Vandenberg Air Force Base in California.To study the reentry physics ofthe ICBMs, ARPA selected RoiNamur, the northernmost islandof the atoll. as the site for a radarsystem. Thus Project PRESS(Pacific Range ElectromagneticSignature Studies). KREMS'soriginal name, commenced andLincoln Laboratory became thescientific director of the project.(At about the same time. the U.S.Army also chose Kwajalein as adownrange test site for ikeZeus, an antiballistic-missileproject.)

In late 1959, ARPA selectedRCA Corp. to install TRADEX, thefirst of Project PRESS's radars.

and TRADEX became operationalat UHF and L-band in 1962. Thefirst Laboratory personnel arrivedon Kwajalein that year to providetechnical supervision during thefinal checkout and acceptance ofTRADEX. The second radar installed was ALTAIR, which became operational at VHF and UHFin 1969. ALTAIR was designedprimarily so that the UnitedStates could see how its missilesappeared to Soviet radars. Oneyear later, KREMS's third radar.ALCOR. became operational atC-band. ALCORs goals were toinvestigate the applications ofbroadband data and to developthe technology necessary to generate and process 500-MHz bandwidth signals. In 1983. MMWbecame operational at 35 GHz,and MMS was added to TRADEXthat year.

Table A shows how an intensiveprogram of additions. modifications. and upgrades has keptKREMS at the forefront oftechnology.

In addition to the four major radars, various other sensors-including optical systems and anactive laser radar-were built andadjunct experiments carried outover the years. AIthough some ofthe sensors have since been deac-

tivated. three of the adjunct systems listed in Table 1 remainoperational today: ALTAIR SpaceDetection and Tracking System(SPADATS), currently referred toas Spacetrack: TRADEX MMS,which uses TRADEX as its illuminator and receiver as well as tworemote receivers located on otherislands in the atoll; and theKwajalein Discrimination System(KDS) , which is currently interfaced to the MMW radar. We discuss these three adjunct systemsin greater detail in the main text.

KREMS is named after U.S.Army Lt. Col. Joseph M. Kiernan.who headed PRESS during theproject's period of rapid growthfrom 1963 to 1966. Kiernan, anARPA engineer, oversaw the addition of ALTAIR and ALCOR tothe project. Kiernan later servedas Commander of the 1st Engineer Battalion of the 1st InfantryDivision in Vietnam. where hewas killed in 1967.

A more extensive history ofKREMS is contained in Ref. 1.

References

1. M.S. Holtcamp. The Historyoj the Kiernan Reentry Measurements Site (Lincoln Laboratory, Lexington, MA. 1980).

The radars provide precise metric data. At arange of 250 km-which corresponds to thedistance from Kwajalein at which many RVsfirst pierce the atmosphere-MMW andTRADEX's Multistatic Measurement System(MMS) adjunct are the most accurate. MMW andMMS provide position accuracy of about 10 m.

252

MMW's accuracy is due primarily to the radar'snarrow beamwidth; MMS's accuracy resultsfrom the system's ability to make precise tri

static range measurements.A complex reentry mission may cost more than

$100 million and take years to plan. The KREMSstaff repeatedly rehearses for each mission

The Lincoln Laboratory Journal. Volume 2. Number 2 (1989)


Table A. Chronology of Major KREMS Milestones

1959 KREMS (originally named Project PRESS) initiated.Roi-Namur site on Kwajalein Atoll selected.

1962 TRADEX operational at UHF and L-band.

1965 VHF capability added to TRADEX.

1969 ALTAIR operational at UHF and VHF.

1970 ALCOR operational at C-band.

1972 S-band capability added to TRADEX while UHF and VHF dropped.Reentry Designation and Discrimination Experiment commences.

1973 Simulate the Perimeter Acquisition Radar (SIMPAR) Project and Solitaire OpticalExperiment commences.

1974 Army Optical Station (AOS) established.

1976 Ground-Based Measurements (GBM) optical system established.

1977 Laser Infrared Tracking Experiment (LITE) and Pacific Barrier (PACBAR) trials commence.

1982 ALTAIR Space Detection and Tracking System (SPADATS) operational.

1983 MMW operational at 35 GHz.Multistatic Measurement System (MMS) operational.

1985 95-GHz capability added to MMW.

1987 Kwajalein Discrimination System (KDS) operational.

weeks ahead oftime by using computer simulations. During these simulations (called nominals) , the KREMS staff follows a time line: ascript that orchestrates what each radar shouldbe doing at each point dUring the mission. Anactual mission takes only a half hour, fromVandenberg lift-off to Kwajalein splashdown,and a missile is within view and detectable byKREMS for just 15 minutes. During those 15minutes, it is imperative that the KREMS radarsperform their assigned tasks with precision togather the appropriate data.

Figure 5 shows the network that connects the

The Lincoln Laboratory Journal. Volume 2. Number 2 11,989)

radars with one another and with the KREMSControl Center (KCC), a central computer andcontrol system that provides data fusion andcentralized control of KREMS. The networkconsists of two fiber-optic Ethemets: one fortransmitting target data and the other for exchanging display data. Data exchanged betweenthe sensors include radar tracks (called targetfiles), object identifications, RCS, waveform information, and information about each radar'smode of operation (e.g., if a radar is independently tracking a target, or if the radar is beingdirected by another radar). KCC and the KREMS

253

Roth et aI. - The Kiernan Reentry MeasurementsSystem on Kwqjalein Atoll

radars also exchange audio and video data overthe network.

When it first receives data from the individualradars. KCC correlates and compares the datawith a priori information. e.g.. predicted ornominal trajectories and RCS static range measurements. Later in the mission. target fileswhich contain information about a target'sposition. velocity. and acceleration-from thevarious sensors are compared to validate thetarget identifications assigned by the sensors.In the event that two sensors compute different identifications of the same target or thesame identification of different targets. KCCresolves the conflict with graphics displays thatutilize the metric and RCS data from all thesensors.

To aid the sensors in acquiring. or lockingonto. their assigned targets. KCC supplies eachradar with the best available directing file byusing a best-choice algorithm. To eliminatenoise in the data. KCC smooths the trajectory

data in real time by using a least-squares fitalgorithm. If necessary. KCC extrapolates thetrajectory forward in time so that it can be usedto direct the radars.

KCC provides all KREMS sensors with alphanumeric and color-graphics-display data. Thedata utilize target files from all of the KREMSradars as well as from other USAKA sensorstwo MPS-36 radars and the FPQ-19 radar located elsewh~reon the Kwajalein Atoll. With thedata, KCC MASSCOMP graphics processorsgenerate color displays. which are used by KCCconsole operators to monitor and direct a mission. Figure 6 shows the operator console forKCC.

During the tracking of an RV. KCC routes allof KREMS external communications to theUSAKA Control Center on Kwajalein Island. Toassist in acquiring targets. the KCC staff cantransmit target file data via the USAKA ControlCenter to the MPS-36 and FPQ-19 radars. telemetry stations. optical sites. and other instru-

Fig. 4-0perating bands of the KREMS radars.

254 The Lincoln Laboratory Joumal. Volume 2. Number 2 (1989)

Roth et al. - The Kiernan Reentry MeasurementsSystem on Kwajalein Atoll

Table 1. KREMS Radar Parameters

ALTAIR TRADEX ALGOR MMWVHF UHF L-Band S-Band G-Band Ka-Band W-Band

Center frequency (GHz) 0.162 0.422 1.32 2.95 5.67 35.0 95.5

Maximum bandwidth (MHz) 7 17.6 20 250* 512 1,000 1,000

6-dB range resolution (m) 37.5 15 15 1.0 0.50 0.28 0.28

Antenna diameter (m) 45.7 45.7 25.6 25.6 12.1 13.7 13.7

Beamwidth (mrad) 48.8 19.2 10.6 5.2 5.2 0.76 0.28(two-way beamwidth measured6 dB from peak)

Antenna gain (dB) 34.7 42.4 48.2 54.2 55.0 70.1 77.3

Transmitter power (kW)Peak 7,000 5,000 2,000 2,000 3,000 25 5Average 98 250 150 30 6 2.5 0.5

Pulse width (J1s) 0.25-600 0.1-1,000 2-565 3-9 10 50 50

Maximum PRF (PPS) 2,976 2,976 1,500 1,500 200 2,000 2,000

Single-hit SNR (dB) on 36** 45** 40** 28** 23 17t -3t

1.0 m2 target at1,000 km range

• equivalent bandwidth via frequency-jumped-burst (FJB) waveform•• using maximum pulse widtht 300 elevation, clear-air conditions

Antenna Descriptions

ALTAIR's antenna is a parabolic dish with VHF feed at its primary focal point and UHF feed that utilizes a Cassegrain focusvia a frequency-selective subreflector (see Fig. 8, p. 258). As with all the KREMS radars, RC polarized energy is radiatedand both LC and RC signals are received.

The TRADEX antenna is a five-horn, L-l"~and, monopulse feed with a concentric S-band horn at the dish focal point. Theantenna can be rotated 2900 in azimuth and 1800 in elevation.

ALCOR's antenna is a parabolic dish that uses a Dielguide feed with Cassegrain optics. A radome encloses ALCOR'santenna, pedestal, and support tower for protection from the highly corrosive Kwajalein environment.

The MMW antenna is a parabolic dish that uses Cassegrain optics with a vertex feed cluster made up of a 35-GHz fourhorn monopulse assembly and a single 95-GHz horn. A radome encloses MMW's antenna, pedestal, and support towerfor protection from the highly corrosive Kwajalein environment.



mentation situated within the Atoll. Conversely,target files from other USAKA radars can betransmitted through the USAKA Control Centerto KCC for utilization by the KREMS radars.

Each radar is also capable of independentoperation outside the KREMS network. Forexample, in its Spacetrack role ALTAIR operatesautonomously for 128 hours a week via a dedicated link to the U.S. Space Command's Cheyenne Mountain Complex.

To keep pace with increasing mission complexity and to reduce dependence on operatorexpertise, KCC's level of automation is beingincreased. New color displays, operator alerts,and decision aids have been recently incorporated in the KCC display system and central

computers, both ofwhich were replaced in 1988.KREMS will continue to evolve as additionaltarget-identification algorithms are added tothe system in the future.

The following sections contain descriptions ofthe individual KREMS radars.

ALTAIR

Initially, ALTAIR's duties were confined toresearch. The radar, which reached its 20thbirthday on 19 April 1989, was constructed togive the United States a view of how U.S. ICBMslooked to Soviet radars. Subsequent modifications, however, transformed ALTAIR for tracking deep-space satellites and NFLs from the

MMW35GHz95 GH~

ALCORC-Band

TRADEXL-BandS-Band

ALTAIRVHFUHF

Spacetrack

Off Site~ ~

USAKAControlCenter

Data

MMSIIleginniL-Band

Ethernet

KREMSControlCenter

MMSGellinamL-Band

SpaceCommand

256

FPQ-19MPS-36-3MPS-36-4

RADOTTelemetry

Optics

Fig. 5-The KREMS instrumentation network.



Fig. 6-The KREMS Control Center's operator console.

Soviet Union, China, and Japan. ALTAIR currently operates 24 hours a day. For 40 hourseach week, the radar prepares for and supportsmissile reentries for USAKA. For the remaining128 hours of the week, it tracks satellites forSpace Command. NFL coverage is provided 24hours a day, seven days a week.

Among the KREMS radars, ALTAIR has thegreatest sensitivity. In November 1984, a traveling-wave-tube (1WT) transmitter replacedALTAIR's original UHF Klystron transmitter.The present transmitter is an array of 241WTs combined through a series of hybrids.The resulting device has an output peak power of 5 MW and a duty cycle of 5%. ALTAIR's

The Lincoln Laboratory JournaL. Volume 2. Number 2 (1989)

VHF transmitter consists of two triode tubeswith a combined output peak power of 7 MWand a duty cycle of 1.4%.

ALTAIR is able to view a reentry target shortly after it breaks the horizon, roughly at a distance of 4,500 km. The radar provides KREMSwith its first view and assessment of a reentrytarget complex, Le., the number of objects andtheir spacing. ALTAIR keeps the range sidelobelevels for the metric waveforms at 40 dB or morebelow the mainlobe returns. Thus the radar canisolate and track a small target even when thetarget is in the vicinity of larger objects.

Figure 7 shows a photograph of the ALTAIRantenna, which has a diameter of 45.7 m and is

257


the largest of the KREMS radars. ALTAIR alsohas the widest beam width: 48.8 mrad in VHFand 19.2 mrad in UHF. ALTAIR's 880,OOO-lbantenna is supported by 16 wheels on a circulartrack with a diameter of 35.9 m. The antennacan be driven 90° in elevation and 380° inazimuth at rates up to 10° Is.

In addition to high sensitivity, one ofALTAIR'smost important assets dUring RV tracking is theradar's dual-frequency capability. In 1973,modifications enabled ALTAIR to simulate thePerimeter Acquisition Radar (Project SIMPAR).At that time, a frequency-selective subreflectorwas added to allow the VHF feed structure toremain at the antenna's primary focal point,while a new UHF feed with tracking capabilitywas installed at the Cassegrain focus (Fig. 8).Now simultaneous UHF and VHF target rangemeasurements permitALTAIR to adjust its ionospheric refraction model in real time. After a

7-MW VHF (162 MHz)48.8-mrad Beamwidth37.5-m Range Resolution

UHF Feed

FrequencySelectiveSubreflector

5-MW UHF (422 MHz)19.2-mrad Beamwidth15-m Range Resolution

~48-m-DiameterAntenna

VHFFeed

\

Fig. 7-The ALTAIR antenna.

258

Fig. 8-The ALTAIR feed structure

missile-reentry mission is completed, dataanalysts use these measurements to constructionospheric models that correct not only themission data from ALTAIR, but also that fromTRADEX and ALCOR.

During recent years, ALTAIR has been in thethroes ofa massive computer upgrade, throughoutwhich time the radar continues to operate 24hours a day. FourVAX-11/785computers, eachwith 16 MB ofmemory, were installed to supportSpacetrack and reentry-mission software improvements. As part of the upgrade, many system enhancements were incorporated, including a replacement of the ALTAIR RecordingSystem (ARS) with an all-digital system thatuses high-speed parallel-transfer disks togather amplitude and phase data based onpremission-designed sample patterns aroundeach target of interest. With the new system, anoperator (Fig. 9) can lock onto and track upto 32 targets in the UHF and VHF beam.


The computer upgrade was completed in 1988;on 2 June 1988, ALTAlR conducted its firstreentry mission with the new VAX system.

In addition to tracking U.S. missile reentries,ALTAlR took on the task of supporting the U.S.Space Command in October 1982. In this capacity, ALTAlR tracks near-earth-orbit anddeep-space satellites. Space Command usesthis information to update its catalog listings ofcurrent satellite positions. Via the Ethernet networks discussed earlier, ALTAlR providesALCOR and MMW with pointing information sothat the two radars can acquire, track, andimage near-earth space objects in support ofSOL

The Kwajalein location enables ALTAlR toprovide the United States with its first view ofmany Soviet and Chinese satellite launches. Totrack an NFL object, ALTAlR's staff needs anadvance warning of less than 15 minutes. Theradar has successfully handled more than 93%of the NFL events within its coverage (approximately 85 a year).

ALTAlR tracks more than 1,000 deep-spaceorbiting satellites every week, which accountsfor approximately two-thirds of all radar tracksobtained by the U.S. Space Command. As aresult of transmitter and software improvements, the figure of 1,000 satellite tracks a weekis an increase of 300% from the radar's initialcapability. The radar has logged more than200,000 tracks to date from its first operationaltrack on 1 October 1982.

ALTAIR Current and PlannedImprovements

A capability to track satellites at synchronousorbit ranges at VHF is being added to ALTAlR'spresent UHF deep-space tracking capability.While the initial efforts are aimed at tying VHFsample patterns to estimates of UHF rangetracker positions, it is expected that the plannedaddition of the Universal Signal Processor (USP)and other signal-processing upgrades will oneday permit ALTAlR to track satellites independently at both UHF and VHF.

The all-digital USP, when installed in 1990,


Roth et aI. - The Kiernan Reentry MeasurementsSystem on Kwcyalein Atoll

will eliminate 18 racks of analog and digitalcompression and weighting filters, and greatlysimplifY the maintenance ofALTAlR's receivers.The USP takes a time-domain transversal-filterapproach to the pulse compression and weighting of the four UHF and four VHF channels.Custom state-of-the-art CMOS chips are beingdesigned and fabricated to perform the multiplication and accumulation functions of the transversal filters. The USP will operate with sampling rates up to 20 MHz to provide all-rangepulse compression and weighting for all existingALTAlR waveforms, which are described inTable 2(a) for VHF and Table 2 (b) for UHF.Indeed, the USP will enable ALTAlR to processcontinuous wave (CW) and linear FM waveformsof any length and bandwidth up to a bandwidthlimit of 20 MHz and a time-bandwidth-productlimit of 2,400.

An ambitious program to upgrade ALTAlR'soverall signal-processing capability is currentlyin the system study phase. The goal is to processthe new USP digital outputs by using specialhardware and modem array processors to provide automatic target acquisition and trackingfor multiple-target complexes at both UHF andVHF. The same digital outputs would be used forARS. Biases between ALTAlR's radar and recording system would therefore be eliminated; consequently, calibrating the separate

Fig. 9-The AL TAIR operator console

259

Roth et at. - The Kiernan Reentry MeasurementsSystem on Kwqjalein Atoll

Table 2(a). ALTAIR VHF Waveforms

Name Duration Bandwidth MaximumPRF Usage

(J1s) (MHz) (PPS)

V600N 600 0.05 20 NFL search

V600W 600 0.25 20 NFL tracking

V238 238 0.345 60 Long-range tracking

V30C 30 CW* 372 Chaff tracking

V30 30 7 372 Exo-atmospheric tracking

V6 6 7 1,724 Reentry tracking

V.25C 0.25 CW* 2,976 Reentry tracking

• continuous wave

Table 2(b). ALTAIR UHF Waveforms


(J1s) (MHz) (PPS)

U1000 1,000 0.050 50 Deep-space search

U400 400 0.25 125 Deep-space tracking

U238 238 0.25 120 Long-range search

U120 120 18.0 372 Exo-atmospheric tracking

U15 15 17.6 372 Exo-atmospheric tracking

U3 3 17.6 1,724 Reentry tracking

U.1C 0.1 CW* 2,976 Reentry tracking

• continuous wave


I'

AID converters in the radar and ARSwould be unnecessary.

A recent improvement to ALTAIR in the springof 1989 was the replacement of the wheel andrail system with a new, longer-life design. Toreduce the load on the wheels and rail thatsupport the antenna, the number ofwheels wasincreased from eight to 16. This upgrade shouldextend the life of the rolling system by an additional 25 years.

TRADEX

A large repertoire of waveforms is TRADEX'sgreatest asset. The radar is capable of usingchirp pulse waveforms to track an RV dUringreentry while interleaving other waveformse.g., bursts and pulse pairs-to gather highresolution Doppler data on the low-velocity,high-electron-density wake that forms behindthe vehicle. Like ALTAIR, TRADEX tracksICBM launches from Vandenberg and simulates Soviet radars tracking U.S. RVs. TRADEXalso acts as ALTAIR's backup for tracking NFLsand deep-space satellites.

Figure 10 shows a photograph of the TRADEXantenna: a 25.6-m parabolic dish with a dualLIS-band feedhorn at the focal point. TRADEXhas a unique combination of two capabilities:long-range (45,000 km) L-band tracking of satellites, and collection of high-resolution (1 m)S-band signature data at shorter range. For itssize, TRADEX's antenna is highly maneuverable; it can be rotated 290 0 in azimuth and 1800

in elevation. Measured axial ratios of the antenna's circular-polarization sum-mode portsare less than 0.5 dB at both L- and S-bands.Because of the small axial ratios, TRADEX provides excellent polarimetric signatures-keyfeatures for identifying targets.

TRADEX can range-track a single target ineither L-band or S-band; angle tracking is performed at L-band only. Right-circular (RC) polarization is radiated at each frequency andright-and-Ieft-circular (RC/LC) polarizationsare simultaneously received. Alternatively,dual-linear polarization may be selected forS-band on a mission-by-mission basis. An array

The Lincoln Laboratory Journal. Volume 2. Number 2 (19891


processor coherently integrates the L-band LCrange and angle channels to provide up to 30 dBof additional system sensitivity in real time.

TRADEX, the oldest ofthe KREMS radars, hasless sensitivity but better resolution thanALTAIR (Table 1). TRADEX can lock onto andtrack synchronous-orbit satellites at ranges upto 45,000 km and RVs at ranges approaching4,000 km. Targets are tracked with either aballistic filter or a polynomial filter with fixed orvariable weighting. The radar achieves S-bandrange resolution of 1 m by using a frequencyjumped-burst (FJB) waveform (with 60-MHzbandwidth subpulses) that covers a total bandwidth of250 MHz. Currently, this waveform canonly be compressed offline. The highest available real-time range resolution is 5 m.

Tables 3(a) and 3(b) summarize respectivelythe characteristics and usage of the currentTRADEX L-band and S-band waveforms. Thesingle-pulse or train waveforms may be runcontinuously. In contrast, the burst waveforms-L2B, S9B, S3B, and SFJB-have maximum numbers of pulses and maximum burstrepetition frequencies that are determined bythe transmitter's average power limits. The variable subpulse spacing for the burst and pulsepair waveforms ranges from 4 fls to 512 fls.

Multiplexing of up to three L-band andthree S-band waveforms is possible within eachO.I-s basic operating interval. Trains and burstsmay be freely mixed with nonrepeating patternsup to 3 s long. However, certain constraintsapply. For example, there must be at least onetrack waveform per interval and each L-bandburst must be accompanied by an S-band burst.

TRADEX was built to study reentry phenomenology. The radar became operational at UHFand L-band in 1962; since then, it has undergone many modifications. The three most significant were the replacement of UHF withS-band in 1972, the addition of the MMS adjunct in 1983, and the implementation ofcoherent integration in 1986.

Figure 11 shows the configuration ofthe MMSsubsystem. In MMS, the TRADEX antenna is thetarget illuminator. Range measurements arereceived and recorded by the TRADEX radar as

261


Fig. to-The TRADEX antenna.

well as by two remote L-band receivers locatedon the Kwajalein islands of Gellinam and Illeginni, which are about 40 kIn from Roi-Namur.Since range can be measured more accuratelythan other target-position parameters, MMS'stristatic measurements of RV positions at atmospheric pierce point is the most accurateobtained by the KREMS radars. MMS also provides bistatic L-band signature data.

The MMS L-band tristatic system operates asan adjunct to the TRADEX radar. It has approximately 14 dB less sensitivity than TRADEX butis sensitive enough to measure RV dynamicsnear atmospheric pierce point. Table 4 showsthe key performance parameters for MMS.

The TRADEX system performs a wide varietyof tracking and measurement missions. Most ofthe missions are to track ICBM launches fromVandenberg and payloads deployed by localmissile launches from Kwajalein Atoll. To develop and study reentry discrimination algorithms and reentry physics phenomena, theBMD community has extensively usedTRADEX's database of burst and pulse-pair

262

waveform data. In addition, by incorporatingand gathering data with specially configuredwaveforms, TRADEXcan simulate howU.S. RVslook when they are tracked by Soviet radars.

Because its antenna is 26.2 m above sea level,TRADEX has an excellent view of the oceanhorizon. Consequently, the scientific community has used the radar to collect extensive seaclutter measurements and surface-ship signature data.

Other miscellaneous applications includepassive reception of signals from remote radiostars via a special X-band receiver that wastemporarily installed near the antenna's L/Sfeedhom. The data, which are correlated withthose received by sensors in other parts of theworld, help determine the motion of the Earth'scrustal plates.

TRADEX Current and PlannedImprovements

TRADEX is undergoing a host ofmodificationsand upgrades. The most significant upgradeunder way is the replacement of the radar'scomputer and timing system.

Two Gould 32/9780 computers are replacingTRADEX's 1970-vintage Sigma 5/Telefile-85machine because the current CPU has reachedits capacity. The Gould computers will increasethe system's computing power by more thanfour times. Furthermore, the new computerswill add, among other capabilities, a 3,000-Hzpulse repetition frequency (PRF) and simultaneous L/S-band tracking. The Gould computersoperate via a reflective memory system in whichthe machines share a common database.

TRADEX's present timing and control system,installed in 1972, is also being replaced witha modem programmable system. The new system enables the testing ofTRADEX through theuse of two software test targets whose individual ranges and velocities can be varied. Scheduled for completion by October 1990, the newsystem will also enable more flexible systemtroubleshooting.

In preparation for SDI experiments, a multitarget tracker (MIT) is being developed for


. I


Table 3(a). TRADEX L-Band Waveforms

Name Duration Bandwidth Maximum PRF Usage, . (J.lS) (MHz) (PPS)

L565W 565 1.6 187 Extended-range tracking

L50N 50 1.0 1,500 Long-range acquisition,chaff tracking

L50W 50 20.0 1,500 Exo-atmospheric tracking

L2 2 20.0 1,500 Reentry tracking

L2B (burst) 28-896* 20.0 100** Reentry signature

• 2-fJ.S subpulse with variable subpulse spacing•• burstsls with variable subpulse spacing

Table 3(b). TRADEX S-Band Waveforms


(f.l.s) (MHz) (PPS)

89 9 17.6 1,500 Exo-atmospheric tracking

83 3 60 1,500 Reentry tracking

8PP (pulse pair) 14-512 17.6 750* Reentry signature

83B (burst) 8-800 60 100* Reentry signature

8FJB (FJB) 8-800 250 100* Reentry signature

.. 89B 28-800 17.6 100* Reentry signature

• bursts or pairs per second

Note: All bursts and pulse pairs have variable subpulse spacing. SPP, S3B, andSFJB use 3-fJ.S subpulses. S9B uses 9-p.s subpulses.



Fig. 11-(a) MapofMMS. (b) TRADEXsite. (c) lIIeginni site.(d) Gellinam site.

-.

. ,

Range Resolution:15 m

Remote-Site Sensitivity:SNR = 19 dB on -25-dBsm targetat 200-km range

Received Waveforms:

50 .us/20-MHz chirp (L50W)2 ,LLs/20-MHz chirp (L2)2 ,LLs/20-MHz burst (L2B)

Table 4. MMS Performance Parameters

TRADEX. The MIT will enable the radar toperfonn simultaneous range/angle tracking ofmultiple targets in the L-band beam. The MITwill noncoherently integrate the received pulses.then automatically detect, track. and collectsignature data on as many as 64 targets. Amaximum of 12 target tracks may be sent toKCC over the sensor Ethernet.

Two new L-band wavefonns. scheduled to beoperational in 1990, will improve TRADEX'sability to perfonn complex evaluation on reentrymissions and to back up ALTAIR for Spacetrackoperations. A digital pulse-compression systemis being developed for two new 565-,us L-bandwavefonns. which will have 50-kHz and 150kHz bandwidths. These wavefonns will be usedfor long-range acquisition and will provide a coherently integrated range window of up to 250kID on the array-processor display. The maximum extent of the range window of TRADEX'scurrent array processor is 4.8 kID. The largerwindow will enable TRADEX to search for andlock onto satellites that are up to 125 km offtheirnominal trajectories. and perfonn RV-complexevaluation at horizon break. The addition of

Metric Accuracy (RV at pierce point):

12-m position accuracy0.1-m/s velocity-vector accuracy0.2-g acceleration-vector accuracy

(d)

(b)

Kwajalein

.... 27 km

l ),.~

(a)

pC} :=6" I

I

35 kmiII

p~ I

(c)

TRADEX L-BANDRoi-Namur


Fig. 12-Photographs of the ALGOR antenna. (a) Interiorantenna. (b) Exterior radome.

noncoherent post-summing, which is almostoperational, will improve TRADEX's ability totrack satellites exhibiting large Doppler spread.Furthermore, new acquisition and trackingalgorithms are also being developed. When all ofthese improvements are completed, TRADEX



will possess almost the same near-earth anddeep-space acquisition and tracking capabilities as ALTAIR.

A new S-band chirp waveform should be operational in 1990. This 94-,us S-band waveformwill increase TRADEX's current S-band sensitivity by 10 dB, which will enhance the radar'smeasurements of S-band target signatures.

In summary, the TRADEX and MMS systemsare continuing to evolve toward better measurement capability, improved reliability, and easiermaintainability.

ALCOR

ALCOR became operational in 1970 as one ofthe first radars in the world to utilize widebandtransmissions. ALCOR's wide bandwidth andnarrow-beam antenna (Fig. 12) enable the radarto measure trajectories more precisely than anyof the other KREMS sensors except MMW. Because of its high range resolution, ALCOR canobserve the individual scattering centers onobjects. During missions, this capability operates in real time to observe the length of objectswithin a target complex (Fig. 13). The lengthmeasurements are used to identifY objects ofinterest and to discard unwanted ones. Thehigh-resolution data are also used postmissionto study RV and wake-scattering behavior.

In addition, ALCOR's coherent high-resolution measurements can be used to generate twodimensional images of orbiting and reenteringobjects. The radar routinely images about 60satellites per year in support ofthe SOl activitiesof the U.S. Space Command. Images are generated, sometimes on short notice, and are rapidlyrelayed to Space Command's Cheyenne Mountain Complex via an encrypted electronic link.ALCOR images have been used to determinesatellites' size, shape, configuration, and stability/ orientation, and to assess potential damage.

RVs often carry beacons to assist radars inlocating and identifYing the targets. ALCOR isthe only KREMS radar capable of tracking abeacon; consequently, it frequently directs theother KREMS radars to their assigned targets.ALCOR can track beacon-carrying targets from

265


40

20

E<fl

en~ 0(J)oa:

-20

-40

RLOS----J.~ I~

!_:III

RLOS. ,

III

I I

:--:I II II I

II

o 5 10 15 20 o 5 10 15 20

Relative Range (m)

Fig. 13-ALCOR's wideband pulse returns for different target orientations.

the point at which they break the horizon,typically about 4,000 kIn away. The radar caneasily identifY beacon-carrying RVs in thepresence of deployment junk (hardware used toeject a vehicle) and other objects.

Prior to a mission lift-off, ALCOR generatesweather scans to observe the local meteorological conditions. The radar's narrow beam andfavorable C-band frequency are valuable forgenerating both azimuth and elevation weatherscans (Fig. 14). These weather scans are part ofthe database used in deciding whether or not tolaunch the missile. ALCOR usually makes trajectory scans immediately following an object'sreentry in order to measure the weather that theobject actually encountered.

The ALCOR transmitter-a three-stage amplifier-is unique in its degree of signal phase andamplitude control over its full 512-MHz bandwidth. This control was necessary to obtain lowtime-sidelobe response. The final high-powerstage of the transmitter is a Twystron tube.

The ALCOR waveform parameters are described in Table 5. Four channels of returnsignal (sum-channel-principal and sumchannel-orthogonal polarizations, and twodifference channels) are amplified by uncooled

266

parametric amplifiers and down-converted to60-MHz IF. Delay lines at IF serially multiplex the receiver channels to a single AID device. Mter conversion, the digital data are storedon magnetic disks and later transferred tomagnetic tapes for transmission to LincolnLaboratory.

With its range resolution of 0.5 m, ALCORcould record an immense quantity of data. Torestrict the quantity to tractable portions, therange interval over which ALCOR records wideband data is limited to a maximum of three30-m windows. This limitation permits stretchprocessing, a time-bandwidth exchange technique, which greatly reduces a recorded signal'sbandwidth. The processing is performed bymixing the received signal, which is linearlychirped over 512 MHz, with a reference ramp ofthe same chirp (Fig. 15). The correlation mixerproduces a steady tone at a frequency determined by the time offset between the chirpedtarget return and the trigger time of the reference ramp. The correlation process thus translates differences in target range into differencesin frequency. The target location is determinedby spectral analysis of the correlation mixer'soutput. With stretch processing, ALCOR's


·.

Fig. 14-Weatherscans generated by ALGOR. (a) Rangeheight intensity plot. (b) Plan-position intensity plot.

10-MHz A/D device is capable of processing the512-MHz chirped pulses and achieving 0.5-mrange resolution after weighting.

ALCOR Current and PlannedImprovements

A major upgrade ofALCOR's computer systemis under way. The system is currently operatingwith its original equipment; it includes twoHoneywell DDP-224 CPUs with a total of 48kilowords of memory. The memory and compu-



tational speed limitations of the Honeywellcomputers, which are over 20 years old, haveseverely restricted ALCOR's growth during thepast decade. Consequently, a Gould 32/9780CPU with 16 MB of memory is replacing theDDP-224 system. Installation of the Gouldcomputer began in December 1988, and thecomputer's system software, which is beingdeveloped at Lincoln Laboratory, will be operational in October 1990.

In addition, the ALCOR timing system is beingmodified to link the radar to the KwajaleinDiscrimination System (KDS). The link willenable KDS to perform real-time processing ofdata from ALCOR as well as from MMW in orderto generate images and to apply candidate discrimination algorithms to reentry objects. (Adescription of KDS is contained in the followingsection and in Ref. 2.)

After the basic computer upgrade is completed, additional improvements will commence. Future plans call for doubling ALCOR'spulse rate from 200 Hz to 400 Hz. The increase,when combined with the addition of real-timeintegration, will improve the radar's range capability. Multitarget sampling will allow simultaneous data gathering on multiple objects withinALCOR's beam. By the early 1990s the multitarget capability will support users' plans to flytarget complexes that contain several closelyspaced objects.

In summary, ALCOR is a valuable componentof KREMS. It provides all-weather precisiontracking and imaging capability; it is the mostfavorable KREMS radar for weather measurements; and it is the only KREMS radar with theability to track beacon-carrying objects. Thenew computer will provide the potential forgreatly expanding the radar's capabilities in thefuture.

MMW

MMW is a high-power, wideband, coherentradar that operates in the Ka- and W-bands. Itis unique in its very narrow beamwidth (760.urad at 35 GHz and 280 .urad at 95 GHz) and1-GHz bandwidth (Table 1). Consequently,

267


Table 5. ALCOR C-Band Waveforms

Name

Narrowband (NB)

Wideband (WB)

Wideband doublet(WBDBLT)

Beacon (BCN)

Duration

(J.Ls)

10.2

10.0

10.0*

0.4

Bandwidth

(MHz)

6

512

512

4.4 (CW)

MaximumPRF

(PPS)

203

203

100

203

Usage

Acquisition and tracking

Satellite imagingReentry trackingReentry signature

Reentry signature

Beacon tracking

* Pulse pair: two pulses of 1O.O-,us duration each; second pulse delayed 10.5 ,us behind first

MMW has the best range resolution-approximately 0.25 m after weighting-of the KREMSradars.

MMW was initially designed as an augmentation to the C-band ALCOR. The radar's originalcharter was to provide a database of millimeterwave signature data of reentry phenomena andto support miss-distance measurements forinterceptor experiments. MMW, however, hassince grown to become a complete and selfsufficient system. Currently, the radar is relatedto ALCOR only in that they share a singleconsole room.

With its 1-GHz bandwidth, MMW collects datafor generating images of orbiting and reenteringobjects. Because ofits high range resolution andshort wavelength, MMW provides sharper images than ALCOR. MMW collects signature dataat both 35 GHz and 95 GHz and performsmonopulse angle tracking at 35 GHz.

Principal applications of MMW include (1)precision tracking, (2) high-resolution RV andwake measurements, (3) RVand satellite imaging, (4) miss-distance measurements, and (5)real-time discrimination. The first three applications are similar to the applications notedearlier for ALCOR. MMW's higher bandwidth

268

and narrower beam, however, provide finerscale measurements.

Because of its ultrahigh range and angle resolution, MMW can accurately measure the missdistances of intercepting objects, as well asmaintain track of selected targets in clutteredenvironments. During missions in which objects of interest pass through the debris of adisintegrating PBV, MMW is frequently the onlyKREMS radar with enough resolution to maintain track of the objects.

The coherent, high-resolution data that MMWrecords provides excellent images of satellites.Since February 1988, satellite images have beentransmitted directly to Cheyenne Mountain.With this new capability, MMW now providesnear-real-time SOl support to Space Command.

Real-time imaging of RVs became possible inthe fall of 1987 with the initial operation of KOS,which the BMD community is using as a testingground for discrimination algorithms. Figure 16contains a block diagram of KDS and its interface to MMW. Currently, KDS is noninvasive inthat the system taps offMMW's 60-MHz IF radarreturns in parallel and then independentlyprocesses (e.g., digitizes and pulse-compresses)the returns. RV images are generated at a rate of


....


60/s. The data are then provided to a set of candidate discrimination algorithms. In additionto RV imaging, the feasibility of generating satellite images in real time was demonstrated with

KDS in the spring of 1989.Technologically, the MMW system embodies a

number of novel approaches. The transmittedwaveforms, which are described in Table 6,

·"

6,892

N 5,672I:2

A = Target 15 m in RangeB = Target at Reference RangeC = Target 15 m out of Range

III1II___________ .1 . __ 1

III

-2 ns --.J r-I+2ns ~I ..-

~TeRamp

:512 MHz

: t1---'-1I

ABC

It"'! 512 MHz

'L t1 Target Returns

at Input ofCorrelation Mixer

1,200 MHz-100 kHz

C---_---......- 1,220 MHz +1,220 - - - - - - - - - - B I-----i----~I 100 kHz

A i ~ Target Returns: : at Output of

:....f-----10 J.1S---". : Correlation Mixer1 11 1

Reference Time

SignalProcessing

andNarrowbandRecording

,.--------;.~E Aoteooa'----,-_......

Mixer CorrelationMixer

Receiver

1,220 MHz r<:/\6,879 MHz

VY •

Active FM Ramp I----()

Generator

Start

.-

Fig. 15-ALCOR's time-bandwidth exchange,

The Lincoln Laboratory Journal. Volume 2, Number 2 (1989) 269


~Antenna

35GHZ)KDS

Front EndCorrelation Mixer

IF Mixer

(8,008 FFT Box STAR-100 AP

60 MHz~ Mix to 5 MHz

Sample r-----. Compress r-----. Generate

QuadratureForm I, Q Pulses Images

DetectorT.E. & Weight

Sample I, QCompress

Track Discriminate

Record Data I

Display/Record

MMW

. ,

" .

Fig. 16-Simplified block diagram of the Kwajalein Discrimination System (KDS) and the system's interface to MMW.

consist of linear FM pulses of 50-,us durationsin which the bandwidths and frequencies canbe selected on a pulse-by-pulse basis. Fourbandwidths are available: 6 MHz, 12 MHz, 500MHz, and 1,000 MHz. MMW uses two independent 1Wf transmitters of similar design, one foreach frequency band. The 1Wfs, which VarianAssociates designed and built, were the firstpractical application of a 1Wf to a millimeterwavelength field radar.

MMW's extremely wide linear FM bandwidth of1 GHz presents a problem to conventional (Le.,dispersive delay line) approaches to pulse compression. Not only is the RF bandwidth near thelimit of (ifnot beyond) the capabilities of currentsurface-acoustic-wave technology, but the

270

compressed signal bandwidth is beyond thestate of the art in AID technology. These problems are circumvented with the same timebandwidth exchange technique used byALCOR.The output of the correlation processor is digitized and recorded at 5 MHz on magnetic disks.A portion of the digitized returns are processedby an array processor that performs the functions of pulse compression and weighting, target-range marking, coherent integration, andmonopulse error computation.

The MMW antenna is a 13.7-m-diameter precision parabolic dish (Fig. 17) that usesCassegrain optics with a vertex feed clustermade up of a 35-GHz four-horn monopulseassembly and a single 95-GHz horn. The an-

The Lincoln Laboratory Joumal. Volume 2. Number 2 (1989)

fl.

v

< •

tenna's surface is precisely aligned and hasyielded a measured gain of 77.3 dB at 95 GHz.Special attention was given to the mechanicalstiffness and the thermal properties of thematerials used to fabricate the structure. Tominimize thermally induced structural deformations, the antenna system uses a radomewith an environmental control system thatmaintains thermal gradients within 3°F acrossthe antenna. The reflector surface is smooth toa.l-mm rms; the antenna is aligned to precisetolerance and yields a beam-pointing accuracyof 65 ,urad.

A MODCOMP 32/85L computer, with twoCPUs in a load-sharing configuration and asingle 6-MB random-access memory chassis,maintains real-time control of the system.


MMW Current and PlannedImprovements

In the fall of 1988, the installation of twosoftware improvements doubled the operationalrange of MMW at 35 GHz. The improvementswere (1) noncoherent integration in range-Doppler space prior to display at the range operator's console, and (2) replacement of the Helmstrack filter with a Kalman ballistic filter. Theseimprovements were first demonstrated during a mission in October 1988. The upgradeshave not only improved performance dUringreentry missions, but also enhanced the radar'sutility for SOl applications.

Three other major improvements to MMW's35-GHz system are currently in progress (Fig.

Table 6. MMW Ka- and W-Band Waveforms

Name Duration Bandwidth MaximumPRF Usage(Frequency) (,us) (MHz) (PPS)

3N1 (35 GHz) 50 6 2,000 Acquisition and tracking




3W1 (35 GHz) 50 500 2,000 Satellite imagingReentry trackingReentry signature

9W1 (95 GHz) 50 500 2,000 Satellite imagingReentry trackingReentry signature

3W2 (35 GHz) 50 1,000 2,000 Satellite imagingReentry trackingReentry signature

9W2 (95 GHz) 50 1,000 2,000 Satellite imagingReentry trackingReentry signature


Roth et at. - The Kiernan Reentry MeasurementsSystem on Kwajalein Atoll

Fig. 17-MMWantenna.

. ,

272 TIle Lincoln Laboratory Joumal. Volume 2. Number 2 (1989)

-.p

..

Fig. 18-RV-tracking performance improvements forMMW at 35 GHz for a typical reentry mission.

18). When completed, the improvements willincrease the radar's sensitivity by 12 dB, whichwill again double the radar's operational range.

The first of the three upgrades will enable realtime processing of all transmitted pulses, up tothe full system PRF of2,000 Hz, by utilizing theKDS pulse-compression system. (In the past,only a fraction of the pulses could be compressed in real time.) This improvement willprovide up to a 5-dB increase in sensitivityduring coherent track mode and a 10-dB increase in noncoherent track mode.

The second ofthe upgrades is the replacementof conventional rigid-waveguide components,which are used to transport RF energy from theoutput tube to the antenna feed. The gUides willbe replaced with a quasi-optical-transmissionsystem, referred to as beam waveguide (BWG).In a rigid-waveguide system, high-loss and limited-power handling capability is a severe limitation to radar sensitivity. The BWG system



(Fig. 19) uses mirrors to transport RF energyfrom the feedhom (which is located close to thepower output tube) to the antenna feed. Byusing free-space transmission, the BWG systemreduces losses by 4 dB when operating in35-GHz mode. In addition, the BWG systemcan carry much higher power levels than theconventional waveguide system. Although initiallyjust the 35-GHz system is being converted,the 95-GHz system will also be modified in thefuture. The planned modification will reduce byapproximately 20 dB the huge waveguide lossesthat currently occur at 95 GHz.

The third and final upgrade, which the BWGconversion will make possible, is the replacement of the original 25-kW final-stage 1WTamplifier with a new 60-kW tube built byVarian Associates. In addition, another suchtube is being added and the two Varian tubeswill operate in parallel. The two-tube system

Fig. 19-The MMW beam-waveguide (BWG) system.

273

.-

Roth et aI. - The Kiernan Reentry MeasurementsSystem on Kwcyalein Atoll

Fig. 20-Planned upgrades for the KREMS computers.

oJ

i.

The authors thank the many Lincoln Laboratory employees who have contributed to KREMSdUring the past 27 years, in particular those

ogy as a result of extensive and continuousupgrades over the years. With the advent of SOltesting, the radars should continue to grow andevolve.

New radar-control computers have been or arebeing installed throughout KREMS to providefor the implementation of extended capabilities as well as for improved reliability. Figure20 describes the extent of the upgrade plan.New Ethernet communication systems havebeen installed for exchange of data between thesensors and KCC and for the transfer of display information throughout the KREMS facility. New color-graphics-display systems havebeen installed at KCC and at each of the individual sensors.

The upgrade of the KCC and radar-controlcomputers began in 1985; the MMW, ALTAIR,and KCC upgrades are now complete. TheALCOR and TRADEX upgrades are scheduledfor completion in 1990. The computer upgradesare providing the computational capabilitynecessary to support multitarget tracking atALTAIR and TRADEX, multiple-object samplingat ALCOR and MMW, increased PRF at ALCORand TRADEX, enhanced coherent integration ateach sensor, and implementation of real-timedecision aids at KCC. In particular, the need formultitarget tracking and sampling and for realtime decision aids is driven by the user's need toinclude more targets per booster, a need thatincreases the complexity of reentry missions.

Waveform and signal-processing improvements are also in progress at each sensor.Additional modifications are under way to improve the radar's data quality and to replaceobsolete equipment.

It is through the continuous effort to upgradeKREMS that the radar system has been able tomaintain its long-standing position as theUnited States' most sophisticated and important R&D radar site.

Acknowledgments

GOULD 32/97

ALCOR1990

2 x MODCOMP

MMW1986

SensorEthernet

DisplayEthernet

4 x VAX 11/785

Summary

will result in an overall quadrupling of powerover the original amplifier.

In summary, MMW's capabilities are beingrapidly extended to acquire and track targets atlong ranges. Once the modifications of Fig. 18are fully operational, we will initiate efforts toincrease the bandwidth of the 35-GHz systemfrom 1 GHz to 2 GHz. This increase will furtherextend KREMS's state-of-the-art capability toexplore issues ofinterest to the user community.

KREMS as it exists today is a flexible set ofhigh-powered instrumentation radars. Througha concerted effort to stay abreast ofuser requirements, the radar system has been able to satistythe diverse needs of the U.S. offense, defense,and intelligence communities.

Although TRADEX, ALTAIR, and ALCOR arerespectively 27, 20, and 19 years old, theseradars have remained at the forefront oftechnol-


adventuresome individuals who have lived andworked at Kwajalein. The accomplishmentsdescribed in this article are the result ofthe hardwork and dedication of these individuals.

The authors would also like to acknowledgethe contributions of GE and GTE, who havebuilt and continue to operate the KREMS radars. Finally, the authors gratefully acknowledge the United States Army KwajaleinAtoll andthe United States Army Strategic DefenseCommand for their continuing support of

KENNETH R ROTH, anemployee of Lincoln Laboratory for 21 years, currentlymanages the KREMS site.Ken received B.S., M.S., andPh.D. degrees in aero- and

astronautical engineering from the University of Illinois. Hewas awarded a National Science Foundation Fellowship forhis graduate work, and in 1978 he received the Universityof Illinois Outstanding Young Alumnus Award. His researchinterest is in radar systems and the analysis of highresolution radar data. Ken has been married for 22 years;he and his wife have three children.



the KREMS site.Special thanks are given to Cynthia Williams

for the preparation of this manuscript, and toRichard McCauley for the photography.

References

1. G. Zorpette, "Kwajalein's New Role: Radars for SOl,"IEEE Spectrum 26.64 (March 1989).

2. S.B. Bowling. RA. Ford, and F.W. Vote. "Design of aReal-Time Imaging and Discrimination System," Lincoln Laboratory Journal 2, 95 (1989).

MICHAEL E. AUSTIN is incharge of the ALTAIR sensorat Kwajalein. Before joiningthe Laboratory 26 years ago.he worked for the GeneralMotors Plasma Physics Di

vision in Santa Barbara. Calif. He received a B.S.E.E. fromthe University of Notre Dame and a Sc.D. in electrical engineering from MIT. An avid genealogist in his spare time.Mike is the editor of Austins ojAmerica. a national newsletter that serves Austin family researchers.

275

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Roth et aI. - The Kiernan Reentry ~asurementsSystem on Kwajalein Atoll

DAVID J. FREDIANI Jr.,Plans and Operations Section Leader of KREMS, isresponsible for the overallplanning, coordination, andexecution of KREMS mis

sions. David received a B.S.E.E. degree, summa cum laude,from the Lowell Technological Institute, where he was thefIrst recipient of the Trustees Key for Academic Excellence.During his 30 years at the Laboratory, he has worked on theLincoln Experiment Satellites (LES) , Military SatelliteCommunications (MILSATCOM) system architecture, andthe Military Strategic Tactical and Relay (MILSTAR) program. From 1984 to 1986, he was an ALTAIR systemengineer responsible for directing missions and implementing upgrades.

A. VINCENT MRSTIK is incharge of the ALCOR andMMW radars at Kwajalein.He received B.S. and M.S.degrees in electrical engineering from the University

of Illinois in 1964 and 1965, respectively, and a Ph.D. inelectrical engineering from the California Institute of Technology in 1968. Upon graduating from Caltech, he joinedGeneral Research Corp. in Santa Barbara, Calif., where heworked on ground-, airborne-, and space-based radarsystems and countermeasures; missile systems; data-processing systems; and emitter-location systems. In 1985, hejOined RCA Corp. as a test director of the TRADEX radar atKwajalein. His duties included the planning and executionof radar operations of ICBM test missions: the validation oftest results; and the identifIcation, development, and implementation of radar hardware and software improvements. In 1987 he joined the Laboratory. working at theALCOR and MMW radars. Vince subsequently acceptedleadership of the two radars.

276

GEORGE H. KNITTEL is incharge of the TRADEX radarat Kwajalein. Before joiningthe Laboratory 17 years ago,George was an associateprofessor at the Polytechnic

Institute of Brooklyn, where he received a bachelor's degreein electrical engineering in 1955 and a Ph.D. in electromagnetics in 1969. He is a senior member of IEEE and formerpresident of the IEEE Antennas and Propagation Society.George's work over the years includes antennas, radomes,phased-array antenna systems, polartzation. and radarsystems. Married for 30 years, George and his wife Maryhave fIve children.


,.

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The Kiernan Reentry Measurements System on Kwajalein Atoll