Apollo Experience Report the ANARD-17 Direction Finding System

8/8/2019 Apollo Experience Report the ANARD-17 Direction Finding System

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N A S A T E C H N I C A L N O T E NASA TN D-7886

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APOLLO EXPERIENCE REPORT -THE ANIARD-17 DIRECTION-FINDING SYSTEM

Lyndon B. Johnson Space CenterHouston, Texus 77058

N AT I O N A L A E R O N A U T I C S A N D S PA CE A D M I N I S T R AT I O N WA S H I N G TO N ,D. C. M A R C H 1975


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1. Report No. 2. Government Accession No.

NASA TN D-78864. Title and Subtitle

A P O L L O E X P E R I E N C E R E P O RTTHE AN/ARD-17 DIRECTION-FINDING SYSTEM

7. Author(s)

Will iam R. Ch ase and Will iam A. Middleton,

9. Performing Organization Name and Address

Lyndon B. Johnson Space CenterHouston, Texas 77058

3. Recipient's Catalog No.

5. Report DateMarch 1975

6. Performing Organization Code

JSC-060268 . Performing Organization Report No.JSC S-416

10. Work Unit No.

076-00-00-00-72L

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

Washington, D. C. 20546Nat ional Aeron aut ics and Space Adminis t ra t ion

16. A b m m

Th is rep or t conta ins a s ta tem ent of the opera t iona l ph i losophy and requ i rem ents lead ing to thedevelop ment of the AN/ARD-17 direct ion-f indin g system .and the solut io ns devised in the AN/ARD-17 development a r e discussed . An evaluat ion of thesys t em under ac tu a l opera t iona l condit ionsis included.

The technica l p ro blem s encountered

13; Typ e of Repo rt and Period Covered

Technical Note14. Sponsoring Agency Code

17. K ey Words (Suggested by Au tho rk) ) I 18. Distribution Statement

19. Security Classif. (of this repo rt) 20. Security Classif. (of this page) 21 . NO. of Pages

Unclass i f ied Unclass i f ied 10

* Rad io D i r ec t i on F ind e r s* Spa cec ra f t Recove rya R eco ve ry Zo nes* Command Modules

22. Price'

$3.25

STAR Subjec t Category :12 (As t ronaut ics , Genera l )

*For sale by the National Technical Information Service, Springfield, Virginia 22151


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APOLLO EXPERIENCE REPORT

EDITORIAL COMMITTEE

The materi al submitted f o r the Apollo Experience Reports(a series of NASA Technical Notes) was reviewed and ap-proved by a NASA Editorial Review Board at the Lyndon B.Johnson Space Center consisting of the following members :Scott H . Simpkinson (Chai rman) , Richard R. Baldwin,J am es R. Ba tes , William M. Bland, J r . , Aleck C. Bond,Robert P . Burt , Chris C. Critzos, John M. Eggleston,E. M . Fields, Donald T. Gregory, Edward B. Hamblett, J r . ,Kenneth F. Hecht, David N . Holman (Editor/Secretary),and Car l R. Huss. The pri me reviewer fo r this repor tw a s Kenneth F. Hecht.


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APOLLO EXPERIENCE REPORT

THEANIARD-17 DI RECTI ON-FINDI NG S Y S T E M

ByWi l l i a m R . C h a s e a n d Wi l l i a mA. M i d d l e t o nLyndon B. Johnson Space Ce n te r

S U M M A RY

Becaus e of the rel ativel y l ar ge landing footprint predicted for an Apollo commandmodule returning from a lunar mission, it was determined that re scue airc raft should

be equipped with an entry direction-finding syste m to minimiz e the se ar ch ar ea i f a non-nominal landing oc cur re d. In effect, such a sys tem would redu ce the si ze of the recov-er y for ce req uir ed fo r rap id location of the command module. Because no system w a savailable at the time, the AN/ARD- 17 direction-finding sy ste m was developed for thispurpose. The sy ste m operated by obtaining bearings on signal s transmitted from thecommand module in the S-band frequency ra nge (2200 o 2300 megahertz) and the very-high-frequency range (225 o 300 megahe rtz) during nonblackout entr y peri ods and dur-ing para chute descent and postlanding periods. The landing point then was establ ishedby means of t riangulation techniques. Although the sys te m per for med well duringoperational testing, seve ral problems that required th e incorp orati on of engineer ingchanges developed during i t s initial use in the field. These changes have proved to besuccessful. Nevertheless, a problem that has not been resolved completely i s the train-

ing of field maintenance personn el to keep t he equipment in peak operat ing condition.

INTRODUCTI ON

During the latter pa rt of Proj ect Mercury, it became obvious to flight plannersand recover y engineers that the possible occurr ence of la rge landing disper sions in theproj ecte d Apollo ent ry and landing profil e would prevent ti mely location and rec overy ofth e command module and cr ewmembe rs. These guidance dispersions could cause land-ing foot prin ts of approximately 9260 kilometers (5000 nautical miles) in length and1852 kilometers (1000 nautical miles) in width. To locate and recover the Apollo crew-members and command module within such a landing footprint, many air cra ft (mo rethan 10) and se vera l ships would be required in the term inal area. To reduce the costand number of supporting aircraft and ships, a capability to predict t he landing are aand to locate the command module without performing an extensive search w as required.To minimiz e the required support, the airc raft normally deployed to provide para res cuesupport had to be equipped with a direction-finding sy st em that was compatible withsi gn als radia ting fr om th e Apollo command module during the en try period. The hard-wa re developed for t his purpose was the AN/ARD-17 direction-finding system (ARD-17).


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The system procurement, testing, and modification resulting fro m problems ari singduring initial operation a r e discuss ed in this report .

A s an aid to the read er, where neces sary the original units of mea sur e have beenconverted to the equivalent value in the SystGme International d'Unit6s (SI). The SIunits a r e written first, and the original units a r e written parenthetically thereafter.

APPLlCABI L l T YOF ARD-17

The feasibility of using direction-finding equipment in an ai rc raf t t o obtain bear -ings on orbiting spacecraft w a s demonstrated on the Mercury-Atlas 8 and 9 missions.A U. S. Air Force (USAF) JC-130B aircraft equipped with a very-high-frequency (vhf)direction-f inding system, which w a s designed to locate descending nose cones used inother rese arch and development prog rams , w a s used to trac k the Mercury telemetrysignal at line-of -sight ranges (2222 kilometers (1200 nautical miles) with the spacecr aftat an al titude of 156 972 meters (515 000 feet) and the aircraft at 7620 meters(25 000 eet)). It w as concluded that a similar system having greater sensitivity and

bett er display capability could be used to tr ac k th e ente ring Apollo command moduleusing the S-band telemetry signal. A block diagram of th e ARD-17 is shown in fi gur e 1.

The entry profile envisioned in 1962 is shown in fi gur e 2. Entry is the part ofthe flight that begins with atmospheric contact (defined as being at an altitude of121 920 meters (400 000 feet)) and ends when the command module begins parach utedes cent to the landing point. The command module norm all y is tracked by ground-based or ship-based rad ar to the radiofrequency (rf) blackout alt itude (91 44 0 m e t e r s(300 000 feet)) . During th is initial phase of ent ry, a pullup maneuver performed byth e command module at an altit ude of approx imate ly 60 960 m e t e r s (200 000 feet)causes the vehicle to skip to an altitude above 91 44 0 meters (300 000 feet) and toemerge briefly from rf blackout. During the ti me when th e command module is above91 44 0 meters (300 000 feet), i t is transmi tting S-band signals that can be received byan air born e direction-finding sys tem . The command module again rea che s the rfblackout altitude and e mer ges a t 45 720 meters (150 000 feet), approximately 370 kilo-meters (200 autical miles) f ro m the landing point.

Based on the 1962 entry profi le (fig. 2), effort s wer e initiated to obtain adirection-finding syst em that would be installed pe rmanent ly on the USAF HC-130 air-craft (fig. 3) assigned to support th e Apollo mission s. This s yst em would have to becapabl e of obtaining ac cur at e bea rin gs on vhf (225 o 300 megahertz) and S-band (2200 o2300 megahertz) signal s fro m the command module during th e nonblackout period s ofthe entry. For nonnominal entry traj ect orie s (oversho ots o r undershoots), two ormor e a ircr aft stationed along the footprint could obtain fixes fo r s om e of t he followingpoints by triangulation techniques, and the approx imate landing point could then bepredicted.

1. Beginning of f i r s t blackout

2. End of first blackout

2


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Radio freque ncysignal- IUltr ahigh frequency

(uhf J and S-band-

ntennas

225 to 300 MHz 2200 to 2300 MHz

Figure 1. - Block diagram of the AN/AFtD-1'7.

uh f lobe 100-Hzswitch oscillator

1 . 8 x l d 6 x 1 3

S-bandlobe switch

Beginning of 11'5t

~ r b E n t r yBeginn ing of first blackout second blackout

u h fpreamplifier

End of fi rst blackout

End of second blackout

wave S-band Spect rumpreamplifier display

un i t

0 1000 2000 3000 4ooo 5000 6Mx)Range from entr y, n. mi.

1 I I I I 10 1852 3704 55% 7408 9260 11 112

Range from entry , km

1

r

225 to 300 MHz Freque ncyconverter

225 to 300 MHz

Figure 2. - Apollo entry t ra jecto ry (asknown in 1 9 6 2 ) showing the S-bandblackout regions.

Greenwichmean timeinformation

Printedtape out

Modeselector

Figure 3. - A USAF HC-130 aircraft,showing AN/ARD-17 rad ome .

-

-225 to 300 MHz Signal Strength

t Receiver strength Digital

relays

3

Audio signal toaircraft intercomsystem

A informationto be print ed

00-Hzerror Automa!ic gain cont rolsignal wltage

Antennadrivesystem

4 Phase

meterlockwise or detector


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3. Beginning of second blackout

4. End of second blackout

5. Recovery-beacon acquisition

U s e of thi s procedure would minimize the s ea rc h area and the requ ired ship and air-craf t support.

PROCUREMENTOF ARD-17

In the fall of 1963, a te am of personn el fr om th e NASA Lyndon B. Johnson SpaceCenter (JSC) form erly the Manned S pacecraf t Center (MSC)) and th e Aeron auticalSystems Division of th e USAF Systems Command pre par ed a specification for the devel-opment and production of sufficient A m - 1 7 syst ems and s par es to equip 60 USAFHC- 130 air cra ft. The following capabilit ies we re specified fo r the AN/ARD- 17.

1. Signal detection in both the vhf (225 t o 30 0 megahertz) and S-band (2200 to2300 megahertz) frequency ranges

2. An antenna having 360" coverag e in the azimuth plane an d the capability ofsignal detection above and below t he ai rc ra ft

3. Manual, sea rch , and track modes of operation (In the manual mode, theantenna is rotated as desi red, and the speed and directio n a r e controlled by an antennaslew control knob. In the sea rch mode, the antenna rot ates automatically unle ss asignal of p rope r freque ncy and sufficient str engt h is rece ived ; in that event, th eantenna locks on and tr ac ks the signal. In the tra ck mode, the antenna automati callytrac ks the received signal unle ss overr idde n by operatio n of t he antenna slew contro l.)

4. Fixed-frequency and variable-frequency operation

5. Display equipment including a signal-level m eter , a spectrum display unit,and an automatic pri nter that gives an accu rate r eco rd of the ti me and the bearing tothe targel (The provision for accura te time requir es a built-in clock that can be rese t . )

6. Detection of almost any type of modulated sign al within th e frequency bandsspecified

7. System sen sit ivit y of 119 dBm (range 370 kilometers (200 nautical miles)) forthe vhf band and 1 2 9 . 5 dBm (range 92 6 kilometers (500 nautical miles )) fo r the S-band

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The three methods by which t h i s equipment could be procured ar e as follows.

1. The USAF could proc ure the sys tem and supply it to the airfr ame contractorfor installation.

2. The NASA could procure the system and supply it to th e airframe contractorf or installation.

3. The air fra me co ntracto r could procure and install the system.

The fir st alternative, with technical monitoring by both USAF and NASA, was chosen asth e optimum method.

TEST1 NGOF ARD-17

Flight testing of th e A m - 1 7 using a prototype system' began in Ja nuar y 1965 a t

the airfr ame contractor facility. Sufficient testing was pe rfor med to verify that t h eARD-17 would tr ac k both vhf and S-band s ign als above and below th e air cr af t withsatisf actory ran ge and bearing accuraci es. After the successful completion of t histest , a se ri es of tes ts w as initi ated in conjunction with spac ec raf t vhf and S-bandtransmit ters. The fir st of these tes ts w a s performed during the Gemini V mission in1965. Othe r vhf t es ts were con cur rent with tes tin g of th e Block I Apollo postlandingrecovery aids, with the Gemini VI and VI1 missio ns, and with the Apollo-Saturn 201flight. The S-band te st s were perfor med during the Apollo-Saturn 202 flight and theApollo 4, 5 , and 6 missions. The tes t re sult s indicated the following facts.

1 . The vhf rec over y beacon had a range of 361 kilometers (195 nautical miles)(line of sight limited ); this value was obtained with th e command module on the waterand the airc raft

atan altitu de of 7620 meters (25 000 feet).

2. The avera ge orbit al vhf range was 2080 kilometers (1123 nautical miles)(line of sig ht limit ed), and the average bearing accura cy was 4 . 9 " ; these values wereobtained relati ve to the spacecr aft in Ear th orbit.

3. The average entry-tracking S-band range w as 667 kilometers (360 nauticalmiles), and the average bearing accuracy was 4 . 5 " ; these values were obtained rela-tiv e to the entering command module.

The re su lt s of flight te st s showed that th e ARD- 17 provides excellent rang e and satis-

ran ge of 9 2 6 kilometers (500 nautical miles) , This range deficiency, which was caused

factory bearing acc uracy in the vhf mode.showed that the syst em provides satisfactory beari ng accuracy but le ss than the desir ed

by a combination of le ss than anticipated radiated power from the spa cec raft and lowerove ral l syst em sensiti vity of t he direction-finding sys tem, w a s minimized by the us eof one additional air cr af t in the landing ar ea.

In the S-band mode, the test res ul ts

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M O DF ICAT1ON OF ARD-17

After a f e w months of A m - 1 7 operational use, sev era l problems developed.ecurrent fa i lures of the two clu tches located in the antenna actua tor w er e encountered.

Exce ssive antenna drift occ urr ed, slew switches stuck, and opera tor s had troubleidentifying t h e dire ction of th e signa l in the vhf mode because of the pr es en ce of two

antenna side lobes.made.

o solve these problems , the following engineering changes we re

1. The antenna actu ator clutch seals wer e wearing out aft er approximately

It was deter mined that the manufacturer could not co rr ec t the defect.20 hours of use, although a minimum requ ire men t of 100 hou rs of u s e had been as se ss edfo r them.rel iab le unit modified at reas onab le cost could not be obtained; the ref ore , a survey Ofclutch manuf actur ers was conducted to obtain replacement clutches having longer life-time s. Two candidate clutches that pass ed a 500-hour life test were selected to replacethe origi nal clutches. The manufacture r of the new clutches also certified the units fo r1000 hour s of operation.

A

2. A newly designed printed circu it board was installed in the contr olset

t oeliminate antenna drif t. Basically, t his modification permitt ed an acc ura te balancingof the clutches that eliminated the antenna drift.

3. The wiring to the s l e w switches had in ter fer ed with the s l e w switch rotationand caused sticking when the switc h was deflecte d in one directio n.solved the slew switch problem.

Rerouting the wir e

4 . The pr es en ce of the antenna si de lobe s when opera ting in the vhf mode wascaused by a radome restriction imposed on the antenna size. Because of this restr ic-tion, the si de lobes could not be eliminated, but the addition of a manual gain controlto th e re ce iv er simplified identification of th e ma jo r lobe. When the manual gain con-tr ol was switched on, the existing automatic gain cont rol was over ridde n and the gainof the recei ver could be se t manually. This change resulted in a greate r difference insignal strength between the m ajo r lobe and the si de lobe s and simp lified identificationof the maj or lobe.

The four preceding engineering changes were incorporated into the sy ste m by u se offiel d modification kit s. The changes have proved to be quite succes sful .

OPERATIONAL-CONCEPT CHANGES

After the pro cur eme nt of the ARD-17, the Apollo en try pro fil e changed signi fi-

cantly; that is , reduction of the r ange fron, 9260 kilo met ers (5000 nautical miles ) t oapproximately 4630 kilometers (2500 nautical miles) redu ced the number of S-bandblackouts t o one (fig. 4). Because of the reduced fo otprint s iz e and the singl e blackoutperiod, the original requirement fo r airbo rne S-band track ing was eliminated. There -fore, the number of HC-130 a i rc ra f t r equ i red to suppor t a landing was reduced from

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1 . 5 ~ 1 2 5 x 1 2

1 .2 -

E

mm .9 -c

m

m

.--L

P .6 -mn.I

r t r ye

m

c _

Range from entry, n. mi.I I I I

0 926 1852 2778Range frpm entry, km

Figure 4. - Fin al Apollo entr ytrajectory.

five o r six to tw o o r three. If two aircrafta r e used, they generally ar e located approx-imately 370 kilometers (200 nautical miles)up range and down range of t he pred ic tedlanding point and offset 185 kil ome ter s(100 nautical miles) from the groundtrack.

The S-band mode is used from t he end ofblackout until approximately 1 minute beforethe predicted main-parachute deployment(vhf recovery-beacon activation) as an aid todete rmin e whether the landing w i l l occur uprange o r down range of a part icular aircraf t .At approximately 1 minute before the predi c-te d main-par achute deployment, the ARD-1'7is switched from the S-band mode to the vhfmode t o a ttem pt rece ptio n of the vhf rec ove ry -beacon signal as soon as signal transmissionbegins at 3048 me te rs (10 000 feet) altitude.

Early signal reception is desirable becausethe l ine -of -sigh t ran ge is approximately556 kilo mete rs (300 nautical m iles ) when

the command module is at a 3048-meter (10 000 foot) altitude compared to the361-kilometer (195 nautical mile) range when the command module is on the water .

FIELDMAINTENANCE

Since th e beginning of the spac e program, a continuing problem has been equip-ment maintenance in the field.and new personn el a r e not trained adequately before being assigne d to a squadron.Because the Aeros pace Rescue and Recovery Service is the only USAF unit equippedwith the Am - 1 7 , personn el do not become fami liar with the sy stem while assigned t oother USAF organizations.accomplished by joint NASA/USAF training teams on a semiannual or annual basis.Although this train ing method has been moderately succ essful, the turnov er of trainedpersonnel is a constant problem. The fi rs t field maintenance facility w a s operated bythe A m - 1 7 manufacturer for 3.5 years , but this arrangement w a s not satisfactorybeca use of ex ces siv e cos t and equipment turnaro und time. In July 1968, the fieldmaintenance responsibility w a s assumed by the USAF Warn er Robins A i r MaterialArea. Thi s change resulted in improved field maintenance. The operation and main-tenance man uals have been revise d and a r e expected to help elimin ate the field main-tenance problems. Th es e manuals were initially incomplete, in accurat e, and noteasily comprehended by USAF technicians.

A rapid turnover of field maintenance personn el occ urs ,

Essentially all field maintenance personnel training is

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CONCLUDINGREMARKS

The AN/ARD- 17 direction-finding system has operated satisfactorily since theincorpora tion of four engineerin g changes. The only disappointment in per for man ce hasbeen th e range obtained on the S-band mode. Thi s deficiency was cause d par tly byinsufficient spac ecraf t tra nsm itt er power, which actually w a s approximately half theorig inal ly stated value f or which the AN/ARD- 17 performance specifications had beenwritten. Because of th e elimination of the S-band entr y-tr acki ng requ ire men t, th eran ge deficiency has not impa ired t he capabi lity of th e equipment a s currently used.In the very-high-frequency mode, th e A N / A R D - 1 7 is the best long-range direction-finding equipment in e xist ence and would have enabled location of the command moduleif a nonnominal landing had occ urr ed.

Lyndon B. Johnson Space Cente rNational Aeronautics and Space Administration

Houston, Texas, October 4, 1974076-00-00-00-72

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Apollo Experience Report the ANARD-17 Direction Finding System