Apollo Experience Report Development and Use of Specialized Radio Equipment for Apollo Recovery Operations

8/8/2019 Apollo Experience Report Development and Use of Specialized Radio Equipment for Apollo Recovery Operations

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N A S A T E C H N I C A L N O T E N A S A T N0-7587

hWm

APOLLO EXPERIENCE REPORT -DEVELOPMENT AND USE OF

SPECIALIZED RADIO EQUIPMENTFOR APOLLO RECOVERY OPERATIONS

by William A , Middleton and H . F. Byeshears

Lyndon B. Johnson space CenterHozlston, Texas 77058

NAT IONA L AERONAUTICS AND SPACE ADM INISTRA TION WASHINGTON, D.C. FEBRUARY 1974


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1. Report No.

D - 7587

APOLLOEXPERIENCEREPORTDEVE LOPM ENT AND USE O F SPECIA LIZE D RADIO

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle 5. Report Date

Lyndon B. Johnson Space CenterHouston, Texas 77058

EQUIPMENT FO R APOLLO RECOVERY OPERATIONS7. Author(s)t

11 . Contract or Grant No.

8. Performing Organization Report No.

William A. Middleton and H. F. Breshears , JSC

9. Performing Organization Name and Address

JS C S-38510. Work Unit No.

924-22-10-08-72

12. Sponsoring Agency Name and Address

Washington, D.C. 20546National Aeronautics and Space Administration

13. Type of Report and Period Covered

Techn ical Note

14. Sponsoring Agency Code

17 . Key Words (Suggested by Author(s))

' Ground-Air - Ground Communications' Radio Beacons *Radio Receivers* Rad io Transmi t t e r s'VHF Radio EquipmentSpacecraft Recovery

18. Distribution Statement

Cat. 31

19 . Security Classif. (o f this report) 20. Security Classif. (of t his page) 21 . NO. of Pages

None None 1 122 . Price

$ 2.75


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APOLLO EXPERIENCEREPORT

DEVELOPMENT AND USE OF SPE CIA LIZE D R AD IO

EQU l PMENT FOR APOLLO RECOVERY OPE RAT IONS

ByW i l l i a m A . M i d d l e to nand H. F. BreshearsLy n d o nB. Johnson Space Cen te r

S U M M A RY

Two specialized, personal radio-equipment items, a survival radio and a swimmerradio, we re developed to suppor t Apollo recovery operat ions. The surv ival radi o isca rr ie d on board the command module to provide postlanding voice communications anddirection-finding capability i f either the command module very-high-frequency/amplitude-modulation trans ceiv er o r very-high-frequency r eco ve ry beacon cannot be used. De-partment of Defense swim mer and parares cue personnel participating in Apollo recove ryoperations a re provided with swimmer radios to permit communications among theastronauts , recovery a irc raf t, and ships before the spacecraft hatch is opened. Thedevelopment, testing, use, and char acte risti cs of these rad ios ar e described in thisreport .

INTRODUCTION

The requirement for a sma ll, hand-held, battery -operate d radi o that would providevoice communications and direction-finding signals for situations in which th e sp acecraftpostlanding communications s ys te ms could not be used was established during theGemini Pro gra m. Survival radios procured for this purpose were c arr ied on all 10manned Gemini missions. The age of the Gemini rad ios c ause d the requ irem ent f or asecond-generation survival radio to be established before the operational phase of theApollo Pro gr am ; however, flight hardware did not become available until after t heApollo 11 mission. Therefor e, Gemini survival radios were c ar ri ed on the f i r s t fivemanned Apollo missions. Apollo surviv al radios w ere used f or the remaining Apollomissions and w i l l be used throughout the Skylab Program.

Another type of specialized personal radio was developed f o r U . S . Air Forcepara rescu e personnel and U . . Navy underwater demolition team swimmers to providevoice communications with recovery aircraft and ships and the Apollo command module(CM). Th is radio , subsequently named the Apollo swim mer rad io, was developed intim e to be us ed during reco very of the cr ew and C M of Apollo 7, the fi rs t mannedApollo mission. A swim mer interphone that had been developed before the Gemini


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Pr og ra m to provide hardline communications between sw im mer s and the astrona utsbef ore hatch opening was used suc cessf ully throughout the Gemini P ro gr a m and wasdesigned to be compatible with the Apollo C M . However, it became evident duringthe Gemini Pro gr am that the para re sc ue and swimmer personnel needed the capabilityto communicate with recovery a irc ra ft, as well as the astrona uts, during the recove ryoperations; theref ore, the Apollo swimmer radio w a s substituted as the prima ry in-s t rumen t f o r swi mme r communications.

These two radi os and the significant as pe ct s of t hei r development, testin g, anduse a re d iscussed in th is repor t .

DEVELOPMENT AND USEOF THEA PO LLO S U RV I VA L R A D I O

The Apollo survival radio (fig. 1)requirement was established in 1967 andwas based on the following consid eratio ns.

1 . The reliability of the Geminisurvival ra dios that had been in use since1964 w a s questionable.

2. There was no requirement fo rparts screening and burn-in when theGemini survival radio w a s procured.

3 . There were not enough Geminisurvival radios to support the Apollo andSkylab Pr ogr am s, and reprocurement

would have been almost as expensive asthe development of a new radio.

4. The us e of advan ces made inelectronics since 1963 would provide aradio with improved performance and re -duced si ze and weight.

The specification for the Apollo radiorequired several improvements over theGemini radio. The major improve mentsa r e g iven i n table I.

In addition to these improve ments,a meter was installed to enable statusmonitoring of t h e bat te ry, t ransmi t te r,and modulator (fig. 2) . Also, 100-percentpa rt s screening and burn-in were required.

Figure 1 . - Apollo surv ival radio andbattery pack.

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TABLE I . - APOLLO RADIO IMPROVEMENTS

Characterist ics

Receiver sensitivity, pV . . . . . . .Receiver bandwidth, MHz

6 dB points . . . . . . . . . . . .60 dB point s . . . . . . . . . . . .

Modulation, percent . . . . . . . . .Duty cycle, percent . . . . . . . .

Tone . . . . . . . . . . . . . . . .

Voice modulation sensitivity(for normal voice), percent . . . .

Speaker sound-level output, dB . . .

Gemini radio 1 Apollo radio 1I I

25 I 100 I40 (2 se c on, 3 s e c

Fixed (1000 Hz)off)

10

103

100 ISwept (1000 Hz to

300 Hz,

2 . 5 times/sec)100

118

Kilohertz.

The contr act, awarded in April 1968, called for production of 2 prototype radios,3 first-article radios, 30 flight radios, and 6 training radios , as well as battery packsand battery tes ter s. The initial design phase w a s completed in 4 months, and theprototype rad ios and bat te rie s we re delivered before the end of the ye ar.

Operationa l te st s of the prototype hardware cons iste d of voice- and beacon-rangingruns using an HC-130 aircraft with the radio being operated both from a life raft (throughthe radi o antenna) and fr om the Apollo CM test vehicle CM-007A (through the te st-v ehic leantenna). The quality of the radi o tra nsm itt er and the rec eiv er w a s excellent, and goodbeacon and voice rang es were attained. The prototype rec eiv er had a partial-squelchcircuit that w a s evaluated during this test. A s a res ult of the test , the parti al squelchw a s deemed unde sira ble fo r the planned application of the surv ival radio . The pre sen ceof receiver noise is more desi rabl e than the lack of it when a person is i n a spacecrafto r liferaft awaiting rescue. Also, the receive range w a s extended by disabling the

partial-sque lch circui t. Thus, the parti al squelch w a s deleted fr om the designrequirements.

After the operational testing w a s completed, a battery-life test w a s conductedthat reve aled the fi rs t problem, The minimum battery life w a s specifie d to be 2 4 hours,but the life recorded during the tes t w a s 13 hours. An investigation revealed that theradio, when connected to its antenna, w a s drawing as much as twice the normal amountof cu rr en t, depending on its proximity to other objects. The cur ren t drai n w a s

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Figure 2. - Side view of Apollosurvival radio.

proportional to the voltage standing wavera ti o (VSWR). Th is was the re su lt of thefollowing two fac to rs .

1. To meet the VSWR requirementsof 1.5: 1 o r less and to make acc ura te VSWRmeasurements, the manufacturer designed

the antenna s o that it w as connected to ala rg e ground plane.

2. The radio tr ans mitt er contained apower-leveling cir cui t designed to maintaina controlled power output over the range ofbattery voltages encountered during the l if eof the bat ter y. When the antenna w a s con.-nected to the radio, the resu lt was a fair lyhigh VSWR that fluctuated to a la rge degree ,depending on the location of the ra dio withre sp ec t to other objects. When the power-

leveling circuit sensed a high VSWR, i t re-act ed by inc re as in g the power output of thetransmitter, thereby creat ing a high currentdrain.

Extensive studie s wer e conducted atthe Lyndon B. Johnson Space Center (JSC)an d by the manufacturer to resolve thisproble m. A solution was attained by r e -designing the antenna using relative field-streng th mea sureme nts made with the antennaconnected to the radio. Acc ura te VSWRmeasurements a r e difficult to make with theantenna connected to the radi o, but the op-timized antenna has a VSWR in the range of1.5: 1. The VSWR is also quite stable withre sp ec t to changes in the location of su r-rounding objects.

As soon a s the antenna design w a sf inal ized, f i rs t-art icle radio fabricat ionwa s ini t iated. A new technique was devel-oped during the fabricati on phase of the con-

tr a c t . Instea d of potting the componentson the cir cu it boards to meet the shock andvibration requirements, a method of applying a cellulose aceta te covering was developed.The acetate is applied in a sheet fo rm while hot and then drawn ove r the components bythe us e of a vacuum. The res ult i s a thin, tr an spa re nt coating that conforms to the shapeof the various components (fig. 3 ) . Thi s method ha s advantages o ver potting. Forexample, retuning or component replacement a r e simplified because all the componentsa r e v is ibl e .

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Figure 3 . - Apollo survi val radio withelectronic assembly removed.

Waterproofing w a s another importantaspec t of the rad io design. Becau se of thepossible us e of the radio in a liferaft underopen-ocean conditions and becau se the rad iocan be tied to the raft by a lanyard (therebymaking it possible to retri eve the radio i fi t falls overboard), the specification required

that the radio be waterproof to a depth of1 5 feet in seawater. The radio cas e was de-signed to be a n investment c ast ing with aremovable back cover to permit access tothe elect ronic components. The design al soincorporated a threaded cap to allow removaland repla cemen t of the batte ry pack. Thepossible areas where leaks could occur andthe methods by which these a r e a s wer e se aleda r e as follows.

1. The back cover was machined, anda Parker sea l w a s installed in i t (fig. 4).

2. An O-ring seal w a s provided forthe battery cap.

3 . The push-to-talk switch w a s in-stalled i n a waterproof housing as procured (fig. 5). The switch w a s secure d by a plateinside the radio, and a commercial potting compound w a s placed around the edges.

4. The meter w a s waterproof as procured and w a s sea led fr om the inside of theca se with a n epoxy res in.

5. The function switch had magnetic-reed switches; therefore, no holes throughthe case were required.

6. A s procured, the antenna connector w a s a waterproof type with an O-ring seal.

7 . The speaker microphone w a s fastened in place fro m inside the ca se with anepoxy re si n. The unit itself w a s waterproof as procured. A proprietary sealing methodis used such that a diaphragm installed over the transducer has a porosity that allowsthe pas sag e of air but not water molecules.

After delivery of the fir st- art icl e units, operational test s were conducted again,and acceptable re su lt s were obtained. Unit ranges were 195 nautical miles for thebeacon and 120 nautical miles for the two-way voice operating either from a liferaft or

f rom CM-OO7A in conjunction with direction-finding and voice equipment on board anHC-130 irc raf t flying at 25 000 feet. In addition to the operational testi ng, a 150-hourreliability demonstration/life tes t on two radios w a s conducted successfully by themanufa cture r. During this tes t, battery-life rang es fr om 27 to 30 hours were achieved.

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Figure 4. - Apollo surviv al rad io withelectronics compartment coverplate removed.

The first-articl e units qualified onal l but the water-immersion tests. Anextensive analy sis of wat er leakage revea ledthat too many threads had been machined onthe battery cap, thereby destroying the in-teg rity of the O-ri ng seal. A qualificationtes t was performed using properly machined

battery cap s, and no problem s were encountered. Production was initiated, and anexpedited delivery schedule enabled the fi rs t radi o to be use d on Apollo 1 2 and thesecond ra dio to be used on Apollo 13. All subsequent Apollo missions were supportedwith this type radio, and the Skylab mission s will also be supported in this manner.

Figure 5 . - Fr on t view of Apollosurvival radio.

DEVELOPMENT AND USEOF THEAPOLLOS W I M M E R R A D I O

The requirement fo r the Apollo swimm er rad io (fig. 6) developed because voicecommunications were needed among U . . Air Forc e pararescue personnel, U . . Navyswim mers , f ixed-wing aircraf t , hel icopters , ships, and the CM during recovery opera-tions. A swimmer interphone had been developed before the Gemini missi ons to providehardline communications between the s wi mm er s and the ast rona uts during the period ofrecove ry operations before hatch opening. Th is device was used s uccessf ully throughoutthe Gemini Program . However, during the Gemini Pr og ra m, the necessity to developthe capability fo r communications among all person nel involved with C M recovery becameevident.

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Fig ure 6.- Apollo swim mer radio,bat te ry pack, and flotation bag.

shock and tem pe rat ur e environments than the Apollo Pr og ra m required. Most important,however, i t had been imm ers ed to a depth of 50 fee t in sea wat er without leaking. T osatisf y the Apollo req uir emen ts, the radio would have to be modified to pro vide bothvoice tra nsmi t/re ceiv e on 282.8 and 296.8 MHz and emerge ncy beacon tran smit on282.8 MHz. Pr el im in ar y testing verified that the power output and battery life of theAN/PRC-90 satisfi ed the Apollo Pr og ra m needs and we re acceptable.

Beca use of th e requi rem ent fo r the 296.8-MHz freque ncy, i t was initially thoughtthat the mic roci rcu its used in the AN/PRC-90 (fig. 7) would need to be completely re-designed. However, it w a s determi ned that with a few component changes and someretuni ng, the 282.8-MHz micr ocir cui t could be conver ted to the 296.8-MHz frequen cy.The only othe r probl em that had to be solved w a s impedance matching of the tr an sm it te rsand r ec ei v er s to the antenna. The impedance of the AN/PRC-90 had been optimized at243.0 MHz. The antenna had an impedance of 90 ohms at 282.8 and 296.8 MHz as op-posed t o 50 ohm s at 243.0 MHz. To solve this proble m, the 50-ohm coaxial cableand matching network (int ernal to the radi o) w a s replaced with a 90-ohm coaxialcable and matching network.

Before the development of the Apolloswimmer radio, the U.S. Air Force para-rescue personnel had car ri ed their ownradios (URC-59) in addition to the s wimme rinterphone. Th is radio was not compatiblewith the CM frequ ency and could only provid ecommunications between the s wi mm er s andthe airc raf t . Numerous fai l ures also wer ecaused by water leakage.

At the time the requirement for theApollo swimmer radio became firm, athorough surv ey of e xis ting equipment wa sconducted. Two new per son nel radi os beingdeveloped fo r the military could, with ce rt ai nmodifications, satisfy the Apollo Programreq uire men ts. A modified ve rs ion of theAN/PRC-90, manufactured fo r the U.S.Navy, would mee t Apollo req ui re men ts andpermit delivery in time to support theApollo 7 mission.

The AN/PRC-90 is a sm al l (24 ounce)two-channel radio/beacon t ra ns ce ive r thatprovides voice transmit/ receive capabilityon 243.0 and 282.8 MHz and emergencybeacon tr an sm it on 243.0 MHz. Thi s radioalso had been qualified for more stringent

Lab orat ory checkout, an operational test, and a battery-life test were conductedon the f i r s t Apollo swim mer r adio as soon as i t w a s rec eive d i n August 1968, and theres u l t s of al l the tes ts were excellent. All input and output pa ram ete rs, as checked inthe lab orat ory , met specifications. The battery life w a s determi ned to be approximately

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Figure 7 . - Apollo swimmer radio withelectronics assembly partiallyremoved.

18 hour s, which was quite satis factory.Voice- and beacon-ranging r u ns were madeusing an airb orne HC-130 ai rc ra ft with theradio being operated from a l i feraft in theGulf of Mexico. On the 296.8-MHz frequency ,two-way voi ce ra ng es of 28, 42, and 67 nau-tical miles were obtained with the ai rc ra ftat alti tud es of 1500, 5000, and 10 000 f ee t ,respectively. Immersion te st s to 40 fe eti n the Gulf of Mexico we re conducted as pa r tof the operational tes t, and th er e were noleak s. Some of the waterproo fing techniquesused on this radio repr esented a technologicaladvance in the sealing of emergency ra dios .The AN/PRC-90 wa s the fi rs t multichannelradio/beacon trans ceiv er to oper ate reliably

fro m the ocean surface after repeated immersions. Thr ee of the major fac tor s thatcontributed to the succes sful waterproofing of thi s radi o were a s follows.

1. The use of a machined back cover plate containing a Par ker sea l ( fig. 8) inconjunction with a cast-aluminum case.

2. A function switch with mag netic-reed switches (thereby making it unne cessaryto have a hole through the c as e fo r the function sw itch)

3 . A special speaker/microphone with a protective memb rane that will allow thepas sag e of ai r but not wate r molec ules.

Figure 8.- Apollo swimmer radiowith electronics compartmentcover plate removed.

Thes e thre e facto rs proved to be sosuccessful that they w er e also incorporatedin the Apollo survi val radio design.

A sufficient number of s wim mer rad ioswere received in time to support the Apollo 7recov ery, and these radios were used tosupport all subsequent Apollo recoveries.During initial operational usag e, the followingfour problems developed.

1. The mercury-cell battery packsfrequently leaked electrolyte. (The Navya l so w a s having t h i s problem with theirAN/PRC-90 battery packs.) The battery pack

manufacturer redesigned the mercury cellto cor rec t th e problem. The redesign wassucc essfu l, and no prob lems with the newbattery we re encountered during 1 yea r ofuse.


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2. Because the radio normally doesnot float, two units we re los t by swimme rsduring the f i rs t few months of use . Toco r r ec t t h is , a brightly col ored flotationbag was designed that completely e nclos esthe radio and allows the swimmer to attachthe bag/radio package to himself by a lan-ya rd (fig. 9). When the swim mer needs theradio, h e removes it fr om the bag. Theradio st ay s attached to the bag throughoutthe operation. The bag/radio configurationworked quite well.

3. The antenna, which consi sted ofcoaxial shield braid over a coiled spri ngcovere d with a silicone-rubber tube (sealeda t both ends ), occasionally leaked salt-

--

Figure 9. - Apollo swimmer radiopartia lly in serted in flotationbag.

water. Investigation revealed that the radios were subjected to much rougher treatmentduring operational u se than was antic ipated originally. A s a resu l t , the s i l icone-rubbercover ing was punctured and torn, allowing saltwater to leak in and ruin the antenna.When the flotation bags we re put into us e, the antenna situation was improved to s om eextent because the bag provided protection for the antenna. To en su re reliability, how-eve r, it was nece ssary to find a tougher covering fo r the antenna than the silicone r ubb er.After investigating se ve ra l different mater ials and methods of application, Tygon tubingwas selected.

4. Although no fa ilu re s occ ur re d during missio n operations, a lar ge number oft ransmi t te r and rece ive r fa i lu re s ( 2 2 of 90 rad ios ) wer e dis cov ere d during bench check-out, in the f i e ld , and at JSC. Fa il ure analysis revealed that two cry st al s we re comingloose becau se the 90-ohm matching coaxial cable (which had a fa i r ly la rge d iameter forthe sp ace available) was putting pr es su re on the crys tal s. Because an antenna modifi-

cation was n ec es sa ry, the 90-ohm coaxial cable was replaced with a 50-ohm coaxialcable that had a much sm al le r dia mete r, the 90-ohm matching network was replac edwith a 50-ohm matching network, and the antennas wer e trimm ed so that they wouldhave a n impeda nce of appro ximate ly 50 ohms at 282.8 and 296.8 MHz ins tea d of 90 ohms.

CONCLUDINGREMARKS

Although cer tai n prob lems with the Apollo swi mmer radio we re experienced, nofa il ur es occu rr ed during mission operations, and both the Apollo survival radio and theApollo sw im me r radio have provided satisf actor y re su lt s. After the minor modifications

requ ire d fo r the swimmer radio were incorporated, this radio was t rouble fr ee .types of ra di os have proved to be m ore than capable of p erform ing the jobs fo r whichthey w er e intended.

Both

Lyndon B. Joh nso n Space Cen terNational Aeronautics and Space Administration

Houston, Texas, November 23, 1973924-22-10-08-72

S-385ASA-Langley, 1974 9


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Apollo Experience Report Development and Use of Specialized Radio Equipment for Apollo Recovery Operations