Apollo Experience Report Command and Service Module Instrumentation Subsystem

8/8/2019 Apollo Experience Report Command and Service Module Instrumentation Subsystem

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N A S A T ECHN I CA L N O T E

APOLLO EXPERIENCE REPORT -COMMAND AND SERVICE MODULEINSTRUMENTATION SUBSYSTEMby Frank A . RotrdmelLyndon B. Johnson Spdce CenterHouston, Texas 77058N A T 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 A T IO N W A S H I N G T O N , D. C. A U G U S T 1973


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1. Report No. 2. Government Accession No.NASA TN D-7374 .-- _____I - -IL_.--- I_---------1-4 T i t l e and Subtit le 5 Report DateAugust 19736 Performing organization CodeAPOLLO EXPERIENCE REPORTCOMMAND AND SERVICE MODULEINSTRUMENTATION SUBSYSTEM I_--_ - - -_---I--7 Au tho r (s ) 8 Performing Organization R eport N o3. Recipient's Catalog No.

JSC S-351___ -II--0.Work Uni t No.Frank A. Rotrame l, JSCI_. _I_" .

17. Key Words (Suggested by Author(s)

9. Performing Organization Name and Address I 914-11-00-00-72

la. Dist r ibut ion Statement

1 1 . Contract or Grant No.-__.__I_ .-13.Type of Report and Period Covered

Lyndon B. Johnson Space CenterHouston, Texas 77058l__l__

19. Security Classif. (of this report ) 20. Security Classif. (of this page)None None 25

21. NO. of Pages

2. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

22. Price"$3.00

Washington, D . C. 20546_ . ~ __--I---15. Suoolementarv Notes.The JSC Di rector ha s waived the use of the International System of Unit s (SI) for this Apollo Ex-perience Report , because, in his judgment, the use of SI units would impair the usefulness of thereport or resul t in excessive cost. _-_--_-

16. Abstract

A review of the Apollo command and serv ice module instrumenta tion subs ystem is presented.The measurements provided, design aspects considered, problems encountered, and flight re -sul ts obtained are discussed.

*For S a l e by th e N a t i ona l T e c h n i c a l I n f o rm a t ion S e r v i ce , Springf ie ld , V i r g i n i a 22151


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CONTENTS

Section PageSUMMARY 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1NTRODUCTIONDEVELOPMENT HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Requirements Determination . . . . . . . . . . . . . . . . . . . . . . . . . . 2Development Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Reliability and Quality Assurance . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3onceptual Design4

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

DOCUMENTARY CONFIGURATION CONTROL . . . . . . . . . . . . . . . . . . 1 1Measurement Requirements List . . . . . . . . . . . . . . . . . . . . . . . . 11Equipment Lis t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Procu remen t Specifications and Specification Control Drawings . . . . . . . .

HARDWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Signal Conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Data Storage Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Central Timing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

DEVELOPMENT DIFFICULTIES . . . . . . . . . . . . . . . . . . . . . . . . . . 17FLIGHT EXPERIENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19CONCLUDING REMARKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Installation

13

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TABLES

Table PageI MATRIX OF QUALIFICATION TEST ENVIRONMENTS . . . . . . . . . 511 COMPONENT QUALIFICATION TEST AND FLIGHT LEVELTEMPERATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

111 VIBRATION QUALIFICATION TESTS AND FLIGHT LEVELS . . . . . 7w QUALIFICATION TESTS AND FLIGHT LEVELS FOR OXYGEN,HUMIDITY, PROPELLANT COMPATIBILITY, AND VACUUM . . . 8V OFF-LIMITS TEST RESULTS . . . . . . . . . . . . . . . . . . . . . . 9

V I INSTRUMENTATION SUBSYSTEM FLIGHT FAILURES . . . . . . . . 20

FigureFIGURES

Page1 Instrumentation block diagram . . . . . . . . . . . . . . . . . . . . . 22 Typical manufacturing and tes t flow . . . . . . . . . . . . . . . . . . . 103 Sample page fr om Apollo 11 measurement requirements list . . . . . 124 Sample page f rom Apollo 11 instrumentation equipment list . . . . . . 135 Typical measurement wiring diagram . . . . . . . . . . . . . . . . . . 156 Typical signal conditioner installation . . . . . . . . . . . . . . . . . 167 Pre ssu re transducer installation 16. . . . . . . . . . . . . . . . . . .8 Occurrences of instrumentation fail ures . . . . . . . . . . . . . . . . 18

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APOLLO EXPER I ENCE REPOR TCOM MAN D AN D SERVl CE MODULEINSTRUMENTATION SUBSYSTEM

B y F r a n k A . R o t ra m e lL y n d o n B . Johnson Space C e n t e rS U M M A R Y

The Apollo command and servic e module instrumentation subsystem provided dataf rom all other subsystems for the evaluation of subsystem performance during checkoutand flight. Measurements of temperatu re, p res sur e, voltage cur ren t, and other param-eters were generated, conditioned, and delivered to the communications subsystem fortransmiss ion. The data were received at ground stations and transmitted to flight con-tr ol le rs and other per sonne l involved in the management of the preflight checkout andof the flight.Because of the repetit ive testing of hardware before launch, few flight fai lures ofinst rumentation occur red . The Apollo instrumentat ion experience emphasized the ad-visability of designing into future spacecraft as much instrumentation flexibility as

pra cti cal because measurement requirements were changed continually throughout theprogram. .

INTRODUCTI ONThe command and service module instrumenta tion subsystem, which w a s com-posed of the spacecraft data acquisition components, included measurement systems(tra nsduc ers and signal conditioners), the cent ral timing equipment, and the data sto r-age equipment. Transducers were placed throughout the spacecraft near the parameterto be measured. Temperature transducers were bonded to surfaces, and pr es su re

tr ansduc ers were installed in special fittings welded into lines. In most places, theaccompanying signal conditioners were mounted on nearby bracke ts, but some signalconditioners were mounted in a central unit in the command module. In either config-uration, the function of the signal conditioner provided fo r each transducer w a s to con-ver t the electrical signal to a standard level for interface with the communicationssubsystem o r for data storage.The cent ral timing equipment provided timing signals for other subsystems andcounted ti me from launch. The accumulated time was encoded and inserted into the


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telemetry strea m fo r transmission to ground stations to provide accurate time informa-tion for each data fr ame required by the measurements.

PressureTemperature

piq-[Acceleration

The data s torage equipment consisted of a multichannel magnetic tape recorderof sufficient capacity to hold all data generated by a spacecraf t when the location of thespacecraf t prohibited telemetry contact with a ground station. This situation occur redduring lunar o r earth orb ital flight when the direct line between spacecraft and groundstation w a s occluded by a portion of the earth o r moon.

2::iioningJunction Cautionbo x - nd:zG$rs warningI _

The components of the instrumentation subsystem, including th e concepts andevents of the prel iminary stages , and the performance of the subsystem during Apollomissions ar e discussed in this report.

Radiation Data *Some storage -located in

Current- ignal - -conditioningEvents- quipment Centralwuipmentoltage-c centrally

timing -quipment

DEVELOPMENT H I STORY

Pulse-codemodulationequipment

The instrumentation subsystem (fig. 1) interfaced with all other spacecraft sub-systems and therefore presented unique development prob lems. The development proc-ess that led to the formulation of this extremely successful subsystem is discussed i nthe following sec tions.

I

Figure 1.- Instrumentation blockdiagram.

Requi r em ent s D e t er m inat i onThe process of compiling the meas-urement requ ireme nts included obtainingf rom data us er s the purposes intended forthe data. Because various data use rs haddifferent viewpoints, it was necessary to

interview a representati ve from each groupto determine the real needs. The practical-ity of the needs was considered fr om thestandpoints of state-of-the-ar t hardwareavailability, implementation possibility,and the spacecraft power, weight, and sizecapabiliti es. The managers of a particularsubsystem required that parameters bemeasured in sufficient detail to describeperformance, whereas the flight controller srequired analytical measurements that wouldyield unmistakable insight into the well-beingof the entire spacecraft. (However, the flightcontrollers required fewer measurementsfor each subsystem. ) These requirementswere assembled, studied, and combinedinto a master list that could be used for satisfying each set of needs. The lists werethen reviewed by instrumentation engineers fr om the viewpoint of implementation prac-ticality and submitted to be reviewed by management per sonnel who had wider interest sthan either the data us er o r the instrumentation engineer.

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Detailed schematics were necessary to facilitate decisions of whether o r not toinclude certain measurements. The schemat ics showed location, function of s enso rs ,power consumption, wiring considerations, and relationships between measurements.The schemat ics were als o used to finalize the appropriation of measurements to eachsubsystem. The inclusion of a measurement into the list w a s under the authority of aboard of managers that determined i f each measurement justified the facilities neces-sa ry to include it.Conceptual Design

Because the instrumentation had to interface wi t h every other subsystem and alsomeet the telemetry interface, cert ain design guidelines had to be established. Theseguidelines were as follows.1. The instrumentation that was integral with another subsystem and that wasdelivered to the pri me contractor already installed in the hardware of that subsystemwould not be part of th e instrumentation subsystem.2. The responsibility for al l measurements not included as pa rt of other subsys-tems would be centralized.3. Every measurement would be converted to a standard electri cal signal. Thisstandardization simplified th e telemetry interface and allowed interchangeability of datachannels. The standard was chosen to be 0 to 5 volts direct current.4. All measurement signals would be routed to a cen tral junction box for distri-bution totelemetry, data storage , spacecraft displays, caution and warning equipment,o r ground support equipment as necessary. This concept had the advantageous effectof simplifying the spacecraft wiring task.5. Th ree separate cl asses of instruments would be determined.

a. Operational equipmentb. Flight qualification equipmentc . Government-furnished equipment

6. The measurement sys tem s selected would be subjected to definitive tests toensure that performance met published specifications.7. An overall sys tem accuracy specification of f 5 percent would be established.This figure was based on a study of reali sti c requirements from the data us er s and ac-cura cies achievable from the available hardware and controlled by reasonable methods.The study considered the er ro rs introduced at each stage of the system, summed thee r r o r s using probability laws, and arrived at an average acceptable from all viewpoints.These ground ru les were established early i n the planning s tage of the ApolloPr og ra m and were adhered to throughout the program. The ground ru le s proved to bebeneficial with the exception of the first one, which deprived other subsys tems of

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experienced instrumentation engineers. The instrumentation chosen to be part of othersubsystems should have been reviewed by professional instrumentation personnel, be-cause some instrumentation design deficiencies were found lat er in the prog ram. How-ever, the reason for the ground rule was to maintain an overall responsibility for p roperoperation of the subsystem equipment ra ther than fragment that responsibility. On atypical spacecraft, approximately 500 measurements were made. Of these measu re-ments, 125 wer e the responsibility of the instrumentation group and the remainder wereconsidered to be par ts of other subsystems.

The most beneficial ear ly concept was probably that requ iring definitive testingbefore an instrument was used on the spacecra ft. This testing removed conjecture andwishful thinking fr om the prog ram and provided assurance of successful performance.

Development PhaseEach type of measurement system (for example, the press ur e measurement de-vice) w a s assigned to a team consist ing of an instrumentation engineer , a reliability

engineer, a quality assurance engineer, and a procurement officer. This team wasresponsible fo r the procurement and followup act ivities. A s measurement requirementswere defined, activities to obtain implementing hardware wer e begun. Proc urem entspecifications were written, and requests for proposals were issued. The proposalswere reviewed and vendors were selected on the basi s of a rating s yst em that includedtechnical acceptability, p rice, and company capability as demonstrated by the facility,management rec ord, and quality assurance techniques.A s the hardware was developed, it wa s subjected to testing to provide assuranc ethat it could perform in the operational environments to which it would be subjected,that it could conform to the accuracy requ irements of the specification, and that it wasreliable. Design proof tes ts, qualification te st s, off-limits te st s to destruct ion, and

accuracy determination were performed for each type of measurement device. Fai lur eso r unsatisfactory resu lts from these tes ts r equired analysis and correcti ve action toeliminate inadequacies in design and fabrication techniques.After procurement was complete, the instrumenta tion enginee r, with reliabilityand quality assurance personnel, directed acceptance, installation, and checkout. Asubsystem manager and an engineer fr om the pr ogr am office at the NASA Lyndon B.Johnson Space Center ( JS C) were assigned to over see these efforts ; to provide direc-tion; to review plans, procedur es, and tes t res ul ts ; and to provide certification ofacceptability.Special developments, which were required for the heat shield instrumentation,

nuclear part icle detection, and quantity gaging, we re accomplished by developmentcont ract s with experienced companies and we re monitored closely by the pri mecontractor.Rel iab i li ty and Qual i ty Assu rance

Each type of measurement sy ste m was subjected to a se r ies of environmental andperformance verification test s aimed at type qualification. Each hardware ite m was

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further subjected to an acceptance tes t at the vendor's plant, an inspection by the primecontractor, a preinstallation test, recalibration every 6 months before installation, andsever al verifications of performance afte r installation. Fail ures at any of these stageswere reported to JSC, and the subsystem manager consulted w i t h the contrac tor to de-termine an appropriate course of action. Failure analysis was begun, and correctiveaction was determined.Qualification test procedures for measuring instruments we re structure d on amatr ix of envi ronments derived from the exact location of each inst rument. This ma-tri x was necessa ry because the instrumentation components were spread throughoutboth the command module and the s ervice module and a common set of conditions didnot exist for all components. The matr ix is shown in table I , and the environmentallevels a r e shown in tables I1 to IV.

TABLE I. - MATRIX OF QUALIFICATION TEST ENVIRONMENTS

Component

Thermocouple, tube sheathThermocouple r efe renc e junctionAmplifier, power supplyDifferential amplifierPower supply, regulatedTemperature measurementTemperature sensorPre ssu re measurement systemDifferential pressure systemPressure/temperature ratioFlow measure ment systemLinear accelerometerSignal conditioning equipmentCurrent l imiter assemblyPower control moduleCentral timing equipmentData stora ge equipment

system

system

P a r tnumber

ME36 1-00 13ME476-0012ME473-0083ME473-0093ME464-0090ME431-0068ME432-0082ME431-0069ME449-0101ME449-0124ME449 -0015ME449-0091ME901-0713V 3 6 - 7 5 9 5 ~ ~V36-759525ME456-0041ME4 3 5- 003 5

0 )z0 )aEF-XXXXXX

XXX

XXXXXXX-

E2z-XXXXXX

XXXXX

XX

X-

E:Q)Mh8-

XX

X

XX

X

XX

X-

E:d&>XXXXXXXXXX

XXXXXXX

415c)

-s20-X

XX

XXXXXXXXX-

E:41P2k0)02-X

X

X

XXX

XX-

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TABLE II. - COMPONENT QUALIFICATION TEST ANDFLIGHT LEVEL TEMPERATURES

ComponentThermocoupleReference junctionAmplifier, power supplyDifferential amplifierPower supplyTemperature transducerPressure transducerDifferential pr ess ur e

Pres sure / temperature ratiotransducer

transducerMa ss - f low transducerAccelerometerCurrent limiterJunction boxSignal conditioning equipmentCen tral timing equipmentData storage equipment

Qualification testtemperature, F0 to 5000

-65 o 600-65 o 200-65 o 200-65 o 200-65 o 200-65 o 200-65 o 200

-65 o 200

-125 o 200-65 o 200-65 o 200-65 o 200-45 o 150-45 o 150-45 o 150

Flight lev e1temperature,4000200

-40 o 150-40 o 150-40 o 200-20 o 150-30 to 200-45 o 150

20 to 150

-30 to 15040 o 125200 to -5040 o 12540 o 12540 o 12540 o 125

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TABLE III. - VIBRATION QUALIFICATION TESTS AND FLIGHT LEVELS

Component

ThermocoupleReference junctionAmplifier, power supplyDifferential amplifierPower supplyTemperature transducerPressure transducerPres sure transducerDifferential pres sur etransducerPressure/ temperature ratiotransducerMass-flow transducerAccelerometerCurrent limiterJunction boxSignal conditioning equipmentCentra l timing equipmentData storage equipment

Qualification,2g /cycles/ sec

0.7.7.7.8.65

.3 and 10

.3 and 10.3.03

2.0

1.2.6.6.06.06.06

.06 survival

.015 operating

Flight launch phase ,g /cycles/ sec

0.2 o 1.6.2 o 1.6

.08

.3

.11.01.0.06.03

1.0

.13

.02

.13

.06

.06

.06

.06

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9s3

cMi?0-

x x x x x x x x x x x x x x x x x x

4 c x x x x x x x x x x x x x 4 4 x

x x x x

x x x 4

x x x x x x x

4cd4 4 x

x x x x x x x x x x x

x x x x x x x x x x x x x x

0.A

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To establish that the instrumentation did not crea te hazards to the spacecraft bybeing the weakest l i n k in other subkystems, destructive tests were made to determinethe fai lure level of transducer s. The res ul ts of these off-limits te st s are shown intable V .

TABLE V . - OFF-LIMITS TEST RESULTS

Range, psia Burst press ure, psia0 to 100-65" F200" F0 to 1000-65" F200" F0 to 15-65" F200" F0 to 30-65" F200" F0 to 8000-65" F200" F

InstalIation

6 0006 000

7 0006 500

3 2502 000

6 3004 100

21 00016 000

Because of the lar ge s iz e of the instrumentation subsystem, both in quantities ofcomponents and in occupation of the spacecraft volume, installation requir ed carefulplanning to achieve successful integration with the st ructure, power, telemet ry, andoriginating subsystems. A wiring diagram was generated by the cognizant ins trumenta-tion engineer, and optimum locations for the transducer s and signal conditioners weredetermined. This information w a s developed into schematics and installation drawingsthat satisfie d those responsible fo r the st ructur al integrity and those responsible for thespacecraft wiring, that met the required interfaces, and that could be used by the manu-facturing shops.

A s manufacturing progressed , the instrumentation engineer provided support inmeeting schedules and resolving difficulties and reviewed the installa tions and inspec-tion documentation. The subsystem manager w a s informed of al l difficulties and w a scognizant of the status of manufacturing at each stage. Shortages, damages, deviations

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in configuration, and other prob lems wer e solved as they arose; work-around plans andother corr ective actions were taken, coordinated, and documented fo r review by manage-ment personnel. The flow of measurement devices in procurement and installation isshown in figure 2 .

Acceptance tests,environmental Receivinginspection,ests, calibration,

noise, power; and damagecontractor andGovernme nt QC

I - isolatiodinsulation.- dentification, -Preacceptancecontractor andGovernment qualitycontrol (QCItraceability

Bonded storage,paper inspection,planning ticket.copy of data pack processing

1Ins tal l on space- Issue to Bonded storagemanufacturingraft by process inspection, paper

End-item datapack retainedby supplier

Inspection.calibration,isolation/

t

Factory checkoutof spacecraftsystems andintegrated tests; -contractor andNASA QCI 1 -

Launch sitecheckout; Laun ch padsystems and checkout:integrated tests; - ontractor andcontra ctor and NASA QCNASA QC

Special testsas requiredby processspecifications;contracbr andNASA QC7-Figure 2. - Typical manufacturing and test flow.

CheckouAfter installation, the first activity on the spacecraft in the checkout phase wasto verify the proper operation of the instrumentation in the spacecraft so that subse-quent checkout procedures could be accomplished. A s other subsystems were verified,a constant flow of instrumentation verifications was obtained as a byproduct. Theseaccumulated considerable instrumentation da ta and provided opportunities to evaluatenot only fai lures but also t rends. It was possible, with these data, to detect incipientfailure s and to schedule removals and repl acements on a timely basis.After checkout at t h e contractor's p l a t , the checkout history was reviewed andthe subsystem was certifi ed as ready for acceptance and shipment to the launch site.

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At the launch facil ity at the NASA John F. Kennedy Space Center, further check-out before flight provided additional verification of the operat ion of the instrumentation.Before launch, the rec or ds were again reviewed and certification of readiness for launchw a s made.

F l i g h tDuring the missions, each measurement was monitored closely by the astronauts,flight operations personnel, subsystem specialists, and instrumentation engineers.This excellent coverage led to rapid identification of instrumentat ion anomalies. It w a sthereby possible to diagnose troubles with tr ansducers and signal conditioners withoutdelay and to provide other means of obtaining missing data in the event of a questionablemeasurement. Fortunately, the instrumentation w a s so arranged that the l oss of ameasurement did not r esul t in los s of a parameter. Ther e were always means to ob-tain the value of a paramet er by other measurements, by calculation, o r by deduction.The technique of purely redundant measurement hardware w a s not used, but rather a

matrix of meas urement s existed whereby an experienced specialist could usually deducemissing data i f necessa ry. For example, the quantity in a fuel tank might be calcula tedon the basi s of pr ess ur e, tempera ture, and volume i f a quantity gage was not opera ting.

DOCUMENTARY CONFIGURA TION CONTROLTo maintain prec ise control of the configuration of the instrumentation subsystem,what w a s known as a "tree" of documentation was established composed of l is ts , spec-ificat ions, schemati cs , and drawings. Two of the important lists will be discussed inthis section. These are the measurement requirements list and the equipment list.

The proc urement specifications and the specification control drawing will also bediscussed.

M e a s u r e m e n t R e q u i re m e n t s L i s tEach group oriented to a par ticula r discipline and charged with the proper manage-ment of a pa rt of the Apollo Progr am ( for example, the propulsion group) had i ts ownpart icular requir emen ts concerning the li st of measurements needed to fulfill its re-sponsibility. An attempt w a s made to provide each group with it s required measure -ments within the necessary const raints of weight, power , and cost . Compilation of themeasurements requirements list w a s centralized in a division of the Apollo Spacecraft

Pr og ra m Office and controlled by the Configuration Control Board. The list was madea contractual document and served as the authority fo r implementing meas urement s.It was a dynamic document that changed as the types of data needed changed, result ingin a different list for each spacecraft. A sample page from the final li st fo r theApollo 11 spacecraft is shown in figure 3 .Each measurement w a s assigned an alphanumeric identification that denoted thespacecr aft module in which i t w a s located, the subsystem o r discipline to which it w a sapplicable, a serial number of four digi ts, and the type of parame ter it measured. The

list for med the management b asis f or the instrumentation subsystem. From the list,

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Figure 3 . - Sample page f rom Apollo 11 measurement requirements li st.authorizations for design, procurement, installation, and checkout were generated.The list also formed the basis fo r decisions concerning hardware to be used, measure -ment ranges, accuracy to be maintained, quality assurance activities, checkout proce-dures, and evaluation techniques. For those who used the data, the measurementnumber served as instant identification of the para met er meas ured and was used fo rrecordkeeping, plotting, and analysis of perf ormance .

E q u i p m e n t L i s tAfter the measurement requirem ents for each spacecr aft were established, ac-tivities were initiated to implement those requi rements . These activities includedpreparation of procurement specifications; issuance of reques ts for proposals; evalua-tion of proposals; selection of vendor s; and preparation of testing procedures, instal la-tion drawings and procedures, process specifications, checkout procedures, and

qualification plans. These activities resulted i n the equipment list of inst rumentationhardware f o r each spacec raft. A samp le page f rom the equipment list for the Apollo 11spacecraft is included as figure 4 . Each measurement was implemented by a devicethat was identified by t h e number of i ts specification contr ol drawing, and the installa-tion drawing number w a s listed. These two number s identified the hardware and it slocation on the spacecraft in sufficient detail to describe the measurement by referenceto the two drawings. The equipment lis t also included a section that identified the se-quence of measurements within the data bit s tr ea m assembled and transmitted bytelemetry.

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Figure 4 . - Sample page from Apollo 11 instrumentation equipment list.P r o c u r e m e n t S p e c i f ic a t i o n s a n d S p e c if ic a t io n C o n t r o l D r a w i n g s

The hardware needed for implementation of each type of measurement requirementw a s described in a procurement specification and the associa ted specification controldrawing. The documents described the measurement device, i ts size , weight, powerconsumption, performance, the environments under which it must per form, and thetest ing to which it must be subjected for qualification and acceptance. Quality a ssu ranceand reliabili ty requirements , packaging, marking, and protection were covered.

Measurement hardware specifications are not included as a pa rt of this report,but the different hardware types a re listed . Each of these types had i ts own set of con-trol documentation.

HARDWAREThe documentation and other control techniques were management tools used to

obtain hardware to be assembled into a system with assurance that the mission objec-tives could be fulfilled. The instrumentation hardware selected for the Apollo commandand se rvi ce modules is described in this section.

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TransducersAlthough between 200 and 1500 measurements a r e included in the equipment lis tsfor each spacecraft, depending on the parti cular mission objectives, the transdu cersmay be categorized as follows.

1 .2 .3 .4 .5 .6 .7 .8.9 .

1 0 .1 1 .1 2 .1 3 .1 4 .1 5 .1 6 .17 .18.

Pres su re , absolute and differentialTemperatureQuantity of fluids such as fuel and oxidizerFlow rates of fluids such as coolant and fuelAttitude of the spacecraf t in yaw, pitch, and rollAttitude change ra te i n yaw, pitch, and ro llVoltages on buses and bat ter iesElectrical currentFrequency of alternating curren t from inve rte rsRadio-frequency power levels, received and transmittedVibration amplitude and ra te of d isplacementStrain in the s truct ural partsAcoustic level within the command moduleAcceleration in t hre e axesHeat shield char , ablation, and heat f l u xNuclear parti cle detectionBiomedical measu remen ts of the ast ron autsGas analysi s of the spacecraf t atmosph ere

S i nal Condi t ioner sSignal conditioners used to convert the detected param eter s to a standard rangeof voltage to meet the telemetry interface are as follows,1 . Direct-current amplifiers, with vario us gains as required2 . Alternating-current-to-direct-current converters

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3. Frequency demodulators

11I I < ' IL - - - A

4 . Direct-current active attenuators

Tubingoxygen::#')"' 5Transducer

5. Attenuator-inverter fo r negative direct-current voltages6 . Phase-sensitive demodulators7. Differential amplifiers8. Reference junction fo r thermocouplesA typical wiring diagram by which a measurement signal may be traced fro m thepoint of data acquisition at the transducer through the termina l boards, signal condi-tioner, spacecra ft connectors, and through the junction box to the te lemetry units , dis-play mete rs, and other data utilization areas is shown in f igure 5. A typical signalconditioner installation is shown in figure 6, and a typical installation of a transducer

is shown in figure 7 . Each of the cylindrical units is a signal conditioner implement-ing an individual measurement.

InstrumentationCircuit paver and control r ign?-Pressurediaphragm

Main B28 V & Stra in gage

Instrumentationjunction box

I totank

I Caution and warningr--------I Dual1 voltage1 comparator-lI

Fuelpressureq-: II L--- l

Caution and warningI t - t - r---------I 1I Dual1 voltage1 comparator-lI

Fuelpressureq-: I

+ 28V dc

II L-- - . lFigure 5.- Typical measurement wiring diagram.

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Figure 6. - Typical signal conditioner installation.Redundant

seal \ Asea17 Da ta S to ra g e Eq u ip me n tFor data s tor age, magnetic tape re-cor ders were used. For the early test ve-hicle s and unmanned flights, data weresto re d on 1-inch magnetic tape by use offrequency modulators on a unit called theflight qualification re co rd er . During themanned flights, the operational data werestor ed in pulse code modulation fo rm o nanother 1-inch tape re cor de r. This opera-tional tape re cor der was called the datastorage equipment.The pulse code modulation data gen-erated by the communications subsystem at51 200 bps (high bit r at e) o r 1600 bps (lowigure 7 . - Pre ssu re transducerinstallation.

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bit rate ) were divided into. four channels for storage. For high-bit-rate storage, thetape w a s run a t 15 in/sec and played back at 120 in/ sec. The la tter mode was usefulfor eart h orbit or lunar orbit operations.The data s torage requirements f or the Apollo 15 to 17 missions were great er thanthe capacity of the tape recorder used on earl ier missions. Thus, the record er had to

be upgraded, which was done by halving the tape speeds and increasing the data density.This upgraded recorder w a s called the data recorder-reproducer .The increased data density resulted in a problem with da ta jitter because theminor tape speed varia tions were proportionally more significant than they had been atthe lower density. It was necess ary to condition the played-back tape recorder datawith a "dejitter" device before the data were delivered to the communications subsys-tem for transmission.

C e n t r a l T i m i n g E q u i p m e ntThe cent ral timing equipment received a timing signal of 1.024 kilohertz f romthe guidance and navigation equipment and provided signals to other subsystems. Inthe event of lo ss of the input signal, an internal oscilla tor within the cen tra l timingequipment became act ive and the outputs continued. The following signals wereprovided.1. A 512-kilohertz signal to the communications subsys tem for synchronization2. A 6.4-kilohertz signal to the electrical power subsystem for inve rte rs3 . A 10-hertz signal to event time rs4. A 1-hertz signal to the communications subsystem for f rame division5. One pulse per 10 minutes to the crew suit water accumulation subsystem6. Day, hour, minute, and second to

The division and accumulator circu its were

DEVELOPMENT

the telemetry subsystemsquadruply redundant.

D I FFI CULT1 ESThe instrumentation hardware was subjected to extensive testing before launch.As a result, nearly all design and manufacturing defects were discovered before anyinst rumentat ion was used in manned flight. The following difficulties, there fore , oc-cu rred in the factory during one of the many inspections, te st s, or checkout procedures(except as noted).The first item to cause concern was a rather high ra te of r ejec tions during theincoming inspection afte r the units had successfully passed the acceptance tes ts at the

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vendor's plant. Linearity, repeatability, and end-point specification limits wereexceeded in many ca ses . Also, cert ain bridge-type transducers occasionally had cal-ibration shifts. Two corrective actions resulted in a lower failure ra te . The fir st cor-rective action was to modify the acceptance test procedure limits to be the same as theincoming inspection limits. The second correc tive action was to change the transduce rbridge mater ial from silicon to platinum, which is more s table over a long period oftime.Another difficulty encountered was the phenomenon of a measurement changingabruptly in output without a change in the measured par ameter . This phenomenon w a sreferred to for convenience as a "calibration shift" and was the subject of much dis-cuss ion and activity. The source was finally determined to be oscillations within thesignal conditioners. Two modes of oscillation occur red. In some case s, the amplifierthat establishes scale range was oscillating; and, in other cases , the regulator i n thesignal conditioner w a s oscillating. Corrective action was easily accomplished by in-stalling small shunt capacitors ac ross the amplifier or regulator terminals. Becauseof the large number of signal conditioners involved, however, the question becamewhether to retrofit all signal conditioners with shunt capacitors even i f they were al-ready on the spacecraft. Retrofitting all the signal conditioners would have caused

prohibitive schedule and cost problems, s o the decision w a s to retrofit only those unitsnot yet installed. As the units on spacecraft failed in checkout, they were replaced withmodified signal conditioners.Other fai lures that did not cause undue trouble, because of only a few occurrences,wer e open bridge circuits, failed diodes, and a few transi sto r and connector failu res.Failure trends are shown in figure 8.

300r

Date

Figure 8. - Occurrences of ins tru-mentation failures.

Some measurements were found to besusceptible to very-high-frequency int er-ference. This interference occurred to onlya few measur ements located near antennasand only during the times the spacecraftvery-high-frequency transmi tte r was in use ,which was infrequent. The inter ference wasnot a source of appreciable data loss.

During the launch of Apollo 1 2 , a fewinstruments were disabled by lightning. Thisloss was the res ult of an internal electrica lconnection between the power leads and thehousings within cer tain signal conditioners.The prac tice of connecting cir cui ts to hous-ings should be avoided in the future. Analternating-cur rent connection between thesigna l conditioner ca se and the signal pathallowed heavy cu rr en ts to flow at the instantof lightning discharge, which over str ess edtrans istors and caused failure.

Experience also showed that somedamage to the instrumentation hardware18


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was caused by installation and checkout personnel working in the spacecraf t. Recur-rence of such problems was reduced by modifying installation and checkout proceduresand requesting the personnel to be mor e careful.During checkout of the first manned spacecraft, it w a s discovered that the dat astor age equipment would not reproduce data. This failu re was trac ed to excessive elec-tr ical noise on the data cir cui ts resulting from impro per connection between the signalground and the chas sis . The problem was solved by installing a large capacitor to con-nect the signal ground to the data sto rage equipment chassi s. This connection met theApollo Pro gra m ru les and still reduced the noise susceptibil ity to a reasonable level.The data s torage equipment problem resulted from the lack of electromagneticinte rfere nce considerations in the initial specifications. The Apollo spacecraft whenpowered up was found to have approximately 3 volts (or 10 percent) noise on the direct-cu rr en t bus es; some elec tronics units would not tol era te thi s percentage of noise. Itwas then necessary to take corrective action through shielding, filtering, and reroutingof grounds.

.

The cen tra l timing equipment also had to be reworked for noise susceptibility.Capacitor s were added to the powerlines and at vario us points within the signal circuitto eliminate re se ts and extraneous updates resulting from noise on the spacecraft buses .

FL I GHT EXPER I ENCEDuring the flights of Apollo 7 through Apollo 11, the re were only six failur es ofhardware included in the instrumentation subsystem. Measurement devices includedas a pa rt of other subsystem hardware experienced fai lur es that are not included inthis report.All the flight failur es that occurred ar e listed in table V I. Two of the s ix fail ure sresu lted in measu rements barely out of the 5-percent overall accuracy requirement.If the measurements had been 5 percent instead of 6 percent, they would not have beenconsidered failures. These failu res were probably caused by the changing of value ofsome r esi sto r o r other component in the electronic circuit.The complete fa ilur es wer e probably caused by open connections. The tape mo-tion slowdown on the Apollo 10 mission w a s caused by deformation of the tape reco rdercase during the pr es su re incre ase of entry. Before subsequent flights, co rrec tive ac-tion (strengthening the case) was taken.

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TABLE VI. - INSTRUMENTATION SUBSYSTEM FLIGHT FAILURES

Apollomission788

9

910

Spacecraft101103103

104

104106

DeviceThermocoupleTemperatureAccelerometer

Flowmeter

PressureTape recor der

Failu re indicationRead zeroDrifted upward 6 percentFailed at maximum dynamicpressure6 percent higher than expectedfor 6 hoursFailed at lift-offTape motion slow during entry

CONCLUDING REMARKSThe ratio of flight fail ure s to instrumentation hardware it em s flown is approxi-mately 0.01. This low failure rate can be attributed to two techniques.1. Careful selection of hardware and insistence that the hardware ad here topublished specifications2 . Repeated testing of the instrumentation hardware before installa tion and con-tinual exe rci se of the hardware from installation to spacecraft launchThese two techniques resulted in a multitiered cross-check of instrumentationhardware at all stages of preflight preparations. Thus, f ail ure s o r incipient fa il ur escould be detected immediately and any hardware of questionable capability could be re-moved and replaced.A reasonable conclusion fro m the Apollo Pr ogram with respect to instrumentation,which parallels the experience of instrumentation managers on previous programs, isthat a measurement list cannot be expected to remain fixed. Data require ments change

continually as a program prog resses . It is advisable, t herefore, to design an instru-mentation subsystem with as much flexib ility as can be afforded. Means should be pro -vided for easy changeout, addition, and remova l of hardware . Standardization of themechanical configuration of t ransducer s and signa l conditioners is a good policy, andstandardization of mechanical fittings would complement th is policy. Providing an ex-cess Of mechanical transduce r connections beyond the number initially envisioned wouldbe beneficial, allowing measurements to be added as desired. Electrical COnneCtOrS

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should be standardized, and a cen tra l junction box o r even a patchboard could increaseflexibility. Ranges should be easi ly changeable.Grounding philosophy must be carefully considered at the beginning of a programto prevent excessive noise susceptibility, and th e rules decided on must be strictly en-forced. Nearly all noise problems on Apollo instrumentation can be blamed on violation

of good grounding practi ces. In par ticula r, the case s of tr ansducers and signal condi-tioners must have no elec trical connection to the signal o r power grounds. Elec tricalconnections between signals and cas es create undesirable c ircui t loops that r esul t i nnoise susceptibility as currents are induced in the spacecraft fra me and the case s. Ifthe case s a r e isolated from the signal circuits, the noise problem is avoided.In the Apollo Program, extreme accuracy of pa ram ete r measurement w a s foundnot to be worth e xt ra money and time. A rea lis tic approach to accuracy can avoid muchdelay and expense. The f 5-percent syst em accuracy specified fo r the Apollo Programwas found to be adequate fo r operational purposes.The Apollo instrumentation experience emphasized the value of type qualification.

The environments must be carefully defined, and qualification tests must be structuredto verify that the hardware w i l l operate in those environments. Most important, there su lt s of the qualification tests must be believed and corr ect ive action taken promptlyto offset fai lures as they occur. It is not wise to "rationalize" fai lures during thequalification phase .A final recommendation is that all instrumentation be reviewed and approved bycompetent, experienced instrumentation engineers. Instrumentation that is selected byspecialists i n other disciplines is not always reliable.

Lyndon B. Johnson Space CenterNational Aeronautics and Space AdministrationHouston, Texas, March 2 1 , 1973914-11-00-00-72

NASA-Langley, 1973- 1 S-351 2 1


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AERONAUTICS AND SPACE ADMINISTRATIONWASHINGTON. D.C. 20546 P O S T AG E AN 0 FEgS P A I D

NAT I O N AL AERO NAUT ICS A NDS P ACE ADM I N I S T RAT I O NFFICIAL BUSINESSPENALTY FOR PRIVATE US E 8300 SPECIAL FOURTH-CLASS RATE 48 1

BOOK U I M A l L

WBTYABmB : If Undellverabh(Section 168PortalManual) Do Not &turn

' The monantical and space activities of the United States shall becorpdrrcted so as to contcibnte . . . o the expmi0rr of bnmm b aw l -edge of pbenomma in the a tmospke and space. The Administdomshall provide for :be widest practuabh and awopr iaJe dissm*&of infomatiofi concerning its actiuities and the results tbsreof."-NATIONALABRONAUTICSND SPACE ACr OF 1958

NASA SCIENTIFIC AND TECHNICAL PUBLICATIONSTECHNICAL REPORTS: cientific andtechnical information considered important,complete, and a lasting contribution to existingTECHNICALNOTES: nformation less broadin scope but nevertheless of im portance as acontribution to existing knowledge.TECHNICAL MEMORANDUMS:Information receiving limited distributionbecause of prdiminary data, security dassificn-tion, or other reasons.Also includes conferenceproceedings with either limited or unlimiteddistribution.CONTRAC'IOR REPORTS: Scientific andtechnical information generated under a NASAcontract or p t nd considered an importantcontribution to existing knowledge.

TECHNICAL TRANSLATIONS: Informationpublished in a foreign language consideredto merit NASA distribution in English.SPECIAL PUBLICATIONS: Informationderived from or of value to NASA activities.Publications indude find reports of majorprojects, monographs, dam compilations,handbooks, ~ e b o o 4nd specialb i b l i o p p h kTBc"oLoGy uTILIwTIoNPUBLICATIONS: Information on technologyused by NASA that may be of particularinterest in commercial and other-non-aerospaceapplications. Publications indude Tech Briefs,Technology Utilization R eports andTechnology Surveys.

knowledge.

Details on the availability of there publications may be obtainod from:SCIENTIFIC AND TECHNICAL INFORMATION OFFICE

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Apollo Experience Report Command and Service Module Instrumentation Subsystem

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