Design and fabrication of personal communication system for spacecrew

Plante, A. F.

Ruseckas, J. A.

English

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Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19710001788 2020-03-12T00:53:48+00:00Z
NAS 9-7976
	 July 1970
COMMUNICATIONS CARRIER ASSEMBLY
(Model A-3C)
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FINAL REPORT
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
Contract NAS 9-7976  
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Joseph A. Ruseckas
Program Manager
Anthony F. P ante
Project Monitor
DAVID CLARK COMPANY INCORPORATED
360 Franklin Street
Worcester, Massachusetts
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iForeword
TABLE OF CONTENTS
	
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PAGE
1.0 Pu rpose
2.0 General History
3.0 Configuration
4.0 Technical Requirements
5.0 Test Requirements
6.0 Discussion of Problems
7.0 Conclusions
3
5
6
7
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FOREWORD
The Communications Carrier Assembly, Model A-3C, is
an advanced design derived from Communications Carrier
Mod_-1 A-2C procured under National Aeronautics and
Space Administration Contract NAS 9-1186.
This report outlines design and fabrication changes that
evolved during the production of the Model A-3C
Communications Carrier Assembly, states the reasons for
changes and also provides test data and illustrations.
This report is submitted in compliance with Article XIV,
paragraph c, Contract NAS 9-7876.
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	1.0	 PURPOSE
The purpose of the effort under NASA Contract NAS 9-7976
was to fabricate, test, and deliver Communications Carriers
(CC) to be used in the Apollo Manned Space Flight Program. 	 '1
	
2.0	 GENERAL HISTORY
The Apollo Flight Communications Carrier Model A3-C,
David Clark Company Incorporated Part Number 16536G,
evolved from the Model A2-C delivered under NASA Contract
NAS 9-1186.
Significant changes were made in the major components of the
assembly resulting in improved performance, particularly in
crew comfort, acoustical attenuation and reliability of the
Personal Communications Assembly.
3.0 CONFIGURATION
The Model A3-C CC consists of two (2) major subassemblies.
These are the skull cap (soft aoods) and the Personal
Communications Assembly (PCA).
	
3.1	 Skull Cap - The skull cap replaces the strap design
used on Model A2-C in order to obtain more stability
for the PCA on the astronaut's head, and to provide
more comfort for long term wear.
The skull cap is made of Teflon and Lycra fabric
which provides a conformal fit to the head without
adjustment lacing or straps.
Optional use of a chin cup or neck strap was provided
by the design.
An ear seal assembly consisting of a foam insert covered
with deerskin was provided in all models.
A sweat pad using Rhovyl fabric was provided as an
attachment to the skull cap. The pad was located in
the front portion of the skull cap and served to absorb
perspiration which might accumulate on the brow of the
astronaut.
	
3.2	 Personal Communications Assembly - Th ; ,. assembly
comprised the earphones, microphones, earcups, cable
i
(2)
tassembly and connector for interface with the Extravehicular
,'Mobility Unit PGA Electrical Harness Assembly.
4.0 TECHNICAL REQUIREMENTS
The technical requirements of the Statement of Work of Contract
NAS 9-7976 specified that the configuration would be based on CC
DCC P/N 10625G-08 or -09 with a skull cap type design in lieu
of the strap design.
4.1	 Electrical Circuit
4.1. 1 Due to modifications under consideration in spacecraft
electrical circuits, it was necessary to contemplate
production of either the P/N 10625G-08 or the P/N
10625G-09 configuration circuitry. The -08contained
a signal slicer circuit and the -09and 8dB attenuator
in the microphone signal output leads.
Contract modification 3S directed thatthe PCA's to be
delivered under the contract would contain the 8 dB
attenuation circuit. See Figure 1.
4.1.2 Redundancy was essential for Space Flight Communications.
A bridging circuit was developed and included in the splice
block assembly to improve the redundancy of the two
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fmicrophones and the earphones. Sec Figure 2.
4.1.3 A contract change notice required some CC's to be
delivered with double shielding on the electrical
wiring. A problem of Radio Frequency Interference
(RFI) was reported during Apollo operations. An
attempt was made to reduce this interference by use
of double shielding on the electrical wiring connecting
the Government Furnished Pacific Plantronics components
of the PCA. This PCA was identified as DCC P/N
16495G-03.
Evaluations conducted by NASA-MSC established that
the double shielding did not improve RFI susceptibility,
therefore, only three (3) CC's were delivered using this
configuration PCA.
-4.2	 Skull Cap
4.2.1 The skull cap design was to provide adequate adjustment
without the use of lacing, provide for easy removal and
replacement of the earcup PCA assembly and provide
a replaceable sweatband.
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(4)
	4.3	 Communications Carrier Assembly Configuration Designations
4.3.1 The two (2) development prototypes were *-dentified by
P/N 16445G-01 and -02 respectively.
4.3.2 P/N 16536G-02. This production configuration used
PCA P/N 10625G-09 with an 8 dB attenuator circuit.
4.3.3 P/N 16536G-04. This configuration was the same as
16536G-01 except that it contained the bridging circuit.
4.3.4 P/N 16536G-05 was the same as the 16536G-04 with the
exception of the double shie!ding.
4.3.5 The 16536G-04 was the configuration ultimately standardized.
See f=igure 3.
5.0 TEST.REQUIREMENTS
	5.1	 Due to the critical use nature of the CC, a test plan was
developed and implemented to provide the required confidence
in the capabilities of the CC.
5.1.1 The major emphasis was on testing the electrical circuits to
establish that no short circuits resulted du ,ingthe fabrication
process. Particular emphasis was placed on verifying the
bridging circuit.
(5)
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5.1.2 The strain relief assembly was redesigned and subjected
to tensile load tests.
6.0 DISCUSSION OF PROBLEMS
6.1	 The major problems encountered in the performance of
the contract and their solutions are described in the
following paragraphs.
6.1.1 Strain Relief Cables. Because of tlic close proximity
of the strain relief cables to the electrical conductors
and the possibility of causing damage to the conductors
because of high heat during silver soldering, a soft
soldering method was evaluated. Tests established that
the soft soldering method provided adequate strength
but also resulted in more consistent performance of the
strain relief assembly under structural load. The reason
for the consistency seemed to be related tc the fact that
the stainless steel cable retained more of its strength
during cold soldering. Breaking strength of the cold
soldered cables was well in excess of 100 lbs. The
standard test for acceptance of production cables was
50 lbs. tensile load.
(6)
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6.1.2 Microphone Boom Failures. Some GFE microphones
received in CC's to be modified had splits in the boom
tubing beyond the bend relief sleeve and the potting
fitted where the boom exited the transducer case.
Analysis showed that the failures were attributable to
sharp bending of the tube.
6.1.3 FailurF analysis of a microphone circuitry on a CC
S/N ;SO disclosed that there was insufficient clearance
between the terminal board potting well and EMI shields.
The analysis concluded `,ic y }his type failure could be
induced on all microphones of this configuration. The
conclusion was that the EMI shield was too narrow for
the potting well (was not 
.
a press fit), and if not properly
positioneu wo;jiu short out one of the terminals when a
little pressure was placed on the shield. Pacific Plantronics
representatives reshaped the EMI shield and verified that
this was effective corrective action. DCC representatives
were trained and qualified by PPi to make in-plant repairs
on cdditional GFE microphones at DCC.
7.0 CONCLUSIONS
7.1	 The requirc-nents of the contract for delivery of CC's and
documentation with quality and reliability were met without
'.1
(7)
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6significant delay or serious problem.
7.2 This Final Report completes the effort under Contract
NAS-97976 except for the requirement for reporting
New Technology under Extract Clause 82 which will
be submitted separately.
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(8)
Figure 1
8db Attenuator Circuitry
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Figure 2
Bridging Circuitry
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Communications carrier assembly, model A-3C Final report

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