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Full text of "NASA Technical Reports Server (NTRS) 19780016332: Molded composite pyrogen igniter for rocket motors. [solid propellant ignition"

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TO: KSl/Scientific & Technical Information Division 

Attn: Miss Winnie M. Morgan 

FROM: GP/Office of Assistant General 

Counsel for Patent Matters 

SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR 

In accordance with the procedures agreed upon by Code GP and Code 
KSI, the attached NASA-owned U.S. Patent is being forwarded for 
abstracting and announcement in NASA STAR. 

The following information is provided: 

U.S. Patent No. 

Government or 

Corporate Employee : U.S. Government 

Supplementary Corporate 
Source (if applicable) 

NASA Patent Case No. : LAR-12 , 018-1 

NOTE - If this patent covers an invention made by a corporate employee 
of a NASA Contractor, the following is applicable: 

YES / / NO HH 

Pursuant to Section 305(a) of the National Aeronautics and Space Act, 

the name of the Administrator of NASA appears on the first page of the 
patent; however, the name of the actual inventor (author) appears at 
the heading of column No. 1 of the Specification, following the words 

"...with respect to an invention of ... 

Bonnie L. Henderson 

United States Patent m tm 4,080,901 

Heier et al. [45] Mar. 28, 1978 


[75] Inventors: Wilbur C. Heier, Hampton; Melvin 
H. Lucy, Virginia Beach, both of Va. 

Primary Examiner — Harold Tudor 

Attorney, Agent, or Firm — Wallace J. Nelson; Howard J. 

Osborn; John R. Manning 


[73] Assignee: The United States of America as 

represented by the Aministrator of the 
National Aeronautics and Space 
Administration, Washington, D.C. 

[21] Appl. No.: 678,520 

[22] Filed: Apr. 20, 1976 

[51] Int. Q. 2 F42B 15/10 

[52] U.S. a 102/49.7; 60/39.82 E; 

102/39; 102/70 R; 285/192 

[58] Field of Search 102/70 R, 39, 70.2 A, 

102/43 D, 49.7; 60/39.82 R, 39.82 E, 256; 
220/288; 285/192, 220, 212; 403/195, 201, 238, 


[56] References Cited 


A lightweight pyrogen igniter assembly including an 
elongated molded plastic tube adapted to contain a 
pyrogen charge and to be inserted into a rocket motor 
casing for ignition of the rocket motor charge with a 
molded plastic closure cap provided for the elongated 
tube and including an ignition charge within the cap for 
igniting the pyrogen charge and an electrically actuated 
ignition squib within the cap for igniting the ignition 
charge. The ignition charge is contained within a por- 
tion of the closure cap and it is retained therein by a 
noncorrosive ignition pellet retainer or screen which is 
adapted to rest on a shoulder of the elongated tube 
when the closure cap and tube are assembled together. 
The interior of the closure cap and the exterior of the 
elongated tube are provided with matching tapered 
spiral buttress threads to serve as the attachment means 




102/70.2 A 



Miller et al 

102/70.2 A X 








60/39.82 E X 




102/70 X 




102/49.7 X 



Puckett et al 

60/256 X 




102/70.2 A 










therefor. A circumferentially disposed metal ring is 
provided along the external circumference of the clo- 
sure cap and is molded or captured within the plastic 
cap in the molding process to provide, along with O- 
ring seals, a leakproof rotary joint as part of the contain- 
ing wall with the rocket motor casing when the igniter 
assembly is installed within the rocket motor casing. 

12 Claims, 6 Drawing Figures 

(NASA) 10 p CSC! 2 1 B, 


One las 



1 2 

igniter of the present invention is itself a miniature solid 
MOLDED COMPOSITE PYROGEN IGNITER FOR rocket motor that bums for short duration and consists 
ROCKET MOTORS of very few inert components and a pyrotechnic train. 


The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 10 


This invention relates generally to rocket motor ignit- 
ers and relates in particular to a molded plastics com- 
posite rocket motor pyrogen igniter assembly that may 15 
be produced on a production line basis and is readily 
adaptable for all present day existing and anticipated 
rocket motors that may be employed by the National 
Aeronautics and Space Administration for sounding 
rocket vehicles and in various military rocket motors as 20 
well as for anticipated space shuttle payload rocket 
launches and the like. 

In the field of rocket motor ignition where solid pro- 
pellant grains are utilized, it is the general practice to 
employ an igniter assembly that includes a pyrogen 25 
propellant material and an initiator for the pyrogen with 
the igniter assembly being, in some instances, formed of 
a two-piece system wherein the initiator charge is re- 
movable from the rocket motor while the pyrogen ma- 
terial is permanently installed and maintained within the 30 
combustion chamber adjacent the solid propellant 
rocket charge. Unitary or single piece non-standard 
igniter assemblies have been employed but these, as in 
the two-piece construction, must be individually ma- 
chined and fabricated for each different rocket motor. 35 
This individual machining of the metallic parts em- 
ployed in constructing the igniter increases the cost of 
the igniter assembly as well as provides unnecessary 
weight to the rocket motor. In propelling payloads, 
such for example in the anticipated space shuttle mis- 40 
sions, and in various sounding rockets and other space 
applications, the additional weight utilized in the igniter 
serves to reduce the prospective payload weight that 
could be transported by the solid propellant rocket 
motor. The firm users identified to date would be the 45 
NASA Scout launch vehicle which employs solid 
rocket motors consisting of Algol III, Castor II-A, 
Antares, Altair III, and the proposed higher energy 
versions of each of these which are presently under 
study; the NASA Delta and Japanese N launch vehicles 50 
using solid motors consisting of the Castor II-A, and 
TE-364; the Air Force Block Five Launch Vehicle, and 
the Astrobee “F” sounding rocket vehicle. Other poten- 
tial users include the second stage Minuteman, Terrier 
Malemute and the Navy HARM missiles. Other poten- 55 
tial users of the concept are any of those who may 
employ solid propellant propulsion systems on space or 
military rocket motors. The invention also applies to 
any solid rocket motor design that utilizes a pryogen 
igniter that is presently known or anticipated. 60 

Most conventional solid rocket motors now em- 
ployed by NASA and the military utilize non-standard 
pyrogen igniters having a design that varies from motor 
to motor and which has changed little over the last 10 to 
15 years. The pyrogen performs a common function 65 
which is to furnish a controlled, high temperature, high 
pressue, particle-laden gas to ignite the propellant sur- 
face in a solid rocket motor. In reality, the pyrogen 

The inert components in presently used igniters of this 
type consist of numerous parts. The caps or rocket 
motor case closures are generally fabricated from steel, 
titanium, or aluminum held in place within the rocket 
motor casing by a steel snap-ring or machined threads 
and this cap must be heavily insulated to protect it dur- 
ing rocket motor burning. These known caps or clo- 
sures contain provisions for initiators and pressure mon- 
itoring ports as well as O-ring seals. The pyrogen case 
or pressure vessel in presently used igniters usually 
consist of a steel, titanium, aluminum or fiberglass shell 
that is also heavily insulated inside and out to protect it 
when the pyrogen and the rocket motor are burning. 
The insulation material is generally a molded phenolic- 
/asbestos or rubber/asbestos compound. The hot gases 
exhausted from the pyrogen must pass through one or 
more nozzles at the end of the shell with the nozzles 
being generally made from molded phenolic/glass, as- 
bestos or graphite material. A steel or titanium slotted 
plate or screen is usually included to retain the pyro- 
technic ignition pellet charge within the igniter and the 
inside surface of the pyrogen case insulator generally 
receives a coating of a rubber liner material to insure 
good adhesion between the insulator and the solid pro- 
pellant charge placed in the pyrogen tube. 

These non-standard pyrogen igniters have proved 
sufficient for present day needs; however, they impose 
unnecessary penalties on the overall systems that use 
solid propellant rocket motors with pyrogen igniters. 
These present day pyrogen igniters contain numerous, 
complex, massive, relatively expensive, heavily insu- 
lated metal and non-metal parts that must be fabricated 
individually and that require many man hours for fabri- 
cation and assembly and meticulous inspection through- 
out for quality control. There is no common or univer- 
sal design for the various igniters employed by different 
rocket motor manufacturers and each new design must 
be evaluated and qualified. Thus, proven reliability 
suffers because of the relatively few number of devices 
that are tested and used. 

All molded pyrogen igniter designs of the present 
invention can be incorporated into their respective solid 
motors during normal operational use and this can be 
done as part of routine surveillance testing, product 
improvements, or new procurements or developments. 

It is therefore an object of the present invention to 
provide a novel molded composite rocket motor pyro- 
gen igniter assembly. It is a further object of the present 
invention to provide a molded composite rocket motor 
pyrogen igniter assembly that is light in weight and less 
expensive to construct than presently used igniter as- 
semblies. It is another object of the present invention to 
provide a novel rocket motor igniter assembly having 
common geometry and materials that is useful as a stan- 
dard igniter for numerous solid rocket motors. 


The foregoing and other objects, which will be ap- 
parent to those of ordinary skill in the art, are achieved 
according to the present invention by providing a 
molded elongated plastics tube adapted to contain a 
pyrogen charge and to be inserted into a rocket motor 
case for ignition of the rocket motor charge with the 
elongated tube having a closed end with one or more 
exit ports or nozzles therethrough and an open end on 


which is formed, during the molding process, spiral 
buttress threads. This elongated tube is closed by a 
molded plastics cap or cover having a circumferentially 
disposed metal ring molded and captured within the 
plastics body for securing the assembly within the 5 
rocket motor casing. The open end of the molded clo- 
sure cap is provided with internal molded spiral buttress 
threads for securing the cap to the elongated tube. The 
interior of the cap contains the ignition charge with 
suitable ports therein communicating with an electri- 10 
cally actuated explosive initiator. In one embodiment of 
the present invention a safe-arm rotor is also contained 
within the closure cap and is movable from a safe posi- 
tion in which the path between the electrically actuated 
initiator and the ignition charge is interrupted to an 15 
armed position in which a port provided through the 
rotor provides communication between the electrically 
actuated initiator and the ignition charge. 

Suitable O-ring seals are provided adjacent the cap- 
tured metal ring on the closure cap to provide an air- 20 
tight or leakproof closure with the rocket motor casing. 


A more complete appreciation of the invention and 
many of the attendant advantages thereof will be 25 
readily apparent as the same becomes better understood 
by reference to the following detailed description when 
considered in connection with the accompanying draw- 
ings wherein: 

FIG. 1 is a part sectional view taken along line I — I of 30 
FIG. 6 and illustrating one embodiment of the light- 
weight molded plastics pyrogen igniter assembly ac- 
cording to the present invention; 

FIG. 2 is a part sectional view showing an alternate 
assembly of the lightweight pyrogen igniter assembly of 35 
the present invention; 

FIG. 3 is a part sectional view illustrating an alternate 
arrangement for the closed or nozzle end of the pyrogen 
igniter of the present invention; 

FIG. 4 is an enlarged part sectional view of the area 40 
shown by line IV — IV of FIG. 1 and illustrating this 
embodiment of the present invention as the igniter as- 
sembly would be installed within a rocket motor casing; 

FIG. 5 is an enlarged part sectional view illustrating 
how the assembly of FIG. 4 would be molded; and 

FIG. 6 is a plan view of the top of the igniter assem- 
bly of the present invention illustrating a manually oper- 
ated safe-arm feature. 

Referring now more particularly to the drawings and 
more particularly to FIG. 1, there is shown one embodi- 50 
ment of the present lightweight, molded plastics pyro- 
gen igniter assembly and designated generally be refer- 
ence numeral 10. 

Igniter assembly 10 includes an elongated molded 
plastics tube 11 having a nozzle exit or port 13 disposed 55 
at the closed end thereof for expelling hot ignition gases 
from the pyrogen charge 12 contained within elongated 
tube 11 when the igniter assembly 10 is ignited. The 
other end of elongated tube 11 is tapered outwardly 
along the exterior surface thereof to provide a relatively 60 
thicker cross-sectional area for tube 11 and then tapered 
inwardly along essentially the remaining length thereof 
with spiral buttress threads 16 formed on the exterior 
surface thereof and terminating slightly short of the end 
of tube 11 to provide a shoulder surface 18 at the end of 65 
tube 11. Elongated tube 11 is closed at the open 
threaded end thereof with a closure cap as designated 
by reference numeral 20. 


Cap 20 is provided with internal spiral buttress 
threads 22 matching threads 16 on tube 11 for engage- 
ment of cap 20 to tube 11. An ignition pellet cup 24 is 
housed within closure cap 20 and contains an ignition 
charge 26 therein. Ignition pellet cup 24 is locked 
against relative rotation within closure cap 20 in a con- 
ventional manner. Ignition pellet charge 26 is retained 
within cup 24 by a noncorrosive ignition pellet retainer 
plate or screen 28. The ignition pellet retainer 28 is 
perforated so as to permit the passage of ignition gases 
from ignition charge 26 to the pyrogen charge 12 con- 
tained within tube 11 but with the perforations thereof 
being of sufficiently small size to prevent the passage of 
any of the ignition pellets from pellet charge 26 there- 
through. Only a small number of the pellets are shown 
in the drawings in the interest of clarity. 

A rotatable safe-arm rotor 30 is disposed within clo- 
sure cap 20 adjacent ignition pellet cup 24. An electri- 
cally actuated ignition squib 32 is secured within squib 
fitting 33. Squib fitting 33 is a threaded stainless steel 
insert that is molded within closure cap 20. Suitable 
electrical lead wires 35 and 36 connect squib 32 to a 
suitable electrical circuit for ignition thereof in response 
to an electric signal in a conventional manner. 

As shown in FIG. 1, the safe-arm rotor 30 is posi- 
tioned in the armed position with bore 38 therein com- 
municating with squib 32 and pellet charge 26 via pas- 
sageway 39 formed within pellet cup 24. 

When in the safe position, rotor 30 would be rotated 
90°, in a conventional manner, about the axis of cylin- 
drical extension 37 to interpose a solid portion of the 
rotor 30 between squib 32 and passageway 39 to thereby 
interrupt the communication between squib 32 and igni- 
tion charge 26. In this position, in the event squib 32 
were accidentally discharged, the explosive gases there- 
from would be harmlessly dissipated within the cavity 
formed within closure cap 20 and adjacent rotor 30 
without any danger of igniting the ignition pellet charge 

As shown in FIG. 6 the preferred embodiment de- 
scribed herein is adapted for two squibs but only one is 
included in this detailed description in the interest of 
clarity, it being understood that where more than one 
squib is employed that they are of identical construc- 
45 tion. 

A metal ring assembly 41 is molded and captured 
within the plastic wall of cap 20 during the molding 
process. During the post-cure process for molded cap 
20 the shrinkage of the plastic material making up the 
cap 20 is such that it will separate slightly from metal 
ring 41 and thereafter permit relative movement be- 
tween the cap 20 and metal ring 41. Suitable O-ring 
seals, provided between the relatively movable parts, 
prevent any gas leakage around or through the assem- 
bly when igniter assembly 10 is installed within a rocket 
motor casing. 

Suitable threaded stainless steel inserts are molded 
within the top of cap 20 for the installation of suitable 
pressure monitoring devices therein. One such insert is 
shown in FIG. 1 and designated by reference numeral 
34 with a pressure monitor 34a threadingly positioned 
therein. Suitable O-ring surfaces are molded at the base 
and top of insert 34 to provide for a double seal with 
O-rings 29 and 31 when pressure monitor 34a is secured 
therein. Insert 34 is similar to squib fitting 33 and al- 
though only two such fittings are shown in FIG. 1, 
obviously any number of pressure monitoring devices 
and electrically actuated squibs may be employed as so 

T.L/OO, 1 


desired. Suitable threaded protective plugs are installed 
within these fittings during the molding process and are 
used until ready for loading of the igniter assembly. 
These protective plugs serve as a form for the O-ring 
sealing surfaces at each end of the inserts and are re- 5 
moved to permit drilling of the necessary ports (small 
arrows in FIG. 1 and reference numeral 51 in FIG. 2) 
through the molded plastics to provide communication 
of the inserts to the area desired. After drilling of the 
ports, the protective plugs or suitable plastics covers 10 
may be placed within the inserts until the pressure mon- 
itors and squibs are to be installed. 

Ring assembly 41 is provided with an annular lip 43 
which extends beyond the exterior circumference of 
closure cap 20. Annular lip 43 is provided with suitable 15 
grooves therein for insertion of conventional O-rings to 
assist in providing a gas-tight seal between the igniter 
assembly 10 and the rocket motor casing. Also provided 
on the exterior surface of ring assembly 41 is a threaded 
annular area designated by reference numeral 46 to 20 
serve as the primary attachment of igniter assembly 10 
within a rocket motor casing. 

Referring now more particularly to FIG. 2, the ig- 
niter assembly partially shown therein is designated 
generally by reference numeral 50 and includes an iden- 25 
tical elongated tubular member 11 with the only differ- 
ences being in the closure cap designated here by refer- 
ence numeral 52. As shown therein, closure cap 52 
contains the ignition pellet charge 56 within a cavity 
formed in the closure cap and retained therein by a 30 
pellet retainer plate or screen 58 in a like manner as in 
the previously described embodiment. The exteriorly 
disposed retainer ring 61 is molded and captured within 
the body of closure cap 52 as in the previously de- 
scribed embodiment. The primary difference being that 35 
retainer ring 61 is a load distribution ring against which 
a suitable snap ring (not shown) rests to retain igniter 
assembly 50 within the housing of a rocket motor case. 

In this embodiment, a suitable O-ring 62 would be dis- 
posed between retainer ring 61, closure cap 52 and the 40 
rocket motor casing to provide the gaseous seal re- 
quired therebetween. Suitable stainless steel inserts des- 
ignated by reference numerals 53 and 54 are also pro- 
vided in closure cap 52 for retaining the electrically 
actuated squib or squibs (not shown) and suitable pres- 45 
sure monitoring devices therein. As in the previous 
embodiment mating O-ring sealing surfaces are molded 
within closure cap 52 for double sealing the squibs and 
pressure monitors therein. Pressure monitoring in this 
embodiment would be through monitor 55 disposed in 50 
insert 54 and would monitor the total motor pressure 
developed within the rocket motor case via channel 51. 
The pressure monitor 34a in FIG. 1, however, leads to 
the inside of the igniter assembly and monitors only the 
pressure within the igniter assembly. Thus, the direction 55 
of the passageway determines whether motor or igniter 
pressure is being measured by that particular monitor. 

Referring now more particularly to FIG. 3, a modi- 
fied closed or nozzle end for elongated tube 11 is illus- 
trated wherein tube 11 is provided with multiple noz- 
zles or exit ports in the base thereof for expelling of the 
hot ignition gases from the igniter assembly into the 
solid propellant rocket motor casing. These ports are 
designated by reference numerals 64, 65, 66 and 67 
herein, but obviously any number of such exit ports may 
be employed. 

Referring now more particularly to FIG. 4, an en- 
larged view of the retainer ring assembly for closure 


cap 20 (as taken along line IV— IV of FIG. 1) is shown 
and designated by reference numeral 41. As shown 
therein, closure cap 20 is attached to elongated tube 11 
and contains the ignition pellet cup 24 with pellet re- 
tainer 28 maintaining the ignition charge (not shown) 
therein. Retainer ring 41 is molded directly into cap 20 
as will be further explained hereinafter. Retainer ring 41 
includes a top surface having an annular lip segment 43 
integrally extending beyond the annular recess 71 pro- 
vided in the closure cap 20. The inner surface of retainer 
ring 41 extends downwardly at an angle of 90° from the 
top surface thereof and has a first portion engaging 
annular recess 71 and a stepped second portion horizon- 
tally spaced from the annular recess as shown in FIG. 4. 
The stepped portion of annular ring 41 terminates with 
a bottom surface parallel to the top surface thereof and 
vertically spaced from the bottom surface of the annular 
recess 71 formed in cap 20. A second annular metal ring 
75 is disposed within the annular recess 71 of cap 20 
with the ring 75 having a top surface short of the 
stepped portion of retainer ring 41 and a suitable O-ring 
seal 77 positioned therebetween. The bottom surface of 
annular ring 75 extends beyond the bottom surface of 
retainer ring 41 and engages the bottom of annular 
recess 71. An inner surface of annular ring 75 engages 
annular recess 71 and the outer surface of ring 75 en- 
gages the stepped portion of retainer ring 41 that is 
spaced from recess 71. As shown in FIG. 4, the bottom 
surface of annular recess 71 is provided with a stepped 
area to form an inner and outer or a two-step bottom 
surface with the inner step thereof being designated by 
reference numeral 79 and the outer step being desig- 
nated by reference numeral 81. Thus, the bottom sur- 
face of annular ring 75 engages step 79. An O-ring seal 
83 engages step 81 and the bottom surface of retainer 
ring 41. 

A circumferential groove 86 is provided in the exte- 
rior surface area of annular ring 75 and is of a substantial 
one-half thickness thereof. As shown in the drawing, 
groove 86 is provided in ring 75 in the area immediately 
adjacent that portion thereof that extends beyond re- 
tainer ring 41 and is disposed adjacent O-ring 83. It is 
thus readily seen that upon deformation of O-ring 83 the 
deformed surface thereof would tend to flow into the 
annular or circumferentially disposed groove 86 to pro- 
vide a gaseous seal between annular ring 75 and retainer 
ring 41 as well as to insure a seal between annular ring 
75 and cap 20 along step 79 thereof. Any gases escaping 
O-ring 83 would be prevented from further movement 
by O-ring seal 77 which would be deformed by pressure 
exerted thereon by annular ring 75. A portion of re- 
tainer ring 41 is provided with a threaded area as desig- 
nated by reference numeral 46 with this threaded area 
serving to engage mating threads 87 formed on the 
interior surface of a rocket motor casing 90, in a con- 
ventional manner. A double O-ring seal arrangement is 
provided by O-ring seals 92 and 94 positioned in suitable 
recesses (not designated) formed in retainer ring 41. 
This redundant O-ring seal pair serves to insure, along 
with O-ring seals 77 and 83, that there is no gas leakage 
from within the rocket motor casing 90 to the exterior 
thereof when the igniter assembly 10 initiates the rocket 
propellant charge contained within motor casing 90. 

Referring now more particularly to FIG. 5 the mold- 
ing process for forming a closure cap 20 shown in FIG. 
4 will be briefly described. The thermosetting plastics 
materials suitable for use in the present process as well 
as the specific process for molding the spiral buttress 

threads on adjacent rocket component parts are dis- 
closed in U.S. Pat. No. 3,780,151. This process will not 
be further elaborated on herein other than to explain 
that in the post-curing process, as described in the refer- 
ence patent, that the retainer ring 41 of the present 5 
invention will be captured by the molded plastics but 
will be relatively rotatable therewith. Retainer ring 41 
and the plastic cap 20 have sufficiently different thermal 
coefficients of expansion that during the post-cure oper- 
ation of the molded plastics, the plastics material will 10 
shrink sufficiently away from the metal retainer ring 41 
and annular ring 75 to permit relative rotative move- 
ment between the metal and plastic parts. This relative 
movement is desirable to assist in alining the igniter 
assembly 10 within a rocket motor casing 90 such that 15 
the safe-arm indicators for the safe-arm assembly and 
consequently the position of rotor 30 would be visible 
to an operator at the same relative station at all times 
regardless of motor casing 90 orientation. During mold- 
ing, ring 41 is maintained in position within mold 101 by 20 
multiple arcuate cavity split inserts, one of which is 
shown and designated by reference numeral 102. A 
multi-segment metal ring 103 is maintained within annu- 
lar groove 86 on ring 75 by split inserts 102 during the 
molding process. Inserts 102 are formed of suitable heat 25 
conductive materials to facilitate transfer of heat to the 
mold cavity during molding and curing of the plastics 

Referring now more particularly to FIG. 6, the im- 
portance of the relative rotating movement between the 30 
retainer ring 41 and closure cap 20 will be more specifi- 
cally explained. As shown therein, cap 20 is provided 
with a suitable safe-arm assembly mounting surface 105 
with an indicator surface 107 thereon. Safe-arm assem- 
bly 105 is attached by suitable screws or the like, desig- 35 
nated by reference numeral 108, to secure cover plate 
105 to closure cap 20. Safe-arm rotor 30 is provided 
with an extension that extends through closure cap 20 
and terminates in a tip portion on which is secured a 
knob 109 which is provided with a knurled exterior 40 
surface 111 thereon. An indicator arrow 112 is inte- 
grally secured to the knob 109 on rotor 30 and is mov- 
able from the safe position shown in solid line to the 
armed position (shown by dotted line) at the upper 
portion or 12 o’clock position on cover plate 105. Thus, 45 
by providing the relative rotative movement between 
cap 20 and retainer ring 41 the igniter assembly 10 may 
always be positioned within a rocket motor casing in 
such position that a quick glance to locate the position 
of the safe-arm arrow 112 (either at the 12 o’clock or the 50 
3 o’clock position) will give an immediate indication as 
to whether the rocket motor is in the armed or safe 
position. This certainty of safe and arm location mini- 
mizes the possibility of inadvertent ignition of the ig- 
niter assembly until desired. 55 

One of the primary causes of accidental ignition of 
explosive devices including, but not limited to, rocket 
motors is the discharge of static electricity. To bleed off 
static electrical charges as they may be accumulated on 
the igniter assembly of the present invention, a graphite 60 
fiber is compounded into the molded material during 
the molding process with a three-to-five percent by 
weight of graphite being employed in the total molding 
composition which prevents a safety hazard without 
affecting the strength of the molding parts. Also, the 65 
final molded parts can be spray-painted with a conduc- 
tive epoxy paint to achieve the same bleed-off results, if 
so desired. 


Thus, it is readily seen that the present invention 
provides a standardized composite pyrogen igniter as- 
sembly that requires very few steps for manufacture and 
large number of identical parts can be made simply and 
expeditiously. The standardized molded pyrogen ig- 
niter, thus formed, provides a gas-seal between the vari- 
ous parts while permitting relative rotation of the re- 
tainer ring on the remaining igniter assembly. This in- 
volves molding an elastomeric seal directly into the part 
where the cap is molded as explained hereinbefore with 
shrinkage of the composite material during the curing, 
freeing the retainer ring for relative rotation. The elas- 
tomeric O-ring materials employed possess “memory” 
and maintains the seal between the metal retainer ring 
41 and the molded plastic cap 20. The molding com- 
pound from which cap 20 and tube 11 are fabricated 
provides all the required structural and thermal proper- 
ties needed and therefore eliminates the need for any 
additional insulation as is required in the prior art metal 
igniter assemblies. These prior art or present day pyro- 
gen igniters employ pyrotechnic trains of ignition mate- 
rials that are readily adaptable for use in the present 
invention and thereby insure an identical ballistic per- 
formance of this invention and that of the presently 
manually machined igniters. 

The composite molded standard pyrogen igniter of 
the present invention will replace the inert portions of 
the presently used pyrogen igniters while duplicating 
the structural, thermal and ballistic functions thereof at 
a lower cost and weight and with increased simplicity 
and reliability. 

To fabricate a standard molded pyrogen assembly, 
using standardized mold cavities and processes, it is a 
simple matter to select the related mold tooling and, 
when molding the cap, set in place the desired threaded 
inserts and other mold components, fill the mold with a 
predetermined quantity of molding compound, close 
the mold, apply the recommended pressure and temper- 
ature for fill-out and cure, relieve the pressure, cool the 
tooling, and eject the molded part from the cavity for 
the post-cure process step. The elongated tube 11 is 
made as in process disclosed in above-referenced patent. 
The only additional machining required in the present 
invention is to drill through the remaining molded plas- 
tics in the port and nozzle exits before the parts can be 

Basically, three inert parts in the molded pyrogen 
assembly replace up to fourteen different parts in the 
prior art conventional rocket igniter design. Pressure 
measurements may be made either inside the pyrogen 
igniter (FIG. 1) or in the rocket motor cases (FIG. 2) 
and such measurements are possible with proper loca- 
tion of the drilled passages formed through the cover of 
closure cap 20. After post-curing the molded elongated 
tube is sand-blasted to improve propellant grain bond- 
ing and the propellant can be cast directly against the 
tube inside diameter without any intermediate bonding 
material, or in lieu thereof, a propellant cartridge can be 
installed and bonded in place within the elongated tube. 
The safe-arm rotor 30 with shaft 37 and ignition charge 
cup 24 are installed within closure cap 20. After loading 
the ignition charge 26 in cup 24 (FIG. 1), or charge 56 
in cap 50 (FIG. 2) the completed tube assembly is then 
torqued into cap 20 (or 50, FIG. 2) after installation of 
the proper O-rings and application of a conventional 
bonding epoxy or the like material to the molded thread 
surface. The molded igniter assembly is then installed 
into the rocket motor case and held in place by either 



the snap ring retainer (FIG. 2) or the threaded joint as 
in the other embodiments. The protective plugs are then 
removed from squib fitting 33 and pressure monitor 
insert 34, and others, if desired and the proper initiators 
with their conventional O-rings are threadedly secured 
within these inserts. The pressure pickup plugs with 
their O-rings are installed and the igniter is then ready 
for firing. Care is exerted throughout this assembly 
process, with regard to the embodiments employing the 
safe-arm rotor, to insure that the rotor is in the safe 
position wherein the passageway and ports separating 
the ignition charge within ignition pellet cup 24 and the 
electrically actuated squib is interrupted. Once the rotor 
is turned to the armed position, the igniter is then ready 
for firing. 

To inspect the molded parts during manufacture 
thereof, they may be weighed, dimensionally inspected 
and x-rayed as necessary. Since they are identically 
processed, it is sufficient to weigh the parts and only 
dimensionally inspect a representative sample. The clo- 
sure caps and tubes are assembled without a bonding 
agent and hydrostatically tested to a proof pressure 
level prior to loading thereof with the pyrotechnics. A 
representative comparison of some present-day igniter 
assemblies is compared with the molded composite 
pyrogen igniter assemblies prepared according to the 
present invention in the following table. 

















Present In- 
ert Weight 







Molded In- 
ert Weight, 







Saved lb. 







Cost to 
of Present 
Inert Comp- 
nents $ ea. 







Cost to 
of Molded 
$ ea.(est) 







Number of 
Uses Plan- 
ned (5Yrs) 







The cost columns in the above table include the costs 
of assembling and inspecting the igniters. 

It is thus seen that the present invention provides a 
savings in weight, cost, time and effort in each of the 
above specific categories. 

Although the invention has been described 
specific embodiments thereof, no exact dimensions are 
given herein and no specific quantities of the pyrogen 
charge or the ignition pellet charge has been given 
'■> inasmuch as these would vary slightly with each differ- 

ent size rocket motor employed. For example, the exter- 
nal diameter and configuration of the closure cap can be 
changed to exactly match mating surface of existing 
motor cases. Also, the number and configuration of the 
squib and pressure ports can be changed as readily de- 
sired. The length of elongated tube 11 can also be 
shorted or lengthened as well as changed in diameter 
without departing from the present invention. Addi- 


tionally, the number, location and configuration of the 
nozzle or exit ports can be maintained and changed as 
desired in a specific ignition system for a particular solid 
propellant rocket. The various O-rings employed may 
5 be any of conventional composition such as silicon, 
buna and viton rubber and the like, that is compatible 
with the uses intended herein. Also, when it is desired to 
improve the relative rotative movement between the 
retainer ring and the molded plastics, the parts may be 
10 provided with a suitable bonded film lubricant such for 
example as Dow Coming’s Molykote 100 or Acheson 
Colloids Company’s Enralon 310, or the like. 

Thus, although the invention has been described rela- 
tive to specific embodiments thereof, there are obvi- 
ously numerous variations and modifications readily 
apparent to those skilled in the art in the light of the 
above teachings. It is therefore to be understood that 
the invention described herein may be practiced other- 
2 q wise than as specifically described and is limited only by 
the following claims. 

What is claimed as new and desired to be secured by 
Letters Patent of the United States is: 

1. A standardized lightweight pyrogen assembly for 
25 rocket motors comprising: 

a molded plastics elongated tube containing the pyro- 
gen charge and adapted to be inserted in a rocket 
motor case for ignition of the rocket motor charge, 
said elongated tube being open at one end and having 
30 at least one passageway at the other end thereof for 
expelling ignition gases into the rocket motor, 
a molded plastics cap closing the open end of said 
elongated tube and serving as a closure for the 
rocket motor case, 

35 said elongated tube being provided with external 
spiral buttress threads on the open end and said cap 
being provided with internal spiral buttress threads 
for attachment to said elongated tube, 
said cap containing an ignition pellet cup and pellet 
40 retention means serving to close the open end of 
said cup for retaining an ignition charge therein, 
the other end of said cup being provided with a 
passageway to permit entrance of ignition gases to 
the interior of said cup, 

** a safe-arm rotor disposed within said cap, 

said safe-arm rotor being provided with a bore there- 
through, and rotatable from an armed position 
wherein said rotor alines the bore with the passage- 
5Q way in said cup and a safe position wherein a por- 
tion of said rotor blocks the passageway in said 

a squib retained within said cap in a port that commu- 
nicates with said rotor bore when said rotor is in 
55 said armed position, 

attachment means circumscribing the exterior surface 
of said closure cap, and 

said attachment means being secured to said cap so as 
to provide relative rotative movement therebe- 
60 tween and serving to sealingly attach the igniter 
assembly within the rocket motor casing. 

2. The igniter assembly of claim 1 wherein said at- 
tachment means includes: 

(1) a first annular metal ring disposed within an annu- 
65 lar recess circumscribing said closure cap, said first 
annular ring including, 

(a) a top surface having an annular lip extending 
beyond the annular recess in said closure cap, 



(b) an inner surface having a first portion extending 

90° from said top surface and having a first por- 
tion engaging said annular recess in said closure 
cap and a stepped second portion horizontally 
spaced from the annular recess, 5 

(c) said stepped portion terminating with a bottom 
surface parallel with said top surface and verti- 
cally spaced from said annular recess, and 

(2) a second annular metal ring disposed within the 
annular recess of said closure cap, said second ring io 
having a top and bottom surface and an inner and 
outer surface and positioned with the outer surface 
thereof engaging the stepped portion of said first 
annular metal ring and the inner surface thereof 
engaging said annular recess in said closure cap, an 15 
O-ring seal separating the top surface of said sec- 
ond annular ring and said first annular ring and, the 
bottom surface of said second annular ring extend- 
ing beyond said first annular ring so as to engage 
the bottom of said annular recess. 20 

3. The igniter assembly of claim 2 wherein said annu- 
lar recess in said closure cap is provided with a stepped 
bottom surface to form an inner and an outer or two- 
step bottom surface and said second annular ring is 
substantially of the same thickness as each of said steps 2J 
and engages the span of the innermost of said steps. 

4. The igniter assembly of claim 3 including an O-ring 
seal engaging the outer step of said bottom surface, the 
bottom of said first annular ring and the exterior portion 
of said second annular ring that extends beyond said 
first annular ring. 

5. The igniter assembly of claim 4 wherein the exte- 
rior portion of said second annular ring that extends 
beyond said first annular ring is provided with a circum- 
ferential groove in the exterior surface thereof. 

6. The igniter assembly of claim 2 wherein at least a 35 
portion of the exterior surface of said first annular ring 

is provided with external threads for attachment of said 
igniter assembly within a rocket motor casing and a first 
O-ring seal being provided in an annular groove on the 
exterior surface of said first annular ring and a second 40 
O-ring seal provided in an annular groove on the bot- 
tom surface of said annular lip of said first annular ring, 
said first and second O-ring seals serving to sealingly 
engage portions of the rocket motor casing when said 
igniter assembly is threaded into the rocket motor cas- 45 

7. A lightweight pyrogen igniter assembly compris- 

an elongated molded plastics tube adapted to contain 
a pyrogen charge and to be inserted into a rocket 50 
motor case for ignition of the rocket motor charge, 
said elongated tube having an open end and a closed 
end with said closed end being provided with at 
least one exit port therethrough for expulsion of 
ignition gases from said tube, 55 

said open end of said elongated tube being provided 
with a tapered exterior surface having spiral but- 
tress threads formed along the length thereof, 
a molded plastics closure cap for said open end of said 
elongated tube, 60 

said closure cap being provided with a tapered inte- 
rior surface and having mating spiral buttress 
threads molded therein for securing said cap to said 
elongated tube, 

retainer means disposed between said cap and said 65 
elongated tube, when secured, for retaining an 
ignition charge within said cap, means formed 
within said cap for securing an ignition squib 


therein in communication with the interior of said 
cap and for igniting the ignition charge in said cap, 
means secured to the exterior circumference of said 
cap for sealingly attaching the igniter assembly 
within a rocket motor casing, 
said means secured to the exterior circumference of 
said cap for sealingly attaching the igniter assembly 
within a rocket motor casing including an exter- 
nally threaded annular metal ring disposed within a 
circumferential groove around said closure cap and 
adapted to engage a threaded recess within a 
rocket motor casing, and 

said metal ring being relatively rotatable with respect 
to said cap. 

8. The lightweight pyrogen igniter of claim 7 includ- 
ing a threaded insert positioned within said closure cap 
and a bore extending therefrom to the interior of said 
cap and pressure monitoring means disposed in said 
threaded insert for monitoring the gaseous pressure 
generated within said igniter upon ignition thereof. 

9. The lightweight pyrogen igniter of claim 7 includ- 
ing said elongated molded plastics tube being provided 
with a shoulder surface at the open end thereof adjacent 
said spiral buttress threads, an ignition pellet cup dis- 
posed within said closure cap for containing an ignition 
pellet charge and wherein said retainer means for retain- 
ing the ignition charge within said cap closes said igni- 
tion pellet cup and rests on said shoulder surface of said 
elongated tube. 

10. The lightweight pyrogen igniter of claim 9 
wherein said retainer means is a non-corrosive metal 

11. A method of providing a gastight seal between 
two parts utilized to separate two areas of different gas 
pressures while maintaining relative rotative movement 
between the two parts comprising: 

providing a first part in the form of a rocket motor 
casing and adapted to withstand high gaseous pres- 
sures therein, 

providing at least one threaded opening in a wall of 
the first part, 

molding a plastics second part to serve as the closure 
for said first part, 

capturing an annular metal ring assembly within an 
annular groove formed on the exterior of the plas- 
tics closure during the molding thereof, 
providing a gastight seal between the captured annu- 
lar metal ring and the molded plastics second part, 
providing external threads on the exterior of the an- 
nular ring assembly to engage the threaded open- 
ing in the first part, 

providing double O-ring seals in the abutting areas 
formed between the first and second part when 
they are threadedly connected, 
securing a rocket igniter within the rocket motor 
casing as an integral portion of the second part, and 
wherein the molded plastics and the metal ring assem- 
bly have inherent diverse thermal coefficients of 
expansion and during the molding process the 
metal ring will be captured within the plastics and 
during the normal post curing of the plastics the 
metal and plastics will separate sufficiently to per- 
mit relative rotative movement therebetween but 
will retain the gastight sealed relation between the 
rotative and stationary parts. 

12. The method of claim 11 including providing safe- 
arm indicia on the plastics closure second part and ro- 
tating the second part relative to the first part to selec- 
tively position the safe-arm indicia.