Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to rocket motors and more particularly to
solid propellant rocket motors operating with a booster and to a method of
making a dual thrust rocket motor.
Certain rocket motors having missions to the outer atmosphere of
the earth require booster charges to penetrate the dense atmospheric layers.
Boosters have been used which are in essence a second rocket motor that is
fixedly attached to the main rocket motor casing. Externally positioned
boosters create the inherent problems of disposal of the spent booster casing,
alignment of the booster casings in relation to the main rocket motor, and
attachment of the booster casings to the main rocket casing.
The present invention provides a solid propellant rocket motor
comprising: a housing having a nozzle means at one end thereof, a first
propellant grain received by said housing, a second propellant grain received
by said first propellant grain, and igniter means containing pyrotechnic
material attached to said housing in communication with said propellant
grains. Preferably the first propellant grain is a sustainer propellant
grain having a plurality of protuberances extending radially inwardly into
the surface of the second or booster grain.
From another aspect, the invention provides a method of making a
dual-thrust rocket motor comprising: filling a rocket motor housing with a
first propellant grain material, forcing a cured second solid propellant
grain within the housing to a desired depth, curing the first propellant
grain with the second solid propellant grain held in place, and attaching
igniter means containing pyrotechnic material and nozzle means to the housing.
Advantages of the present invention, including simplicity and cheap-
ness of manufacture, and convenience in use, will be apparent as the
description herein progresses. The embodiments and features of the invention
will be more readily understood by reference to the accompanying drawings in
which:
Figure 1 is a full longitudinal cross sectional view of the integral
sustainer and booster propellant grains in the rocket motor of the present
invention,
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Figure 2 is a cross section of the rocket motor of the present
invention taken along lines 2-2 in Figure 1,
Figure 3 is an end view of the igniter and electric squib in
position in the rocket motor housing,
Figure 3a is a cross section of the electric squib taken along
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line 3-3 in Figure 3,
Figure 4 relate~ to the proce~s of Pabricating the present invention
and is a graphic drawing of the ~ustainer propellant poured into the rocket
motor houslng under a vacuum,
Figure 5 relates to the proces3 of fabricating the present inven-
tion and is a graphic drawing of the booster propellant grain being inserted
in the sustainer propellant,
Figure 6 relates to the process of fabricating the present invention
and i9 a graphic drawiDg of the booster propellant grain fully inserted iD
the sustainer propellant,
Figure 7 i3 a partial cro3s sectional view of the centering de~ice
for the boocter and sustainer propellant, and
Figure 8 is a flow diagram of the method of making ~he present
invention.
Referrin8 to all the figures and more particularl~ to Figure 1,
there is illustrated a dual-thrust rocket motor 10 having integral booster and
sustainer propellant grains. For simplicity, the propulsive portion of the
rocket motor has been illustrated, and the warhead portion of the rocket is not
shown. A suitable warhead may be fixedly attached to the motor and may contain
~uidance instruments or explosives.
The rocket motor 10 comprises an elongated cylindrical housing 12
of substantially nn~form circular cross section and having longltudinal axis
nCn. One end of the housing is closed by an end cap 14 which is fixedly attach-
ed thereto, as for example, by welding. A threaded centrally located bore 16
in the end cap 14 receives an iBniter 18 that extend3 inwardly within the
rocket tor 10.
As shown in Figure 3a, a sleeve 20 may be po~itioned radially to the
rocket motor longitudinal axio "C" and fi~ealy attached to the end cap 1~. The
sleeve 20 has a passageway 22 therethrough, providing access to the interior
of the rocket motor 10 for an electrical squib 2~. The ignitor 18 and squib 24
are the sub~ect of Canadian Patent No. 792,985 issued August 27, 1968 to
Lawrence J. Bornstein, and assigned to the same assignee
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as the subJect invention.
A3 sho~n in Figure 1, wing-support annulus-shaped ring 30 is
received by the rocket motor hou6ing 12 and i8 fixedly attached thereto. Suit-
able rins or wings (not shown) extend through the openings 32 in the housing
12 and are locked into position within the wing-support holes 34 in the ring.
These fins or wings may be used ror aerodynamic stability,
The nozzle 40 is rixedly attached to the housing 12 on the end
opposite the end cap 14. T~o maJor components comprise the nozzle 40 and they
are the a~t closure 42 and the exit cone 44. A ~nap-ring 46 pro~$des a locking
member by engaginK the opposing groo~es in the housing 12 and srt closure 42.
An "0~-ring seal 4~ rests ~ithin the groo~e 50 within the aft closure 42.and
is in sealing engagement with the housing 12. The enlarged portion 52 of the
art closure 42 extends rearwardly into a conical section 54 and thereaMer
into a cylindrical-shaped section 56, all Or which are integrally rormed. The
outer shell 56 Or the art closure 42 i~ pre~ersbly constructed Or a metallic
material such 88 steel. A plastic congruent second shell 58 is contiguously
~ormed withln the metallic rirst shell 56 and constructed o~ material such as
riber glass reinrorced phenolic having an asbestos riller ror heat insulation
purposes, The throat 60 or the nozzle 40 is recei~ed by the second shell 58
and abuts the stop 62. The internal conriguration Or the throat 60 may be o~
the De La~c type~ The throat 60 may be constructed Or heat and erosion resist-
ant materials such as graphite or the like.
The exit cone 44 is composed Or a metallic slee~e 64 and a plastic
sock 66 contiguously rormed therewith. The internal conriguration Or the
metallic slee~e 64 is a continuation Or the throat shape. The exit cone 44
and the art closure 42 are fixedly attached by the mating threads 68, 70. An
erosion resistant thermal barrier paint 72 is applied to the interior of the
metallic shell 64 and may be a mixture Or powdered oxides of zirconium and
alumhnum suspended in a suitable ~ehicle. A protector cap 71 may be installed
between the art closure 42 and exit cone 44 to pre~ent contamination of the
rocket motor 10 prior to ~iring.
The entire interior of the hQusing and end cap are painted with a
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heat-insulation material 74 such aq a phenolic-asbe~tos paint.
Sustainer and booster solid propellant grains are formed integrally
within the housing 12. The chief difference in physical properties between
a booster and a sustainer propellant grain iB the relative burning rate and
also the specific impulse of the ignited grains. The booster propellant
generally has a hiBher relative burning rate and a higher specific impul~e of
the ignited grain than the sustainer propellant in order to propel a rocket
motor through the earth~s atmo~phere to a predetermined altitude and veloc~ty
a~ rapidly a3 possible.
A dual-thrust rocket is broadly a rocket motor having more than one
~ource of thrust and may have boo~ter and ~u~tainer propellant grains attached
to the same rocket motor hou~ing.
A first or 3ustainer solid propellant Brain ~0 i8 formed around
the internal periphery of the housing 12 in intimate contact with the heat
insulatlon material 74. As ~hown in Figure 2, a plurality of protuberances
or ribs 82 formed integrally with the ~ustainer propellant grain 80 pro~ect
radially lnwardly toward the housing longitudinal axis nCn and extend parallel
to the same axi~. Polyurethane binder propellants may be used for the sus-
tainer propellant grain and a suitable propellant formulation is disclo3ed in
Canadian patent No. 721,696 issued November 16, 1965, to Karl Klager, et al,
and assigned to the same assignee as the sub~ect invention.
While polyurethane binder propellants are preferred for purposes
of this invention, it is within the scope of the invention to employ any other
solid propellant in the rockot motor. For example, resinous binders such as
a~phalt, rubberq, polysulfides, rubber-polysulfide mixtures, resins, other
combustible polymeric organic materials, etc., are all suitable for this
purpose. Examples of combustible polymeric organic materials suitable as
propellant binders are phenol-aldehyde resins, polyester resins, acrylate
resins, and polyalkylene resins.
Solid propellant compositions are ordinarily composed of a resin
fuel and an oxidizing material. Exanples of suitable oxidizing ~alts are the
chromates, dichromates, permanganates, nitrates5 chlorates, and perchlorates
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of the alkali or alkaline earth metals (such as potassium, sodium or calcium);
ammonia, hydrazine, or guanidine.
The boo~ter propellant grain 8~ is received by the sustainer pro-
pellant grain 80 and iq in intimate contact along its entire periphery. A
~tar-shaped passageway 86 extends through the entire length of the booster
propellant grain and is concentric with the housing longitudinal axis ~cn.
In the present embodiment, the passageway 86 has four interconnected channels
extending radially outwardly from the housing longitudinal axis ~-cn. These
channels form an extended area of the exposed grain surface thereby aiding
ignition thereof. It would be obvious to one skilled in the art to modify the
shape of the passageway 86 and to thereby modify the burning time of the pro-
pellant. The pas~ageway is tapered to facilitate the removal of a core used
in the construction of the booster propellant grain.
A suitable booster propellant would be an aluminized polyurethane
binder propellant ~uch as diclo~ed in the copending Canadian patent application
Serial No. 826,520, filed June 28, 1961, by Robert L. Duerkson and Jo~eph
Cohen, and assigned to the same assignee as the sub~ect invention.
It is conceivable that the rocket motor 10 wvuld be exposed to
ambient temperatures ranging between -~0 to ~140F thereby causing pos3ible
stres~es to be created within the sustainer and booster propellant grains. Un-
le~s precautions are taken to relieve the stresses in the propell~nt grains,
thermal expansion and contraction could cause cracks within the grains. Cracks
are detrimental to uniform burning of the propellants and could adversely
affect the average and maximum propulsive force created by the rocket motor.
Grain cracks at the bond of the propellant to the housing could allow the grain
to burn ad~acent to the housing thereby causing a hole to be burned through the
housing and subsequent loss of gases.
Therefore, a feature of the present invention i~ the utilization of
a band of parting compound (not shown) applied to the forward and aft sections
of the housing 1~ to allow the sustainer solid propellant grain to expand and
contract under ambient temperature changes.
As an example, in a rocket motor having a housing length of approxi-
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mately 83 inches and a di~meter Or 14 inches, a 22 inch band o~ parting com-
pound is applied to the insulation material 74 in both the forward and aft
sections. Additional insulation or restriction material 75 is applied to the
rear section Or the boaster and su~tainer ~ropellant grains 80 and ~4 adJacent
to the nozzle 40 to prerent burning Or the grains in that area. A suitable
parting compound i8 microcrystaline wax (1195 F melting point) or the like.
The sust&iner solid propellant grain is in intimate contact with the insula-
tion materlsl 74 in the central portion of the housing 12 thus preventing the
propellant ~rain in rlight.
The operation of the above described in~ention can best be under-
stood by rererring to the attached drswings. The rocket motor 10 i8 placed
on a launching platfor~ and directed in a desired proJectory. The electric
squib 24 is connected to a source Or electric current (not shown). The pyro-
technic material withln the squib 24 ignites, after current passes therethrough
and thereafter burns at a controlled rate. Hot gases generated by the squib 24
are directed at the igniter 18 which is directly in the path Or the squib 24.
The pyrotechnic material ~ithin the igniter 18 is ignited and consumed at a
controlled rate. The hot gases generated by the igniter 18 impinge upon the
booster propellant charge which is also ignited and burns progressi~ely along
the entire periphery and length Or the star-shaped passageway 86. It is
important to note that as the booster propellant grain burns closer and closer
to the sustainer propellant grain, the protuberances or ribs 82 Or the sus-
talner grain 80 are ignited. The position Or the ribs 82 within the booster
grain 84 insure a positi~e ignition Or the entire sustainer grain. For
example, had the sustainer grain only been in abutting relation to the booster
grain without the protuberances or ribs, it is possible that the sustainer
would not be ignited or possibly ~ould be ignited une~enly causing an erratic
propulsi~e rorce to be generated.
An example Or the dual-thrust rocket in actual physical sizes and
shapeæ is given only for purposes of illustration; a typical rocket motor uses
a booster grain weighing 290-1/2 pounds that has a burning time Or 5.5 seconds
and a sustainer grain weight Or 317 pounds with a 26.4 second burning time.
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Exemplary materials for the booster snd sustainer have previously been mention-
ed. Tbe booster has a maximum pressure of 1794 psia and a maximwm thrust of
20,999 pounds. The sustainer has a maximum pressure Or 194 psia and a maximu~
thrust of 875 pounds. The total impulse ror the entire rocket is 119,431
pounds per second.
The principsl steps o~ the process Or building a dual-thrust
rocket tor are set forth in Figures 6, 7 and 8 and the bloc~ diagram and
rlow chart shown in Figure ô.
Starting with the booster propellant grain, a ~old is prepared rOr
casting and a core is installed having a shape Or the star-shaped pass~geway.
A booster propellsnt i8 cast in a vacuum and cured in an appropriate manner as
~or oxample in an stmosphere Or dry nitrogen at a positive pressure o~ 100 psia
ror 96 hours at ~110F. The baoster mold is then strlpped O~r and the grain i8
therea~ter ~craped to re~ove all traces Or the mold release compound. An
alternate method o~ casting the booster grain is to cast the grain solid and
therea~ter to machine the star-shaped passageway arter the grain has solidified.The rocket-motor housing 12 i8 degreased, sandblasted, and the
insulation lining 74 is applied and cured. The parting compound i8 applied
to the Soruard and art portions o~ the housing 12.
Referrine to Figure 7, the cap 90 is screwed into the central
threaded bore 16 Or the end cap 14. The pin 92 is pressed into the central
opening in the booster grain 84 to centrally locate the booster grain 84 with-
in the hou~ing 12. A plug (not shown) is inserted in the star-shaped passage-
~ay to prevent roreign matter rrom entering the interior of the boo~ter grain.
A~ graphically illustrated in Figure 4, the suYtainer propellant
is poured to the housing 12 under a vacuum. The booster propellant i6 there-
arter displaced within the 6ustainer propellant as it is ~orced into the ~inal
position shown in Figures 5 and 6. The pin 92 enbers the cap 90 centrally
locating the booster grain 8~. After the sustainer propellant is initially
set, the grain is cured in a dry nitrogen gas atmosphere at 100 psig for 24
hours at ~70F and then ~or 72 hours at +110F~
Although certain particular embodiments Or the in~ention are herein
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disclosed ror purposes Or explanation~ various modirications thereof~ arter
studying the speci~ication, ~111 be apparent to those ~killed in the art to
~hich the inventio~ pertains., Rererence should accordingly be had to the
appended clai~s in deter~ing the scope Or the invention.
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