The present invention relates to an improved Through Bulkhead Initiator (TBI). More
particularly, it relates to Through Bulkhead Initiator (TBI) wherein both the donor
5 and acceptor cavities are filled with PBXN-5 composition for initiating solid rocket
motor.
BACKGROUND OF THE INVENTION
10 Usually, electrical means of initiating solid rocket propellant is adopted for various
space and missile applications. The technique employs the use of electrically
conducting wires in close proximity to the propellant which is hazardous due to
unintentional currents being caused to flow and prematurely can cause the ignition of
the propellant. This kind of unexpected current arises from stray electromagnetic
15 energy from various energy sources, may lead to abortion of the particular mission
A
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rn desired. It is well understood from the prior art that initiation of rocket motors by
- Ca
e means of TBI is a non-electric means of igniting a solid propellant.
At the advent of TBI, solid propellant rocket motor can have ability to fire more than
20 once. That is a rocket motor with a 'start-stop-restart' capability generally known as
pulsed rocket motor by providing within the same case two or more solid propellant
units separated by a membrane seal structure. This makes the ignition of propellant
units independent of each other whereby discrete impulses are available an'command.
0
c?l
4 25 Through bulkhead initiators are well known and commonly employed in ordnance
applications. It consists of donor and acceptor which are separated by a metallic
barrier called bulkhead and the bulkhead is the integral part of TBI unit. .
TI31 of the prior art are disclosed in the following publications: "Development of the
30 Saturn V Thru Bulkhead Initiator", Convin et al, Nodh ~rnericanR ockwell Corp, 6'h
2
Symposium an Electro explosive devices, July 1969, 'Through Bulkhead Initiator
Development" by Hecks, Sandia Laboratories, A l buqueque, New Mexico, 6'h
Pyrotechnic Seminar, 1978, '"Thermal ignition of Pyrotechnics Through a Bulkhead",
by Kjeldgaard et al, Sandia Laboratories, Albuquerque, New Mexico, Symposium
5 on Electro explosive devices, 1974, and "Development of a Shock Initiated Through-
Bulkhead Actuator", Schwartz et al, Sandia Laboratories, Albuquerque, New Mexico,
6' Pyrotechnic seminar,l980.
Further, TBI's are also discussed in following US patents as well: US Patent No.
10 5959236 issued to Alliant techsystems Inc. entitled "Through bulkhead initiator'" US
Patent No. 3238876 issued to Robert C. Allen et al, Mar. 8, 1966 entitled "Method
for Through-Bulkhead Shock Initiation'" US Patent No. 4608926 which was issued to
' George LaStevens, Sept.02, 1986 entitled "Swivel Type Through bulkhead initiator",
US Patent No. 4660472 issued to George L. Stevens, Apr.28, 1987 entitled "Optical
15 Through Bulkhead Initiator and Safe-Ann Devices', US Patent No. 4699400 issued to
Gary V. Adms et al, Oct. 13, 1987, entitled "Inflator and Remote Sensor with
Through Bulkhead Initiator", US Patent' No. 4829765 issued to Christopher
W.Bolieau et al, May 16, 1989, entitled 'Tulsed Rocket Motor".
20 US publication 201 110308414 relates an electronic safe, arm, and fire device
configured to reject signals below a predetermined 'all-fire' voltage.
NEED FOR TFIE PRESENT INVENTION
2
W 25 TBI is a subsystem of pulsed rocket motor technology and the development of TBI
a I with secondary high explosive fillings as per Mil-Std-1316 is of paramount
a
importance in today's ordnance industries so as to meet particular mission
requirements.
The peculiarity of secondary high explosives mentioned in the military standard is
their less sensitivity.
The present inventors have found that selection of less sensitive polymer bonded
expIosive composition, PBXN-5 to fill both donor and acceptor cavities overcomes
the limitation of the through bulkhead initiator of the.prior art which uses sensitive
explosives such as pentaerythritol tetranitrate (PETN), cyclotrimethylene trinitrate
IrnX).
10 The present inventors have established a bulkhead thickness, made of SS304 material
which acts as a pressure seal rearward by withstanding the operating pressure of
rocket motor. This bulkhead thickness is optimized in such a manner that it is capable
of withstanding the entire detonation sequence of TBI.
15 The present inventors have designed a donor in such a way that it can receive a
detonator output even from a distance of 8mm air gap via Safety Arming Mechanism
(SAM) and it is capable of producing a steady detonation shock front. The filling
density of donor secondary explosive is established by in-situ pressing methodology.
20 The present inventors have designed the acceptor in such a fashion that it undergoes
low order detonationldeflagration without damaging the structural integrity of
bulkhead. The filling density of acceptor is established by in-situ pressing
methodology. Acceptor filling is established in a manner in which it will further
ignite the pyrotechnic composition adjacent to it in the form of pellet.
25
The filling density of donor charge is maintained higher than that of its acceptor
counterpart so as to have a high order detonation at donor side and low order
detonation at acceptor side respectively.
The present invention overcomes the limitation of using sensitive explosives such as
pentaerythritol tetranitrate (PETN), cyclotrimethylene triaitrate (RDX) by choosing a
less sensitive polymer bonded explosive composition, PBXN-5. The present
invention is also having an igniter pellet housed as part of main TBI unit so as to
5 facilitate the flash emerging out of TBI to travel up to main igniter.
ADVANTAGES OF THE 'INVENTION:
Through bulkhead initiator is a detonation transfer element from donor charge to
10 acceptor charge through a metallic barrier without imparting any adverse effect on its
integrity. The detonation output of TBI is capable of igniting the pyrotechnic
compositions that in turn initiates the rocket motor. In addition to its intended
purpose, it provides certain additional advantages as given below
15 Post-function pressure seal (withstands temperature & pressure of the solid
rocket motor throughout the motor burn).
Simultaneous ignition of multiple motors possible with suitable detonating
fuses.
TI31 with safe and arm mechanism prevents any premature or unplanned
20 initiation arising out of EMI (Electromagnetic Interference), RF (Radio
Frequency) or ESD (Electrostatic Discharge).
Weight savings, by reducing the number of onboard electrical sources, and by
eliminating the safety ignition heads, since ;the TI31 only has secondary
explosive charges.
25 Reducing ignition time dispersion.
* Functioning reliability of TBI of the present invention is increased due to
presence of PBXNd on both donor and acceptor sides as its decomposition
temperature is less than that of hexani trostil bene used in prior art.
Advantages of usinp PBXN-5: Decomposition temperature of PBXN -5
(-280°C) is less than that of WNS (-31S°C) use in prior art, therefore, the
initiation reliability of acceptor charge having PBXN-5 as filling is always
high. In addition, the shock sensitivity of PBXN-5 is less than that of HNS;
5 therefore, the initiation reliability of PBXNS is much higher than HNS. In the
present invention, the TI31 is able to get initiated from the shock emerging out
of a detonator located at a distance of 8mm air gap thereby meeting the
mission requirement.
Use of PBXNJ in both donor and acceptor charges reduces the number of
10 high explosive inventory required for the mission 'requiremeht whereas prior
art TBI increases the overall mission logistics.
The TBI of the present invention requires Iess space than EFI (Exploding foil
initiator) or EBWI (exploding bridge wire initiators) based ignition
mechanism where the space requirement is high in order to accommodate
h a, 15 high voltage batteries and insulating materials.
rn
Stronger bulkhead made of stainless steel 304 of thickness > 2.0mm is able to
withstand the shock loading during functioning.
The bulkhead thickness of TBI of the present invention can withstand a
C V .
E
differential pressure up to 1,00,000 psi.
20 Filling parameters on donor and acceptor sides are such that donor charge
undergoes high order detonation and acceptor charge undergoes deflagration /
7
0 low order detonation.
9
4 w OmCTS OF TFIF, INVENTION
n
4 25 It isan object sf the present invention to provide a through bulkhead initiator (TBI)
thaving
a metallic bulkhead with sufficient thickness and strength to withstand both
4a*3; the detonation sequence of TBI and the operational pressure of solid rocket
propellant.
It is another object of the present invention to provide a through bulkhead initiator
(TBI) wherein less sensitive high explosive composition, PBXN-5 is selected on both
donor and acceptor cavity of TBI.
5 It is another object of the present invention to provide a through bulkhead initiator
(IBIS wherein structural integrity of bulkhead is retained even after the detonation
sequence of TBI is completed,
It is yet another object of the present invention to provide a through bulkhead initiator
10 (TBI) wherein the donor cavity is designed in such a way that it is capable of getting
initiated on arrival sf detonation output fbm a detonator located at a distance of 8mm
air gap using electro explosive devices (EED) via Ignition Safe and Arm Mechanism
(ISA). The acceptor cavity is designed in such a way that it effectively receives the
donor output via bulkhead without damaging its structural integrity and igniting the
15 igniter pellet.
It is further object of the present invention to establish the filling technique in donor
and acceptor cavity in such a fashion that donor will produce a steady detonation
shock front while the acceptor will undergo a low order detonation or deflagration.
20 Since the acceptor is in close proximity with the igniter pel let (BKNQ3) and the said
igniter is part of TBI Unit, the said igniter initiates and produces a flash which in turn
initiates the main igniter.
SUMMARY OF THlE INVENTION
According to an aspect of the present invention there is provided an improved
through bulkhead initiator (TBI) comprising:
5 A secondary high explosive donor charge;
A secondary high explosive acceptor charge;
A through bulkhead initiator (TBI) body constructed of a stainless steel
material, said TBI body includes first and second cavities separated by a
,metallic barrier member integral with said TBI body, said first cavity
10 substantially filled with said secondary high explosive donor charge, said
second cavity substantially filled with said secondary high explosive acceptor
charge;
Detonator located at a distance of 8mm from the said secondary high explosive
donor charge;
15 Ignition, Safe and Arm USA) barrier between the said detonator and said
secondary high explosive donor charge.
- wherein the said secpndary high explosive donor charge and said secondary
high explosive acceptor charge is PBXN-5 composition,
- wherein said metallic barrier member has a sufficient central thickness in the
20 range of 2.0mm-2.5mm and is located between the said secondary high
explosive donor charge and said secondary high explosive acceptor charge so
that a shock wave initiated by detonating said secondary high explosive donor
charge from adistance of 8 mrn using said detonator via said Ignition Safe and
Arm Mechanism (ISA), is. transferred through said metallic barrier member
25 without rupturing its structural integrity to impact said secondary high explosive
acceptor charge so as to cause detonation of said secondary high explosive
acceptor charge.
BRl"F,F DESCWPTIOM OF THE DRAWINGS
Figure I: Cross sectional view of a through bulkhead initiator (TBI) in accordance
with the present invention.
5
Figure 2: Enlarged vim of showing a more detailled schematic of a through bulkhead
initiator in accordance with present invention.
Figure 3: Assembled view of fi1Ie.d TI31 in accordance with present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention ;elates to an improved Through Bulkhead Initiator (TBI). More
particularly, it relates to Through BuIkhead Initiator (TBI) wherein both the donor
15 and acceptor cavities are filled with PBXN-5 composition for initiating solid rocket
motor.
, In an embodiment of the present invention there is provided an improved through
bulkhead initiator (TBI) comprising:
20 A secondary high explosive donor charge;
A secondary high explosive acceptor charge;
A through bulkhead initiator (TBI) body constructed of n stainless steel material
(SS304 material), said TBI body includes first and second cavities separated by
a metallic barrier mernbe; integral with said TBI body, said first cavity
25 substantially filled with said secondary high explosive donor charge, said
second cavity substantially filled with said secondary high explosive acceptor
charge.
Detonator located at a distance of 8mm from the said secondary high explosive
donor charge;
30 Ignition, Safe and Arm (ISA) barrier between said the detonator and said
secondary high explosive donor charge.
- wherein the said secondary high explosive donor charge and said secondary
high explosive acceptor charge is PBXN-5 cbmposi tion,
- wherein the said metallic barrier member has is sufficient central thickness in
the range of 2.0rnrn-2.5mm and is located between the said secondary high
5 explosive donor charge and said secondary high explosive acceptor charge so
that a shock wave initiated by detonating said secondary high explosive donor
charge fiom a distance of 8 mm using said detonator via said Ignition Safe and
Arm Mechanism '(ISA), is transferred through said metallic barrier member
without rupturing its structura1 integrity to impact said secondary high explosive
10 acceptor charge so as to cause detonation of said secondary high explosive
acceptor charge.
The thickness of the bulkhead of the said through bulkhead initiator (TBI) of the
present invention, made of SS304 material is > 2.0mm, The bulkhead of the said
15 through bulkhead initiator (TBI) is able to withstand the shock loading during
functioning, c q withstand a differential pressure up to 1,00,000 psi and is capable of
withstanding the entire detonation sequence of TBI.
The Secondary high explosive donor charge employed in the present invention
20 consists of PBXN-5 composition, and said secondary high explosive acceptor charge
. L
0 employed in the present invention also consists of PBXN-5. The said high explosive
donor charge and said high explosive acceptor charge conforms to'MiI-Std-1316.
Secondary high explosive donor charge is in-situ pressed into said first cavity and
25 said secondary high explosive acceptor charge is in-situ pressed into said second
cavity so'as to enhance produced shock wave and enhance transfer of said shock
L
CY ' wave to said sewndary explosive acceptor charge.
C<3 '
a*3 The donor of through.bulkhead initiator is designed in such a manner that it can be
30 initiated on arrival of detonation output from a detonator located at a distance of 8mm
air gap away from detonator. The detonator used is electro explosive devices (EED),
voltage require to initiate the same is 40V, whereas voltage require to initiate EFT
used in prior art is 2500V.
5 The acceptor of through bulkhead initiator is designed in &h a manner that it
effectively receives donor detonation output via metallic bulkhead without rupturing
its' structural integrity.
The filling technique in donor cavity is established in such a manner that it produces
10 a steady detonation shock wave front (i.e. high order detonation) while the filling
technique in acceptor is established in such a manner that it undergoes a low order
detonation dr deflagration sufficient to ignite the igniter pellet.
The filling density of donor charge and acceptor charge is optimized so as to have a
15 high order detonation shock output at donor side and low order
detonation/deflagration at acceptor side respectively.
The filling density of donor charge is maintained higher. than that of its acceptor
counterpart so as to have a high order detonation at donor side and low order
20 detonation at acceptor side respectively.
In an embodiment, an optimized quantity of secondary high explosive (PBX-N-5i)s
pressed in the donor cavity with a pressing load of 300kgf for a dwell time of 10s. An --.
optimized quantity of secondary high explosive (PBX-N-5i)s pressed in the acceptor
25 cavity with a pressing load of 200kgf for a dwell time of 10s.
Illustrated in Figure 1 is a cross sectional view of through bulkhead initiator (TBI), in
accordance with the present invention that is particularly applicable far deployment
of rocket motor. Figure 2 is an expanded view of a portion of Figure 1 showing a
more detailed schematic figure of a through bulkhead initiator (TBI) in accordance
with the present invention.
Now ~eferAnto~ F igure 1, Through Bulkhead Initiator is a cylindrical shaped unit
5 and a threading 6 is threaded in to an ignition safe and arm device (ISA) which
consists of detonator axially assembled, a metallic barrier called shaft in which a hole
is made to maintain arm and safe mode by means of energized solenoid, not shown in
Figure 1. The distance between detonator and TBI unit 10 is maintained via a shaft
having hole. .The distance between detonator and TBI is 8mm air gap, not shown in
TBI igniter sleeve housing cavity 7 is introduced to abode igniter pellet. TBE nozzle
cavity 8 is introducedto housk TBI nozzle which channels the flash generated from
igniter pellet to travel through flash communication tube, hereaRer referred to as FC
A 15 tube, not shown in this Figure 1. As shown in Figure 1, an undercut 9 of 0.2 mm
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al depth is provided to house the aluminium foil 15 shown in Figure 3.
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a I As shown in Figure 2 in expanded view, donor cavity 1 is defined by a bottom end
.C-r
F surface 4 which is integral with TBI unit 10. Similarly, acceptor cavity 2 includes a
V
CV 20 bottom end surface 5 which is integral with TBI unit 10.
E s LL 'It is again referred to Figure 1 and Figure 2 wherein donor cavity 1 and acceptor
G- cavity 2 are cylindrical and axially united with TBI igniter sleeve housing cavity 7
and TBI nozzle cavity 8. Open end of cavity 1 shown in Figure 2 may be sealed by an
2
LI 25 aluminium foil 15 shown in figure 3 as is well known in the art. Cavities 1 and 2 are
a I cylindrical and axially aligned. Cavities 1 and 2 are fabricated in such a fashion that
opposite bottom end surfaces of 1 and 2 are in juxtaposition so as to be separated by a
metallic bulkhead 3 which is integral part of TBI .unit 10.
Referring again particularly to Figure 2, donor cavity 1 is meant for in-situ pressing
of secondary high explosive charge and acceptor cavity 2 is intended for in-situ
pressing of secondary high explosive charge.
5 As shown in Figure 3, donor filling 13 is achieved by adopting in-situ pressing of
secondary high explosive composition, PBXN-5 and acceptor filling 14 is also
achieved by using in-sit,u pressing of secondary high explosive composition, PBXN-
5. The filling density of donor charge is maintained higher than that of its acceptor
counterpart so as to have a high order detonation at donor.side and low order
10 detonation at acceptor side respectively. Aluminium foil 15 is used to seal the donor.
BKNQ (boron potassium nitrate) is a known igniter composition. A perforated
igniter pellet 17 is prepared by adopting pre-pellet pressing technique. BKN03 (boron
potassium nitrate) is filled in the igniter pellet with a pressing load of 5OOkgf for a
15 dwell time of 10s. The base of igniter sleeve 11 is having a hole in which two
numbers of circular ammunition paper disc 16 is positioned before assembling
perforated igniter pellet 17. Thereafter, perforated igniter pellet 17 is axially
assembled into igniter sleeve 11 so as to effectively receive the output from the
acceptor charge 14 and to ignite rocket propellant reliably. The open end of ignitor
20 sleeve 1 1 is sealed with aluminium foil 18. Then, the nozzle 12 is assembled over
' igniter sleeve assembly.
Warkinp mechanism of TBI of the mesent invention: When the shock wave
produced by the detonator (not shown) located at a distance of 8mm impacts on the
25 donor charge 13 made of PBXN-5, it undergoes detonation and produces shock wave
which propagates through the bulkhead 3 and initiates the acceptor charge 14 made of
PBXN-5 without damaging the structural integrity of the bulkhead 3. The acceptor
charge 14, in turn, initiates the BKN03 pellet 17 which produces flash to ignite the
main igniter (not shown) and subsequently, propellant (not shown). The filling
density of acceptor charge 14 is kept low in order to enable it to get initiated from
attenuated shock wave after passing through bulkhead 3.
Mechanism of Ignition Safe & Arm Device USA): ISA device is a rectangular
5 shaped, stainless steel body in which two threaded holes are made to accommodate
TBI and detonator in alignment with each other and also to maintain 8mm standoff
distance between them. A metallic shaft having a hole at its centre is assembled
perpendicular to the axis of TBI and detonator to maintain safe and arm condition by
moving it to &d fro by using an energised solenoid or other suitable means.
10
The foregoing description of the invention is necessarily detailed so as to provide
understanding about the present invention. Nevertheless, the present invention is
susceptible to modifications by those skilled in the art. Such modifications, changes
are intended to be within the scope of the present inventions.

WE CLAIM:
1 . An improved through bulkhead initiator (TBI) comprising:
, A secondary high explosive donor charge;
- A secondary high explosive acceptor charge;
5 A through bulkhead initiator (TBI) body constructed of a stainless steel
material, said TBL body includes first and second cavities separated by a
metallic barrier member integral with the said TBI body, said first cavity
substantially filled with said secondary high explosive donor charge, said
second cavity substantially filled with said secondary high explosive acceptor
10 charge;
Detonator located at a distance of 8mm from the said secondary high explosive
donor charge;
Ignition, Safe and Arm (ISA) barrier between the said detonator and said
secondary high explosive donor charge.
PI 15 - wherein the said secondary high explosive donor charge and said secondary
a I.*- high explosive acceptor charge are comprised of PBXN-5 composition,
- wherein the said metallic, barrier member has' a sufficient central thickness in
the range of 2.0mm-2.5mm and is located between the said secondary high
4 g explosive donor charge and said secondary high explosive acceptor charge so
LL - * 20 that a shock wave initiated by detonating said secondary high explosive donor
7 o charge from a distance of 8 mm using said detonator via said Ignition Safe and
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Arm 'Mechanism (I SA), is transferred through said metallic barrier member
without rupturing its structural integrity to impact said secondary high
4 L explosive acceptor charge so as to cause detonation of said secondary high
explosive acceptor charge.
2. The improved through bulkhead initiator of as claimed in claim 1 wherein the
detonator is electro explosive devices (Em).
3. The improved through bulkhead initiator of as claimed in claim 1 wherein
5 secondaty high explosive donor charge is in-situ pressed into said first cavity and
said secondary explosive acceptor charge is in-situ pressed in to said second
cavity.
4. The improved through bulkhead initiator as claimed in claim 3 wherein said
I0 explosive donor charge is press loaded into said first cavity with a pressing load
of 300kgf for a dwell time of 10s and said explosive acceptor charge is press
loaded into said second cavity with a pressing load of 200kgf for ,a dwell time of
10s.
15 5. The improved through bulkhead initiator as claimed in claim 4 wherein said
explosive .donor charge and said explosive acceptor charge is comprised of
PBXN-5 composition.
6. The improved through bulkhead initiator as claimed in claim 5 wherein the donor
20 charge undergoes high order detonation and acceptor charge undergoes a low
order detonation or deflagration sufficient to ignite the igniter pellet.