U.S. patent application number 10/726460 was filed with the patent office on 2005-06-02 for multiple pulse segmented gas generator.
Invention is credited to Abel, Stephen G., Christensen, Donald J., Woessner, George T..
Application Number | 20050115439 10/726460 |
Document ID | / |
Family ID | 34620516 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050115439 |
Kind Code |
A1 |
Abel, Stephen G. ; et
al. |
June 2, 2005 |
Multiple pulse segmented gas generator
Abstract
A method and apparatus for producing gas, for example for
propulsion. Propellant grains are segmented, preferably in
symmetrically arranged pairs and preferably about a central channel
extending longitudinally between the ends of the grains.
Longitudinally extending grains may be ignited at one end only of
each grain, at both ends, and/or at one or both ends along with at
an interior portion of a grain. In order to maintain a relatively
constant center of gravity, symmetrically arranged pairs of grains
can be ignited simultaneously. In order to produce a desired
pressure versus time profile, the number of ignition points on a
grain can be varied.
Inventors: |
Abel, Stephen G.; (Chandler,
AZ) ; Woessner, George T.; (Phoenix, AZ) ;
Christensen, Donald J.; (Phoenix, AZ) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Family ID: |
34620516 |
Appl. No.: |
10/726460 |
Filed: |
December 2, 2003 |
Current U.S.
Class: |
102/288 |
Current CPC
Class: |
F02K 9/24 20130101; F02K
9/12 20130101; F42B 3/04 20130101; F02K 9/26 20130101 |
Class at
Publication: |
102/288 |
International
Class: |
C06B 045/12 |
Claims
What is claimed is:
1. A gas propellant grain assembly comprising at least two
pie-shaped grain segments positioned on opposite sides of a line,
each of the pie-shaped segments extending longitudinally along the
line between respective first end portions and second end portions,
and wherein each pie-shaped grain segment includes an inner edge
portion adjacent the line and wherein the inner edge portion of
each pie-shaped segment is spaced from the line between the first
and second end portions forming a channel between the opposite
pie-shaped segments.
2. The assembly of claim 1 wherein the at least two grain segments
are a first pair of grain segments and further including a second
pair of grain segments, wherein the grain segments in the first
pair have a size different from a size of the grain segments in the
second pair.
3. A gas propellant grain assembly comprising at least first and
second pairs of grain segments, each grain segment in a pair being
substantially similar to the other segment in the pair; and igniter
leads extending from an ignition source, and wherein igniter leads
are coupled to respective grain segments and wherein the ignition
source is configured to ignite simultaneously the individual grains
in a pair.
4. The assembly of claim 3 wherein grain segments in the first pair
are symmetric with respect to each other.
5. The assembly of claim 3 wherein the grains in the first pair
have a first configuration and the grains in the second pair have a
second configuration different from the first configuration.
6. The assembly of claim 5 wherein the grains in the first pair
have a different size from the grains in second pair.
7. The assembly of claim 3 wherein grains in the first pair are
pie-shaped and the grains in the second pair are pie-shaped.
8. The assembly of claim 3 further including a third pair of grain
segments having a size different from a size of the first pair.
9. The assembly of claim 3 wherein the grains in the first and
second pairs of grain segments include respective end portions and
wherein the assembly further includes a passage way between the
first and second and portions.
10. A gas propellant grain assembly comprising a grain segment
having first and second end portions and an interior portion, the
end and interior portions contained in an inhibitor material so
that once ignited the entire grain segment burns, and an igniter
lead contacting the interior portion.
11. A gas generating grain assembly comprising: a first grain
element having a first size and shape and having a first inner
portion; a second grain element positioned on a side of a
longitudinally-extending line opposite the first grain element
having a second size and shape substantially similar to the first
size and shape and having a second inner portion; and wherein the
first and second inner portions are spaced apart from each
other.
12. The assembly of claim 11 wherein the first and second grain
elements are arranged substantially symmetrically relative to each
other and to the line.
13. The assembly of claim 11 wherein each of the first and second
grain elements include respective surface portions covered with an
inhibitor material.
14. The assembly of claim 13 wherein the inhibitor material is a
material bonded to the respective surface of the respective grain
element.
15. The assembly of claim 11 further including a cylindrical
element extending along the line and between the first and second
inner portions.
16. The assembly of claim 11 wherein the first and second grain
elements are substantially pie-shaped.
17. The assembly of claim 11 wherein the first and second grain
elements are a first pair of grain elements and wherein the
assembly includes a second pair of grain elements wherein each
grain element in the second pair is positioned on opposite sides of
the line relative to the other and wherein the grain elements in
the second pair are substantially similar in size and shape to each
other and are not substantially similar in both size and shape to
the grain elements in the first pair.
18. The assembly of claim 17 further including a controller for
controlling a sequence of ignition of the grain elements.
19. The assembly of claim 18 wherein the controller is configured
to ignite the grain elements in a pair simultaneously.
20. The assembly of claim 18 wherein the controller is configured
to ignite one end of each grain element or both ends of each grain
element in the pair as a function of the desired characteristic of
the output.
21. The assembly of claim 18 wherein the controller is configured
to ignite the pairs of grain elements either sequentially or
simultaneously as a function of the desired characteristic of the
output.
22. The assembly of claim 11 wherein the first and second grain
elements are substantially symmetrical with respect to each
other.
23. The assembly of claim 11 wherein the first and second grain
elements each include fore and aft end portions and wherein the
assembly includes igniter elements on each of the fore and aft end
portions of each of the first and second grain elements.
24. The assembly of claim 11 wherein the first and second grain
elements each include end portions and interior portions and
wherein the assembly includes igniter elements and each of the end
and interior portions include igniter elements.
25. The assembly of claim 24 wherein the assembly includes igniter
elements at each of the end portions of each of the first and
second grain elements.
26. A gas generator assembly comprising: a grain capable of being
ignited for producing a gas and having first and second surfaces
facing in different directions, and first and second igniter
elements applied to respective ones of the first and second
surfaces and configured in such a way that the first and second
igniters can be ignited separately.
27. The assembly of claim 26 wherein the grain is a first grain
element, wherein the assembly includes a second grain element
spaced apart from and on a side of a line opposite the first grain
element to form a first pair of grain elements, wherein the first
and second grain elements are substantially symmetrical about the
line, wherein the assembly includes a second pair of grain elements
spaced apart with respect to each other and substantially symmetric
with respect to each other, and wherein the grain elements in the
second pair of grain elements have a size and shape that are not
the same as both the size and shape of the first pair of grain
elements.
28. A system for producing gas selectively according to a desired
pressure and time profile, the system comprising: a gas-producing
grain element; first and second ignition elements on discretely
separate parts of the grain element; and a control system for
controlling the application of ignition pulses to the first and
second ignition elements and configured such that the control
system can apply selectively ignition pulses separately to each of
the separate parts of the grain element.
29. The system of claim 28 wherein the control system is configured
to ignite the separate parts of the grain element at different
times.
30. A method of generating a gas comprising: positioning a
plurality of gas producing grains having end portions and having at
least two grains positioned with respect to each other to provide a
channel between the two grains for gas movement from an end portion
of a grain to the other end portion of the grain; and igniting at
least one of the grains to produce gas from the grain and allowing
the gas to enter the channel.
31. The method of claim 30 wherein the step of igniting at least
one of the grains is igniting a first grain, and further including
the step of igniting a second grain after igniting the first grain
where the second grain is smaller than the first grain.
32. A method of producing a gas comprising: arranging a plurality
of grains so that there are at least two grains shaped and oriented
in such a way that they are symmetrical with respect to each other
about a line; and igniting the symmetrical grains in such a way
that they are consumed in a manner that is substantially
symmetrical with respect to the line.
33. The method of claim 32 wherein a step of arranging includes the
step of arranging a plurality of grains in pairs wherein the grains
in each pair are substantially symmetrical with respect reach
other.
34. The method of claim 33 wherein the step of igniting includes
the step of igniting the grains only in pairs.
35. The method of claim 32 wherein the at least two grains are
ignited simultaneously.
36. The method of claim 35 wherein the step of igniting the at
least two grains simultaneously includes the step of igniting the
at least two grains simultaneously at two different points on each
grain.
37. The method of claim 32 wherein the step of arranging includes
the step of arranging a pair of grains different in at least one of
size and shape from the at least two grains, and wherein the step
of igniting includes the step of igniting the at least two grains
before igniting the pair of grains.
38. The method of claim 32 wherein the step of arranging the at
least two grains includes the step of arranging the at least two
grains so that they extend from respective first end portions to
respective second end portions and wherein the at least two grains
are arranged so as to provide a channel between the first and
second end portions of at least one grain.
39. A method of producing a gas comprising: arranging at least one
grain for producing a gas within an enclosure and including
ignition elements associated with the grain; and initiating burning
of the grain at a point on a surface of the grain and at a point
interior to the grain.
40. The method of claim 39 wherein the step of arranging the at
least one grain includes the step of arranging a first grain and a
second grain within the enclosure and the step of initiating
burning includes the step of initiating burning of the second grain
before the first grain at only a single ignition point on the
second grain.
41. A method of producing a gas comprising: arranging first and
second grains so as to be symmetrical with respect to each other in
a first pair of grains and arranging third and fourth grains so as
to be symmetrical with respect to each other in a second pair of
grains and arranging the grains in the first and second pairs so as
to provide a passage between the grains; and igniting the first
pair of grains before igniting second pair of grains.
42. The method of claim 41 wherein the step of arranging includes
the step of arranging the first and second grains where the first
and second grains are larger than the grains in the second pair of
grains, and wherein the step of igniting the first pair of grains
includes the step of igniting the first pair of grains at only one
point on each of the grains, the grains in the second pair of
grains are ignited at more than one point on each of the grains and
wherein the grains in the second pair of grains are ignited at
opposite ends of each of the grains.
Description
BACKGROUND OF THE INVENTIONS
[0001] 1. Field
[0002] These relate to gas generators, for example solid propellant
gas generators, including those used to supply warm-gas and hot-gas
thruster valves. Other examples include inflation devices,
including air bags and the like.
[0003] 2. Related Art
[0004] Solid propellant gas generators are used in rocket, missile,
interceptor and other space vehicle flight control systems, among
other applications. One or more solid propellant masses, such as
grains, rods or other structures, are included in a pressure vessel
or other structure having one or more openings. The openings lead
to a rocket motor and/or reaction jets that vary the thrust, pitch,
yaw, roll or spin rate and other dynamic characteristics of a
vehicle in flight. Once a given propellant mass is ignited,
combustion or consumption of the fuel typically cannot be stopped,
and the entire mass is eventually consumed. Assembly of several
discrete masses of solid propellant permits greater flexibility in
controlling the vehicle, but each must be constructed separately
with its own discrete ignition source or other means for starting
combustion and assembled into the vehicle.
[0005] Propellant grains are constructed as single-burn grains,
layered grains, spiral grains or concentric ring grains. Layered
grains and concentric ring grains can be multiple pulse or
sequenced ignition grains. Multiple pulse grains extend capability
on certain missions, for example for interceptors, by allowing a
moderate early thrust, a low-level sustain or mid-range thrust, and
a high-end-game thrust. However, some multiple pulse grains may
require ignition in a fixed sequence or taking into account a
specific geometric configuration, such as require burning from
inside out.
SUMMARY OF THE INVENTIONS
[0006] Propellant grains, solid propellant gas generators, and
similar structures, including those for use in missiles,
gas-generators and thruster valves, can be improved with new
configurations and new methods of operation. The apparatus and
methods can be used to maintain a substantially constant center of
gravity in the generator during operation, and they can provide
flexibility in ignition and pressure versus time characteristics
developed during operation. While a number of benefits can be
provided through these apparatus and methods, one or more
significant benefits can still be achieved without adopting every
one of the improvements or without following all the steps of the
various procedures discussed herein. Additionally, various aspects
of the apparatus and methods can be implemented in a number of
combinations while still achieving significant benefits.
[0007] In one example described herein, a gas propellant grain
assembly is provided with at least two pie-shaped grain segments
positioned on opposite sides of a line, for example a center line
or center axis. The grain segments are spaced apart from each other
to provide a channel or passage way axially from end-to-end so that
gas produced by consumption of a grain segment can flow in the
channel. Where the two pie-shaped grain segments are approximately
the same size and substantially symmetrical with respect to each
other on each side of the center line, simultaneous ignition of the
grain segments helps to maintain a substantially constant center
gravity for the assembly, namely the center of gravity remains on
the centerline of the propulsion system. In this context, "constant
center of gravity" is taken to mean that the center of gravity
remains on the centerline of the propulsion system.
[0008] Pie-shaped grain segments can be assembled in pairs, and
where segments in a pair are ignited simultaneously, constant
center of gravity can be more easily maintained. Where the grain
segments in one pair are different from those in another pair, for
example different in size and/or shape, different in burn rate, or
different in gas production, those differences can be used
selectively to produce a desired pressure versus time profile for
the assembly. The profile can then be used to operate the assembly
as desired, for example moderate early thrust, low-level sustained
thrust and high end thrust.
[0009] Selectivity can also be provided through the configuration
and use of igniters or initiators. Grain segments within a pair are
typically configured with igniters identically, and the pressure
versus time profile through ignition of a given pair can be
selected to produce the desired result. For example, each grain
segment in a pair can have igniters or initiators on multiple
surfaces, and the number of surfaces ignited can be selected based
on the desired pressure versus time profile. In several specific
examples, each grain in a pair can have igniters on opposite end
surfaces, or interior to the grain segment. The pressure produced
as a function of time increases when more surfaces or parts of the
grain segment are ignited at the same time.
[0010] In another example, an assembly includes pairs of grain
segments wherein each grain in the pair is substantially similar to
the other. Igniter leads extend from an ignition source and are
coupled to respective grain segments so that the grain segments can
be ignited simultaneously. The grains in each pair are preferably
oriented symmetrically with respect to each other, and the igniter
configuration for the grains in each pair are preferably identical,
or at least symmetrical as well, or they can be ignited in such a
way that the burns in opposite grains are symmetrical. The grains
in one pair may be configured differently from the grains in
another pair, for example in size, shape or other characteristic
allowing a different burn result. In one aspect of this example, a
passage way extends between fore and aft portions of the grains so
gas produced can flow in the passage way. Therefore, if a pair of
grains are ignited at both ends, the gas produced at each end can
be applied to valves at one end, as desired. Additionally, if a
pair of grains are ignited at interior portions thereof, the gas
produced thereby can be applied to more than one set of valves.
[0011] Ignition sequence and application (whether one, two or more
ignition points for each grain) can be controlled by a controller,
for example as part of a vehicle guidance and navigation control.
The ignition configuration can then be determined in real-time if
desired, and modified as circumstances change. More degrees of
freedom are provided with more ignition points and with a larger
number of discrete grain segments, for example discrete grain
pairs. The grain pairs can be all the same size and shape, or
different sizes and shapes. For example, two grain pairs configured
to produce the same output as a single pair of grains can be
simultaneously ignited to produce the same result as ignition of
the single pair of grains, but the controller has the flexibility
of igniting the two pairs separately or igniting the two pairs
separately or at different ignition points or at different
times.
[0012] In a further example of a gas producing assembly, first and
second grain elements are positioned apart from each other and the
first grain element has a first size and shape and the second grain
element has a second size and shape substantially similar to the
first. A passage way or channel extends between ends of the first
and second grain elements. In one example, the passage way is
between the grains so that gas produced from the grains can enter
the passage way. Preferably, the grains are symmetrical with
respect to each other, and may be pie-shaped. The tube or other
cylindrical element may extend between the grains and may form the
passage way. Additional pairs of grain elements may also be
included, preferably where the grain elements in each pair are
oriented substantially symmetrically with respect to each other.
The additional pairs may include grain elements that are
substantially the same in size and shape to the first and second
grain elements, or they may be different. Igniter elements can be
positioned as desired, for giving the desired flexibility in
igniting the grains. Ignition of the grain elements can be
controlled by a controller, for selectively igniting the grains to
produce a desired effect.
[0013] In a further example of a gas producing assembly, a gas
producing grain includes first and second surfaces facing in
different directions with respect to each other. Igniter elements
are applied to the surfaces for igniting the grain, either
simultaneously or selectively as desired. The igniter elements can
be applied to end surfaces, facing in opposite directions, and/or
applied to adjacent surfaces, for example facing approximately
perpendicular to each other. Igniter elements can also be applied
to interior portions of the grain, for example, to change the
characteristics of the burn. The same or similar configurations can
also be applied to other grains in the assembly, which may provide
greater selectivity in producing a desired effect. For example,
where grains are arranged in oppositely arranged pairs, the grains
in each pair can have the same igniter configuration, and can be
ignited in the same way simultaneously, making it easier to
maintain a constant center of gravity.
[0014] In a system for producing gas selectively, for example to
produce a desired pressure and time profile, a gas-producing grain
element can include first and second ignition elements controlled
by a control system for selectively igniting the grain element at
one or more parts of the grain element. Where grain elements are
arranged in symmetrical pairs and ignited in symmetrical pairs, a
constant center of gravity may be more easily maintained. With a
number of pairs of grain elements, the control system has greater
flexibility in producing the desired burn characteristic. Greater
flexibility is also provided through multiple igniter elements
applied to discretely different surfaces on a grain or grain pair.
Igniting a grain at a larger number of discrete surfaces produces a
larger pressure versus time profile. Greater flexibility can be
further provided through different-sized grains or grain pairs,
allowing the system to select the sequence in which the surfaces on
a given grain are ignited and the sequence in which the grain pairs
are ignited.
[0015] Various steps or methods can be followed to produce the
desired effects. For example, where one or more grains are provided
with a channel extending between opposite ends of the grain, either
or both ends of the grain can be ignited and still have gas
available to valves at either or both ends. The channel allows
greater flexibility in locating igniter elements on the grains and
selecting which locations on the grain are to be ignited. For
example, a pair of symmetrical grains can be arranged on each side
of a channel with one or more igniter elements on each grain. Where
the grains have igniter elements on each end, both ends can be
ignited at the same time, if desired. Where the grains have igniter
elements on each end and at an interior area of the grain, a
controller can decide which igniter elements to trigger.
[0016] In another example of a process for producing a gas, a
plurality of grains can be arranged so that there is at least a
pair of grains symmetrical with respect to each other and the
symmetrical grains are ignited or consumed in a manner to keep a
constant center gravity for the arrangement. For example, the pair
of grains can be ignited so the grains are consumed at the same
rate, such as being ignited at the same locations on the respective
grains. Where multiple pairs of grains are ignited, they are
preferably ignited so as to maintain a constant center of
gravity.
[0017] In a further example of a process for producing a gas, at
least one gas producing grain is provided within an enclosure and
wherein the grain is ignited at discretely different locations
substantially simultaneously. In one configuration, opposite ends
of the grain can be ignited simultaneously, and where there is
fluid communication between the two ends, the gas produced can be
applied to valves at either or both ends. In another configuration,
the grain can be ignited at an interior location, typically in
conjunction with ignition at other points on the grain. Multiple
ignition points increase the consumption rate and the pressure
versus time profile.
[0018] These and other examples are set forth more fully below in
conjunction with drawings, a brief description of which
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a side and partial cross-sectional view and
partial schematic of a gas producing canister assembly for use with
the present embodiments.
[0020] FIG. 2 is a schematic of the end of a grain assembly for use
in the gas producing assembly of FIG. 1.
[0021] FIG. 3 is a schematic view of a canister assembly similar to
that of FIG. 1 showing fore and aft plenums and a grain assembly
between.
[0022] FIG. 4 is a longitudinal section view of one end portion of
the canister assembly of FIG. 1 with a thruster valve assembly.
[0023] FIG. 4A is a schematic of an end view of the grain assembly
of FIG. 4.
[0024] FIG. 4B is an isometric view of a fore end of the grain
assembly of FIG. 1.
[0025] FIG. 5 is a flow chart showing a possible control scheme for
controlling the ignition of the grains in the grain assembly.
[0026] FIG. 6 is a graphic illustration of the burn pressure and
motor thrust as a function of time for a possible ignition
sequence.
[0027] FIGS. 7A-E are schematic representations of an example of an
ignition configuration and pressure versus time profile for a two
pair grain assembly.
[0028] FIGS. 8A-E are schematic representations of an example of an
ignition configuration and pressure versus time profile for a three
pair grain assembly.
[0029] FIGS. 9A-E are schematic representations of an example of an
ignition configuration and pressure versus time profile for a four
pair grain assembly.
[0030] FIGS. 10A-E are schematic representations of another example
of an ignition configuration and pressure versus time profile for a
four pair grain assembly.
[0031] FIGS. 11A-E are schematic representations of another example
of an ignition configuration and pressure versus time profile for a
two pair grain assembly.
[0032] FIGS. 12A-F are schematic representations of another example
of an ignition configuration and pressure versus time profile for a
two pair grain assembly.
DETAILED DESCRIPTION
[0033] The following specification taken in conjunction with the
drawings sets forth the preferred embodiments of the present
inventions in such a manner that any person skilled in the art can
make and use the inventions. The embodiments of the inventions
disclosed herein are the best modes contemplated by the inventor
for carrying out the inventions in a commercial environment,
although it should be understood that various modifications can be
accomplished within the parameters of the present inventions.
[0034] Gas producers take a number of configurations and have a
number of applications. One application is providing propellant for
rockets, missiles and other flight and space vehicles, and the
examples given herein will be directed to those types of
applications. However, it should be understood that the examples
described herein apply to a number of apparatus and configurations
used for producing gas, whether as a propellant, for inflation, or
otherwise. Therefore, the discussion herein is not limited to any
particular application. Additionally, the examples given herein are
a small number of applications to which these inventions can be
applied, and it should be understood that other examples and other
applications can be made without departing from the inventions.
[0035] More than one invention is discussed herein and each has
benefits that can be derived from using the inventions. However, it
should be understood that not all aspects of each invention need to
be used to take advantage of one or more of the benefits provided
by these inventions. Some applications may achieve a significant
benefit without adopting all of the aspects and features described
herein.
[0036] In one example of a housing for a gas producing assembly 100
(FIGS. 1-3), a pressure vessel in the form of a canister 102
typically includes a cylindrical wall 104 sized in diameter to
suitably fit within an appropriate vehicle. The cylindrical wall
104 includes a fore end wall 106 converging to a forward polar boss
108. The use of the terms "fore" and "aft" with respect to the
assembly are used solely as a point of reference for the structures
depicted in the drawings, and are not limiting as to particular
types of structures to which those terms are applied. However, in
the context of a vehicle in which these assemblies may be used,
these terms are used as an indication of their anticipated
orientation once in place in the vehicle. In the context of other
applications, other terms may be used to refer to the same parts of
the assembly without connoting direction or orientation. As
depicted in FIG. 1, the fore end wall 106 is substantially the same
as the opposite wall on the right side of the drawing, and the two
ends can be interchangeable in the example shown in FIG. 1 until
the assembly 100 is configured to be mounted to output valves, for
example. For purposes of the present discussion, it will be assumed
hereafter that the polar boss 108 is to be coupled to a valve
assembly 108a; for example divert thrusters of a vehicle and their
respective nozzles (shown schematically in FIG. 4).
[0037] The valve assembly is fed by a manifold attached to an exit
duct, in the form of the polar boss 108. O-rings 108b and 108c or
other seals prevent leakage in the area of the polar boss and the
corresponding manifold.
[0038] The cylindrical wall 104 includes an aft end wall 110
converging to an aft polar boss 112 (FIG. 1). The aft polar boss
112 is connected through a manifold (not shown) to an attitude
control system and corresponding attitude control valves, as is
known to those skilled in the art. Corresponding O-rings or other
seals are included to prevent leakage between the aft polar boss
112 and its manifold and the attitude control system. In an
alternative configuration, the aft polar boss 112 can be omitted in
favor of a single output. The canister is a carbon fiber reinforced
resin shell wrapped about the grain assembly, described below.
[0039] An insulating layer 114 extends from the fore polar boss 108
to the aft polar boss 112. Each end of the insulating layer is
integrated with the respective polar boss structure, and the
insulating layer intermediate the ends has the same contour as the
canister wall around it.
[0040] A gas propellant assembly may include one or more discrete
propellant segments or elements, shown in one example in FIG. 2 as
substantially pie-shaped elements including a first grain 116, a
second grain 118, a third grain 120, a fourth grain 122, a fifth
grain 124 and a sixth grain 126 in the illustration. The grains are
substantially pie-shaped except for a center opening area 128
extending longitudinally the length of the grains and concentric
with a center axis 130 (FIGS. 1-2). Each grain can take a number of
sizes, shapes, orientations and configurations, but in the examples
described, each grain is shown as having a pie-shape and each grain
is shown as having the same length as all of the other grains.
While all of the grains can be formed to have the same size, the
example of the grain assembly 132 shown in FIG. 2 has grains of two
different sizes for purposes of illustration. The grains can also
be formed to be all different sizes or to have some of the grains
the same size and other grains different sizes. Additionally,
grains can be formed with various and different propellant
formulations. Formulations can provide low pressure slow burns,
high pressure fast burns or burns in between, as desired. However,
a preferred example has the grains in a given pair being consumed
in such a way as to help to maintain a constant center of
gravity.
[0041] There are also other factors that may be considered in
determining grain configuration, as may be seen by considering
common equations used in gas generators. As reflected in those
equations, the pressure can be considered by equating the generated
mass flow rate (Eq. 1) and the exhaust mass flow rate (Eq. 2), as
follows:
Mdot=(P/P.sub.0).sup.n*r.sub.b0*As*.rho..sub.s (Eq. 1)
[0042] where
[0043] P=pressure
[0044] P.sub.0=reference pressure (typically, 1000 psia)
[0045] r.sub.b0=reference burnrate at P=P0
[0046] As=burning surface area
[0047] n=pressure exponent
[0048] .rho..sub.s=propellant solid density
[0049] and
Mdot=P*Ae*K/{square root}T (Eq. 2)
[0050] where
[0051] Ae=exit (exhaust) area
[0052] K=gas flow constant
[0053] T=gas burn temperature.
[0054] By equating both flowrates, the steady pressure P is:
P=((r.sub.b0*As*.rho..sub.s*{square root}T)/(Ae*K)).sup.(1/(1-n))
(Eq. 3).
[0055] Therefore, among others, additional factors that may be
considered when selecting a grain configuration include the burn
rate, burning surface area, and the exhaust gas exit area. These
factors may be used by a design team to select the grain
configuration to suit the desired function or result.
[0056] A gas propellant grain assembly may be formed by at least
one grain element 133 having a first side portion in the form of a
fore end 134 (FIG. 2A) and a second side 136 facing in different
directions from each other. The second side 136, in the form of the
grain shown in FIG. 2A, is one side of the pie-shaped grain or
wedge shape, and the grain may include another wedge side 138 also
facing a different direction than the fore end 134. The grain
element 133 has an inner portion or side 140 also facing in a
direction different from the fore end 134, and an outer surface
142, also facing in a direction different from the fore end 134.
The grain element 133 includes an aft end 144 likewise facing a
direction different from fore end 134.
[0057] The gas propellant grain assembly shown in FIG. 2A also
includes a first igniter element or initiator 146 adjacent and
preferably in secure contact with the fore end 134 and a second
igniter element 148 adjacent and preferably in secure contact with
the aft end 144. The igniter elements can be used to selectively
ignite the grain at one or both surfaces of the grain. The
selection of which surface to ignite and whether to ignite both
surfaces simultaneously or sequentially can be made under the
control of a suitable processor or controller. In the configuration
shown in FIG. 2A, the igniter elements are placed on oppositely
facing surfaces of the grain. However, the igniter element 148 can
also be placed on one or more of the other surfaces, as desired. It
should be noted, however, that use of an igniter element on the
outer surface 142 is generally not desirable where the outer
surface 142 would be bonded, adhered to or otherwise fixed to the
insulating layer 114, which in turn is fixed relative to the
canister 104. Igniting the outer surface 142 may lead to loosening
of the grain element 133 relative to the pressure vessel in which
it is contained. Additionally, igniting of opposite surfaces tends
toward symmetrical consumption of the grain relative to a midpoint
between the two opposite surfaces.
[0058] Instead of or in addition to one of the igniter elements 146
and 148, an igniter element 150 may extend into an interior portion
of the grain 133. "Interior" in the present context refers to a
location between surfaces, for example a location between the end
surfaces. Where the igniter element 150 is interior to all of the
surfaces 134, 136, 138, 140, 142 and 144, the igniter element 150
would most likely enter through an opening, for example a slot, in
the grain structure, formed for example when the grain is formed.
The slot preferably includes an opening facing the curved surface
140. In this context of an igniter lead on an interior portion of
the grain, the grain is still considered a grain element or grain
segment when the portions of the grain on each side of the slot and
igniter element 150 are connected to each other by burnable grain
material. By applying an ignition pulse to the interior igniter
element 150, combustion of the grain can proceed more quickly,
producing a larger propulsion magnitude as a function of time.
Placement of the interior igniter element 150 is preferably made so
as to encourage relatively symmetrical consumption of the grain
while minimizing the possibility of separation of the grain from
the insulating layer or from the canister 104.
[0059] The grain assembly can also include a control system or
controller 152 (FIG. 2A) for controlling each of the igniter
elements. The controller would be positioned within the vehicle as
desired, in accordance with conventional practices. The controller
is programmed to send ignition pulses to one or more of the igniter
elements in accordance with a predetermined sequence or schedule.
Alternatively or additionally, the controller may be programmed to
acquire data on a real-time basis and ignite one or more of the
igniter elements according to criteria stored in the control system
or communicated to it externally. The extent to which the ignition
mode is predetermined or determined in real-time may depend on the
mission, purpose or assignment for the vehicle.
[0060] The grain 133 is preferably a solid propellant grain. It is
cast into an insulated and inhibited mold in accordance with
procedures known to those skilled in the art. Igniters are embedded
between the grain and respective peel-away inhibiting covers at the
desired locations. The inhibiting layer at other locations are
bonded to the respective grain segment. The shape of the grain can
be formed so as to provide a passage way between the fore and aft
ends 134 and 144, respectively, so that propellant gas may flow in
the passage way. In the grain 133 shown in FIG. 2A, the inner
surface 140 may be formed concave to form the passage way. Other
forms may be used to form the passage way. Formation of the passage
way may depend on the shape of the grain in combination with the
shape of the pressure vessel the grain is placed in. Alternatively,
the passage way may be formed through the shape of the grain (or
several grains where more than one grain is used) without regard to
the shape of the pressure vessel.
[0061] While a gas producing assembly may be formed from a single
grain, such as that having the characteristics described with
respect to the grain 133 of FIG. 2A, assemblies having more than
one grain are used also. An assembly having two grains will be
described for purposes of illustration in the context of FIG. 2,
formed from the first grain 116 and the second grain 118. Each of
the grains will be considered to have one or more of the
characteristics described previously with respect to the grain 133,
the characteristics to be selected as desired. Additionally, the
characteristics selected with respect to the first grain 116 are
preferably the same as, though need not be, the characteristics
selected with respect to the second grain 118. The characteristics
of the two grains may be selected to be identical, for example to
help in maintaining a constant center gravity if the grains are
ignited simultaneously and at complementary locations. However, it
should be understood that the grains can be configured otherwise if
constant center gravity is not a significant concern.
[0062] A gas producing assembly may include a first grain 116 and a
second grain 118 having surfaces such as inner surfaces 154 and
156, respectively, spaced apart from each other. In the example
shown in FIG. 2, the first and second grains and their inner
surfaces are spaced apart from each other on opposite sides of the
center line 130 and form part of the opening 128 forming a passage
way extending axially concentric with the center line 130. The
first and second grains are shown in FIG. 2 as being separated from
each other by the third, fourth, fifth and sixth grains, but in the
present example the first and second grains are considered as
substantially semi circular grain portions bonded together to form
a two-piece pie-segmented cylinder with a passage way extending
between them centered on the center line 130 between the fore and
aft ends. In this configuration, the first and second grains 116
and 118, respectively, are substantially similar in cross-section
and are preferably substantially similar in length. In this form,
the first and second grains are substantially symmetrical with
respect to each other, and they are shaped and positioned so as to
be substantial mirror images of each other with respect to a plane
separating the two. Each of the grains also preferably has the same
number and configurations of igniter elements so that the grain
assembly is formed from a pair of substantially identical
pie-shaped grain elements that are symmetrical with respect to each
other. The first and second grains each include respective bonded
layers and peel-away inhibitor layers, as necessary (as do all of
the grain elements described herein), and they are covered with an
insulating layer, with their outside surfaces bonded to the
insulating layer so as to support the grains within the pressure
vessel. Upon ignition, the propellant gas may enter the passage way
128 and be applied to valve assemblies as desired.
[0063] In the configuration of the gas producing assembly just
described with first and second grains 116 and 118, respectively,
the grain assembly is formed from two substantially similar grains.
Upon ignition, they are preferably consumed as a pair, preferably
maintaining a constant center of gravity, for example by applying
ignition pulses at identical locations on the grains in the pair. A
suitable controller selects which of the surfaces or grain portions
are ignited.
[0064] In another configuration of a gas producing assembly, the
assembly may include the first pair and a second pair of grain
elements formed from the third and fourth grains 120 and 122,
respectively. In this configuration, each grain is selected to
include one or more of the characteristics of the individual grain
133 described above with respect to FIG. 2A. Each grain is also
preferably formed in the same way. The third and fourth grains 120
and 122 have surfaces, such as inner surfaces 158 and 116 spaced
apart from each other on each side of the center line 130 so they
form part of the passage way defined by the opening 128. The grains
in the first and second pairs are bonded together to form a
pie-segmented cylinder with grains in each pair oriented opposite
each other relative to the center line 130, and with the grains in
each pair preferably substantially similar to each other. While the
grains in the second pair may have a length different from each
other and from the length of the grains in the first pair, the
example of this configuration of a gas producing assembly has the
lengths of the grains in both pairs identical to each other. While
the grains in the second pair can be the same size as the grains in
the first pair (see, for example, the configurations shown in FIGS.
7A-7E and 11A-11E), the third and fourth grains 120 and 122,
respectively, are preferably a different size, for example having a
shorter arc length, compared to the grains in the first pair (see,
for example, the configurations shown in FIGS. 12A-12F). Having
grain pairs of different sizes allow a controller to selectively
ignite grain pairs to produce a desired pressure versus time
profile. Likewise, the ignited surfaces on the grains within a
given grain pair may also be used to determine the output profile
for the grain assembly. The grains in the first and second pairs
are covered with an insulating layer, with their outside surfaces
bonded to the insulating layer so as to support the grains within
the pressure vessel. Upon ignition, the grains in each pair are
preferably consumed together, at the same rate, as determined by
the application of the ignition pulses by a controller (as well as
the makeup of the grain), while ignition of one pair does not cause
ignition of the other pair.
[0065] Grain segments within a pair, or grains from one pair to the
next may be formed from different materials or molded in ways
different from each other so as to produce a different pressure
versus time profile. Consequently, a controller can select the
grain segments or the grain pairs based on their makeup to provide
the desired output. However, it will be assumed for present
purposes of illustration that the grain segments in each pair, and
the pairs of grain segments from one pair to the next have the same
chemical composition or propellant formulation.
[0066] In a further configuration of a gas producing assembly, the
assembly may include the first and second pairs of grain segments
formed from the first, second, third and fourth grains 116, 118,
120 and 122, respectively, as well as a third pair of grain
segments comprised of grain segments 124 and 126 (FIG. 2). In this
configuration, like those described before, each grain is selected
to include one or more of the characteristics of the individual
grain 133 described with respect to FIG. 2A. The grains are also
preferably formed in the same way. The fifth and sixth grains are
preferably symmetrical with respect to each other about the center
line 130, and include inner surfaces 162 and 164 spaced apart from
each other on each side of the center line 130 to form part of the
passage way defined by the opening 128 along with the inner
surfaces of the other grain segments. The grains in the third pair
of grains as shown in FIG. 2 have substantially the same shape as
the second pair of grains, and in this example, have substantially
the same length as the other grains in the assembly. However, the
third pair grains may have a different size, length, shape or other
characteristics so that consumption of the grain produces a
different result compared to consumption of the other grains. The
grains in the first, second and third pairs are bonded together to
form a pie-segmented cylinder with grains in each pair oriented
opposite each other relative to the center line 130. As before,
having grain pairs of different sizes allow a controller to
selectively ignite grain pairs to produce a desired pressure versus
time profile. Similarly, selecting surfaces on the grain pairs to
be ignited may also be used to determine the output profile for the
grain assembly.
[0067] The grains of the first, second and third pairs are covered
with an insulating layer, with their outside surfaces bonded to the
insulating layer so as to support to grains within the pressure
vessel. Upon ignition, the grains in a given pair are preferably
consumed together, at the same rate, as determined by the
application of the ignition pulses.
[0068] A given grain assembly may be formed about a tube 166 (FIG.
3) extending along the passage way formed by the inner surfaces of
the grain segments. The tube 166 forms a channel along with the
polar bosses 108 and 112, so that gas produced from any portion of
the grain segments can be applied to the valve assemblies at either
end through either the fore plenum 168 or the aft plenum 170. Where
a single polar boss is used, for example only fore end polar boss
108, gas generated through ignition at or near the aft end reaches
the polar boss 108 through the tube 166, for example through
openings therein. The tube may be formed from a high temperature
phenolic, and may include reinforcement such as carbon fiber
reinforcement. The tube forms part of each polar boss, provides a
gas flow path between fore and aft burning surfaces and it carries
igniter leads embedded in its wall, as shown in FIG. 4.
[0069] If desired, the tube 166 supports the grains interiorly. In
one example, the interior surfaces of each grain (once they are
covered with their respective inhibitor layers), such as inner
surfaces 154, 156, 158, 160, 162 and 164 (FIG. 2) are bonded to the
respective adjacent surface portions of the tube 166. The bonding
is done in substantially the same way that the perimeter surfaces
of the grain inhibitor covers are bonded to the outer insulation of
the pressure vessel.
[0070] Solid propellant grains are cast into insulated and
inhibited molds, and the segments are then bonded together to form
a pie-segmented cylinder. Bonding and inhibiting material 171
extends between each of the pie segments, between each pie segment
and the tube 166 and around the perimeter surface of each pie
segment. One or more igniter leads 172 extend from a respective
igniter 174 embedded between the grain and its inhibiting cover
174A at the fore end, as shown in FIG. 4, and/or at the aft end
(not shown). The igniter leads 172 extend from the grain
substantially radially inward to the tube 166 and inboard of the
respective polar boss 108. The igniter leads are embedded in the
tube and exit through a wire pass-through 175. The leads then
extend axially forward to be coupled to a suitable control system,
for example control system 152 described with respect to FIG.
2A.
[0071] If igniter leads are embedded in the aft end surfaces, they
may be embedded in the tube and exit out the aft polar boss and
extend to the control system. If there is no aft polar boss or
exit, the aft igniter leads may extend through the tube to the
forward end. Igniter leads could also be routed to the grains to
allow mid-section burning, and suitable openings would be formed in
the tube 166 to allow the gas to enter the tube. Igniter leads can
also be routed along the canister wall, inside the carbon fiber
envelope (referenced below) and outside the insulation layer (also
referenced below). Such case wiring with the outer disposed igniter
leads can exit through their own separate electrical connector boss
adjacent or around the polar boss or in the area of the plenum.
[0072] In the example of the assembly shown in FIG. 4, the igniter
leads 172 are imbedded in the tube 166 during fabrication or
forming of the tube 166 so as to exit the tube radially. In the
preferred form, each igniter 174 on a given grain includes its own
igniter lead 172 separately and individually controllable through
the controller 152. As depicted in FIG. 4B, where part of the fore
end of the tube 166 is removed, each of the individual igniter
leads is shown. Leads 172A and 172B are coupled to grain 120 and
leads 172C and 172D are coupled to grain 124, etc. Each of the
igniter leads are preferably coupled to respective switches or an
appropriate switch or control array in the controller in such a way
that the leads can be independently and separately energized or
triggered as determined by the controller. With such a
configuration, each igniter in the assembly can be controlled
separately and ignited separately, both in terms of whether or not
the igniter will be energized and the timing of any such ignition.
Therefore, each of the igniters 172A-172L is preferably separately
controllable by the controller, allowing the controller to
separately control any ignition of any igniter on any point on a
grain, as well as the timing of any such ignition.
[0073] Openings 176 (FIG. 4) extend radially through the side walls
of the tube and/or polar boss 108 at the fore end of the tube to
allow gas flow from the grain surface into the center of the tube
and out any exit to which the tube is connected. Preferably the
openings are uniformly distributed about the tube and are sized to
allow unrestricted gas flow.
[0074] The grain assembly or bonded cylinder is then covered with
an insulating layer 178 and then encased within the generator case
180. The generator case 180 is a wrap of carbon fiber and resin
bonded to the insulating layer 178 and to the tube and polar boss
combination outboard of the openings 176 to the forward end 182 of
the polar boss 108. The generator case 180 is also bonded to the
aft tube portion and polar boss. Thruster valve assemblies are
attached to the tube and polar bosses outboard of the lead exits.
O-rings or other seals around the polar bosses guard against
pressure leakage. The valve assemblies can be tied together about
the canister or to lugs formed on the canister to help stabilize
the valve assemblies against the thrust developed in the gas
generator. Each gas exit may include a sonic choke feature to guard
against the effects of manifold back-pressure.
[0075] Assemblies incorporating the concepts represented by the
foregoing examples provide greater flexibility and options for
vehicles and other systems in which these assemblies can be used.
They can provide greater flexibility and selectability in ignition
sequences and/or ignition locations and in propulsion profiles, as
illustrated below. Advantages are available by relying on symmetry
in grain geometries, igniter locations, the igniters fired, the
sequences of ignition as well as other grain
characteristics/configurations. Grain assemblies can be more
reliably supported, and ignition profiles can be tailored to
maintain a relatively constant center of gravity in the
assembly.
[0076] A controller or other means for determining the timing and
sequencing and location of grain ignition, such as controller 152,
can be used to give the desired level of flexibility and control
over operation of the gas producing assembly. Hardware and
algorithms or firmware can be incorporated into the controller as
desired to give the desired level of control.
[0077] As an example of steps that can be followed in a controller
for operating a gas producer such as those discussed herein,
possible steps are depicted in FIG. 5. Once the assembly is
initiated, started or armed, either separately or as part of an
overall system of which the gas producer is a part, the controller
may undergo a system check 184, including incoming data
connections, sensor testing, and the like. Once all systems are
operational, the controller will continue checking for incoming
data or instructions, and upon receipt of an ignition signal 186,
the controller can evaluate using the algorithms and data available
to it and select a grain pair and ignition point configuration 188
for producing the desired gas production and pressure versus time
profile. In the case of a launch of a vehicle, the ignition
sequence may be predetermined to make the requirements of
separating the vehicle from the launch system, protecting
surrounding structures, minimizing detectable gas trails, or the
like. In other situations, the ignition sequence may be determined
as a function of incoming data from sensors, master controllers or
other sources.
[0078] Based on control signals from the controller, the first
grain pair is ignited 190, through hot gas pressure from an
igniter, and ignition of the grain segment causes the inhibiting
cover to split and peel back, allowing gas to escape from the grain
pair. For example, a medium-sized grain pair can be ignited to
start a mission, producing a medium gas pressure with productive
divert maneuvering in the early stages of the deployment. As shown
in FIG. 6, ignition of a first grain pair can produce a first
thrust profile 192 having a relatively uniform pressure that may
last an extended period, for example approximately 20 seconds.
Other initial ignition schemes are also possible. While the
discussion focuses on igniting grain pairs as examples, it should
be understood that grains can be ignited in a number of
configurations and combinations. In the present examples, grains
are ignited in symmetric pairs to help in maintaining a constant
center of gravity for the gas producing assembly.
[0079] With successful ignition of the first grain pair, the
controller evaluates the target configuration and time of flight
194 (FIG. 5), for example by receiving information about the target
speed, acceleration, direction or vector, and by evaluating the
elapsed time from the first ignition. On this basis, the controller
can select the next grain pair and their ignition points to achieve
the desired propulsion or pressure versus time curve for the next
stage. Information about the available grain pairs, their ignition
configurations and their gas producing characteristics can be
maintained in a database, lookup table or other suitable
information area for use by the controller. The configuration of
this information may be determined as a function of the vehicle
type, missions for which the vehicle is designed, and the like.
[0080] Based on the outcome reached by the controller, a second
grain pair is ignited 196, for example to produce a sustained
thrust 198 (FIG. 6), for example for another 20 seconds. Upon
successful ignition, the controller may continue to evaluate the
target configuration, the estimated time to intercept and the
elapsed time of flight 200. Based on that evaluation, the
controller continues selecting grain pairs and ignition points for
ignition in the next phases of the vehicle operation. For example,
the controller may produce signals to the selected set of igniter
leads to ignite the next to last (N-1) grain pair for producing a
pulse 204 (FIG. 6) for high thrust and pressure. These grains may
have the greatest surface area and may be ignited from the largest
number of ignition points possible to produce maximum pressure and
thrust, even though for a shorter elapsed time. The process of
evaluation and grain selection continues 206 (FIG. 5), if and as
necessary, and grain pairs are ignited until the last grain pair
(Nth pair) is ignited 208.
[0081] Examples of steps 188-196 are depicted in FIGS. 7A-E, 11A-E
and 12A-F, showing ignition of two pairs of grains, where N=2. The
ignition configurations for the examples shown in FIGS. 7 and 11
are different while the grain sizes are substantially the same, and
the ignition configuration and the grain sizes in FIG. 12 are
different from the other examples. Examples of steps 188-202 are
depicted in FIGS. 8A-E showing ignition of three pairs of grains
with a given ignition configuration and where the second and third
grain pairs are the same size but different in size from the first
grain pair. In this example, N=3. Examples of steps 188-208 are
depicted in FIGS. 9-10, showing ignition of four pairs of grains,
where N=4. The first pair of grains is larger than the other pairs
of grains taken separately, and the other pairs of grains may be
different in size or similar in size. All of the grains in FIG. 10
are the same size as each other. The ignition configuration in FIG.
9 is different than the ignition configuration in FIG. 10. It will
be assumed for purposes of these examples that all of the grains
are substantially the same length, as represented by the grain
lengths in FIGS. 7B-12B, and have substantially the same chemical
composition, though other configurations of grain segments can be
used by changing the length and/or the chemical composition either
with or without others of the changes described herein. It is also
noted that both grains in a given pair are ignited simultaneously
at identical ignition locations with identical ignition
configurations. While other ignition configurations are possible,
non-symmetrical consumption of grain pairs may make difficult
maintaining a constant center gravity for the assembly. The grain
pairs of the examples of FIGS. 8-12 are also combined in such a way
as to provide a passage way or channel between them. The channel
provides an opening for gas to travel between the ends of the grain
pairs. Such a channel is useful if there is a single output for the
gas producer and both end surfaces of a grain are ignited, or where
gas produced at multiple locations of a grain are to be made
available at more than one output. However, other means may be
provided for allowing gas flow, if desired.
[0082] The grain and ignition configurations 210, 212 and 214 of
the example of FIG. 7 are depicted in FIGS. 7A, 7C and 7D, which
show that only the fore end surfaces are ignited, they are ignited
in sets of oppositely-facing or symmetrical pairs and that they are
ignited in sequence as opposed to simultaneously. The lower case
"f" in FIG. 7A indicates that the fore end surfaces are ignited for
both pairs. FIG. 7C depicts a representation that none of the aft
end surfaces are ignited. FIG. 7D illustrates the sequence of
ignition of the pairs of grains as well as the ignition surfaces.
Additionally, the second pair of grains is ignited before the first
pair of grains are consumed, as indicated in the pressure versus
time chart 216 depicted in FIG. 7E. It will be assumed for purposes
of this example that the grain compositions in each grain segment
are identical, that their lengths are substantially the same as
indicated in 218 of FIG. 7B, that their ignition lead
configurations are substantially the same, and that the other
aspects of the grain segments and their configurations are
otherwise substantially the same.
[0083] FIG. 7E is a schematic depiction of a pressure versus time
chart along the lines of the burn pressure and motor thrust chart
of FIG. 6. FIG. 7E depicts a moderate level of pressure for a
sustained length of time. The numeral "1" represents the thrust
attributable to simultaneous ignition of the first pair of grains.
Before the complete consumption of the first pair of grains, the
controller ignites the second pair of grains, the pressure for
which combines with the pressure produced from the gases resulting
from the combustion of the first pair of grains to provide a burst
of pressure for a given length of time, as indicated by the width
of the peak numbered "2".
[0084] The grain and ignition configurations 220, 222, and 224 of
the example of FIG. 8 are depicted in FIGS. 8A, 8C and 8D. These
schematics show that the fore end surfaces 1-3 of the grain pairs
are ignited, and that the aft end surfaces of the third pair ("3a")
of grains are ignited. Additionally, the example depicted in FIG.
8, like the other examples, show the grain segments are ignited in
symmetric pairs. FIGS. 8D and 8E show that the grain pairs are
ignited with a discrete delay between each ignition, and not
simultaneously. While the configuration of the ignition leads can
be different for the three pairs of grain segments, having a full
complement of ignition leads provides the most flexibility in
igniting the grain pairs. For example, even though the aft end
surfaces of two of the pairs are not ignited, igniter leads on the
aft end surfaces may be preferable to provide the controller with
greater flexibility in the ignition capabilities.
[0085] The pressure versus time chart 226 FIG. 8E depicts a
relatively high level pressure for a moderate length of time
developed through ignition of the first grain pair. As the first
grain pair approaches complete consumption, the controller ignites
the fore end surfaces of the second pair of grain segments, which
are smaller in size than the first pair. The second pair produces a
sustained level of pressure for a similar length of time, near the
end of which the controller ignites the fore and aft end surfaces
of the third grain pair. Even though the second and third pairs of
grains are substantially the same size, ignition of both ends of
the third pair of grains results in greater gas production over a
shorter period of time, thereby producing a high-pressure pulse.
From these FIG. 8, the effects of grain size and ignition
configuration can be seen in the resulting pressure versus time
profile.
[0086] The grain and ignition configurations 230, 232, and 234 of
the example of FIG. 9 are depicted in FIGS. 9A, 9C and 9D. Only the
fore end surfaces of the first grain pair, the largest of the four
grain pairs, are ignited, while both the fore and aft end surfaces
of the second, third and fourth grain pairs are ignited. The grain
pairs are ignited in a discrete sequence rather than any two pairs
being ignited simultaneously, and each of the second, third and
fourth pairs are ignited in their order before the first pair of
grains is consumed. While aft end leads for the first grain pair
are not required in this ignition sequence and configuration, and
interior ignition leads are not used on any of the grains,
including such leads provides greater flexibility for the
controller and the ignition configuration.
[0087] The pressure versus time chart 236 of FIG. 9E shows the gas
production from the first pair of grains has a moderate level and a
relatively sustained period of time, and the ignition of the second
pair of grains follows shortly after the ignition of the first
pair. The second pair is consumed well before ignition of the third
pair, so that gas produced from the second pair does not contribute
to thrust developed upon ignition of the third pair. Likewise,
ignition of the fourth pair receives no contribution from gas
produced through ignition of the third pair. However, pressure
produced from ignition of the first pair contributes to the
pressure and thrust developed through ignition of each of the other
pairs of grain segments.
[0088] FIGS. 10A, 10C and 10D show the grain and ignition
configurations 240, 242, and 244 of the example of FIG. 10, showing
that only the fore end surface portions of the first and third
grains are ignited, while both the fore and aft end surfaces are
ignited in the second and fourth pairs of grains. Here all of the
grains are approximately the same size and preferably have the same
ignition lead configuration, for flexibility for the controller.
The second pair of grains is ignited before complete consumption of
the first pair of grains, and ignition of both ends of the second
pair of grains results in faster consumption of the second pair. In
this example, a level of sustained pressure and a peak pressure are
provided with essentially identical pairs of grains by using
different ignition configurations. The first pair burns longer
because only one end surface of the grains was ignited, while the
grains in the second pair are consumed more quickly with a higher
pressure result when both ends are ignited simultaneously. Similar
comments apply to the geometric and ignition configurations of the
third and fourth grain pairs. It should also be noted that the
overall pressure versus time profile 246 of the example of FIG. 10
is similar to the pressure versus time profile created by the
ignition configuration created through the first, second and third
pairs of grains in FIG. 9. Therefore, similar results can be
obtained even though grain segments in the two examples may not be
the same, and the ignition configurations may not be the same.
[0089] The grain configurations 250, 252, and 254 of the example of
FIG. 11 has fewer grains than the examples of FIGS. 8-10, but the
ignition configuration and timing produce a relatively more complex
pressure versus time profile. The fore end surfaces of both pairs
of grains are ignited, in sequence, but only the aft end surfaces
of the second pair of grain segments are ignited simultaneous with
ignition of the fore end surfaces of the second pair grains.
Consequently, the second grains burn faster, producing more gas in
a shorter amount of time than the first pair. Additionally, the
timing of the ignition of the second pair of grains is set to occur
in such a way that gas production from the first grain pair ends
about halfway through the burn phase of the second pair. Therefore,
the pressure versus time profile 256 drops after the first pair of
grains is completely consumed.
[0090] The grain and ignition configurations 260, 262, 264 and 266
of the example of FIG. 12 are depicted in FIGS. 12A, 12C, 12D and
12F. As with the examples of FIGS. 7 and 11, the gas producing
assembly has only two grain pairs, but the grain pairs are
different in size, and the ignition configuration of the two grain
pairs are different. Only the fore end surfaces of the first grain
pair are ignited. The first grain pair provides a pressure versus
time profile 268 having a relatively low-level pressure sustained
for a relatively long period of time. In contrast, the second pair
of grain segments, while smaller, produce a much higher gas
pressure, though over a relatively short period of time, through
the ignition of the grains in the second pair at three different
locations. The grain segments in the second pair are ignited at the
fore end surfaces, the aft end surfaces and at interior locations
in the second grain pair, as indicated by the designation "2c" in
FIGS. 12D and F. Consequently, the grain segments in the second
pair burn from three different locations, namely from the two
opposite end surfaces, and as shown in 270 in FIG. 12B, from an
approximate middle portion of the two grain segments. The igniter
leads can produce ignition if they are located interior to the
grains, or adjacent the tube 166. It is preferable that burning of
the grains does not occur from the outside in, so igniting the
grains near the outer walls is not as desirable. Because the grain
segments are supported at the outer walls, burning of the grain
segments at the outer walls first is not desirable.
[0091] The pressure versus time profile shows a sustained level and
a relatively high pressure peak due to the simultaneous ignition of
three surfaces or three locations on the grain segments of the
second pair. The first pair of grains burn relatively slowly while
the second pair of grains burn relatively quickly.
[0092] Having thus described several exemplary implementations of
the invention, it will be apparent that various alterations and
modifications can be made without departing from the inventions or
the concepts discussed herein. Such operations and modifications,
though not expressly described above, are nonetheless intended and
implied to be within the spirit and scope of the inventions.
Accordingly, the foregoing description is intended to be
illustrative only.
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