Abstract:
A method and apparatus for augmenting thrust in a rocket traveling through atmospheric gas. Rocket motor designs are provided where a throat(s) from one or more rocket motors eject high-speed primary exhaust gas in a configuration which peripherally surrounds an outlet for induced, secondary gas. The secondary gas is mixed with the jet of primary exhaust gas to add momentum, and therefore thrust. Either expansion deflection or plug type rocket discharge nozzles can be utilized. In one embodiment, a thrust augmentation of over one hundred percent is achieved. In another embodiment, a plurality of rocket motor assemblies each containing a thrust augmenting rocket motor design is affixed to a rocket body. Such rocket motors enhance rocket thrust performance, and enables more efficient payload to rocket motor selection, or, alternatively, allows higher loads to be carried with the same amount of thrust.

Description:
TECHNICAL FIELD 
     This invention relates to rockets, and more specifically, to methods and apparatus for increasing the effective thrust developed when utilizing rocket motors. 
     BACKGROUND 
     In applications for rocket motors, and especially for rocket motors used to lift earth orbit payloads, a primary concern is the amount of thrust provided for a given amount of fuel consumption, i.e, the specific fuel consumption for a given propulsion device. Specifically, in the various nozzles used in propulsion devices that consume chemical fuel stocks, it would be advantageous to increase the momentum transferred to the rocket nozzles from the combusted fuels, in order to increase thrust of the device. And, although some types of steady flow ejectors have been documented and sometimes used to augment the thrust created by a propulsion device by entraining ambient air into the exhaust stream at the nozzle exit, such devices are, for the most part, not particularly efficient. Many prior art thrust augmentors employ a configuration wherein the primary flow injector is surrounded by the secondary flow at the point of injection. Other prior art thrust augmenters rely on the injection of primary flow through the duct wall through holes, a circumferential passage, or a series of passages, in such a fashion as to cause the primary flow to hug the wall between the secondary flow and the passage wall upstream of the nozzle throat. Also, some prior art thrust augmentation injectors use both internal injection and wall injection. However, many of the prior art thrust augmentors required a containment passageway for the fluid mixing and momentum transfer step. So, although various methods and structures have been provided for augmenting thrust in rocket nozzles, in so far as is known to me, conventional designs known heretofore have not provided for induction of secondary flow in a manner wherein the primary thrust flow from the rocket nozzle(s) surrounds an induced secondary flow downstream of the nozzle throat. 
     In short, conventional thrust augmentation design for propulsion devices, and in particular, for earth or air launched propulsive devices, has not matched the developments in rocket motor design and reliability. For the most part, conventional rocket designs currently in use have ignored the use of a thrust augmentation component. Thus, it would be desirable to provide an improved propulsion device, and in particular, an improved rocket booster design, that utilizes an efficient thrust augmentation device to improve fuel efficiency, and thus, improve payload performance. Alternately, it would be desirable to enable the use of smaller rocket motors, or even fewer rocket stages, or with smaller rockets having smaller motors and smaller fuel and oxidant tanks, than currently necessary in accomplishing the lift of equivalent payloads. 
     SUMMARY 
     A novel rocket thrust augmentation system has been developed, and is disclosed herein. Various embodiments described herein include the provision of a ring of exhaust gases from one or more rocket motors located on the rocket launch vehicle. Two flows, a primary flow of hot exhaust gases, and a secondary flow of ambient air, share the same axis, with the secondary flow inside of, and confined by, the primary hot exhaust flow. By virtue of its high velocity, the surrounding primary flow is at lower pressure than the secondary flow of ambient air, which causes the ambient air to flow into and downstream along the secondary airflow duct, and ultimately to be thrown rearward by the primary, hot exhaust gas flow. Consequently, this aspirator action causes a significant and beneficial secondary flow of air through the duct. This secondary flow adds its mass, and thus its momentum, to that of the primary flow, thus increasing the overall thrust of the rocket. Consequently, the thrust provided is much higher than a simple unaugmented rocket. Moreover, when air for augmentation is no longer present, the rocket motor(s) will continue to operate without restriction from the passive thrust augmentation design structure. 
     In one embodiment, an expansion deflection type outlet nozzle is located peripherally, and preferably circumferentially about a central secondary flow pathway, and the primary flow induces the central secondary flow, thereby enhancing thrust. In yet another embodiment, a plug flow outlet nozzle is provided, and the primary flow is ejected peripherally about the plug outlet, to induce the secondary flow which travels downward and outward while being peripherally confined, at least at the nozzle outlet, by the primary flow of hot exhaust gas. More generally, the present invention involves providing, in a rocket propulsion device, an outlet jet of hot exhaust gases about a centrally located secondary air flow path, so that the hot exhaust gases velocity entrains a secondary air flow, to increase the overall momentum provided for reaction against the rocket motors. In any case, jet nozzle means are supplied with hot exhaust gases, under pressure, and the energized hot gases surround a core of secondary air, resulting in mixing of the primary and secondary flows, adding to the total thrust of the propulsion device. 
     Compared to prior art rocket designs, the rocket design disclosed herein, utilizing a passive thrust augmentation method, produces much more thrust for a given fuel consumption. This added thrust is in proportion to the density of air in which it operates, and the mass throughput of such air. Consequently, as the rocket gains altitude, the thrust augmentation percentage will drop. This fortunately coincides with the profile of benefit from additional thrust, since as conventional rockets gain altitude they consume massive quantities of fuel with a constant high thrust. Thus, in prior art, conventional rockets, the thrust is constant until the rocket motor is shut down. Of course, the constant high thrust pushing against the decreasing mass (due to fuel and oxidant consumption) of such a conventional rocket results in increasing acceleration or G forces. Such forces rapidly become problematic for manned vehicles, as well as for certain other payloads. With the rocket design provided by the instant invention, thrust augmentation is greatest at the lowest altitudes, where the payload is heaviest, i.e., where the most fuel and oxidant is being carried. Consequently, the decrease in thrust augmentation with increasing altitude, as occurs in rockets designed in accord with the present invention, results in a smaller increase in G forces with fuel consumption when compared to prior art conventional rocket design. Consequently, a rocket designed according to the present invention has improved performance, and is more amenable to manned space flight. 
     The thrust augmentation system encounters no difficulty upon reaching thin air at high altitudes. That is because the system is technically straightforward, and is preferably implemented with no moving parts. In the new design disclosed herein, the various embodiments are self regulating with altitude and thus achieve good nozzle efficiency with increasing altitude after launch. 
     Various embodiments of the invention are disclosed in which the mechanical or functional features described above are achieved in disparate physical configurations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In order to enable the reader to attain a more complete appreciation of the invention, and of the novel features and the advantages thereof, attention is directed to the following detailed description when considered in connection with the various figures of the accompanying drawing, wherein: 
         FIG. 1  is a generalized system schematic that shows a rocket having an expansion deflection type nozzle, with a centrally located secondary flow and a preferably annular propulsive device (or annular distribution of propulsive devices) surrounding the secondary flow path. 
         FIG. 2  shows a generalized system schematic that shows a rocket having a plug flow type outlet nozzle, also having a centrally located secondary flow and a preferably annular (distribution) of propulsive device(s) surrounding the secondary flow path. 
         FIG. 3  shows a generalized rocket schematic that provides details of the use of multiple rocket motors surrounding a central secondary flow path, and wherein the rockets motors are of the type configured for fuel and oxidant flow regulation, so that thrust can be varied about the circumference of the rocket, to control directional stability. 
         FIG. 4  illustrates a cross-sectional view of one test device wherein the principles of the present invention were evaluated to determine the amount of thrust augmentation achieved. 
         FIG. 5  is a top view of the test device just illustrated in  FIG. 4 , now showing the large central space for secondary flow, and the small passageways for primary flow alongside of the expansion flow nozzle, where high speed primary jets are utilized to induce the secondary flow to augment thrust. 
         FIG. 6  is a detailed cross sectional view, taken at the area noted as  FIG. 6  in  FIG. 4 , now showing in even greater detail the relatively small primary flow passageways provided to induce secondary flow for thrust augmentation. 
         FIG. 7  is a cross sectional view of another embodiment for rocket with thrust augmentation, here showing a plurality of rocket motors mounted about the periphery of the lower reaches of a rocket, showing a large secondary air flow passageway, as well as an expansion deflection flow outlet nozzle. 
         FIG. 8  illustrates a cross-sectional view of yet another test device, this one directed to the test of a plug flow type outlet, wherein the principles of the present invention were evaluated to determine the amount of thrust augmentation achieved by inducing secondary air flow through a central passageway via momentum from high velocity discharge of gas circumferentially to the outlet of the secondary air flow passageway. 
         FIG. 9  is a detailed cross sectional view, taken at the area noted as  FIG. 9  in  FIG. 8 , now showing in even greater detail the relatively small primary flow passageways for passage of high velocity gas discharge, which are provided to induce secondary flow for thrust augmentation. 
         FIG. 10  is a simplified cross-sectional view of yet another embodiment for rocket with thrust augmentation, similar to that first shown in  FIG. 1  above, but now utilizing a continuous circumferential rocket motor structure with integral expansion deflection outlet nozzle, as well as showing the walls of an oval secondary air flow passageway. 
         FIG. 11  is a bottom view, taken looking up into the bottom of the apparatus just illustrated in  FIG. 10 , along line  11 — 11  of FIG.  10 . 
         FIG. 12  is a simplified cross-sectional view showing the embodiment just illustrated in  FIGS. 10 and 11 , now showing a cross-section through the minor axis of the rocket, taken along line  12 — 12  of FIG.  11 . 
         FIG. 13  is a simplified cross-sectional view of yet another embodiment for rocket with thrust augmentation, similar to that first shown in  FIG. 2  above, but now utilizing a continuous circumferential rocket motor structure with integral plug flow outlet, as well as showing the walls of a preferably oval large secondary air flow passageway. 
         FIG. 14  is a bottom view, taken looking up into the bottom of the apparatus just illustrated in  FIG. 13 , along line  14 — 14  of FIG.  13 . 
         FIG. 15  is a simplified cross-sectional view showing the embodiment just illustrated in  FIGS. 13 and 14 , now showing a cross-section through the minor axis of the rocket, taken along line  15 — 15  of FIG.  14 . 
         FIGS. 16 ,  17 ,  18 , and  19  show the application of the present invention to strut mounted rocket motors positioned about a payload body being lifted. 
       In  FIG. 16 , one rocket motor is shown mounted to a rocket body via a strut; the rocket motor utilizes a central secondary air flow passage for flow of thrust augmenting air that is mixed with hot exhaust gases from the rocket motor. 
       In  FIG. 17 , a vertical cross-sectional view is provided of the rocket motor first illustrated in  FIG. 16 , now showing the presence of a central secondary air flow passageway, one or more rocket motors, and an expansion deflection type outlet nozzle. 
         FIG. 18  illustrates an alternate embodiment for a rocket motor for attachment to a rocket body as shown in  FIGS. 16 and 19 , wherein the thrust augmentation type rocket motor is provided with a central secondary air flow passageway, one or more rocket motors mounted circumferentially to the air flow passageway, and a plug flow type outlet. 
         FIG. 19  illustrates a cross sectional view of a rocket having a plurality of rocket motors attached thereto (here, three motors), each of which utilizes a thrust augmentation design such as one of those just illustrated in FIGS.  17  and  18 . 
     
    
    
     The foregoing figures, being exemplary, contain various elements that may be present or omitted from actual implementations depending upon the circumstances. An attempt has been made to draw the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the invention. However, various other elements of the thrust augmentation devices are also shown and briefly described to enable the reader to understand how various optional features may be utilized in order to provide an efficient, reliable, thrust augmentation system for rocket motors. 
     DETAILED DESCRIPTION 
     Attention is directed to  FIG. 1 , where a generalized system schematic shows the aft portion of a rocket  10  having a centrally located secondary air flow containment casing  12  with an inner wall  13 . The casing has an inlet (upstream of reference numeral  14 —see FIG.  17  and inlet  15 , for example) and an outlet  16  running along a central axis C 1 . In this  FIG. 1 , a portion of the outer wall  18  of the casing  12  provides a nozzle internal throat portion  20 . For simplicity, and to direct attention to the gas flow path rather than to details of materials of construction, casing  12  is shown here as being of one continuous piece of material. However, in actual practice, the nozzle internal throat portion  20  and the inner wall  13  of the containment casing  12  would normally be made of different materials. The nozzle internal throat portion  20  is located adjacent to (but preferably at least slightly upstream from) the outlet  16  of the secondary air flow containment casing  12 . A rocket motor  21  is provided, and a primary flow of energetic hot exhaust gases  40  passes through the rocket throat T (i.e. between nozzle internal throat portion  20  and nozzle exterior throat portion  22 ) and leaves the rocket motor  21 . The nozzle internal throat portion  20  is positioned slightly upstream of, and circumferential to (or peripheral to, depending on the surface shape provided) the outlet  16  of the secondary airflow casing  12 . An outlet nozzle  30 , having a preselected contour such as the expansion deflection profile shown in  FIG. 1 , is provided. The outlet nozzle  30  extends for a preselected distance D 1  downstream from the pinch point provided between nozzle interior throat portion  20  and nozzle exterior throat portion  22 . An energetic hot gas stream primary flow indicated by reference arrows  40  that results from the combustion in rocket motor  21  of a fuel and an oxidant (see  FIGS. 3 and 7 , for example) is discharged through the passageway between the rocket nozzle exterior throat portion  22  and the nozzle interior throat portion  20 . The pinch point length H of the throat T, as well as the exact shape of the nozzle exterior throat portion  22  and of the nozzle interior throat portion  20  can be varied as appropriate for a given rocket motor service and rocket design. Circumfluently, the outlet flow pathway between nozzle exterior throat portion  22  and nozzle interior throat portion  20  may be circumferential, in the case of circular or generally curvilinear designs, or may otherwise peripherally surround the casing  12  in case of other shapes thereof. 
     The secondary atmospheric gas stream as indicated by reference arrows  42 , which has passed through casing  12 , then mixes with the primary flow  40 . Mixing occurs along the interior free jet boundary  50 , which, as depicted, substantially is in the shape of an upwardly opening cone; however, this shape will vary with altitude. Upon mixing, momentum is added, and thus additional reaction thrust is achieved from rocket  10 . The energetic hot gas stream primary flow indicated by reference arrows  40  runs along the interior wall  60  of outlet nozzle  30 , and after the downstream end  62  of outlet nozzle  30 , an exterior free jet boundary  64  forms at the radial distal periphery of the hot gas exhaust stream  40 . 
     Turning now to  FIG. 2 , rocket  100  is shown with a plug flow shaped outlet nozzle  102 . Nozzle interior throat portion  104  and the nozzle exterior throat portion  106  cooperate to define a pathway for hot energetic exhaust gases  110  to escape outward from rocket motor  120 . That pathway may be circumferential, in the case of circular or generally curvilinear designs, or may otherwise peripherally surround the secondary containment casing  122  in case of other shapes. Rocket  100  has a centrally located secondary air flow containment casing  122  with an inner wall  124 . The casing has an inlet (upstream of reference numeral  126 —see FIG.  17  and inlet  15 , for example) and an outlet  128  and runs along a central axis C 2 . As indicated in  FIG. 2 , a portion of the outer wall  130  of the casing  122  provides a nozzle interior throat portion  104 . For simplicity, and to direct attention to the gas flow path rather than to details of materials of construction, casing  122  is shown here as being of one continuous piece of material. However, in actual practice, the outer wall  130  and nozzle interior throat portion  104 , as well as the inner wall  124  of the containment casing  122  would normally be made of different materials. As indicated in this embodiment, the nozzle interior throat portion  104  is located adjacent to (but preferably at least slightly upstream from) the outlet  128  of the secondary air flow containment casing  122 . The flow of primary energetic hot exhaust gases leaves the rocket motor  120  through the throat T, between nozzle interior throat portion  104  and nozzle exterior throat portion  106 . The nozzle exterior throat portion  106  is positioned upstream of, and circumferential to, the outlet  128  of the secondary airflow containment casing  122 . Note that although in this embodiment a single rocket motor is described, as will be further explained hereinbelow, it is also possible to utilize multiple rocket motors, each having its own throat, which will be circular in one embodiment thereof, and the use of the term interior throat portion  104  is merely provided for convenience with respect to the present embodiment of a circumfluent type rocket motor. An outlet nozzle  102 , having a preselected contour such as the plug nozzle profile indicated in  FIG. 2  is provided. The outlet nozzle  102  extends for a preselected distance D 2  downstream from the rocket primarily flow outlet  132 . That portion  42 , of the secondary atmospheric gas stream  42  which has completely passed through the secondary airflow containment casing  122  then mixes with the primary flow hot exhaust gases  110 . Mixing occurs along the interior free jet boundary  50 , which, as depicted, substantially is in the shape of an upwardly opening cone; however, such shape will vary with thrust and altitude. Upon mixing, momentum is added, and thus additional thrust is added to the rocket performance. 
     Attention is now directed to  FIG. 3 , where the aft portion of a novel rocket  200  is illustrated. This design is shown with a plug flow shaped outlet nozzle  202 . Nozzle interior throat portion  204  and the nozzle exterior throat portion  206  cooperate to define an exit pathway for hot energetic exhaust gases  210  to escape outward from each rocket motor  220 . A plurality of rocket motors in a series  220   1 ,  220   2 ,  220   3 , through  220   x , (where x is a positive integer) are provided to peripherally or circumferentially (depending on shape) surround the secondary air flow containment casing  222 . In such an embodiment, the nozzle interior throat portion  204  and the nozzle interior throat portion  206  are in reality just indications of opposing portions of a single circular throat T. Rocket  200  has a centrally located secondary air flow containment casing  222  with an inner wall  224 . The casing has an inlet (upstream of reference numeral  226 —see FIG.  17  and inlet  15 , for example) and an outlet  228  and runs along a central axis C 3 . A portion of the outer wall  230  of the outlet nozzle  202  may provide the nozzle interior throat portion  204 , either separately or integrally with a particular rocket motor  220   x . As indicated in this embodiment, the nozzle interior throat portion  204  is located adjacent to (but preferably at least slightly upstream from) the outlet  228  of the secondary air flow containment casing  222 . The flow of primary energetic hot exhaust gases escapes from combustion chamber(s) of the one or more rocket motors  220  through the throats T. The throats T are preferably positioned upstream of, and peripherally to (or circumferential to), the outlet  228  of the secondary airflow casing  222 . The casing outlet nozzle  202  extends for a preselected distance D 3  downstream from the throats T. That portion  42   I  of the secondary atmospheric gas stream  42  which has passed through the secondary airflow containment casing  222  then mixes with the primary flow hot exhaust gases  210 . As earlier noted, fluid mixing occurs along the interior free jet boundary  50 , which, as depicted, is substantially in the shape of an upwardly opening cone; however this shape will vary with rocket motor thrust output and with altitude. Upon mixing, momentum is added, and thus additional thrust is added to the rocket motor performance. 
     Fuel  250  and oxidant  260  lines provide fuel  252  and oxidant  262 , respectively, to rocket motors  220   x . In this embodiment, also provided are regulating valve  254  on the fuel line  250 , and regulating valve  264  on the oxidant supply line  260 , so that either or both fuel  252  and/or oxidant  262  supply can be controlled. With regulation on either fuel supply lines  250  or oxidant supply lines  260 , a directional control device or guidance system  270  can be provided that individually controls the supply of fuel  252  and oxidant  262  to one or more of the rocket motors in the plurality of rocket motors  220   1 ,  220   2 ,  220   3 ,  220   x . In this manner, the guidance system  270  can be used to control the regulating valves  252  or  262  on the fuel  250  and/or oxidant  260  supply lines, in order to control the amount of thrust about the perimeter of the rocket  200 , and thus control the direction of the rocket  200 . Thus, stability inputs as appropriate can be easily provided to achieve desired orientation and trajectory. 
     Turning now to  FIGS. 4 ,  5 , and  6 , one exemplary embodiment of my test apparatus for evaluating the amount of thrust achievable with the novel thrust augmentation designs provided herein is disclosed.  FIG. 4  provides a cross-sectional view, and  FIG. 5  provides a top view. Details of the peripheral gap G that provides the induction jet outlet are shown in FIG.  6 . In the design illustrated in these figures, a simulated rocket body  400  is shown with an expansion deflection type outlet nozzle  402 . As better seen in  FIG. 6 , a nozzle interior throat portion  404  and the nozzle exterior throat portion  406  cooperate to define a substantially circumferential pathway having a gap G therebetween. Although only cold gases were utilized in this test model, in an actual rocket motor, hot energetic exhaust gases  410  would escape outward from rocket motor  420  combustion chamber  421 . Rocket body  400  has a centrally located secondary air flow containment casing  422  with an inner wall  424 . The casing has an inlet  426  and an outlet  428  and runs along a central axis C 4 . As indicated in  FIG. 6 , a portion of the outer wall  430  of the secondary air flow containment casing  422  provides the nozzle interior throat portion  404 . As indicated in this embodiment, the nozzle interior throat portion  404  is located adjacent to (but preferably at least slightly upstream from) the outlet  428  of the secondary air flow containment casing  422 . The rocket motor outlet  432  is positioned adjacent of, and circumferential to, the outlet  428  of the secondary airflow containment casing  422 . An outlet nozzle  402 , having a preselected contour such as the expansion deflection profile indicated in  FIGS. 4 ,  5 , and  6 , is provided. The outlet nozzle  402  extends for a preselected distance D 4  downstream from the rocket outlet  406  to an outlet end  440 . That portion  42   I  of the secondary atmospheric gas stream  42  which has passed through secondary airflow containment casing  422  then mixes with the primary flow exhaust gases  410 . Mixing occurs as already described above. Upon mixing, momentum is added, and thus additional thrust is added to the rocket performance. In one test of this design, I have found that the amount of thrust augmentation is up to as much as two hundred and sixty four percent. 
     In a different, plug flow type embodiment, the test apparatus for which is now shown in  FIG. 8  (similar in configuration to the rocket motor shown in  FIG. 2  above), the amount of thrust augmentation is up to as much as one hundred and thirty five percent, as evaluated in a non-combustion test environment.  FIG. 8  illustrates a cross-sectional view of a test device used that is directed to the test of a plug flow type outlet, wherein the principles of the present invention were evaluated to determine the amount of thrust augmentation achieved by inducing secondary air flow through a central passageway via momentum from high velocity discharge of gas circumferentially to the outlet of the secondary air flow passageway. In this design, rocket body  600  is provided with a plug flow shaped outlet nozzle  602 . As more clearly seen in  FIG. 9 , nozzle interior throat portion  604  and the nozzle exterior throat portion  606  cooperate to define an exit pathway for hot energetic exhaust gases  610  to escape outward from the rocket motor  620 . One or more rocket motors  620 , such as a series of motors  620   1 ,  620   2 ,  620   3 , through  620   x , (where x is a positive integer) are provided to peripherally or circumferentially (depending on shape) surround the secondary air flow containment casing  622 . Rocket  600  has a centrally located secondary air flow containment casing  622  with an inner wall  624 . The casing has an inlet  626  and an outlet  628  and runs along a central axis C 5 . A portion of the outer wall  630  of the outlet nozzle  602  may provide the nozzle interior throat portion  604 , either separately or integrally with a particular rocket motor  620   x . As indicated in this embodiment, the nozzle interior throat portion  604  is located adjacent to (but as shown upstream from) the outlet  628  of the secondary air flow containment casing  622 . The flow of primary energetic hot exhaust gases escapes from combustion chamber of the rocket motor  620   x  through the throat T between nozzle interior throat portion  604  and the nozzle exterior throat portion  606 . The throat T is preferably positioned upstream of, and peripherally to (or circumferential to), the outlet  628  of the secondary airflow casing  622 . The casing outlet nozzle  602  extends for a preselected distance D 5  downstream from the throat T. That portion  42   I  of the secondary atmospheric gas stream  42  which has passed through the secondary airflow containment casing  622  then mixes with the primary flow hot exhaust gases  610 . As earlier noted, fluid mixing occurs along the interior free jet boundary  50 , which, as earlier depicted (see FIG.  3 ), is substantially in the shape of an upwardly opening cone; however this shape will vary with rocket motor thrust output and with altitude. Upon mixing, momentum is added, and thus additional thrust is added to the rocket motor performance. 
     Attention is directed to  FIG. 10 , where a simplified cross-sectional view of yet another embodiment for rocket with thrust augmentation is provided, similar to that first shown in  FIG. 1  above, but now utilizing a continuous circumferential rocket motor structure with integral expansion outlet nozzle, as well as showing the walls of a generally oval secondary air flow passageway.  FIG. 10  shows the aft portion of a rocket  700  having a centrally located secondary air flow containment casing  712  with an inner wall  713 . The casing has an inlet (upstream of reference numeral  714 —see FIG.  17  and inlet  15 , for example) and an outlet  716  running along a central axis C 10 . In this  FIG. 10 , a portion of the outer wall  718  of the casing  712  provides a nozzle internal throat portion  720 . The nozzle internal throat portion  720  is located adjacent to (but preferably at least slightly upstream from) the outlet  716  of the secondary air flow containment casing  712 . A rocket motor  721  is provided, and a primary flow of energetic hot exhaust gases  40  passes through the rocket throat T (i.e. between nozzle internal throat portion  720  and nozzle exterior throat portion  722 ) and leaves the rocket motor  721 . The nozzle internal throat portion  720  is positioned slightly upstream of, and peripheral to the outlet  716  of the secondary airflow casing  712 . An outlet nozzle  730 , having a preselected contour such as the expansion deflection profile shown in  FIG. 10 , is provided. The outlet nozzle  730  includes a section of length D 6  which is divergent, for the purpose of allowing the primary flow to go supersonic before it contacts the secondary flow. The outlet nozzle  730  extends for a preselected distance D 10  downstream from the pinch point provided between nozzle interior throat portion  720  and nozzle exterior throat portion  722 . An energetic hot gas stream primary flow indicated by reference arrows  40  that results from the combustion in rocket motor  721  of a fuel and an oxidant (see  FIGS. 3 and 7 , for example) is discharged through the passageway between the rocket nozzle exterior throat portion  722  and the nozzle interior throat portion  720 . The pinch point length H of the throat T, as well as the exact shape of the nozzle exterior throat portion  722  and of the nozzle interior throat portion  720  can be varied as appropriate for a given rocket motor service and rocket design. The secondary atmospheric gas stream as indicated by reference arrows  42   I , which has passed through casing  712 , then mixes with the primary flow  40 . Mixing occurs along the interior free jet boundary  750 , which in this embodiment, would be different than earlier depicted, since a oval shape should be expected, particularly in view of the outlet shape as indicated by FIG.  11 . In any event, upon mixing, momentum is added, and thus additional reaction thrust is achieved from rocket  710 . The energetic hot gas stream primary flow indicated by reference arrows  40  runs along the interior wall  760  of outlet nozzle  730 , and after the downstream end  762  of outlet nozzle  730 , an exterior free jet boundary  764  forms at the radial distal periphery of the hot gas exhaust stream  40 , generally as set forth above. For purposes of testing, it was unnecessary to utilize hot gas or utilize multiple motors in the devices illustrated in  FIGS. 4 and 8 . However, by use of suitable gas flow parameters, the principles of the present invention were suitably confirmed. 
     As seen in  FIG. 10 , but better appreciated from further comparison with  FIGS. 11 and 12 , in this embodiment, a continuous circumferential rocket motor structure  721  is provided, with a preferably integral expansion deflection outlet nozzle  730 . Note that the walls of the secondary airflow containment passageway  722  are generally oval in shape, as well as the outlet nozzle  730 , as well as the generally oval secondary air flow passageway defined by containment walls  713 . In the bottom view provided by  FIG. 11 , both a major and a minor axis are shown. 
     Further definition of the unique shape provided by this embodiment is illustrated in  FIG. 12 , which shows the embodiment just illustrated in  FIGS. 10 and 11 , but now showing a cross-section through the minor axis of the rocket taken along line  12 — 12  of  FIG. 11 , (as contrasted with the cross-section of  FIG. 10  taken along the major axis of the rocket). 
     Turning now to  FIGS. 13 ,  14 , and  15 , these are similar to those embodiments just shown in  FIGS. 10 ,  11 , and  12 , but yet another embodiment for rocket with thrust augmentation is illustrated, utilizing a continuous circumferential rocket motor structure with integral plug flow outlet, as well as providing an oval secondary air flow passageway.  FIG. 14  is a bottom view, taken looking up into the bottom of the apparatus illustrated in  FIG. 13 , along line  14 — 14  of FIG.  13 .  FIG. 15  shows the minor axis of this embodiment (as contrasted to the major axis shown in FIG.  13 ), taken along line  15 — 15  of FIG.  14 . In  FIG. 13 , the aft portion of rocket  800  is shown with a plug flow shaped outlet nozzle  802 . Nozzle interior throat portion  804  and the nozzle exterior throat portion  806  cooperate to define a pathway for hot energetic exhaust gases  810  to escape outward from rocket motor  820 . That pathway peripherally surrounds the generally oval shaped secondary containment casing  822 . Rocket  800  has a centrally located secondary air flow containment casing  822  with an inner wall  824 . As illustrated in  FIGS. 13 ,  14 , and  15 , wall  828  has opposing ends along a major axis, each depicted as walls  828   A , and opposing sides along a minor axis, each depicted as  828   B . The casing has an inlet (upstream of reference numeral  826 —see FIG.  17  and inlet  15 , for example) and an outlet  828  and runs along a central axis C 13 . As indicated in  FIG. 13 , a portion of the outer wall  830  of the casing  822  provides a nozzle interior throat portion  804 . For simplicity, and to direct attention to the gas flow path rather than to details of materials of construction, casing  822  is shown here as being of one continuous piece of material. However, in actual practice, the nozzle interior throat portion  804  and the outer wall  830  of the containment casing  822  would normally be made of different, and some embodiments, separable materials As indicated in this embodiment, the nozzle interior throat portion  804  is located adjacent to (but preferably at least slightly upstream from) the outlet  828  of the secondary air flow containment casing  822 . The flow of primary energetic hot exhaust gases leaves the rocket motor  820  through the throat T, between nozzle interior throat portion  804  and nozzle exterior throat portion  806 . The outlet  829  includes a section of length D 14  which is divergent, for the purpose of allowing the primary flow to go supersonic before it contacts the secondary flow. The nozzle exterior throat portion  806  is positioned upstream of the outlet  828  of the secondary airflow containment casing  822 . An outlet nozzle  802 , having a preselected contour such as the plug nozzle profile indicated in  FIG. 13  is provided. The outlet nozzle  802  extends for a preselected distance D 13  downstream from the rocket throat T. That portion  42 , (the induced airflow) of the secondary atmospheric gas stream  42  which has completely passed through the secondary airflow containment casing  822  then mixes with the primary flow hot exhaust gases  810 . Mixing occurs along the interior free jet boundary  850 , which, as depicted, substantially is in the shape of an oval of decreasing cross section; downstream; however, such shape will vary with thrust and altitude. An exterior free jet boundary  864  forms at the outer periphery of the hot gas exhaust stream  810 , generally as set forth above. Upon mixing, momentum is added, and thus additional thrust is added to the rocket performance. 
     Attention is now directed to  FIGS. 16 through 19 , where the use of externally mounted rocket motors is illustrated. On one embodiment, such a mounting technique may be enabled by affixing thrust augmented rocket motors  900  to rocket  902  via way of struts  904 , as depicted in FIG.  16 . Note the mixing of the primary hot exhaust gas stream  40  along an inner free jet boundary  50 , and the contact of the hot exhaust gas stream with an outer free jet boundary  64 . As depicted in  FIGS. 16 ,  17 , and  19 , a thrust augmented rocket motor assembly  900  having a secondary airflow containment passageway defined by inner sidewall  910  can be advantageously utilized. Secondary airflow containment passageway has an inlet  15  and an outlet  914 . In this configuration, an expansion deflection type nozzle  930  may be used, as shown in FIG.  17 . In such a configuration, the details are fundamentally as earlier described, with respect to fuel and oxidant supply; here, the same may be provided via struts  904 . Also, the details as to the rocket motors  920 , and the outlet nozzle  930 , as well as mixing, etc, along an inner free jet boundary  50 , are fundamentally as set forth in FIG.  10 . For example, see details as set forth in conjunction with  FIG. 10  regarding the rocket motor  721  throat T and accompanying hot gas stream  40 . However, in the externally mounted configuration illustrated in  FIGS. 16 through 19 , the rocket motor assembly  900  is provided in a compact, aerodynamic pod  940  that efficiently and preferably integrally supports and encloses rocket motors  920  and the outlet nozzle  930 . 
       FIG. 18  illustrates an alternate embodiment for a rocket motor for attachment to a rocket body as shown in  FIGS. 16 and 19 , wherein the thrust augmentation type rocket motor assembly  950  is provided with a central secondary air flow containment passageway  958  defined by inner edge wall  960 . The secondary air flow containment passageway has an inlet  15  and an outlet  962 . One or more rocket motors  966  are mounted circumferentially in support structure  968  adjacent to the central secondary air flow containment passageway  958 . A plug flow type nozzle  970  is provided. This configuration and its operation is thus similar to the plug flow nozzle  102  and rocket motors  120  depicted in  FIG. 2  above. An aerodynamic outer surface  974  is provided for support structure  968  of rocket motor assembly  950 . 
     The techniques just described herein can be used in a method of augmenting the thrust of a rocket passing through atmospheric gas. To practice the method, the first step is providing a rocket body having a secondary air flow containment casing along a central axis (at least at or near the exhaust end), with the casing having an inlet and an outlet. However, at the inlet end of the casing, it is not necessary (although it is preferred) that the casing central axis be aligned with the radial center of thrust from the rocket motors. Next, rocket motor(s) are provided wherein each has a throat portion, and the throat portion(s) should be positioned upstream of, and substantially circumferential to, the outlet of the secondary airflow casing. The next step in practicing this method is to provide a nozzle throat portion located in juxtaposition to the rocket motor outlet(s). The nozzle throat portion is located along the flow path just prior to the outlet of the secondary air flow containment casing outlet. Then, an outlet nozzle must be provided. The outlet nozzle should have a preselected contour based on the design flows and velocities, and the outlet nozzle should extend for a preselected distance downstream from the rocket motor outlet(s). The nozzle throat portion discharges a primary, hot exhaust gas flow. The primary hot exhaust gas flow induces a secondary, atmospheric gas to pass through the casing. Downstream from the outlet nozzle, the secondary atmospheric flow mixes with the primary flow, thereby augmenting momentum and thus augmenting thrust of the rocket. 
     As set forth above, this method is applicable to either expansion deflection type or to plug flow type outlet nozzles. 
     It is to be appreciated that the various aspects and embodiments of the structures for rocket thrust augmentation described herein are an important improvement in the state of the art, especially for boosting payloads into earth orbit. Although only a few exemplary embodiments have been described in detail, various details are sufficiently set forth in the drawings and in the specification provided herein to enable one of ordinary skill in the art to make and use the invention(s), which need not be further described by additional writing in this detailed description. The aspects and embodiments described and claimed herein may be modified from those shown without materially departing from the novel teachings and advantages provided by this invention, and may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, the embodiments presented herein are to be considered in all respects as illustrative and not restrictive. As such, this disclosure is intended to cover the structures described herein and not only structural equivalents thereof, but also equivalent structures. Numerous modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention(s) may be practiced otherwise than as specifically described herein. Thus, the scope of the invention(s), as set forth in the appended claims, and as indicated by the drawing and by the foregoing description, is intended to include variations from the embodiments provided which are nevertheless described by the broad interpretation and range properly afforded to the plain meaning of the claims set forth below.