Patent Publication Number: US-8975565-B2

Title: Integrated propulsion and attitude control system from a common pressure vessel for an interceptor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to attitude control systems for a self-propelled interceptor. 
     2. Description of the Related Art 
     Interceptors such as self-propelled rockets, missiles or counter-missile missiles may be launched from air, land or sea-based platforms to engage a target. The interceptor may be used offensively against other platforms, fixed emplacements or other targets or defensively to intercept and destroy enemy missiles. The interceptor may use explosive or kinetic energy to defeat the target. 
     The interceptor is propelled by a rocket motor. Rocket propellant is ignited and burns creating a high-pressure gas. This gas is expelled in a generally axial direction through one or more main nozzles that convert the high-pressure gas into a high-velocity gas. 
     The interceptor is maneuvered by an attitude control system (ACS). In general, the ACS produces a “moment” offset from the center of gravity (Cg) of the interceptor that interacts with the main axial thrust vector to change the attitude of the interceptor. This moment may provide yaw, pitch and/or roll control. One approach known as “thrust vector control” uses a servo motor to physically reorient the one or more main nozzles to produce the desired moment. Another approach known as “aerodynamic control” uses servo motor to physically deploy one or more aerodynamic control surfaces such as fins. Some interceptors use a combination of thrust vector control at low speed with aerodynamic control at high speed. Another approach is to selectively ignite one or more explosive guidance units (EGUs) placed on the airframe to generate impulse moments to control the attitude. In any of these approaches, a flight control system responds to guidance commands to command the ACS to maneuver the interceptor. Guidance may be provided as a command line-of-sight (CLOS) in which a targeting system tracks the target and the interceptor, calculates the appropriate guidance commands that will result in an intercept and send these commands to the interceptor to execute, a “beamrider” in which an IR sensor mounted aft of the interceptor “rides” an IR beam from the platform to the target, or a Homing Guidance (active, semi-active or passive) in which a sensor mounted forward of the interceptor locks onto the target. 
     SUMMARY OF THE INVENTION 
     The following is a summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and the defining claims that are presented later. 
     The present invention provides an integrated propulsion and attitude control system (ACS) for an interceptor. 
     This is accomplished by providing the interceptor with a rocket motor having ports both forward and aft of the rocket propellant. Propellant burn forms a common pressure vessel for high-pressure gas to provide both propulsion and attitude control. One or more main nozzles in communication with the aft port convert high-pressure gas into a high-velocity gas that is expelled in a generally axial direction to propel the interceptor. The main nozzle(s) and stabilization fins are fixed, there is no servo control to the main nozzles or fins to affect attitude control. An ACS comprises one or more fixed attitude control nozzles in communication with the forward port to convert high-pressure gas into a high-velocity gas and expel the high-velocity gas in generally radial directions offset from the interceptor Cg to change the attitude of the interceptor. In an embodiment in which the main nozzle(s) are configured to produce a rolling airframe, a single attitude control nozzle provides both pitch and yaw control. In another embodiment, a set of four attitude control nozzles provides pitch, yaw and roll control. The multi-nozzle configurations may share a common throat for converting the high-pressure gas to high-velocity gas. A flight control system responsive to guidance commands, commands one or more valves to control the flow of the high-velocity gas through the one or more attitude control nozzles to maneuver the interceptor. 
     These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of engagement CONOPOS for firing an interceptor in accordance with the present invention from a helicopter to engage and defeat a MANPADs threat; 
         FIG. 2  is a diagram of the interceptors and other systems mounted on a helicopter wing for engaging and defeating the MANPADS threat; 
         FIGS. 3   a  and  3   b  are perspective and cut-away views of an embodiment of the interceptor revealing the common pressure vessel for integrated propulsion and ACS; 
         FIG. 4  is a cut-away view of an embodiment of the integrated propulsion and ACS from the common pressure vessel; 
         FIG. 5  is a perspective view of an embodiment of the ACS for providing yaw, pitch and roll control; 
         FIG. 6  is a diagram of an embodiment of an asymmetric nozzle arrangement in which different pairs of nozzles are actuated to provide yaw, pitch and roll control; and 
         FIG. 7  is a cut-away of an embodiment in which a single attitude control nozzle provides yaw and pitch control to a rolling airframe/ 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides an integrated propulsion and attitude control system (ACS) for an interceptor. Propellant burn forms a common pressure vessel for high-pressure gas. An aft port in the rocket motor directs gas through one or more main nozzles that expel high-velocity gas in a generally axial direction to propel the interceptor. A forward port directs gas through one or more attitude control nozzles that expel high-velocity gas in a generally radial direction to control the attitude of the interceptor. The main nozzle(s) and stabilization fins are fixed, there is no servo control to the main nozzles or fins to affect attitude control. 
     The use of a common pressure vessel enables an integrated propulsion and ACS that can be compact, lightweight and inexpensive. The elimination of a second energy source to power the ACS, and specifically servo motors for mechanical control, streamlines the ACS and reduces the overall size, weight and cost of the combined propulsion and ACS. These attributes are generally desirable and are in particularly necessary for interceptors configured as counter-missile missiles in which the interceptor must be quite small and inexpensive. 
     Without loss of generality, the integrated propulsion and ACS will be described for an embodiment of a counter-missile missile launched from an airborne platform such as a jet fighter, helicopter or unmanned aerial vehicle (UAV). For context and clarity, an embodiment of a weapons system that employs the interceptor and the engagement CONOPS for using the interceptor to engage a MANPADS launched missile and the MANPADS operator are presented. 
     Referring now to  FIGS. 1 and 2 , in an embodiment a helicopter  10  is provided with a tube-launched missile system  12  for offensive engagement of targets and a counter-threat missile system  14  for defensive operations to protect the helicopter. These systems may be mounted on a wing  15  of helicopter  10 . Tube-launched missile system  12  launches missiles  16  such as Hydra 70 System that are launched from a tube  18  and designed to engage and defeat air-to-air or air-to-ground target packages. Accordingly, these missiles need the range and explosive or kinetic energy to defeat targets such as other helicopters, airplanes, tanks, ground installations etc. Counter-threat missile system  14  launches interceptors  20  from a launcher pod  22  in response to a detected threat such as a rocket  24  launched from a MANPADS  26 . The system suitably includes a missile-warning sensor  28  to detect threat launches with a field-of-view (FOV)  29  and a directed infrared counter measures (DIRCM) system  30  (See U.S. Pat. No. 7,378,626) to track the threat and provide guidance to interceptor  20 . Accordingly, the interceptors are designed to engage and defeat the rocket and possibly the MANPADS operator  32 . As such, the interceptor requires limited range and firepower but must be small, lightweight and inexpensive while exhibiting the necessary thrust and maneuverability to engage the threat. These requirements render conventional ACS approaches such as thrust vector control and aerodynamic control impractical. 
     In a typical engagement scenario, missile-warning sensor  28  detects a threat launch of rocket  24 , which activates DIRCM system  30  to track the incoming rocket with a laser beam  34 . The helicopter&#39;s defense system selects the counter-threat missile system  14  to engage the threat and launch interceptor  20 . In this embodiment, interceptor  20  has an aft facing IR sensor that rides laser beam  34  to engage and defeat rocket  24 . Alternately, the interceptor may have a forward facing IR seeker to acquire, track and perform end game maneuvers. Or the interceptor may be configured for command line-of-sight (CLOS) guidance. A UAV in the theater of operations may detect the launch of rocket  24  from MANPADS  26  and direct DIRCM system  30  to illuminate the MANPADS  26  with a laser beam  36 . Counter-threat missile system  14  launches a second interceptor  20  that rides laser beam  36  to engage and defeat the MANPADS launcher  26  and operator  32 . 
     In an alternate scenario, the helicopter surveillance system detects the MANPADS launcher and operator as a potential threat and activates the DIRCM system  30  to acquire and track the MANPADS launcher  30 . Counter-threat missile system  14  fires a pair of interceptors  20  in quick succession. Operator  30  fires the MANPADS rocket  24 . Missile warning sensor  28  detects the MANPADS launch. The DIRCM system acquires the rocket  24  and directs the first interceptor  20  to engage and defeat the rocket. The second interceptor  20  holds its original course. After the rocket is defeated, the DIRCM system reacquires the MANPADS launcher and operator and the second interceptor  20  resumes beam rider guidance to engage and defeat the MANPADS launcher and operator. 
     Referring now to  FIGS. 3   a  and  3   b , an embodiment of interceptor  20  comprises a warhead  40  and a target detection module  42  for detonating warhead  40  in the nose of an airframe  44 . Target detection module  42  may include a proximity or impact sensor to trigger detonation. A mid-body integrated propulsion and ACS  46  placed behind the warhead includes a rocket motor  48  that burns propellant to form a common pressure vessel. An aft port  50  in the rocket motor directs gas through a pair of fixed main nozzles  52  on opposite sides of the air frame that expel high-velocity gas in a generally axial direction to propel the interceptor. A forward port  54  directs gas through four fixed attitude control nozzles  56   a ,  56   b ,  56   c  and  56   d  that expel high-velocity gas in a generally radial direction to control the attitude of the interceptor. Valves  58   a ,  58   b ,  58   c  and  58   d  are commanded in pairs to control the flow of high-velocity gas through the nozzles to maneuver the interceptor in yaw, pitch and roll. The beam rider IR sensor  60 , electronics for the guidance system  62  that produces guidance commands and the flight control system  64  that is responsive to those commands to command the ACS  46 , and more particularly valves  58   a - 58   d , to maneuver the interceptor, and a battery  66  to power the electronics, valves and other systems on the interceptor are placed at the aft end of the interceptor. Four fixed fins  68  provide aerodynamic stabilization for the interceptor. The main nozzle(s)  52  and stabilization fins  68  as well as the attitude control nozzles  56   a - 5   d  are positionally fixed, there is no servo control to change the orientation of the main nozzles or fins to affect attitude control. 
     The use of a common pressure vessel to provide energy to both propel and maneuver the interceptor combined with the elimination of all servo control for ACS allows for an ACS and overall interceptor that is small, lightweight and inexpensive. In an embodiment, the interceptor is less than approximate 6.8 kilograms (15 pounds), 61 cm (15 inches) in length and 8 cm (3 inches) in diameter. These weights and dimensions are merely exemplary for a counter-missile missile but illustrate the ability to provide full 3-axis attitude control in a small interceptor. The ACS does consume energy provided by the rocket motor that is not available for propulsion. In a typical counter-missile missile the ACS will consume less than 10% of the energy produced from propellant burn. 
     Referring now to  FIGS. 4 and 5 , the integrated propulsion and ACS  46  includes rocket motor  48  that comprises a cylindrical motor can  70  having ports  54  and  50  forward and aft, respectively and a rocket propellant  72  therein. Propellant burn forms a common pressure vessel  74  with can  70  for high-pressure gas. In this embodiment, rocket propellant  72  is formed with a cylindrical hole along a longitudinal axis  76  of the interceptor. When ignited, rocket propellant  72  burns radially inside-to-out forming a single combustion chamber coextensive with the common pressure vessel. In an alternate embodiment, rocket propellant  72  is solid. When ignited, the propellant burns axially from both ends forming a pair of combustion chambers on either side of the remaining rocket propellant. 
     The pair of fixed main nozzles  52  receive high-pressure gas from common pressure vessel  74  through all port  50 , convert the high-pressure gas to a high-velocity gas and expel the gas in a generally axial direction (along longitudinal axis  76 ) to propel the interceptor. For the mid-body design, the main nozzles must be canted to expel the high-velocity gas outside the airframe. In general, the nozzles are canted to remove any non-axial thrust. However, the nozzles may be canted to produce a moment with respect to the axial thrust vector that produces roll to create a rolling airframe. For an aft-body design, a single main nozzle may be oriented along the longitudinal axis. To induce roll, the main nozzle may be formed with helical flutes. 
     Each main nozzle  52  has an associated throat  78  that converts the high-pressure gas to high-velocity gas  80  and an output port  82  that expels the high-velocity gas in a generally axial direction  84 . In this embodiment, each main nozzle  52  has its own throat  78  to convert the high-pressure gas to high-velocity gas inside the nozzle. In an alternate embodiment, the main nozzles could share a common throat. 
     The four fixed attitude control nozzles  56   a ,  56   b ,  56   c  and  56   d  receive high-pressure gas from common pressure vessel  74  through forward port  54 , convert the high-pressure gas to a high-velocity gas  86 , and expel high-velocity gas  86  in generally radial directions  88   a ,  98   b ,  88   c  and  88   d  (approximately normal to longitudinal axis  76 ) to control the attitude of the interceptor in pitch, yaw and roll. The nozzles may be canted forward a couple of degrees e.g. 1-3 degrees to compensate for the velocity of the airstream so that the resulting force vectors more closely approximate a true radial direction orthogonal to the longitudinal axis. The expulsion of high-velocity gas  86  through any one or more of the nozzles produces a moment with respect to the main thrust vector along longitudinal axis  76 . This moment may cause the interceptor to yaw, pitch or roll. 
     Each attitude control nozzle  56   a ,  56   b ,  56   c  and  56   d  has an associated throat  90  that converts the high-pressure gas to high-velocity gas  86  and an output port  92   a ,  92   b ,  92   c  and  92   d  that expels the high-velocity gas in the generally radial directions  88   a ,  98   b ,  88   c  and  88   d . In this embodiment, the attitude control nozzles share a common throat  90 . A manifold  94  provides the common throat  90  to meter and direct flow of the high-velocity gas  86  to the four output ports  92   a ,  92   b ,  92   c  and  92   d  via the four valves  58   a ,  58   b ,  58   c  and  58   d . In an embodiment, the common throat  90  is a Mach 1 choke port. The use of a common throat, as opposed to individual throats within each nozzle, provides a uniform metered flow rate for each nozzle. 
     Referring now to  FIG. 6 , the output ports of the four attitude control nozzles are labeled “1”, “2”, “3” and “4” to illustrate an embodiment for providing yaw, pitch and roll control. Each of the output ports is offset from the center  96  of the interceptor (and from the Cg of the interceptor) to produce a moment with respect to the main axial thrust vector. Actuating the valves for “1” and “2” produces a moment that causes the interceptor to pitch left. Actuating the valves for “3” and “4” produces a moment that causes the interceptor to pitch right. Actuating the valves for “1” and “4” produces a moment that causes the interceptor to yaw down. Actuating the valves for “2” and “3” produces a moment that causes the interceptor to yaw up. Actuating the valves for “1” and “3” produces a moment that causes the interceptor to roll counter clockwise. Actuating the valves for “2” and “4” produces a moment that causes the interceptor to roll clockwise. It will be apparent to one skilled in the art that there are other configurations of more or less attitude control nozzles that produce 3-axis attitude control. 
     Referring now to  FIG. 7 , an embodiment of an integrated propulsion and ACS  100  produces a rolling airframe and 2-axis pitch and yaw control with a single attitude control nozzle  102 . System  100  includes a rocket motor  104  comprising a motor can  106  having ports  108 ,  110  forward and aft and a rocket propellant  112  therein. Propellant burn forms a common pressure vessel  114  for high-pressure gas. A fixed main nozzle  116  having a throat  118  in communication with the aft port  100  and the common pressure vessel converts high-pressure gas into a high-velocity gas  119  and expels the high-velocity gas in a generally axial direction  120  to propel the interceptor and to impart roll  122  to the interceptor. In this embodiment, the main nozzle  116  is formed with helical flutes  124  to impart the roll. In an alternate embodiment, a pair of main nozzles could be canted to impart the roll. Single fixed attitude control nozzle  102  has a throat  126  in communication with the forward port  108  and the common pressure vessel to convert high-pressure gas into a high-velocity gas  128  and expel the second high-velocity gas through an output port  130  in a generally radial direction  132  offset from a center of gravity (Cg) of the interceptor. A valve  134  controls the flow of the high-velocity gas through the attitude control nozzle. 
     The creation of the common pressure vessel to provide a single source of high-pressure gas to both propel the interceptor and provide attitude control is critical to providing an ACS and full-up interceptor that is small, lightweight and inexpensive with required maneuverability performance. However, the use of the common pressure vessel to source two different systems complicates the motor design process. The propellant grain design has to support the boost-sustain thrust profile requirement to maintain control via the main and attitude control nozzles all the way to the target. If both throats are sized correctly, an appropriate portion of the gas will flow to the rear and the rest to the front. The rocket motor and both throats must be designed and the nozzles controlled to main the common high-pressure vessel and flame front without causing overpressure when the attitude control thrust is not required. For a rocket motor that burns radially inside-to-out, propellant burn forms a common combustion chamber for both propulsion and attitude control. When attitude control thrust is not being used, the high-pressure is vented through the main nozzle. For a rocket motor that burns axially from both end, propellant burn forms a combustion chamber aft for propulsion and a combustion chamber forward for attitude control. If the valves for attitude control are normally closed, the forward combustion chamber may overpressure and cause the motor to fail. Operating the ACS with the valves in a normally open position vents the high-pressure gas and maintains conditions for efficient and safe motor operation. 
     While several illustrative embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.