Abstract:
A system for controlling attitude about pitch, yaw, and roll axes and axial thrust of a body. The system comprises a main thrust generator located on an aft portion of the body and at least one reaction control system (RCS) located on a forward portion of the body. A thrust vector controller (TVC) is connectable to the main thrust generator and at least one RCS controller is connectable to the RCS. The RCS controller and the TVC are synchronized to adjust the direction of the principal line of thrust through the body center of gravity.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to thrust vector control systems and, more particularly, to synchronized forward and aft thrust vector control. 
     2. Prior Art 
     Referring to FIG. 1, thruster positioning mechanisms and systems are used on spacecraft  1  or similar bodies for the purpose of directing the propulsive force from a thruster. Such systems are often used to align the thrust vector  5  reaction through the center of mass  3  of the spacecraft  1  to enable straight line acceleration. Vectoring of the thrust away from the center of mass  3  is often done to initiate vehicle rotation or for course changing maneuvers. Such thrust vectoring is used to control the pitch and yaw rate of the spacecraft  1 . 
     In zero-length launch of aircraft, the jet engine is used with a rocket motor to accelerate the aircraft to flying speed in a brief interval of time. In early designs of such aircraft, such as described in the patent to Mathiesel et al, U.S. Pat. No. 2,922,602, the rocket motor was positioned to direct its thrust through the center of gravity of the aircraft. 
     In later designs, wherein the jet engine is displaced from the longitudinal axis of the aircraft, the rocket motor is positioned to balance the respective aerodynamic, engine thrust and motor thrust moments around the aircraft center of gravity. A major problem of this later design encountered during zero launch is the control of the aircraft pitching moments which are dependent upon: the magnitudes and variations of engine and rocket motor thrust; the variations in the center of gravity during the boost phase; the variations in the aircraft aerodynamics; and the engine exhaust impingement on the rocket motor assembly. 
     It has been suggested in the prior art that a thrust vector control system (TVCS) be used with a control device in the rocket exhaust nozzle or aft of the rocket exhaust nozzle. Since the rocket motor is normally jettisoned after launch, such a control system would be jettisoned with the boost motor, thus increasing launch costs. 
     In addition, such conventional TVCSs located in the rocket exhaust nozzle require rapid response performance capability. Which, when coupled with a very high reliability requirement necessitates the need for a very complex and expensive TVCS. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the invention a system for controlling attitude about pitch, yaw, and roll axes and axial thrust of a body is provided. The system comprises a main thrust generator located on an aft portion of the body. The aft portion of the body being aft of a calculated dynamic center of gravity of the body. A thrust vector controller (TVC) is connectable to the main thrust generator. The system also comprises at least one fast reaction control system (RCS), located on a forward portion of the body. The forward portion of the body being forward of the calculated dynamic center of gravity of the body. An RCS controller is connectable to, and synchronized with the RCS and the TVC. 
     In accordance with another embodiment the invention is directed towards an attitude control system for controlling momentum vector force about a center of gravity of a rocket. The system comprises a main propulsion nozzle having a main propulsion axis wherein the main propulsion nozzle is disposed aft of the center of gravity. The main propulsion nozzle is steered by a main propulsion controller. The system also comprises a forward located reaction control system having a plurality of selectively and independently controlled radial force generating nozzles. The plurality of radial force generating nozzles are synchronized to work in conjunction with at least one controllable aerodynamic vane and the main propulsion controller. 
     In accordance with another embodiment of the invention a rocket controller is provided. The rocket controller is disposed within a rocket having forward and aft sections, a central axis, and a dynamic center of gravity. The rocket controller comprises a principal thrust generator located aft of the rocket dynamic center of gravity and a thrust vector controller. The thrust vector controller is adapted to control the thrust generator. The rocket controller also comprises a second thrust generator located forward of the rocket dynamic center of gravity, and a second thrust vector controller. The second thrust vector controller is adapted to control the second thrust generator. 
     In accordance with another embodiment the invention includes a method for synchronizing forward and aft thrust vector control for a body traveling in a fluid. The body is adapted to minimizing fluid resistance and having forward and aft sections; and has a primary thrust generator disposed in the aft section, and a secondary thrust generator disposed in the forward section. The method comprises the steps of initiating the primary thrust generator and calculating a dynamic center of gravity for the traveling body. Next, the principal thrust axis generated by the primary thrust generator is calculated and compared with the calculated center of gravity to determine an offset between the principal thrust axis and the dynamic center of gravity. If the offset exceeds a predetermined value then the offset is adjusted to the predetermined value or lower by synchronized operation of the primary and secondary thrust generators. 
     The invention is also directed towards a program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform method steps for synchronizing forward and aft thrust vector control for a body traveling in a fluid. The body is adapted to minimizing fluid resistance and having forward and aft sections, a primary thrust generator disposed in the aft section, and a secondary thrust generator disposed in the forward section. The method comprises the step of initiating the primary thrust generator and calculating a dynamic center of gravity for the traveling body. The next step calculates a principal thrust axis generated by the primary thrust generator and determines an offset between the principal thrust axis and the dynamic center of gravity. If the offset exceeds a predetermined value the next step adjusts the offset to the predetermined value, or lower. The step of adjusting the offset further comprises the step of calculating a torque required to adjust the offset to the predetermined value and initiating the secondary thrust generator to apply the calculated torque. In addition, the primary thrust generator is steered to assist in adjusting the offset to the predetermined value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
     FIG. 1 is a pictorial view of a body in a fluid, illustrating relationships between a moveable thrust force vector, center of mass, and vehicle axis; 
     FIGS. 2A-2C show a series of pictorial views of a body in a fluid illustrating one embodiment of this invention; 
     FIG. 3 is a pictorial view of a body incorporating features of the present invention; 
     FIG. 4 is a method flow chart using the invention shown in FIG. 3 
     FIG. 5 is a cross-sectional view of a rocket body showing distribution of thrusters arranged radially around the rocket body; 
     FIG. 6 is a cross-sectional view of a rocket body showing thrusters arranged tangentially to the rocket body; and 
     FIG. 7 is a pictorial view of a body incorporating features of an alternate embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 3, there is shown an perspective view of a rocket body  32  incorporating features of the present invention. Although the present invention will be described with reference to an embodiment in a rocket as shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments, and it is not intended that this invention is limited only to that particular type of embodiment. In an alternate embodiment the present invention could also be used in any suitable type of body in a fluid where thrust vector control is required; such as, for example, torpedoes or submarines. 
     With general regard to rocket propulsion, reference can be had to “Rocket Propulsion Elements”, by George P. Sutton, 6 th  ed., 1992, the disclosure of which is incorporated by reference in its entirety. 
     Referring now to FIG. 3 there is shown a pictorial view of a body  32  incorporating features of the present invention. A reaction control system (RCS)  34  is operated synchronously with a main thrust vector control system  36  to correct a thrust vector TV generated by a main propulsor  38 . The combined RCS  34  and TVC  36  subsystems can be made to have a lower complexity and cost than a single RCS or a single TVC subsystem that performs singly and independently. The subsystems complement their respective performances in term of response capability, eliminating the need for either to have a wide dynamic range. The RCS thrusters and propellant storage are located in the forward section and respond to autopilot signals with a relatively fast band pass to control short-term dynamic disturbances. The complementary TVC is a relatively simple positioning device for repositioning the engine thrust vector. The TVC eliminates the principal rocket attitude disturbance, which is offset of the thrust vector and the vehicle center of gravity (CG)  39 . This disturbance is the largest in the vehicle system and moves slowly as the main propulsion propellant is depleted. CG offset is uncertain at liftoff and is determined only after the vehicle is in powered flight. The TVC  36  can be a relatively simple positioning device, possibly electro-mechanical or hydraulic, with high mechanical advantage, since relatively slow dynamical motions are to be controlled by it. Rapid dynamical motions are controlled by the RCS  34 , which stabilizes the vehicle until the TVC  36  has had sufficient time to align the thrust vector and the CG  39 . 
     Still referring to FIG.  3  and now FIGS. 5 and 6, the RCS  34  may consist of any suitable thrust generator system. For example the RCS may comprise at least three radial thrusters FIG. 5 item  52  or at least two tangential thrusters FIG. 6 items  53  comprising mass expulsion devices, arranged in a pattern around the forward section of the body  58 . The radial thrusters  52  are arranged to selectively produce a radial thrust vector, where the vector sum of the radial thrust vectors is perpendicular to the axial thrust generated by the main propulsor  38 . The tangential thrusters  53  produce thrust in opposing directions to control rotation of the vehicle around its long axis  59 . In an alternate embodiment the RCS system may comprise a combination of radial and tangential thrusters. 
     The main thrust vector generated by the main propulsor  38  is gimbaled, and has a thrust vector controller (TVC), so that its line of action can be steered through the CG  39  to minimize disturbance torque TD. The slower TVC  36  also operates in synchronicity with the faster RCS in order to steer the main thrust vector through the body&#39;s center of gravity CG  39 . 
     This may be illustrated by referring also to FIG. 2A where the initial line of action LOA of the engine  2 A 1  thrust is shown not to pass through the center of gravity CG of the launch vehicle  1 ; resulting in a disturbance torque TD. Referring also to FIG. 2B, the disturbance torque TD is initially corrected by the reaction control system RCS generating a corrective torque TC to counteract the disturbance torque TD. The control torque TC generated by the fast acting RCS thruster prevents the vehicle from rotating under the influence of TD while the slower thrust vector controller TVC gimbals the engine  2 A 1  to align the thrust line of action LOA through the center of gravity CG as shown in FIG.  2 C. The RCS is operated over very short time scales to generate torques of high magnitude, thus providing fast control with respect to the slower main thrust vector controller. 
     The TVC is designed to steer the direction of thrust at a rate slower than typical thrust vector control systems, thus enabling the gimballing system to be built for a lower cost. Over a predetermined time frame the disturbance torque TD is reduced to an acceptable level via TVC. In this manner, the control torque TC generated by the RCS can be reduced to zero in a reasonable interval and the RCS propellant is conserved since it is expended at a high rate only for short spans of time. In addition, the line of action of the engine is maintained in a constant direction throughout this operation. To achieve this, a small counterclockwise rotation of the vehicle is obtained by making TC slightly greater in magnitude than TD during this operation. 
     Referring now to FIG. 4 there is shown a method flow chart using the invention shown in FIG.  3 . The primary thrust generator  41  is initiated to generate the primary thrust vector. The next steps determine  42  the center of gravity of the body and the line of action, step  44 . The line of action is then analyzed  43  for intersection with the body&#39;s center of gravity. If the LOA passes within a predetermined distance from the body&#39;s center of gravity the process is repeated by again determining  42  the body&#39;s center of gravity and the LOA  44 . If the LOA does not pass through the center of gravity the complementary reaction control system RCS and the thrust vector controller TVC are operated  45  until the LOA passes through the body&#39;s center of gravity. 
     In this manner, the advantageous complementary action of a fast acting mass expulsion RCS with a low complexity TVC offers a simple and low-cost alternative to high-performance TVC systems, and to RCS systems with excessive propellant requirements. 
     Referring also to FIG. 7, in an alternate embodiment the RCS may comprise a combination of radial thrusters  52  and/or tangential thrusters  53  and at least one aerodynamic vane item  71 . The radial thrusters are then operated in synchronicity with the aerodynamic vane  71  in order to produce the corrective thrust. 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.