Abstract:
A method for adjusting a control moment gyroscope array includes receiving a stream and directing the stream to adjust momentum in the control moment gyroscope.

Description:
BACKGROUND 
       [0001]    Embodiments of this disclosure generally relate to a control moment gyroscope (CMG), and more particularly, to managing momentum in CMGs using vectored air and/or bleed exhaust from a propulsion system. 
         [0002]    CMGs may be commonly employed in aircraft systems for controlling attitude. A generalized CMG may include a housing that supports an inner gimbal assembly (IGA). The IGA may include a rotor having an inertial element, for example, a rotating ring or cylinder coupled to a shaft. Spin bearings may be disposed around the shaft ends to facilitate the rotational movement of the shaft, which may be rotated about a spin axis by a spin motor. 
         [0003]    The IGA, in turn, may be rotated about a gimbal axis by a torque module assembly (TMA) mounted to a first end of the CMG housing. To facilitate the rotational movement of the IGA, gimbal bearings may be disposed between the IGA and the CMG housing. A sensor module assembly (SMA) may also be mounted to a second portion of the CMG housing opposite the TMA to deliver electrical signals and power to the IGA. The CMG may include a number of sensors suitable for determining rotational rate and position of the IGA. 
         [0004]    A CMG may include a spinning rotor and one or more motorized gimbals that tilt the rotor&#39;s angular momentum. A plurality of CMGs may be arranged to form an array. Control of the CMGs in the array may be performed individually or in concert as part of a momentum management system. 
         [0005]    Losses and external disturbances may saturate the momentum in a CMG array. The saturated moment may result in loss of effectiveness of the CMG for control that may prevent desired attitude. By desaturating, the CMG momentum may be brought back into nominal values and function properly. 
         [0006]    Therefore, it would be desirable to provide a system and method for desaturating CMGs in aircraft. 
       SUMMARY 
       [0007]    A method for adjusting a control moment gyroscope array on board an aircraft includes receiving a stream and directing the stream to reduce momentum in the control moment gyroscope. 
         [0008]    A control moment gyroscope array has saturated angular momentum and a channel receiving airflow for removing the saturated angular momentum. 
         [0009]    A system has a control moment gyroscope array and at least one channel vectoring thrust to act on the control moment gyroscope array for desaturating angular momentum. 
         [0010]    The features, functions, and advantages may be achieved independently in various embodiments of the disclosure or may be combined in yet other embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments of the disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0012]      FIG. 1  is an array of exemplary control moment gyroscopes (CMGs); 
           [0013]      FIG. 2  is a number of illustrative planes formed by rotating the CMGs; 
           [0014]      FIG. 3  is an exemplary graph providing momentum vectors of the CMGs; 
           [0015]      FIG. 4  is an exemplary graph providing vector sums in a zero momentum state; 
           [0016]      FIG. 5  is an exemplary graph providing residual momentum that is non-zero; 
           [0017]      FIG. 6  is an illustrative system for mitigating residual momentum in CMGs; 
           [0018]      FIG. 7  is an illustrative system for desaturating the CMGs through an airstream; 
           [0019]      FIG. 8  is an exemplary block diagram providing generalized components for desaturating the CMGs; and 
           [0020]      FIG. 9  is a flow chart providing illustrative processes for desaturating the CMGs. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Control moment gyroscopes (CMGs) may be used for many applications including platform stabilization and vibration control of machinery. CMGs may be commonly used in transportation systems such as spacecraft, aircraft or watercraft. As part of their use, losses and periodic disturbances may result in momentum buildup in spacecraft for which magnetic torque rods or jets are used for desaturation. External disturbances may give rise to the accumulation of residual momentum. The residual momentum may build up to a point where the CMG array becomes saturated. When saturated, the useful torque and momentum transfer provided by the CMGs may be limited. 
         [0022]    Typically, at least three CMGs may be used to perform three-axis stabilization as CMG momentum may be constrained to an aircraft. In one embodiment, two CMGs in a scissor-pair arrangement to control torque and momentum in one axis may be used. Referring to  FIG. 1 , an array of exemplary CMGs  102 A,  102 B and  102 C (collectively  102 ) may be shown. The CMGs  102  may be in a box configuration with their momentum vectors oriented in a nominal +Z direction. Each CMG  102  may include an inner gimbal assembly (IGA)  104 A,  104 B and  104 C (collectively  104 ) that has a rotational degree of freedom about its gimbal axis  106 A,  106 B and  106 C (collectively  106 ). 
         [0023]    The IGAs  104  may contain a rotating inertial mass (rotor) that may store angular momentum. This rotor  102  may be suspended in a rotating mount. The angular momentum vectors H 1 , H 2  and H 3  of the IGAs  104  may be processed about their gimbal axis  106  thereby creating control torque. H 1  may be associated with CMG  102 A, H 2  may be associated with CMG  102 B and H 3  may be associated with CMG  102 C. Gimbal actuation may be accomplished using a mechanism often called a torque module assembly (TMA)  108 A,  108 B and  108 C (collectively  108 ). Each momentum vector H 1 , H 2  and H 3  may be oriented in a plane formed by the rotation about each gimbal axis  106 . 
         [0024]    While multiple CMGs  102  have been shown, other configurations may exist. CMGs  102  may be single or multiple gimbaled devices. Applications requiring significant levels of torque may tend to have a single-gimbal in order to take advantage of what is often referred to as “torque multiplication”. Double gimbal devices may be used where low torque, high momentum may be required. Furthermore fewer or more CMGs  102  may be used that do not have to be constrained to a plane. 
         [0025]    In  FIG. 2 , a number of illustrative planes  202 A,  202 B and  202 C (collectively  202 ) formed by rotating each CMG momentum vector H 1 , H 2  and H 3  for the CMGs  102  depicted in  FIG. 1  may be shown. The momentum vector H 1  of CMG  102 A may be provided in plane  202 A. The momentum vector H 2  of CMG  102 B may be provided in plane  202 B, while the momentum vector H 3  of CMG  102 C may be provided in plane  202 C. The three planes  202  may form a box configuration  200 . 
         [0026]    In one embodiment, the momentum vectors H 1 , H 2  and H 3  may be oriented such that the net momentum for the CMGs  102  may be zero. Turning to  FIG. 3 , an exemplary graph providing momentum vectors H 1 , H 2  and H 3  of the CMGs  102  may be shown. H 1  and H 2  may have momentum vectors angled at thirty degrees that may cancel their Y-axis components along with the vertical component of H 3  along the Z-axis.  FIG. 4  may show how the momentum vectors H 1 , H 2  and H 3  sum to a zero momentum state. 
         [0027]    When saturated, the momentum is non-zero which may make the CMGs  102  loose effectiveness and control. When an array  102  is completely saturated, there is no amount of momentum that may be extracted in that particular direction (in the saturated direction). In one embodiment, “saturated” may describe when the momentum is above a threshold, but may be interchangeable with completely saturated. Utilization of CMG momentum in attitude control may include creating torque by rotating the individual CMG momentum vectors. That torque may be reacted by the host structure that in turn rotates. The relative rotation of the host structure may tend to balance the momentum in the CMG array  102 . In other words, the host platform may rotate with momentum equal to and opposite that of the CMG array  102 . In a condition where the host platform is at rest and the momentum of the CMG array  102  is non-zero, the residual may act to mitigate the amount of torque and momentum that may be used to control the angular attitude and rate of the host structure. Management of that momentum residual may be used to have effective attitude control so desaturation may be utilized. In rare cases, an operator or system may elect to create a bias momentum vector prior to a large momentum maneuver in order to extend the amount utilized in a maneuver, later to be desaturated towards a nominal, zero momentum state. The same methods may be utilized to desaturate a CMG array  102  and may be used to build up a momentum bias in anticipation of such a maneuver. 
         [0028]    In  FIG. 5 , an exemplary graph providing residual momentum  502  may be shown. This residual momentum  502  may result from frictional losses, bias torque on the system or a number of other contributors. Ultimately, the residual momentum  502  may limit the amount of torque that may be extracted from the CMGs  102 . 
         [0029]    The combination of vectors H 1 , H 2  and H 3  shown in  FIG. 5  has a non-zero residual momentum  502 . Residual momentum  502  in the CMG array  102  may be mitigated by applying an external torque in the direction equal to and opposite to the system. The torque may be provided through a process referred to as desaturation. The residual moment  502  of the CMGs  102  may be driven to a desired momentum state by generating a command equal to the difference between the desired state and the momentum residual times some gain. The Law of Conservation of Angular Momentum provides that the residual momentum  502  may be determined by summing the momentum of the platform and the momentum stored in the CMGs  102 . In a zero residual momentum state, the platform and CMG momentum may be equal and opposite. The goal of desaturization may be to drive the residual momentum  502  in the CMGs  102  to zero or within a threshold of zero. A bias momentum state may be created in anticipation of a specific maneuver. When a bias momentum state is generated, the amount of momentum transfer may be extended beyond that available by initiating the maneuver from a zero-bias state. 
         [0030]    In an aircraft  602 , as provided in  FIG. 6 , utilizing dedicated or existing aero-control surfaces may be used to produce the torque  604  counter to the residual momentum  502  on the CMGs  102  when saturated. The torque  604  may be in a vectored direction that reduces the stored angular momentum in the CMGs  102 . This airflow over the aero-control surface may produce positive torque  604  on the aircraft  602 . In one embodiment, airflow over the tail section may be used. 
         [0031]    As depicted, the aero-control surfaces of the aircraft  602  may produce a roll axis torque M  604  that may cancel a CMG residual momentum  502  in that direction. By utilizing existing sources of thrust from an aircraft  602 , desaturation of residual momentum  502  may no longer require dedicated surfaces or thruster mechanisms. The system may be used in other vehicles having CMGs  102  such as watercraft. A stream of air or liquid may be used. 
         [0032]    Turning to  FIG. 7 , an illustrative system for desaturating the CMGs  102  through an airstream may be shown. The airstream may be taken from outside the aircraft  602 . In the shown embodiment, the airstream may be captured through an air intake  702 . More than one air intake  702  may exist on the aircraft  602 . The intake  702  may include a scoop that receives the airstream. The intake  702  may project from the outer surface of the aircraft  602 , which may be designed to utilize the dynamic pressure of the airstream to maintain a flow of air. The airstream may be taken in through an under carriage of the aircraft  602 . 
         [0033]    The air intake  702  may re-direct air into a duct and manifold management system  704 . The aircraft  602  may have a number of valves  706  that may receive the airstream from the duct and manifold management system  704 . The airstream from the valves  706  may be directed in a manner that produces thrust via nozzles  708  strategically placed on the aircraft  602 . The thrust may then be used to generate torque  604  to desaturate the CMGs  102 . 
         [0034]    While the system for desaturating the CMGs  102  is shown in the tail section of the aircraft  602 , the system may be placed in other locations. For example, the air intake  702  and duct and manifold system  704  may be provided in a middle portion of the aircraft  602  or at least a portion thereof. Portions of the desaturation system may be placed in the wings of the aircraft  602 . 
         [0035]    In one embodiment, the thrust may be generated from another on-board source, for example, an auxiliary power unit (APU) within the aircraft  602 . Bleed thrust from an engine exhaust or a dedicated gas or liquid pressure generating device may also be used. The amount of desaturation torque  604  to be generated may be calculated, commanded and controlled via a processor  710  that utilizes sensor input from the aircraft  602  and CMG sensors. 
         [0036]    In  FIG. 8 , an exemplary block diagram providing generalized components for desaturating the CMGs  102  may be shown. The airstream  802  may be taken from a variety of sources. As shown above, the airstream may be taken from an external source. The airstream  802  may be received by a channel  804 . The channel  804  may include the air intake  702 , duct and manifold management system  704 , valves  706  and nozzles  708 . 
         [0037]    As also shown, the airstream  802  may be taken from a propulsion device on the aircraft  602 . The bleed air may be taken from a compressor of the propulsion device. The bleed air may then be provided to the channel  804 . The channel  804 , in this embodiment, may include fewer or more parts than that described above. For example, the airstream  802  may be directed to the nozzles  708  within the channel  804  without using the air intake  702 , duct and manifold management system  704  and valves  706 . In one embodiment, a combination of both the outside vectored air and the bleed air may be used. 
         [0038]    In each, the channel  804  may have one or more nozzles  708 . The nozzles  708  may be fixed. The fixed nozzles  708  may be selected to direct the airstream  802  to produce a desired torque  604  to desaturate the CMGs  102 . For example, the nozzles  708  may be selected based on angle and amount of torque  604  that may be generated therefrom. Alternatively, the nozzles  708  may be maneuverable. The nozzles may be moved to direct the airstream  802  and to produce the desired torque  604 . 
         [0039]    By gimbaling the nozzles  708  within the channel  804  in a coordinated set of directions, torque  604  may be produced via a steering law or modulating the thrust from fixed nozzles  708  via a selection control law. Similarly, the torque  604  may be generated via commanding aero-control surfaces to generate a torque in a direction opposite to that of the residual  502  and for a duration to produce an equivalent momentum thereby reducing the residual  502  to a near or zero residual state. 
         [0040]    In both the fixed and maneuverable nozzles  708 , software  806  may be used to vector the airstream  802 . The software  806  may also be used for detecting saturation within the CMGs  102 . Sensors may be attached to the CMGs  102  where saturated angular momentum within it may be detected. Saturation may be calculated based on the known orientation of the gimbal axis  106  of the CMGs  102 . In addition to a gimbal angle, an estimation of the individual CMG momentum vectors which may be determined by knowledge of the inertial mass about its spin axis and a sensor that determines the rotational speed may be used. 
         [0041]    The appropriate amount of thrust may be determined within the algorithm and the nozzles  708  therein may be used to generate enough torque  604  to counteract the saturation within the CMGs  102 . Through the channel  804 , torque  604  may be provided to deplete the residual momentum through a combination of aero-control surfaces. 
         [0042]    Referring to  FIG. 9 , a flow chart providing illustrative processes for desaturating the CMGs  102  may be shown. The processes for desaturation the CMGs  102  may begin at block  900 . At block  902 , the system may receive thrust. The thrust, as described above, may come from a variety of sources including outside the aircraft  602  through an air intake  702 . Alternatively, the thrust may be bleed air received from a propulsion device. 
         [0043]    Saturation of the CMGs  102  may be detected at decision block  904 . When saturated, or above the threshold where desaturation is desired, the useful torque and momentum transfer provided by the CMG  102  may be limited. The saturation may be detected by an algorithm or other control circuitry within the array  102  or other control processor. The momentum state may be calculated with an estimation of the stored angular momentum in the individual CMGs along with knowledge of their relative angular orientation through vector math/algorithms. When no saturation has been detected, the processes may end at block  908 . Otherwise, the system may direct torque  604  to desaturate the CMGs  102  at block  906 . The amount of torque  604  to desaturate the CMGs  102  may be computed by the algorithm. Furthermore, nozzles  708  may be either fixed or maneuverable by the algorithm to redirect the airflow. The processes may end at block  908 . 
         [0044]    The features presented herein may be extended to other technologies. For example, the system may be converted such that reaction wheel arrays may be desaturated. Other angular momentum storage systems that combine various momentum devices may also be desaturated using those features presented above. 
         [0045]    The data structures and code within the software  806 , in which the present disclosure may be implemented, may typically be stored on a non-transitory computer-readable storage. The storage may be any device or medium that may store code and/or data for use by a processor. The non-transitory computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing code and/or data now known or later developed. 
         [0046]    The methods and processes described in the disclosure may be embodied as code and/or data, which may be stored in a non-transitory computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the non-transitory computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the non-transitory computer-readable storage medium. Furthermore, the methods and processes described may be included in hardware modules. For example, the hardware modules may include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules. 
         [0047]    The technology described herein may be implemented as logical operations and/or modules. The logical operations may be implemented as a sequence of processor-implemented executed steps and as interconnected machine or circuit modules. Likewise, the descriptions of various component modules may be provided in terms of operations executed or effected by the modules. The resulting implementation is a matter of choice, dependent on the performance requirements of the underlying system implementing the described technology. Accordingly, the logical operations making up the embodiment of the technology described herein are referred to variously as operations, steps, objects, or modules. It should be understood that logical operations may be performed in any order, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language. 
         [0048]    While embodiments of the disclosure have been described in terms of various specific embodiments, those skilled in the art will recognize that the embodiments of the disclosure may be practiced with modifications within the spirit and scope of the claims.