Patent Publication Number: US-2018037340-A1

Title: Satellite management system comprising a propulsion system having individually selectable motors

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The instant application is a continuation-in-part of U.S. patent application Ser. No. 14/844,597 entitled “PROPULSION SYSTEM COMPRISING PLURALITY OF INDIVIDUALLY SELECTABLE SOLID FUEL MOTORS” and filed Sep. 3, 2015, which prior application claims the benefit of Provisional U.S. Patent Application Ser. No. 62/045,493 entitled “SOLID STATE PROPULSION AND ATTITUDE CONTROL SYSTEM FOR SATELLITES” and filed Sep. 3, 2014, the teachings of which are incorporated herein by this reference. 
    
    
     FIELD 
     The instant disclosure relates generally to satellites, and, more particularly, to a satellite control system comprising a propulsion system having a plurality of individually selectable solid fuel motors. 
     BACKGROUND 
     Artificial satellites have long been in use for space or earth observation, reconnaissance, navigation, communications and scientific measurements. Satellites typically consist of a mission payload and a payload platform or bus. The mission payload performs one or more of the aforementioned functions and the payload platform provides electrical power, thermal management, payload pointing, terrestrial communications, and attitude and orbit control to support the mission payload. Electrical power is typically supplied using solar cells and batteries for power storage and supply when the satellite is in earth&#39;s shadow. Thermal management may include heaters when in the earth&#39;s shadow, and payload pointing and reflective materials to avoid solar heating. Communications takes place using an omnidirectional antenna between the satellite and ground stations for state of health telemetry, command and control. Finally, most satellites include an attitude determination and control system (ADCS) consisting of sensors and momentum wheels for keeping the satellite pointed in the correct direction and removing residual momentum. In addition to the ADCS, many satellites include an on-board propulsion system for maneuvering and positioning the satellite. 
     Existing choices for satellite propulsion include monopropellant and bipropellant liquid propellants, cold gas propellants and electric propulsion. Unfortunately, most satellite propulsion systems have significant disadvantages. For example, liquid propellants are frequently toxic, require complex plumbing, valving and pressurization systems and, when firing rocket motors, consume significant power. Cold gas systems, while less complex than liquid propellant systems also require plumbing and valving, have poor mass and delivered impulse efficiency and also require significant power when firing motors. Electric propulsion systems have very high impulse efficiency, but are heavy and typically require very high power levels to operate and produce very low thrust levels. 
     Thus, it would be advantageous to provide a propulsion system that overcomes many of the above-noted deficiencies. 
     SUMMARY 
     The instant disclosure describes a management system for a satellite comprising a power source, a propulsion system comprising individually selectable solid fuel motors, a communication interface and an attitude determination and control system (ADCS). The ADCS receives power from the power source and further receives desired orbital or positional instructions via the communication interface, which may comprise a wireless communication interface. Based on the desired orbital or position instructions, the ADCS generates and provides commands to the propulsion system. In turn, the propulsion system selects and fires one or more motors of the individually selectable solid fuel motors responsive to the commands received from the ADCS. In an embodiment, the propulsion system comprises a substrate, a communication network and a cluster of individually selectable solid fuel motors mounted on the substrate and operatively connected to the communication network. The propulsion system further comprises a controller that is also operatively connected to the communication network and operative to select any one of more motors of the cluster of individually selectable solid fuel motors and transmit signals to fire the one or more motors of the individually selectable solid fuel motors based on the commands. In another embodiment, a satellite may comprise a satellite management system in accordance with the instant disclosure. In addition to the satellite management system, a satellite may further comprise attitude control components and/or sensor components operatively connected to the satellite management system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features described in this disclosure are set forth with particularity in the appended claims. These features and attendant advantages will become apparent from consideration of the following detailed description, taken in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings wherein like reference numerals represent like elements and in which: 
         FIG. 1  is a schematic block diagram of a propulsion system in accordance with the instant disclosure; 
         FIG. 2  illustrates a partial cross-sectional view of a one embodiment of a substrate and a cluster of solid fuel motors in accordance with the instant disclosure; 
         FIG. 3  illustrates perspective view of another embodiment of a substrate and a cluster of solid fuel motors in accordance with the instant disclosure; 
         FIG. 4  illustrates a perspective view of the propulsion system of  FIG. 3  mounted within a deployment pod; 
         FIG. 5  is a cross-sectional view of a solid fuel motor in accordance with the instant disclosure; and 
         FIG. 6  is a schematic block diagram of a first embodiment of a satellite incorporating a pair of propulsion systems in accordance with the instant disclosure. 
         FIG. 7  is s schematic block diagram of a second embodiment of a satellite incorporating a satellite management system in accordance with the instant disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTS 
     Referring now to  FIG. 1 , a propulsion system  100  in accordance with the instant disclosure is illustrated. In particular, the propulsion system  100  comprises a substrate or housing  102  having a cluster of solid fuel motors  106  mounted on the substrate  102 . As used herein, a cluster constitutes a group of same or similar items gathered or occurring closely together. Thus, as illustrated in further embodiments described below, the motors  106  are grouped together with relatively little space between them in order to minimize the overall size of the propulsion system  100 . A controller  108  is operatively connected to each of the motors  106  via a communication network  104 . A feature of the instant disclosure is that each of the motors  106  is individually selectable or addressable by the controller  108 . As further shown, the propulsion system  100  may constitute a component of a satellite  110 . The nature and construction of the satellite  110  is not limited to any particular types, though, as described in further detail below, the beneficial application of the propulsion system  100  to the satellite  110  may depend on the size of the satellite  110 . 
     In an embodiment, the controller  108  and communication network  104  may be implemented using a Smart Energetics Architecture (SEA™) bus as provided by Pacific Scientific Energetic Materials Company of Hollister, Calif., and described, for example, in U.S. Pat. No. 7,644,661, the teachings of which prior patent are incorporated herein by this reference. As known in the art, the controller  108 , as implemented in the SEA bus, can select any one of the individual motors  106  and transmit signals to the selected motor to, among other things, cause that motor to fire. For example, as shown in  FIG. 1 , the controller  108  could send a signal to only the first motor  106   a  of the n different motors. In an embodiment, the number of motors, n, mounted on the substrate  102  may typically number from  10  to  1000  individually addressable motors. In practice, the number of motors used will depend largely upon the nature of the particular application. As used herein, it is understood that the controller  108  may include components that are specific to, and collocated with, respective ones of the motors  106 . For example, in the SEA bus implementation, the controller  108  may comprise a centralized, network controller (implemented as an application specific circuit (ASIC), microprocessor, microcontroller, programmable logic array (PLA), etc.) that communicate with integrated circuits deployed in connection with each of the motors  106 . Because each of the integrated circuits includes a unique identifier stored therein, the network controller can effectively select any individual motor  106 . Generally, the SEA bus is a flight-proven, very low volume and power, multiple-inhibit, space radiation tolerant, ASIC-based control and firing system. In practice, the SEA bus enables firing of hundreds of motors with microsecond repeatability and sub-millisecond sequencing. As indicated by the input signal provided to the controller  108 , the SEA bus is capable of interfacing with a satellite control system via an RS-422 compliant serial bus or other parallel or serial interface options as known in the art. 
     Referring now  FIG. 2 , an exemplary propulsion system  200  is illustrated. In particular, the system  200  comprises a substrate  202  having a substantially (i.e., within manufacturing tolerances) circular perimeter and planar upper surface  203 , as shown. The substrate  202  may be manufactured out of any suitable material such as aluminum, steel, titanium, etc., or a non-outgassing space rated plastic/polymer as known in the art. Each motor  206  is mounted such that its nozzle (see  FIG. 5 ) is substantially flush with the upper surface  203 . Though the substrate  202  is illustrated having an essentially planar surface  203 , this is not a requirement and the surface  203  may be curved as in the case of a cylindrical, hemispherical or other curved shaped. Further still, the upper surface  203  may comprise multiple planar surfaces. As further illustrated in  FIG. 2 , though not a requirement, the cluster of motors  206  is arranged in an array, i.e., according to regular columns and rows. 
       FIG. 5  illustrates an example of a solid fuel motor  506  shown in cross section. As shown, the motor  506  comprises a tubular housing  530  encasing a solid propellant  532 . The tubular housing  530  may be fabricated from any suitable metal such as aluminum, steel or titanium. Preferably, the solid propellant  532  is “green” in that it is free of (or at least minimizes) any metals and is smokeless, and may comprise a single or double base or a composite material. The propellant  532  is hermetically sealed within the housing  530  by an igniter  534  on one end and a burst disk  536  on the other end. The igniter  534  may comprise any suitable igniter as known in the art, including but limited to, including an exploding foil initiator (EFI), a semiconductor bridge (SCB), reactive semiconductor bridge (RSCB), thin film bridge (TFB) or a bridgewire initiator. As shown, the igniter  534  is coupled to a signal path  504  that carries an electrical signal (initiated, for example, in response to a control signal provided by the controller  108  of  FIG. 1 ) capable of firing the ignitor  534 . The burst disk  536  is preferably petaled so as to minimize any debris upon ignition. As further shown and known in the art, the motor  506  may also comprise a nozzle plate  538  to beneficially guide the combustion products provided by the propellant  532 . In an embodiment, each motor  506  is dimensioned to carry 14 g of propellant  532 , and has an overall mass of approximately 20 g. Thus configured, each motor  534  provides 27.4 N-s of impulse upon ignition. 
     Referring once again to  FIG. 2 , in the illustrated embodiment, the substrate  202  is 15 inches in diameter and 5 inches tall, though these dimensions may vary as a matter of design choice. As configured, and assuming motors  206  in accordance with the embodiment of  FIG. 5 , the substrate  202  and cluster of motors  206  fits within a separation system volume of a typical satellite and provides 5500 N-s total impulse or 55 m/s delta-V (i.e., the impulse available to perform a desired maneuver of a satellite) on a 100 kg spacecraft. Although the substrate  202  in  FIG. 2  is shown mounted with approximately 80 motors, it is once again understood that the substrate  202  may include tens or hundreds of such individual motors. Additionally, while the motors  206  illustrated in  FIG. 2  are all of the same size, and therefore possess the same impulse capability, it is understood that this is not a requirement. That is, the cluster of motors may include subsets of motors, where the motors of each subset are of the same size/impulse capability, yet different in size/impulse capability than the motors of each of the other subsets. 
     Referring now to  FIG. 3  an alternate embodiment of a propulsion system  300  in accordance with the instant disclosure is illustrated. In this embodiment, the substrate  302  is once again planar and has a substantially rectangular outer perimeter. In keeping with the so-called CubeSat reference design standard. As known in the art, the CubeSat design standard requires modules that fit within a 10 cm×10 cm×10 cm cube, often referred to as “one unit” or “1U” module. Thus, in the embodiment illustrated in  FIG. 3 , the height (H) and width (W) dimensions of the substrate  302  are selected to be 10 cm each and the depth (D) dimension is selected to be 5 cm, thus forming what is typically referred to as “½U” configuration. Additionally, so-called ¼U or “tuna can” configurations are also possible. It noted that the motors  306  in  FIG. 3 , while clustered as in  FIG. 2 , are not arranged in the column and rows of a rectangular array, but are instead arranged in diagonal rows of differing lengths. As shown in  FIG. 4 , the propulsion system  300  of  FIG. 3  may be mounted within a so-called 3U deployment pod  420 . Assuming compliance with the CubeSat standard and use of the motors  504  described above relative to  FIG. 5 , the propulsion system  300  can provide approximately 40 m/s delta-V for a 3U CubeSat. 
     With reference to  FIG. 6 , an exemplary satellite  610  may comprise pairwise deployments of propulsion systems in accordance with the instant disclosure. More particularly, each pair of propulsion systems may be mounted on the satellite  610  in complementary positions about a center of gravity  640  of the satellite  610 . For example, a first pair of propulsion systems, PS  1 A and PS  1 B, may be configured to induce clockwise rotation of the satellite  610  about the center of gravity  640 , whereas a second pair of propulsion systems, PS  2 A and PS  2 B, may be configured to induce counter-clockwise rotation of the satellite  610  about the center of gravity. Those of skill in the art will appreciate that other pairwise deployments of propulsion systems in other rotational planes may be additionally deployed on the satellite  610 . Alternatively, the pairs of propulsion systems PS  1 A, PS  1 B, PS  2 A, PS  2 B may be configured such that opposing motors can be actuated to induce strictly linear translation of the satellite  610 . Further still, a single “plate” of motors may also be mounted on an axis intersecting the center of gravity  640  with opposing motor pairs actuated for pure linear translation along the axis. 
     In this manner, propulsion systems in accordance with the instant disclosure may be used in addition to or as part of the ADCS (not shown), or linear propulsion system, of the satellite  610 . That is, such propulsion systems, in addition to performing delta-V maneuvers for station keeping, can also perform pointing or attitude control maneuvers. A particular advantage of the presently described propulsion systems is that, by enabling such attitude control capability, satellite operators are able to use lower power momentum wheels and perform “momentum dump” maneuvers. Additionally, since motors are can be fired in pairs around the satellite center of gravity  640 , the random, very small variations in motor impulse result in lower overall residual spacecraft momentum compared to prior art, liquid propulsion systems, once again resulting in less momentum wheel use and energy consumption. 
     Furthermore, use of as SEA bus as described above enables reduction of satellite power requirements and solar panel size. The lack of ancillary hardware of the instant propulsion systems as compared to liquid propellant systems, such as propellant and pressurant tanks, valves, plumbing, and fittings, greatly reduces the package volume of the propulsion systems. Additionally, due to the modular and flexible design of the instant propulsion systems, they are easily adaptable to fit in unused space within satellite structures including separation rings, mounting areas for star trackers, seekers, solar arrays, etc. Further still, the construction of propulsion systems in accordance with the instant disclosure result in a very favorable shipping classification and the “bolt on” nature of a solid propulsion system is possible, thereby greatly reducing life cycle costs due to ease of handling, workflow simplification and design simplicity. 
     Referring now to  FIG. 7 , a second embodiment of a satellite  710  is illustrated. In this embodiment, the satellite  710  includes a management system  720  that, in turn, includes a propulsion system  730  in accordance with the various propulsion systems described above. In particular, the propulsion system  730  includes a controller  734  that communicates with a plurality of individually selectable solid fuel motors  732  as described above. As further shown, the management system  720  further comprises an attitude determination and control system (ADCS)  740 , a communication interface  742  and a power source that includes a battery  744  and a power controller  746 . The battery  744 , which may comprise, for example, a radioisotope thermoelectric generator (RTG) as known in the art, provides electrical power that is controlled and distributed by the power controller  746  to not only the ADCS  740 , but all other components in the satellite  710  requiring electrical power. Optionally, rather than receiving power only from the battery  744 , an external power supply  772  may be used with the power controller  746 . For example, the external power supply  772  may comprise additional known batteries or fuel cells. Alternatively, or additionally, the external supply  772  could take the form of one or more solar cells or solar panels. Furthermore, as known in the art, the power controller  746  may comprise various components used to condition power provided by the battery  744  and/or external supply  772  including but not limited to linear regulators, DC-DC converters, analog dividers, transient voltage suppression (TVS) diodes, combinations thereof, etc. 
     As shown, the satellite  710  may comprise one or more attitude control components including, but not necessarily limited to, one or more momentum wheels  752  and/or one or more magnetic torquers  754 . As known in the art, such components may be used to adjust the orbit or attitude of the satellite  710  as needed. As further shown, the satellite  710  may comprise one or more sensor components including, but not necessarily limited to, a Global Positioning System (GPS) receiver  750 , one or more gyroscopes  756 , one or more magnetometers  758 , a sun sensor  760  and/or a star sensor  762 . As known in the art, such components may be used to determine the actual location and/or attitude of the satellite  710  at any given time. Through use of these components  730 ,  750 - 762 , the ADCS  740  may effectuate any desired corrections or adjustments to the orbit and/or attitude of the satellite  710 . 
     As known in the art, the ADCS  740  may comprise one or more computing devices (such as, but not limited to, a microprocessor, microcontroller, digital signal processor, application specific circuit, programmable logic array, etc.) and other related components (e.g., memory, peripheral interfaces, etc.). The ADCS  740  is configured to receive desired orbital or positional (attitude) instructions via the communication interface  742 . In an embodiment, the communication interface  742  may comprise a wireless communication interface capable of operation at various radio frequencies and using various well-known communication protocols. As shown, the communication interface  742  may receive the desired orbital or positional instructions via a ground- or space-based controller  770  capable of transmitting such instructions to the satellite  710 , as known in the art. Based on these received instructions, and using known techniques, the ADCS  740  determines commands that may be used to control operation of the propulsion system  730  and/or other attitude control components  752 ,  754  to effectuate the desired orbital or positional instructions. For example, if it is desired to adjust the rotation of the satellite  710  about a given axis (and assuming appropriate configuration of the motors  732 ) by a certain number of degrees, this change can be transmitted to the satellite  710  and provided, via the communication interface  742  to the ADCS  740 . In turn, the ADCS  740 , having stored knowledge of the motors  372 , such as availability (i.e., which motors have and have not been previously fired), configuration (i.e., the direction of the force vector that could be applied to the satellite by a given motor) and properties (e.g., the impulse of any given, available motor), provides commands to the propulsion system  730  (specifically, the controller  734 ) to select and fire one or more of the motors  732  to effectuate the desired change. Such knowledge may be stored in suitable memory or the like used to implement the ADCS  740  and updated as the status of individual motors changes. Using appropriate feedback (as provided, for example, by the various sensors  756 - 762 ), the ADCS  740  can assess the effect of the provided commands to determine whether further commands are necessary to properly effectuate the received instructions. 
     As a specific example, the communication interface  742  may receive a suitably encoded transmission embodying an instruction to “translate the spacecraft linearly in the x-direction by 10 m/s for 1.5 seconds.” This instruction is passed to the ADCS  740  and, based on its stored knowledge of the motors  732  and using known algorithms to translate the capabilities of the motors  732  into the desired performance, the ADCS  740  determines one or more commands that can be provided to the controller  734  in order to actuate the necessary motors  732  and/or check sensor measurements for feedback. Suitable algorithms for this purpose may be found, for example, in “Fundamentals of Spacecraft Attitude Determination and Control,” F. L. Markley et al., Springer Science+Business Media (2014) or “Space Mission Engineering: The New SMAD,” edited by J. R. Wirtz et al., Microcosm Press (2011). 
     For example, in light of the received instruction described above, the ADCS  740  can determine that motors labeled 2, 4, 6 and 8 in a first array of motors should be fired at a specific time (i.e., at t=0 ms) to initiate the desired translation. In addition to the issuance of those commands, the ADCS  740  can check sensor inputs to determine if any further commands are necessary, or the ADCS  740  can continue with issuing further commands. Continuing with the current example, after the commands to fire motors 2, 4, 6 and 8 in the first array have been issued, the ADCS  740  can check sensor inputs (e.g., one or more accelerometers) to assess whether recalculations and further commands are needed. That is, the ADCS  740  can incorporate feedback into its determination of commands necessary to effectuate the received instructions. Alternatively, the ADCS  740  can simply proceed with issuing further commands, e.g., fire motors 3, 9 and 12 in the first array after a delay of 0.5 ms (at t=0.5 ms), notwithstanding any intervening sensor measurements. As known in the art, such commands can be embodied by the ADCS  740  in a matrix form, as illustrated in Table 1 below. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Time  
                   
                   
                   
               
               
                   
                 Seq. # 
                 Command 
                 (ms) 
                 Array 
                 Device 
                 Group 
               
               
                   
                   
               
             
            
               
                   
                 1 
                 Fire 
                 t = 0 
                 1 
                 0 
                 0 
               
               
                   
                 2 
                 Status 
                   t = 0.1 
                 1 
                 0 
                 0 
               
               
                   
                 3 
                 Fire 
                 t = 0 
                 1 
                 0 
                 1 
               
               
                   
                 4 
                 Status 
                   t = 0.1 
                 1 
                 0 
                 1 
               
               
                   
                 5 
                 Fire 
                 t = 1 
                 1 
                 1 
                 1 
               
               
                   
                 6 
                 Fire 
                 t = 1 
                 1 
                 1 
                 2 
               
               
                   
                 7 
                 Fire 
                 t = 1 
                 1 
                 1 
                 3 
               
               
                   
                 8 
                 Fire 
                 t = 1 
                 1 
                 1 
                 4 
               
               
                   
                   
               
            
           
         
       
     
     In the example of Table 1, the ADCS  740  can create simultaneous commands such as firing motor 0 in array 1/group 0 at the same time as firing motor 0 in array 1/group 1 at t=0 (sequence numbers 1 and 3) or firing motors 1-4 in array 1/group 1 at t=1 ms (sequence numbers 5-8). Additionally, opportunities for adjustments may be provided by assessing status, e.g., checking status of motor 0/array 1/group 0 and motor 0/array 1/group 1 at t=0.1 ms (sequence numbers 2 and 4). It is noted that, although the examples above concern commands issued by the ADCS  740  relative to the motors  732  of the propulsion system  730 , such command may also be used to actuate attitude control components  750 ,  752  as well. Furthermore, as noted above, having caused individual ones of the motors  732  to be fired, the ADCS  740  can update its stored knowledge of the motors, e.g., update the status of which motors remain available after completion of the issued commands. 
     While particular preferred embodiments have been shown and described, those skilled in the art will appreciate that changes and modifications may be made without departing from the instant teachings. It is therefore contemplated that any and all modifications, variations or equivalents of the above-described teachings fall within the scope of the basic underlying principles disclosed above and claimed herein.