Abstract:
A modular device for a spacecraft includes a propulsion system having a tank, a plenum, and a manifold, wherein the propulsion system is integrally formed with a structural frame of the spacecraft. A method of manufacturing the modular device is also discussed, the method including utilizing an additive manufacturing process to construct the propulsion system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. Section 119 to U.S. Provisional Application No. 61/798,739, filed on Mar. 15, 2013, the entire content of which is incorporated herein by reference. This application also relates to U.S. application Ser. No. 13/869,643, filed on Apr. 24, 2013, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     In just a matter of years, the CubeSat platform has evolved from a low-cost experimental platform for the academic community into an industry-accepted standard with a robust community of industry, military, and scientific applications. In light of the continuing budgetary pressures for civilian and military space programs, CubeSats, and nanosatellites in general, provide an increasingly appealing and expeditious alternative to traditional spacecraft developments. In addition, the adoption of this platform has resulted in an expanding industry providing commercial off the shelf (COTS) components and subsystems specifically for CubeSat applications, including avionics, attitude determination and control, and power generation and storage. One area that remains under active development is enabling low-cost micro-propulsion systems for CubeSat-scale spacecraft. Without propulsion, CubeSat missions are resigned to a limited scope due to lack of maneuverability and station-keeping capability, and are rarely even considered for missions requiring significant (100s to 1000s of m/s) Delta V. Innovations in electric propulsion are of note but require significant power resources and a mission of sufficient duration to take advantage of low-thrust trajectories. 
     Presently, the commercial, government, and academic communities are developing systems to meet the needs of mission designers. The commercial aerospace industry has, in the past decade, moved to miniaturize propulsion technology for the CubeSat platform. Advancements are also occurring in the civilian government, military, and academic communities. For example, in 2005-2006, JPL created a multi-functional tank (MFT) for the Micro-Inspector spacecraft. The Micro-Inspector was a 10 kg spacecraft with a vaporizing butane propulsion system. The MFT contained a central butane liquid propellant tank, surrounded by a plenum, into which the butane was allowed to expand and vaporize completely. The low tank pressure (less than 100 psi even in worst temperature cases) allowed for a flat tank geometry except for slightly curved internal tank surfaces to facilitate the desired maximum tank pressure. The flat surfaces provided interfaces for avionics board mounting to provide the heat of vaporization to the butane propellant and in turn allowing for cooling of the avionics. From the plenum tank, eight thrusters were fed to produce attitude control and small delta-v for Micro-Inspector (only 15 m/s). 
     Despite some advancement in micro-propulsion systems, existing systems still consume a significant amount of the mass, volumetric, and financial resources. 
     SUMMARY 
     According to an embodiment, provided is a modular device for a spacecraft comprising: a propulsion system including a tank, a plenum, and a manifold, wherein the propulsion system is integrally formed with a structural frame of the spacecraft. According to another embodiment, provided is a method of manufacturing the modular device, the method comprising: utilizing an additive manufacturing process to construct the propulsion system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages will be apparent from the following, more particular, description of various exemplary embodiments, as illustrated in the accompanying drawings, wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. 
         FIG. 1A  depicts a bottom-side perspective view of an embodiment of an integrated propulsion and primary structure module (IPPSM) according to the present invention. 
         FIG. 1B  depicts a top-side perspective view of the IPPSM of  FIG. 1A . 
         FIG. 2  depicts an example propulsion schematic for the IPPSM of  FIGS. 1A and 1B . 
         FIG. 3A  depicts an embodiment of the primary structure of the IPPSM of  FIGS. 1A and 1B . 
         FIG. 3B  depicts an embodiment of the microthruster module structure of the IPPSM of  FIGS. 1A and 1B . 
         FIG. 4  depicts an example delta-V performance chart for the IPPSM of  FIGS. 1A and 1B . 
         FIG. 5  depicts an embodiment of the IPPSM in different launch configurations. 
         FIG. 6  depicts the IPPSM in combination with a spacecraft. 
         FIG. 7A  depicts a front-side perspective view of another embodiment of an IPPSM according to the present invention. 
         FIG. 7B  depicts a cross-sectional view of the IPPSM of  FIG. 7A . 
         FIG. 8  depicts a perspective view of an embodiment of an asteroid mining spacecraft according to the present invention. 
         FIG. 9  depicts an example propulsion schematic for the IPPSM of  FIGS. 7A and 7B . 
         FIG. 10A  depicts a side-perspective view of an embodiment of an IPPSM according to the present invention. 
         FIG. 10B  depicts a partial, enlarged view of a portion of  FIG. 10A . 
         FIG. 11  depicts an example delta-V performance chart for the IPPSM of  FIGS. 7A and 7B . 
         FIGS. 12A and 12B  depict perspective views of alternative configurations of IPPSMs according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the invention are discussed in detail below. While specific embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without departing from the spirit and scope of the invention. According to embodiments, the invention provides an integrated propulsion and primary structure module (IPPSM) for microsatellites, and related methods. According to embodiments, IPPSM can be used by microsatellite developers as an “off the shelf” propulsion integration structure. Embodiments of the IPPSM and related methodology allow microsatellite developers to integrate propulsion, primary spacecraft structure, and launch interface into a common unit, thereby reducing cost, mass and volume. Embodiments can use additive manufacturing processes to create a simplified, modular, and multi-functional propulsion subsystem. 
     Embodiments of the IPPSM can serve as a spacecraft&#39;s structural backbone, as well as a launch interface and a universal payload interface. This can provide significant benefits, including, without limitation: providing cold-gas propellant options for both attitude control and station keeping; cost reduction from use of high-reliability, high-cycle, non-aerospace COTS components; simplification of design and integration through additive manufacturing; capability to perform more sophisticated missions on CubeSat platforms; and enhancements in spacecraft mass, volume, performance, and mission flexibility. 
       FIG. 1A  depicts a bottom-side perspective view of an embodiment of an integrated propulsion and primary structure module (IPPSM) according to the present invention.  FIG. 1B  depicts a top-side perspective view of the IPPSM of  FIG. 1A . As shown, the IPPSM  10  can integrate the propulsion system&#39;s tank, plenum, and manifold geometries directly into the spacecraft&#39;s primary structural strongback. This integration of geometries into, for example, an Al 6061-T6 structure can be enabled by utilization of an additive manufacturing process, such as the direct metal laser sintering (DMLS) fabrication technique. By employing an additive manufacturing process for the component, geometries that would have normally existed as separate components, each requiring interface features, can now be included in a single manufactured element. This can result in a structure within which one or more—or all—features serve a dual purpose, e.g., as a critical geometry of a propulsion system and also as a load-carrying element of the spacecraft&#39;s structure. 
     Still referring to  FIGS. 1A and 1B , embodiments of the IPPSM  10  can include embedded prop electronics  12 , a maneuvering thruster  14 , such as a resistojet maneuvering thruster, a payload interface  16 , and an RCS microthruster module  18 . As discussed above, these elements can all be included into a single manufactured element. 
     Embodiments of the IPPSM can range from approximately 25 mm tall to approximately 500 mm tall. The embodiment of IPPSM  10  shown in  FIGS. 1A and 1B  is approximately 50 mm tall, and contains an integral tank volume of approximately 2060 cm 3 . An alternative embodiment (not shown) can have be approximately 100 mm tall, resulting in a considerably expanded tank volume of nearly 4700 cm 3 . According to an embodiment, the baseline propellant can be ammonia (NH 3 ) with a nominal operating pressure at 20° C. of about 900 kPa, although embodiments of the IPPSM can be compatible with a variety of propellant options depending on the end user&#39;s requirements. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Performance Summary for IPPSM 
               
             
          
           
               
                 IPPSM - 50 mm tall 
                 units 
                 value 
                 IPPSM - 100 mm tall 
                 units 
                 value 
               
               
                   
               
             
          
           
               
                 Total Mass 
                 kg 
                 3.5 
                 Total Mass 
                 Kg 
                 5.5 
               
               
                 Propellant Mass 
                 kg 
                 1.3 
                 Propellant Mass 
                 Kg 
                 2.9 
               
               
                 Total Impulse 
                 N * s 
                 2048 
                 Total Impulse 
                 N * s 
                 4660 
               
               
                 System Effective Isp 
                 s 
                 59.5 
                 System Effective Isp 
                 s 
                 86.5 
               
               
                 Unloaded System  
                 m/s 
                 640 
                 Unloaded System  
                 m/s 
                 1060 
               
               
                 Delta-V 
                   
                   
                 Delta-V 
                   
                   
               
               
                 6 kg Payload  
                 m/s 
                 205 
                 6 kg Payload  
                 m/s 
                 415 
               
               
                 Delta-V 
                   
                   
                 Delta-V 
               
               
                   
               
             
          
         
       
     
       FIG. 2  depicts an example propulsion schematic for the IPPSM of  FIGS. 1A and 1B .  FIG. 3A  depicts an embodiment of the primary structure of the IPPSM of  FIGS. 1A and 1B .  FIG. 3B  depicts an embodiment of the microthruster module structure of the IPPSM of  FIGS. 1A and 1B . According to embodiments, the IPPSM  10  can include a plurality of control system (RCS) thrusters  20 , located at the corners of the assembly. For example, the IPPSM  10  can include eight thrusters  20  as shown in  FIG. 2 , however, other numbers are possible. As shown in  FIGS. 3A and 3B , the thrusters  20  can integrate in modules  22  of two valve/thruster nozzle combinations  24 , that can seal to the structural strongback  16  upon installation. As shown in  FIG. 2 , the IPPSM  10  can also include vapor plenums  26  corresponding to groups of the thrusters  20 . The module can also include a liquid propellant tank  28  connected to a fill line  30 , as shown. 
     According to embodiments, the IPPSM  10  can utilize COTS micro-dispensing solenoid valves  32 . 
     These valves  32  can be used to service plenum volume and system cutoff. According to embodiments, the IPPSM  10  shown can provide up to six degrees of freedom control authority to the end user. Each RCS thruster unit  20  can have an estimated thrust level of around 10 mNm, and an effective impulse bit of 40 μNs, sufficient for fine control of a 6-12 U CubeSat in the 10-20 kg mass range. In order to provide phasing, plane change, and/or station-keeping activities, the IPPSM  10  can further include a resistojet maneuvering thruster (RMT)  32 , e.g., at the aft end of the module. At 50-mNm total thrust, the thruster  32  can give a small satellite the ability to perform significant orbital modification. According to embodiments, the thruster  32  can be integrated into the IPPSM platform. 
     According to embodiments, the power and control required for the IPPSM can come from a built-in propulsion control electronics (PCE) unit, which may reside within a volume on the underside of the module  10 . According to embodiments, the PCE can provide all or substantially all power switching required to operate the module&#39;s solenoid thruster valves  20  as well as the power required for operation of RMT  32 . Additionally, embodiments of the PCE can have an onboard energy storage capability of about 10 W-hr by means of an integrated lithium polymer battery module. By providing this capacity, the end user&#39;s energy storage and power switching requirements can be independent from the needs of the propulsion system. Accordingly, the end user can have a single electrical interface for connection to its power bus and data communications via standard protocols, for example, such as the I2C protocol. 
     Embodiments of the IPPSM provide a launch vehicle interface compliant with a variety of commercially available containerized satellite deployers, such as, for example, the Containerized Satellite Deployer (CSD) 6 U and 12 U CubeSat deployment systems, available from Planetary Systems Corporation of Silver Spring, Md. For the end user, the IPPSM can provide a flat, strong, and mechanically stiff interface free of configurational encumbrance and ready for accommodation of spacecraft subsystem and payload hardware. Embodiments of the IPPSM can allow the module height to be easily altered to allow the end user to actively trade between propellant volume and available payload space. 
       FIG. 4  shows the expected delta-V performance as a function of payload mass for exemplary embodiments of 50 mm tall and 100 mm tall IPPSM, assuming an NH 3  propellant stored at 20° C. As can be seen from the figure, embodiments of the module provide significant delta-V within a small, integrated package. For reference, a fully populated 6 U (6 kg) spacecraft utilizing an IPPSM with 100 mm height could expect a total system delta-V capability of over 415 m/s. 
     The ease of module propellant capacity and clean physical interface makes the IPPSM attractive for a variety of small spacecraft payloads within the 6 and 12 U size regime.  FIG. 5  depicts example configuration alternatives for the IPPSM, including applications in both the 6 U and 12 U launch configurations. The right-hand side of  FIG. 5  depicts a 6 U configuration of the IPPSM  10 . Reference  40  indicates the payload volume. The left-hand side of  FIG. 5  depicts a 12 U configuration of the IPPSM  10  docked inside a CSD  42 . 
       FIGS. 7A and 7B  depict an alternative embodiment of the IPPSM  10 .  FIG. 7B  is a cross-sectional view of  FIG. 7A . According to the embodiment of  FIGS. 7A and 7B , the module  10  integrates a iN High Performance Green Propulsion (HPGP) monopropellant rocket engine assembly  44  along with a plurality of ammonia (NH3) cold gas Reaction Control System (RCS) thrusters  46 . According to the embodiment shown, the IPPSM  10  can have eight of the RCS thrusters  46 , however, other quantities are possible. The IPPSM can also include storage for both propellants. A portion of the tank  74  depicted as volume  84  can be dedicated to HPGP monopropellant while a portion of the tank  74  depicted as volume  82  can be dedicated to ammonia saturated liquid. Pressurant and propellant management for HPGP may be supplied by saturated ammonia separated from the HPGP by an EPDM polymer bladder  48 . The saturated ammonia can provide feed pressure to the iN thruster within its nominal operating range over a wide temperature range and provides a reservoir of cold gas for the RCS system. Manifold  88   a  can connect the HPGP monopropellant rocket engine assembly  44  to the tank  74 . Still referring to  FIGS. 7A and 7B , the IPPSM  10  can also include propulsion control electronics  52 , and microvalve assemblies  50  for thruster valve control and fluid and gas management. According to embodiments, the microvalve assemblies  50  can comprise COTS microvalve assemblies such as the Extended Performance Solenoid Valve (EPSV) from The Lee Company of Westbrook, Conn. 
     The Applicant is currently developing a line of spacecraft for operation in both Earth orbit and deep space. These spacecraft range from 150-250 kg in size and rely on secondary (rideshare) launch manifest. The mission requirements of near-Earth asteroid exploration may require very large amounts of delta-V (up to 5 km/s). A green monopropellant architecture may be based on flight-proven system such as, for example, HPGP systems developed by ECAPS, a division of the Swedish Space Corporation of Solna, Sweden. An IPPSM as described herein may be central to Applicant&#39;s spacecraft design in order to enable greater payload mass fraction at the targeted destination. 
       FIG. 8  depicts a perspective view of an embodiment of an asteroid mining spacecraft according to the present invention. As shown, the asteroid mining spacecraft  60  can include a propellant tank  62  and an external tank  64 . In addition, the spacecraft  60  can include a plurality of thrusters, such as  22 N thrusters  66  and IN thrusters  68 , however, other configurations of thrusters are possible. 
     Embodiments of the IPPSM can be manufactured using additive manufacturing process. As a result, geometries that would have normally existed as separate components, each requiring interface features, can now be in a minimum number of multi-purposed manufactured elements. Pressurant can serve as RCS cold gas and aid in propellant management. The primary structure can serve as launch interface, critical propulsion geometry, and both propellant and pressurant tank. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 IPPSM Performance Summary 
               
             
          
           
               
                 Mass 
                 Units 
                 Value 
                 Impulse 
                 Units 
                 Value 
               
               
                   
               
             
          
           
               
                 Total IPPSM Wet  
                 kg 
                 8.4 
                 HPGP Specific  
                 Sec 
                 235 
               
               
                 Mass 
                   
                   
                 Impulse 
                   
                   
               
               
                 HPGP Propellant  
                 kg 
                 4.0 
                 NH 3  Specific  
                 sec 
                 90 
               
               
                 Mass 
                   
                   
                 Impulse 
                   
                   
               
               
                 NH3 Pressurant/ 
                 kg 
                 0.4 
                 HPGP Total  
                 N * sec 
                 9221 
               
               
                 Propellant Mass 
                   
                   
                 Impulse 
                   
                   
               
               
                 Expected System  
                 kg 
                 4.0 
                 NH 3  Total  
                 N * sec 
                 353 
               
               
                 Dry Mass 
                   
                   
                 Impulse 
               
               
                   
               
             
          
         
       
     
     Table 2 is a summary of IPPSM mass and impulse capabilities according to the embodiment of  FIGS. 7A and 7B , and  FIG. 9  is a schematic of an exemplary implementation. When fueled, about 80% (depicted as volume  84 ) of the available volume may be dedicated to the HPGP monopropellant, corresponding to 3.2 L, 15% (0.6 L) (depicted as volume  82 ) to liquid ammonia, and 5% (0.2 L) to gaseous ammonia. The HPGP thruster may have nominal operating pressures ranging from about 22 bar to about 5.5 bar, corresponding to saturated ammonia temperatures of about 7° C. to about 52° C. 
     Referring to  FIG. 9 , the module can include a plurality of reaction control system (RCS) thrusters  46 , located at the corners of the assembly. The thrust chamber, nozzle, and plumbing of each RCS thruster  46  can be formed integrally to the IPPSM component to save assembly complexity. This may be made possible by using additive manufacturing methods. The module can also include a HPGP thruster  44 , which can also be formed integrally to the IPPSM. Additionally, the module can include a liquid rocket propellant tank  74  and fill line  76 . 
       FIG. 10A  depicts a side-perspective view of an embodiment of an IPPSM according to the present invention. As seen from  FIGS. 10A and 10B , manifold  88   b  can connect RCS thrusters  46  with the tank.  FIG. 10B  depicts a partial, enlarged view of a thruster of  FIG. 10A . The embodiment of  FIGS. 10A and 10B  can utilize COTS micro-dispensing solenoid valves  78 . When fully integrated, the RCS thrusters may provide 5-DOF control authority to the end user. Each RCS thruster unit may have an estimated thrust level of around 10 mNm and effective impulse bit of 40 μNs, sufficient for fine control of a 12 U CubeSat in the 10-20 kg mass range. The IPPSM may also include a iN HPGP thruster through the center of the module, providing the 6th degree-of-freedom for spacecraft propulsive capabilities. As shown in  FIG. 10A , manifold  88   a  can connect HPGP thruster  44  with the tank. This main engine thruster can give the small satellite the ability to perform significant orbital modification on impulsive timescales. 
       FIG. 11  depicts an example delta-V performance chart for the IPPSM of  FIGS. 7A and 7B . 
     According to embodiments, the ease of module integration and clean physical interface make the IPPSM attractive for a variety of small spacecraft payloads within 12 U size regime.  FIGS. 12A and 12B  illustrate example configurations of the IPPSM, where a payload  80  has greater than 8 U (202 mm×224 mm×213) at its disposal. 
     As mentioned previously, embodiments of the IPPSM integrate the needs of the spacecraft&#39;s propulsion, primary structure, and launch interface into a single common element. By employing this system, payload and spacecraft developers can focus their efforts towards the optimization of their mission and the successful design, integration, and test of their instruments. The marriage of these disparate spacecraft needs—propulsion, primary structure, and launch interface—may significantly reduce the mass, volume, and cost when compared to the present implementation by means of separate and distinct subsystem components. 
     Through the use of the additive manufacturing techniques, such as, for example, Direct Metal Laser Sintering (DMLS), or Stereo Lithography investment casting (QuickCast™) additive manufacturing techniques, it is possible to fabricate a single primary structural element that contains all of the geometries required to perform the following, usually separate, functions: launch structural interface; spacecraft structural backbone; spacecraft propulsion tank, plenum, and manifold geometries and structures; built-in PCE interface and harness vias; integral valve and thruster assembly locations; and universal flat interface for multiple payload configurations. 
     Applicant is developing a series of spacecraft platforms for operation in Earth orbit and deep space.  FIG. 6  depicts an embodiment of the IPPSM  10  in combination with an example of Applicant&#39;s Arkyd® series spacecraft  90 . 
     The development of a low-cost, integrated propulsion and structure module for small satellites has the potential to assist in the progress towards the achievement of near-term and long-term scientific and technical goals of NASA and those of other space faring entities. For example, embodiments of the IPPSM can facilitate economical access to space, space debris hazard mitigation (e.g., when used in conjunction with robotic platforms), and new tools of discovery. 
     Other potential applications of the IPPSM can include low-cost, rapid deployment of LEO/SSO telecommunications constellation as secondary payloads, and deployment of secondary payload imaging constellation. 
     From the foregoing description, one skilled in the art can readily ascertain the essential characteristics of the invention, and without departing from the spirit and scope thereof, can make changes and modifications of the invention to adapt it to various conditions and to utilize the present invention to its fullest extent. The specific embodiments described here are to be construed as merely illustrative, and not limiting of the scope of the invention in any way whatsoever. Moreover, features described in connection with one embodiment of the invention may be used in conjunction with other embodiments, even if not explicitly stated above. The entire disclosure of all applications, patents, and publications cited above are hereby incorporated by reference in their entirety.