Abstract:
A method and apparatus is provided for mating (e.g., structurally and sealingly securing) two components of a spacecraft to one another. The apparatus and method may include a first spacecraft component having a first mating surface, a second spacecraft component having a second mating surface adapted to align with the first mating surface, and a shape memory ring constructed from a shape memory material, adapted to mate the first mating surface to the second mating surface when subjected to a temperature change.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to spacecraft assembly and, more specifically, to joining spacecraft components (e.g., in orbit about the earth) to form spacecraft structures, such as, for example, pressurized spacecraft modules.  
         [0003]     2. Background Description  
         [0004]     Attachment devices required to assemble primary structural components, such as pressure vessels used in spacecraft that need to be assembled in space, are typically complex and extremely expensive. Such devices must meet very high reliability requirements since once in orbit, little can be done to remedy problems with the devices. In addition, pressure vessels used in spacecraft must typically be delivered into orbit in a single piece, resulting in the size of the pressure vessel being limited by the payload volume of the launch vehicle that is used to place the pressure vessel in orbit. Attaching two large pressurized vessels on orbit has not been accomplished without substantial mating hardware (e.g., complex docking systems) between them.  
         [0005]     The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with one aspect of the invention, a mating apparatus, including a shape memory ring, is provided for joining together two components of a spacecraft. The shape memory ring is constructed from a shape memory material, and may provide a structural connection as well as a sealing ring for the spacecraft. The mating apparatus according to one aspect of the invention provides drastically reduced complexity and provides additional benefits such as, for example, reduced payload mass and volume, high reliability, and the ability to attach two sections of a spacecraft together (e.g., to form a large pressurized volume), with minimal intrusion into the interior volume of the spacecraft. The shape memory ring may be used to provide a continuous mechanical clamp around the entire circumference of the spacecraft and may eliminate the need for discrete fasteners and latches that would require separate mechanical actuation mechanisms.  
         [0007]     In accordance with another aspect of the invention, a method of mating two components of a spacecraft together is provided. The method includes placing a first spacecraft component in close proximity to a second spacecraft component, providing a shape memory ring, made from a shape memory material, around a mating interface, and altering the temperature of the shape memory ring (e.g., by heating the shape memory ring) to contract and secure a mating interface in place. The shape memory ring may be electrically heated to cause the shape memory ring and/or a bias ring to contract around clamping ridges provided on mating rings associated with each of the spacecraft components.  
         [0008]     The features, functions, and advantages can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of an exemplary spacecraft pressure vessel that may incorporate a mating system for pressure vessels in accordance with an aspect of the invention;  
         [0010]      FIG. 2  is an enlarged perspective view of the mating system that may be used to form the spacecraft pressure vessel of  FIG. 1 ;  
         [0011]      FIG. 3  is a perspective view in partial cross-section of a mating system in a docked, unclamped configuration;  
         [0012]      FIG. 4  is a view similar to that of  FIG. 3  of the mating system in a sealed, clamped configuration;  
         [0013]      FIG. 5  is a plan view of a mating ring assembly according to a first alternative embodiment of the invention;  
         [0014]      FIG. 6  is a cross-sectional view of the mating ring assembly of  FIG. 5  taken along lines  6 - 6  of  FIG. 5 ;  
         [0015]      FIG. 7  is a cross-sectional view of a mating ring assembly according to a second alternative embodiment of the invention, showing the mating ring assembly and a first cylindrical pressure vessel component in a stowed configuration;  
         [0016]      FIG. 8  is a cross-sectional view of the mating ring assembly of  FIG. 7  in an open configuration, additionally showing a second cylindrical pressure vessel component being mated with the cylindrical pressure vessel component;  
         [0017]      FIG. 9  is a cross-sectional view of the sealing ring assembly of  FIGS. 7 and 8  in a clamped configuration;  
         [0018]      FIG. 10  is a cross-sectional view of a mating ring assembly according to a third alternative embodiment of the invention in a stowed configuration;  
         [0019]      FIG. 11  is a cross-sectional view of the mating ring assembly of  FIG. 10  in an open configuration;  
         [0020]      FIG. 12  is a cross-sectional view of the mating ring assembly of  FIG. 10  in a clamped configuration;  
         [0021]      FIG. 13  is a cross-sectional view of a mating ring assembly according to a fourth alternative embodiment of the invention in a stowed configuration;  
         [0022]      FIG. 14  is a cross-sectional view of the mating ring assembly of  FIG. 13  in an open configuration;  
         [0023]      FIG. 15  is a cross-sectional view of the mating ring assembly of  FIG. 13  in a clamped configuration;  
         [0024]      FIG. 16  is a cross-sectional view of a mating ring assembly according to a fifth alternative embodiment of the invention in a stowed configuration;  
         [0025]      FIG. 17  is a cross-sectional view of the mating ring assembly of  FIG. 16  in an open configuration;  
         [0026]      FIG. 18  is a cross-sectional view of the mating ring assembly of  FIG. 16  in a clamped configuration;  
         [0027]      FIG. 19  is a cross-sectional view of a mating ring assembly according to a sixth alternative embodiment of the invention in a stowed configuration;  
         [0028]      FIG. 20  is a cross-sectional view of the mating ring assembly of  FIG. 19  in an open configuration; and  
         [0029]      FIG. 21  is a cross-sectional view of the mating ring assembly of  FIG. 19  in a clamped configuration. 
     
    
     DETAILED DESCRIPTION  
       [0030]     With reference initially to  FIG. 1 , a spacecraft pressure vessel is generally indicated at  10 . The spacecraft pressure vessel  10  may be, for example, a spacecraft module, and may include a first cylindrical spacecraft component  12  and a second cylindrical spacecraft component  14 .  
         [0031]     An overall view of an example of a docking system  16  that may be used to structurally and sealably connect the first cylindrical spacecraft component  12  to the second cylindrical spacecraft component  14  in accordance with one aspect of the invention is shown in  FIGS. 1 and 2 . The docking system  16  may include a shape memory ring  18 , made from a shape memory material, such as, for example, a shape memory alloy material. An example of a shape memory alloy material that may be suitable for use in forming the shape memory ring  18  is Nickel Titanium, also known as NiTi or Nitinol. Shape memory alloys have unique properties that permit them to undergo a solid state phase change when heated (e.g., from a deformed martensite phase to an austenite phase). As will be described in further detail below, the shape memory ring  18  may provide a structural connection as well as a sealing ring for the spacecraft pressure vessel  10 .  
         [0032]     In order to join the first cylindrical spacecraft component  12  to the second cylindrical spacecraft component  14 , the first cylindrical spacecraft component  12  and the second cylindrical spacecraft component  14  may be placed in close proximity to one another using a capture procedure (e.g., using any suitable means, such as thrusters, torquers, reaction wheels, etc. to properly position the respective components, and/or using any suitable grappling mechanisms to maintain the respective components in close proximity to one another). As described in further detail below in connection with  FIGS. 3 and 4 , after capture, a structural connection and pressure seal at a mating interface between the first cylindrical spacecraft component  12  and the second cylindrical spacecraft component  14  may be created by heating the shape memory ring  18 . This may be accomplished, for example, using an electrical heating system that uses the inherent resistance of a shape memory alloy material that may be used to form the shape memory ring  18 .  
         [0033]     As seen in  FIGS. 3 and 4 , the shape memory ring  18  may have a U-shaped cross sectional geometry, and each of the first cylindrical spacecraft component  12  and the second cylindrical spacecraft component  14  may include a clamping ridge,  20  and  22 , respectively, that, when abutted against one another, may together engage a circular groove  24  that is defined by the U-shaped cross sectional geometry of the shape memory ring  18 .  
         [0034]     When the shape memory ring  18  is heated to a phase change temperature, a resulting phase change from a deformed martensite phase ( FIG. 3 ) to an undeformed austenite phase ( FIG. 4 ) forces the shape memory ring  18  to contract around the clamping ridges  20  and  22 . This results in ring compression around mating surfaces  26  and  28  adjacent to the clamping ridges  20  and  22 , respectively, as shown in  FIG. 4 . The shape memory ring  18  thus forms a continuous mechanical clamp around the entire circumference of the clamping ridges  20  and  22 , and eliminates the need for discrete fasteners and latches, which would have required mechanical actuation mechanisms.  
         [0035]     Guide members  30  may be provided at various positions around the circumference of the first cylindrical spacecraft component  12 , in order to maintain the shape memory ring  18  in a proper position (e.g., in alignment with the clamping ridges  20  and  22 ) before and during heating of the shape memory ring  18 . Heating of the shape memory ring may be accomplished, for example, by passing an electric current through the shape memory ring  18 , using the resistance of the shape memory ring  18  to heat the shape memory ring  18  to a temperature at which it transitions from the martensite phase to the austenite phase.  
         [0036]     Alternatively, and as shown in  FIGS. 5 and 6 , a first alternative mating ring assembly  31  may include a plurality of Peltier effect modules  32  and heat sinks  34  that may be used to regulate the temperature of a flat shape memory ring  36 . The flat shape memory ring  36  may be made from a shape memory material such as, for example, NiTi. A bias ring  38 , that may be made from a composite material, such as, for example, a carbon epoxy composite material, may be located between the flat shape memory ring  36  and the clamping ridges  20  and  22 . The bias ring  38  may be manufactured to a diameter slightly larger than that of the clamping ridges  20  and  22 , to provide an expansion force on the flat shape memory ring  36 . When in the austenite phase, the flat shape memory ring  36  may have a diameter slightly smaller than that which is required to force the bias ring firmly against the clamping ridges  20  and  22 .  
         [0037]     A second alternative embodiment of the invention is shown in  FIGS. 7 through 9 , in which a second alternative mating ring assembly  100  includes a shape memory ring  118  that may be manufactured from a shape memory material having a two-way shape memory effect and a one-way strain effect. For example, in order to achieve a difference in radius, due to the shape memory effect, of approximately one inch (2.54 centimeters) for a 15 foot (4.57 meter) diameter shape memory ring  118 , a cross-sectional area of approximately 6.9 square inches (44.5 square centimeters) may be required for a material such as NiTi. Thus, the width, W, of the cross-section of the shape memory ring  118  may be approximately 5.4 inches (13.7 centimeters) and may have a cross-sectional height, h, of approximately 1.7 inches (4.3 centimeters). The shape memory ring  118  may include a wedge-shaped channel  122  that will engage clamping ridges  120  and  122  of a first cylindrical spacecraft component  112  and a second cylindrical spacecraft component  114 , respectively.  
         [0038]     In  FIG. 7 , the shape memory ring  118  is shown in a stowed configuration at a first or ambient temperature. In  FIG. 8 , the shape memory ring  118  is shown at a lowered or cooled temperature at which the shape memory effect causes an increase in radius of the shape memory ring  118  thereby providing clearance for the docking of the second cylindrical spacecraft component  114  with the first cylindrical pressure component  112 . The shape memory ring  118  may then be heated back to an elevated temperature, which may be the same temperature as in the stowed configuration of  FIG. 7 , in order to clamp the first cylindrical spacecraft component  112  together with the second cylindrical spacecraft component  114 , as shown in  FIG. 9 .  
         [0039]     With reference to  FIGS. 10 through 12 , a third alternative embodiment of the invention, in which a third alternative mating ring assembly  200  may include a plurality of Peltier effect modules  232  and heat sinks  234  that surround a shape memory ring  236  that in turn surrounds a bias ring  238 . The shape memory ring  236  may be made from a shape memory alloy material. A retaining/guide ring  230  may be provided, that surrounds the shape memory ring  236 , the Peltier effect modules  232 , the heat sinks  234 , and the bias ring  238 . The retaining/guide ring  230  may be attached to a transverse circular flange  240  of a first cylindrical spacecraft component  212 . As depicted in  FIG. 10 , in a stowed configuration, the shape memory ring  236  is at a first radius such that the bias ring  238  is pressed against the first cylindrical spacecraft component  212 . The shape memory ring  236  may be made from a one-way shape memory effect material, having a one-way strain effect, such that when cooled (e.g., by the Peltier effect modules  232 ), the shape memory ring  236  will relax and be pushed outward by the bias ring  238 , as depicted in  FIG. 11 , thereby providing clearance for the introduction and mating of a second cylindrical spacecraft component  214  with the first cylindrical spacecraft component  212 . Next, the shape memory ring  236  may be heated using the Peltier effect modules  232 , to provide a smaller radius of the shape memory ring  236 , thereby clamping the first cylindrical spacecraft component  212  together with the second cylindrical spacecraft component  214 , as depicted in  FIG. 12 .  
         [0040]      FIGS. 13 through 15  depict a fourth alternative embodiment of the invention, in which a fourth alternative mating ring assembly  300  may utilize a two-way shape memory effect and two-way strain of a shape memory ring  318  constructed from a shape memory material, is used.  FIG. 13  shows the shape memory ring  318  and a first cylindrical spacecraft component  312  in a stowed configuration at a first temperature.  FIG. 14  shows the shape memory ring  318  at a second lower temperature, at which the shape memory effect results in strain, ε x , in an axial direction, as well as strain, ε y , in a circumferential direction, resulting in a clearance in a channel-shaped opening  32  in which mating ridges  324  and  326  of first and second cylindrical vessel components  312  and  314 , respectively may be inserted, as depicted in  FIG. 14 . Subsequently, the shape memory ring  318  may be re-heated such that the shape memory effect provides two-way strain thereby reducing the radius of the shape memory ring  318  as well as reducing the width of the channel-shaped opening  32  to provide both axial and radial clamping forces on the clamping ridges  324  and  326 , as shown in  FIG. 15 .  
         [0041]     A fifth alternative embodiment of the invention is shown in  FIGS. 16 through 18 , in which a fifth alternative mating ring assembly  400  includes a shape memory ring  418  that may be located radially outward of a bias ring  438 .  FIG. 16  depicts the shape memory ring  418  and the bias ring  438  along with a first cylindrical spacecraft component  412 , in a stowed configuration. By cooling the shape memory ring  418 , an open configuration, as depicted in  FIG. 17  may be achieved in a manner similar to that of  FIG. 14 . This provides a clearance in a channel-shaped opening  422  of the bias ring  438  allowing the first cylindrical spacecraft component  412  to be mated with a second cylindrical spacecraft component  414 . Subsequently, the shape memory ring  418  may be re-heated to achieve a clamped configuration, as shown in  FIG. 18 .  
         [0042]     A sixth alternative embodiment of the invention is shown in  FIGS. 19 through 21 , in which a sixth alternative mating ring assembly  500  includes an outer shape memory ring  518   a  that may be located radially outward of pairs of Peltier effect modules  532   a ,  532   b , that may be distributed circumferentially around an inner shape memory ring  518   b , and located within a bias ring  530 . The bias ring  530  may provide a means of load transfer between the shape memory rings  518   a  and  518   b , while enveloping and providing a load path around the Peltier effect modules  532   a  and  532   b.    
         [0043]     The outer shape memory ring  518   a  may be made from a shape memory material that is in an undeformed (e.g., austenite) phase at a first temperature, and the inner shape memory ring  518   b  may be made from a shape memory material that is in a deformed (e.g., martensite) phase at the first temperature. Thus, the shape memory effects of the outer shape memory ring  518   a  and the inner shape memory ring  518   b  may counteract one another.  
         [0044]     By transferring heat from the outer shape memory ring  518   a  to the inner shape memory ring  518   b , a larger effective radius may be achieved, thereby placing the shape memory rings  518   a  and  518   b  in an open configuration, as shown in  FIG. 20 . For both of the shape memory rings  518   a  and  518   b , the solid arrows in  FIG. 20  indicate the direction of overall strain produced in the mating ring assembly  500  by cooling, and the dashed arrows in  FIG. 20  indicate the direction of overall strain produced in the mating ring assembly  500  by heating. Thus, heating the outer shape memory ring  518   a  results in an overall compression strain (shrinkage) of the mating ring assembly  500  in the axial and circumferential directions, and heating the inner shape memory ring  518   b  results in an overall tension strain (expansion) of the mating ring assembly  500  in the axial and circumferential directions.  
         [0045]     In  FIG. 20 , the shape memory rings  518   a  and  518   b  are shown after heat has been transferred from the outer shape memory ring  518   a  to the inner shape memory ring  518   b.  This provides additional clearance between the bias rings  530   a  and  530   b,  allowing a first cylindrical spacecraft component  512  to be mated with a second cylindrical spacecraft component  514 . Subsequently, heat may be transferred from the inner shape memory ring  518   b  to the outer shape memory ring  518   a  to achieve a clamped configuration, as shown in  FIG. 21 .  
         [0046]     In all of the foregoing embodiments, additional heat rejection devices (not shown) may be provided to dissipate unwanted heat.  
         [0047]     The invention drastically reduces the complexity required to connect and seal spacecraft components, for example, to form large spacecraft pressure vessels, and provides additional benefits such as reduced payload mass and volume and high reliability. It also provides the ability to attach two sections of a pressurized volume together with minimal intrusion into the interior volume. The invention self aligns the structures together with minimal intervention and overhead, providing for autonomous assembly of large scale space structures. Other benefits include a uniform geometry, thereby simplifying the manufacturing process.  
         [0048]     Other aspects and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.