Abstract:
An integrated separation system and interface structure is disclosed for a variety of deployment applications. In one embodiment, a Universal Spacecraft Separation Node ( 100 ) includes a separation nut assembly ( 102 ), a separation spring assembly ( 104 ) an LV node fitting ( 106 ) and an SC node fitting ( 108 ). The LV node fitting ( 106 ) is connected to a launch vehicle ( 210 ) and the SC node fitting ( 108 ) is connected to a spacecraft ( 216 ). The separation nut assembly ( 102 ) holds the fittings ( 106  and  108 ) together until separation is desired. Upon separation, the separation spring assembly ( 104 ) provides a force to urge the launch vehicle ( 210 ) and spacecraft ( 216 ) apart. Prior to separation, an annular tongue ( 224 ) of fitting ( 108 ) mates with an annular groove ( 226 ) of fitting ( 106 ) to resist shear forces.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to space vehicle separation systems and, in particular, to a separation system employing an interface ‘node’ between a deployable space vehicle and a space launch vehicle. The invention provides a standardized interface for space vehicles thereby reducing, or substantially eliminating, interface integration efforts between the space vehicle and launch vehicle builders. The invention also provides improved structural response characteristics under applied loading when compared to other interface designs. 
     BACKGROUND OF THE INVENTION 
     Separation systems are used in a variety of contexts to provide controlled deployment of a deployable unit from a support structure. For example, in aerospace applications, separation systems are used in the space launch business to attach a space vehicle (i.e. spacecraft or satellite) to, and deploy from, a launch vehicle. They may also be used to deploy solar panels, scientific equipment, or other units from a stowed position on the space vehicle. Other possible applications of separation systems include, for example, aircraft ejection seat release, parachute actuation, and other applications involving controlled separation of two surfaces or structures. It will thus be appreciated that separation and associated deployment may involve complete detachment of the deployable unit from the support structure or movement from a non-deployed position to a deployed position. Although the present invention has been developed primarily for use in attaching a space vehicle to a space launch vehicle, it is apparent that further applications and adaptations of the invention are possible. 
     Generally, the interface between the space vehicle and the launch vehicle is defined by abutting interface surfaces between the two. The separation system typically includes one or more release assemblies that hold the spacecraft and launch vehicle together until the desired time of release. At the desired time of release, the separation system detaches, or disengages, releasing the space vehicle from the launch vehicle. Common separation systems include pyrotechnically actuated clamp-bands, separation nuts, and separation bolts. The present invention is intended for use where an interface incorporates a separation nut or bolt. These types of interfaces can incorporate any number of release mechanisms, typically the same type and size. This type of interface is sometimes referred to as a ‘hard-point’ or ‘node’ interface. 
     The interface between a space vehicle and a launch vehicle must be capable of transferring loads between the two structures. These loads can include vibration, acceleration, thermal, and static loads. For this reason, features of the interface must be tightly controlled with respect to tolerances associated with machining or forming processes. The longitudinal loads acting along the primary axis of the launch vehicle (i.e. the axis parallel to the primary vector of travel) are reacted by the separation bolt and bearing surfaces between the two structures. The shear loads, or side loads (those normal to the longitudinal loads), are reacted by shear pins or lips. 
     Because the interface features of a space vehicle and launch vehicle are generally controlled by separate manufacturers or groups within an organization, extensive integration efforts are required to ensure compatibility between the two pieces of hardware. In addition, typically a space vehicle will not be fit checked with a launch vehicle until both are nearly fully assembled. Moreover, it may be required that a space vehicle be compatible with several launch vehicles from the same manufacturer or different manufacturers. As a result, existing separation systems and associated interface configurations entail significant risk associated with new unit development, complicated integration efforts, and limited system interchangability. Furthermore, historically, each unique space vehicle has incorporated a unique, and often dramatically different, node design for the launch vehicle interface. The present invention is an attempt to provide a standardized node design. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a novel interface structure for interfacing a space vehicle or other deployable unit and a launch vehicle or other support structure, and to an associated separation system. The invention allows for interfacing the space vehicle and launch vehicle via an intermediate node that preferably incorporates both the separation system and structural interface functions. In this manner, the space vehicle and launch vehicle can be interfaced without extensive integration of the associated designs. Such an interface structure lends itself to standardization so as to mitigate risk associated with new support structure and/or deployable unit development, streamlines integration efforts, and provides a unique capability with widespread application. 
     The present invention incorporates the complex interface features within the system itself while providing an easily controlled interface to both the space vehicle and launch vehicle. The tightly controlled load carrying features are internal to the ‘node’ while simple bolt hole patterns, controlled by common tooling, provide easy to produce interfaces to the two vehicles. The load carrying features can be verified at the node component level while bolt hole patterns are verified through ‘matched’ tooling. This virtually eliminates any concerns of mismatch between the two vehicles. 
     According to one aspect of the present invention, an interface apparatus is provided for selectively connecting a deployable unit such as a space vehicle and a support structure such as a launch vehicle. The deployable unit includes a first interface surface and the support structure includes a second interface surface wherein, prior to deployment, the first and second interface surfaces are disposed in opposing relationship to define an interface. As set forth below, the interface surfaces need not be abutting. The deployable unit is deployable from an undeployed state where the first and second interface surfaces are proximate to one another in a deployed state wherein the interface surfaces are separated. The interface apparatus includes a support structure node member, interconnected to the support structure including a first contact surface and a deployable unit node member, interconnected to the deployable unit including a second contact surface. The first and second contact surfaces are disposed in an abutting relationship when the deployable unit is in the undeployed state so as to define a separation plane. The separation plane is located at the interface and separated from at least one of the first and second interface surfaces such that the support structure node member and deployable unit node member provide an interface structure, thereby reducing first and second interface surface design integration. 
     Preferably, the support structure node member and the deployable unit node member are configured so that the interface surfaces of the support structure and deployable unit are separated. In this manner, the need to integrate the support structure and deployable unit designs can be reduced or substantially eliminated. Such separation can be achieved with a variety of node configurations. For example, each of the node members can extend from its respective interface surface such that the contact surfaces are disposed between the interface surfaces prior to deployment, one of the node members can extend from its interface surface such that the contact surfaces are substantially flush with the other interface surface prior to deployment, or one of the node members can extend from one interface surface and the other node member can be recessed relative to the other interface surface such that the contact surfaces are outside of the area between the interface surfaces prior to deployment. In the last of these cases, it will be appreciated that the depth of the recessed node member will generally be less than the height of the extended node member so that the interface surfaces may remain separated. 
     According to another aspect of the present invention, an interface apparatus is provided that includes structure for bearing lateral loads. In a variety of deployable unit applications including, for example, dispensing payload spacecraft into orbit from a launch vehicle, substantial lateral loads may be experienced at the separation plane. Such loads may result, for example, from vibrations as the launch vehicle is launched and travels through the Earth&#39;s atmosphere. Such loads can generate substantial shear at the separation plane, potentially resulting in unintended separation if not adequately supported. In accordance with the present invention, a separation apparatus includes a support structure node member and a deployable unit node member including contact surfaces defining a separation plane. The apparatus further includes a lateral load bearing element associated with the contact surfaces at the separation plane for bearing loads having a component aligned with the separation plane so as to reduce the likelihood of unintended shearing separation prior to planned deployment. The lateral load bearing element preferably includes structure extending across the separation plane at the contact surfaces. Such structure may be provided by forming the contact surfaces of the node members in a non-planar configuration or by otherwise providing structure extending across the separation plane at the interface between the contact surfaces. In one embodiment, one of the contact surfaces includes a tongue and the other contact surface includes a mating groove such that the resulting tongue-in-groove structure provides resistance to shear forces. 
     According to a further aspect of the invention, an apparatus is provided for integrating the separation assembly and interface structure in connection with a deployment system. The apparatus includes a support structure node member, a deployable unit node member and a separation bolt assembly. The bolt assembly has a first portion connected to the support structure node member and a second portion connected to the deployable unit node member. The bolt assembly is separable between the first and second portions to effect deployment. Preferably, the bolt assembly includes an elongate element extending from one of the node members to the other across the separation plane there between. In one embodiment, the node members define an internal passageway extending between the node members and the separation bolt assembly extends within the passageway. By virtue of such structure, the separation and interface functionality is integrated into a single unit that can be standardized for use in connection with different types of support structure/deployable unit interfaces. 
     According to a still further aspect of the present invention, a biasing assembly is provided in combination with interface node members to facilitate deployable unit separation. The associated apparatus comprises a support structure node member and a deployable unit node member including contact surfaces defining a separation plane. The apparatus further includes a biasing assembly connected to at least one of the deployable unit and support structure, for urging the contact surfaces apart so as to facilitate deployment of the deployable unit. The biasing assembly, which may include a spring or any other mechanism suitable for exerting a separation force, may act on one or both of the node members or directly on the support structure and/or deployable unit. In a preferred embodiment, the biasing assembly is interconnected to one of the nodes and bears against the other of the nodes in order to provide the desired biasing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and further advantages thereof, reference is now made to the following detailed description taken in conjunction with the drawings, in which: 
     FIGS. 1A-1B are perspective views of a Universal Spacecraft Separation Node (USSN) assembly in accordance with the present invention; 
     FIGS. 2A-2B are cross sections of the USSN assembly of FIGS. 1A-1B and shear feature detail; 
     FIGS. 3A-3D are top, partial side, cross-sectional and shear feature detail views, respectively, of a USSN launch vehicle (LV) node fitting in accordance with the present invention; 
     FIGS. 4A-4D are top, partial side, cross-sectional and shear feature detail views, respectively, of a USSN space vehicle (SV) node fitting in accordance with the present invention; 
     FIGS. 5A-5B show the USSN of FIGS. 1A-1B incorporated on a spacecraft support structure (dispenser) in accordance with the present invention; 
     FIGS. 6A-6B show the USSN of FIGS. 1A-1B incorporated on another spacecraft support structure (dispenser) in accordance with the present invention; 
     FIG. 7 is a digital photograph of a USSN prototype test program separation test set-up; 
     FIGS. 8A-8B are partial perspective and partial side cross-sectional finite element models, respectively, of the USSN of FIGS. 1A-1B; and 
     FIG. 9 is a graph showing the USSN structural response to applied tension loads. 
    
    
     DETAILED DESCRIPTION 
     In the following description, the invention is set forth in the context of various separation system embodiments adapted for selectively separating a space vehicle (i.e. spacecraft) from a space launch vehicle. It will be appreciated, however, that the invention is applicable in a variety of contexts where it is desired to maintain a deployable unit in an non-deployed state until a desired time and then allow for separation of the deployable unit from a support structure. Accordingly, it will be understood that the following embodiments are provided for purposes of illustration and the invention is not limited to any such specific embodiments. 
     Referring to FIGS. 1A-1B, two views of a Universal Spacecraft Separation Node (USSN) assembly  100  in accordance with the present invention are shown. The USSN  100  includes a separation nut assembly  102 , a separation spring assembly  104 , a launch vehicle node fitting  106 , and a spacecraft node fitting  108 . As will be described below, the USSN  100  is used to hold a spacecraft on a space launch vehicle support structure until separation is desired, e.g., to insert the spacecraft into a desired orbit. Multiple USSNs  100  may be used to secure and release a spacecraft and multiple spacecraft may be carried by a single launch vehicle. It will thus be appreciated that numerous USSNs  100  may be used in connection with a single launch vehicle in multiple cooperating groups. It will be appreciated that the USSN may be used in a variety of configurations. In the illustrated embodiment, the node fittings are generally cylindrical, defining an internal passageway for accommodating the separation nut assembly  102 . 
     The separation nut assembly  102  is operative for holding the LV node fitting  106  and the SC node fitting  108  together until release of the spacecraft is desired, and then to allow the fittings  106  and  108  to separate relative to the axis  110  of the assembly  102 . The LV node fitting  106  is connected to the launch vehicle structure via aerospace quality fasteners extending through bolt holes  112  in the mounting flange  114 . The SC node fitting  108  is connected to the spacecraft via similar fasteners extending through the bolt holes  116  in the mounting flange  118  into the spacecraft structure. Note that the mounting flanges  114  and  118  can be modified to accommodate a variety of mounting configurations without impacting the functionality of the USSN assembly  100 . Accordingly, operation of the separation nut assembly  102  to allow separation of the fittings  106  and  108  is effective to permit release of the spacecraft from the launch vehicle. 
     The separation spring assembly  104  provides the force for initial separation of the spacecraft from the launch vehicle once the separation nut  102  has released. This force can be applied directly to a feature on the spacecraft or, more preferably, it can be integrated into the USSN  100 . By integrating the spring interface features into the USSN  100 , integration efforts between the spacecraft and launch vehicle are reduced. In addition, structural enhancements to the spacecraft to accommodate the spring are eliminated. The USSN assembly  100  mounts the spring assembly  104  to the LV node fitting  106  to minimize separated spacecraft weight. However, if required, the spring could be mounted to the SV node fitting  108 . The spring assembly  104  includes a piston  120  contained within a cylindrical housing  122 . The housing  122  is mated to a mounting feature  124  which is an integral feature of the LV node fitting  106 . The piston rod  120  extends through the end of the housing  122  and abuts against a feature  128  on the SV node fitting  108 . A spring  130  provides the force to push the piston rod  120 . The characteristics (e.g. the spring constant) of the spring  130  can be selected in relation to the spacecraft mass and the total number of USSNs  100  acting on the spacecraft to impart the desired separation force. This force can be varied to obtain a desired separation velocity of the spacecraft. 
     FIGS. 2A and 2B show details of the USSN assembly  100  and the interface features between the LV node fitting  106  and SV node fitting  108 . As mentioned, the USSN  100  is capable of accommodating different separation nut assemblies  102 . The illustrated embodiments show the baseline configuration of the USSN  100  which incorporates a Fast Acting Shockless Separation Nut (FASSN) marketed by Starsys Research Corporation of Boulder, Colo. (see www.starsys.com). The FASSN is described in U.S. Pat. No. 5,603,595 entitled “Flywheel Nut Separable Connector and Method”. The illustrated separation nut assembly  102 , which includes the LV mounted actuator  200  and SV mounted bolt extractor  202 , are interconnected prior to release via a threaded rod  204 . The actuator  200  mounts to an internal web feature  212 , which is integral to the LV node fitting  106 , using common aerospace quality fasteners. Fastener holes  222  can vary dependent on what separation nut assembly  102  is used. The bolt extractor  202  mounts to an internal web feature  218 , which is integral to the SV node fitting  108 , using common aerospace quality fasteners. Fastener holes  222  can vary dependent on what separation nut assembly  102  is used. The actuator  200  and the bolt extractor  202  remain attached to the node fittings  106  and  108  at disengagement of the node fittings  106  and  108  at the separation plane  211 . 
     The separation plane  211 , i.e. the plane where the launch vehicle  210  (including the node fitting  106 ) and the spacecraft  216  (including the node fitting  108 ) are in contact until separation, can be positioned at various locations depending on requirements or constraints relative to a specific spacecraft. In FIG. 2A, the dimension P can be increased to effectively enclose either the actuator  200  of the separation nut assembly  102 , the bolt extractor  202 , or both such that they are internal to the USSN assembly  100 . This configuration could be used if the LV structure  210  or SV structure  216  is not tolerant of intrusions. The reconfiguring of the USSN  100  as stated above does not affect the functionality of the assembly. 
     Because the USSN  100  defines the structural interface between the launch vehicle  210  and spacecraft  216 , it incorporates features for bearing loads between the two. These loads include lateral loads, i.e. loads having a component in the separation plane  211 , as well as longitudinal loads, i.e. loads normal to the separation plane  211  along the axis  110 . Compressive longitudinal loads are reacted by the interfacing features of the node fittings  106  and  108  at the separation plane  211 . Tensile longitudinal loads are reacted by the separation nut assembly  102 . The lateral, or shear, loads are reacted by an circular tongue and groove feature as illustrated in FIG.  2 B. The baseline USSN  100  configuration incorporates the tongue feature  224  into the SV node fitting  108  and the groove feature  226  into the LV node fitting  106 . However, these could be reversed without affecting the functionality of the USSN assembly  100 . The side walls  228  of the tongue and groove are where the node fittings  106  and  108  bear against each other to resist the shear loading. The side walls  228  are angled relative to the separation plane  211 . The angle is critical to allow proper separation while preventing the shear loads from being converted into longitudinal loads which could cause gapping of the interface. In other words, the angle is steep enough such that the lateral loads are not translated into separation loads (ideal angle for load reaction is 90 degrees from the separation plane, i.e. a square tongue and groove). However, as the angle approaches 90 degrees, friction between the surfaces will affect separation between the spacecraft and launch vehicle. A side wall angle of 60 degrees from the separation plane was chosen. 
     FIGS. 3A-4D illustrate the USSN launch vehicle and space vehicle node fittings. These fittings are preferably made from common aluminum alloy material. For convenient cross-reference, certain reference numerals from FIGS. 1A-1B are shown. 
     FIGS. 5A and 5B illustrate a multiple spacecraft support structure (dispenser)  300 . In this configuration, four USSN assemblies  100  are used to mount a spacecraft to the support structure. This support structure is designed to accommodate four spacecraft. Thus, a total of  16  USSN assemblies  100  are used. 
     FIGS. 6A and 6B illustrate a second multiple spacecraft support structure (dispenser)  400 . In this configuration, four USSN assemblies  100  (FIG. 6B) are used to mount the spacecraft. There are seven spacecraft for a total of 28 USSN assemblies. 
     The present invention integrates the structural interface and separation system into one or more standardized nodes thereby mitigating risks associated with launch vehicle support structure and spacecraft development, streamlining spacecraft integration efforts, and providing a unique capability with widespread application. The two support structures illustrated in FIGS. 5 and 6 are examples of many applications investigated for use of the USSN  100 . These examples set forth above demonstrate the flexibility of the USSN to be used in a variety of configurations. 
     Testing of the Invention 
     To support the design and analysis efforts of the present invention, a prototype test program was performed. Both separation and structural tests were performed to demonstrate functionality and load carrying capabilities. FIG. 7 is a photograph of the separation test hardware. 
     Twenty one separation tests were performed. These tests were performed with a wide range of separation nut assembly  102  (FIG. 1) pre-loads. Some of the tests induced a tip-off rate to demonstrate that the USSN  100  would still separate under worst case conditions. 
     Thirteen load cases were performed in the structural tests. Gapping and fatigue testing were included. The objectives of the structural testing were to characterize the USSN  100  structural responses with applied loads and to produce a test-correlated finite element model of the USSN  100  (reference FIGS.  8 A- 8 B: The USSN Finite Element Model, where the reference numerals correspond to FIGS.  1 A- 1 B). The results of the testing indicated that the USSN reacted loads more efficiently than other separation nut interface designs. One very important characteristic of any ‘hard-point’ or ‘node’ separation interface is how the separation nut assembly  102  bolt  204  loads are affected by externally applied tension (or combined tension and moment) loads on the node. Pre-loads are set as required for the node to react all predicted load environments. In FIG. 9, the structural response, of the USSN, to applied tension loads is compared to other node interface designs designated PLF Sep Fitting, PLF modified fitting, LMA S/C and IELV. As can be seen in the figure, as tension loads are applied to other designs, bolt  204  loads generally increase prior to the applied tension load being equal to the initial pre-load. Ideally, when the applied tension load is equal to the initial pre-load, there will be no increase in the separation nut assembly bolt  204  load. The figure illustrates that the USSN provides such a response. 
     While various embodiments and implementations of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention can occur. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.