Abstract:
A spacecraft isolator including shape memory alloy components that are electronically heated to unlock the isolator. The isolator can be manually unlocked with an adjustment bolt.

Description:
BACKGROUND  
         [0001]    Components on spacecraft frequently are mounted on flexible isolator devices (damper struts), like the one in U.S. Pat. No. 6,003,849, configured in a hexapod arrangement in U.S. Pat. No. 5,305,981, or some other strut/truss support system. However, when a spacecraft is launched the components are sometimes restrained on a launch retention mechanism for many reasons, including decreasing deflections of the isolation systems beyond design limits. The launch retention mechanism can be an integral part of the isolation struts or a separate supporting structure. Current launch restraints pull the isolator into a fixed latch position away from the isolator&#39;s neutral in-orbit position, known as isolator bias. The bias can present difficulties when precise alignment between the isolator mounted payload and the base structure, to which the isolator is attached, is important for pre-launch preparations. Alignment adjustments between the payload and spacecraft are made on earth, where gravity sags the isolator away from the zero-gravity orientation that it will assume in outer space. This makes accurate payload positioning prior to launch problematic.  
         SUMMARY  
         [0002]    A device is included in the isolator strut for locking the isolator in either a zero bias position (the damper is not loaded at either of its two extreme possible positions) or known/predetermined bias position and electronically overcome to unlock the strut. Another mechanical element is included to temporarily unlock the isolator without disturbing the other devices.  
           [0003]    Objects, benefits and features of the invention will apparent to one of ordinary skill in the art from the drawing and following description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0004]    [0004]FIG. 1 is a cross-section of an isolator with an integral device which according the invention locks the isolator in a biased position.  
         [0005]    [0005]FIG. 2 is a cross-section showing a different version of the isolator, where the isolator is locked in a zero-bias (neutral) position.  
     
    
     DESCRIPTION  
       [0006]    The isolator strut  10  in shown in FIG. 1 connects a payload, at one end, and to a base structure surface with a bracket  14 . A strut base plate  16  is attached to the bracket  14 . The tubular-shaped isolator strut  10  contains a piston  18  that moves back and forth (arrow  20 ) displacing fluid between bellows  22  through internal passages  24 , providing fluid damping. In addition, a coil spring  26  is installed around the outside of the isolator strut  10 , also connecting with the piston (damper) the payload and base structure surface.  
         [0007]    A tapered cap  30  is attached to one end of the piston  18  by threads  30   a.  A threaded bolt  32  extends into the cap  30 , attaching to a tapered nut  34  that fits into the cap  30 . The plate  16  is threaded at  16   a  to screw on the top section  36 . The cap of bolt  32  is located in a chamber  38 , accessible when the plate  16  is removed. Belleville washers  40  tension the cap  34  firmly against the section  36  at point  42  by pulling the bolt  32  to left, displacing the piston  18  to the left (towards the base structure surface) and locking the payload on the bracket  14 .  
         [0008]    Also located in the chamber  38 , a tubular-shaped unlocking component  39 , constructed of “shape-memory” alloy such as Nitinol, is situated between the bolt  32  and screw-on end fitting  36  and surrounded by a heating coil  44 . The special characteristic of the alloy is that once heated, it holds an expanded state. Power is applied to the heating coil through a control  46 , causing the unlocking component  39  to expand, compressing the bolt  32  against the belleville washers, which frees the nut  34  from the cap  30 , freeing the piston  18 , thereby returned to its normal operating or zero-bias position, towards the payload, where it is free to move normally.  
         [0009]    A manual unlocking bolt  46 , threaded through the plate  16  and the end of the bracket  14 , can push on the bolt  32 , making it possible to manually move the bolt  32  to the right (compressing the belleville washers  40 ) to release the piston  18 , which unlocks the strut. The use of the bolt  46  makes it possible adjust the payload relative to the bracket  14  and the surface to which it is mounted prior to launch with the isolator active or unlocked (as it would during flight operations after launch) without activating the unlocking component  39 . Once those adjustments are made the bolt  46  can be removed, relocking the payload.  
         [0010]    In FIG. 2, all the previous components are the same except additional components are added so that when the strut  10  is locked, piston  18  is held in a normal or zero-bias configuration. To accomplish that, additional belleville washers  50  are placed between the plate  16  and a tubular insert  52  that passes through section  36 . The insert  52  contains longitudinal (in the direction of the bolt  46 ) slots (not visible) for longitudinal surfaces section  36  that extend radially inward, through insert  52 , provide stop points  36   a,    36   b  explained below. Insert  52  presses against section  36  at point  36   a,  controlling the location of contact between insert  52  and cap  30 , so that piston  18  is in its free or unbiased position. Belleville washers  40  press bolt  32  and nut  34  against cap  30  and insert  52 , providing a substantially more rigid connection. The clamping force exerted by belleville springs  50  must be substantially larger than the clamping force exerted by belleville  40  springs to maintain the zero bias location of insert  52 . As before, the control unit  46  heats the coils  44 , causing unlock component  39  to expand, but in this instance this releases the insert  52  and the nut  34  from the cap  30 , but the piston  18 , already in its zero bias position, does not move. As the unlock component enlarges, it pushes the bolt  32  to the right until the bolt engages stop point  36   a  and then the tubular insert  52  is forced to the left against the belleville washers  50 , disengaging it from the cap  30 . Bolt  46  is provided, as before, to manually unlock the payload, but is screwed into insert  52  (only for this unbiased configuration), releasing insert  52  and bolt  32 .  
         [0011]    One skilled in the art may make modifications, in whole or in part, to a described embodiment of the invention and its various functions and components without departing from the true scope and spirit of the invention.