assembly are performed automatically by the asse mbly berthing mechanism or with the help of  astronauts performing manual tasks during Extra-Vehicular Activities (EVA). 

The distance between the two mating elements at the final pre-assembly locations will be within 15 to 20  cm (6 to 8 in). At this point, all attachment mec hanisms have similar specific functions that support the  berthing operation. One of the functions is alignment and the other is forming secure, structural joints at  the end of the mating phase. The mechanisms are com posed of two halves: a passive half and an active  half, each residing on opposite sides of the mating elem ents. All powered, moving parts that affect the  berthing operation reside in the active half.  These parts typically consist of gear-driven capture latches  and bolts. The automated mechanisms are motorized and actuated by means of commands sent through  remotely controlled computers. In the case of EVA- driven mechanisms, astronaut tools drive the capture  latch and bolts7. 

At the start of the berthing phase, each attachment  mechanism provides the alignment function between  two elements. Alignment guides or cup and cone arrangem ents that center the modules or trusses with  respect to each other accomplish the alignment func tion. The alignment phase is performed in parallel  with the capture phase. Mechanical attachment syst ems perform this operation by computer-controlled  motors or EVA-driven latches. Capture is the most critical phase of operat ions. The final alignment or fit  of the elements must be such that  the active bolts can acquire the passive nuts to join the mating  elements structurally. 

During capture, the two elements being assembled interact through the berthing mechanisms and with  the Space Station Remote Manipulator System. ( SSRMS). The SSRMS positions the incoming truss  within the prescribed positioning limits of the capture latch. Each mec hanism has a capture system that  may be composed of latches, or other devices that  hold the two elements until bolts can be operated to  final preload. The SSRMS provides a limited amount of push force due to the nature of its design. This  force is also dependent on the confi guration of its robotic joints. For one of the truss attachment  mechanisms on Space Station, the MR TAS, the capture mechanism intera ction forces must always stay  below these limits in all conditions for capture to  be successful. The interaction of this particular  mechanism and the SSRMS during the alignment and capture phase is the s ubject of this paper. 

Statement of the Problem   The criticality of fit and functionality of the mati ng ISS elements require assurance that the design  verification methods used are accurate and that the mechanisms behave as analyzed and predicted.  Mathematical models that quantify t he forces of interaction between the active and passive mechanisms  use techniques to correlate the predictions to component and system-level ground test data, on-orbit  behavior with regard to friction, dynamic response and interaction with the robotic manipulator. These  models are then incorporated into simulations that ta ke into account the crew interaction with the  manipulator and the environmental conditions during berthing3. Final predictions considering the  integrated manipulator/mechanism t he contact dynamic analyses yield quantified assurances that the  mechanism can successfully achieve c apture during berthing using the SSRMS. 

Purpose of the Study   The purpose of this paper is to provide a brief summa ry of the initial contac t dynamic analyses that  account for the major variables that come into play to define the capture forces of the berthing  mechanism for the P5 Truss, the Modified Rocketdy ne Truss Attachment System (MRTAS). Due to the  unique structural geometry in the ar ea of the mating interface, the MR TAS is the one berthing mechanism  on the ISS that does not have a long-reach capture me chanism. Therefore it must rely on the robotic  manipulator to “push” the P5 Truss into the “soft dock” position a couple millimeters away from the final  fully mated position. This of course  requires precise guidance of this lar ge truss segment into place by the  SSRMS to avoid high resistive loads or “jamming” of the mechanism prior to achieving soft capture. In  addition, the force that would hav e been provided by a long-reach mechanism to “seat” the interface,  where it can be bolted, must also be provided by the SSRMS. Hence, it is necessary to accurately define  the engagement and seating forces to assure berthing success. 

Hardware Description   317