Mechanism Analy sis and Verification Approach for ISS Truss Assembly  

Wesley Bruner *, Carlos Enriquez* and Sreekumar Thampi* 

Abstract 

Analysis and verification of an International Space St ation (ISS) element berthing mechanism is a highly  integrated problem, due to its dependency on other sy stems like robotic manipulators. Yet the  mechanism is required to be verified stand-alone with the understanding of all the integrated variables.  Failure to do so, can severely constrain the functi onality of the mechanism to the point of operational  failure during on-orbit operations. This paper explores some of these va riables as they are accounted for  and imbedded in the analysis and simulations that must  be performed to declare the mechanism verified  and ready to fly, particularly in the area of contact dy namic simulations. Considerat ion is specifically given  to Modified Rocketdyne Attachment System (RTAS) mating mechanism coarse and fine alignment  geometry, friction coefficient, mechanism behavior under  load during capture operations, and the ability of  the mechanism to achieve “soft” capture. These and other areas yield the variables that are described,  quantified and analyzed in an effort to make sure t he mechanism performs without anomalies during the  truss assembly operations. This paper discusses these challenges in an effort to state lessons-learned  that can lead to advancements in the arena of ve rification of on-orbit assembly mechanisms. 

Introduction 

The Boeing Company is the largest aerospace company in the world.  Since the early 1900s, Boeing has  been building commercial airplanes. It now builds nine co mmercial jet aircraft product lines that service  airlines and countries throughout the world. The B oeing Company also builds military aircraft and other  defense products. Boeing’s involvement in space dates  back to the Apollo Program with achievements  such as the responsibility for integrating the 363-f oot-tall Moon-bound Saturn V rocket. On the final three  trips, Apollo astronauts also explored the Moon with the Boeing Lunar Rover. Today, The Boeing  Company builds commercial satellites and commercial l aunch vehicles. In addition, it is the nation's  larges t NASA c ontrac tor1. 

In 1993, Boeing was chosen to lead the US industry team  for the International S pace Station. Since then,  Boeing has undertaken the task to develop the proce sses to design, build, and integrate the largest  space vehicle that has ever been a ssembled. Multiple pieces of the ISS are brought from Earth to be  assembled in orbit. There will be a total of 43 assembly flights using hardware developed and  manufactured in five different countries. After sev en American assembly flight s and four Russian flights,  the ISS received a permanent crew on-board. Each assembly flight adds elements weighing  approximately 15,875 kg (35,000 lb). Ea ch of these elements brings critical components of every system  that make the ISS self-sustaining until t he next element is brought to be assembled. 

To support the micro-gravity research and experiment goals of the ISS, it is composed of pressurized  modules and trusses. Figure 1 shows repres entative modules and trusses of the ISS. 

                                                  * The Boeing Company, Houston, TX  

Proceedings of the 37th Aerospace Mechanisms Symposium, Johnson Space Center, May 19-21, 2004  315