NASA-LLIS-0191

Abstract

<strong>Description of Driving Event:</strong> <br>The use of truss segments, which are preintegrated with distributed systems and verified on the ground instead of erected on-orbit, has reduced technical risk and made the space station a more viable program. The preintegrated truss members (PIT) must be heavier than the original truss elements per running foot because the entire mass of the PIT is subjected to launch loads. <br>PIT members are aluminum I-beams bolted together instead of the more flexible graphite composite elements that previously were part of the design. The heavier construction allows orbit replaceable units (ORUS) to be located in their optimum positions for accessibility. <br>One benefit of the restructured design is that EVA time has been reduced considerably so that EVA targets are now feasible. This has been accomplished by reducing the demand for EVAs and increasing the efficiency of those that must be performed. <br>In the assembly of the PIT sections on-orbit, a capture latch provides final alignment by engaging guide pins after the sections are brought into proximity by the space shuttle remote manipulator arm. Motorized bolts then make the final latch-up. There is a chance that these sections may not line up correctly; therefore, damage may occur to the guide pins and bolts when the motorized bolts engage. Because the PIT sections will be assembled on the ground, the opportunity exists to test the alignment and mating procedures prior to flight.