Analysis of Crew Time Optimization for External Maintenance Activities 921901
Extravehicular Activity (EVA) will be required for maintaining the Space Station Freedom during both the assembly phase of the program (1995-1999) and steady state, or permanently manned configuration.. Currently, several contractors are involved in the developing of the external hardware which will interface with the EVA crewmember. This hardware includes: the Extravehicular System; Unpressurized Logistics Carrier; the robotic systems; and all external orbital replacement units (ORUs). An integrated analysis of the hardware is essential to design an overall system which is not only EVA compatible, but also allows the EVA crew to optimize their workload during external maintenance activities. The use of graphic simulations of end-to-end external maintenance activities offers a relatively inexpensive method to identify design and operational concerns of the integrated hardware. This paper discusses how a graphic simulation produced by the NASA/JSC Flight Crew Support Division Graphic Analysis Facility (GRAF) assisted the McDonnell Douglas Space System Company Crew Time Utilization Team in identifying several design concerns and interface issues.
Several methods can be used to identify design and operational concerns including timelines, real time operations using life size mockups, and computer graphic simulations. Both the timelines and the mockups have several technical shortcomings including the lack of a zero-g environment. Also, the mockups have a relatively high cost impact. Using graphic simulation provides the only means of allowing the analyst the ability to view an end-to-end scenario prior to the actual assembly. The graphic simulation is a tool for evaluating specific details with a relatively low cost impact to the program.
This paper discusses the task scripting required to produce a frame by frame graphic simulation using timelines created for an end-to-end maintenance activity. The simulation shows the EVA crewmembers egressing the airlock, preparing the Crew and Equipment Translation Aides (CETA) carts, gathering the spare orbital replacement units, and then finally preforming the remove and replace scenarios. The paper lists several assumptions and groundrules used for the scenario including the configuration, spare location, and nominal operations.
The paper lists several design and operations issues identified by the animation. These included handrails on the airlock, CETA cart, Mobile Base System (MBS), truss structure and the Unpressurized Logistics Carrier (ULC). The placement of ORUs on the ULC was an issue because the crewmembers cannot reach the ORUs placed in the center. Translation with an ORU and the location of the EVA Support Equipment and Tool (ESE&T) Box were also identified as issues. A list of follow on studies which could reduce crew time required to complete external maintenance activities is included.