Performing checkout, servicing, and maintenance of an Extravehicular Activity System (EVAS) on board the Space Station presents several unique challenges. This paper reviews the progress that has been made in the initial effort to define, design, and develop a system that will perform this function.
The need for rapid “turnaround” of the EVA capability has not been a significant requirement for the Shuttle program where EVA is only an occasional occurrence (two missions per year). Because of this in frequency and because reservicing is performed on the ground rather than on orbit, the current expenditure of approximately 3,000 manhours to process each Shuttle Extravehicular Mobility Unit (EMU) is acceptable. However, current estimates on the EVA frequency required to support Space Station operations is projected at twice weekly. In light of this greatly increased EVA frequency and the prohibitive labor costs associated with manually processing the EMU on orbit, NASA has chosen to support the development of an operational system for the Space Station that will minimize the time normally spent on EVA preparation activities as well as facilitate efficient on-orbit EVAS checkout, servicing, and maintenance. This system, which will be flight qualified and fly aboard the Space Station, is the EVAS Servicing Performance Checkout System (SPCS). Its preprototype counterpart, (currently under development and described in this paper) is referred to as the Checkout, Servicing, and Maintenance System (COSM). COSM is composed of interactive control software interfacing with software simulations of hardware components and is intended to serve as the model for eventual SPCS development.