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Primary source of electric power for the International Space Station (ISS) is the photovoltaic module (PVM). At assembly complete stage, the ISS is served by four PVMs. Each PVM contains two independent power channels such that one failure will result in loss of one power channel. During early stages of assembly, the ISS is served by only one PVM and one power channel failure has a more significant impact on the ISS electric power capability. In the limited context of this study, the early stages are limited to stages 4A and 5A. Power channel components are arranged in orbital replaceable units (ORU) and repairs are accomplished by replacing these ORUs. While a power channel is operating, all of its ORUs are maintained within their allowable temperature ranges by a balance between the heat generated and heat removed. Heat removal is accomplished either passively or by an active thermal control system, called photovoltaic thermal control system (PV TCS).

International Space Station (ISS) hardware is designed for operation in space, therefore, testing these on ground poses special problems. One such problem is the potential of water vapor condensation. Water condensation on electronics components may cause electrical short and/ or corrosion. ISS batteries are designed to operate within a temperature range of 32 to 50°F. In order to maintain batteries within this range, cold ammonia is circulated through their coldplates. During testing, ammonia chiller temperature setpoint is typically set at 20°F and the test room dew-point temperature is typically about 50°F. These operating conditions will result in considerable water condensation on cold surfaces. In order to minimize water condensation, test hardware is enclosed in a tent within which air dew-point temperature is controlled at 0°F or lower. This is more than adequate to prevent any moisture condensation on batteries.

Recent Leonid meteor showers have rekindled general awareness that meteoroid/orbital debris (M/OD) will impact the International Space Station (ISS) hardware and may cause damage and disruption of service. Large surface areas, photovoltaic (PV) arrays and PV radiators, have a higher probability of such an impact. The power generation, storage, and distribution system on the ISS is a channelized system, such that a malfunction affects only one channel. At assembly complete configuration, the ISS consists of eight power channels, and a temporary loss of one channel can be easily accommodated. However, during early stages, the ISS consists of only one PV module, which has two power channels, and a loss of one channel results in a significant loss of capability. Each PV module is supported by a photovoltaic thermal control system (PV TCS), which consists of two independent recirculating cooling loops.

The early external active thermal control system (EEATCS) is designed to cool the U.S. Laboratory (USL), during early assembly stages of the International Space Station (ISS), to support assured early research (AER). The ISS is assembled on orbit over a period of about 5 years and over 40 stages. During later stages, about half way through the assembly, the USL is cooled by the external active thermal control system (EATCS), but that system is not available during early stages. To assure research, during early stages, the USL is cooled by the EEATCS; at a later stage, the USL cooling is switched to EATCS. During early stages, electric power is provided by the integrated truss segment (ITS) P6, which consists of photovoltaic (PV) arrays to convert sunlight into direct current power, an integrated equipment assembly (IEA) to support hardware required to store and condition electric power, and a long spacer to provide spacing between outboard power modules.