51 SYSTEMS: STRUCTURE AND MECHANISMS—THE INTERNATIONAL SPACE STATION’S SKELETON CHAPTER 3 staged hardware usually covers the window of that particular hatch. That leaves three primary window locations for viewing events outside the US Segment of the ISS for research, educational events, or crew viewing and photography. The US Laboratory has a single, large- diameter window (Figures 19-21). Research experiments are mounted into the Window Observation Rack Facility, which is installed over the top of this window, thus enabling detailed observations of Earth. The JEM has two large-diameter windows on its port bulkhead these windows are used to monitor operations of the JEM robotic arm, activities on the JEM Exposed Facility, and operations of the JEM Airlock. The Cupola is a module of windows attached to the bottom of Node 3 (Figure 18). It has one large, round window at its center and six trapezoidal windows around its perimeter to provide a breathtaking bay-window view of Earth. The Cupola is used by the crew not only for Earth viewing, but also to monitor the arrival and departure of visiting vehicles as well as EVAs and robotics occurring on the bottom of the ISS. Figure 18. “The ‘Cupola’, attached to the nadir side of the space station, gives a panoramic view of our beautiful planet,” said Expedition 25 Commander Doug Wheelock (shown in photo) about this module that has seven large windows. The Earth-facing science window in the US Laboratory was specially designed and manufactured to support scientific investigations. This was accomplished through specific and fine polishing specifications, and through application of coatings on the glass surfaces (as well as specific decisions on which coatings to leave off the window). This detail on the US Laboratory window enables excellent optical qualities that allow the use of various cameras and telescopes that operate in both the visible and non-visible light wavelengths. The windows in the Laboratory, JEM, and Cupola, as well as many of the windows in the Service Module, are also protected with shutters to ensure as little debris as possible makes its way onto the high-quality optical glass. These shutters—some manually controlled