Boeing engineers provided the designs for the specially made windows and attaching mechanisms for the Italian-built cupola, a seven-window observatory for the International Space Station (ISS).

In the early 1990s, Boeing completed preliminary designs for the cupola when a NASA barter agreement resulted in the European Space Agency and Alenia Spazio assuming responsibility for design and construction. Boeing engineers in Huntsville, Ala., played a significant role in developing the window assemblies for the dome-shaped structure, including the large 29-inch window on the top and six trapezoidal shaped windows on the sides of the cupola.

Besides the windows, Boeing provided the Common Berthing Mechanism (CBM), also designed in Huntsville, used on all habitable U.S. and international modules. The CBM provides the crucial mechanical link for locking the cupola structure to a node module already installed on ISS. Boeing also supplied some audio terminal units.

In conjunction with the CBM, a Boeing-built berthing mechanism simulator was supplied for use by the international partners.

This simulator mimics the node module's interface and provides the means to accomplish pressure and leak testing of the cupola to ensure its structural and sealing integrity. Along with the hardware, Boeing also provided technical expertise for structural analysis of the cupola being linked to node 3 and leak testing of the numerous CBM and window seals.

Boeing processed and inspected the pressure panes and sent them to Italy. "For scratch and debris windows, we integrated the glass from our suppliers into window frames and delivered them to Alenia after testing," said Allen Hall, Boeing ISS glass and windows project lead in Huntsville. The last window deliveries for the cupola flight article were in February 2003.

Each window assembly is made up of three separate types of windows, and all presented unique design challenges. At the center of the window assembly is the pressure window, which holds in the ISS cabin pressure much like a window in an airplane but at almost twice the pressure. This window contains two panes of glass where each pane ranges from an inch to one and a half inches thick.

"It is a rather complex item because of the nature of the material," said Hall. "With coatings that are only angstroms thick, glass that has to be within a certain spectrum of reflectance with the optical clarities of laminates, fine polishing and the nature of handling glass to prevent defects has been very challenging from an engineering perspective." He added each pane is thoroughly tested. The Boeing Huntsville team employed about a dozen people on the project. The second is the scratch window, located on the inside of the cupola. It provides three unique functions: a barrier between the astronauts and the pressure window to prevent accidental damage to the pressure bearing glass; a special anti-spall film to prevent tiny particles of glass from floating into the cabin should the window break; and heaters, much like a car window defogger, to warm the window pane and frame to avoid condensation.

The third window is called the debris window, which is located on the outside of the cupola. This window provides protection for the pressure bearing glass from micrometeoroids, or accidental contact by an astronaut or his tools during a space walk.

Besides multiple windowpanes, each of the windows has a debris shield or shutters which covers each of the windows when not being used, opening like the pedals on a flower. On each pane, there is an anti-reflective coating to prevent reflection when the panes are stacked together. The coatings also filter out ultra-violet and infrared light, but do not affect the physical clarity of the glass.

Additional spare windows have also been procured. "We have enough glass on hand to replace two top and two side windows," said Hall. He added the plan is if a window is broken by debris, the astronauts could place a pressure cover on the outside and can remove the entire window assembly from inside of the cupola.

Inside the cupola, astronauts will have a panoramic view for observing and guiding operations on the outside of the ISS. The ergonomically-designed interior is equipped with workstations from which astronauts can control the Station's Canadarm2, the 60-foot Space Station robotic arm, and view the Earth, celestial objects and visiting vehicles, such as Japanese H-2 supply craft.

The cupola is slated for launch on Station assembly mission 14A (Shuttle Mission STS-133) in early 2009. It will be installed on the forward port of Node 3, a connecting module to be installed in 2008.

The Boeing-built U.S. Laboratory, Destiny, which is currently flying on orbit, has a more advanced window designed for scientific experiments and was the forerunner for the windows now installed in the cupola.

The Boeing Kennedy Space Center (KSC) team will support KSC and ESA team members in a joint inspection leading to the turnover of the module to NASA.