Windows on the universe

Boeing provides panes, attaching mechanism for observatory on ISS

BY ED MEMI

Future visitors to the International Space Station will enjoy a room with an astounding view, thanks in part to Boeing.

Company engineers provided the designs for the specially made windows and attaching mechanisms for the Italian-built cupola, a seven-window observatory for the ISS.

Boeing completed preliminary designs for the cupola in the early 1990s, 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 trapezoid-shaped windows on the cupola's sides.

Besides the windows, Boeing provided the Common Berthing Mechanism, 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 (connecting) module already installed on ISS.

In conjunction with the CBM, Boeing built a berthing-mechanism simulator for use by the international partners. This simulator mimics the node module's interface and provides the means to test for pressure and leaks, to ensure the cupola's structural and sealing integrity. Along with the hardware, Boeing also provided technical expertise for structural analysis of the cupola being linked to the station's Node 3 and for leak testing of the numerous CBM and window seals.

Boeing processed and inspected the pressure panes and sent them to Italy. "For the 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, Ala. Boeing delivered the last windows for the cupola 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 ranging from 1 to 1.5 inches thick.

"It is a rather complex item because of the nature of the material," Hall said. The glass has coatings that are only angstroms (one ten-billionth of a meter) thick, and it has to be within a certain spectrum of reflectance with the optical clarities of laminates. Working with this material, Hall said, "has been very challenging from an engineering perspective," adding that each pane is thoroughly tested. The Boeing Huntsville team employed about a dozen people on the project.

The second window type is the scratch window, located on the cupola's inside. 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 antispall 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, 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 cover each of the windows when not being used, opening like the petals on a flower. On each pane there is a coating to prevent reflection when the panes are stacked together. The coatings also filter out ultraviolet and infrared light but do not affect the physical clarity of the glass.

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 robotic arm, and view the Earth, celestial objects and visiting vehicles.

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 team at Kennedy Space Center, Fla., will support KSC and European Space Agency team members in a joint inspection leading to the turnover of the module to NASA.

edmund.g.memi@boeing.com