The U.S. Destiny Laboratory on ISS features an Earth observation window with the highest quality optics ever flown on a human occupied spacecraft. Images from space have many applications: e.g., they can be used to study global climates, land and sea formations, crop weather damage and health assessments. Special sensors can also provide important data regarding transient atmospheric and geologic phenomena (hurricanes and volcanic eruptions), as well as a test bed for collecting data for new sensor technology development.
The WORF design uses existing EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack hardware which includes a Rack Interface Controller box for power and data connection, Avionics Air Assembly fan for air circulation within the rack, rack fire detection, and appropriate avionics to communicate with the ISS data network. The WORF will maximize the use of this window by providing sensors (cameras, multispectral and hyper-spectral scanners, camcorders and other instruments) to capture imagery of the Earth and space. WORF also provides attachment points for power and data transfer and the capability for multiple instruments to be mounted and used in the window simultaneously. WORF will include a means of preventing the formation of condensation on the interior surface of the window and a retractable bump shield to protect the interior window surface from impacts of loose tools and hardware being used in the payload area during the set-up and changeout of sensor packages by the crew. The interior of the WORF provides a non-reflective, light-tight environment to minimize stray reflections and glare off the window allowing use to payloads that are sensitive to extremely low energy phenomena such as auroras. An opaque fabric shroud can be attached to the front of the rack to allow crew members to work in the WORF without the problem of glare from the U.S. Lab interior lights.
The high quality optical window is located on the nadir (Earth facing) side of the U.S. Destiny laboratory module. The window provides a view of 39.5 degrees forward along the axis of the ISS, 32.2 degrees aft, and a total of 79.1 degrees from starboard to port.
The window is 508 cm (20 in) in diameter. The window is made up of an assembly of four separate panes. The outermost pane is a replaceable debris pane a little more than 1.0 cm (one third of an inch) thick. It is designed to protect the window from small orbital debris or micrometeoroids that might strike the station. If it is severely damaged, it can be replaced during an EVA. The two middle panes serve as the primary and secondary pressure windows, ensuring that the laboratory module stays pressurized. Each of these panes is 3.2 cm (1-1/4 in) thick. The innermost pane, a multi-layer scratch pane, is a little less than a 1.7 cm (half-inch) thick. The scratch pane has an integral heater element to prevent condensation from forming on the pressure panes, and has a special anti-scratch coating that protects against accidental bumps from camera lenses and other equipment during set-up work inside the WORF rack. Although the scratch pane can support normal photography, it is often necessary to remove the scratch pane during the operation of other high-resolution sensors. When the scratch pane is removed, the WORF provides a deployable metal and acrylic bump shield to protect the primary pressure panes while equipment is set up in front of the window. When the sensors are ready for use and the interior of the WORF rack has been secured with a hatch cover, the bump shield can be retracted using controls on the outside of the WORF rack, giving the cameras/sensors a clear view through the window to the Earth below. When the scratch pane (and its heater element) is removed, the WORF rack provides a variable air flow across the window to prevent condensation.
When the WORF is not in use, when visiting spacecraft are docking with the ISS, or when the window is exposed to orbital ram conditions during special orientations of the ISS, the research lab window is protected by a metal cover on the outside of the Destiny lab module. This external window shutter pivots on hinges and is rotated open and closed by the crew using controls on the WORF rack.