In 1995 PSL built the WHAM telescope for the UW-Madison Space Physics Program. The telescope is designed to map the density and motion of ionized hydrogen in the galaxy. Because it is significantly larger than the previous telescope, WHAM was able to map the entire northern hemisphere within three years. PSL designed and built the siderostat, which includes the light-collection casing, the mechanics and electronics for rotation, and the software allowing the siderostat to interact with the control panel. The siderostat stands almost 4.3 meters (14 feet) high and weighs about 5 tons. The siderostat rotates around the vertical and horizontal axes, allowing the telescope to map north to south and from horizon to horizon across the sky. The interior is painted a diffuse black, with special low outgassing paint to minimize contamination of optics surfaces. The exterior is painted with special low absorptance white paint to minimize solar heat gain during daylight hours. The siderostat is designed to survive up to 200 kilometers per hour (125 miles per hour) winds.