Sunnyvale is the seventh most populous city in the San Francisco Bay Area and one of the major cities comprising Silicon Valley. As part of California's high-tech area known as Silicon Valley, Sunnyvale is the headquarters location of many technology companies and is a major operating center for many more. It is also home to several aerospace/defense companies. Sunnyvale was also the home to Onizuka Air Force Station, often referred to as "the Blue Cube" due to the color and shape of its windowless main building. The facility, previously known as Sunnyvale Air Force Station, was named for the deceased Space Shuttle Challenger astronaut Ellison Onizuka. It served as an artificial satellite control facility of the United States armed forces until August 2010 and has since been decommissioned and demolished.