Boeing Space Exploration division, headquartered in Houston, is at the forefront of development of new spacecraft systems, as it has been since the beginning of the Space Age. Boeing is the leading global supplier of reusable and human space systems and services. For more than 50 years, Boeing has designed, developed, built, and operated human and robotic space vehicles as well as supporting hardware: from the X-15 to Gemini, Apollo, Skylab and continuing with the space shuttle and International Space Station (ISS). Now, Boeing is working with NASA to develop spacecraft under the next-generation Constellation Program. Space Exploration, a division within Boeing Defense, Space & Security's Network and Space Systems business, employs more than 3,500 employees in Texas, California, Alabama and Florida.