Anticipating that FATE would require a flying testbed, AFRL reserved the X-39 designation and began an aggressive research program. Experiments included developing damage-resistant composite airframes and a shape-changing wing to replace hinged surfaces. Drawing on advances in computer technology, work began on artificial intelligence systems that would allow an autonomous aircraft to make minute-by-minute flight-planning decisions to accommodate revised targeting plans and unexpected changes in the weather in the combat zone. Although all of the major airframe manufacturers in business during the late 1990s were involved in some aspect of FATE, none has claimed credit for building a complete X-39. So much of the project is classified, it cannot be confirmed if the plane itself ever progressed beyond engineering studies and wind-tunnel tests. Andreas Parsch, a recognized expert on weapons designations, suggests that the aircraft that started the X-plane revolution is not a proper X-plane at all. He points out that although the X-39 designation was reserved by the Air Force, no formal written request to allocate X-39 to FATE was filed. "Therefore X-39 remained officially unassigned," he concludes. Regardless of the official standing of the X-39, there is little question of the impact of the FATE project with which it is so closely linked. "FATE served as the catalyst for Unmanned Combat Air Vehicles," says aviation historian Jay Miller. These UCAVs, as they are now commonly known, will change the face of combat itself by allowing the United States to project force farther and with greater accuracy than field commanders ever imagined possible. But to fight with such precision would require precise intelligence about enemy positions and movements. To obtain this information, other X-planes would be created to extend the battleground into space. In the days immediately after World War II, Allied intelligence made a remarkable discovery. Agents scouring German factories found plans for a piloted, winged rocket capable of reaching the United States. Space planes have fascinated aerospace designers ever since. In the 1960s, the X-15 came closest to realizing this dream, as military pilots flew to altitudes above 50 miles to earn astronaut wings. The design of the space shuttle's large delta wing was a result of the Air Force's interest in flying single-pass orbital flights over the Soviet Union--the pilots would take off and land at Vandenberg Air Force Base in California. Launch facilities were built, but the idea proved impractical. And after the Challenger disaster the Air Force returned to relying upon expendable launch vehicles. Later, the Air Force considered using a modified version of NASA's X-33 single-stage-to-orbit space plane concept. NASA pulled the plug after more than a billion dollars of research and development. Simply put, the X-33 was too heavy to fly.