The US space agency is preparing to put in the sky an array of new experimental aircraft -- known as X-planes and intended to carry on the legacy of demonstrating advanced technologies that will push back the frontiers of aviation. Called "New Aviation Horizons", NASA's renewed emphasis on X-planes was announced as part of the US budget for the fiscal year that begins from October 1 this year. The plan is to design, build and fly the series of X-planes during the next 10 years as a means to accelerate the adoption of advanced green aviation technologies by industry, the space agency said in a statement. "They [X-plnes] certainly are all interesting in their own way. Each one of them has a unique place in aviation that helps them make their mark in history," said Bill Barry, NASA's chief historian. Although it may not wind up being the first of the New Aviation Horizons X-planes to actually fly as part of the three-legged stool of research, design work already has begun on "QueSST" (Quiet Supersonic Technology). A preliminary design contract was awarded in February to a team led by Lockheed Martin. This new supersonic X-plane could fly in the 2020 timeframe. QueSST aims to fix something the X-1 first introduced to the flying world nearly 70 years ago -- the publicly annoying loud sonic boom. "We know the concept is going to work, but now the best way to continue our research is to demonstrate the capability to the public with an X-plane," said Peter Coen, NASA's supersonic project manager. The goals include showcasing how airliners can burn half the fuel and generate 75 percent less pollution during each flight as compared to now, while also being much quieter than today's jets -- perhaps even when flying supersonic. "If we can build some of these X-planes and demonstrate some of these technologies, we expect that will make it much easier and faster for US industry to pick them up and roll them out into the marketplace," added Ed Waggoner, NASA's Integrated Aviation Systems Programme director. The very first X-plane called the "X-1" was built by Bell Aircraft. The "X-1" was the first plane to fly faster than the speed of sound, thus breaking the "sound barrier". It was October 14, 1947, when Air Force captain Chuck Yeager climbed into the bright orange Glamorous Glennis and flew the "X-1" into its moment in history. The "X-1" also marked the first in what became a long line of experimental aircraft programmes managed by the NASA, the air force, the navy, and other government agencies. Perhaps of all the X-planes NASA has been associated with, none was more cutting edge and became more famous -- rivaling even the X-1 -- than the "X-15" rocket plane. "The X-1 was certainly the most historic for being the first and for what it did for supersonic flight. But the X-15 was probably the most productive model of an X-plane," Barry said. Flown 199 times between 1959 and 1968, the winged X-15 reached beyond the edge of space at hypersonic speeds, trailblazing design concepts and operational procedures that directly contributed to the development of the Mercury, Gemini and Apollo-piloted spaceflight programmes as well as the space shuttle.