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GUY NORRIS / LOS ANGELES

In the 1960s it was taken for granted that development of a supersonic airliner was a natural evolution. Now higher speed is firmly back on the agenda

The desire for faster transport has been a constant. At no time since humans progressed from horseback to wheeled travel has an increase in speed not turned out to be a best-seller - with one significant exception, the Anglo-French Concorde. Yet in the 1960s it was taken for granted that the market would follow a natural evolutionary course. Forecasts presented to an International Air Transport Association technical conference in 1967 predicted that there would be a market for 1,250 supersonic transports (SSTs) between 1972 and 1978. British Aircraft Corporation, then in the midst of developing Concorde with Aerospatiale, modestly estimated its share of the market over the period would be "at least 250".

Even Boeing, at the time working on the 747 and what would become the 2707 SST project, believed the need for speed would soon relegate its new widebody to cargo duties. Joe Sutter, the legendary engineering director of the 747 programme, recalls that "many of the airlines, and the people here at Boeing, thought that the 747 was an aircraft with a limited future because the SST was going to take all the business. I even had difficulty getting people to work on the 747. They would come up to me and say: 'Keep working on the 747, and when you get done, there might be a place for you on the SST'."

The pervasive threat of the SST to the future of the larger 747 was felt by Boeing to be so strong that it designed the subsonic jet with a single main deck wide enough to accommodate two 2.4m (8ft)- square sea-going containers side-by-side, convinced, as it was, that the dominance of the SST would consign the 747 to the role of a plodding freighter. Ironically, this created the blueprint for the world's first widebody and the best-selling large jet airliner in history.

Of course, in 1967 few could have predicted the onslaught of environmental pressures and economic woes that would come on the heels of the Arab-Israeli conflict that year, and the subsequent oil crises. Notwithstanding, Concorde soldiered on to achieve fame as the world's only operational SST, excluding the short career of the Tupolev Tu-144, although subsonic designs have continued to dominate the commercial world ever since.

The field of high-speed civil aircraft lay fallow until the advent of the Mach 0.9 Cessna Citation X business jet in the mid-1990s, and the more recent Sonic Cruiser project reluctantly revealed by Boeing in March. Crucially, both are specifically subsonic designs, the Boeing project edging closest to the sound barrier with a planned cruise speed of Mach 0.98.

Unlike Convair's flawed 880 and 990 high-speed transports, which were aimed at the transonic category in the 1950s and 1960s, the newer concepts are able to take advantage of advanced aerodynamics, lighter materials and improved engine technology.

The tricky problem of overcoming the sound barrier, and the environmental, technical and economic difficulties this entails still remain, however. These were deemed so insurmountable that even NASA's High Speed Research programme, aimed at the long-running US high-speed civil transport, was axed in 1999.

Gulfstream and Lockheed Martin, which had been working together since 1998 on a possible supersonic business jet (SSBJ), subsequently approached NASA for support. The move attracted interest from Congress, which allocated up to $35 million in funding to support research into a dual-use commercial/military supersonic platform. By March last year, the US Defense Advanced Research Projects Agency (DARPA), was leading what had by then become the Quiet Supersonic Platform (QSP) project - the key target of which is the development of an efficient aircraft that could cruise long distances at supersonic speeds without generating asignificant sonic boom.

The possibility of US government support, and the intriguing chance of a military application in the form of a Mach 2.4 medium bomber substantially re-stimulated serious US and international industrial interest in supersonic technology. Although Gulfstream and Lockheed Martin parted company over the SSBJ, the former continues detailed studies of the concept, and predicts a market for up to 400 aircraft.

Lockheed Martin, along with Boeing, Northrop Grumman and its QSP partner Raytheon, are all working on DARPA contracts. Dassault of France has meanwhile announced its intention to pursue possible the SSBJ concepts, most likely as part of an international partnership.

While DARPA's programme is expected to lead to a flying demonstrator, perhaps as early as 2006, the commercial high-speed focus remains for the moment on the Sonic Cruiser, which could make its first flight the same year. After several years in the doldrums it seems the omens are right for a fast-jet revival - at least in the USA.