High-Speed Civil Transport (HSCT)

As envisioned by NASA's High-Speed Research (HSR) program, the next-generation High-Speed Civil Transport (HSCT) would fly 300 passengers at 2.4 times the speed of sound - crossing the Pacific or Atlantic in less than half the time presently required on modern subsonic, wide-bodied jets - at an affordable ticket price, estimated at less than 20 percent above comparable subsonic flights. The technology to make the this HSCT possible is being developed by an unprecedented teaming of major U.S. aerospace companies in the multi-year HSR program. Although actual development of such an advanced supersonic transport (SST) is currently on hold, commercial aviation experts estimate that a market for up to 500 such aircraft could develop by the third decade of the 21st Century.

Phase I of the HSR program, which began in 1990 and continued through 1995, focused on environmental challenges: engine emission effects on the atmosphere, airport noise and the sonic boom. Much research remains to be accomplished in these and other areas, but Phase I established some clear lines of approach to major problems and spawned confidence among team members that environmental concerns can be satisfied.

Phase II, initiated in 1994, focused on the technology advances needed for economic viability, principally weight reductions in every aspect of the baseline configuration, because weight affects not only the aircraft's performance but its acquisition cost, operating costs and environmental compatibility. In materials and structures, the HSR team is developing, analyzing and verifying the technology for trimming the baseline airframe by 30-40 percent; in aerodynamics, a major goal is to minimize air drag to enable a substantial increase in range; propulsion research looks for environment-related and general efficiency improvements in critical engine components, such as inlet systems. Phase II includes computational and wind tunnel analyses of the baseline HSCT and alternative designs. Other research involves ground and flight simulations aimed at development of advanced control systems, flight deck instrumentation and displays.

In December 1995, a single aircraft concept was chosen to focus the intensive technological development planned for the next three years of the HSR program. This aircraft, the Technology Concept Aircraft (TCA), is not an actual design or airplane that will be built, but rather serves as a common reference point for HSR technology development. The TCA evolved from separate Boeing and McDonnell Douglas HSCT designs. Computer modeling and wind tunnel tests were used to produce a single concept with superior aerodynamic performance and operational characteristics, which also satisfied environmental goals. The technology focus also was significantly narrowed in the areas of propulsion and airframe structural components. Technical challenges remain in each area, however, though significant progress has been made.

Improvements in materials, structural, and systems technology that are available or currently being developed could make a second generation of supersonic aircraft more widely affordable. Studies have concluded that an aircraft with between 250 and 300 seats cruising at Mach 2 to 2.4 (at altitudes between 16 and 20 km) is most likely to be successful. To make such aircraft effective for the long overseas routes that benefit most from the increased speed and maintain viability with regard to viewpoint of sonic booms, the projected range must be at least 8000 km (and possibly 10400 km).

The Concorde has already demonstrated the practicality of Mach 2.05 as an achievable cruise speed with aluminum alloys for the basic structure. For speeds above Mach 2.2, more exotic materials would be required including titanium alloys and organic composites for structural items and more complex air intakes. At speeds between Mach 2 and 2.4, airframe characteristics currently dictate cruise altitudes between 16 and 20 km. Optimization studies are planned to investigate lower cruise altitudes, recognizing the potential benefit of minimized ozone impact. To enable the inclusion of route segments over populated areas without sonic booms, an advanced supersonic airliner must also be capable of cruising efficiently in an environmentally acceptable manner at subsonic speeds and lower cruise altitudes.

Studies have examined a wide range of speeds and concluded that speeds higher than Mach 2.4 offer little gain in block time, whereas they exacerbate airframe materials and propulsion problems, hence increase technical risk. Prior projections concluded that aircraft with a cruise speed of Mach 2.0 to 2.4 were feasible for entry into service in 2005, and a hypersonic vehicle cruising at Mach 5 might enter service by about 2030. Events have shown that these projections were optimistic, and it is unlikely that a new Mach 2 to 2.4 vehicle will enter service much before 2020. By the same token, required research for the hypersonic vehicle and its economics would make entry into service of a hypersonic vehicle unlikely before 2050 - and possibly later unless scheduling and airport curfews could be accommodated to demonstrate higher cruise speed benefits. Therefore, the focus of the remaining discussion is on vehicles cruising at speeds up to Mach 2.4.

The NASA High-Speed Research (HSR) Program was phased out in fiscal year 1999.