A look at the direction of NASA’s supersonic research under its Fundamental Aeronautics programme makes an interesting comparison with its High-Speed Research programme, cancelled in 1999. The focus of HSR was the High-Speed Civil Transport, a 300-seat, Mach 2.4 airliner intended to fly at supersonic speeds only over the oceans.
NASA’s HSCT – a 1998 vision of a 2015 SST
NASA’s renewed supersonics effort takes a more incremental approach, setting targets for three generations of high-speed transport: a business jet that could enter service by 2015; a small airliner by 2020; and an “efficient multi-Mach aircraft” that could see service by 2030-35. The latter is the closest analogue to the late-1990s HSCT.
What is different this time round is the greater emphasis on efficiency and the environment. The overall goal is a 30% improvement in efficiency over HSR and all three generations are expected to be low boom, allowing supersonic flight over land. NASA has set a “corner of the trade space” target for sonic boom of 65-70PLdB, compared with more than 100 for Concorde.
NASA’s “N+1 generation” is similar to the quiet supersonic business jets currently being studied by Gulfstream and others. The N+2 “vision vehicle” is intriguing: a 35- to 70-seat supersonic airliner with transatlantic range at Mach 1.6-1.8 – very reminiscent of the “business express” aircraft once talked about as a possible successor to Concorde.
NASA’s Icon – a 2007 vision of a 2020 QST
Things to note about this reference design, which I think is called “Icon”, is the telescoping nose spike for sonic boom suppression, the engine location for noise shielding and the return to variable geometry for airport performance. (Boeing’s 1960s SST, the 2707, started out with a swing wing, but ended up a delta like the HSCT.) Here’s NASA’s visualisation of the concept:
NASA has not put a shape to its N+3 supersonic transport, at least not publicly, but the “corners of the trade space” include 100-200 seats, transpacific range, and a Mach 2 cruise over water and land where supersonic flight is unrestricted, perhaps slowing to Mach 1.6 where low-boom flight is required.
The overriding goal is a supersonic transport that has no greater impact than equivalent subsonic airliners – a challenging task as it means SSTs must deliver substantial airport noise and fuel burn improvements while also tackling the sonic boom and high-altitude emissions issues unique to supersonic flight.
NASA’s incremental approach to developing foundational technologies looks wise. Cancellation of the high-profile HSR programme, a fall-out of the Boeing-McDonnell Douglas merger, ripped the heart out of NASA’s aeronautics research, and it is only now beginning to recover. Maybe it will take flight this time round.