On 7/15/2011 6:23 AM, Jeff Findley wrote:

No, it's mostly the acknowledgment that SABRE is a bleeding edge
technology in much the same way as a hypersonic air breathing engine
(e.g. NASP and more recent technology demonstrators). We've been down
this road more than once, and it's burned us each and every time.

In the case of the NASP/Copper Canyon, the scramjet technology may have
been at least partially a chimera, to mislead the Soviets and drive them
to the bargaining table.

Pat