Isinglass was a the code name for a heavily classified, rocket-powered, air-launched aircraft studied by the Central Intelligence Agency as an A-12/SR-71 successor in 1964-1968. It studied several technologies that would be used in later shuttle and SSTO programmes, including light weight structure and thermal protection system concepts, and diffusion-bonded titanium. A large scale test article was built and tested to prove these features.
The initial Isinglass concept was designed by General Dynamics based on work done on the B-58-launched Super Hustler, Fish, and Kingfish programs of 1958-1960. The new design would use modern avionics and hydraulics systems developed for the F-111 and be capable of air-breathing Mach 4-5 cruise at 30 km altitude. The General Dynamics feasibility study was completed in the fall of 1964. An alternative design completed by McDonnell Aircraft in 1965 was designated Project Rheinberry. This would be a rocket-powered aircraft launched from a B-52 and flying at a near-orbital speed of Mach 20 at 60 km altitude. For the CIA's reconnaissance purposes, neither of these concepts were found to have advantages in comparison to satellites to justify the high development and operating risk and costs.
Status: Cancelled 1968.