First airborne nuclear reactor

The first airborne nuclear reactor was a one-megawatt air-cooled reactor called the Aircraft Shield Test Reactor (ASTR) designed by General Electric for a joint US Air Force–Atomic Energy Commission project called Aircraft Nuclear Propulsion (ANP). The reactor was flown inside the bomb bay of a converted B-36 bomber, redesignated the NB-36H "Crusader" (also known as the XB-36H), a total of 47 times between 20 July 1955 and March 1957. The reactor was inert on its initial flight, but was fully operational on many flights from September 1955 onward. The reactor was not connected to any of the aircraft's systems, and was only there to assess the effects of radiation on the aircraft and its (heavily shielded) crew.

The NB-36H was commissioned as part of a sub-project of the ANP called the X-6 program, which sought to produce two airframes (heavily modified Convair B-36s) to test nuclear propulsion systems. One would be fitted with a direct-cycle engine (where the jet-engine intake air was heated by passing it through the reactor itself) and one would be fitted with an indirect-cycle engine (where the intake air would be heated by a liquid-metal coolant loop connected to the reactor). Problems developing a viable version of either design meant that the X-6 program was cancelled in June 1953 before either aircraft was built.

This setback was not the end of the ANP program, however, so work on the cheaper and less ambitious NB-36H continued. Rather than a purpose-built airframe, the NB-36H was adapted from a B-36 whose nose section was destroyed by a tornado that stuck Carswell Air Force Base on 1 September 1952. As the plans for the NB-36H would have required an almost complete reconstruction of the nose section of the plane anyway (to add shielding and reactor control equipment) this plane was transferred to the program.

During the test flights, the NB-36H had a crew of five – A.S. "Doc" Witchell (pilot), L. C. Brandvig (co-pilot) and J.D. MacEachern (flight engineer), as well as nuclear reactor engineers James Nance and Steve Andrich. The reactor engineers had their own control station at the rear of the crew compartment, with a control console and closed-circuit television screens for monitoring the reactor. The whole crew compartment was shielded with around 11 tons of lead and borated rubber.

The total lifetime costs of the ANP programme and its predecessor Nuclear Energy for Aircraft Propulsion (NEPA, which ran from May 1946 to April 1951) was estimated at $1.04 billion at the time of its termination in March 1961. That's approximately $8.8 billion adjusted for inflation to 2020. In a scathing report published in 1963, the US Government Accountability Office criticized the project for having unclear and constantly changing objectives, poor financial management and no obvious path to a practical end-product.