commands up to its failsafe point, whereafter it would rely on a terrain contour matching (TERCOM) radar system to navigate to preprogrammed targets. Development The primary innovation was the engine of the aircraft, which was developed under the aegis of a separate project code-named Project Pluto, after the Greek god of the underworld. It was a ramjet that used nuclear fission to superheat incoming air instead of chemical fuel. Project Pluto produced two working prototypes of this engine, the Tory-IIA and the Tory-IIC, which were successfully tested in the Nevada desert. Special ceramics had to be developed to meet the stringent weight and tremendous heat tolerances demanded of the SLAM's reactor. These were developed by the Coors Porcelain Company. The reactor itself was designed at the Lawrence Radiation Laboratory. Although a prototype of the airframe was never constructed, the SLAM was to be a wingless, fin-guided aircraft; its appearance giving it the nickname "Flying Crowbar". Apart from the ventral ram-air intake it was very much in keeping with traditional missile design. Its estimated airspeed at was Mach 4.2. The SLAM program was scrapped on July 1, 1964. By this time serious questions about its viability had been raised, such as how to test a device that would emit copious amounts of radioactive exhaust from its unshielded reactor core in flight, as well as its efficacy and cost. ICBMs promised swifter delivery to targets, and because of their speed (the Thor could reach its target in 18 minutes, whereas the SLAM would take much longer) and trajectory, were considered virtually unstoppable. The SLAM was also being outpaced by advances in defensive ground radar, which threatened to render its stratagem of low-altitude evasion ineffective. Reactor design The reactor had an outer diameter of and length ; the dimensions of the reactor core were diameter and length. The critical mass of uranium was 59.90 kg, and the reactor's power density averaged at 10 megawatts per cubic foot (350 MW/m3), with total power of 600 megawatts. The nuclear fuel elements were made of refractory ceramic based on beryllium oxide, with enriched uranium dioxide as fuel and small amount of zirconium dioxide for structural stability. The fuel elements were hollow hexagonal tubes about long with distance between the outer parallel planes, with inside diameter of . They were manufactured by high-pressure extruding of the green compact, then sintering almost to its theoretical density. The core