America's Crazy Attempts to Build Nuclear-Powered Aircraft
Ah, the Atomic Age, when nuclear energy seemed the ticket to a future of limitless possibilities. For a generation after 1945 the United States explored all kinds of nuclear propulsion concepts. Some, like naval power plants for subs and ships, proved both revolutionary and effective. Others proved possible to develop but impractical to pursue.
Of these concepts the nuclear-powered aircraft now seems the most fanciful, but billions of dollars and years of top-flight research sunk into the Aircraft Nuclear Propulsion (ANP) program chased the idea before its demise. Between the end of World War II and the dawn of Camelot American engineers figured out how to fit a reactor in an airplane and make it generate thrust without frying the crew. American leaders couldn't figure out how to pay for it or why they needed it.
Today the ANP program is remembered as an Atomic Age boondoggle whose only remains consist of three-story-tall experimental units and giant hangars with six-foot-thick walls. When cancelled, the program was about to create flight-ready hardware and an airframe to put it in for a flight test program. However doubts about the future of manned bombers and concerns about accidents clouded a costly program ripe for cuts.
But all that money and effort produced some wild ideas about what you could do with all that technology. After the Kennedy administration cancelled the ANP program in early 1961, the program's largest contractor—General Electric—produced a 21-volume report on the project.
In dry prose and black-and-white figures one blandly-named volume, APEX-910 "Aircraft Nuclear Propulsion Application Studies," painted a Tomorrowland future of atoms in motion. The report summarizes a stunning variety of studies into small, lightweight nuclear engines for everything from seaplanes to rockets and even helicopters (!)
To get a small reactor to fly, you essentially strip it of shielding and use its heat output to expand air instead of burning fuel to produce thrust. Little shielding means crew hazard and contamination. Turbojet and turboprop designs require complicated arrangements to transfer heat from the reactor core to the engines. Some designs used liquid metal for coolant and heat transfer. The pumps and plumbing involved in multi-megawatt liquid metal cooling loops presented interesting issues. GE opted for the air-cooled, direct- or open-cycle design.
The ANP program solved most of the shielding and plumbing problems before it ended, but only for open-cycle systems. Closed-cycle systems like those aboard nuclear submarines, where the radioactive heat transfer loop remains isolated from the turbomachinery, proved too difficult for the era. The first generation of atomic aircraft were going to be pretty dirty.
Subsonic aircraft concepts included airlift, seaplane and testbed vehicles. Convair's huge C-99 double-deck cargo derivative of its B-36 strategic bomber, Martin's P6M SeaMaster jet seaplane and Boeing's B-52 strategic bomber each received nuclear hot-rodding studies.
As part of the stepwise flight testing program the B-52 and Britain's "Princess" flying boat, albeit disfigured by unsightly protrusions and appendages, could carry the big prototype power plants into the air.
Supersonic designs took advantage of certain performance improvements when nuclear engines operated at high speeds and altitudes. Designers considered the B-70 supersonic bomber for nuclear propulsion but determined that performance gains didn't outweigh the additional weight and complexity.
The intriguing "Hunter-Killer" aircraft concept was one very large, very fast plane. This was a "counterforce system capable of destroying enemy strategic weapons such as ICBM's, long-range aircraft, and their associated bases." Mission requirements defined an airplane like a Mach 3 attack sub, capable of "airborne alert for extended periods of time, [penetrating] enemy territory either at sea level or at high altitudes and high speeds [and carry] large payloads (50, 000 to 100, 000 pounds)."
Nuclear-powered missiles enjoy the advantages of both nuclear propulsion and unmanned operation. The 1954 ACA-8 nuclear-powered reconnaissance drone concept featured tremendous endurance and no crew to endanger. A nuclear-powered cruise missile could be unstoppable and might prove better than the ICBMs in development at the time.