Flying nuclear reactor: The USA’s risky experiment

From Sydney to London, without a stopover: The Australian airline wants to start from October 2027 Qantas offer one of the longest non-stop flight connections in the world. This is supposed to be made possible by something specially developed for this purpose Airbus A350-1000ULRwhich can stay in the air for up to 22 hours. During a test flight in July, the machine covered more than 23,000 kilometers.

As impressive as these figures are, the desire for the longest possible flights without a stopover is by no means new. Decades ago, engineers dreamed of aircraft that could stay in the air for days, maybe even weeks. An almost forgotten chapter in American aviation history shows how far people were willing to go to realize this vision.

On September 17, 1955, takes off at a military airfield in the US state Texas an aircraft that has never existed in this form before. There is a conspicuous warning sign on the tail of the American long-range bomber: the international symbol for radioactivity.

There is actually one in the fuselage of the machine functioning nuclear reactor. The aircraft will operate intermittently as it flies over the southwestern United States. The US Air Force is pursuing an ambitious goal: it wants to find out whether aircraft can one day be powered by nuclear power.

A bomber that would hardly have to land

What sounds like science fiction today was the subject of a billion-dollar research program in the 1950s. The atomic bombings Hiroshima and Nagasaki demonstrated the devastating effects of nuclear fission in 1945. American researchers are now investigating whether the technology could also be used to power aircraft.

With the beginning Cold War the project gained additional importance. In an emergency, American bombers also had to attack distant targets Soviet Union can achieve. To do this, they required large fuel reserves or were dependent on stopovers and aerial refueling.

A nuclear-powered aircraft, on the other hand, could theoretically stay in the air for days or even weeks. This would have meant significant strategic advantages for the US Air Force.

How do you protect pilots from a nuclear reactor?

The US Air Force chose a bomber of this type for the tests Convair B-36 „Peacemaker“. With a wingspan of more than 70 meters, the machine was one of the largest military aircraft of its time. It was powered by six piston engines and four additional jet engines.

One example, which was damaged in a tornado in 1952, was converted for the nuclear program. It received the designation NB-36H and the nickname „Crusader“.

The engineers installed an air-cooled nuclear reactor with a thermal output of around one megawatt in the bomb bay. With its shielding, it weighed just under 16 tons. Side air inlets provided the necessary cooling.

This turned out to be particularly complex Protection of the crew. The original cockpit cockpit was replaced by a specially constructed, round one eleven tons heavy protective cabin replaced. The windows were made of up to 28 centimeters thick Bleigl. Due to the strong insulation, it was said to be eerily quiet in the cockpit.

There was space for five people in the cabin: two pilots, a flight engineer and two nuclear engineers. The latter were responsible for monitoring the reactor and radiation levels.

The reactor could be removed from the fuselage after flights and was stored in a protected facility on the ground between missions.

If the nuclear bomber crashes

A crash of the NB-36H could also have resulted in the release of radioactive material. The test flights therefore mainly took place over sparsely populated areas in the southwest of the USA. The reactor was only switched on after the aircraft had reached a safe altitude.

The bomber was accompanied by one Boeing B-50which contained additional technicians. Some of them had completed parachute training. In the event of an accident, they should jump off in order to secure the crash site as quickly as possible.

However, no such use occurred during the entire test.

What the 47 test flights actually proved

Between September 1955 and March 1957 the NB-36H completed a total of 47 test flights. She spent 215 hours in the air, including 89 hours with the nuclear reactor running. The last flight finally took place on March 28, 1957.

The tests provided insights into how the radiation affected the aircraft systems and whether the shielding provided the crew with sufficient protection.

The reactor itself was not connected to the engines. The NB-36H flew with theirs throughout the testing conventional engines. The engineers were able to prove that a nuclear reactor could be operated on board an aircraft. However, further developments would have been necessary for an actual nuclear drive.

Worked in parallel General Electric and Pratt & Whitney on corresponding engines. Different concepts were tested on the ground in which the heat from a nuclear reactor was to be used for propulsion. This did not result in an airworthy system.

Why the billion dollar project failed

And there was a reason for that: there were technical difficulties considerably. The necessary shielding alone resulted in many tons of additional weight. Added to this were the cooling of the reactor, the high development costs and the risk of radioactive contamination in the event of a crash.

At the same time, military requirements changed. Advances in aerial refueling allowed conventional bombers to fly ever greater distances. With the development of intercontinental ballistic missiles, the idea of ​​an aircraft that could stay in the air for weeks became even less important.

After the last test flight in March 1957, the NB-36H was no longer used. A year later, the US Air Force had the machine scrapped. Work on nuclear aircraft engines initially continued until President John F. Kennedy the program finally ended in 1961.

By then the United States had almost a billion dollars invested in development. An aircraft whose engines were actually powered by a nuclear reactor never emerged.