Sharing the friendly skies with a nuclear reactor is probably enough to keep even the most seasoned travelers awake throughout an overnight flight, but nuclear power would have a few advantages. In addition to not needing to refuel between flights, a nuclear-powered airplane in theory would not pollute the environment as long as the radioactive waste from its reactor could be contained (the Air Force's project never progressed far enough to come up with a practical way to address this).

Nuclear reactors are routinely used by the U.S. Navy to power its aircraft carriers and submarines. The U.S. commissioned the first of its nuclear sub fleet, the USS Nautilus, in 1954, and continues to rely on them today as part of its nuclear war deterrent. The U.S.S.R. reportedly built 245 nuclear subs during the Cold War, according to the Monterey Institute of International Studies's Center for Nonproliferation Studies.

Poll proposes nuclear-powered airplanes using reactors with engines on the wings. "The risk of reactors cracking open in a crash could be reduced by jettisoning them before impact and bringing them down with parachutes," he told the Times of London, adding that, in the worst-case scenario, if the armor plating around the reactor was pierced "there would be a risk of radioactive contamination over a few square miles." Poll declined to be interviewed for this article.

But many nuclear physicists and engineers are not on board with nuclear airplanes, especially in the aftermath of the September 11, 2001, attacks during which terrorists plowed jumbo jets into the World Trade Center and Pentagon. "We've been worried since 9/11 about how to protect against bad guys hijacking an aircraft and crashing it into a nuclear power plant upwind of a heavily populated area," says David Lochbaum, director of the Union of Concerned Scientists's Nuclear Safety Project, a group that monitors the performance of nuclear plants and the NRC, which regulates them. "Let's now put the nuclear reactor in the plane itself, so they can target big cities without a nuclear plant upwind," he adds, with sarcasm. "What a Christmas present for the terrorists of the world."

Lochbaum worries that terrorists could hijack and use jets as nuclear missiles or take them apart for materials to build their own so-called dirty bombs.

No matter how well shielded, crew and passengers would still run a high risk of exposure to radiation (on top of cosmic radiation that all travelers are exposed to simply from taking to the skies). What's more, the planes would have to be so large—about twice the size of a 747—that airports would have to build special docking stations apart from their existing terminals.