The US Patent Office has approved Boeing's application for a patent upon its laser and nuclear fuel pellet powered jet engine designs. According to the patent, the new engine would work by firing laser beams at ejected nuclear fuel pellets to create thrust. The large amount of heat generated by the successive nuclear blasts would in-turn be harvested to create electricity to power the laser beams.
This newly unearthed patent was filed in October 2012 and published by the USPTO just a fortnight ago. Three inventors are listed as follows; Robert J Budica, James Herzberg, and Frank Chandler of California. The patent applicant and assignee was The Boeing Company.
Boeing's summary of the invention is headlined as a 'Laser-powered propulsion system'. Cutting through the technical jargon of the point by point legaleese patent explanations Evan Ackerman wrote a good summary of how the engine works on the IEEE Spectrum journal:
"Here's the basic idea: you've got a cavity that's a sort of hemisphere shape, kind of like the business end of a rocket engine. You toss a pellet of fuel into that cavity, and then lasers blast the fuel pellet, causing it to release a bunch of energy (by exploding, fissioning, fusing, or whatever). That energy pushes against the walls of the cavity, and the cavity moves forward. At the same time, the explosion heats the walls of the cavity, and this heat is harvested to drive the lasers."
You can get a good grasp of this engine process from the diagrams above. The first diagram shows the nuclear fuel pellet being blasted by lasers. Looking at the second diagram you can see that the heat from the previous explosion(s) reacts with the Uranium-238 reflector lining and this is used to drive a turbine to create electricity to re-power the lasers.
Overall, Boeing's patent looks to be an idea before its time. As Ackerman says in his IEEE post, the idea is "mostly crazy." Many of the fundamental technologies that the laser-nuclear engine would rely upon do exist or are on the verge of becoming possible... probably. Having all of this tech working in concert in an engine would be quite an achievement and it will probably be quite some time in the future before it is realised.
