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Boeing has patented a laser powered propulsion system for airplanes. A number of sites reported on the patent, with eye-rubbing headlines that told the story. BusinessInsider headline read, "Boeing just patented a jet engine powered by lasers and nuclear explosions." Benjamin Zhang said the US Patent and Trademark Office approved Boeing's application for a laser and nuclear-driven airplane engine.
Zhang noted that presently the Boeing Dreamliner is powered by multiple turbofan engines with their fans and turbines in place to compress air and ignite fuel to provide thrust. The engine presented in Boeing's patent application takes another route. Zhang said the laser engine may also be used to power rockets, missiles, and spacecraft.
The new engine would work "by firing high-power lasers at radioactive material, such as deuterium and tritium," said BusinessInsider. "The lasers vaporize the radioactive material and cause a fusion reaction—in effect a small thermonuclear explosion," said the article. "Hydrogen or helium are the exhaust byproducts, which exit the back of the engine under high pressure. Thrust is produced."
In this approach the inside wall of the engine's thruster chamber coated in uranium 238 reacts with the neutrons from the nuclear reaction and generates immense heat. "The engine harnesses the heat by running coolant along the other side of the uranium-coated combustion chamber," said Zhang. "This heat-energized coolant is sent through a turbine and generator that produces electricity to power the engine's lasers."
Three inventors named in the patent application are Robert Budica, James Herzberg and Frank Chandler of California. The applicant is listed as The Boeing Company in Chicago. The patent was filed in 2012.
Original Submission
(Score: 2) by Immerman on Monday July 13 2015, @08:36PM
Okay, so at first glance this patent sounds like a prior art "safe harbor" investment - by the time we master fusion well enough to pull it off efficiently, the patent will likely have long since expired. Unless Boeing has been keeping quiet about some really interesting research.
On the other hand this seems like it just might hold the seeds of the "holy grail" of a high-power adjustable radiothermic generator. Instead of a rocket bell, cover the inner walls of a vacuum chamber with U238. Then install an energetic neutron source, even a simple Farnsworth Fusor, in the center. Those have been getting tantalyzingly close to break even for over half a century, but even that's not the point - the point is that most of the energy is released as energetic neutrons which would then trigger fission reactions in the walls of the reaction vessel, generating far more energy which then gets captured as heat in the coolant. Want more heat, pump more power/fuel into your fusor and bombard the walls with more neutrons.
Runaway reactions would be virtually impossible, since the fissile material is at sub-critical densities - the instant you cut power to the fusor, the fission essentially stops as well. You'd still have issues with lingering radioactivity, but so long as the fusor is insufficiently powerful to trigger a runaway reaction a meltdown would be impossible. In fact, forget traditional fusion reactor triply-redundant safety system, I'd bet it could be relatively easily to design a fusion-catalyzed fission reactor such that a runaway reaction was physically impossible.
Hmm, actually, that's sounding not completely unlike the fusion reactor under development by Lockheed Martin [eweek.com] and partners. The difference being that instead of trying to generate power from fusion, and then breeding new fuel incidentally from the low-energy fission of the lithium shielding, you're using a far more fissile shielding to generate the bulk of the power, and a far simpler fusion "catalyst" that need not even be break-even itself.
(Score: 2) by turgid on Tuesday July 14 2015, @01:22PM
The fusion doesn't have to be energy-positive or even break-even as long as the total energy from the fusion, fission and decay is greater than the energy required for the fusion. I doubt the heat to electricity conversion could be much more than 40% efficient in practice. Still, why they'd use such an expensive fusion method isn't clear other than to bagsy the patent. Big companies often have PHB, legal and Marketing-driven patent quotas. At one place I worked, towards the end of the quarter the email would go out to the engineers saying "you're 40% short of your Invention Proposal target again."
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 2) by Immerman on Tuesday July 14 2015, @04:40PM
>The fusion doesn't have to be energy-positive or even break-even as long as the total energy from the fusion, fission and decay is greater than the energy required for the fusion.
Exactly.
As for their engine, it has a rather different design goal - instead of generating energy efficiently, it's designed to produce thrust, which means you need high-velocity exhaust, which is what the fusion is providing. Fission doesn't do "fast" very well - the energy-to-mass ratio of the fragments just isn't high enough. Plus they tend to be locked into solid fuel pellets so that the energy is thermalized almost instantly. The fission is just there to power the lasers to sustain the fusion.
As for an "expensive" fusion method - for extended operation in a rocket chamber I can't really think of any better alternatives offhand. Farnsworth-style fusors are unlikely to provide an attractive energy density without vaporizing themselves, tokamaks are far too massive to incorporate into a rocket, and most other techniques are still unproven laboratory curiosities.