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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 turgid on Monday July 13 2015, @12:11PM
Would the U-238 not breed Pu-239 via neutron capture? I can foresee political problems, not to mention technical ones. How much fusion is being done, and how much heat needs to be extracted to keep the engine from melting and to produce the electricity to drive the lasers?
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 1) by AnonymousCowardNoMore on Monday July 13 2015, @04:20PM
Would the U-238 not breed Pu-239 via neutron capture?
That's exactly it. U-238 has an insane half-life of more than 4e9 years, making it useless for power generation. The reactor must breed Pu and run off that.
How much fusion is being done, and how much heat needs to be extracted to keep the engine from melting and to produce the electricity to drive the lasers?
Keeping the engine from melting shouldn't present much of a problem over other thermal rockets but your other observation is notable: Even the best fusion reactors in the world release barely more fusion energy (I mean total, not usable) than it takes to run the reactor. This rocket looks like it will be twenty years in the future for the next forty years.
I can foresee political problems
Agreed. I don't see how it could fly without major changes in the political climate.
(Score: 3, Interesting) by turgid on Monday July 13 2015, @07:49PM
So, the Pu-239 is fissile. However, it also decays, producing heat. If the energy spectrum of the neutrons produced during the D-T fusion is suitable, then there would be induced fission in the 239Pu, so there would be another source of heating. If not there would only be heating from the 238U to 239Pu conversion (decay) and maybe the odd neutron hitting the casing.
If it's just decay heating, then you've effectively got an RTG to produce your electricity and a fairly low pressure but high speed exhaust from the fusion reactions.
Otherwise, you've got a hybrid fusion/fission fragment rocket, since the (very hot) fission products from the 239Pu fission will be ejected out the back of the engine with the fusion products, significantly adding to the thrust.
I would imagine that with fission going on as well, you would probably want some kind of neutron reflector to get better neutron efficiency and to keep the neutrons away from the rest of the craft. Gas-cooled reactors (Magnox, AGR) used graphite bricks, cooled with carbon dioxide or carbon dioxide mixed with methane to limit erosion.
Would you want to contain the fusion plasma in some kind of electromagentic rocket nozzle to keep it from physically touching the walls of the engine.
These are idle thoughts, but since Boeing marketeers are shouting about it, I don't feel too stupid putting in my tuppence-worth.
I'd really, really like to live to see a nuclear-powered space craft used for scientific exploration, especially one with a human crew. I won't be the one building it, because my brain isn't big enough, but I can dream...
There was a significant amount of research and development done decades ago for nuclear engines to put on the upper stages of the Saturn V. What might have been!
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 2) by turgid on Monday July 13 2015, @07:58PM
What a goat. I originally read this story on my phone and the text was so small I didn't notice the link to the phys.org story, just the Business Insider one. Yes, they're expecting fission from the 238U. I suppose fission fragments are the way to go. Not sure about the fusion part. If it's insignificant in terms of thrust, maybe there could be a cheaper and simpler source of neutrons? Tritium isn't cheap, it's difficult to handle and has a short half-life.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 2) by gnuman on Tuesday July 14 2015, @04:12AM
Yes, they're expecting fission from the 238U.
Which means it is dead concept for terrestrial engines. It is also a dead concept when it comes to rocketry considering other, more exotic means,
https://en.wikipedia.org/wiki/Spacecraft_propulsion#Table_of_methods [wikipedia.org]