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The Nuclear Lightbulb (2020)

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Re: The Nuclear Lightbulb (2020)

#31

Post by d_silin »

philipkglass wrote: post #15

I read some of the old United Aircraft Corporation reports about the nuclear light bulb reactor the other weekend. The design parameters are delightfully extreme. You can see why it wasn't tested in later years. By the 1970s there was already much diminished tolerance for experiments that ejected fission products into the environment, and effective release prevention for testing this design would be expensive. Here's…

Just saying that 200 atm + 23,300K alone would push the design feasibility firmly into 22nd century. Modern rocket engines can only handle 3000-4000K on the inside with roughly the same pressures.

Re: The Nuclear Lightbulb (2020)

#33

Post by philipkglass »

d_silin wrote: post #31
philipkglass wrote: post #15

I read some of the old United Aircraft Corporation reports about the nuclear light bulb reactor the other weekend. The design parameters are delightfully extreme. You can see why it wasn't tested in later years. By the 1970s there was already much diminished tolerance for experiments that ejected fission products into the environment, and effective release prevention for testing this design would be expensive. Here's…

Just saying that 200 atm + 23,300K alone would push the design feasibility firmly into 22nd century. Modern rocket engines can only handle 3000-4000K on the inside with roughly the same pressures.

They posited a clever solution for the irresistible temperatures. They didn't plan on having any structural material survive contact with with the fuel plasma. The quartz inner wall would be protected by a vortex of neon. Most energy transfer to the hydrogen propellant would be as radiated visible and UV light through the gas boundary and quartz wall. (There would also be some direct heating by neutrons.) The hydrogen propellant on the other side of the wall would be seeded with finely divided tungsten to make it absorb 98% of the radiant energy. The propellant would be much cooler than the plasma fuel, though still blazing hot [1]. The whole concept is in the intriguing fuzzy transition zone that separates AM engineering from FM [2]. It seems more likely to go "boom" than "whoosh" but I Am Not a Nuclear Rocket Scientist.

[1] https://www.osti.gov/servlets/purl/4729955

[2] Actual Machines / Fucking Magic, from the Turkey City Lexicon: https://www.sfwa.org/2009/06/18/turkey-city-lexicon-a-primer...

Re: The Nuclear Lightbulb (2020)

#38

Post by pfdietz »

I think you should be able to achieve an Isp approaching that of this rocket with a solid core nuclear reactor, without radiators, although at much lower T/W ratio.

The idea would be to not just dump hydrogen into the reactor to heat it, but gradually warm that hydrogen, extracting as much power as one could along the way. At the end, this power would be used to superheat the hydrogen after it went through the reactor (by some sort of electrical heating), to a temperature greater than the reactor's temperature limit. Alternately, the exhaust stream could be further accelerated by some sort of MHD afterburner.

The observation here is that a nuclear rocket is not energy limited, but rather is entropy limited: the exhaust can only carry away so much entropy. So, the goal is to make the engine as internally efficient as possible, with as little thermodynamic irreversibility as possible.

Re: The Nuclear Lightbulb (2020)

#39

Post by markc »

tyingq wrote: post #4

"For those of us of a certain age, there was a toy that was quite popular: the Easy-Bake Oven...Rather than having a more normal resistive heating element as you find in a normal oven, though, a special light bulb was mounted in the oven, and the waste heat from the bulb would heat the oven enough to cook the food." I can't find any evidence that the Easy Bake oven used a "special" light bulb. It just used 2 normal 1…

>Easy-Bake Oven

You can buy a Panasonic FlashXpress toaster oven and get the Easy-Bake experience. Great toaster! Fast and very predictable. It starts cooking immediately and every toast cycle is the same duration. In a regular toaster oven it takes a while for the heating element to get hot before it starts to actually toast the bread. If you immediately cook a second batch of toast for the same amount of time it burns.

Re: The Nuclear Lightbulb (2020)

#40

Post by chipsa »

JulianMorrison wrote: post #18
th8700 wrote: post #10

Earlier quoted context omitted.

Nobody would accept the fallout if it's a ground launch. And if it's a space launch, why not go directly to Project Orion?

Nobody would accept the fallout if it was a space launch either, given that crud might either hang about in LEO poisoning it for everyone else, fall out onto the planet below, or drift around in space forming a radiation hazard for future travel. You'd have to get its speed up to solar escape velocity to ensure it wouldn't be captured somewhere .

Not with an isp measured in the thousands of seconds. This is greater than earth escape velocity. Past the earth, it'll diffuse enough to not be a significant issue.
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