[Breakable]

Great news everyone. Rezwan promised to put attribution license on the gallery, so everyone can share images on Wikipedia. I will get to it eventually, but meanwhile everyone will be able to do it as well.

[Breakable]

Rezwan wrote: Hi guys,
Looks like this can be split off starting at Breakable’s post on shielding requirements. Should it go under a new “shielding requirements for flights” post, or merge with “FF for jet engines” post?

I think less management is better than more, because it is easier to track the posts and topics.
If we had a Tree-like instead of single Thread forum (such as Reddit, or Slashdot comments) – that could help manage itself.
Reddit btw allows creating your own sub-reddit’s that have all kind of nice features for management, voting and thread display.

[Breakable]

Tulse wrote: That’s a lovely utopian scenario, nemmart, but I doubt FF would bring it about. While fuel costs are a significant part of the cost of airline operations, they are by no means the only costs involved — labour costs and capital outlays will always be there, and FF does nothing to address those. At best you might get a 30% reduction in the cost of air transportation, which is not small, but of course transportation is only a small part of the cost of transported goods, so that reduction will play a very small role in the final price of a product, and likely be washed out by other competitive factors.

If FF works it will indeed be fantastic, but I don’t think it’s enough to produce the radical changes you posit.

Labor costs can be reduced by robotization. Capital requirements will be reduced trough price drop in materials and manufacturing costs.
Imagine a standard small airport kit produced in a factory and assembled by robots on site. In case it is VTOL the cost could probably be less than a large house – nothing compared to current multi-billion airports. I can imagine that happening in 10-20 years in case we have FF now.

And btw flying cars don’t need airports, just a lawn.
http://www.brysonmeunier.com/assets/2008/8/11/flying-car-m400.jpg

[Breakable]

Is the neutron output energy not a probabilistic distribution? If so does that mean the high energy neutrons are just a negligible fraction?

[Breakable]

zapkitty wrote: Walking before running…. let’s start with known electrically-powered aircraft and see what they can do with the limited resources available pre-fusion…

http://en.wikipedia.org/wiki/Electric_aircraft

… yes, the FF is much heavier than any other power source currently flying… but the power level is amazing for an electric aircraft and the range, of course, is unlimited…

… then begin looking not at “jet engine substitutes” but at industrial air-moving products that operate in the multi-megawatt range we need for FF-powered flight. These industrial units won’t be designed flightweight but that’s just engineering 🙂 and the figures you get will make sense…

The important part is not weight, but weight divided by power output.
The solar aircraft (Centurion) weight is 862 kg,
power output 31 kw.
If FF output is 5 MW
then the weight of aircraft it should carry with similar limitations is about 139 tons.
Comparably 747 is 442 tons
Where Cesna is 0.658 ton
so basically something in between should work on the lighter side if we want more speed.

[Breakable]

Brian H wrote:
What longer-term byproducts? Slow neutrons don’t make any, AFAIK. Remember, max levels are about what you get from a classroom full of children.

By “longer-term” I assume products that take longer to decay to background levels than a length of a single shot. I am sure there are such products, that means they are accumulating during run and I wonder what is the function describing their accumulation.

[Breakable]

zapkitty wrote:
Why should it?

Because the longer term byproducts can be accumulating and their combined radioactivity can increase the longer you run the reactor.

[Breakable]

Tulse wrote: Commercial aircraft operate between extremely well-equipped points, so there is really no reason that they have to carry their power generation actually on board — they could more easily be run on batteries that are swapped out between flights, or (as has been pointed out before), powered with conventional jet engines using synthetically-produced fuel. Successful and cheap FF will be a game changer, but it doesn’t have to be directly used to have that effect — no one is going to drive a FF-powered car, and there’s no real reason to use FF in jets. (It makes far more sense for vehicles like ships and submarines, where travel times are very long, and space, where refueling isn’t really much of an option.)

Short term (5-10 years) – probably you are right.
But for long term (10-50 years) I don’t see why such a cool idea as a plane that needs no refueling would be passed out.
Maybe we are solving a problem that does not exist, but in a resource unconstrained world that might be a habit.

[Breakable]

Aeronaut wrote:
Eric stated in the Google Talks video that the core cools down to background radiation levels in 13 hours, citing a half-life of something like 20 minutes. He compares the starting radiation level to a room full of school kids- not much compared to fission plants

I think it should depend on how long you run it.

[Breakable]

The units are wrong – it’s 6.4 kj not mj. See the “how_will_we_get_there_from_here” doc. Also, I think in Eric’s google tech talk, he mentioned 330 hz.

Nothing seems to add up
6.4 kj * 330 hz = 2.112 MW
Lets just say the generator will produce from a few kilowatts to a few gigawatt’s. I fully understand that there can be great uncertainty ATM.
Probably much will be cleared up at the end of this year or next when unity is achieved.

[Breakable]

Brian H wrote:
AFAIK, all the X-rays are captured as part of the photoelectric current generation. And the water/boron shells catch the soft neutrons from side-reactions.

I am not an expert in radiation management, but I think that shielding is a function of radioactivity. And until I see some number I think that radioactive isotopes will probably accumulate in a running FF module until it is turned off and “cools” down.

[Breakable]

It seems the output is ~6.4 mj per shot.
https://focusfusion.org/index.php/site/article/how_will_we_get_there_from_here/
So its not MW or MWH but joules(not power but work), because it is per shot not per second.
If we have 1000 shots per second the the power would be ~6.4 gw
if 1 shot per hour then only 1.7 kilowatts.
It probably boils down into thermal and radiation flux management. EE part probably is hard only at mult-hertz.
I think the first prototypes as well as first generation units will be low frequency to reduce complexity of radiation and thermal management.
As the escaping radiation flux is probably a function of frequency, at this low frequency the shielding requirements probably can be considerably reduced
to fit a FF unit into a backyard, a truck, maybe with improved shielding materials even into a car.
Probably after a few generations of reactors are developed we will see it climb into MW or GW range and made smaller to fit onto a plane.

[Breakable]

Just to clarify FF module output is MW and not MWH?

[Breakable]

Is it silly me or is the 0.282 kN = 0.282 MW?
Edit:
Boeng output is probably per second
Where FF is per hour, in that case we need ~203 modules with electrical output
or 102 with full output in case efficiency is similar.

[Breakable]

The first prototypes FF will be probably heavy and large, but with time miniaturization will probably run its course…

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