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Brian H wrote: About the 320 units sharing cap banks: AFAIK, the positioning (connector length etc.) to each core from its caps is critical. That would seem to me to rule out any “sharing”. That is, I don’t think it’s going to be possible to “gang” operate multiple FF’s as though they were a single unit, all firing simultaneously. In clusters, each is going to have to be a stand-alone complete operating entity, sharing current output and possibly thermal waste handling capacity, but not much else. IMO.

I don’t know if the lengths are that critical but if it turns out
that way at initial production then at least the dual inline core should still work… if a radial setup is still required then have the cap bank in a ring equidistant between the cores with the business ends of the caps facing inwards (or outwards depending on the engineering.)

That way both cores should see the same cap bank with the same connector environment… I think… 😉

[zapkitty]

Aeronaut wrote: Inline dual-core designs double shielding size and weight, while unnecessarily shielding the cap bank. A tandem multi-core design does little to increase shielding size, yet keeps the caps and cores out where they’re fairly easy to replace during a service call. Reducing downtime is going to be a huge selling point, imo, figuring a quick swap on-site followed in the depot by a nearly complete tear-down to replace the electrodes.

Errr… nope… that was a block diagram, not a blueprint 🙂 The caps in my concept would be no more shielded than required. Actual shields would be in sections and removed as needed for DPF servicing.

As to placing two cores adjacent in the same shielded volume… how close can the cores be before interfering with each other via heat, EM fields, radiation etc ? How would your concept be laid out?

[zapkitty]

Brian H wrote:
Excellent find. Slightly edited for spelling, etc., here’s the relevant excerpt:

The main shielding is for the residual neutrons—about 80-100 cm of water and 20 cm of boron-10 with a small, few-cm layer of lead to absorb the gammas. None of the x-rays will get through that.
…
5) What are the approximate dimensions of the proposed reactor?

Reactor plus shielding is 2 meters across but the whole thing, including capacitor bank may be more like 3x2x2 meters.

Which are the figures I’ve been working with for my notional first-gen application implementations… so an inline dual-core could be about 5x2x2?

core |caps| core } 2m
<—- 5m—->

… 10MW at the proposed initial 5MW/core settings… damn that’s small…

[zapkitty]

rashidas wrote: Does the boron have to be very pure – reagent grade? or will 20 mule team borax do?

Fun question “_)

What I do know is that the proposed fuel at the moment is decaborane, which is composed of boron and hydrogen and I would think it’s normally manufactured to closer tolerances than the borax detergent…

It would be nice to be able to scoop raw borates and hydrates into a DPF reactor and keep it going but I suspect there’d have to be built-in miniaturized chemical refining plant to make that happen with the current designs 🙂

Then again if it’s a fusion reactor and you have enough fuel to get it started then an additional module containing such refining gear might just be a regular accessory…

… edits… can’t type worth beans today…

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… er…

… 30 short tons to orbit would be 60000lb @ $20/lb = $1.2 million… fusion SSTO costs to orbit should be cheaper than that and with a vastly less expensive infrastructure.

My stated reservations about the viability of fusion SSTO will only be valid for the short term after the introduction of fusion powerplants… and even the most optimistic beanstalk is a long term project…

[zapkitty]

“The grid is dead! Long live the grid!”

🙂

[zapkitty]

Brian H wrote: But it’s so much fun watching the astronauts do spacewalks to fiddle with and replace the solar panels! And they’re so … wingy!

Yes, those are clear and convincing arguments for replacing spacecraft solar power systems with onboard fusion systems.

[zapkitty]

Brian H wrote:

A wild-ass guess says that we’re looking at 400 MW or more in excess of primary power needs to enable a switch to jet-style propulsion.

that’s just 80 anodes, tessellating a spherical shell, cooled by 160 kg/s of helium in a closed cycle. hardly any challenge, at all 🙂
Yeah — 160 tons of FF, a ton or 10 of helium, and maybe 160 lbs. of fuel? No problemo! :cheese:

All we need to do is install all that gear into a clone of the Spruce Goose!

… more seriously…

… while FF, as it is currently described, is not power-dense enough to directly displace jet engines FF deployment can still make a huge impact in the world of aviation by directly slotting into the spaces currently occupied by subsonic carriers. FF can do this by using transports that have low maintenance and unlimited range…

…. which is a large advantage in a huge market.

One example: A Taiwanese chip fab receives an emergency order from the ITER installation for two dozen replacement chips for a blown heater control array.

ITER has to have the new chips as soon as possible or the reactor budget will implode and take the facility administrators with it.

An FF transport would not even be as fast as a 747… mach 0.72 as opposed to mach 0.85… but the transport gets the chips to ITER before any other commercial carrier could because it does not stop. Does not refuel. Does not have to transfer the package to another aircraft.

… that sort of tortoise and the hare stuff…

[zapkitty]

Brian H wrote: I wonder if MHD can be used for jet transport. FF seems like a natural for this; I’ve seen designs for SSTO spacecraft that use it in atmosphere, and ion drive thereafter.

Still just not enough power, it seems. FF units, as currently described, are just too heavy

The currently proposed uses of MHD in aerospace propulsion are decelerating incoming air and using the power extracted from that to accelerate the outgoing exhaust (more of a power transfer than actual propulsion) and for external airflow control at supersonic and hypersonic speeds…

These uses alone have power overhead requirements measured in 10’s of MWs.

This would seem to indicate that MHD just can’t be used for primary propulsion at the notional ~50 MW power levels I’ve floated in this thread and that any MHD enhancements to the primary propulsion would eat the entire power supply… including the power that was budgeted for the primary propulsion.

A wild-ass guess says that we’re looking at 400 MW or more in excess of primary power needs to enable a switch to jet-style propulsion.

But once that raw power plateau has been reached (whatever the actual numbers may be) then the entire panoply of MHD tricks should be available and fusion-powered craft will occupy all niches of the aerospace ecology…

… and…

… and what everybody and their dog keeps insisting on jamming sideways into all fusion flight discussions…

…flying to orbit…

… becomes theoretically possible 🙂

[zapkitty]

… and, less pleasant to contemplate, but the fact that the transports aren’t stuffed with jet fuel even before transoceanic flights makes them much safer than jets in many regards…

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Tulse wrote:
I’m not convinced the economics and engineering involving in putting FF directly on planes makes a lot of sense. There are a lot of numbers tossed around here, but I’m doubtful that any of them indicate it is better to fly directly with FF rather than using it as a fuel source. Anyone have a convincing analysis (or have I missed a convincing analysis already presented)?

You missed at least one because it’s at the center of your argument… fuel 🙂

What are the savings advantages that accrue to a transport that never has to refuel?

I did not develop the idea much because I was just interested in pointing out that there is indeed at least one set of viable real-world numbers to compare dpf with for fusion-powered flight.

But given the propfan-replacement transport concept (propfans are based on the fancy new propeller concepts that make the huge propeller diameters of the older high-power turboprops unecessary) other savings come to mind… electric engines based on superconductors are lighter and less maintenance intensive than non-sc motors, and motors that use frictionless magnetic bearings have greatly reduced wear and need even less maintenance than motors that use standard bearings.

And it would seem that this is pretty much a very large advance over the wear and subsequent maintenance costs incurred by jet turbines.

So… it doesn’t seem out of line to propose a transport that uses standard airport runways and facilities, that never needs refueling and is only taken out of service one day every 90 days for an electrode change and a general maintenance checkup and fuel top-off while the techs are waiting for the dpf to cool.

If it works then that looks like some very big savings for a standard air transport company.

[zapkitty]

… at the oft-given single dpf dimensions of 2 meters x 3 meters it’d be more like 2 dpfs per standard 20 foot container… so most likely 1 per container (1-2 cores running off of 1 set of caps) and whatever support and cooling/heat transfer gear is needed to make it a turnkey power solution… could a standard 40′ container hold a 20 MW setup?…

[zapkitty]

vansig wrote:
i like it. now, can we bring it up to hypersonic speeds?

First it might be best to see if there’s any advantage at all to doing this… wouldn’t be much fun to get your craft up to a thousand meters and 300 kph, switch over to “10 MWt mode”… and fall out of the sky for lack of power…

But it’s something that came to mind and seems worth checking out.

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Just had a thought about vansig’s jet analogue… heat won’t give you the torque electric will, but heat has advantages at speed and altitude… the early jets had trouble low and slow but were in their element high and fast… the modern turbofan is a compromise, really…

… but to be efficient props (and fans) need to be big… in some cases so big the landing gear couldn’t reach the ground 🙂

… so what if that 5 MWt from the standard FF were to become 10 MWt once the plane was airborne? Take vansig’s presumed flow-through FF module and slide a sheath of an appropriate x-ray opaque material between the core and the onion once in the air… the air flowing through gets twice the thermal whammy but would it make up for feathering the prop? … run it hybrid?… duct design would be everything…

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vansig wrote: the more i think about this, the more i believe, that in an aircraft engine, you want the highest air flow nearest the pinch, so that you can cool the anode and cause gases to expand, increasing thrust

I don’t know…

one: the 5 MWt provided by the typical FF unit to the airstream is not going to generate the amount of thrust that the 5 MWe gets from the propeller.

two: the pinch is, perforce, insulated by a vacuum. You’ve got to get the helium out of the core and to a cold plate exposed to the airstream first…

Undoubtedly there will be optimized aircraft engines as people develop the tech after functional FFs are introduced. Things I couldn’t dream of now…

The point here being that, given the standard starting stats for the FF, right off the bat you’ve enabled a revolution in the air freight business and air passenger transport won’t be far behind…

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