[zapkitty]

Will wrote:

Microwaving air is a really bad idea – you end up with lots of nasty NOx compounds

Does it generate more NOx than a kerosene powered turbojet?

While an interesting question in itself it seems pretty much moot. 5 MWt at 426 degrees C isn’t going to move much air by heating. Even times 20… assuming you could somehow duct the air past the FF cluster…

… but an FF-powered fanjet could have a sideline in de-icing runways while waiting for takeoff clearance… 🙂

[zapkitty]

Breakable wrote:
If FF gets too efficient I think we can add microwave heating with oxygen or nitrogen resonant frequency.

Arrgh! 🙂

Please let FF get more efficient… do you know what trying to jettison 5MW of low-temp waste heat in return for 5MW of electrical power gained does to spacecraft margins? It should be a crime… 🙁

[zapkitty]

Hmmm?

I thought that the production DPFs, boron-fueled, were to have a low radiation
footprint?… That is, once you’re outside of the x-ray converter shell.

[zapkitty]

Er… just my opinion of course, but… no 🙂

However you do make it clear that in this case you are asking for funding for… something. Such clarification is a step in the right direction 🙂

Now, if that’s the case, what are you asking funding for? And where do you hope the funding will come from? Are you asking for government support? Private support? Any support you can get?

If instead you want more of a PSA about the possibilities of aneutronic fusion as opposed to current energy sources then your script should go down another path, I think.

[zapkitty]

Hmmm…. glitch in editing my post…please stand by 🙂

… okay… can’t delete an erroneous post?… lemonade mode activated!…

In fact the need for extensive desalinization and water-generating plants
to handle the water scarcity problems in the western half of the U.S.
would seem like a pretty guaranteed market in and of itself for both spare
DPF output and transmission line maintenance during the transition to
fusion power.

[zapkitty]

JimmyT wrote:
I actually think that it might. It may well become cheaper to generate more power where
it’s needed then to maintain the infrastructure to transport it.

Then doesn’t that answer your question?

Existing transmission line maintenance costs are supposed to be a small
part of the total power bill. It’s the need for building new lines and added
extras such as underground installation that drives the high prices you see
quoted for transmission line projects.

As DPF installations begin propagating the existing lines will do nicely.

And part of the economic “fuel” for DPF propagation will be the
selling of excess power over transmission lines.

As the situation develops the existing lines that are judged to to be no longer
needed will be allowed to lapse.

But this need not create a “power bubble”…

(… unless you allow the oligarchs to make it one… they just loves them some
bubbles as they don’t pay any real penalty when the bubbles burst…)

… but this need not create a “power bubble”as DPFs should be built so
as to supply local power needs plus a certain margin.

And the Feds will have a distinct (and valid) interest in encouraging the
maintenance of a basic method of intercity power transport.

It seems that the fact that anyone who wants to buy or build a DPF will
usually also want backup power of some kind (even if it’s just a spare
DPF) makes this a self-resolving issue… not a dilemma 🙂

[zapkitty]

JimmyT wrote: This subject of servicing the generator units has bothered me a lot. How to provide uninterupted power to communities or factories which are widely dispersed?

Solution 1: Maintain an interconnecting grid to provide power when units are down.
This strikes me as a terribly inefficient use of resources. Maintaining a grid for use only a few hours each year.

Solution 2. Have duplicate generator units at each station. Or alternatively place units where power demands dictate the placement of two or more units. Then, service them during off-peak hours.
Again, idle units are a waste of capital, and would be intolerable until the market is virtually saturated.

Comments? This post probably doesn’t belong here. New thread maybe?

The current practical solution would be a combination of 1 and 2.

Communities and large installations such as factories and hospitals will demand
backup units… and the low price of DPF units will make that option especially
attractive.

And the grid will retain its current extents for the same reason it currently exists…
shifting power to where it’s needed while buying and selling power produced in
excess of local needs.

Another way of thinking of this is that the ready availability of cheap, clean power
will in no way reduce the current demands for power generation and its transport.

Will there be changes in the grid structure? Yes. But DPF by itself will not render
the concept of the grid obsolete.

[zapkitty]

Aeronaut wrote:
And it’s going to be online forever if we do it in such a way as to embarrass ourselves in the longer sweeps of history- say a year or ten, when the spill’s memory in the public’s collective memory is about the same as the Exxon Valdez incident.

Leaving aside the wisdom of trying to ride the coattails of this monumental disaster without even achieving a waste-free net power device first, there is a serious misunderstanding of the scale of events in the Gulf implied in your phrasing.

A slighting reference to “Exxon Valdez”? No. There are businesses which are still impacted by that spill every day… even after all these years.

And this flood of oil into the Gulf is already much worse than Exxon Valdez and is guaranteed to get worse each day every day for months on end.

If you can attempt to equate this cataclysm to the Exxon Valdez then you do not understand what is happening.

As for the secondary role of oil in lubricants, solvents, plastics, asphalt, pharmaceuticals etc etc…. that does not amount to so very much compared to the oligarch’s insistence that we burn coal and oil to power our civilization.

Without needing to throw away (burn) those insane amounts of oil the petroleum needs of the world would contract greatly and, in the U.S. at least, even what domestic production we have now would need to contract in turn.

[zapkitty]

Been figuring on what I think is the quickest implementation of FOOF yet.

This can be inplemented on any station currently planned, and I use ISS
here strictly as an example.

Even Excalibur’s small Almaz stations would work… although the reactor
module would be as big as the station 🙂

(Maybe a custom Almaz for the reactor?)

*ahem*

In this concept there would be a separate station module to hold the DPF
box, a heat-sink based on a vacuum-insulated water tank in the same
module and a few tons of supercaps stashed somewhere.

The supercaps can be in the module as well if there’s room… depends
on the module type… but they are not required to be module itself and can
even be mounted externally.

No large and red-hot radiators required.

The limitation, of course, will be that you can only run the DPF intermittently.

Let the station heat rejection system chill the heat sink back down,
and repeat.

But, unlike my previous 1 MWe low-power concept, during this power cycle
you can run the reactor at whatever power setting gives the greatest efficiency.

Full-tilt boogie… be it 5 MWe or 11 MWe.

With supercaps able to accept the surge of power at rates that are a pretty
good match for the reactor output and then distribute it to station systems
over an hour or two (or three) between surges… that would still be a huge
bonus in available power from the point of view of current station
operations and some high-powered experiments that were previously
unfeasible could be implemented and run with the reactor/supercaps
system.

For a spaceship the extra weight of the supercaps would be a cruel penalty…
for a current-design space station it wouldn’t be a problem and the increased
power would be well worth the mass penalty..

And it’s scalable. Add more conventional radiators to the station and get
more usable power.

When the concept is proven safe enough add a second reactor module for
backup… and ditch the solar arrays. Except for stubs of the main wings
as backups for emergency power… or ditch them altogether for some
SLASR-type boxes on the truss for backup instead.

And that would free up a big heat load from the dedicated radiators for the
arrays and their batteries… with ISS that’s 4 x 9kWt of radiator capacity of
which some might be adaptable for aiding the heat sink cool down.

But first off is just the module, heat sink and supercaps… fusion is validated
on orbit and the lucky station is maxed out on as much power as it can handle.

Thoughts?

(post edited… no, really!)

[zapkitty]

vansig wrote:
I like it!

So what you need, then, is for your thermo-photovoltaics to weigh
in at < 500 kg total. I think these could be made quite compact,
especially if they can be built into the radiator structure.

Hmmm… wouldn’t it be simpler to get the heat while it’s close to the
source? You can optimize your thermal bandwidth to boot…

And also there is the problem of ionizing radiation… with passage
through the van allen belts being sufficient to degrade standard
photovoltaics these thermovoltaic nanostructures aren’t going to be any
less susceptible as the tug slowly spirals through them and into the
radiation environment of cislunar space…

Perhaps it would be best to surround them with copious amounts
of coolant near the fusion and drive cores and accept the somewhat
increased size of the cooler-running radiators…

… still come out ahead I think…

[zapkitty]

QuantumDot wrote:
controlling thermal emission radiation

Micropits are an excellent way of increasing
emissivity, and there’s ongoing research on using
atomic oxygen to pit standard radiator surfaces*,
but it seems that the fancy shutters described in
that link would be a waste of time for a spacecraft
trying to deal with heat in the megawatt range.

*(The atomic oxygen in LEO is always too busy
trying to eat the things you don’t want it to eat to
be bothered with evenly pitting a given surface 🙂 ).

QuantumDot wrote:
micron-gap thermal photovoltaics

This could be excellent if it compares favorably
with the equivalent increase in power/radiators in
mass and volume.

But the recovery of 80% of the thermal from reactor
and drives as electric would do great
things for radiator size etc if the mass of the dots
gear doesn’t eat the margin gained.

With the current stats that would give us a DPF
box running at .35 MWe (!) and a double-faced
radiator of 66 m2… a square just over 8 meters on
a side that masses 1.3 tons…

QuantumDot wrote: spacecraft skin

Good for microcraft but apparently does not scale
well with volume. Fusion-powered ships will by
necessity not be… micro 🙂

QuantumDot wrote:
planks law breakdown

Yes, I know you’re not breaking the laws of
thermodynamics 🙂

Quantum dots have great potential but are not
quite to the point where we could build a ship
around the concept… yet.

[zapkitty]

Aeronaut wrote:
I’m reading a 100% duty cycle assumption into both the FF and the VASIMR,

That is the fate of nuclear-electric tugs… never a
break 🙂

Aeronaut wrote:
as well as 2 distinctly separate cooling challenges.

Apparently they have the supercon cooling
problem in hand. The article mentions 10-12 cryo-
coolers each lifting 15 watts from a VF-200 in flight
mode.

That would mean that they expect that 180 watts of
cooling will serve to handle the thermal leakage of
one VF-200 in operation.

That means 4 such engines would require less
than one kilowatt of cooling to keep the supercons
superconning.

The coolers for the VF-200 are to be custom-built,
but the specs for the referenced Cryo-Tel units say
the operating temp is -196 C while the output side
needs to be at 70 C or less.

The VASIMR supercons need to be at -233 C so
the output might have to come down. Let’s say
degree for degree so that the output side needs to
be at 33 C.

That’s not a problem… that’s some fancy trim
around the edge of the main radiator 🙂

So the engines can stay at 100 percent?

Now handling the thermal output of the rest
of the VASIMR drive is of the same order of
magnitude as the DPF (remember the DPF is
running at .86 MWe) so I was hoping to have them
on the same coolant line. If the DPF can handle
being at 300 C then perhaps we can cool the
drives first and then pipe it into the DPF.

But at this stage, before these latest supercon
modifications, there doesn’t seem to be any
showstoppers. The essential numbers for the main
radiator were:

temp (c) 300
area needed (m2) 188
mass (tons) 1.88
rejection (MWt) 0.98

… adding the needed stuff for the supercons won’t
change it that much… that is assuming my basic
assumptions were viable in the first place… 🙂

[zapkitty]

Oooops… NASA cruelly shatters my dream of a steampunkish nightmare kludge of pipes, tanks and fins cycling and venting away on orbit…

http://microgravityuniversity.jsc.nasa.gov/SE/theProjects/project-detail.cfm?experimentID=24

… sealed commercial cryo-coolers… who would have thought it? 🙂

We still have to deal with hundreds of watts through cold plates that must be kept at 70c but that’s simple compared to what’s already required for the DPF box and VASIMR engines.

As for choice of coolant… I still want to check out using the water (water/antifreeze) coolant for all of it. Savings in mass and power there as opposed to He when you begin budgeting for storing and pumping the stuff. Instituting a strict no-freeze operations regime while simultaneously building the radiator freeze-tolerant and using isotope heaters in the plumbing at critical points should handle that problem.

Regardless of coolant, an appropriate radiator assembly in line with with the main radiator should do the trick and also handle the other intermediate cooling tasks you mention as well.

Numbers coming up…

[zapkitty]

Just a note: the supercons won’t generate heat in and of themselves like a regular electromagnet would. The way they heat up is conduction via their physical contacts and radiation from adjacent structures… and these particular magnets are wrapped around a plasma rocket engine operating for weeks on end.

Well, there’s a caveat… if their electromagnetic limits are exceeded the supercon effects break down and the material returns to being a normal conductor and will heat up rapidly… quite rapidly… very very very rapidly… a job for Joe Viskocil, methinks 🙂

But potential pyrotechnics aside, the supercons will stay cold except for what heat is introduced into them by conduction or radiation so they will need to be isolated somehow and engineering such thermal isolation is where the power costs will come in, I think.

[zapkitty]

So to be clear their “200 kW VASIMR” is actually two 100 kW units strapped together… my notional version was a single engine operating at 200 kW…

…5 newtons at 5000 seconds would be great 🙂 …

… argon as both coolant and propellant simplifies the plumbing but we’re still going to need an additional radiator edge-on to the sun at -157 c and a liquifaction plant to compress, cold-soak, and expand the used argon in a classic refrigeration cycle… which takes more power which needs more cooling and thus more radiator mass..

… so can we keep the magnetic cores somehow insulated and running at -185 C while we pump up the engines to 300 C? Theoretically possible but the power cost would go through the roof…

… have we forgotten something…?

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