Project FOOF with FF-DPFs

[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…

[vansig]

Ok. i’m squinting at the image, here
http://en.wikipedia.org/wiki/File:Vasimr.png

the ICRH antenna, situated aft of the magnets, generates most of the heat. there is already a vacuum between the plasma and the superconducting magnets. yes, the magnet cores touch parts of the engine chassis.. is that a thermally-insulating ceramic?

i assume the magnets have low-temperature coolant running through their cases, which are also given mirror-reflective surfaces?

[Aeronaut]

I’m reading a 100% duty cycle assumption into both the FF and the VASIMR, as well as 2 distinctly separate cooling challenges. What would be likely to happen if the engine were pulsed at around 300hz (eliminating or minimizing the FF onion’s output storage system) and were at least pre-cooled by the FF coolant?

[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… 🙂

[QuantumDot]

controlling thermal emission radiation
http://availabletechnologies.pnl.gov/technology.asp?id=82

micron-gap thermal photovoltaics
http://greeneroz.net/component/content/article/5105-thermal-photovoltaics-breakthrough-by-mtpv-corp.html
http://www.greendiary.com/entry/mit-researchers-set-to-defy-carnot-limit-in-reusing-90-of-waste-energy/
http://www.energy-review.info/blog/quantum-dots-photovoltaics/

spacecraft skin
http://www.msnbc.msn.com/id/26294999/
http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=222&content_id=WPCP_010576&use_sec=true&sec_url_var=region1&__uuid=f9d2789c-bb62-4ae4-a6d6-a0bab194394a

planks law breakdown
http://www.sciencedaily.com/releases/2009/07/090730154025.htm

check out these sites for current and upcoming technologies.

[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.

[vansig]

zapkitty 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…

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.

By the way, One of the links to their description was broken, but here’s another,
http://www.treehugger.com/files/2009/01/thermal-photovoltaics-solar-power-mtpv-higher-efficiency.php
seems to me, that the vibrating mushroom cap generates an alternating current, which is rectified. Since heat is broad spectrum, the sizes of these would vary along the temperature gradient, making them extremely efficient emitters, too (e >.99).

[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…

[vansig]

well, where ever they end up, it looks like you want them to mass < 500 mg for each watt they generate.

[Aeronaut]

What about mil-spec radiation hardening (or at least screening?).

[vansig]

seems like we’ll want everything radiation-hardened. we have neutrons and xrays in the DPF, and plasma in the van allen belts as well.

plus,
it’s looking like these MTPV cells like it hot: if i’m reading this right, that’s 1000 – 1500 °C; but they generate 5-10 watts/cm².
http://www.economist.com/science-technology/technology-quarterly/displaystory.cfm?story_id=15582193&fsrc=rss

so we set them up to blanket the high temperature equipment, and scrounge 100 kW for each m² they cover.

[vansig]

vansig wrote: it’s looking like these MTPV cells like it hot: if i’m reading this right, that’s 1000 – 1500 °C; but they generate 5-10 watts/cm².

okay, the newer prototype can work at temperatures as low as ~550 °C. I’m reading 7.4 W/cm² at 640 °C, and 11.8 W/cm² at 780 °C.
— http://tinyurl.com/22rxahe

[vansig]

vansig wrote: well, where ever they end up, it looks like you want them to mass < 500 mg for each watt they generate.

So their off-the-shelf product is this 20 kW panel.
http://www.mtpvcorp.com/product-meter.php?tab=3&btn=13

Note, however, to meet mass limits we’ll want this to be < ~10 kg. Though theoretically possible, i'm not seeing it in this unit.

[QuantumDot]

If you are interested in looking at some materials check out this site https://www.inventables.com/

its crazy some of the stuff they have listed but they also don’t have some of the other great stuff like demron, but what ever check it out.

[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!)

[Author]

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