Project FOOF with FF-DPFs

[zapkitty]

“Fusion On Orbit Fastest” – Project FOOF

This is meant to be a DPF-oriented complement to my FOOF thread on talk-polywell…

http://www.talk-polywell.org/bb/viewtopic.php?t=2139

Just as I said with the polywell thread: if DPF and boron 11 fusion pan out I’ve been considering the best methods to implement a DPF-powered spacecraft as quickly and as economically as is feasible. I believe that research enabling the quick application of such systems in space is important to overall fusion research and development and I’ve postulated that one way to Fusion On Orbit Fastest is to use current launch vehicles to loft a prototype fusion power supply for a small commercial space station for testing and validation.

Now, unlike first-gen polywells, an assembled DPF core can fit in standard launcher payload fairings and it would not be a big technical deal to install one in a custom ISS-style module…

… but the very necessary custom radiator would make a big change to ISS structure and operations…

… and the older ISS solar arrays would be hard pressed to store up the juice to start the DPF without impacting ongoing research… it’s a big deal just to charge and store enough energy for the 200kw VASIMR drives for a few minutes…

… and of course you’d have to deal with NASA and the established ISS environmental parameters and the partner nations…

… but it could be done.

But there is an alternative, the same one I suggested for a polywell: a Bigelow Aerospace inflatable “Sundancer” module. One or more of these 8.7 meter by 6.3 meter pods would easily hold a prototype space-based DPF with net power in the 5 megawatt range.

(Damn… a lot of the boilerplate I needed with polywell just gets deleted for DPF… that thing is small in more ways than one 🙂 )

Attached is some crude space pr0n generated from volume estimations… do not mistake it for an actual station design 🙂

Two Sundancers with nodes. One module holds crew and control gear and the other module holds the reactor and testing gear. The reactor is represented by a block 2mx2mx3m. The attached nodes have some needed stuff docked, including a 64kw SLASR solar array (up-to-date tech), an arcjet thruster module (the massive fusion radiator needs more Isp and less thrust than a standard Bigalow propulsion module), a separate radiator for station needs (I don’t know that the standard Sundancer radiator can handle the stuff that will be working through the hab module)…

…and a rather large radiator for the reactor… 500 m2 double-sided makes for a square almost 16 meters on a side… a water/antifreeze mix not that different from that in your car delivers 2.6 megawatts of thermal energy at a temperature of 300c… caveat is that the water must not be allowed to freeze and the radiator must be designed freeze-tolerant just in case it does… (it gets a lot colder in space than on Earth)

… and optimistically a pair of VASIMR units to help pay the rent… unlike the ISS a DPF-equipped station can power megawatt-class VASIMR thrusters for weeks on end… as long as the reactor is online… just the thing to validate an interplanetary engine assembly. Each module has paired engines as on ISS to balance their magnetic fields and the two modules face in opposing directions as this is a space station and not an interplanetary ship… 🙂

… a Crew Dragon is docked and a Cargo Dragon approaches bearing pizza, fresh underwear, and argon propellant to refuel the VASIMRs…

Finally there’s a similar setup using the BA-330 module. The 330 is the followon to the Sundancer at the same diameter and about twice the length and is intended to be the main module for Bigelow stations after Sundancer validates the concept.

So maybe this happens sometime after FOOF…

One BA-330 easily holds two complete DPF cores… one as a ready spare… a box containing a set of Control Moment Gyros (momentum wheels) is now attached to the central node to handle the increased stationkeeping chores… fresh SLASR arrays are stored in their boxes ready for deployment if needed… the hab module now holds a complete station crew…

… the station radiator is still there as backup although by now the station cooling system will be dumping its hot water into the reactor helium outlet feed… where it will find a new definition of “hot” …

… and a BA-330 lab module has been attached… usable volume on the ISS is often apportioned out in “racks”… International Standard Payload Racks… approx 1x1x2 meters these racks serve to house station equipment and controls, the crew themselves… and of course the varied lab experiments… while Bigelow modules don’t have the cramped confines of ISS that led to the rack system and the following example would never be implemented in this mutant ISS style… the rack count does serve as an apples-to-apples comparison of available volume… and available power…

32 ispr @ 6kw = 192kw
(as these are all dedicated science racks ready for rent we’ve surpassed ISS already)

72 subracks @ 2.2kw = 158.4kw
(subracks are normally part of a rack but the expansive volume in the module gives us a chance to set up additional separate tiers of these)

68 mdl racks 1.8kw = 122.4kw
(Mid Deck Lockers are named after the space shuttle compartments but also serve as a standard payload volume and can be found on ISS as well)

= 472.8kw

… the DPF says “give me something hard to do”… the big radiator won’t even notice the waste heat if it’s dumped into the reactor feedwater in advance of the helium outlet…

ISS… surpassed.

At a minute fraction of the original price thanks to fusion.

thoughts?

[vansig]

ok, brainstorming here…

refrigerant
isnt ammonia the more common coolant in space?
i hear that helium would be used to cool the DPF anode?

VASIMR
is the shape realistic?
pictures i’ve seen show the accelerators as longer cylinders

xenon propellant tank for VASIMR?

if opposing nozzles, then each VASIMR engine would connect at about the centre of mass?

can the VASIMR nozzles be positioned?
if they hinge/twist at or near the station’s centre of mass, then they could be
positioned quickly and effectively for acceleration in any direction

mass of the modules?

total station mass?

[zapkitty]

vansig wrote: ok, brainstorming here…

Yay! 🙂

vansig wrote:
refrigerant
isnt ammonia the more common coolant in space?
i hear that helium would be used to cool the DPF anode?

Ammonia is used in current external ISS radiators because it stays liquid at very low temps. But there is a drawback if you want to operate at higher power levels because ammonia is not quite so good as water at handling higher heat loads (although it’s better than anything else but water at the temperatures and pressures we currently deal with)

In fact the interior coolant loop of the ISS uses water in the hab modules, which dumps the heat to an outside ammonia loop via heat exchangers.

But engineering an ammonia loop to handle megawatts of heat at hundreds of degrees is not properly matching the coolant to the project and results in notable engineering inefficiencies. In fact even with the minimal fusion plant discussed here we’re pushing the limits for unpressurized water… but it’s a well understood tech and is both quicker and cheaper to implement than other, more robust options that will require research on orbit before they can even be used.

We are not escaping the eventuality of liquid metal coolants when it comes to fusion plants in space, but water cooling can keep our initial units running while we hash out the more advanced tech… and a lot of time and money will be saved by having an operational reactor in a genuine space environment ready and willing to test out new cooling ideas and systems.

btw, quite a few proposed nuclear spacecraft designs use water as well… so I’m not exactly apostate here 🙂

As for inside the DPF: I’ve been treating it as a black box that puts out electricity and heat. (also magnetic fields but that is another subject) The heat is supposed to be delivered from the reactor by a helium loop but my own little project stops there. Is the helium stored cryogenic? Is it liquified after heating? Are there sufficient hamsters to run the pumps? I don’t know.

I’ve just been told that a certain amount of heat will be delivered via helium gas at a certain temperature.
(well I presume it’s a gas at that temp, I think someone would have mentioned a high-pressure system otherwise… I hope…)

vansig wrote:
VASIMR
is the shape realistic?
pictures i’ve seen show the accelerators as longer cylinders

It’s a placeholder, not a miniature 🙂

And a serious note: I did the pics because others find them useful but I can’t really see very much of them at one time myself. They are just mass and volume estimations assembled as needed… the veriest epitome of the epithet “lego spacecraft” 🙂

The Bigelow modules use the exterior dimensions and wall thickness given by Bigelow.

The nodes are approximate in size based on the CBM hatches that Bigelow uses on all its modules and nodes. (Imperial NASA strikes back!)

The SLASR arrays use the 2.5x5m 4kw units developed by the SLASR people so they’re in the ballpark at least.

Dragon Crew and Dragon Cargo w/ extended trunk are copyright for all eternity by SpaceX.

The station radiator is an external ammonia loop radiator swiped directly from ISS… I wonder when they’ll notice it’s gone…

The arcjet propulsion module uses 4 commercial ammonia arcjets operating at 30kw for 2.37 newtons each at an Isp of 1012 seconds. The implementation thereof is a figment of my imagination.

The CMG box is something else that the inhabitants of ISS will notice is missing… sooner rather than later, I think…

The ISPR racks are done European style instead of the more curved style used elsewhere… (socialist science racks! 🙂 )

vansig wrote:
xenon propellant tank for VASIMR?

… xenon, argon… as long as it’s something easily distributed through the gas or fluid interfaces of the CBMs it doesn’t otherwise matter. LH2 is right out for the initial tests 🙂

vansig wrote:
if opposing nozzles, then each VASIMR engine would connect at about the centre of mass?

Rather, the center of mass of the axis of the station node that they are mounted on… they can be located most anywhere otherwise. I stuck them next to the fusion radiator.

vansig wrote:
can the VASIMR nozzles be positioned?
if they hinge/twist at or near the station’s centre of mass, then they could be
positioned quickly and effectively for acceleration in any direction

They are there to be tested and measured.

They are not there to be a part of station operations.

This is a good thing 🙂

vansig wrote:
mass of the modules?

Usually less than the mass of whatever is put in them… usually…

vansig wrote:
total station mass?

As above. I will have better estimations later on but this will do for a start. The only certainty is that this station will be quite a bit more massive than what Bigelow envisioned the original Sundancer assemblies as weighing in at, thus my substitution of the high-ISP arcjets for the Bigelow hypergolic propulsion module.

[vansig]

For testing only, yes, mounting them opposite would be appropriate.
But, VASIMR engines are due to be tested at ISS soon, arent they? Provided that they work as expected, turning this module into a useful orbit to orbit transport vehicle, (perhaps LEO to LLO and return, with big payloads?) would be the first thing I’d want to do.

It would seem to be a no-brainer to mount hinges and swivel points, and begin operation.

if memory serves, VASIMR VX-200 are ~300 kg each; 80 tonnes of propellant is plenty for pulling bulk supplies to/from lunar orbit.

[zapkitty]

Why would you build a deep-space ship before building a space station?

Testing a 200kw drive by charging batteries for weeks just to get a few minutes operation gets data… needed data… but it’s not the same as testing the drive at full power for weeks on end.

And that’s the kind of testing it’s useful to do before entrusting lives to those drives for an interplanetary journey.

You can rush off to Mars in your fusion-powered torchship… but you’ll be missing a few vital technologies. Just to start with you’re still going to be hauling that big-ass hot water radiator around. And there’s much more…

We Americans skipped over building a proper space station in our rush to get to the moon before the Soviets and we’ve been paying real and measurable engineering penalties for that ever since.

In-space refueling depots using whatever fuels we choose should have been a fact of life… half a century ago.

The radiators and support technologies for high-powered solar and nuclear systems should be an accomplished albeit still-developing art as well.

And radiation countermeasures for extended deep-space missions should have been topic one rather than swept under various rugs over the decades.

… the first generation of ships assembled in space should have been nearing their retirement age by now…

Instead we’ve finally got ISS… decades late even from its late start, underpowered and understaffed… and it can’t do all that needed research if at the same time it’s trying to keep its ongoing research agreements among the partner nations.

If you want fusion-powered ships roaming the solar system then you need to do your “homework” first. And a fusion-equipped station that has power and room and crew to spare is the key to testing and validating current ideas for such ships and researching new ideas.

This particular station concept is not only a way to try to get fusion on orbit and validated ASAP… it is a neccesary precursor to those high-powered ships you want to build.

We shouldn’t try to skip the basics this time.

[vansig]

I’m not advocating cutting corners; but rather adding to capabilities at relatively low incremental cost. Modern concepts that appear to work include multi-purpose missions: involving both science and commercial interests, and maximizing what you can still accomplish when things go wrong.

If building a proper space station must be done before an interplanetary supply tug, then so be it. It’d be frustrating if ISS cannot be that station, but i do see your point about ongoing research agreements among the partner nations.

I totally agree that so many of these things, radiators and support technologies, radiation countermeasures, ships assembled in space,
should have occurred decades ago.

it seems to me, that swivels and hinges, and the motors to drive them, are low tech, low cost, and add a lot of capability.

[zapkitty]

“Ah, I see…” said the blind kitty 🙂

My cheap and tawdry space pr0n has worked against me.

The VASIMR units are not permanent attachments to the FOOF station.

They represent a multi-megawatt interplanetary drive configuration that someone has sent to the station for testing after the reactor has been proven to be more online than off.

Let us omit the temptation for joyriding that those drives embody.

Delete the drives! 🙂

And instead for the FOOF initial secondary research projects (the primary research project is the reactor itself) we add two important testing and research rigs… one is for improved radiators via a liquid droplet radiator unit and the other is a radiation deflection scheme that uses electrically-powered fields to deflect both solar particle events and galactic cosmic radiation away from the station.

Both are vitally important to the future of spaceflight and both can be tested as soon as a station capable of hosting and powering them is fielded.

(And that isn’t going to be ISS, perhaps not for a decade… if even then. It’s not designed to handle the changes projects like these would entail.)

As before these are placeholders, and are not intended as CGI work for the sequel to Avatar. Do not confuse the playing pieces with the game. Specifically, the LDR rig is an upside down shower head and the deflector antennas are hydrophone emitters swiped from an old project. I’m lazy 🙂

But these changes should help curb the temptation to hijack the station… I hope 🙂

Attached files

[vansig]

okay, then.

but those moon buggy tires will be mine, soon enough..
http://www.youtube.com/watch?v=Vv8rWd1c0b8

🙂

[zapkitty]

In honor of Cislunar Pirates Association Day I’m trying to set up an automated DPF-powered tug for you to terrorize the geosynch belt with but the thermodynamics are proving… interesting.

I have a set of four notional 200 KWe VASIMR drives running at an Isp of 5000 with 1 newton of thrust each. I have the engines massing the same as the 100 KWe versions at 300 kg apiece.

In order to cut down on radiator mass I have the standard 5 MWe DPF box operating at a yield of .89 MWe… 800 KWe for the engines and 9 KWe to run the tug. Not only does this decrease the needed cooling, but it should increase electrode life to match the expected time frames of missions for such tugs.

A DPF efficiency of 50% of electric gives us ~.45 MWt but the 40% efficiency of the 4 200 KWe VASIMR units gives us an additional .48 MWt that we need to reject.

So unless I botched the math (always a possibility 🙂 ) we have .93 MWt minimum to reject and I added an additional 5 KWt to reject for misc spacraft thermal output for a total of .98 MWt.

So that gives us a radiator of 188 m2 operating at 300 C. Double-faced it’s about 9.7 m2,

And then the kicker… while I’ve been working under the assumption that the DPF box could run at a temp of 300 degrees C with my water-based coolant, I realized that the VASIMR has at its core a superconducting magnet array that must be cooled by liquid helium at -268 C… and that that helium must be cooled in a separate array after cooling the magnets if it is to be reused.

And the lower the temperature the bigger the radiator… to the 4th power…

The helium could just be vented after cooling but that would put a strict time limit on deployments. A limit based on the capacity of your LHe dewars.

Fun times 🙂

There have been proposals to use helium to cool very high temperature reactors (up to 1000 C) and that would simplify things a little but the mass of the gear needed to move enough helium fast enough through such a system seems likely to be a severe blow to the mass margins of even a fusion-powered craft… and at least some of the helium must still be cooled back down to a liquid state after the high-temperature rejection phase…

… are we having fun yet?

Maybe there’s just not that much LHe needed to cool the magnets… I still have to work through the numbers. But it did occur to me that it would sure be nice if the drive version of the DPF could be implemented sans superconductors…

… but that would still delay out-of-the box implementation of fusion-powered spaceships as opposed to fusion-powered space stations.

Any corrections or suggestions?

[vansig]

Lots of fun!

A VX-200 engine is predicted to have 5 N thrust at Isp=5000s. Let’s run YBCO tape (Tc~93K) to make the superconducting magnets (2 Tesla per engine), and cool them with liquid argon, which, after it also cools the hot parts of the whole system, becomes propellant. The hotter the Argon gets on its way to the nozzle, the less work you have to do to heat it to plasma temperatures before acceleration.

Not sure how to calculate the amount of argon needed to cool the magnets, but this will feed into the equation for optimal Isp.

[vansig]

vansig wrote:
Not sure how to calculate the amount of argon needed to cool the magnets, but this will feed into the equation for optimal Isp.

It seems 80 kW waste heat per engine would boil .5 kg/s Argon at ~85 kelvin; but that’s much more than we want (by a factor >100), so most of that heat will have to be rejected another way. Keeping 80 kW at below Tc~93K implies a hectare-size radiator.

Yikes! Please tell me those magnets wont produce that heat.

[vansig]

after meditating on what’s been gleaned and slopped into the wikipedia article,
http://en.wikipedia.org/wiki/VASIMR#Research_and_development
i’m thinking i may have overestimated the refrigeration requirements for the magnets, by as much as a factor of 8. so with four engines, that reduces the coolant problem to only 16 times too much. :-/

ideas:
liquid N2 maybe gives a bit more head room, there?
further progress on high Tc superconductors?
make use of a thermal mass, (such as solid CF4 or propane?) and pulse the thing?

[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…?

[vansig]

I’m guessing the magnetic cores themselves may consume 5%, (~10kW) per engine. From a standing start, a thermal mass such as methane at or near its triple point, 90.67 K (-182.48 °C), 0.117 bar, seems like a good way to manage temperature there (CH4 heat of vapourization (~500 kJ/kg) is almost 1000 times greater than argon’s).
And switching YBCO out, in favour of the current high Tc record holder (Hg·Ba·Ca·Cu·O, Tc~135 K) would let the system run hotter, overall. This reduces radiator size by a factor of 4.

But I’m starting to favour helium in the radiator itself, since we wont have to worry about it freezing when the engines are down.

If we get smart about radiator design, we seem to have quite a temperature gradient available, based on what parts of the system run the hottest. Because of that, hotter areas will radiate faster than cooler areas; so, can some parts of it bypass? –returning higher-temperature fluid to less-sensitive equipment?

The low-temperature fluid return (~85 K ?) then needs ΔT·flow ~ -2 kg·K/s for the magnetic cores only, for each engine; while the high-temperature return (~270 K ?) is doing the bulk of the cooling for the system, ΔT·flow ~ -200 kg·K/s.

[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.

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