Humans Fast, Machines Slow

Rand Simberg talks about impedance matching. So I’d like to make a post of my comment there (I’ve always wondered why this obvious alternative gets mentioned so little…)

What to do when you arrive at Mars or Earth with your solar electric propelled vessel?

So, the problem with most low fuel demand velocity change schemes is that they only give slow accelerations. Low fuel high velocity change means solar or nuclear electric propulsion and aerocapture mainly.

High delta vee aerobraking is hard to do in one pass – it gets dangerous because of atmospheric variability and potentially other reasons.

Simple: detach a small capsule with the humans that goes directly to the surface (with only days of life support) and leave the untended craft to do multi-pass aerobraking. Hitting van Allen belts a few more times or taking a long time doesn’t matter that much with no humans onboard.

You could also potentially ultimately leave the long distance craft at some Lagrange point instead of LEO. (Cue some clever and complex maneuvers to save fuel – maneuvers that take long.)

Something similar could also be done when a long distance stack is assembled in LEO: send the humans there only after it’s through the belts. They can go with a smallish capsule again. Potentially at some Lagrange point, or in space without any fixed reference, just along the way. It could be dangerous though if the capsule doesn’t have much life support.

Many of these things have potential delta vee penalties as well as timing inflexibilities, but they could have enough other benefits that they should be considered.

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All Tarkovski Films Free Online

Noticed by Things Break. I’ve only seen Solaris. It had a lot of good in it, although it was quite uneven and somewhat overlong. Certain acting is very intensive and memorable. Having read the book twice, I even experienced it completely differently both times. The American version from 2002 with George Clooney I haven’t seen completely, but from the first quarter, it seems to have some large stylistic jumps from the book which I find odd – the props in the seventies Soviet version actually seemed much more fitting to me! Probably everybody just reads the book differently.

One of the great themes of Stanislaw Lem seems to be dysfunctional organizations. This should ring a bell with my readers… 😉 Though Solaris is very different from all of his other stories. But I don’t want to spoil too much.

I have also read the Strugatski brothers’ Stalker, which was also cinematized by Tarkovski. It was a peculiar book and felt somehow like a weird mishmash with too much familiar and unreal blended to work as a whole. With some changes it might actually work well with modern special effects – or I hear that the computer game of the same name actually is great, though maybe not very plot intensive. Stalker was actually filmed in Tallinn, Estonia I hear and you can see the place somewhere there (if they haven’t torn it down, they’re rebuilding at a pace there).

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Far Away, Yet So Close

He who controls the [Earth-Moon Lagrange points/Phobos/Deimos/Lunar North Pole], controls the solar system.

Why?

Because in space, it is not the tyranny of distance that sets the rules – it’s delta vee instead.

Since there’s no resistance, traveling large distances just takes longer, but doesn’t necessarily require more propellant. Unmanned craft can take this long trip time just fine. This is completely different from the implicit mental models of everyday life or historical exploration, travels and colonization. Even places that are far away in distance can be close in delta vee, and vice versa.

The Earth-Moon Lagrange (EML) points have really low energy trajectories to all the other places, including low Earth orbit (or Earth re-entry). They’re the crossroads. They’re probably not controllable though, like you can’t control low Earth orbit either, it’s just a figure of speech* to stress their significance.

For example, Phobos and Deimos have really low delta vee needs from EML2. And they have really low gravity. This means that it’s cheap to send stuff to them, but perhaps more importantly, it’s cheap to bring stuff from them. Since a lot of space faring is limited by mass that can be brought to locations, a low energy source of material is a real paradigm changer.

The Lunar north pole’s peaks of eternal light are much closer to Earth, but the Moon is so heavy that it takes quite a lot of propellant to descend to and ascend from the surface. The good constant sunlight is an asset though. The area is limited so this is the best incentive so far for a “race”, though I’m skeptical of that.

This post was written partly inspired by Paul Spudis’ and Clark Lindsey’s talking about the importance of the Moon as an enabler for other stuff – I am somewhat less certain. (On VASIMR and JIMO I can refer to Kirk Sorensen who has good reasons for skepticality – the power to mass ratio needed is huge and that’s the really hard part, yet it’s rarely talked about. Space reactors are much harder than Earth ones because of the cooling problem.)

We must dismiss analogies that do not work, since space is a different medium. We must use completely different planning than for exploration on land or the seas, because of the completely different role distance plays. And we must also plan on advancing from exploration ultimately to infrastructure, colonization and self sufficiency.

*: From Frank Herbert’s Dune of course.

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Jeff Greason

The Man. On Space Review. [EDIT: About a month ago, but I only just read it.] This is just excellent. So many things I agree with, that go against the stupid myths of spaceflight and space policy. If you read one space policy interview this year, this should be it!

“NASA is an organization that is dominated by fixed costs. In business terms everything is in the overhead,” he said. The committee found, with some effort, that the fixed cost of NASA’s human spaceflight program is $6–7 billion a year. “The bottom line is that they can’t afford to keep the doors open with they money they’ve got, let alone do anything with it.”

…

However, he said, if you’re trying to minimize costs, it makes more sense to use a smaller launch vehicle that flies more frequently and has other users and applications. The key to making that work for exploration architectures that require large amounts of propellant—and hence have driven the planning for heavy-lift vehicles like the Ares 5—is the use of propellant depots and in-space propellant transfer. “If you use in-space propellant transfer, it’s no longer true that you have to have a really big piece,” he said.

…

He said that while he had his own opinions on the right selection of launch vehicles, he didn’t have any insights on what direction the White House and Congress would go. “It’s really up to policymakers whether we have a space program or a jobs program.”

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Lunar Bases Must Be Buried

Concept art of lunar bases tends to show spherical or cylindrical structures, but they suffer from one problem: radiation. (Both of the gamma / particle and heat kinds). The lunar environment has lots of solar and cosmic radiation. Nights also last for two weeks, during which a badly insulated thing will freeze.

If you bury your moon base under a layer of regolith, you can avoid both of these problems. You don’t have to bring heavy shielded modules from earth, or heat during the night with nuclear batteries. Regolith is thermally well insulating.

NASA seems to catch onto this a little in some clearly low budget “alternative configuration” posted at Nasawatch, but it only goes halfway, putting some shallow “berms” around cylindrical structures, for shielding.

In reality, lunar bases (if crews are to spend many lunar nights there) would probably be completely buried.

Burying might actually be easy: a small automated/remotely controlled snow blower style rover vehicle might be able to do it slowly with the help of just solar power. Since there is no air, tiny amounts of regolith can be thrown large distances. A thin wheel with whiskers spinning rapidly would throw the sand to the wanted direction. A lunar day is 336 Earth hours. Even if the “regolith lobber” robot can not survive the night and is expendable, it could manage to move significant amounts of regolith. A sub-MER size rover with large solar cells could throw perhaps 20 grams of regolith per second, or 72 kg in an hour. That’s 7 tons if there is 100 hours of efficient sand throwing time.

Say, landing at 50 hours from dawn, setting up 50 hours (survey area, lower rover from lander, unfold solar cells etc), operating for 150 hours (which includes maneuvering 50 hours and sand lobbing 100 hours), and finally stopping at a low sun angle 50 hours before dusk.

Such concepts are probably unlikely to work in an atmosphere, though I would be happy if proved wrong. The 2009 lunar regolith excavation challenge is coming up, after all…

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Anarchy In The High Seas

Testing Quickpress (EDIT: it didn’t really work.)
Stuff like this happens when using a common resource not owned by anyone. In this case, fisheries.

Via Michael Tobis. Go read the post.

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Living on a Finite Size Planet

FAO published some numbers on fishing today:

Global marine catches have been stagnant for over a decade, hovering at around 85 million tons per year. Meanwhile fisheries productivity — measured in terms of catch per fisher, or per fishing vessel — has declined, even though fishing technology has advanced and fishing effort increased.

Naturally, with a global resource that nobody owns or regulates, everybody is trying to exploit it before others can, leading to its decline and reduced benefit for all. Actually, it’s even worse than a grab free for all – governments subsidize vast overfishing fleets.

This is a game theoretical problem. If people can’t do agreements or there can’t be any agreed regulation, the situation leads, perhaps not to the last fish being caught, but at least to the state of fisheries being kept so low that fishing is very barely profitable.

A local optimum (everybody fishes for themselves as much as they can) is very far from the global optimum (total fish catch is increased and it is easier to fish since there are more fish when everybody limits the amount they fish), but the lack of coordination prevents from reaching the global optimum.

This nicely and sadly illustrates how things like contracts, agreements, treaties or regulations could improve the situation for everyone involved.

Of course from one fisherman’s viewpoint, it’s not his fault that everyone is fishing, and any regulations would only hurt him (in the short term they would).

In the past many such things were not a matter of much attention. Technology was so primitive that one could not overfish the seas. Or in other, smaller places where the limits of exploitation could be reached, nations controlled their resources wholly, meaning they could enforce regulation by themselves. It is mostly in the twentieth century that the effects of human action have been so vast that there have been needs for international regulation.

It would be interesting to hear how a libertarian takes these things into account. In my view “everybody for themselves” is a good strategy for many problems, but too simplistic to be used for everything. We see now where it has lead with global fishing.

Central control has also resulted in vast environmental damages, and hurting people as well. The Aral sea is one example.

Hence one would need some kind of negotiations between all the effecting and effected parties, and science and justness based decision making to manage the global fisheries. It is a very hard problem, not technically (you just fish less, nothing could be easier!), but politically.

At the same time, it is a test for humanity. Can this 6 billion bunch of apes engage in decision making that results in the medium term in positive results for all, even though it can be bad for some persons in the short time (though they can be compensated). On this finite size planet, as our capabilities grow, more and more actions are having longer term effects on the whole system. That means the future of both the actor as well as others.

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Thorium MSR Design Possibilities

There are a huge array of design possibilities for a Thorium molten salt reactor / liquid fluoride thorium reactor, but this post takes a very simplified approach to map a small part of the fascinating and diverse landscape with a little rough drafting. We concentrate on thermal spectrum designs. I’m strictly an amateur in these matters so everything I write should be taken with a grain of salt and checked more carefully with people who actually know what they are talking about. 🙂

My references are Kirk Sorensen’s energyfromthorium.com and David LeBlanc’s excellent slide set. Highly recommended!

One or Two Fluids?

One choice is having two fluids (core and blanket) or just a single one (Thorium-232 and Uranium-233 salts mixed in the same vessel).

The single fluid reactor seems like a much simpler alternative. There are problems though that when Thorium-232 absorbs a neutron, it becomes Protactinium-233 (Pa) before becoming Uranium-233. The half-life of Pa is about 30 days, and if it catches a neutron, it becomes U-234, which is not a fissile material. So the neutron was wasted. This is pretty bad since Pa’s neutron cross section is over twice that of Th’s so it wants to catch those neutrons. But there are ways around this.

Protactinium Extraction?

For one, you can perform protactinium removal from the single fluid core. This involves liquid bismuth and I’m not very familiar with the process, but it is more complex than U or FP separation (see below). The separated Pa-233 is put into tanks to wait for its decay into U-233 before it is put back into the core. This also enables pure U-233 extraction which is somewhat problematic in a proliferation sense (I’m not very knowledgeable in this direction).

In a two fluid reactor, you can probably get by without Pa removal by just making the blanket bigger, so there is much more Thorium than Pa at any given time, giving a better statistical chance for a given neutron to hit a Thorium and not a Protactinium atom. This can also involve fancy geometries, since the core stays the same size. For example there can be a long empty gap between the core and the blanket through which the neutrons fly.

Uranium Extraction?

In a single fluid design the new Uranium is already in the core after it is produced from the Thorium, so this step is not needed. But in a two fluid design it is practically mandatory. The ThF4 and UF4 mix is bubbled with Fluorine gas, and the UF4 turns into UF6, which is a gas. The gas is separated from the liquid. UF6 handling is already a known 60 year old industry from nuclear fuel processing. The UF6 is changed back to UF4, which is then inserted into the core. The ThF4 is inserted back into the blanket of course.

Moderation, How?

The most traditional way would be to moderate the reactor with solid graphite rods. There are thermal spectrum spreading and since the fuel is in liquid form, expansion and convection effects that mostly help with control here, but single fluid reactors still can have situations of positive power coefficients. Graphite has issues of swelling and shrinking under radiation and a limited lifetime. Regularly changed moderator pieces would be radioactive waste as well. Loose graphite rods or even pebbles could be ways to prevent stress cracking.

There have been designs without any solid moderators as well. The salts moderate some anyway, and some reactors run simply at faster spectrums, the latter again bringing control problems.

And lastly, there is the heavy water moderated MSR, of course loved by many Canadians because of their CANDU expertise, the current heavy water moderated solid fuel reactors. The heavy water would not act as a coolant at the same time, but would be separated in thermos style vacuum jacketed pipes. Any breach would boil the moderator away, reducing reactivity. This jacketing would enable easy low pressure vessel construction, like for the rest of the reactor.

Geometry?

The first MSR designs were naturally small and spherical. A number of geometry proposals have surfaced: pipes coming from many directions into a bundle of criticality or a cylindrical core with a cylindrical blanket around it. There are many conflicting requirements like maintaining criticality, preventing overcriticality, minimizing neutron waste, minimizing inventory size, coping with thermal expansion, passive safety, ease of construction and transportation, scalability…

Inventory Size?

A small fissile inventory has a number of benefits. The reactor is simply smaller for a given power ratio, making it cheaper. Also less U-233 for the starting load needs to be produced elsewhere. If the breeding ratio is low and the fissile inventory large, it takes long (perhaps twenty years) for an MSR to produce enough U-233 to start another new MSR, probably requiring big production of U-233 elsewhere, changing overarching infrastructure plans significantly.

Fission Product Removal?

This is a very common feature of MSR designs (some once-through no-refuel systems for ships and spacecraft can take this out), but how often it is done, varies. Vacuum distillation means reducing the pressure until the most volatile stuff starts boiling. Only UF4 fuel salt should be left after this. With a single fluid salt there is a problem that the Thorium Fluoride salt boils as easily as some of the fission product fluoride salts and hence something else would need to be done, or just some Thorium be “thrown away” together with the fission products. On the other hand, some fission products are gases like Xenon, which boil already in the core. Many of the fission products are also valuable rare elements by themselves and can be sold. The MSR naturally separates fission products from fuel, unlike current solid fueled reactors, making this line of technology look unexplored and interesting. Since there is less waste sucking up neutrons in the reactor, the neutron efficiency of an MSR can be high and it can get by with little fuel and a small physical size.

Power Extraction, How?

This is more of an “auxiliary” function. The most common design is connection to a helium heat exchanger probably through another salt loop to reduce radiation loads, and the helium would drive a heat engine. High temperatures (compared to solid fueled traditional nuclear reactors) are achievable and all kinds of thermal processes become attractive as well. Since the molten salt solidifies at a certain temperature, the heat exchanger can not go below that. Coupled with the high efficiency and high top temperature, you get small radiators and cooling towers and small water usage compared to traditional reactors.

Control, How?

An ideal MSR is extremely easy to control because of the natural negative feedback of the reactor – increase power usage by increasing coolant flow, the reactor cools and increases reactivity and gets to a steady level. As far as I know, the original aircraft reactor experiment was not throttled in any other way. There simply are no control rods. An MSR would automatically operate in a designed, relatively narrow temperature region of a few tens of Kelvins. In the event of a significant overheating accident, a freeze plug at the bottom of the reactor would melt and the salts would drain into tanks below for slowly cooling down.

Waste Handling

First the most valuable materials like Xenon, Tritium and various other substances could be sold. Since the waste would by majority be fission products and barely no heavy transuranics, they could be stored on-site until they quickly lost enough radioactivity and cooled for final storage of a few hundred years inside rock.

So, What Is The Best Configuration?

As a personal preference, my best guess for the best of all worlds is a two fluid design, with a cylindrical “LeBlanc” geometry. Adding power would simply involve making a longer cylinder. No Pa removal, but the blanket could be oversized. Remember that all the vessels would be at low pressure, and the blanket isn’t even that hot and is only filled with Thorium, which is cheap. Initial core load U-233 amount would still be low.

Next to the reactor would be the fluoridation tower for taking U from the blanket and putting it to the core. Hydrogen would be needed to change the UF6 back to UF4. (Generating chemically nasty HF at the same time.) A vacuum still would remove the fission products from the core, and this would be located close by too.

Since there would be no high pressure vessels, the reactor core and blanket could be quite light and probably road transportable as a whole. The material of choice for the high temperature salt sections would be Hastelloy.

Moderation could either be nonexistent, by loose graphite profiles inside the core, or Hastelloy pipes containing a vacuum walled heavy water pipe. This is an area that needs lots of innovation to minimize maintenance and waste.

According to calculations made by David Leblanc, a 1 m diameter 6 m long “pipe style” reactor (easily truck transportable for construction!) could produce 400 Megawatts of electricity (900 MW thermal) with only a few hundred kilos of fissile inventory! Most of the salt mass would be “filler” (Fluorine, Lithium, Beryllium) and Thorium.

This is a very stark contrast to the current nuclear plants with their huge high pressure vessels, currently probably only manufacturable in one steel plant in Japan, requiring many years of ahead time for ordering, and lots of welding on the build site as well.

End Note

There is real small MSR hardware that has been demonstrated to work, and there are good conceptual designs for real powerplants that could change the world energy generation picture completely. I am not aware of any other energy production technology which is so based on reality and still potentially revolutionary at the same time. This thing has a very good chance of working well. It does not require significant new scientific developments or a fifty year timetable, like fusion. It is not as limited in availability and dependability like wind or solar power. It is good that those alternatives are pursued too, but the MSR is a bigger answer to a bigger problem.

-the Molten Salt Reactor, Real and Revolutionary!

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European Lunar Program Alternatives

ESA’s Architecture for Exploration Study (AES) is overviewed in Lunar Base Quarterly 1/2008 (EDIT: to be clear, the Quarterly was released in January):

Lots of Ariane 5, Angara and Soyuz launches with space docking, a space station in Earth-Lunar L1 and many new crewed and non-crewed craft and capabilities.

They had a red team / blue team approach at this point.

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A 3D Glue Gun Does Not Self-Replication Make

I’ve been wondering at this ever since the meme has been circulating. People make a printer that shoots glue, layer upon layer and thus it can print 3d objects.

But saying such 3d printers will replace factories and manufacturing is very clearly wrong. Take a look at almost anything you’re using or wearing right now. It’s a mishmash of materials gathered from various sources all around the world. Yet the 3d printers can only make single material objects, usually of some hardened glue. The rest has to be added later.

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