Thursday, October 29, 2009

Designing a Space Habitat

A range of designs have been proposed for space habitats. Some appear to be mostly artistic concepts, others are much more serious. They include:

(From Wikipedia http://en.wikipedia.org/wiki/Space_habitat)

  • Bernal sphere - "Island One", a spherical habitat for about 20,000 people.
  • Stanford torus - A larger alternative to "Island One."
  • O'Neill cylinder - "Island Three", the largest design.
  • Lewis One[4] A cylinder of radius 250m with a non rotating radiation shielding. The shielding protects the micro-gravity industrial space, too. The rotating part is 450 long and has several inner cylinders. Some of them are used for agriculture.
  • Kalpana One, revised[5]A short cylinder with 250 m radius and 325 m length. The radiation shielding is 10 t/m2 and rotates. It has several inner cylinders for agriculture and recreation.

There are other well-known structures from science fiction literature, including

  • Rama (a 20x50km rotating cylinder) from Arthur C. Clarke’s novel, Rendezvous With Rama
  • Space Station V (from the movie 2001: A Space Odyssey)
  • Babylon 5

Of these, the most complete design is “Kalpana One, Revised,” which properly accounts for issues such as shielding and rotational stability. Most designs presume that it is best to provide windows to admit natural sunlight, but there are many reasons to prefer artificial light sources, primarily involving heat, but also the need for shielding. For adequate shielding from radiation and meteors, the outer walls of the habitat must mass about ten tons per square meter. While transparent quartz windows could be built of this thickness, most designs involving natural sunlight use mirrors to deflect sunlight around shields of stone. But the admitted heat is the real problem (discussed below).

In my previous posts, including Our First Colonies In Space, Life in an Asteroid, and Our Homes, the Comets, I assumed that we would tunnel into asteroids and comets, enclose and spin them for gravity if they were small enough, or build spinning structures inside them if they were too large.

But while writing a sequel to my short story Apophis 2029, I realized that the best choice was simply to build one or more space habitats from the raw materials of the asteroids and comets. I came to this conclusion because of considerations for effective use of space, the stresses of spinning large objects for gravity, and (most importantly) thermal dissipation.

People consume energy in their homes, workplaces, and travel. Much more important, food requires a large amount of energy in the form of light for growing crops. After extensive research on plant needs, high-intensity farming, and lighting technologies, I concluded that the minimum light levels needed requires 4 kilowatts of very-high-efficiency LED lights to grow the food for one person (assuming a primarily vegetarian diet – you need more to grow additional crops for livestock). Add to that the per-capita electric consumption in the U.S.A. of about 1.5 kilowatts, add a little more for contingencies, and I realized we need to plan on 6 kilowatts of energy consumption for every human aboard the habitat.

That’s not too bad, especially considering that readily available solar power can easily provide such levels and at a modest cost.

But energy consumption turns into heat, and heat must be radiated away. The bottom line is that we must allot 19 square meters per person of surface area assuming black body radiation at a temperature of 0 degrees C. It does not help to plant little radiators all over the surface, as they interfere with each other. All that matters is the apparent size of the habitat from a distance, and how closely it approaches the ideals of a black body radiator. Of course, we could use active cooling to heat radiators to much higher temperatures while cooling the interior, but I prefer passive techniques so that a failure of the cooling system doesn’t rapidly result in cooking the inhabitants.

There goes my idea that a million people could thrive in a cubic kilometer of comet. There is plenty of room, more than enough materials. Unfortunately, their waste heat would rapidly boil their home away.

Also, solar light has a large content of heat – and that excess, too, must be radiated away. Sunlight is not energy efficient for growing crops in a thermos bottle (which is what a habitat in space effectively is).

So, my revised plan calls for 20 square meters of surface per person. Also, to provide radiation and meteor shielding equivalent to the Earth’s surface requires 10 tons of shielding per square meter of surface – and thus 200 tons of shield mass per person (regolith is fine, slag works well and is dense, ice is best as long as it doesn’t boil away). But the needed surface area and shield mass per person are constants.

My earlier thoughts on structure did not consider rotational stability, and the folks that designed Kalpana One came up with some very strong arguments that a spinning cylinder is best, and that the width of the cylinder should be 1.3 times the radius. Thus, a cylinder of radius 100 meters (spinning at 3 rpm for 1 G gravity along the outer rim) should be 130 meters wide. That gives a 1-G living area of a little over 80,000 square meters, a total surface area of over 144,000 square meters, and thus a maximum population of 7,200. This structure provides 11.25 square meters (121 square feet) per person of 1-G living space. Is that enough?

It’s comparable to the space provided (per person) in many hotel rooms and cruise ships. But few couples want to live in a 242 square foot efficiency for long, although 28 sm (300 sf) studio apartments are common in many expensive cities.

There is no need to live only on the outer 1-G surface. Assuming 3-meter intervals, the next level up provides 97% of a G. Surely that is adequate. And now we have 22.5 square meters per person of available living space, equivalent to 450 square feet per couple – or 900 square feet for a family of 4. A third living level raises the per-person space to over 33 square meters – 675 sf per couple – 1350 sf for a family of four. Not spacious, but certainly comfortable.

Humans need space for living, working, and of course for growing food. We must allot some space for office space, work space, schools. A single level should suffice (11 square meters per person), partly because some people will work in the farms, or in their homes, or outside the habitat entirely (such as in the mines, the smelters, the steel mills, the solar power satellites, etc.).

Each person requires approximately 64 cubic meters for crops, but crops don’t require 3-meter ceilings. Allocating 2 levels for agriculture may be tight, but 3 levels is more than enough and provides some excess capacity for the production of meat, milk, and eggs.

We need a little more space for overhead: storage, aisles, conduits for air, water, sewage. So we add an 8th level for good measure. That still leaves an interior cylinder with a radius of 75 meters as a park or recreation area. It has 3/4ths of a G of gravity. The opposite side is more than 500 feet overhead – it will feel spacious enough, and 15+ acres of playgrounds, hiking paths, trees, and grass will provide a little bit of Earth in space.

But there’s no need to leave the end caps – the walls of our cylinder – as bare metal. We should build offices, low-gravity facilities (perhaps hospitals), hotels, etc. along those walls. Allocating 15 meters of depth along each end-cap for such purposes still leaves a hundred-meter-wide park, now with only 12 acres of usable space, 100 meters wide by 470 meters around. The lowest level of the end caps is a perfect place for shops and restaurants.

The above ramble describes the capacity of a 100-meter radius cylinder, spinning at 3 rpm to provide Earth-normal gravity. This spin rate is often considered the maximum for a rotating space habitat, as most people (but not all) can adjust to it. More people can adjust to 2 rpm, and essentially everyone has no problem with 1 rpm.  So how much room do we get with these and larger structures? Can they be built?

This table shows the size, possible population, and mass (in kilotons or kT) of the external steel shell, the internal steel infrastructure, and the shield (total mass of steel shell plus rock). Note that once the steel shell reaches a mass of 10 tons per square meter, additional shielding is not needed. For a reference point, the total mass of steel in a modern aircraft carrier is about 60,000 tons, about 20% less than the smallest habitat. The dimensions given are of the habitable volume; the outer walls are assumed to be an extra 5 meters in thickness to provide the volume needed to contain the shield mass (but that extra external area raises the maximum population as well). The thickness of the outer steel shell is also given, in meters, and it ranges from 3cm (1.2 inches) in the 100 meter cylinder to 1.31 meters (4 feet) in the largest. The table also shows the percentage of the asteroid Apophis needed to build this structure, or alternatively the minimum size of a rocky asteroid large enough to build it. *Note that the largest structure would require a nickel-iron asteroid, as there is no rocky shield mass needed.

RPM 3.0 2.5 2.0 1.5 1.0 0.8 0.4
Radius 100 143 224 398 895 1,590 4,621
Width 130 186 291 517 1,163 2,067 6,007
Population 8,087 16,010 38,005 117,491 585,398 1,839,804 15,457,797
Central Park 100 156 261 487 1,133 2,037 5,977
Ceiling 150 236 397 745 1,739 3,131 9,191
Acres 12 29 80 281 1,529 4,949 42,625
Steel Shell (kT) 38 105 385 2,092 23,258 129,560 3,154,722
(thickness) 0.03 0.04 0.06 0.11 0.25 0.45 1.31
Steel Structure (kT) 36 71 168 519 2,584 8,117 68,166
Shield (kT) 1,580 3,096 7,216 21,406 93,822 238,401 0
Total Mass (kT) 1,653 3,273 7,769 24,018 119,664 376,078 3,222,888
% Apophis (27 mT) 6.12% 12.12% 28.78% 88.95% 443.20% 1392.88% 11936.62%
min.asteroid 107 134 179 260 445 651 924*

It is clear that Apophis contains enough raw materials to build habitats supporting 125,000 colonists in up to 16 structures. It is interesting that a 1-kilometer nickel-iron asteroid (of which there are approximately 50,000 in the main belt) provides enough iron that (adding the resources of a small carbonaceous chondrite for carbon, oxygen, and water) a 9x6 kilometer cylinder could be built, supporting over 15 million people. Still larger structures may be constructed; steel has adequate tensile strength for structures large enough to support a billion people, but they become wildly inefficient, requiring nearly 10 times the steel per person.

I plan additional posts providing details on farming in space, on solar power satellites, and on the economics of life in space. It is clear that space habitats are feasible, and that commerce based upon tourism and the construction and maintenance of solar power satellites can pay for it. The obstacles are the difficulty of the bootstrap process:

  • capturing an asteroid such as Apophis into Earth orbit
  • Launching the tools to mine the riches of the asteroid, the tools to smelt its ores into steel and other valuable materials, the tools to shape that steel into the plates, beams, and girders needed to build things
  • Launching the people to make it possible with enough consumables to get past the bootstrap.
  • Designing and implementing closed-system recycling facilities capable of efficiently converting human wastes (and crop residues) into food, oxygen, and water.

Once enough infrastructure is in place, the colony should not need the addition of oxygen, water, food, or structural materials. High tech tools will be needed, including whatever is needed to construct solar cells, but the raw materials would already be in place. The Earth will export technology, tools, vitamins, pharmaceuticals, and people. In exchange, the Earth will receive bountiful energy from the Sun, with zero carbon footprint.

But that, too, will take time, energy, and especially people. In the long run, the demand for people in orbit is likely to exceed our capabilities of putting them there. And that, too, is the subject of a future post.

36 comments:

michael Hanlon said...

A cylinder is good. The reason I like it is cylinders are hollow through the centers. and that fact would allow the passage of a hugs and kisses orbiting express to pass through the interior of the structure. I do hope you plan to park it at L1? Anywhere else starts defeating the benefit of attaching econmical values to its existence and not just purely scientific efforts.
So, lose the central park (REM: the space is still there, it just needs vacating every seven days. Otherwise, all manner of 'weightless' activities can go on there.)
The next question which I see no posit for in your ramble is, "Will your structure have a second axis of rotation?" I understand the revolving at 100's of seconds intervals, but have you considered also the impact of that center axis rotating to follow the sun or some other reason? Or, does the structure need to remain motionless in the y and z planes? Will there be a gyroscopic resistance to any changes or vector additions against the rotation axis? Will the construction you've outlined (massive walls and steel girdering) also be able to withstand the tortional forces of a movement in the other planes?
Please, don't reply to this right away. Finding the answers could make you hugs and kisses, i.e., loopy.
Consider, at L1 those planes need fixing while other parking places, L2, L3, or at a Horseshoe orbit those rotations could be allowed to vary.
The L4,5 points would allow a synchronization with the period of rotation so one side could always face the Earth like the Moon, which would be beneficial if it were to be used as a platform for power beaming arrays. (Oh, would they be on your station or floating nearby? another nightmare situation)(On board best. Phase locked 2nd plane rotation to continuously face the Earth, good.If the solar E collectors are made out of the new Cinese EMF black hole structure, only the end walls of the cylinder may need to be involved in power generation and that'd be a big consideration.
I'm a bit regretting only offering questions and not answers here. Sometimes though the right question can lead to the answer.
Your population figures are only space based. I envision that bootstrap period you mention as having only low multiple hundreds in space for short periods (allowing for slower rotation of the habitat) of duty and having a ground based support effort in the tens of thousands. You have omitted the landside employment opportunities. I sense that if you can get a good figure there, more dominoes will stand in line to be part of the big tumble later.

Stephen D. Covey said...

Several points:
1) In my design, the cylinder is closed, not open. You must hold oxygen in, and putting a roof over the top simply moves the endcap shielding over your head. Still, a wedding ring design does work in the larger sizes (it is cramped for a 2rpm (225 meter radius) ring, has a modest recreation area for a 1.5 rpm (400 meter radius) ring, and may offer nearly a 20% improvement in maximum population for still larger rings. But additional structure would be needed for zero-gravity industries and recreation, not to mention a dock for visiting spacecraft.
2) There would not be a second axis of rotation because of gyroscopic resistance (and resulting stability concerns). The spin orientation that makes the most sense is one of (a) line up with the Earth's spin axis, or (b) line up with the ecliptic (so we are always edge-on to the Sun). Others have recommended the latter, and I tend to agree.
A big concern is avoiding solar heating. In fact, the habitat requires more solar power than it intercepts, by a factor of three (more if you want to include external smelters, refineries, mills, and the like). So the smallest habitat (210 meters by 140 meters outside dimensions) would likely need about a 500x500 meter solar array. This you would want to face the Sun, so you either don't spin it, or apply corrective thrusts to keep it pointed toward the Sun. Stability concerns suggest that you don't attach it to the habitat (but if you did, it would only touch at the spin axis poles). In an ideal world, it would stay sunward to keep the habitat in its shadow, but that, too, requires constant small thrusts.
Of course, by using 4 times as much area of solar cells as you need, it is possible to have a solar cell extension to the habitat (a ring twice as large) that is rotationally stable and solidly affixed. In addition to being somewhat wasteful of materials, the solar cells would be subjected to 2 G's of gravity, which is not in itself a problem, but it does make maintaining them a problem. Alternatively, we could limit the population to one-third of my figures in which case the outside of the habitat could be covered with solar cells and that alone would provide adequate power.
Your last point, including ground-based support personnel, is certainly an important aspect of the total economic impact. Every billion dollars spent "in space" translates to roughly 50,000 person-years of employment back on Earth, mostly near home. Likewise, every billion dollars of annual income from solar power satellites translates to a similar impact, part of which is local (where the power is used), and part of which is global (whomever builds them reaps the profits), and that is where the rest of the economic impact occurs. If we build them, we reap the profits and the wealth. If the Saudi's build them, their pockets (and their economy) gain the benefits.

michael Hanlon said...

At about paragraph 13 (do Tables count as Para's?) you start "My earlier thoughts on structure... rotation.. ", you perform some math right before our eyes. You propose a 100m radius by 130 m high cylinder. Then you calculate the surface area of the cylinder. First cicumference is about 600m and multiply that by the height 130 and you correctly state the surface area (approx.) as 88,000 sq.m's. Next you state 144,000 sq.m as living area. Where did that extra 56,000 sq.m come from?
.I'm sure you have the figures but perhaps forgetted to pen them? Did you add in other levels of living space from some other blog point without rederencing it?
Switching if I may, in this blog area to provisions. You have called for some quite common victuals. All well and good but I'm sure long term success of such an endeavor is going to hinge on our ability to alter our diet. Genetically engineered fungi and their mushrooms grown in the dark will be a big nutrient source. Slime molds which grow so rapidly and provide for recovery of minerals and extracting acids from waste water and other liquid sources, when dried would make a nice type of powdered egg. No sun or artificial light required for either of these crops which means you can further reduce your coefficient of heat production.

michael Hanlon said...

And you know what mushrooms grow in!

michael Hanlon said...

Now for some nitty-gritty "Architecture in Space". Rings don't need spokes to insure a cylinder's form rigidity in an environment that doesn't have weight or other forces pressing inward from outside the ring. The reason we use a spoking system for our bike wheels here on earth is that they help reduce that force from the outside by transferring it through the axis to the opposite side. Ferris wheels, the same thing only the force this time is its own weight succoming to gravity. Since the only force impinging on the outside of your ring at L1 I hope, would be solar photons and 'cosmic rays'. That factor is easily compensated for by choosing a material or framework shape to the ring which would allow minor flexing (Think xxxxxx all the way round with each x 130m high.)
Here comes some beauty, (well to some of us anyway) the area inside the ring is completely force free. You can build your stucture out of rope!! laying rigid planks to walk on, double-walled foil sides to effect a thermos bottle environment. If you were really adept at doing puncture repairs, a simple radar/laser combination could take care of incoming. Want to add a room somewhere? Just lash some new ropes to your superstrutope. hand holds made of loops. etc. etc,.
.Of course this is just for the start. As time goes by more can be invested to better define the living space, but to start, you just need that strap to hang on inside the
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
x x
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Gee, I hope hat came out right. It should show up as a loop of x's 44 wide and 3 high. If 44 is the blog column width?

michael Hanlon said...

Try again on an emoticon x-ring (I neglected a CR <=.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
x
. x
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

michael Hanlon said...

Try again on an emoticon x-ring (I neglected a CR <=. And again with a spoke, sorry.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
x...........................................................x
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Stephen D. Covey said...

Michael Hanlon: in my description, the 88,000 square meters is the area of the 1-G level of the cylinder, while the 144,000 square meters is the external total area (including the side walls of the cylinder). The total external area provides the surface that radiates waste heat and thus limits the population. This architecture then provides 11 square meters per person of 1-G living space, which is not quite enough. So, we need to live on multiple floors (how many is determined by our desire for personal space versus the cost of building it).
I provide my own suggestions resulting in a total of 8 floors, with the bottom 3 for living, 3 floors for agriculture, and two more for work space, offices, storage, and required incidentals like air ducts, plumbing, storage, etc.

Stephen D. Covey said...

Michael Hanlon: we certainly can grow fungi, yeasts, and other food sources, however these are not primary. All of the calories we eat ultimately depend upon plants turning light into carbohydrates and oxygen. I greatly favor clever uses of crop residues and wastes as they are recycled back into CO2 so that our plants can turn that back into more food and oxygen.If we don't grow mushrooms, or feed rabbits, or goats, or chickens we'll have to burn the wastes (which don't taste nearly as good that way). Ultimately, ALL of the plant products (the edible portions plus the leaves, stems, roots, etc.) will need to be recycled back into CO2 to start the process over again.

Stephen D. Covey said...

Michael Hanlon: We only need spokes on a wheel-shaped habitat to provide a way to get to the zero-G area in the middle.

I think that most of the wheel-shaped habitats we've seen in movies and the literature have spokes for aesthetic reasons, or the designers simply didn't realize (or find) the engineering formulas for the construction of pressure vessels including spheres and cylinders. Those formulas show that steel is more than strong enough, that an inch of steel formed into a hundred-meter radius ring has adequate strength to hold 10 tons per square meter of shielding plus the atmospheric pressure.

michael Hanlon said...

I just put some initial thought into the structural members of a scissoring structure built with 'X' segments and its difficult to arrive at a compromise specification for each member h by w, so I'm going back to the drawing board on that aspect. But I did give serious thought to what material you're not going to have available to you: sheet steel!
The factory requirements which count the weight of each operation in tons of equipment are rock crushers, magnetic separators, conveying systems, blast furnaces and crucibles, billet forms, roller/shapers,and cutting equipment. If you can crush those operations into a garage sized factory, maybe, but otherwise, think of poured regoment (Regolith and Water and a binder[human waste?]) That operation is a crusher and forms. Also to consider in that material is a surface protection product (paint) so the sun doesn't melt and evaporate the water). Much simpler and there can be great flexibility in the shapes poured.
First machine: the Crusher. Here on Earth we use them to make small rocks successively smaller. What we are doing is overcoming chemical bonds by applying brute force because we can. There are other ways to sublimate though. Chemical bonds can be broken by brute mechanical or electrromechanical force, chemical reaction or heat or a combination of them. I think the regolith and even small stones can be run through a combination of heat, electrical rf vibration, mechanical vibration, perhaps a catalyst could help in a chemical effort. You wouldn't need the tons worth of brute crusher to make a few pounds of product. You need a few pounds of crusher to give tons of product. I can envision the mix of systems I outlined as fitting in a garage sized operation! As it spit out its product, instantly hardening, you roll along and spew new wall where wanted. And round it does not have to be. Niven, the great and glorious, in "The Smoke Ring" told us of the assorted dwelling shapes which can be established in a weightless environment.(Think house of cards with no chance of falling due to gravity. square boxes and pyramids and cones and cylinders all strung together with ropes.

michael Hanlon said...

So, we have our wall material and former/shaper. A roller painting attachement should be easy (that's water and glue of some sort{human waste again?). Next comes how to make rope in space? Ideally, there should be two kinds, smart and dumb. The smart would be shielded cable and I see no way in the near trem of moving that manufacturing operation into space. But, goodnews, once it's lifted it will last a long time and can be dedication variable if needed. The tough question is the dumb rope.
If a source of carbon is stumbled upon out there, then it can be made of carbon nanofibers. otherwise, that's a lift to space for bootstrap (hey rope as actual strap!)

Stephen D. Covey said...

Michael Hanlon: I think you may be wrong on the availability of steel sheet as well as on the use of bound regolith as a structural material.

Steel should be available in large quantities, as by weight iron is at least 20% of any asteroid, much more for most of them. We can certainly smelt iron from ore, process that into steel, and then form steel into girders, plates, and sheet. We can even form it into wires and twist those into cables.

Another concern is that concrete (which I presume you speak of as a building material) has a great deal of compressive strength, but has very poor tensile strength, which is what is needed for a spinning habitat (and which steel excels at).

Also, the cement in concrete requires large volumes of water and concrete may not be the best use of that resource.

Lastly, the human waste you propose to use as a binder contains valuable carbon, which (like water) we need to recycle into foodstuffs. However, if we capture a comet or carbonaceous chondrite asteroid, we'll have plenty of water and carbon to spare.

michael Hanlon said...

Stephen, you will not in the near term be able to do any raw stock steel shaping processes. They require tons and tons of pressurs to re-arrange (is that better than breaking?) the crystal bonds. The only way I can imagine it being done without the brute involved, would possibly to sputter deposit it atom by atom in a magnetron, It would take a year to make one panel that way though.
Yes you may have the raw material but processing it away from a gravity well will be near impossible and therefore economically unfeasible. Now if you were to have a well handy which wasn't as accelerative as the Earth's, like the Moon, that type of operation (reduction alloying and shaping) may be do-able. But you delay the asteroid program until the moon is ready.
You overlook the aboundance and availabilit of water from an asteroid. You melt the ice solarly, mix it with your powder and you got yourself "space adobelith" bricks. Glue them with more ice, and recalculate the forces on the product friend. If no g is okay, no stresses due to torsion or torque are involved. If you need a 1g field it exists at the end of a 100m rope! or a lasso with a 600m circumference That doesn't need rigidity. just volume and there's plenty of that there for free! well, except for my claimed areas around the L1 point.

michael Hanlon said...

I shoot foot and put in mouth, okay vit yu?
The X member cylinder is impractical even if the proper ratio of hxw is arrived at, even if the material is decided on. To each 'X' member there are 5 pinning/pivoting points and they would pose as leak sources preventing the thermos bottle from holding air. Each time the ring flexed, there is a good chance that one of those thousands of pin/pivots will pop a gasket, like the Challenger lost its sealdue to temperature flexing alone.
Oh damn, that point of a rotating habitat, thermal stress gradients continually flowing through the structure lagging the terminator. It will soon break just like flexing a coat hanger wire (REM THOSE? one theory is they all fell into a black closet hole and are out there waiting for us to go get them)10-20 rotations and cracking will begin to evidence. If you build in flexures at joints, they too will need continual attention and for sure periodic replacement. So, high on your recycle list will be consumable structural members and their attachments. (That's a lot of scrap steel, recrushing adobelith made of regoment will be more feasible)

Stephen D. Covey said...

Michael Hanlon: regarding the ability to forge steel or roll sheets in a low-G environment: You are right that many tons of force are required. However, that may be applied by squeezing, and does not require gravity. A pair of pliers can apply a force many times greater than the weight of the pliers.

I will agree that we do have much to learn about manufacturing in a zero-G environment. For example, you can't simply pour the molten iron into a mold. High volume welding may have similar problems. How do you keep the molten metal in place until it cools enough to solidify?
I'm sure that the engineers can figure it out.

Stephen D. Covey said...

Michael Hanlon: your comment about flexing of steel due to thermal cycling is certainly a serious one. I believe that (a) some steel alloys are not very susceptible to flexing (like the ones we make springs out of), and (b) we probably need to keep the rotating habitat in the shade of a nearby solar power satellite, anyway. No thermal cycling if you are always in the shade.
When welding together plates of steel to make the external shell, the strength and characteristics of the weld itself is important, since welds (by definition) don't have the strength gains due to forging. This will limit the alloys that can be used.

Canada Guy said...

Space based solar power is an unrealistic solution. Not just because of the complexity and funding, but because so much energy and resources are required, compared to what you get back. We also need solutions today, not 20-50 years in the future. By then, there won't be much of a world left.

http://www.selfdestructivebastards.com/2009/09/space-based-solar-power.html

Stephen D. Covey said...

Canada Guy, I certainly agree that solar power satellites (SPS) are not a viable solution if we have to launch them from Earth. The cost is orders of magnitude too high, not even considering the impact on our atmosphere of that many rocket launches.

But I would argue that this is precisely the reason we need space based resources such as asteroids - the cost of the materials to build an SPS drops to less than the cost others based their rosy projections on, resulting in a viable option.

Note that EVERY long term energy solution (geothermal, hydro, wave, ground based solar energy, fusion) will take 20-50 years to fully implement. We need to get started.

The status quo is not a solution.

Canada Guy said...

Agreed, status quo is not acceptable. But we don't need giant funding to just conserve and reduce our massive overconsumption. We need to get started, laws need to be passed, treaties need to be signed.

Stephen D. Covey said...

Sorry, Canada Guy, but I must disagree with the simplicity of your solution - to simply conserve and reduce our massive overconsumption.

I will agree that it has merit - we use our resources very inefficiently, including excessive use of disposable products (paper plates, paper cups, paper towels, paper bags, paper diapers, paper toilet paper, etc.).

But the REAL problem is that the western world has a high standard of living, and the rest of the world wants to catch up. The U.S.A. per capita income is about $46,000 per year (Canada is $39,000), while the global average is barely $10,000 per year. Do you want to drop your living standard to the global average (so we can fairly maintain the status quo), or would you prefer the cost of the wars that WILL happen as the HAVE NOTS attempt to take from the HAVES?

The ONLY acceptable solution is to raise the global standard of living to something closer to what we enjoy, although I'll agree that we should do it with as low an impact on mother Earth as possible.

But to raise the global standard of living will absolutely require huge increases in global energy consumption, and likely some serious ecological impacts, unless we can find some new resources.

Personally, I don't have much hope. I fully expect that there will be a World War III (possibly fought primarily by well-meaning terrorists), and the safest place to be is in orbit.

If mankind doesn't leave the cradle of Mother Earth at some point in the near future, someone will push the wrong button, or release some pathogen, or simply do nothing and 90% of us will die. After all, Mother Nature has always used plague and pestilence as her #1 solution for overpopulation.

Canada Guy said...

Steve, yes, we in the west will have to lower our standard of living. It will either happen voluntarily, and it will be forced upon us, but it will happen. The planet just can't support everyone being at the western standard of living. In fact we're already over carrying capacity, so our current standard of living is already unsustainable.

It the end, it's not that big a deal. So, we live in smaller houses, and maybe more people live together, and we take transit or walk instead of driving. And we might have less gadgets and toys. We can still live happy and healthy lives.

I suspect though, that most people will have to be dragged kicking and screaming and it won't end well. :(

michael Hanlon said...

Both of you sit down and shut up or I'll send you to the Principal's office. This isn't gym or an civics class. The issue here is, whether it's desirable and not one's opinion of what we should be doing. It is a discussion of what it would take to specify a space habitat given that certain materials are available from the stockroom. We need to know what materials to put into what parts of out structure, what materials we'll need to outsource to a different vendor (Earth) What the most economic and safe habitat shape will be. If we decide on a particular piece to the puzzle, are there any drwabacks we need to be aware of with that decision. and more...
So please, no debates about solar vs coal gasification here. Just the problems our pioneers will face when they construct their sod dwellins and what precautions need be taken to guard against the savage natives (Sun, gravity and vacuum)
How nice, my swirly word is embed!

michael Hanlon said...

The plier (singular, you only need one side move-able) analogy is interesting and I take it the jaws are equal to the rollers? If, for arguments sake, you want to make 2KM of sheet, coming out of a 1M round roller (against a flat convex surface I think). If the sheets are to be 2M wide, that roller will have a dimension of 1M diam. x 2M high. It'll have to be steel to stand up to the amount of use you intend to put it through. The volume of the cylinder is h x (pi x r**2) = 2 x (0.785)= 1.57 cu M Dang I need to show this in weight we can grasp, which I'll say is 1 cu cM = 1lb agreed? Returning to the Calculation, 200cM x (pi x 50 cM**2) = 1,571,000 cu cM's @ 1 lb /cu cM and 2,000 lbs per ton = 800 tons!!
If I was wrong in my factor for weight per cubic Centimeter by an amount of twice (each 1 cu cM = 0.5 lbs[8 oz]) then the cylinder will mass 400 tons to lift to orbit! If you hollow it to lighten it, it may not provide the required KM's of use before deforming and needing replacement.
That's just the roller side, The fixed convex base you intend to press it against should be at least as massive (400 Tons).
To run it you have to incorporate gears and a 10KW motor. That's not from off the shelf out there. That has to be delivered by the Conastogas. I expect that weight to mass near ten tons. So, reasonable assumptions made, you need to lift near a KiloTon of Mass into space! May be a rail gun? Oh, don't go down that road please. They cost too much and destroy half the things you fire from them. No, it has got to be chemical rockets to do the lifting, but I'm open of course to be swayed . I still have one foot left to shoot.
Another thing about the pliers analogy, they are used to mangle softer metals. The harder the metal you intend to deform, the stronger your jaws have to be. You want sheets of high grade steel? You need Higher grade Jaws.

To the earlier process of smelting the ore. You brought up a point I think didn't register as a problem and it will be a big problem of melting metal in a vacuum. Once you've poured your billets, where does the heat go to accomplish the cooling you describe? The vacuum of space is one of the best thermal barriers in the universe. The Thermodynamics will tell you that if you pour round balls into perfect black bodies, it will take centuries to dissipate the energy that keeps the atoms in the excited state which manifests it self as 'heat'. You slowly radiate infra-red waves until the energy is depleted. again I think at the risk of my third foot, other means need be taken to accomplish cooling and if you intend using mechanical methods, that machinery weighs, well Tons. (Quenching you can use the water for but not for adobelith?)

Lastly in this brain draining foot losing missive, the topic of "Alloys". Steve, dig deep into your experience and learning and find me an alloy that doesn't require some exotic element be included in the chemical mix. There be two problems: How to mix it in? at smelting? now you're talking more tons of stiring equipment. Second where do these exotics come from? The asteroid will no doubt have insufficient quantities or have them so dispersed that extraction becomed a major machine intensive effort. No, they, have to be sourced from the vendor also and then you gotta shop shippers who can handle the lifting of (you know they are ) toxic materials to a far distant destination. Unless you only want to go to L1?

michael Hanlon said...

Did I just say Quenching? by gosh, I did. I gets to sew a foot back on. Quenching, a critical step in the proper crystaline structure development in high quality steels. You can use oil, but that's not available (it is used because it discourages the rapid formation of surface iron oxide [rust]), a by-product of elevated temperature and air moisture - no air problem there but no oil either. No, you have to use the available quenching liquid, water. And some lab development would be required before a good process can be come up with to make steel that way.
Problem one with H2O quench is it transfers heat to the H2O. All well and good but at a point that H2O changes from a liquid which you can manage in an open vacuum to a gas which you cannot. So, unless you already have a large chamber available, you can't make the walls for that chamber until the chamber is made which requires the walls which you ned to make inside the walls which you are making. Chicken or egg salad, sir?
Thusly you've changed you invaluable commodity from liquid gold to individual molecules of H2O which you would need to collect one by one.
Is the plan to employ the retro-fitted shuttle fuel tanks as that container to contain the steam? by what process do you extract the energy from the steam to getit back to liquid? REM: there's already a heat build up occurring in the habitat.
Canada guy would love my swirly word: decity

michael Hanlon said...

Water quenching makes rust surfaces. Can we live with that? Right at the manufacturing we encounter the first obstacle, inspection. Visual is out unless you intend to grade color. No faws will be evident through the rust. X-ray inspection can be performed, as can lab analysis, but that means you have to create two new spaces for those activities to go on in.
Next comes the challenge stephen touched on, joining. There are three major ways metal joining is accomplished: melt and mix, chemical gluing/bonding and three, explosive impinging. I don't see any TNT stores out in spaceso, the Clint Eastwood method is out (Cigarillos probably will be unavailable too) The other two methods require join surface preparation to be sucessful in the joining. The rust has to be removed. It is an Iron prodoct. It will find its way toany other ferro=magnetic mateerial nearby when yiou grind it off. So, extra precautions need be taken when tthat activity occurs and until all particles have suredly been removed.
Chemical bonding tends to be brittle after out gassing has occured. On Earth in the atmosphrer that could take years to happen (try flexing an old pair of sneakersand you'll notice all the bonds are broken) In the vacuum of space that outgassing will transpire rapidly. Probably befor the worker has left the area, (s)he will need to start the repair process and continue until the next shift arrives and arrives and arr....never ending.
With all these drawbacks, doesn't a fluid which hardens in place seem more effective in function, ease of manufacture (remembeer, we haven't thrown the iron away, it's just tied up inside the adobelith and can be recovered later, this is bootstrap, this is sod house this is hole in the ground type of intrusion into the wilderness), lees suseptible to thermal stresses, sturdy enough to stop meteorites, adaptible and end user friendly?
I really have avoided this aspect of shit use but it needs to be brought up. It comes in a variety of colors! If the diet of the colonists were to be manipulated, for a while the excrement would be a light tan color, which would suffice as a relective coating with the addition of available trace minerals, aluminum maybe? devote that production to the exterior painting and then switch the regimen back to normal (fisrt feast: Spinach for everyone)

michael Hanlon said...

Stephen, It occurs tome that maybe we are both correct in our proposals? Perhaps we are talking about separate PHASES of the development? You outlined already the 'foot-in-the-door' step using he fuel tank. I think I'm at the next step to build a slightly larger habitat. And you are designing what will be appropriate when , though not quite ind3ependent, the final phase should be like? Before we wring our ideas on the gutter of futility, let's establish that the phase approach to the program may be beneficial.

michael Hanlon said...

Stephen, It occurs tome that maybe we are both correct in our proposals? Perhaps we are talking about separate PHASES of the development? You outlined already the 'foot-in-the-door' step using he fuel tank. I think I'm at the next step to build a slightly larger habitat. And you are designing what will be appropriate when , though not quite ind3ependent, the final phase should be like? Before we wring our ideas on the gutter of futility, let's establish that the phase approach to the program may be beneficial.

michael Hanlon said...

Speaking of strength for rotation, twisting, torsion or torque, That little construct I built and am using the photo of as an avatar currently is tremendously strong in all three planes. It is efficient in transferring loads to the other planes. I think it might make a nice intermediate shape in the city of the future. You can load up all the faces with dtructures for whatever endeavor..

Just adding options to the debate.

michael Hanlon said...

More on that little 3-D construct:
Imagine yourself at an inner intersection of the three planes point (actually move out a little along one plane). Imagine the far side of the construct as pointing at a radiation source(Sun) The energy has to travel through three layers of the planes to get to you!
Yes, in some spots it's only two and some it's only one. But if the design were oriented toward the source all the time, there would be a highly safe spot there towards the center.
In a habitat that was going to risk its pioneers to lethal rads, a safe quick to access refuge should be provided. In the 3-D construct the area would be easily recognizable. Go to it and wait out the storm.The cylinder never gets safer at any point, unless you continually run with the rotation to the other side. That would require the inhabitants to know at all moments, even upon waking to an alarm, which way provided the most dense cover and begin to move with it once there. Yes, later on when you've built the thing out of steel and added lead shielding, most places could be called safe.
Each plane of the 3-D can be made both larger in area and thicker in depth as time goes by. Expansion isn't limited to huge increases as the cylinder would be. Another aspect unique to this form and one which I think contributes to it's strength is, star at a two plane intersection and move along one in a 90 deg arc to the third plane. Now from that point move 90deg around to the first plane you left behind. Do this one more time and you're back where you started. You moved through 270 degs to do a complete circle. I think this means stresses are transmitted more quickly and efficiently through the structure distributing them before they can build up and cause damage.
More on the cylinder: if it's rotating as you propose, it cannot be tied to the stockroom (asteroid). All deliveries will have to be fed-exed. Where does this fuel/energy come from? One way empty trips and return with a load? That's a bad business model with two separate places of work going on, an efficient mode of transport is a must. My non rotating habitat can be a walk back and forth. For sleeping and exercise and minimal g interchanges, the end of a rope of 100 M spinning at 3rpm (?math right?). Tether an automobile sized sleep chamber at the end of the rope and go to sleep. When woken, crank in the line and exit t your zero g work environment. As time goes on, the autos could become bus sized, sleeping more and more. Or segueing into next topic, growing G intense crops.
An aside at this point. Have you seen the Bruce Dern Movie with music by Joan Baez, "Silent Running"? Your next recent blog discusses 'farming in space' and that's essentially the background for the whole film. I'm going to try to find a DVD and re-watch it. They used no evident gravity simulators and yet all the habitats grew. Maybe if there's a book, it'll explain it.

Thomas said...

The solution to the issue of how to hold the solar array in such a position as to shade the habitat:

At each pole of the cylinder, there is a bearing assemble connected to an external superstructure. This superstructure holds the array in place and contains docking facilities.

However, this presents an obvious problem with rotation.

The solution is to have a second cylinder attached to the same superstructure, but rotating in the opposite direction. This also solves the issue of how to get all that mass rotating in the first place: electric motors accelerate the two cylinders simultaneously.

There are some additional complications with this method, but I think it is good.

michael Hanlon said...

Welcome, Thomas. Can you give me some feelings about this structure. Think giant pringles can in space. Point the plastic cap toward the sun. Cover the plastic cap in photovoltaic cells. Even though they may be spinning, they are at all times perpendicular to the sun. No
rotation-allowing joints necessary. At the other end you can cut an entry port and require approaches just like in 2001, where spin matching maneuvers take place.
That orientation also solves the problem I pointed out about where to hide in solar storms. You just head away from the solar panel end, putting the mass of everything sunside between you and the "Rays". Of course not all storms can be forecast accurately, so some sunside safe rooms would need to be built.
Thanks for thinking enough about this to contribute. Hope to get your report on this orientation of Stephen's cylinder.

michael Hanlon said...

Stephen, I have just remembered another way of doing metal joining. I based my previous inputs on my Manufacturing Processes studies and experiences. But My Metrological studies and experiences point to a fourth way , besides melt & mix, chemical joining and impinging, Under the right conditions some metals can be "wrung" together. The act of wringing is to push and twist together. If two metal surfaces are flat to within only a few wavelengths of lights, when wrung together, they form a bond by allowing the exchange of electrons from one surface to the other. Though it doesn't take much energy to pull a single electron away from its nucleus (depending on the element) when you have a surface composed of millions and billions of atoms, the force becomes rather large. No air can leak through the bond. No rust builds in the bond area. They are almost impossible to pull straight apart without tearing away some of the surface crystals. An advantage of this joinery is that it doesn't take much energy at all to slide one surface along the other and still have them joined together, meaning it could be the perfect answer to the need for a joint that will stand up to the thermal stresses due to rotation in the sun' heat.
The surface preparation which you would have had to make accomodations for both in preparation and welding, just needs to add one more step: polishing. You,I'm sure, would understand the requirements of the lapidary process better than me. Another benefit is that you eleiminate the "add heat and wait for it to cool" step!!
If you desire to experience the wring type of bonding , it can be done easily in the home. In Calibration we used to use this technique all the time with guage blocks. At home you can accomplish the same type of bond using glass. The manufacturing processes used to make glass for windows or mirors is near a few light wavelengths. Simply put a drop of water or oil between the two surfaces and push and twist and push and twist and in a couple of repititions, they will be bonded. Now try to pull them straight apart! To separate them, you have to twist and slide them away from each other, Why the lubricant before the push and twist? If you didn't lube it the joining would become permenent(not in the glass because it is a liquid but in metal, yes, because it is a crystal)! And no further twisting would be allowed and you wouldn't have the 'slide' advantage. If you do this at home with glass, be sure to wear gloves and safety goggles.

jack.123 said...

Michael-You were asking about alloys.Why not spider silk?Much stronger than steel.I have heard that some goats are now being used to produce it in their milk.plus they could be used for food as well.Using the silk like fiberglass is now being used would solve many probems.Storing water in the outer shells could also shild the cylinder from cosmic rays.

Stephen D. Covey said...

Jack.123, spider silk certainly has its uses, although limited to near room-temperature. Can't use it outside in space where it is subjected to extreme colds (it becomes brittle) or heat (the proteins decompose). Fiberglass remains strong over a much greater temperature range.

Your comment on storing ice in the shield area is correct, but we won't have a surplus until we can access the resources of a comet (active or extinct). Water is one of the best possible radiation shields due to its high fraction of hydrogen.

Michael was correct when he said that our needs are different in the bootstrap phase than in the long term, and I would add an intermediate phase where we will be concerned with access to adequate hydrogen, carbon, and nitrogen. After we grab a comet, nearly all of the shortages will abruptly turn into surpluses.

Michel said...

Hello M. Covey,

A very enjoyable discussion. I think the use of concrete might be quite interesting for the space station you describe. A post-tensioned concrete structure could be both strong and heavy, providing radiation shielding. Concrete in really mostly rock, after all, with only about 7 to 12% cement. This composite nature greatly reduces the need for water, to about 3% of the mix. Steel would still be used, but in the form of cables, that require much less equipment to fabricate than a rolling mill.
There would probably be no need to pass the water through the astronauts first!

I imagine a construction plant building a series of annular structures, slightly angled at the ends. A single form might be sufficient, with a curing time of a few days. 36x 10 degree sections, each about 10m in length would be produced for a complete circular structure 120 m in diameter. Hollow tubes would be left in the structure for the installation of steel cables. These cables would be threaded through the tubes, and then tensioned to draw all the pieces together into a circle.

However, with standard cement I fear the might be trouble with carbonation, rust and leaks, if we want the station to last more than a century or so. The solution might be some kind of liner, to both protect the cement and make it airtight, or some other binder better adapted to space conditions than cement.

As you mention in your text, the larger the station, the stronger it has to be. Eventually, for future stations, the concrete would no longer be required and the station would be made directly from steel or aluminum. But for the first ones, using steel and concrete could be a more optimum solution.

On another note, do you think a tether stabilized structure would solve the stability issue of long cylinders? I’m thinking of a tether a few km long, with a large mass at the end. I wonder if this might also help in keeping the station’s rotational axis aligned towards the sun?

Regards,

Michel Lamontagne
Otterburn Park, Qc