Space Construction Materials J. H. L. Lawler 16 June 2004

In WWII Geoffrey Pyke invented an interesting material, a composite of 14% by weight sawdust and water frozen to ice. It was named Pycrete by the Canadian developers in 1943.

This material was both much stronger and much more resistant to melting than normal ice, and Sir Winston Churchill approved investigation of building super aircraft carriers of “Pykrete” as it became known by the Canadian investigation team. These proposed ships would have been over 2000 feet long, and 300 feet wide, large enough to launch B-29 bombers, and made of a refrigerated hull and flight deck over 30 feet thick. This thickness would be sufficient to resist Torpedoes and all known bombs of that time (a metric tonne of explosives would only chip at the structure which could be easily repaired by just freezing more Pykrete into any “crater or hole”). It would have carried up to 1000 aircraft, perhaps 20,000 to 50,000 men and allowed projection of massive air /sea power in total control over the local skies and this force could be brought to the enemy homeland. The more conventional existing methods had already swung the balance of power so far that the project was abandoned to divert resources to “more” of what we were already using, so it never moved past the construction of one experimental hull; a structure, 60 feet long by 30 feet wide and 19.5 feet high on a lake in the Canadian Rocky Mountains - Patricia Lake in Jasper, Alberta.

Mr. Pyke correctly also surmised that floating cities of perhaps a several square miles (as large as many inhabited islands) could be made of the material to roam the high seas, perhaps even to act as new sovereign nations. This was only a dream.

However, the properties and similar materials can be applied to massive space colonies with great success. There are massive quantities of ice in the rings of Saturn. Sawdust is another matter but substituting silicon / silicate foam for hydro-carbon based material, by foaming asteroid rock, and / or lunar rock should be quite as good as (in may ways even better than) cellulose. The Iron bearing material of the asteroids also should supply material for structural steel required in other place in the space colonies.

There are two distinct “foams” possible and each has its advantages and disadvantages. The first consists of a foam of small bubbles of a gas inside a continuum of silicate. The alternative is spheres of silicate fused together with open space being the continuous interstitial space between spheres. The last can be “filled” with vacuum of very low-pressure gas to give a very high insulation value (low thermal conductivity), while the foam bubbles in a continuous silicate matrix should in theory at least be substantially stronger. The Pykrete strength came largely from the ice with “holes” in the ice matrix, that disrupted transmission of cracks in the ice, so either of the silicate structures should do that. The open foam bubbles should potentially be lighter, and also stronger, since the ice is the main load carrying material, so the foamed silicate would be preferred for most bulk applications.

My concept would for “smaller” colonies follow the rotating cylinder (1 g in the living space) concept of Dr. O’Niel perhaps 5 km in diameter and 100 km long with about half of the shell being occupied by living space about 200-400 meters thick, (about 2000-4000 sq Km of living space) which could accommodate perhaps 50,000 –200,000 people in a balanced ecosystem:::: Longer larger cylinders could easily accommodate up to a million people each, with banks of associated cylinders making up a huge colony system at each of the Lagrange points in Earth orbit (E-1, E-2, E-3, E-4 and E-5 @ 180°, 120° lagging, 120° leading 60° lagging and 60° leading earth position at 1 AU from the sun).

Or perhaps this could take the form of a Dyson Sphere perhaps 16 Km (10 miles) in radius and with occupied surface structure of perhaps 1 Km (0.6 mile) thick –think of a rugged valley mountain like structure to get light into the living part of the shell – onion like layers cut by valleys – 1000 sq Km in each layer 100 layers or 100,000 sq km of living space and upwards for upwards of a million people. This would require an artificial sun in the core, and some form of gravitational conrol so is in the far distant future, and ring world (an artificial ribbon, a few miles wide with rotation to maintain 1 g in a earth distance orbit) would accommodate up to a trillion (10 exp 12) people. That is even further out in technology. The stresses demand diamond tube type bond strengths, and the active control of negative feedback to offset inherent positive system type feedback oscillations (disastrous – increasing exponentially) present challenges, but this is not completely out of reason. Even today’s systems appear to be within development R & D range of the engineering required.

O’Neil colonies ctd.

The thick ‘Pykrete-S” shell would provide both pressurization containment and radiation shielding, - multiple layers of “clear ice” (multiple for redundant pressurization containment in case of accidents) would allow windows for light, and a thin vapor deposition of metal (such as Al or glass) would halt sublimation of the ice to vacuum, while the ice could be insulated at say

–20C (or for that matter much lower depending on external conditions) from the +25C interior temperatures; this is easily done by just including more Silicon base foam. The exterior if near enough to the sun (as in Earth @ 1 AU orbits) could be coated with electrical power solar cells, to reclaim solar electrical energy. Etc. The technology is here now today to mine natural resources of the known solar system and build habitat for billions of people. It will require a huge investment in work and control of resources, but the resources are there if we are just smart enough to use them. Colonies orbiting Saturn can provide the ice by mining he rings, and others in the asteroid belt can reclaim that material, thus making space navigation in that area much safer by removal of irregular unpredictable asteroids. In fact I can envision more people living off Earth in a few centuries than now / or then would live on Earth.