Colonies in Space
by T. A. Heppenheimer
Copyright 1977, 2007 by T. A. Heppenheimer, reproduced with permission
Chapter 7: Construction Shack
In astronautics there is an important concept which has stimulated and guided much work and research. It is an old concept, older than the first liquid-fuel rockets. It was worked out in fair detail as long ago as 1929 in a manner that even today would be regarded as essentially correct. Many of the leading pioneers in astronautics have proposed their versions of it, including Hermann Oberth, Wernher von Braun, and Krafft Ehricke. It has been studied in great detail under the well-known system of hiring a thousand ordinary engineers to do the work of a few men of genius. At least twice in NASA's history, it has come close to being the focus of the nation's space efforts. Yet it has never been built and never flown. The concept is the space station.
Space station, space base, manned orbiting laboratory—it has been studied under these names and many others, as well as under the three-letter acronyms (e.g., MOL, Manned Orbiting Lab; OLS, Orbiting Lunar Station) so loved by the aerospace industry. It is as old as the idea of space flight, as new as next year's NASA budget. It has been proposed to serve a variety of purposes but has never been built because there has never been a compelling need for it. Until now, perhaps.
The original discussion is in Hermann Oberth's 1923 work, The Rocket into Interplanetary Space. This small book set forth an agenda which spaceflight advocates will spend a century fulfilling. Oberth suggested that a station in space would be valuable for use in building large structures as well as for a refueling depot for spaceships. He wrote that stations could serve for observing the earth and aiding navigation: "The station would notice every iceberg and warn ships . . . the disaster of the Titanic in 1912 would have been avoided by such means." [Footnote by author: This is not true, by the way. The Titanic had plenty of iceberg warnings but ignored them.]
Six years later in 1929, an Austrian engineer writing under the pen name of Hermann Noordung gave a detailed design of a station. His "Wohnrad" ("living wheel") was a wheel-shaped structure, 100 feet in diameter. It would spin to provide artificial gravity at 1 g, and it would obtain its power from the sun, focusing sunlight onto boiler tubes by means of mirrors. There would be a hub with an airlock, counter-rotating to stop spin and connected with large shafts to the rotating wheel. This was the first description of the type of space station made famous in the movie 2001.
Twenty years later Wernher von Braun independently came up with a very similar design. Though he had never read of the Wohnrad, his station also was wheel-shaped, 250 feet across, and rotating to give 1/3 g artificial gravity. He proposed the wheel have two or three floors and the atmosphere be oxygen and helium at one-half sea level pressure. He also devoted attention to pumping water into ballast tanks so the station would continue to spin evenly as people went about their business inside, redistributing the masses within the wheel. Von Braun proposed to use this station as a base for the outfitting of expeditions to the moon and Mars.
His ideas received considerable attention. Walt Disney put together an hour-long TV program, Man in Space. Time put space flight on its cover (December 8, 1952) and the now-defunct Collier's ran a series of articles on von Braun's ideas, quite in the fashion that other magazines, a quarter-century later, would treat O'Neill's.
When the U.S. space program started a few years later, space stations ceased to be Walt Disney cartoons and began to be matters for public policy. Early in 1961 when President Kennedy was seeking a way to beat the Russians in the space race, he briefly considered the space station as the goal for the United States, before settling on the moon landing. Kennedy thought the Soviets might beat the United States in the race to build a station, but he felt we had at least an even chance of beating them to the moon.
In retrospect, it might have been better if Kennedy had picked the space station as a goal. All the major proponents of space flight had envisioned, after the initial orbital flights, the buildup of a space station as an essential prerequisite for any sustained program of activity in space. Instead, we bypassed this to go directly building a manned lunar program. When this program could no longer attract public support late in the 1960s, the whole space program was left largely without a theme to keep it going. The result was NASA's rapid downslide.
Throughout the 1960s there were several major space-station projects, all of which in time were cancelled or cut back. Douglas Aircraft worked on its manned orbiting research laboratory (MORL) until the funding ran out. The Air Force had its manned orbiting laboratory (MOL), which actually got to the point of flying an experimental unmanned station to orbit before this program, too, was cancelled. Late in the decade North American Aviation and McDonnell Douglas churned out reams of paper space-station studies until Congress told NASA to have them quit.
For all this though, there actually was a project somewhat like a space station which was carried through and flew. This was Skylab. It never was intended as a space station in the classic sense as a permanent orbiting facility. But it was occupied, off and on, for nearly a year and periods as long as three months. It used ferry rockets to carry crews into space for their tours of duty, and they were able while there to do useful Earth observation and astronomical work. Had there been a space shuttle, and Skylab been in a slightly higher orbit not subject to decay, it is likely that it would have become a true space station.
NASA still is very interested in stations. One of the people in charge of that work is Jesco von Puttkamer, who is among the leaders of the bright-eyed visionaries in the space agency. He's originally from Germany, though he is too young to have been part of the Peenemunde group of World War II. He worked for von Braun in Huntsville, Alabama, then came to Washington to direct advanced planning for NASA's Office of Space Flight. He's the man who had primary responsibility for looking at Gerard O'Neill's work on space colonization.
Not only is he involved with space colonies, he also has been connected with "Star Trek." The Star Trek people put out a set of blueprints of the starship Enterprise, along with a space cadet manual. Their first printing ran to 450,000 copies. A Star Trek convention in Chicago drew 15,000 people and a second one in New York a few weeks later drew 30,000.
Von Puttkamer went to the one in Chicago, taking graphs and slides to show his planning through the year 2000. They asked him to show his presentation. Five thousand people attended and he repeated the show two or three times.
It is von Puttkamer who is responsible for NASA's current interest in space stations. He envisions a facility for 200 people in geosynchronous orbit. It would be used for assembling power satellites and for development of what he calls "space industrialization." He expects it could be ready by 1983 or 1984. In March 1976 his office let contracts to Grumman Aerospace Company and to McDonnell Douglas to study the concept. Such a station could be the next major space project after the shuttle, and von Puttkamer sees it as an essential first step toward a space colony.
Should it go forward, it almost certainly will undergo the same sort of changes and transformations that the space shuttle experienced on its way to becoming an official program. Von Puttkamer's recent award of study contracts appears to put the space station in about the same position that the shuttle was early in 1969. It will probably be two or three years before any firm designs are established. In the meantime, it is appropriate to describe some space-station concepts which are particularly applicable to building a space colony.
The particular space station to be used for this purpose is usually referred to as a "construction shack." "Construction" refers to its reason for existing and "shack" is a good description of the on-board amenities. It can house over two thousand workers and affirmative-action hiring procedures will ensure that about half of them are women. The station will be built in low Earth orbit then transported out to the site of the colony. Its construction and transport will take place during the same years that the lunar base and mass-driver are built up. When the first mass starts coming up from the moon, the construction shack will be there to work with it.
Much of the basic work in designing the construction shack has been done by Gerald W. Driggers of the Southern Research Institute, Birmingham, Alabama. His work draws heavily upon earlier space-station studies.
Driggers' construction shack will house 2232 workers. It is built around 36 modules which provide room for the crews to live, eat, sleep, and enjoy themselves as best they can. Each module will be 3 stories high and 50 feet in diameter, providing as much room as 2 or 3 four-bedroom suburban homes. Suburban homes might house at most a dozen or so people; each module on average will hold 62.
The modules will be arranged in groups of 3, each group providing for 186 people. The available space for these 186 is to be broken down like this:
Although this is not exactly the same as gracious suburban living, it still is rather better than life on an aircraft carrier or submarine. There, crewmen sleep in bunks stacked one above the other with less than 10 square feet per man. Fifty-four square feet is about the size of a bathroom with toilet and sink only; if the men and women of the crew are accommodated two to a stateroom, the quarters will be about the size of dormitory rooms on college campuses.
Driggers proposes that there be two construction shacks, one to do the extraction of metals, the other to do the actual construction. Each will have eighteen modules, the modules being arranged in clusters of nine at the ends of large spokes. The spokes run through a central core which is equipped with airlocks and a docking port. This core, in turn, has on its top a very large sphere over three hundred feet in diameter. This is the construction sphere and each construction shack has one. It is in these spheres that the main work activities take place.
There is one other major item which is required: the power supply. There is good reason to use solar power since there is no day-night cycle as on the moon. The construction shacks will be equipped with their own power satellite, generating 300,000 kilowatts of power and transmitting it a mile or so to each of the two shacks. The power satellite will be no small project—its solar mirrors will be over a half-mile wide.
The power plant will not only provide for the construction shack, it will serve as a demonstration of satellite solar power. In developing the power satellite as a source of energy for Earth, there is need for some method of testing the whole system in a way that does not involve building an entire 10-mile-square powersat launched from Earth. The power needs of the construction shack can provide the opportunity for an overall test. Years before the first powersat is built for Earth all its necessary elements can be tested and proved out in the construction shack power plant.
The whole construction consists of two shacks, each having a core with clusters of modules set out on the ends of spokes. Atop each core is a construction sphere with a rectenna. Feeding microwave power to each rectenna is a single powersat with two transmitters a mile or so away. The two shacks together weigh 7000 tons, with another 3000 tons for the power plant.
All this is assembled in low Earth orbit, 300 miles up, then moved into deep space to the site of the colony. The supplies and equipment for the lunar base are shipped in 150-ton lots by ordinary rockets which burn hydrogen and oxygen, 6 lots to a shipment. The components of the construction shack equal the masses of naval destroyers and their transfer calls for slightly different methods.
The transfer begins with the transport into low orbit of huge stores of hydrogen. Eight thousand tons of liquid hydrogen must be lifted, and it takes about two years to do this. Ordinarily there would be little hope of keeping it liquid for that time, but the construction shack is large enough to be fitted with its own hydrogen liquefiers. Then, when hydrogen boils off within the tanks, it need not be lost. When the tanks are nearly full, the rocket engines arrive. These are of a new type and they heat the hydrogen directly to a high temperature, letting it blow out a nozzle to give thrust.
In the 1960s and early 1970s, there was a great deal of work on rockets of this type. This was project Nerva, which was named not for the second-century Roman emperor but as an acronym for Nuclear Engine for Rocket Vehicle Application. It involved a nuclear reactor to heat a block of carbon to over 40000; the hydrogen was to flow through this block. For the construction shacks, there is no reason for the rocket to be nuclear since the power plant can supply energy enough. The rocket engine will actually be a sort of carbon arc, heated white-hot by an electric current. The carbon arc has been around since the days of Michael Faraday, a century and a half ago, and its use represents just another demonstration of how little in space colonization has to be newly invented.
These arcjets, as they are called, each give a thrust of 3000 pounds. One is on each major item: the two shacks and the power plant. This will give them a leisurely acceleration, and it is not hard to fly formation. The performance is about the same as using an auto engine to run a ship, but in space such slow accelerations can build up. It takes only a couple of months for that small fleet to reach the moon's distance from Earth. Later it is a simple matter to adjust position and wait for the first mass-catcher to come over, full of lunar material. At this point, operations at the site of the colony are ready to begin.
The operations involve the most difficult technical problems to be faced in the whole space colonization effort. We know about the rockets we will need, the power systems, even the mass-driver and the lunar base. All these represent problems for which major parts of the solutions have been studied or designed, or in some cases actually built. No one has ever tried to build an aluminum smelter to perform in space.
The smelting of metals, their extraction from lunar rocks and soil, represents a problem quite different and novel. Our terrestrial experience with aluminum production or steelmaking will be of only limited use. On Earth, metals usually are smelted from their oxides or from other simple compounds. Then the metals can be extracted through essentially a single chemical step. For iron the ore is heated together with carbon and limestone. For aluminum a current is passed through a solution of alumina in molten cryolite. In these industrial operations, air and water are available free or at low cost, and disposal of wastes is not usually a problem.
In the construction shack, everything will be different. The "ores" are complex chemical substances similar to ordinary rocks or clays. Water will be available only in limited quantities and all materials will have to be recycled. It is entirely hopeless to use the processes of Earth directly, and the processes which are used must operate in an environment where even gravity must be manufactured.
There is, however, plenty of solar energy, both for power and for heating of materials. Even more important is cost; the processes need not give their yields at prices competitive on Earth. On Earth a process for making aluminum might not be economic unless it could meet the world price, about $1 per pound. In space, a $20 billion construction shack which produces a million tons of aluminum ‘.ould be practical. The production cost would be $10 per pound, which still is 4 times cheaper than the alternative of hauling aluminum up from Earth.
Moreover, the production of metals will also give a valuable by-product: oxygen. Oxygen, chemically bound, represents about 40 percent of typical lunar rocks. This is not only enough to provide for the breathing needs of people in space, but will also furnish rocket propellant. Once metal-producing operations are underway, it will become much easier to conduct rocket flights into lunar space. Rockets bound for the moon or the colony will need less hydrogen fuel than they would need if they were nuclear-powered. The combination of an ordinary hydrogen-oxygen rocket, together with oxygen being available at the construction shack, gives better performance than a nuclear or arcjet rocket would, using hydrogen alone.
How to produce the metals? Suppose, for instance, we want to get a ton of aluminum. The "recipe" would be:
"Take ten tons of anorthosite. Melt in a solar furnace at 3200°. Add water and quench the melt to give a glassy solid. Allow to settle in a centrifuge; pipe off the steam from the quenching to a radiator to condense it to water. Remove the glassy material from the centrifuge, grind fine, and mix with sulfuric acid. Pipe to another centrifuge to separate off the aluminum-bearing liquid which has resulted. Mix with sodium sulfate and heat to 400°; pipe to still another centrifuge to allow the resulting sodium aluminum sulfate to settle. Remove it after it has settled, and bake at 1470° to produce a mixture of alumina and sodium sulfate; wash out the latter with water. Mix the alumina with carbon, and react the mixture with chlorine. This gives aluminum chloride. Put the aluminum chloride through electrolysis. Result: One ton of molten aluminum."
The first steps of this recipe are called the melt-quench-leach process and have been tested by the Bureau of Mines. It has succeeded in recovering over 95 percent of the alumina present. The treatment with carbon and chlorine is carbochlorination. This process, along with the electrolysis, was developed and patented by Alcoa. All in all, it is quite a difficult and roundabout procedure; yet it appears to be among the simplest available. For instance, it is easier to electrolyze chlorides than oxides. This is why the alumina, or aluminum oxide, is carbochlorinated.
The whole process also has to provide for the recycling of chemicals. Sulfuric acid is reformed following the removal of the sulfate. The electrolysis recovers chlorine. Finally, the carbochlorination produces carbon dioxide, which can be "shifted," as a chemist would say, to produce methane by combining it with steam over a catalyst. When the methane is heated to high temperature, it breaks down so that carbon is recovered as a form of soot.
The initial step, melting the rock in a furnace, also releases small quantities of elements blown out from the sun in its solar wind, and implanted in the grains of lunar soil. Only traces of these elements will be found; yet the construction shack will be processing such huge quantities of material that these traces can add up to significant amounts. In 1 million tons of lunar soil, there are about 40 tons of hydrogen. This is sufficient to make enough water to fill an Olympic-size swimming pool and will be much appreciated. There are 100 tons of nitrogen and 200 of carbon, which will help the agriculture. There are over 500 tons of sulfur, to help keep up supplies of sulfuric acid, and 2000 tons of sodium.
Titanium will be easier to produce. It comes from the lunar rock ilmenite, which also contains iron, and can be separated easily from other rocks since it is magnetic. The ilmenite is heated together with hydrogen, producing water, iron, and titania (titanium dioxide). Iron comes off easily as a by-product. The water is electrolyzed to recover the hydrogen. The titania goes through the same carbochlorination and electrolysis used for the alumina. This gives molten titanium.
Glass, real glass for windows, is another byproduct of the smelting. After acid leaching, the material left behind is nearly pure silica. This is remelted in a solar furnace then shaped into panes of high quality.
The smelters will get their ores from the moon but will rely on Earth for their chemicals. The trace elements from the moon will be useful mainly to replenish supplies lost in processing. The smelter will need several hundred tons of chemicals, including water, sodium sulfate, sulfuric acid, chlorine, and carbon. When operating at full capacity (150 tons per day of aluminum), the aluminum smelter will weigh 7600 tons. It will use 115,000 kilowatts of power (40,000 of which are to recover carbon via the shift process) and require 1 million square feet of radiator surface for cooling.
Not all of the smelter will come from Earth along with the construction shack. To a large degree, the smelter will have to be built up in space. Some of the growth will come by shipments from Earth, bringing chemicals and specialized items of equipment. But to a large extent, the smelters and construction areas will grow the same way as the colony: from lunar-derived metals. At the construction shack, the first construction will not be on parts of the colony or even on power satellites. It will be directed to expanding the metal-producing facilities of the shack itself.
This represents a new and challenging topic, the construction of large facilities in space. There is already considerable interest at NASA in this. The prevailing view is that it will involve many routine, repetitive operations which can be carried out by automated machines. The roles of human workers would be those of supervisors, expediters, and troubleshooters.
While the conditions of space make smelting difficult, the same conditions make construction and assembly easy. In terrestrial construction projects the actual assembly or joining is not difficult; it is a matter of installing fasteners or of putting in rivets. The difficult parts all involve gravity. There are heavy beams which must be hoisted, carefully balanced, and swung into place; for the unwary worker, there is a thirty-story drop down to the street. But in space, even the largest structural sections can be handled by small machines or by individual workers. The high-steel worker of weightless space does not have to cross girders or beams with a sure-footed stride. He simply launches himself in the direction he wants to go.
It will not be difficult to develop TV-controlled mobile assemblers. These will remove structural units from a pallet, place each one in correct position, and make a weld to fasten it in place. For the welding, there will be charges of thermite at appropriate places on the structural units, fired by remote control. Thermite is useful since, like rocket fuel, it burns with an intensely hot flame, even in a vacuum. After completing one set of tasks, the assembler will move on command to another location to repeat the assembly sequence.
The assemblers will not be robots. They will be linked to small computers, programed to guide the assemblers through repetitive operations on command. For instance, there will be a computer routine which will direct the assembler to make a weld in a given spot; the operator only has to specify the spot. Rather than looking like robots, the assemblers will be similar to numerically controlled machine tools. Such tools have been used for many years. Some of the largest are at the Boeing Company to rivet and assemble jetliner wings without the need for human riveters.
The assemblers will work with fabricated subsections and parts. Some fabrication operations will change little from terrestrial machine shops; for example, the drawing of wire for cable. Hot and cold rolling of steel and aluminum plate will change little in space. Casting becomes easier in zero gravity.
There are some operations which do become more difficult in space. For instance, it is difficult to run a drop-forge. Machining of parts will produce metal chips and cuttings which will float around and wind up in odd places unless there are precautions. On the whole, however, zero gravity aids the fabricating of parts nearly as much as it aids their assembly.
In addition to these methods, there is an entirely new process which builds up large structures by squirting them out of a spray can. This is vacuum-vapor deposition. In this technique, a solar furnace heats aluminum not to its melting point but to the boiling point. The metal vapor squirts out an opening and is directed against a balloon-like form where it condenses. Provided the underlying surface for the aluminum spray is at room temperature, the condensed aluminum vapor will have the metallurgical properties of rolled and heat-treated sheet metal.
The simplest application is fabricating large seamless hulls, such as the main pressure shell for the space colony. First it is necessary to have an enormous balloon of the proper size and shape—a mile wide. This would be similar to, though much larger than, the Echo satellite of 1960 made of thin plastic film. The vapor-spraying facility would stand still while the balloon rotates past, receiving layer after layer of sprayed-on aluminum.
These are the kinds of processes which will serve to build the power satellites and the space colonies. They will need careful trial and development before they will be ready for use in space. The smelters can be set up on Earth and proved out before being disassembled for transport into space. The main problems there will involve corrosion, the operation of pumps and centrifuges, and avoiding leaks or major maintenance problems. All these can be checked out on the ground. Vacuum-vapor deposition can be checked out on space shuttle flights. Flights will carry a test balloon to orbit and a small vapor-deposition facility. The experience gained from this simple test will apply directly to the much larger task of space colony construction, just as when we paint a small wall we are confident we can paint a large one.
With the smelter operating, the construction spheres busy, and with its other facilities also in action, the crews of the construction shack will be prepared to start their work. They will have more to build than the colony, but the colony will be the focus of their greatest interest.
The construction shack will not be a very pleasant place to live. It will be more than just a work camp, and there will be opportunity for the crews to enjoy themselves when not at work. There will be microfiche libraries, videotape centers, and TV from Earth as well as frequent opportunities to make phone calls back home over the excellent communications which will be available. Nor will the work be particularly hard or difficult. Still, the people there will look ahead eagerly to the day they can move into the colony out of the cramped cubicles of the construction shack. That will mean the opportunity to eat lunch with a few close friends only, take a shower in privacy, or make love in a real double bed once again.
There will be little romance about the construction shack and even less adventure. Its inhabitants will be there simply to do the hard, necessary work of building. Nor will all of them wish to stay through the entire construction effort. Many of them will sign to serve a set tour of duty and go back to Earth. There will be a regular system of shuttle rockets to rotate crew members home to Earth; and those who go will sing the song of Kipling:
So it will be for those who choose to return to Earth. But those who stay, those who commit their futures to space, will be the ones to inherit the colony which they build.