|Chapter 19 ♦ Planetary Engineering and Galactic High Technology||© 1979 Robert A. Freitas Jr. All Rights Reserved|
Big and Costly are
Living on the surface of a single planet almost inevitably forces us to think small. We tend to view with awe the mighty works of human technology — the Panama Canal, the Empire State Building, the Aswan Dam, the Saturn V rockets. But alien engineers may command vastly greater energies and forces than human scientists can dream of today. We are the backwoodsmen of the Galaxy, the poor inhabitants of a primitive Type I energy economy.
It appears to be
Imagining themselves to be galactic engineers, imaginative xenologists must train themselves to think big. This requires a temporary relaxation of quite normal and natural planetary chauvinisms (respecting both subject and scale). We must recognize and reject the Fallacy of the Big and Costly. Just because a project seems physically huge, even monstrously so, or incredibly expensive does not suffice to rule it out. The Great Pyramid of Cheops bears mute testimony to the obvious fact that anything physically possible can be accomplished, provided only that it is desired badly enough!
In short, we must learn to recognize that Big and Costly are no match for Want.
The purpose of this chapter is not to speculate on every conceivable extraterrestrial technology that might possibly exist, from force fields and perpetual motion machines to flushless toilets with frictionless bowls.668 Rather, the intent here is to attempt to visualize the broad limits on the technical achievements of alien civilizations of a higher order than our own. Not surprisingly, we shall discover that most of the grandiose projects that have been proposed from time to time by scientists and science fiction writers can be accomplished by ordinary Type II stellar cultures. It appears to be extremely difficult to conceive of technologies appropriate to Type III galactic civilizations.
The ultimate goal of any technology
is to enhance survival and to create
comfort, convenience, and wealth.
|Comfort, convenience and wealth|
The ultimate goal of any technology is to enhance survival and to create comfort, convenience, and wealth. Princeton physicist Gerard K. O‘Neill has pointed out that there are three necessary conditions for the rapid multiplication of wealth via technical advancement: Energy (see), materials, and land area or living space. That is, a population of wealthy and secure corporeal sentient beings must have:
- The energy to accomplish great deeds.
- The materials with which to build and to create magnificence.
- The physical space in which to live out their immortal lives.
Before considering the question of living space and artificial habitats, it is interesting to consider the kinds of materials and tools ETs may be able to use on their construction projects.
- We may be assured that any currently available human technology will also be known to alien engineers as well, and probably in its most perfected form.
- More intriguing perhaps are those technical skills which presently elude our grasp, yet which theory predicts are possible.
One teaspoon of neutronium
would weigh about
one hundred million tons.
Terran scientists concede the possible existence of ultradense matter, tiny clumps of material into which vast amounts of mass are compressed. Neutron stars formed by the partial gravitational collapse of massive suns are believed to consist of at least 80% pure "neutronium." Such an astronomical object is essentially a gigantic atomic nucleus, reaching a density of 1017 kg/m3 inside a typical 20-kilometer-wide star. Put into proper perspective, a single teaspoon of neutronium would weigh about one hundred million tons — roughly the equivalent of 30,000 Saturn V moon rockets.
Ultra-thin sheets of superdense
matter would be more than a
trillion times stiffer than the
hardest steel known to man.
A sheet only 1 mm thick would
have the strength of a 1000-
kilometer-thick block of steel.
While there are many technical difficulties to be surmounted, it is conceivable that matter of this density could be used as a building material. Ultra-thin sheets of superdense matter would be more than a trillion times stiffer than the hardest steel known to man. Projectiles could not pierce of dent it until they too were made of the same material. Neutronium shields would be impervious to almost all forms of radiation even at extreme intensities. A sheet only 1 mm (10-6 meter) thick would have the strength of a 1000-kilometer-thick block of steel.
Neutronium plates could also be used to design a local antigravity field.2740 While the gravity around a spherical mass (e.g. planets) is radial, the field across a disk is uniform except for edge effects. Newton's law for disks is g = 4Grt, where r is density, t is thickness, and G is the universal gravitation constant.
We can imagine placing a 0.4 mm-thick neutronium disk above ground, care fully supported by a structure with four stilts. The gravity beneath the sheet would be zero, the upward 1-gee pull of the neutronium exactly canceling the 1-gee downward pull of the Earth. A similar trick could be employed to enable astronauts to withstand higher accelerations in their starships. A vessel accelerating at a steady one gee could be designed with a 0.4 mm-thick neutronium disk embedded in the forward bulkhead. The crew would feel weightless when under weigh at one gee.
Another useful advanced alien technology is the production of elementary particle gases. In order to make a gas, the particles must be long-lived and electrically neutral.2821 Only two particles satisfy both of these criteria: neutrons and neutrinos. There is much recent evidence that it may be possible to design a magnetic bottle to hold condensed cold neutrons,2822 although preliminary calculations indicate that the maximum attainable gas density would be no more than about 10-6 gm/cm3.2740 A neutronium box lined with beta emitter perhaps could be used to contain and store a neutrino gas.2014
If ETs manage to assemble and store dense
neutron and neutrino gases, they will have
practical alchemy at their disposal.
They will be able to transmute virtually any
chemical element into any other by immersing
the object to be transmuted into the gas.
If ETs manage to assemble and store dense neutron and neutrino gases, they will have practical alchemy at their disposal. They will be able to transmute virtually any chemical element into any other simply by immersing the object to be transmuted into the gas. Depending on the object and the gas, any one of the following four nuclear reactions may occur:
|zMa + no —>zMa+1||zMa + anti-no —> zMa-1|
|zMa + n —> z+1Ma||zMa + anti-n —> z-1Ma|
where M is any atom, z is atomic number (protons in nucleus), a is atomic weight (neutrons and protons in nucleus), no is neutron, n is neutrino, and
|Lead into gold|
To turn lead into gold, the ancient alchemists' dream, we treat 82Pb208 in a condensed cold antineutron gas until it transmutes to 82Pb197, after which it is immersed in a trapped antineutrino gas to convert it into 79Au197 — the naturally-occurring isotope of gold.
More interesting and useful, however, is the creation of new superheavy elements that do not occur in nature. Transuranic elements from
It should be possible in principle
to design a hand pistol whose
“bullets“ are really
miniature atomic bombs.
|Miniature atomic bombs|
For instance, a piece of plutonium placed in a magnetic bottle containing condensed cold neutrons would sponge them up quickly and transmute into an extremely high atomic weight isotope — perhaps a denser and more stable form of matter. Subsequent immersion in neutrino gas could convert this superheavy plutonium into a different element altogether. Elements 118 and 168 — which have not yet been produced in human laboratories — should be heavy inert gases like argon and xenon. Element 126 is predicted to have properties similar to normal plutonium, and might permit much smaller nuclear reactors because of the greater atomic
Trapped neutrinos would have many other fascinating uses. These particles interact little with ordinary matter, so neutronium-collimated beams could be used for point-to-point straight-line communication directly through solid masses such as planets. Objects made of ultradense matter could be “x-rayed“ by neutrino beams focused by neutronium lenses.
Material objects as we know them are held
together by electromagnetic forces.
The nuclei of atoms are held together by
the “strong force,“ which is about 100 times
more powerful than the electromagnetic.
Material objects as we know them are held together by electromagnetic forces. But the nuclei of atoms are held together by the “strong force,“ which is about 100 times more powerful than the electromagnetic. It may be possible to produce neutronium wire utilizing the strong force, spools of which would be many orders of magnitude stronger than any material known to present human science. Another possibility is subnuclear rope or quark thread. Nuclear physicists today believe that all elementary particles are themselves built up from combinations of “quarks“ stuck together by “gluons.“ A macroscopic chain of these subnuclear building blocks, fastened by gluons, should be incredibly strong and thin.
According to theory, monopoles should weigh
together would generate a force 18,000 times
greater than the normal electromagnetic
interaction between two protons.
■ The science of quantum magnetodynamics,
if it ever comes into existence, will deal with
the strongest nuclear interaction imaginable.
Many years ago the famous Italian physicists P.A.M. Dirac hypothesized the existence of magnetic charges analogous to the electron, which he called magnetic monopoles.2823 According to theory, monopoles should weigh more than 200 times the mass of a proton. Physicist Paul B. Price at the University of California at Berkeley has predicted that two monopoles together would generate a force 18,000 times greater than the normal electromagnetic interaction between two protons.2824 The science of quantum magnetodynamics, if it ever comes into existence, will deal with the strongest nuclear interaction imaginable.
Given the high binding energies available in monopole-monopole interactions, there may exist a whole new class of elements we‘ve never seen
* Experimental searches for magnetic monopoles haven't found any yet. See Carrigan,1506 Ross,1499 and the summary of early work compiled by Karlssen.1513
Chunk of metal size of a pen
Its continuous energy output:
Imagine a chunk of dense grey metal, roughly the size of a fountain pen and weighing less than half a kilogram. Its continuous energy output is nearly 4 megawatts of power, falling off to 2 megawatts after two months have elapsed. Even after a year it is putting out as much heat as a large domestic furnace.
This substance actually exists!81 It is the radioisotope
Subcritical nuclear reactors
■ Normally, atomic fission piles must be
made of a certain minimum [critical] size.
■ This is because the neutrons which initiate
fission reactions arise randomly from
within the fissionable material itself.
■ There is some evidence that nonstatistical
means for controlling neutrons may exist.
■ Thus controlled, neutron emission would
no longer be random and vastly improved
efficiencies should be possible.
|Subcritical nuclear reactors|
Robert Forward has suggested that it might be possible to build "subcritical nuclear reactors."2014 Normally, atomic fission piles must be made of a certain minimum size. This is because the neutrons which initiate fission reactions arise randomly from within the fissionable material itself. But there is some evidence that nonstatistical means for controlling neutrons may exist.2822 Thus controlled, neutron emission would no longer be random and vastly improved efficiencies should be possible. Tiny, portable fission reactors could probably be built to service aircraft and surface vehicles. Reactors using nonradioactive lightweight metals such as beryllium or lithium would also be possible.
There are a number of other unusual energy sources. Although we don‘t ordinarily think of it as such, planetary rotation is an excellent storehouse of energy. The spinning Earth, if slowed to a dead stop, would free about 2.6 × 1029 joules — enough to power human civilization at its current rate of consumption for a billion years into the future. Sol, if similarly halted, would liberate
Although we don‘t ordinarily think of it as
about 2.6 × 1029 joules - enough to power
human civilization for a billion years.
■ Sol, would liberate 1.2 × 1036 joules.
An even better place to store huge
|Hawking black holes|
An even better place to store huge quantities of energy is in rotating chunks of ultradense matter. Hawking black holes would be ideal for the purpose. A 1016 kg HBH would be heavy enough not to evaporate very energetically (only about 16 kilowatts spontaneous), light enough to utilize in a space-based power storage station (mass equivalent to a
A wide variety of new mining techniques can also be imagined. In one of his science fiction novels, Larry Niven speculates on the possibility of specially bioneering organism which he calls “mining worms“:
A mining worm is five inches long and ¼-inch in diameter, mutated from an earthworm. Its grinding orifice is rimmed with little diamond teeth. It ingests metal ores for pleasure, but for food it has to be supplied with blocks of synthetic stuff which is different for each breed of worm — and there's a breed for every metal. … What breaks down the ores is a bacterium in the worm's stomach. Then the worm drops metal grains around its food block, and we sweep them up.231
This idea is not at all farfetched. Various plants and animals are known to be "hyperaccumulators" of specific minerals or metals. For instance, the so-called “copper flower“ native to Zaire has a dry weight that is 1.3% copper.2852 The subject of artificial mining organisms has already been discussed in.
Arthur C. Clarke proposes that subterranean automated probes — “subterrenes,“ as he calls them — be designed to explore and exploit at least the entire crustal region of any terrestrial planet. Burrowing through solid rock using powerful rf radiation, ultrasonics, or laser heating, subterrenes could circumnavigate whole worlds down to depths of hundreds of kilometers, searching for deposits of rare minerals and lodes of precious metals.2841 Says Clarke:
The main problem with materials mined from planets
is that they lie at the bottom of a deep gravity well.
As we have already seen, space is the proper
environment for stellar and galactic civilizations.
So it is far more economical for such cultures
to mine material that is already aloft.
All the scientific observations and collection of samples could be done automatically according to a prearranged program. With no crew to sustain, the vehicle could take its time. It might spend weeks or months wandering around the roots of the Himalayas or under the bed of the Atlantic before it headed for home with its cargo of knowledge.55
|Deep gravity well|
The main problem with materials mined from planets is that they lie at the bottom of a deep gravity well. As we have already seen, space is the proper environment for stellar and galactic civilizations. So it is far more economical for such cultures to mine material that is already aloft.
Asteroid mining is within the abilities even of human Type I technology. The late Dandridge M. Cole and Donald W. Cox once calculated that to move a 3 billion ton iron meteoroid from the asteroid belt to a parking orbit around Earth would require about 8.4 × 1018 joules of energy.563 (Recent analyses put this figure slightly higher.2843) This is the same as two hundred 100-megaton H-bombs assuming a 25% propulsive efficiency.
According to Cole and Cox, a small atomic bomb would be set off near the asteroid's surface to form a crater. Subsequent blasts could then be fired in this crude thrust chamber. Another proposal offered by Gerard O‘Neill is to use a “mass driver“ to propel the flying mountain of metal.2710 Using electromagnetic forces, small pieces of the asteroid would be flung from the driver as reaction mass, propelling the giant mother lode to Earth. A prototype mass driver has already been constructed and was successfully tested at the Massachusetts Institute of Technology in 1977.
Table 19.1 Power, Energy, and Mass Available to Extraterrestrial
Civilizations in Various Stages of Their Development
|Power, Energy and Mass Available to ET Civilizations|
Ultimately the key
Most of the discussion thus far has centered on the technical advances that could be achieved by Type I civilizations. Domiciled on a planet, living space will not be a major problem for such cultures. But emergent Type II societies will find no such ready-made living quarters in orbit. A species that wishes to expand its energy base and move into space must learn how to design and construct its own artificial habitats with a closed ecology and a controlled environment.
Yet ultimately the key to all technological accomplishment is energy. We have discussed this at great length in an earlier, but it is now necessary to make explicit the critical difference between energy and power.
Simply stated, energy defines what a
civilization can do whereas power defines
how fast the civilization can do it.
The distinction is important because the
maximum technical achievement of any
race is energy-limited, not power-limited.
|Difference between energy and power|
Simply stated, energy defines what a civilization can do whereas power defines how fast the civilization can do it. The distinction is important because the maximum technical achievement of any race is energy-limited,
In, in the interests of straightforward exposition, we made the tacit assumption that the rate of hydrogen fusion burning in stars was the maximum rate at which energy could be delivered to a technical culture from its sun. This assumption may not be valid for many advanced extraterrestrial societies.
|Proposed Planetary, Stellar, and Galactic Engineering Projects|
By tampering with the normal
By tampering with its sun, a Type II
Table 19.1 gives the total energy available to each class of civilization. The alert reader will have noticed that the energy figures on the one hand, and the power and lifetime figures on the other hand, cannot be reconciled. The reason for the discrepancy is this: Some alien cultures may choose to use up their total energy reserves in a manner which is far more efficient than a stellar furnace normally permits. In other words, by tampering with the normal processes within its sun a technical civilization can increase the total amount of energy that is available to it. Over its normal lifespan the typical star will convert its hydrogen to energy with a net lifetime efficiency of perhaps 0.06% — a far cry from the 1% efficiency that may be had if the aliens turn off their sun and use their own fusion plants to burn the fuel.
The situation is rather like a suicide mission.
Since shortened life has been accepted, one is
free to devote more resources to the present.
There is much less future to save for.
While this may be viewed as irresponsible by
some, it may also be argued that it is better
to experience a brief but glorious career than
a drawn-out bland existence.
|Increased burn rate|
Furthermore, ETs may elect to burn their hydrogen legacy at a faster rate than natural processes would normally allow. This will inevitably result in a shorter lifetime for the civilization, but this penalty is offset by the grander technological feats which may be accomplished with the vastly greater power expenditure (Table 19.2). To take a simple example: By accepting a lifetime of only one million years, and by tampering with its sun, a Type II civilization should be able to boost its useful power output to 6 × 1031 watts — an increase of nearly six orders of magnitude over the nominal value.
The situation is rather like a suicide mission. Since shortened life has been accepted, one is free to devote more resources to the present. There is much less future to save for. While this may be viewed as irresponsible by some, it may also be argued that it is better to experience a brief but glorious career than a drawn-out bland existence.
In the final analysis, an intelligent race that chooses to expand into space is ultimately limited only by the amounts of energy and raw mass that are available to it.
From the point of view
of a Type II culture
should represent a fairly
If living space is in short supply on the home planet, one logical alternative is to move some of the population and growth activities to other worlds. The typical habitable solar system will have from
Saturn's rings — If water proves to be too
scarce or too difficult to exploit, scientists are ready
with the most grandiose scheme proposed to date.
Saturn's rings are believed to consist primarily of
flying chunks of water-ice. These icy boulders
could be gathered together and welded into “a string
of huge, frozen pearls, each the rival of Phobos.“
Outfitted with propulsion and automated guidance
systems, the caravan of giant icebergs majestically
peel away from Saturn in a long, steep dive sunward.
|Engineering on a grand scale|
Terraforming is a form of planetary engineering on a grand scale. Just as buildings and cities are designed to suit human comfort, it is entirely feasible to consider the modification of planetary environments to suit human (or alien)
There have been many proposals and suggestions as to how to go about terraforming the planets and moons of our own solar system. Only a few of these will be considered briefly here, because it turns out that in all cases the energy and mass requirements are well within the operating budgets of Type I planetary civilizations. In other words, from the point of view of a Type II culture terraforming techniques should represent a fairly primitive technology.
|The Big Rain|
Perhaps inspired by Poul Anderson's short story entitled “The Big Rain,“ published in 1955, Dr. Carl Sagan in 1961 proposed a terraforming project to modify the environment of Venus.1481 Our sister planet has a hellish climate, with temperatures upwards of 750 °C and pressures of 90 atm at the surface. To prepare it for human habitation it will be necessary to lower the surface temperature and pressure, and to elevate by at least two orders of magnitude the fraction of molecular oxygen present in the atmosphere. Most of the air is carbon dioxide, and this must be eliminated as well.
Our sister planet has a hellish climate,
with temperatures upwards of 750 °C
and pressures of 90 atm at the surface.
Sagan suggests the injection of blue-green algae into the Venusian atmosphere at high altitudes where it is relatively cool. These tiny organisms would consume the CO2 by growing more algae cells with water and aerial nutrients. Molecular oxygen would be expired as a waste product. Over a period of several years the carbon dioxide level begins to drop, thus reducing the green-house effect and cooling the planet overall.2633 When the ground was sufficiently cool, cargo landers armed with fusion bombs could be de-orbited and set down on the surface. These machines, able to burrow like moles and detonate beneath the surface, may be used to trigger new volcanic chains in order to help percolate more water into the dry atmosphere.2836 Eventually the first “big rain“ will fall. Says Sagan: "The heat-retaining clouds will partly clear away, leaving an oxygen-rich atmosphere and a temperature cool enough to sustain hardy plants and animals from Earth."
How reasonable is the astronomer's proposal? In 1970 a number of biologists conducted experiments to see if earthly algae would actually grow under the extreme initial conditions found on Venus.2847, 2846 It was discovered that the most suitable strain is Cyanidium caldarium, a single-celled form that is found in hot springs on Earth. This algae produced oxygen vigorously in a hot, high-pressure atmosphere of CO2. In a typical experiment the researchers found that each million algae cells were increasing the oxygen concentration in the test tank by 380% per day.
To terraform the atmosphere of Venus is not a very difficult undertaking from the standpoint of energy and mass requirements. If we dispatch an armada of 500 seeding probes to our neighbor world, each armed with a thousand in-dependently-targetable payload capsules containing 1 ton of Cyanidium caldarium per capsule, this would result in the dispersal of a kilogram of living blue-green algae cells over each square kilometer of the planet's surface. The total mission mass is about 109 kg, and the total energy required is about 1018 joules — both well within the budgetary limitations of a Type I civilization.
The present lunar air has a total mass of about
10 tons. This arises mainly from outgassing from
the interior, without which the entire atmosphere
would quickly be swept away by the solar wind.
If the atmosphere of the Moon was increased
to a mass of at least 100,000 tons it would be
driven into a “long-lived state“ which would
drastically reduce losses to the solar wind.
To produce a breathable “shirtsleeve“
atmosphere, about 1018 kilograms of O2
must be pumped into the lunar environment.
This should require a total energy expenditure
of about 1024 joules.
Small, airless terrestrial worlds such as Luna are also suitable for terraforming projects. Richard R. Vondrak of the Department of Space Physics and Astronomy at Rice University recently suggested a method for creating a comfortable artificial lunar
Vondrak calculates that if the atmosphere of the Moon was increased to a mass of at least 100,000 tons it would be driven into a “long-lived state“ which would drastically reduce losses to the solar wind. According to him:
If one wanted intentionally to create an artificial lunar atmosphere, gases can be obtained by heating or vaporization of the lunar soil. Approximately 25 megawatts are needed to produce 1 kg/sec of oxygen by soil vaporization. [Another] efficient mechanism for gas generation is subsurface mining with nuclear explosives.
A 1-kilotonnuclear device will form a cavern approximately 40 meters in diameter from which 107 kg of oxygen can be recovered.656
To produce a breathable “shirtsleeve“ atmosphere, about 1018 kilograms of O2 must be pumped into the lunar environment. This should require a total energy expenditure of about 1024 joules. Again, both mass and energy figures lie within the budget of an ambitious mature Type I civilization.
Researchers once speculated that the proper
positioning of large masses in orbit around
the planet [Mars] would alter its equinoctal
precession period. This would cause
a perpetual “Spring“ season planetwide.
A wide variety of Martian terraforming techniques have been proposed from time to time. Joseph A. Burns and Martin Harwit of the Center for Radiophysics and Space Research at Cornell University once speculated that the proper positioning of large masses in orbit around the planet would alter its equinoctal precession period.1282 This would cause a perpetual “Spring“ season planetwide, similar to that predicted by Sagan's "Long Winter" model of the Martian climate.1267
One scheme involves pushing Phobos from its present equatorial orbit to a new one inclined 45° to the Martian equator. The total energy required to execute this maneuver would be about 1023 joules. Unfortunately, Burns and Harwit admit, the orbit of Phobos would begin to precess and might foil the entire scheme. Their second proposal involves capturing roughly 25% of the matter in the nearby asteroid belt and using that mass instead of Phobos to swing Mars around. While this might work, at least two orders of magnitude of energy would be required.
Carl Sagan may have hit upon the cheapest way to terraform Mars.1288 He suggests that about 1010 tons of low albedo matter — such as lampblack or dark-colored vegetation — be transported to the permanent Martian polar icecaps over a period of about a century. The caps would be less reflective and would thus absorb more of the sun's energy. The ice would warm and thaw, increasing the atmospheric pressure (and the greenhouse effect) and speeding north-south convective stirring of the planetary atmosphere. A minimum of 1021 joules would be needed to accomplish this feat, and hundreds of years. There are ways to do it faster. An enormous orbiting mirror could be stationed in polar orbit to melt the icecaps by reflected or concentrated sunlight, or thermonuclear bombs could be set off to achieve similar effects perhaps in a matter of decades.1978
A more complete analysis was undertaken
by a study group at NASA-Ames in 1976.
Entitled On the Habitability of Mars: An
Approach to Planetary Eco-synthesis,
The final report of the study attempted
to pin down the specific requirements for
successful terraforming of the Red Planet.
It was concluded that “no fundamental
limitation to the ability of Mars to support
terrestrial life has been identified.“
|On the Habitability of Mars|
A more complete analysis was undertaken by a study group at NASA-Ames in 1976. Entitled On the Habitability of Mars: An Approach to Planetary Eco-synthesis, the final report of the study attempted to pin down the specific requirements for successful terraforming of the Red Planet.1926 It was concluded that “no fundamental limitation to the ability of Mars to support terrestrial life has been identified.“
The scientists proposed a two-pronged attack on the problem. First, atmospheric mass should be increased by vaporizing the polar icecaps or the subsurface permafrost. If the reflectivity of the icecaps was reduced by only 5% for a period of 100 years, a kind of runaway de-ice age might be triggered “and a new high temperature climatic regime established.“ Secondly, mechanisms of genetic engineering currently available or under development could be used to construct organisms far better adapted to grow on Mars than any present terrestrial organism. In principle, the entire gene pool of the Earth might be available for the construction of an ideally adapted oxygen-producing photosynthetic Martian organism.
It was estimated that the creation of an oxygen atmosphere using known terrestrial photosynthetic lifeforms might take hundreds of thousands of years. But by altering the environment of Mars and by seeding it with appropriately bioneered organisms, the length of time to project completion could be reduced a thousandfold. Total energy expenditure for the NASA-Ames scheme: Roughly
Academician N.N. Semenov, a Soviet scientist, suggests that the water locked in permafrost and polar icecaps by subjected to simple electrolysis.2849 Water molecules would be split into oxygen, which could be released into the Martian air eventually to result in a breathable atmosphere, and hydrogen, which could be collected and used for fuel in fusion power plants needed to operate the electrolysis factories. Earthlike air would result from the electrolysis of about 15% of all water believed to be present at the Martian surface, at a cost of about 1023 joules.
|Caravan of giant icebergs|
If water proves to be too scarce or too difficult to exploit, scientists are ready with the most grandiose scheme proposed to date. Saturn's rings are believed to consist primarily of flying chunks of water-ice. These icy boulders could be gathered together and welded into “a string of huge, frozen pearls, each the rival of Phobos.“2828 Properly outfitted with propulsion and automated guidance systems, the caravan of giant icebergs majestically peel away from Saturn in a long, steep dive sunward. What happens next has been eloquently described by Freeman Dyson:
A few years later, the night-time sky of Mars begins to glow bright with an incessant sparkle of small meteors. The infall continues day and night, only more visibly at night. Soft warm breezes blow over the land, and slowly warmth penetrates into the frozen ground. A few years later, it rains on Mars. It does not take long for the first oceans to begin to grow.2829
By staying on planets,
the species condemns
itself to a permanent
Type I energy status.
While we may expect that Type II civilizations will certainly have the energy, mass, and technological sophistication to terraform virtually any terrestrial world in their system, the pressures of population expansion are not long alleviated by inhabiting other planets. Living area is increased by an order of magnitude at best, a bounty gobbled up in only 300 years assuming population expands at the modest rate of 1% per annum. And by staying on planets, the species condemns itself to a permanent Type I energy status.
|Cities in space|
The remedy to this dilemma is to build giant habitats in free space, far from the baleful encumbrances of planetary surfaces. In recent times Gerard K. O‘Neill and others have advocated the construction of enormous artificial habitats in Earth orbit (see especially Heppenheimer,2826 Johnson and Holbrow,2627 and O‘Neill2710) using materials lofted from the lunar surface by electromagnetic mass driver.2844 Preliminary estimates from several sources indicate that it is technically feasible to construct cities in space able to house 10,000 people and having a total mass of about 1010 kg. The main cost in energy comes from pitching the construction materials off the lunar surface. This cost amounts to about 1017 joules altogether. This is low enough to be feasible even for Type I civilizations such as our own — provided we do not build too many of them. A Type II culture, of course, is rich enough to build all of them it wants.
An Island Three community would measure
more than 6 km in diameter and 32 km in length,
with a total land area of 1300 square kilometers
and a human population of several million persons.
Structures up to four times larger are possible
within the limits of current human technology.
These Island Four communities would have land
areas more than half the size of Switzerland, and
populations numbering in the tens of millions
|Island Two community|
After a sufficient number of habitats have been erected in space — which O‘Neill calls Island One communities, the process of expansion would become self-sustaining. A group of Island One communities could pool their resources to form an economic cooperative, and engage in the construction of an even larger Island Two community. This monstrous edifice might be a giant, slowly-spinning cylinder perhaps 2 km in diameter and 6 km in length, housing a total of 140,000 people. The interior could be designed with a number of small villages separated by parkland or forest areas, each similar in size and population density to a small Italian hill
|Island Three and Four community|
Still larger habitats could be built, since there is no gravity in free space to give engineers headaches. An Island Three community would measure more than 6 km in diameter and 32 km in length, with a total land area of 1300 square kilometers and a human population of several million persons. And, according to O‘Neill, structures up to four times larger are possible within the limits of current human technology. These Island Four communities would have land areas more than half the size of Switzerland, and populations numbering in the tens of millions (Figure 19.1).
Hollow planetoid cities, similar in size and mass
to the largest of the O‘Neill communities, could
be constructed in a fairly straightforward manner.
Once the hollow world has solidified and cooled
off, a giant mirror is affixed to direct solar power
down the central axis to bring sunshine to
Water, soil, and biology are now moved in.
More than 780 km2 are available for habitation.
|Hollow planetoid cities|
Many scientists believe that it is wasteful to construct space cities out of lunar materials. It is cheaper, they claim, to use raw materials that are not trapped at the bottom of a gravity well. So, we mine the asteroids.2864 Dandridge Cole and Donald Cox showed in 1964 that hollow planetoid cities, similar in size and mass to the largest of the O‘Neill communities, could be constructed in a fairly straightforward
The first order of business is the erection of a giant solar mirror several kilometers in diameter.2848 Formed under conditions of zero gravity, it could have a very lightweight construction. Perhaps an old Echo balloon could be inflated, sprayed with a thin layer of something to harden it, then cut in half and silvered on the inside.
Next, an elongated asteroid should be selected, perhaps measuring a kilometer in diameter and two kilometers in length with a mass of about 1013 kg. The mirror is then used to bore out a hole down the central axis of the object. This is done by focusing the sun's rays on the mountain of nickel-iron and vaporizing away some of the metal. After it has cooled, the longitudinal hole is charged with large tankards of liquid water. The ends are securely plugged and welded shut using heat from the large mirror.
The planetoid is set spinning slowly around its long axis. The entire metal body is bathed in concentrated solar heat directed at its surface by the mirror. Gradually the temperature rises, finally reaching the melting point all over the surface. Slowly the heat creeps inward until virtually the entire object is molten or soft.
The central axis is the last place to melt if the procedures have been correctly executed. So long as this region remains solid, the melting body retains a cylindrical shape rather than coalescing into a formless spheroid. Just before the central region melts, the axial water tanks explode into super-heated steam. The immense pressure blows the asteroid into a giant nickel-iron balloon some 10 km in diameter and 20 km in length.
|Sunshine to the interior|
Once the hollow world has solidified and cooled off, construction crews affix the giant mirror to one end and direct solar power down the central axis to bring sunshine to the interior. Water, soil, and biology are now moved in. More than 780 km2 are available for habitation.
Life would be interesting inside a large O‘Neill community or Cole planetoid. The horizon, and landscape, rises overhead in the distance. Since only 3 km of air are required to appreciably scatter sunlight, the sky will be blue. If the planetoid is given a slight equatorial bulge and the endcaps are shaded from the sun, perpetual rain and snow will fall at the poles. The ice melt flows down rivers carved into the inside walls into a wraparound central circular lake that rises skyward in a beautiful blue arc at either horizon. Artificial spin-gravity may be set as low as desired, so it is possible to don a pair of wings and take to the air like birds.2429
Table 19.3 Energy Requirements for Planetary,
Stellar, and Galactic Transport Operations
They will have
We are still thinking small, unfortunately.* We have not yet mentioned a single engineering project that could not be successfully mounted by a Type I planetary culture, at least in theory. A Type II society living in the space surrounding its sun will be a proud, vigorous, expansive large-scale civilization. They will have magnificent dreams, and their technology will not lag far behind their ambition.
A stellar culture will have access to the entire mass and derivable energy from all the matter in its own solar system. From Table 19.1 we have already seen that this represents considerable potential for energetic economic development of interplanetary space. Theoretically, a stellar society has at least 1030 kilograms and more than 1043 joules to play around with.
How grand may be their monuments to civilization? As even terrestrial engineers are well aware, any construction project has two basic requirements: (1) Delivery of materials to the construction site, and (2) proper deployment of those materials once they have arrived. So what can Type II cultures do?
While the technology needed to move planets and stars around is absolutely huge when measured against the normal human scale, the energy requirements for such operations turn out to be well within reach of Type II civilizations.
While the technology needed to move planets and
Asteroid and planet-moving are no real problem.
The complete fusion combustion of all the
If the hotter-burning hydrogen fusion reactions
Table 19.3 above shows the energies necessary to move several different kinds of bodies. Values are given both for solar escape velocity
Clearly, asteroid and planet-moving are no real problem. The interstellar transport of stars will give Type II societies some trouble, and it may take a Type III organization to perform the maneuver gracefully.
Darol Froman, Technical Associate Director of the Los Alamos Scientific Laboratory in New Mexico, has pointed out that the complete fusion combustion of all the deuterium in Earth's oceans would be insufficient to impart solar escape velocity to the planet.2831 If the hotter-burning hydrogen fusion reactions are used, however, Earth's seas could be drained and used as fuel to propel our world to the stars.
Froman suggests that roughly a quarter of the fuel be used to escape from Sol, another quarter to enter the target stellar system many light-years away, and the remaining half for heat, lighting, and propulsion en route. The planetary fusion thrusters should be located at the South Pole, so that Earth's natural rotation can be used for guidance and directional stabilization. Science fiction writer Stanley Schmidt has done a creditable job in describing the local effects of terramotive operations.2832
* A sobering example of this appears in Isaac Asimov's Foundation Trilogy.2944 Trantor, the Imperial capitol of all the Galaxy, is described as a giant ecumenopolis, a “planetary city“ of gleaming metal covering 190 million km2 (about the surface area of Mars) and extending nearly 2 km deep.
- There are 40 billion human bureaucratic inhabitants.
- This seems a rather impressive piece of architecture, especially since each person would have a generous 107 m3 all to himself which is at least two orders of magnitude more room than most people have on Earth today.
- But the mass and energy requirements are far less impressive. If made of steel the total mass of the city of Trantor would come to about 1019 kg. Only a million average-sized asteroids need be captured for this purpose, and only about 1026 joules would be required to transfer them to the site of construction — say, Eart orbit. (This is the major energy cost of the project.)
- So mighty Trantor, pride of the Galactic Imperium and capitol world of the entire Milky Way, could be constructed with some difficulty by a mature Type I civilization or with ease by a Type II civilization.
|Fusion Pogo Rocket|
How might gas giants be pushed around the solar system? We know Type II societies have the energy, but what kind of technology might be involved? In one of his science fiction tales of the distant future, Larry Niven describes how it might be possible to use what he calls a Fusion Pogo Rocket. A tremendous fusion motor hooked up to a reworked military laser cannon might turn the trick on our Uranus:
It's a double-walled tube, very strong under expansion shock. It floats vertical in the upper air. Vents at the bottom let in the air, which is hydrogen and methane and ammonia, hydrogen compounds, like the air that the sun burns. You fire laser cannon up along the axis, using a color hydrogen won‘t let through. You get a fusion explosion along the axis, and the explosion goes out and up. The whole mass blasts out the top, through the flared end. It has to have an exhaust velocity way higher than Uranus's escape velocity. The motor goes smashing down into deeper air. You see there's a kind of flared skirt at the bottom. The deep air builds up there at terrific pressure, stops the tube and blasts it back up. You fire it again... The atmosphere is fuel and shock absorber both — and the planet is mostly atmosphere.2636
Stars, too, may be moved about, using a tuned
Shklovskii Mining Graser at reduced power.
This powerful gamma-ray laser could be aimed
to strike a glancing blow at the target star on the
side opposite the direction you want it to move.
The sun will spew out star-stuff and begin to move off
in the direction dictated by Newton's laws of motion.
|Interstellar transport of stars|
Stars, too, may be moved about, using a tuned Shklovskii Mining Graser (see next page) at reduced power. This powerful gamma-ray laser could be aimed to strike a glancing blow at the target star on the side opposite the direction you want it to move. The sun will spew out star-stuff and begin to move off in the direction dictated by Newton's laws of motion. Scientists agree that this technique may work, because the same basic principle of propulsion has been observed to occur naturally with comets. These “dirty snowballs,“ swinging close to our Sol, are heated on the sunward side. Material boils off asymnietrically and jets out into space, deflecting the orbit by a kind of rocket effect.*
So delivery of the materials to the construction site is no problem for stellar cultures. What about deployment? Once a planet or star has been moved to where it is needed, how do we get the mass out?
One of the most popular techniques for taking
planets apart is called centrifugal disruption.
This requires the accelerated rotation of a planet up
to the point at which it fractures under internal stresses.
When the rotation rate of a planet the size of Earth has
been brought up to about 100 minutes per revolution,
the equator is just ready to take off into space.
The process of disassembling the planet will proceed
steadily as its angular momentum is increased.
One of the most popular techniques for taking planets apart is called centrifugal disruption. This requires the accelerated rotation of a planet up to the point at which it fractures under internal stresses. Slowly the world unravels, sloughing off outer layers like a successive molting. If the speed-up is continued long enough, the entire body will be disrupted into asteroid-sized chunks of mass.
Freeman Dyson has suggested that centrifugal disruption could be accomplished by laying a net of conductive windings around a planet along the lines of latitude, each strand carrying a current on the order of microamperes per square centimeter.1450 These cables would give rise to a magnetic field. Orbiting electrical generators (which produce an opposing magnetic field) then trace out paths which produce a net torque on the body, causing it to spin faster. A continuous stream of generators must pass through the correct maneuvers to maintain the electromagnetic accelerative force, each unit converting its orbital momentum into planetary spin momentum. An alternative disruption technique is available to civilizations that have mastered fusion power — simple tangential reaction thrust generated by sideways-firing equatorial fusion rockets would also spin up a world to destruction.2833
When the rotation rate of a planet the size of Earth has been brought up to about 100 minutes per revolution, says Dyson, "the equator is just ready to take off into space. From this point on, the process of disassembling the planet will proceed steadily as its angular momentum is increased." The total energy required to spin Earth up to the transition point is about 4 x 1030 joules; for Jupiter, about 9 × 1034 joules will be necessary. (After 97% of Jupiter's mass has been stripped away, we are left with a large terrestrial world that was once the core of the jovian — a mass of from 5-10 Earth-masses. We may decide to cannibalize it for heavy metals, or it may be saved for reasons of aesthetics, nostalgia, or terraforming and habitation operations.)
Gas giants disassembled bit by bit
Suborbital fusion satellites and nuclear ram-scoops
■ could dip down into the jovian atmosphere,
■ scoop up some hydrogen,
■ fuse it into heavier elements,
■ use the resulting energy to propel the transmuted
matter into a parking orbit near the construction site.
J.H. Fremlin and Anthony Michaelis have suggested that gas giants could be disassembled bit by bit.2955 Suborbital fusion satellites and nuclear ram-scoops could dip down into the jovian atmosphere, scoop up some hydrogen, fuse it into heavier elements, and use the resulting energy to propel the transmuted matter into a parking orbit near the construction site. The energy needed to move Jupiter's entire mass into an Earth parking orbit along a minimum energy transfer trajectory is about 1036 joules.
Still a third possibility is Explosive Disruption. Theoretically, with enough energy under harness any planetary body can quite literally be blasted into rubble. While we don‘t know what kind of explosive device might be used (perhaps a 6-km-wide antimatter asteroid?), it is a simple matter to calculate how much energy would be required. The total energy to disrupt a world expIosively is on the order of its gravitational potential energy. This works out to about 2 × 1032 joules for Earth and 2 × 1036 joules for Jupiter. Again, no problem at all for Type II cultures.
* Galaxy-moving should be possible for Type III civilizations using a related technique. Synchronized application of the Graser to a few percent of the stars in a galaxy would cause billions of suns to move off in the preferred direction. The rest of the galaxy, bound to the moving stars by gravity, would slowly follow.
The Mining Graser will
In a related manner, stars too may be disassembled. The energy required to blow a sun to bits by brute force explosive disruption is about 2 × 1041 joules, which would be quite a challenge for an enterprising stellar society. But this is not very elegant. The renowned Soviet astrophysicist Iosef S. Shklovskii has considered the possibility that an artificial supernova might be induced in a single star.20 Shklovskii believes that a Type II civilization should have no difficulty constructing a gigantic gamma-ray laser (or “graser“) operating at a wavelength of 1 Angstrom and at power levels of at least 1015 watts. This Mining Graser (Figure 19.2) would have a forward aperture diameter of about 10 meters and could focus on a 10-km-wide spot at a star's surface from a safe distance of 10 light-years. (Unmanned automated devices can venture closer.) The Mining Graser will probably be “self-critical“ — that is, an enormous nuclear reactor that emits most of its laser energy directly as coherent light.284)
According to an astrophysical theory proposed by British astronomer Geoffrey Burbidge, a concentrated gamma-ray flux should cause exceedingly high temperatures to arise in the outer layers of a star. If this temperature was hot enough, a spontaneous supernova might result. It is estimated that a flux of
When this occurred, perhaps 0.1% of the star's mass would be converted directly into energy — about 1043 joules. In addition to the release of copious amounts of x-rays and other radiative energy that could be collected and stored, a significant fraction of the stellar mass will be propelled outward at speeds up to 1000 km/sec.
The beam strikes a glancing blow first on one side,
then the other.
Star-stuff spews equally from either side,
so the sun goes nowhere.
Sweepships collect and store the unburned stellar
hydrogen as it streams from the photo-sphere.
Slowly the star is whittled down to size as the
bulk of its mass is siphoned off and taken away.
This rich expanding gas cloud may be harvested by diligent interstellar mining engineers, using squadrons of robot drones equipped with giant electromagnetic ramscoops. Heavy elements generated by the explosion would be swept up, refined and milled by a flotilla of gargantuan factory sweepships in a "cage" of circular orbits surrounding the demolished star.
|Turn stars off|
The Shklovskii Mining Graser can also be used to turn stars off. The beam strikes a glancing blow first on one side, then the other, and so forth. Star-stuff spews equally from either side, so the sun goes nowhere. Sweepships collect and store the unburned stellar hydrogen as it streams from the photo-sphere. Slowly the star is whittled down to size as the bulk of its mass is siphoned off and taken away. Finally, down to less than 1% of its original weight, the once-mighty celestial furnace flickers out. The hot jovian planet that remains may now be disassembled by the more conventional means discussed earlier.
The Sphere is massive
about 15 solar masses.
Assuming a Type II civilization can find all the materials and energy it may require, normal expansive development and material growth may proceed. As it matures, the stellar culture may place more and more artifacts in solar orbit in an attempt to soak up every last joule of the sun's output. They may not want to go to the trouble of turning their star off, or they may lack the technological acumen to do it, or they may find the idea unethical, unnatural, and morally repugnant.
"a ping pong ball with a star in the middle"
■ If the entire planetary mass of Sol's system was
■ the resulting artifact would run a bit less than
■ The interior surface area would be the equivalent
■ about three hundred million billion square kilometers
So while it is not inevitable, the chances are good that at least some extraterrestrial Type II cultures wish to preserve their sun in its natural state. On the basis of this assumption, Freeman Dyson predicted more than twenty years ago that the end result of interplanetary industrialization may be a shell of artifacts completely encasing the star. Seen from a great distance this "Dyson Sphere" would radiate only waste heat at a wavelength of about 10 µm in the deep infrared.1022
Theoretically, a normal solar system should have plenty of mass with which to construct a solid Dyson Sphere around a star. (At least one writer has likened this to "a ping pong ball with a star in the middle."673) If the entire planetary mass of Sol's system was spread into a solid shell at the radius of Earth's orbit, the resulting artifact would run a bit less than 10 meters thick. The interior surface area would be the equivalent of a billion Earths, about three hundred million billion square kilometers of habitable land.
|Mechanical difficulties of the Dyson Sphere|
There are a number of mechanical difficulties associated with the solid Dyson Sphere. If rotating, the equatorial section would bow outward due to centrifugal force. Similarly, the "poles" would lack support and flatten, causing dynamic instability and collapse of the structure. If stationary, solar tidal forces would give rise to large compressive stresses.* The shell seems too thin to maintain proper rigidity. Furthermore, the gravity on the outer surface would be only 0.6 milligees so no reasonable atmosphere could be held. Objects or gases or people living on the inside would fall gently into the sun. There have been many attempts to save the Sphere by positing antigravity devices at critical points along the surface, but these heroic efforts remain unconvincing. For a Type II society, at least, a solid Dyson sphere is out of the question.
The Square-Cube Law predicts that we'll get more
square meters of living area out of each kilogram
of building materials used if we construct the smallest
habitable structures possible.
Dyson himself proposed that the Sphere should be
comprised of swarms of relatively small space habitats.
Anyway, the Square-Cube Law predicts that we'll get more square meters of living area out of each kilogram of building materials used if we construct the smallest habitable structures possible. For this reason, Dyson himself proposed that the Sphere should be comprised of swarms of relatively small space habitats. If we use Cole Planetoids equipped with large, very thin solar collector mirrors, we could build about 1014 of them interior to Earth's orbit. Each would weigh about 1013 kg, and could be pressurized with a breathable oxygen atmosphere. If they were constructed with a doubling time of 25 years, only 1200 years would be required to complete the transition to a mature Type II stellar industrial civilization.
* This may not be fatal to the project. According to equations for gravitational tidal stress on large structures provided by Dyson,1450 the minimum materials strength needed to hold a solid Dyson Sphere together should be no more than 1012 N/m2. Flawless diamond has a theoretical maximum compression strength of ~1012 N/m2 and shearing strength ~1011 N/m2 so it may be possible to work something out.2838 At compressions above 1011 N/m2, the normally colorless diamond takes on a delicate light brown color.2939
a great ribbon of matter
with the same diameter
Larry Niven has come up with a fascinating alternative to the Dyson Sphere. His proposal: A giant Ringworld (Figure 19.3), a great ribbon of matter shaped like a hoop with the same diameter as Earth's orbit.753 The great structure whirls around the sun at 1240 km/sec to provide a constant 1-gee gravity across the Ring. If the entire planetary mass of our solar system was used, the Ringworld would measure about 1000 meters thick. At last — a project truly worthy of a stellar culture.
Walls 2000 kilometers high at either edge of the Ringworld ribbon, aiming toward the central star, would be enough to hold in most of the atmosphere. An inner ring of shadow squares — orbiting panels to block out parts of the sunlight — provide a day/night cycle for Ringworld inhabitants. By bobbing the structure up and down, the apparent angle of the sun changes and we get seasons. You could even see the stars, as well as a beautiful checkered arc, traversing the nighttime sky.
The interior surface area would be equivalent to three million Earths, and the artifact would require on the order of 1036 joules to assemble — a project well within reach of a Type II civilization. The engineering effort would necessarily be a massive one. Looking at the outer surface of the Ringworld, Niven says:
The Niven Ringworld
Click for Synopsis
Seas would show as bulges, mountains as dents. Riverbeds and river deltas would be sculptured in; there would be no room for erosion on something as thin as a Ringworld. Seas would be flat-bottomed — as we use only the top of a sea anyway — and small, with convoluted shore lines. Lots of beachfront. Mountains would exist only for scenery and recreation. A large meteor would be a disaster on such a structure. A hole in the floor of the Ringworld, if not plugged, would eventually let all the air out, and the pressure differential would cause storms the size of a world, making repairs difficult.673
More than one Ringworld could circle a sun, although this would require additional mass borrowed either from the local star or from a neighboring system. Many different intelligent races could wrap noncoplanar Ringworlds around the same star, with differing radii to avoid collision and provide a variety of temperature regimes.
A strand of hollow metal macaroni
■ About a trillion meters long
■ Only a kilometer or two in cross-sectional diameter
■ And a few hundred meters thick
The two ends are joined together
A great hoop around the sun
■ It rotates in smoke ring fashion
to get artificial gravity on the inner surface
■ With a complete artificial biosphere set up inside
■ And solar collectors set up outside for energy
■ This huge tunnel world would have a habitable
surface area of only about 20 Earths
■ Each one we make costs only about 3 × 1027 joules
■ Weighs about one-thousandth as much as the Earth
|Interstellar travel on Ringworld|
There is also the possibility of harnessing the basic Ringworld structure for interstellar travel on a massive scale. Niven elaborates:
The Ringworld rotates at 1240 km/sec. Given appropriate conducting surfaces, this rotation could set up enormous magnetic effects. These could be used to control the burning of the sun, to cause it to fire off a jet of gas along the Ringworld axis of rotation. The sun be-comes its own rocket. The Ringworld follows, tethered by gravity. By the time we run out of sun, the Ring is moving through space at Bussard ramjet velocities. We continue to use the magnetic effect to pinch the interstellar gas into a fusion flame, which now becomes our sun and our motive power.673
Pat Gunkel has designed a structure analogous to the Ring but of considerably lower mass. Imagine a strand of hollow metal macaroni, about a trillion meters long but only a kilometer or two in cross-sectional diameter and a few hundred meters thick. Gunkel joins the two ends together in a great hoop around the sun, sets it rotating in smoke ring fashion to get artificial gravity on the inner surface, and calls it Topopolis.673 With a complete artificial biosphere set up inside, and solar collectors set up outside for energy, this huge tunnel world would have a habitable surface area of only about 20 Earths. But each one we make costs us only about 3 × 1027 joules and weighs only about one-thousandth as much as the Earth.
So far we've discussed projects for Type II civilizations. Let's have a look at a few designs that will require the muscle of a galactic Type III civilization.
The Alderson Disk
Useful living surface would
be the equivalent of more
than 4 billion Earths.
Dr. Daniel Alderson proposes a massive structure shaped like a giant phonograph record with the star in the center hole (Figure 19.4). Gravity will be uniform and perpendicular to the Disk everywhere except at the edges. A slow spin should partially counteract the sideways inward pull of the central star and provide a stable celestial pole. A 1000-km-high retaining wall should be constructed on the lip of the inner hole, to prevent the leakage of atmosphere into the sun.673
The Alderson Disk weighs in at about 6 × 1033 kg, or about 3000 solar masses. The innermost radius is about 50 million kilometers, just inside the orbit of Mercury; the outermost radius is set at 600 million kilometers from the sun, about midway between the asteroid belt and Jupiter. The Disk is 5000 km thick, so the surface gravity is 0.14 gees (about like Luna). If the air is pressurized to 1 atm at the surface, then the total weight of the atmosphere is only 2 × 1029 kg, less than one-tenth of a solar mass extra. Since gravity is so low, the air thins out very slowly with altitude: 40 kilometers up, the pressure is only down to 0.5 atm which is still breathable. Also, note that both sides of the artifact can be inhabited.
The Alderson Disk
Click for Synopsis
Since the Disk is far more massive than the central star, the sun should be bobbled up and down to create seasons. Computer-controlled Shklovskii Grasers mounted on the inside edge could induce vertical motion, and would also serve to nudge the star back to center if it begins to stray towards the inside annular edge of the Disk. The energy required to assemble the Alderson Disk should be about 5 × 1044 joules, which should be fairly trivial for a galactic culture.
One science fiction writer waxes enthusiastic about the idea:
The Disc would be a wonderful place to stage a Gothic or a sword-and-sorcery novel. The atmosphere is right, and there are real monsters. Consider: We can occupy only a part of the Disc the right distance from the sun. We might as well share the Disc and the cost of its construction with aliens from hotter or colder climes. Mercurians and Venusians nearer the sun, Martians out toward the rim, aliens from other stars living wherever it suits them best. Over the tens of thousands of years, mutations and adaptations would migrate across the sparsely settled borders. If civilization should fall, things could get eerie and interesting.673
Due to its size, the Alderson Disk would probably have to be a cooperative venture of a group of Type II cultures (perhaps 10-100 of them) or of a single emergent Type III galactic civilization. The additional land area made available is enormous. The useful living surface would be the equivalent of more than 4 billion Earths.
The Sphere is massive
— about 15 solar masses
■ The shell is equivalent to a wall of
solid steel more than 3 km thick
■ Much of the room is taken up by
living quarters, passageways, etc.
■ The hull is more than 60 km deep
■ The total energy needed to assemble:
probably run on the order of 1043 joules
■ To propel it through space at 17%c
(the stated velocity)
will require an additional 4 × 1046 joules
■ Surface gravity is only 1% that of Earth
■ Enough to hold a tenuous atmosphere
just above the external armor plating
■ Part of this is interstellar gas, but
most of it is a helium-oxygen mixture
left over from nuclear power plants
which use water for fuel
■ The oxy-helium air is barely breathable
at the lower altitudes
The value of large-scale economic cooperation is fairly obvious. Perhaps, in view of this, we should take a second look at the solid Dyson Sphere concept. Is it possible for a galactic community to build one?
Probably. It will be recalled that the main problem, other than simple lack of mass, was the matter of dynamical instability. Even if the hollow sphere was rotated fast enough to support the equatorial zone of the structure against collapse, the polar regions would fall in and destroy the Sphere. Veteran science fictioneers Jack Williamson and Frederick Pohl pondered the problem and came up with a most ingenious, workable solution. Here, in their own words, is how it's done:
Surround the star with several layers of ring-shaped tubes. The tubes themselves are stationary, but they contain a heavy, low-viscosity fluid flowing fast enough to create the centrifugal force required to support the tubes and loads above them. One set of parallel tubes holds up the “equator“ — which isn‘t really moving — and other sets, tilted at suitable angles, support the regions near the “poles.“ The tubes are also heat engines, with the fluid driven by energy absorbed from the sun and flowing through generator stations which supply power to all the inhabited levels. Master computers adjust the velocity of flow to fit the loads.2834
The Sphere is massive — about 15 solar masses. The shell is equivalent to a wall of solid steel more than 3 km thick, but since much of the room is taken up by living quarters, passageways and so forth, the hull is actually more than 60 km deep. The total energy needed to assemble the Sphere would probably run on the order of 1043 joules, but to propel it through space at 17%c (the stated velocity) will require an additional 4 × 1046 joules of energy.
Though the surface gravity is only 1% that of Earth, this is still enough to hold a tenuous atmosphere just above the external armor plating. Part of this is interstellar gas, but most of it is a helium-oxygen mixture left over from nuclear power plants which use water for fuel. The oxy-helium air is just barely breathable at the lower altitudes, with predictable consequences:
The outer surface was at first an endless plain of bare metal, but much of it is now covered with soil from accumulated cosmic dust and the industrial wastes dumped from the occupied levels. Plant life has evolved there, supported by the energy-flow from below through a process of thermosynthesis. These plants are often luminescent, so that vast landscapes glow with varied color. There's animal life, adapted to the low gravity and to varied local conditions of light or darkness, heat or cold, wild storms or unending calm — with no rotation and no external sun. Most of these beings evolved on the surface, but some are migrants from below. A few are human.2834
Figure 19.5 The Megaring
What kinds of projects would really tax the abilities of a Type III civilization? Galactic cooperation among literally billions of worlds will permit construction on a scale never before dreamt of by mankind. From our limited terrestrial perspective, there is no way that we can easily imagine the technical skills of a race which commands nearly twenty five orders of magnitude more energy than we. Nor can we imagine the legitimate rationale, if any exists, for building such massive architectures. Fortunately, we can make a few educated guesses what might be possible based solely on the limitations of finite energy and mass resources. No matter how big and how powerful, every culture has its limits.
A good example of a galactic megastructure which humans have no idea how to build is the Megaring (Figure 19.5). Megaring is a mammoth ringworld stretching twenty light-years in diameter. The flat habitable surface is a million kilometers wide, with 60,000-km-high atmospheric retaining walls at the edges. The surface gravity of 1 milligee is slightly augmented by the 0.03 milligee acceleration caused by the rotation of the artifact: Megaring rotates at 10%c.
Click for Synopsis
The air pressure at the base of the Megaring floor is a normal 1 atm, and falls to 0.5 atm only at a height of 6000 kilometers. A man weighing 70 kg on Earth would weigh 70 grams on Megaring. If he could jump 1 meter on Earth, he can leap at least a kilometer on Megaring — and it will take him 7½ minutes to come back down. Still more fascinating, the gravity is low enough and the air thick enough that mankind could fulfill one of its oldest and dearest dreams: A human being could take to the air from a standing start and fly as a bird, simply by flapping his arms like wings. And he could soar literally thousands of kilometers high.
Perhaps not surprisingly, most of the mass of the Megaring is air. About 330 solar masses are used in the structural frame, which is then filled with 3130 solar masses of atmosphere. The ring itself constitutes a mere 3% of the total system weight. Most of the mass — some 126,000 solar masses worth — consists of non-disassembled stars. More than a hundred thousand suns circle the Megaring in helical orbits at a distance of 1 AU. (More accurately, the ring orbits the stars and so must be extremely flexible — but let's not quibble about dynamics.) Held in place by graser assemblies or powerful magnetic fields, this circulating stellar bucket brigade provides Megaring inhabitants with warmth and illumination.
The total energy cost of this project is somewhere in the neighborhood of
Figure 19.6 The Big Megaring
|The Big Megaring|
Leaving aside all considerations of ethical energy use, and considering only mass-energy consumption and ignoring structural and construction details, still grander projects are possible in principle, but they will sorely strain the resources of a single Type III civilization. The Big Megaring (Figure 19.6) is a ringworld a thousand light-years in radius, spinning majestically at 10%c along the circumference. Due to the extremely low floor gravity (measured in tens of microgees), the breathable atmosphere doesn‘t drop to half-pressure for many tens of millions of kilometers. As a result, the basic shape of the habitat changes. Rather than a thin ribbon, the Big Megaring more closely resembles the outer section of a very thin canister of movie film — a kind of hollowed-out Alderson disk, 600 million kilometers wide and a million kilometers deep with kilometer-thick walls.
The Big Megaring
Click for Synopsis
Again, the mass of the air predominates. The Big Megaring structure takes only 34 million solar masses, but 3 billion solar masses of air are needed to provide 1 atm base pressure. The estimated assembly energy is 1051 joules, not counting the quasar which has been moved to the center for heat and light. While the construction of the Big Megaring seems a vast undertaking indeed, a galactic culture will have both the mass and the energy to do the job. There may be quite sound reasons for designing a gigantic space habitat which affords a living area equivalent to 130,000 trillion Earths or more than 240 million Dyson Spheres.
Click for Synopsis
An even bigger artifact is the Megadisk, a scaled up version of the Alderson Disk. The radius of the central hole is 1 light-year, and the distance to the outer edge is 10 light-years. The design is that of a “floppy disk“ configuration, as the base structure is only 100 kilometers thick. The total weight is 11 galactic masses
Click for Synopsis
The Megasphere is probably the ultimate in biosphere engineering. It is a Dyson Sphere 200 light-years in diameter, with a surface area of more than 130,000 square light-years. The surface gravity is measured in milligees, and the air pressure falls to half about 6500 kilometers from the surface. The base structure is 10 kilometers thick, and both sides are equally habitable.
The Megasphere is far beyond the resources of Type III civilizations. About 1300 galactic masses are needed as raw materials, and 1056 joules are required for initial assembly. Over a billion year span of time, another 1056 joules must be expended simply to maintain the Megasphere at a comfortable 25 ºC. The bill for upkeep is staggering. Only an emergent Type IV universal civilization would dare such an incredible feat.*
|Still larger structures|
* In theory, larger structures are possible. For instance:
- A 2000-light-year-diameter Big Megasphere could be constructed with 4000 galactic masses and a thickness of 1 kilometer.
However, if the air pressure at the surface is more than 0.01 atm (about like Mars):
- The Big Megasphere is smaller than its Schwartzchild radius and thus becomes a black hole.
- This should not adversely affect its habitability.
- However, all journeys to it will be one-way unless tachyonic propulsion is available.