Subject: Space-tech Digest #76 Contents: Henry Spencer Re: space farm Bill Davidsen Re: space farm Keith Henson Re: space farm/starflight Brian Yamauchi Nanotech and Spaceflight Keith Henson Re: Nanotech and Spaceflight (long article) ------------------------------------------------------------ From: henry@zoo.toronto.edu Date: Tue, 27 Nov 90 23:35:09 EST To: space-tech@CS.CMU.EDU Subject: Re: re space farm > Bio2 exchanges light and heat with the outside and it also draws > electric power for air conditioning; otherwise the system is sealed > during experiment runs. This is very much what, for instance, a Moon > colony would do... Nonsense. A Moon colony sits on top of 16 billion cubic kilometers of outside resources; there is no reason why it needs to be independent of the outside, and every reason to rely on outside resources substantially. The Bio2 experiment is of some long-term interest for large space colonies. It is, as Keith commented, of no relevance whatsoever to near-future efforts, even under an optimistic model of what "near future" means. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Wed, 28 Nov 90 08:30:55 EST From: crdos1!davidsen@crdgw1.ge.com To: space-tech@CS.CMU.EDU Subject: Re: re space farm > Nonsense. A Moon colony sits on top of 16 billion cubic kilometers of > outside resources; there is no reason why it needs to be independent of > the outside, and every reason to rely on outside resources substantially. Applies to long term space flight, too. I'm thinking of a mission to several of the nearest stars using current tech. -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) VMS is a text-only adventure game. If you win you can use unix. ------------------------------ From: portal!cup.portal.com!hkhenson@Sun.COM To: space-tech@CS.CMU.EDU Subject: Re: re space farm/starflight Date: Wed, 28 Nov 90 09:35:53 PST X-Possible-Reply-Path: hkhenson@cup.portal.com bill davidsen (davidsen@crdos1.crd.GE.COM) writes: (re Henry Spencer's comments re space farm) >I'm thinking of a mission to >several of the nearest stars using current tech. Why bother? I am as ardent an interstellar fan as they come, but *I* sure wouldn't start out given the current state of the art. Be like crossing the Atlantic in a leaky row boat. Want to do something useful, work on nanotech or do some planing on how you would deal with either political problems in that era or technical ones. Since it has been published, (New Destinies, fall '90) I could post an article Nanotechnology and Megascale Engineering if most of you have not seen it. Has some on this topic. Keith Henson ------------------------------ To: space-tech@CS.CMU.EDU Cc: yamauchi@cs.rochester.edu Subject: Nanotech and Spaceflight (was Re: re space farm/starflight) Date: Wed, 28 Nov 90 14:26:13 -0500 From: yamauchi@cs.rochester.edu Keith Henson writes: >I am as ardent an interstellar fan as they come, but *I* >sure wouldn't start out given the current state of the art. >Want to do something useful, >work on nanotech Is there anyone working on the "exploratory engineering" (as Eric Drexler calls it) for applications of nanotech to space exploration and/or development? Anything beyond general speculations? Yes, it would be nice to have diamond hulls and spaceships grown in nanotech vats, but the important question is "What are the scientific and engineering problems that need to be solved in order to make this possible?" Do we need general-purpose, self-replicating assemblers first? Or will some more limited form of nanotech be sufficient? _______________________________________________________________________________ Brian Yamauchi University of Rochester yamauchi@cs.rochester.edu Computer Science Department _______________________________________________________________________________ ------------------------------ From: portal!cup.portal.com!hkhenson@Sun.COM To: space-tech@CS.CMU.EDU Subject: Re: Nanotech and Spaceflight (long article) Date: Thu, 29 Nov 90 01:59:33 PST X-Possible-Reply-Path: sun!portal!cup.portal.com!hkhenson Nanotechnology and Megascale Engineering (or Party Animals Loose in Space!) By H. Keith Henson [This is close to the final version published in the Fall '90 edition of Jim Baen's New Destinies magazine. By the way, there are two other items in that issue which make it well worth the price, a short "Thus I Refute Kafka" by John Ordover, and "The B2 Lottery" by Marc Steigler. Copyright (c) 1990 Keith Henson. Permission is given to reproduce in electronic form provided this notice is included. Contact the author (hkhenson@cup.portal.com) for other forms.] What will we be able to do with nanotechnology tools and nearly unlimited lives and wealth? Will we reshape planetary systems and stars, and change the courses of galaxies? Will someone accidentally convert an entire galaxy to beer cans? I first began hearing about molecular scale construction from my old friend and fellow advocate of space colonies, Eric Drexler over 10 years ago. It is only since the publication of his book, _Engines of Creation_ in '86, that the ideas (memes) of a nanotechnology future have spread out much beyond Eric and his close associates. I'm sure most of you have noticed that SF stories have begun to use a nanotechnology background, even as they used the L5/space colony concepts in the 1970s. When Dr. O'Neill's space colony ideas were first published in 1974. They sparked a new view of the future, and changed the background on which a lot of science fiction was painted. The L5 background was easy for writers and readers to work with, because other than being translated to inside out worlds at L5, everything from social systems to farming was left almost the same. I was always comfortable with stories based around the old (choke!) space colony ideas. A nanotechnology world is much harder for even SF writers to grasp. It offers many of the attractive features of O'Neill colonies: new lands, personal involvement, and grand adventure. It has a significant advantage for those of us who are galloping through middle age--our age need not bar us from personal participation. Yet, in spite of the obvious attractions this view of the future holds, the technical and social changes are so radical that it took years of exposure to the concepts before I finally became comfortable with them. _Most_ people who do adjust take a long time. Perhaps for this reason, nanotechnology has yet to spark an "L5-like" social movement, though one could argue that the recent rapid growth of cryonics is being caused by nanotechnology memes. You can see that exposure to nanotechnology has caused a wrenching readjustment of my world view from the fact that I am signed up for cryonic suspension, and no longer believe that any significant number of us will get into space by "conventional" (non-nanotech) means. In spite of that, I still put a little effort into the political and economic aspects of space (habit, I suppose). I have wanted to explore space since my mother read Heinlein's _Farmer in the Sky_ to me when I was 8 years old, and I still do. But conventional advances leading to a breakout into space have kept receding into an ever more remote future, probably well beyond my unaugmented lifetime, while the nanotechnology breakthrough seems to be looming over the horizon. The future I now see for space exploration--and the ordinary person's chance to take part in it--is much brighter than the old L5/space colony paradigm. So just what is the "nanotechnology breakthrough," what relation does it have to exploring space, and what do either have to do with "MegaScale Engineering" anyway? THE ULTIMATE TOOL The key to nanotechnology is the replicating assembler, a microscopic, complex device with the capacity to build almost anything, including copies of itself, that can be built out of atoms. That doesn't leave much out! The size and speed of replicating assemblers can be estimated. Natural replicators, bacteria, are all around us--and in us too. Microorganisms can double in about 20 minutes in ideal conditions such as those found in industrial vats. Design studies indicate that assemblers will be about the same order of magnitude in size, complexity, and doubling time as natural ones. Design is one of the two bottlenecks in developing replicating assemblers and other nanotechnology tools. Many groups are forging ahead on molecular-design computer programs. (Tektronix released a system last year.) The other bottleneck is building tools which can reach down into the realm of molecules. IBM, several other companies, and numerous universities are working on scanning tunneling microscopes and related devices which allow "viewing" and manipulating atoms one at a time. IBM made a big splash recently by spelling out IBM in xenon atoms with an STM. There isn't a great deal of money being spent right now to develop nanotechnology tools, but this could change quickly. Governments might go after the nanotechnology breakthrough in "Manhattan Project" mode. The military consequences of being second are highly motivating! "Growing" vast numbers of diamond armored tanks would be a trivial application of nanotechnology; real war preparations might result in microscopic computer (and brain) subversion devices. Another way the breakthrough might come about was proposed by Roger Gregory (of Xanadu Hypertext). He predicts that molecular design software will be in the hands of an army of self-funded hackers within the next few years. Simulation programs are available now for molecules of several thousand atoms. They burn a lot of computer time, but given the ever rising capacity of personal computers, who cares? These tools can be used to design (i.e., build in computer space) and run a whole family of molecular manipulators. Eventually "molecular hackers" seeking prestige and perhaps prize money will design one that can make a copy of itself in computer space. We then have a target to link with what we can do in the known world of chemistry/ biotechnology. Once we have all the steps down (this object with this input and this outside help can generate the next one in the chain to this more capable device, etc.), it should become a relatively short-term project of months, or at the most a few years, to produce the first replicating assembler. When we figure out how to make, feed, and control replicating assemblers, the base of our "industrial capital" (which roughly translates to wealth) will depend on something that replicates in 20 minutes. Planning, design, transportation, and such human factors will slow down the pace, but even a factor of 10,000 slower would leave us with more than a doubling of the industrial base per year. Currently the industrial base in the developed world doubles in about 20 years. Human populations have minimum doubling times of about 15 years. The ratio between population and industrial growth rates equals the increasing (or decreasing) wealth per capita. Rich societies, with low birth rates, are getting richer, and some poor societies with high birthrates are getting poorer on a per capita basis. With replicating assemblers, wealth per capita for everybody will rapidly increase if we can harness even a small portion of the nanotechnology potential. (This assumes that the human populations are not using replicators to copy or make people!) A capital base doubling on a time scale of a year or less would make us almost arbitrarily wealthy, at least until we run into hard-to-define resource limits. Nanotechnology offers an opportunity for widespread personal wealth on a scale that can only be compared to today's gross world product (GWP). I leave it as an exercise for the reader to calculate the number of doublings their personal worth, or even their pocket change, would need to reach one GWP--something in the range of $100 trillion/year. Such a vast increase in wealth in a short time is without precedent. But over centuries, perhaps not. Vernor Vinge (in a personal communication) thinks that in many ways individuals of today have more wealth than a thirteenth-century nation state. Isabella I had to hock the crown jewels to cross the Atlantic, something most of us can afford without credit. It is hard to compare wealth across a few centuries, but the computer on which I wrote this article is more powerful than the ones the government of the United States could afford only forty years ago. The growth of wealth on this scale might make the sum of all the technological and social changes since we started chipping flint look tame. What the technological applications will permit us to do is easier to predict than what we might actually do: the options seem limitless at this point. For example, the human race (or some significant fraction of it) might use nanotechnology to move into hardware where thinking and social interaction went on a million times faster. Such a society might "collapse" into 600 foot spheres to minimize speed-of-light communication delays, or spread over everything to control malicious replicators. Others might design devices to restore the environment to "pristine" conditions. Along this line Freeman Dyson has proposed engineering turtles with diamond-edged jaws designed to seek out and eat bottles and tin cans along the roadways. How would nanotechnology capabilities and vast wealth get us into space? Being rich won't automatically get us into space, but the few of us who want to go there will no longer have to get a government or a large corporation to pay our way. The resources of a few people, or even a single person would be enough. We won't have to sell our dreams to anyone, but we will have to remain true to our dreams, and that (see below) may not be an easy task! The process of reaching energy or material limits in a nanotechnology world could provide interesting backgrounds for science fiction stories. For example, the real carbon dioxide crisis will come when there is too little in the air because people are mining carbon (the strongest engineering material) from the air to build houses, roads, tunnels through the Earth's mantle, industrial works, and spacecraft in large numbers. Some civic-minded types (the Audubon Society? Sierra Club?) might burn the Western US coal fields to bring the level back up so plant productivity wouldn't be seriously hurt. A small engineering project would be to leave some of the coal underground, reworked into diamond arches to hold up the roof and keep from disturbing the surface. Illuminate this space with light pipes from the surface, and you have hundreds of square miles of 200 foot ceilings a thousand feet underground to play in. Around the edges there would be mining to churn out CO2 as the main product, energy as a minor byproduct, and heat as an unavoidable waste product. Toxic trace elements in the ash could be walled up in the arches to keep them from harming "unimproved" life. They certainly wouldn't bother people who were using cell repair machines to stay healthy. Remember the Hunter in Hal Clements classic story _Needle_? The Hunter was a few pounds of intelligent protoplasm that lived between the cells of larger animals and helped keep them healthy. Cell-repair machines, an obvious product of replicating assemblers, could kill bacteria and stitch together cuts like the Hunter. Even better, they could heal damage right down to the molecular level. They could clean out clogged blood vessels, inspect DNA for errors, reverse the effects of aging, and rebuild damage from stray cosmic rays. We can assume the avant-garde will not be satisfied with maintaining a youthful physique, and will make modifications, like growing new teeth out of diamond, or will answer the little ad that says: "Reverse Your Retinas--Get Rid of Unsightly Blind Spots!" As soon as they become available, I want the integrated memory package so I can recognize the 10,000 people who expect me to know them, and the enhanced math/science/engineering "thinking aid" that would let me design a starship in an afternoon (and build it in a few months). The general availability of such things might split the race into those who don't want to change, and those who know how pitifully limited their abilities are and want improvements. Cell repair machines have another use. They won't revive the dead, but they may well change who we consider "dead." This has happened before. Not so many years ago, doctors gave up on people whose hearts had stopped; now they reach for the defibrillators. Even arch conservatives Chris Peterson and Eric Drexler admit that cell-repair machines could cure "severe, long-term, whole-body frostbite." This is an obtuse way to say that the concepts of nanotechnology and cell-repair machines changes cryonic suspension from a long shot to something that only requires "the faith of Goddard." Robert Goddard (the father or modern rocketry) _knew_ from calculation that the Moon was in reach. There were only two things about Apollo that might have surprised him. It occurred much sooner than he thought it would, and he would have been dismayed that we didn't stay. Anybody who looks at the nanotechnology/cell repair machine concepts will come to same conclusion Goddard did: it can be done, and likely will--within a generation or two. It is possible the nanotechnology breakthrough might come soon enough for many of us to avoid the need for all that chilly liquid nitrogen, but even if it were to take a hundred years to develop the technology, we can still get there. It costs little enough to keep you in liquid nitrogen that it can be funded with the proceeds from a small insurance policy. The biggest problem with cryonic suspension is that most people have made a virtue of what has been a necessity, and will tell you that they don't *want* to live a long time. I have found that a lot of folks simply cannot adjust their world view enough to give up the concept of inevitable death. For those who can, cryonic suspension offers us a ticket to the future. If cell repair machines can revive us at all, they will let us live long enough to reshape the galaxy. Well, what do we do when faced with vast wealth and lives as long as we want? Like the 500 pound gorilla, just about anything we want to, especially for those willing to leave the planet. There is plenty of material and energy out there for the small number of people willing to go off planet. Getting around the solar system is simple even now, and with arbitrarily long lives, the stars are within our reach. THE LAST FEW PAGES Besides the ability to rework the Earth and the rest of the solar system and lives as long a we want, what else can we do with nanotechnology? The information gluttons among us can contemplate a monstrous but short-lived feast. A few years after the nanotechnology breakthrough we will have the ability to sift through the Earth's crust with "designer earthworms" right down to the mantle. This should be accomplished at trivial cost and without disturbing anything. There is no particular reason for nanotech deep-delving earthworms to cost more than ordinary worms--that is, practically free. By sifting through the crust, we can suck all the available information out of the Earth. We will be able to revive at least some of the dinosaurs by sorting through amber for their DNA. A few years ago it was reported in _Discover_ that readable DNA from 70-100 million-year-old insects has been found embedded in this natural plastic. Surely a few of these bugs were blood-sucking or biting, like deer flies, and we will find DNA from at least a few of the dinosaurs. We may find enough in an exhaustive search to revive the Neanderthals and possibly some of our other ancestors. Neanderthals seem to have made their living by wrestling cave bears, were immensely strong, and highly coordinated. The first guy to raise enough for a football team will clean up. We can clone or computer-simulate the famous people from history in cases where we can locate enough fragments of undecayed tissue to decipher their genome. Leonardo de Vinci, for example, is known to have painted with the tips of his fingers, leaving bits and pieces in hardened oil paint. There is a fair chance that enough cells rub off on envelope flaps to clone anyone from whom you have an envelope, so save those envelopes from Heinlein! There is enough left of Einstein's brain, and it was preserved soon enough after death, that really advanced nanotechnology might allow us to recover his memories and personality. With even the faintest hope of doing so, it seems a shame for researchers to keep whittling on it. Preserving the pieces left in liquid nitrogen with the cryonics patients might be a good idea. The cold would at least stop further degradation. The feast won't last very long. Extracting information from the rest of the solar system will take only a few years and promises to be much less interesting. (I don't expect traces of life or unexpected artifacts to be found on Mars.) We can argue the next million years over the consequences of what we have found. However, after we have discovered all the local information, know where all the fossils and artifacts are buried, and know exactly what they look like right down to the placement of atoms, where can we find new material to fill the post-nanotechnology equivalent of _Scientific American_? Or will the science journals act like their English Department equivalents, constantly arguing over the same materials? THE FAR EDGE PARTY Some new information can be obtained with large telescopes. And, given replicating assemblers to build space-based telescopes, we will be limited only by the amount of material we want to move and tie up in mirrors. I expect we will resolve continent-sized features on planets out to 1,000 light years or better within a few years following the nanotechnology breakthrough, and locate the oxygen atmospheres (if any) out to a much further distance. But there are real limits to what we can find out with remote sensing, so someone (or thing) will have to take a closer look. What is the optimum way to sweep out the Galaxy and obtain most of the available information? Sending out machines and letting them send back information works, but takes too long for my taste. Besides, I want to _see_ the wonders of our galaxy. _All of them_. There are 100-200 billion stars in our galaxy alone and even with nanotechnology it will take a year or two to explore each star system, not counting travel time between stars. Visiting every interesting object in serial is literally impossible, since the interesting places won't last long enough. I don't want to take such a long time looking over this one small flock of stars that most of them burn out. The only way clearly available is to explore the Galaxy in parallel. This is a topic that's hard to discuss, even with readers of science fiction. My friends, even the ones in the cryonics organizations, are very uneasy about Xeroxing people. Some of them claim, in jest, I hope, :) to have nightmares about going to a party in the remote future and finding that every third person is a Keith Henson copy. IS THAT ME OR ME? To explore the Galaxy in parallel, we need to make only a few starships, perhaps 100, and recruit crews for perhaps 10, but we make copies of the 10 crews to fill all 100. At 1,000 people per ship, and 100 ships (100,000 adventurers) this would probably be necessary anyway. I doubt there are as many as 10,000 people in the entire world who would board a starship. Misfits who want to _do_ something as opposed to watching or reading about space exploration are a very rare compared to the number of _Star Trek_ fans or even _New Destinies_ readers. They may not be very common even among National Space Society members. An assembler doesn't care what it is making, and unless there really is some special "vitalizing" force, we won't have to make hard choices about which way to go--we take all roads (or at least a fair sample of them). People have talked about making a copy of themselves and having the copy do the unpleasant chores. That's silly. A good copy would be indistinguishable from the original right down to desires. You could neither make a copy to go visit the stars nor one to stay on Earth that would be happy unless you didn't care which you did (unlikely) or someone messed with their personalities in the copying process (unethical). In fact, I think it would be unethical to distinguish among copies (a case where the Golden Rule applies in its strongest form). The only case I can see where copies are justified is a situation where a person really has no preference between two mutually exclusive choices. The copying process might best be fixed so as to split the original material in half, so neither of the individuals coming out of the process (and starting to diverge) would have a better claim to being "original." The ethical questions about copying people, reprogramming them, mapping yourself into faster hardware, and the rights of constructed personalities is a topic I would like to see getting more serious discussion both inside and outside the Science Fiction community. Another problem is how to improve ourselves without getting completely lost. Today the mental modules at the root of our personalities change slowly if at all. When our deepest desires can be quickly modified with trivial effort, how much of us will survive? The results of modifying ourselves could be as tragic as being modified by others.** This and nanotechnology based infectious "super dope" that made everyone happy but without ambition (or even the desire to eat) are among the dangers we face. I think these dangers are far more serious than the "gray goo" (uncontrolled replicator) problem. **footnote Marvin Minsky has a good deal to say about these problems in _Society of Mind_. ------- Philosophical problems of identity aside, and assuming we avoid these and other as-yet-un-thought-of dangers, I expect starships to exit the solar system within a decade of the nanotechnology breakthrough. They might be pushed by laser, or powered in one of several other ways. The way to travel between stars on laser beams is amusing. You send a probe ahead to the target star. The probe doesn't slow down, but fires nanotech "seeds" backwards to nearly zero velocity as it rips through the target star system. The seeds are scattered toward the planets of the target star which have atmospheres. They are braked by the atmospheres, and settle to the surface. There (I hope not in someone's back yard!) they grow from the size of a bacteria into a rocket, similar to a Larry Nivin "stage tree." The stage tree launches into space, sets up a base on a stray asteroid, and builds a deceleration laser. Either before it leaves the ground, or in space, information in the seed is used to build a microwave receiver. Any information on how to build the deceleration laser that cannot fit in the seed can be sent later by microwave, along with instructions on when to turn on the beam. If it doesn't work . . well, this is how you have an adventure in an otherwise overly safe era. At the target stars, the explorers build new launch facilities and an appropriate number of copies of the ship and crew for the targets ahead. How many stars do they get to visit? If 100 ships go out to inspect our galaxy, each ship and its descendants will have to visit a billion stars (neglecting losses and overlaps). Fortunately exponential growth comes to the rescue. A ship needs to copy itself only about 30 times since 2 exp 30 is about 10 exp 9. If thirty is too few stars for your taste, double yourself less often; if too many, make more copies per generation. Doubling, the last generation looks at half the star systems in the galaxy at once. Do we go out and come back to exchange information? With 50 billion starships? Even if there is room to park them, where in our solar system could we hold a meeting for 50 trillion intrepid explorers? We will need an economy sized ringworld, and getting a permit to build one around Sol might take longer than the round trip. Besides, coming back home takes twice as long as needed. There is no point in wasting time even if we have plenty. So we will sweep across the Galaxy and converge for a giant party, scientific meeting, and memory merge so we can say we have seen all the wonders of the Galaxy. Oh yes, the convention committee will have to get a little ahead of the pack to construct party hotel(s) for 50 trillion. BUG-EYED MONSTERS As you can imagine, discussions about the Far Edge Party get rather lively. Someone came up with the suggestion of prizes for strangest or most interesting aliens. Someone else pointed out that with nanotechnology and tens of thousands of years the judges will have a very hard time detecting cheating with constructed aliens, or life forms raised to sentient status. Debate on aliens rages between the Saganites and the Tiplerites. Carl Sagan and Co. hold the opinion that technological life is fairly common, with radio capable civilizations every few hundred light years. His school proposes vast listening posts to eavesdrop. Frank Tipler points to the lack of any evidence that our galaxy, or the universe at large, is inhabited by technophiles. I have come to lean very strongly toward Tipler because I think that before very many years go by _our_ existence in this particular part of the universe will become very obvious. Laser cannons pushing light sails would be seen as obviously unnatural beacons far across the universe. It may be that life is fairly common, but the time it takes for technology to arise is much longer than the time available on most planets. This may be the real answer to the Fermi question. *** (***Footnote: when Fermi realized that nuclear energy would suffice to cross between stars he is reported to have asked, "Where are the aliens?"). But I am willing to withhold judgment 'til we sweep across our Galaxy. That should give us a representative sample. How long will it take to cross the Galaxy looking for life and getting a look at all the galactic "hot spots?" Light takes about 100,000 years. If travel speed is, say, half the speed of light, it should take some 200,000 years. BACK AT THE RANCH The stay-at-homes, or those who colonize and stay around a single star, won't have as much fun, but they will have plenty of interesting things to do. Conservation for example. Have you ever thought of how much energy the Sun wastes? But I am getting ahead of myself. "a long enough lever... Some years ago, James E. Lovelock, an English chemist and prolific inventor, and Lynn Margulis, discover of the mixed linage of our cells, developed the biosphere-regulation Gaia concept. Lovelock later calculated that the ability of "Gaia" to compensate for the rising output of the sun will fail within the next 50-100 million years. Without intervention, the Earth will become a post-biotic planet. (David Brin speculates this may be the common fate of life bearing planets.) Lovelock proposed that planetary sunshades be deployed when they are needed. We could do it with today's technology if we really needed to. However, cluttering up our neighborhood with sun shades is not the most aesthetic approach. Being familiar with Eric Drexler's work on solar sails, I proposed (partly in jest) hanging a large collection of them ahead of the Earth in its orbit. The sails would be gravitationally coupled to the Earth, and gradually accelerate the planet into a larger orbit. The numbers work out that we had better get started right away. It would take about 100 million years to pull the Earth back far enough from the fire! There is another way to move the Earth. We could use much of the mass of the asteroid belt to transfer momentum from Jupiter to the Earth. It takes about the same time as using solar sails to change the Earth's orbit. It might take almost that long to convince me that we could play interplanetary billiard balls that long and not accidentally put a cue ball in the pocket! The best scheme to cope with stellar aging is not to move the Earth, but to cool off the sun. David Criswell has called this process "star lifting" and worked out, at least in theory, how an advanced and wealthy culture would go about cooling their sun by removing mass and storing the mass to heat it up later. You want to take good care of your star, otherwise it gets all dark and icky. AN EVEN LONGER LEVER A much wilder scheme came out of this line of thinking. The _very_ patient can move stars. The truly desperate might move a galaxy. An advanced civilization (even without nanotechnology) could hang a hemisphere of actively controlled light sails over a star. (They have to be actively controlled since the light and gravity forces which the sails balance obey the same force vs. distance law.) The sails couple gravitationally to the star, and turn the star (and sails) into a fusion/photon drive. The ultimate change in velocity is about the same fraction of the speed of light as the fraction of mass turned into energy. This is not a large number, in the hundreds of km/second. Still, it is comparable to the velocity of stars against the cosmic background, or the orbital velocity about the center of our galaxy, and much larger than our 80 km/sec closure rate with the Andromeda galaxy. If enough of the mass of a galaxy is in stars, we may be able to prevent or at least greatly modify galactic collisions by moving stars. The gas, dust, black holes, and dark matter should tag along if we move the stars slowly enough. Moving galaxies could be used as background for SF of a scale that hasn't been seen since the days of Doc Smith, or Clifford Simak's Cosmic Engineers. A nice fresh G-type star can actually cross the average distance between galaxies before it burns out. This is for people who want to travel and stay home. Reminds me a little of Larry Niven's Puppeteers. Naturally small stars, or ones reduced by "star lifting" have inconvenient (dull red) spectral characteristics, at least for those of us evolved in the light of a G-type star. Two solar sail hemispheres could be used to reflect light back on the star and change its spectral type. The surface layers would heat up to look like a G type, and the light would escape in a narrow band between the hemispheres of sails to light planets or space habitats ranging up to a ringworld. The interior temperature and burn rate of the star should not be affected, but it might inhibit the star's normal convection patterns. If someone in stellar physics wants to work out the consequences of heating up a small star, I would like to see the results. LITTLE RINGWORLDS Do we really need Larry Niven's "scrith" to build ringworlds or can we get by with known, or at least projected, materials? If you leave most of the structure non-spinning (or spinning retrograde very slowly) and support a much lighter spinning part on superconducting magnetic bearings, O'Neill-type cylinders can be built large enough to house a continent. I have my doubts about cooling such a thing, because radiator mass per unit of radiation goes up as the square root of the absolute size of a radiator. Giant O'Neill cylinders are not a particularly efficient use of mass to get living area. But, as Eric Drexler pointed out, there is an even _less_ elegant way to build one-g ringworlds. You spin a ringworld supported by bearings, pile all the non-spinning mass on the outside, and let the star's gravity acting on the mass keep the ringworld from flying apart. A small ringworld built this way around a warmed-up M type star might be about the right size to hold the Far Edge Party--thought it better be near a big hot O-type. Decelerating fifty billion starships at once is too much to ask of a small star. See you there! (RSVP) Bibliography Lovelock, James "Gaia and the End of Gaia." _CoEvolution Quarterly_, No. 31, Fall 1981 Drexler, K. Eric. _Engines of Creation: The Coming Era of Nanotechnology_. Anchor Press/Doubleday: Garden City, New York, 1986. Criswell, David R. "Solar System Industrialization: Implications for Interstellar Migrations" in Finney, R. & Jones, E.M. (eds.) "Interstellar Migration and the Human Experience," pp. 50-87, University of California Press (1985). Burrows, John D. and Tipler, Frank J. _The Anthropic Cosmological Principle_, University of Oxford Press, 1986 Minsky, Marvin. Society of Mind. Simon and Shuster: New York, 1986. [RSVPs may be sent to The Far Edge Committee, 1685 Branham Lane, Box 252, San Jose, CA 95118 or hkhenson@cup.portal.com] About the author: H. Keith Henson was one of the founders and first president of the L5 Society. Memes, computers, nanotechnology, cryonics, email privacy, and planning for the Far Edge Party are among his current interests. The Far Edge Committee may be a precursor to the infamous "Last Proton Club," unless "baryons are forever." ------------------------------ End of Space-tech Digest #76 *******************