|Posted by Rohvannyn on May 25, 2011 at 3:32 AM||comments (0)|
I’m taking a departure this week from my usual writings on the wherewithal to get into space and remain there, the only commonalty between this and other entries being the general subject of leaving Earth. That you are reading this is an indication you have an interest in space flight and by likely extension, in the long-term fate of Humankind. The state of technological sophistication we at least in advanced nations occupy is the result of hundreds of millennia of progress from the first chipped stone and the first tree bark or animal skin cloak. The fact that we are here at all with brains, hands and knowledge sufficient to literally remake a planet is due to biological and planetary processes (however conceived and executed) which extend back billions of years into the past. There is no indication that we are anywhere near the pinnacle of our technological potential or even our maturation processes as intelligent beings. Why then do at least somewhat intelligent persons continue to look at localized and historically recent predictions and “signs” as indications that all of this should go away and Humanity's progress in space and time go entirely away?
A surprising amount of hype has been recently made as a a result of Harold Camping’s dubious predictions of a Rapture predicted for the 21st of this month and of course as always before, nothing happened. In October he and his followers will be at it again in one more of a series of predictions that have been going on in my experience since the 1970s and have actually been with us since the time of the historical Jesus. I’m not so much surprised at these so-called prophecies per se but the fact that they are so popular, that they gain so much attention in the media and in the Blogosphere. I know the Bible talks about the end of the world and this isn’t limited to Revelations but aside from the fact that it is stated in John’s Gospel and elsewhere that the day and hour won’t be known beforehand, the whole process of “endtiming” within our own lifetimes or within the next few millennia for that matter, appear to me to be incredibly wasteful. We have many environmental and social problems today but nobody familiar with the social history of London, or Boston, for that matter, or with the Middle ages as they really were could dare to say with a straight face that progress has not been made and as our problems in some directions have grown, our capabilities in most directions have also increased. The point I’m making is if things are to be nipped in the bud at this time in history then why should we have bothered at all? I’d say that our race is about 14 years of age when held to a Human yardstick and who’s never wanted to slap an adolescent? However, successful parents exercise patience, or try to.
The thing that troubles me most about the trend toward Millennialism since the advent of the Jesus Movement around 1970 is the inchoate cowardice of the process. If things are going wrong we needn’t worry about it because we’re living in the last days and these things are supposed to happen. If we aren’t successful in life then that’s fine because solutions are from God and not from Man (sorry ladies). If our condition is unpleasant, well we’re just waiting for the Rapture. It’s not entirely coincidental I think, that Millennialism has grown apace with the passion for lottery tickets and a trend away from focusing on what we can do with our own hands, brains and social connection and toward what we might win or be handed free.
Having said what I’ve said here I should identify myself as to where I stand on spiritual grounds. In short, I don’t believe the hand of God/dess is necessarily all that evident in biological evolution because it’s far too imperfect, whereas I think cosmic/universal evolution speaks quite evidentially of a divine influence, even Design. Yes I do believe in God and feel that the things Jesus said are among the most important legacies sent down to us from the Ancient World but I believe in a God who continuously gives birth and nurtures existence to develop toward independence. I don’t believe in a god who designs a universe then sets traps with which to apprehend and punish “beloved children” who have only the temerity of being curious, an inborn human trait if ever there was one.
I’m not here to say that the world won’t ever end or the Universe itself but the more we’ve learned about ourselves, our planet, the processes of life’s development the more it’s been apparent that we are participants in a universe billions of years old and extending tens of billions of light years in all directions. Why then do we continue to listen to prophecies of humanity's ultimate destiny measured in terms of one planet and dated in multiple generations or by the rise and fall of agrarian nations?
|Posted by Rohvannyn on May 19, 2011 at 12:50 AM||comments (0)|
In order to keep a human being alive in what can be seen both as a hardened space suit or a flexible space craft with minimal cabin space beyond the volume occupied by the human body, we see that some paradigms hold which won’t be necessarily true in a multi-occupant capsule. While spacecraft cabins normally have equipment for scrubbing carbon-dioxide from the air, precipitating water out and controlling hazardous volatiles in the cabin interior our single astronaut will have his or her head in a helmet so by flowing an air mixture into the helmet and venting stale air at the wrists and ankles we can minimize harmful build-ups of respiratory products in the user’s face area. This requires more air per day than would be required if we actively removed CO2 and water from a semi-closed environment but the weight of the life-support equipment just mentioned is apt to be greater than the extra air used in the constant flow ventilation process.
A human being breathes about three pounds of air per day and we’ll estimate that 12 to 20 pounds per day will be used by our astronaut with the majority of respired air being exhausted to space. The air will be supplied by the decomposition of nitrous oxide (N2O) which yields a mix of nitrogen and oxygen not that different from Earth’s atmosphere, as well as heat in the amount of about 2/53 Million Joules per 3 pounds decomposed. This energy is useful for power in the form of hot, compressed gas, to power suit joints. If we were to use 12-20 pounds of N2O per day for air supply, and allowing for the inefficiency inherent in converting heat to work, we could expect something in the neighborhood of 150 watts power around the clock which doesn’t seem like a lot but consider that a person peddling a bicycle generator is doing well to accomplish 100 Watts continuous power. Though mechanical power use would be intermittent, the air would flow and power would be available continuously, so power would be wasted but we’re trying to transit to the moon over about three days, not run a year-round power supply.
Converting N2O gas at around 1,300 C under catalysis, liberates a lot of heat and together with the heat given of by the body, (circa 8.5 Million Joules per day) we have a significant cooling problem. Around 26 Million joules of heat needing to dissipate in a single day. It turns out the liquid hydrogen because of it’s extreme cold temperature, about 20 degrees C above Absolute Zero, can, in being warmed up toward cabin temperature, absorb this extra heat in about seven kilos of LH2 per day. This is around 60 pounds in three days. Or 21 kilograms. That translates to 300 liters of tank space or something about 40 inches long and two feet in diameter. Imagine a water heater on your back though we’re in space and not walking around on the ground. The liquefaction temperature of Nitrous Oxide is very close to it’s freezing temperature so it would likely be best all things considered, to carry this in highly compressed form rather than as a large ice cube. Sixty pounds of N2O at 100 Atmospheres could fit into a tank perhaps 36 inches long and 18 across., (perhaps worn T-fashion across the hydrogen tank on the back.)
So we have N2O flowing out under pressure to a catalytic bed, being fed to mechanical joints as needed and then being cooled by venting cryogenic hydrogen gas en route to the user’s helmet. Now heated and (pressurized) hydrogen can vent harmlessly to space or be used as needed as attitude thrust. Exhaled air can be vented into space or diverted as needed to fuel cells where the still largely unbreathed oxygen can react with warmed hydrogen to generate electricity for communication, suit conditioning or other purposes. We could get four to five kilowatts of electricity from the hydrogen and oxygen available and likely won’t need that much most of the time. It’ll probably be more trouble than it’s worth to condense drinking water either from respired air or the fuel cell output. Drinking water is only a few kilos a day.
We’ve passed over some issues such as liquid and solid waste disposal, hygiene, scratching one’s back while in a suit etc. so we may visit the Humanform spacecraft later but I think we can fly someone from orbit to the vicinity of the Moon in a spacecraft weighing less than a ton.
|Posted by Rohvannyn on May 12, 2011 at 2:53 AM||comments (3)|
Last time we asked if a human being could be lofted to the moon or other distant points in a craft weighing less than a ton. I think this is possible if we overcome claustrophobia by means of a capsule which is also a hard space suit with movable arms and legs. Since movement in space suits tends to be fatiguing owing to the internal pressure within the suit against the vacuum of space, the suit would likely be provided with simple piston-type actuator motors, fastened to strategic portions of the suit such as shoulder, thigh, knee, elbow, etc. or located sin a backpack perhaps and exerting force via cables rather like macroscopic puppet strings. Motors could operate in pairs as voluntary muscles do or in some cases strong springs could counteract a given movement to restore a limb to a straightened position for example.
Though actual walking in space isn’t generally necessary, it will be important for the wearer’s legs to be able to move and bend and in some situations having relatively free use of arms and legs might assist in assembly or maintenance operations away from Earth. I think if the suit was sufficiently loose in the torso area to allow the wearer to draw arms inward, out of the sleeves and is a small bay could be provided in the abdominal region sleeping might be accomplished in a comfortable position or internal activities could be facilitated such as eating or personal hygiene. A back and shoulder support might snug the wearer up toward the front of the suit during active periods, so arms would be held within the sleeves with their gauntlet ends.
The suit would allow legs to move inward, outward, to move independently back and forth in a striding motion. Knees would bend. There may even be some rotational ability for the feet. Arms would be allowed some shoulder movement as well as elbow bending, wrist rotation and fairly normal glove movement, possibly enhanced with artificial tactile senses for the fingers. It could be that each suit would need to be sized to some degree for a normalized span of wearer sizes, lengths and girths but I suspect that by adjusting the saddle on which the wearer sits, analogous to the crotch in one’s pants, the sole of the boot and possibly by modularizing the arm-hand sleeves, we should be able to accommodate a wide range of wearers with essentially one size.
Of course besides powering the actuators mentioned above and providing electricity for communication and air/water circulation, the suit must carry sufficient fuel and other reagents to provide oxygen, water and temperature control. I suspect these functions will be fulfilled with Nitrous Oxide, liquid hydrogen, probably some stored water and some hygiene items. We’ll see how in Part II.
|Posted by Rohvannyn on May 3, 2011 at 10:15 PM||comments (0)|
So let’s assume we are able to loft metric ton payloads into high orbit, even send them toward the moon if we like. Where does that really get us? A couple tons of freeze-dried foods mixed with some grain and legumes is all we really need to keep twelve people on the Moon for a year. We’ll discuss this point later. Water frozen into miniature icebergs can be melted in space then cracked and liquefied in miniature solar-powered factories to yield hydrox propellants which can be stored in silvered tanks until sufficient has been gathered to launch a mission to the moon’s surface or to another planet. Most of the technology we need to explore the solar system could be broken down into modules weighing a ton or less. I’m not convinced that we’ll ever have spacecraft of the chemical variety at any rate, which will continue to function in space for decades or centuries so we’ll either need to bring even deep space craft down to earth for dry-docking or take a light bulb approach to replacing the comparatively low-powered engines, control and guidance systems, life support hardware. (By the way, the matterbream if it works, can lower payloads to earth as well as lift them.)
The only part of a deep space ship which would be difficult to raise with a matterbeam of rather low lifting capacity would be the hull itself. We can imagine quite conventional craft that are just tanking, that being the payload and possibly launched with discardable boosters (such as aluminum/water-ice solid motors) or even dropped from a 747 or lifted to 10 miles or so by a balloon. Once the tank/hull reaches low earth orbit it could climb to high orbit by means of silvered balloons acting slowly but steadily as solar sails, being inflated on the sun-driven side of it’s orbit and deflated on the sun-breaking side of the orbit. Once in place the space drive modules and all else necessary to complete a true space cruiser could be installed by astronauts in powered suits.
If our large rockets are only fuel tanks destined to be hulls, do we have a way of sending human crews into space, perhaps via the matter beam. Yes, I believe that we can develop a small spacecraft weighing a ton or less, able to carry a human being. It will work largely because it will look like a human being and be life support system as well as power system, acting as an extension to the astronaut’s body. We’ll discuss this possibility next time.
|Posted by Rohvannyn on April 27, 2011 at 2:42 PM||comments (0)|
The science fiction writer Murray Leinster employed in many of his stories a system called a Landing Grid for getting spaceships off planet and to soften returns from space. The concept involved a number of Force Beams, a standby of early to mid 20th Century SF; to impart momentum to an outbound ship or absorb it’s in-bound kinetic energy. I don’t recall a great deal being said about relative velocities of ships with respect to the ground and the impression generally given was spacecraft left Earth and returned vertically.
Contemplating a payload being launched vertically from a point on earth or some location above that point, we’ve seen that due to Earth’s axial spin, said payload would have a velocity tangential to the ground of right about 1,000 miles per hour. Should be lift directly from this point the payload would experience a continual diminution of downward force due to gravity as altitude is gained but the tangential velocity would not be sufficient to establish a stable orbit about the Earth until an altitude of more than a million miles has been achieved. The force due to gravity upon the payload decreases as a square of the distance from the center of the earth. (8,000 miles or two radii from Earth’s center results in one Fourth of Earth surface gravitational force.) The equation orbital speed squared divided by the orbital radius lets us calculate how fast a body must be traveling at any given altitude to counteract the gravitational pull at that altitude.
While simply pushing a body into orbit with a continuous vertical shove from below will tend to populate the outer fringes of our planetary neighborhood with wanderers apt to take up independent orbits as solar stepchildren, we’ve seen that in pushing our projectiles to the point at which the gravities of Earth and Moon balance, we can now accomplish something worth doing in putting our craft into orbit about the moon or into a trajectory on which it might be captured by a lunar freight tug of some kind. It is also true however that if it works at all, the matter beam system could shove payloads into space not vertically but slightly angled from the vertical so the craft acquires a component of tangential motion so it might be able to take up an orbit much closer to the earth than the orbit of the moon. Should a craft be raised to an altitude of 36,000 miles for instance, (40,000 miles from the center of the earth,) it could experience a downward force of about .32 feet per second squared. Or 100th of a G. It’s orbital velocity would be on the order of 8,000 feet per second, What’s exciting about this is that an additional 3,300 or so feet per second would be able to bring our craft at that altitude up to escape velocity. This is important because electric propulsion systems for spaceships, though much more fuel efficient than chemical rockets, provide very low thrust levels which could see us spending months trying to break out of a near-earth orbit. A typical acceleration of 1/10,000th of a G could reach escape velocity from our 36,000 mile orbit in about 10 days. In the long run therefore the matter beam might be the link not only to cheaper space access but efficient access to our solar system.
|Posted by Rohvannyn on April 19, 2011 at 3:42 PM||comments (0)|
Following up on the issue of what happens to a matter stream as it passes through Earth’s atmosphere I’ll propose a scaled down version of our beam launcher which operates at the same level of acceleration as our 70 megawatt system but attempts only about 20 % of the larger model. If we shot a matter beam at 2,200 meters per second and maintained a similar mass flow of a kilogram per second our system would draw power in the range of 2.5 Megawatts. If we only need 2,200 M/sec exit velocity our launcher could be only a meter or so in length. That means we could use one-gram projectiles and fire at a rate of 1000 per second, keeping the launcher constantly active.
Part of our experiment would be to use a projectile material which is designed to melt or vaporize at moderate temperatures to see if degradation indeed occurs in a continuous ultra-fast matter stream through air. I’m proposing a carbonate of iron, Siderite (FeCO3) which decomposes at around 700 degrees C. Siderite is diamagnetic, meaning that it can react against an externally-applied magnetic field. The effect can be enhanced by making the material superconductive through cryogenic cooling. This means that a chilly piece of Siderite should be throwable with an electromagnetic catapult.
Once we’ve determined what characteristics our matter beam has (if any) after traveling through the air we could use cheap dummy vehicles, possibly a heavy base plate with a conical cap. The vehicle might be spin-stabilized to keep it more or less on track. We’d still want a powerful laser to vaporize the propulsion pellets of the matter beam. We should be able to launch vehicles up to 200 kilograms of mass.
Some advantages of this system would be that being designed to intentionally combat atmosphere rather than avoiding it, we’d have it at ground level and the size would be unremarkable. Also the power draw would continue for a few minutes at most, perhaps 300 seconds and though energy flux is still high overall consumption is tiny, on the order of a 2 gallons of kerosene per launch. Even if the matter particles are destroyed by air friction before reaching a capsule’s pusher plate, we know that it would operate on the Moon!
|Posted by Rohvannyn on April 12, 2011 at 3:47 PM||comments (0)|
How do we go about shooting an 11,00 meter per second beam vertically upward, what powers it and where would the launcher for such a beam be located? It appears that we’d need an electromagnetic track of some kind, elevated most likely. It need only contain 6 or so grams of accelerating matter at any particular instant so though about 100 feet long, may not need to be terribly massive. If powered by an independent source capable of being set up in a remote location (or at some point above the earth) we’d probably be served best using a MHD ( Magneto Hydrodynamic Device) which uses rocket exhaust cutting across lines of magnetic force to generate high levels of electrical current. A Kilogram of hydrogen burned with oxygen generates around 143 Million Joules of energy, about enough to heat 10 bathtubs of water to bathing temperature. To power our matter beam of circa 70 million Joules per second power draw for half an hour would consume about 2.4 metric tons of hydrogen burned at 100 % efficiency, which of course we can’t do. Even at 40 % efficiency however, first combusting fuel then generating electricity and pumping the current into our beam launcher, we’d use about Six tons of hydrogen to loft a ton of payload. Of course we need oxygen to burn the hydrogen. In some cases we might choose to use highly compressed air to do this or we might desire to use liquid oxygen, perhaps that resulting from the electrolysis of water to make the hydrogen in the first place.
A rocket used to combust this hydrogen fuel and provide thrust to run the MHD need only be in the range of 15 to 30 thousand pounds thrust which is a pretty small rocket as commercial propulsion engines go. The package of launcher, MHD, rocket engine and fuel supply may be something which could actually be lifted above the Earth’s surface by balloon in order to avoid enormous amounts of frictional heating resulting from firing an ultra-fast steam of matter particles through Earth’s atmosphere.
If we contemplate placing a package at a point in the atmosphere where air density is 1 percent of that experienced at sea level, we need about 1,500 cubic feet of helium for every pound of balloon and package. Using hydrogen (H2) would halve the size of our balloon. Should we wish to lift 100 tons of hardware and fuel for instance we’d need a balloon of about 300 Million cubic foot capacity or a sphere about 830 feet across. It would probably be best to design an inner tube or doughnut shaped balloon, perhaps made up of several spheres or sausages, with a hole in the middle which the gyroscopically stabilized launcher could be suspended. Downward thrust from the not 100 % efficient MHD could serve to counteract much of the recoil force from the launcher.
A huge floatation craft at the fringe of the atmosphere might be an extreme answer to the issue of countering atmospheric resistance to matter particles but I’m sure it could be done given modern plastic films for balloon construction. We’d have some problems keeping it in one place but might counteract drift by adjusting our matterbeam. Before contemplating this too much farther however, we might ask ourselves, why can’t we fire our beam from Earth’s surface or at least from a tall mountain? While one particle of matter fired at eleven thousand meters per second would most likely vaporize in transit through sea level air, what happens if we fire a rapid succession of such particles? Wouldn’t the air along the pathway of such a particle steam rarify or become less dense with sustained firings? Has anyone every tried anything like this? While horizontal or upward-angling catapults and high velocity artillery pieces have been used for high altitude tests, I don’t believe anyone has ever fired vertically upward at escape velocity with a matter stream rather than a single projectile.
|Posted by Rohvannyn on April 5, 2011 at 3:43 PM||comments (0)|
We said in the last entry that a matter beam traveling on the order of 11,000 meters per second could drive a payload from Earth into a pathway toward a lunar capture within 30 minutes or so of acceleration. Through fairly simple calculation we can see that our matter beam must throw mass at this velocity at the rate of 1.05 to 1.10 kilograms per second. If we used a launcher of 30 meters or about 98 feet in length, an acceleration of 2.2 Million meters per second squared (about 220,000 Gs) would accelerate a matter pellet to 11,000 meters per second in about .0055 seconds (about 1/183 of a second.) A military rifle accelerates a high velocity slug at about half that acceleration.
Probably for greatest efficiency of power utilization it would be better to accelerate our matter chunks in units of about six grams 183 times per second instead of a solid kilo ever second. The actual size of the matter “Meso-particles,” a term in somewhat common usage now, will depend on factors relating to their passage through part or all of the atmosphere so let’s look a bit at what the particle is meant to do and how it might get to it’s destination.
Clearly we wouldn't propose to hit our proposed space craft one one-ton metric mass on it’s base with a stream of solid 11,00Mpsec bullets. The Science fiction writer G. David Nordley and others, have proposed a concept for vaporizing such bullets before they strike the craft and absorbing their momentum by means of a magnetic field surrounding the ship. We’d like therefore to use pellets or Mesoparticles which can first be accelerated to a velocity of 11,00 meters per second or more, survive the transit from launcher to craft, then be turned into charged gas or plasma in the near vicinity of the ship. Later we’ll discuss the possibilities for delivering the particles from Earth to ship but for now I’ll suggest a form of iron oxide called Magnetite (Fe3O4) as a possible pellet material. This compound has strong magnetic properties so could be catapulted electromagnetically. It has a fairly high melting point of 1538 C and the energy needed to decompose it into charged iron and oxygen is low compared to many other ceramics, about 3.08 million Joules per second if we’re firing 1.05 KG per second. While this is about 5 percent of the energy used to accelerate the mass in the first place the energy cost might be much more depending on how the vaporization/ionization process is carried out. I’m envisioning a large laser, possibly ground-based which could intersect the matter beam at a point directly behind the accelerating craft. Last efficiencies are fairly low however and the energy to ionize our pellets could well approach that needed to accelerate them. Still we are a fraction of the power draws needed for orbital catapults or pure laser launchers.
Next time we’ll discuss the generation of energy to run our accelerator and the possibilities of getting ultra-high-speed matter particles from here to there.
|Posted by Rohvannyn on March 29, 2011 at 4:17 PM||comments (0)|
As we’ve pointed out elsewhere, it takes a lot of energy to get into orbit. For every kilogram orbited, energy in the order of 32 Million Joules must be expended at minimum and the numbers in practice are much higher. To catapult a metric ton of mass into orbit, allowing 30 seconds to accelerate, requires a power draw of a Gigawatt or more. By accelerating our orbiter with secondary booster rockets, themselves catapulted from an electro-magnetic track, we can spread power use out a bit and get the draw down into the hundreds of megawatt range, but that’s still a lot of power. Laser systems which have been proposed for orbiting 1-ton payloads, operate in the Gigawatt range and require several times that amount of input power to generate the laser.
These rather stupendous energy bills result largely from the shape of the Earth. It’s round, and if we want to orbit something we have to impart energy to it before it’s too far away to be seen or operated upon. It’s just possible that we’re looking in the wrong direction. As everyone knows it’s possible to place a payload in Earth orbit in such a way that it covers over a point on Earth’s equator because it’s orbital velocity is such that it keeps pace with a spot on Earth. (This doesn’t mean it’s speed is the same as that of the point on Earth but that it accomplishes an orbit in 24 hours.) Conceptually we could climb directly from Earth in a vertical direction till we reach this Geosynchronous orbit and that would put us in a stable orbit about the Earth.
Things aren’t quite as simple as that because a point on the equator travels eastward at about 1,000 MPH while a point in Geosynchronous orbit goes around at about 7,000 MPH. The moon orbitsaround the Earth at around 2,000 miles per hour so if we could endow a body with sufficient velocity it could travel to the vicinity of the moon.
Of course we already knew that! The point is though, while putting something in near-Earth orbit requires fast accelerations (circa 30-100Gravities) and vast outpourings of energy, climbing vertically requires enough acceleration to counter Earth’s pull, plus a bit more. Let’s say for instance, that we have a vehicle weighing one ton. Let’s accelerate it at about1.2 G.s so the force on it is about 12,000 Newtons. Let’s say further that we accelerate by hitting the vehicle’s base with mass accelerated to something on the order of 11,000 meters per second. We’d use about one Kilo per second to do the accelerating. The amount of power we’d expend in such an operation would be around 70 Megawatts, an order of magnitude less than orbital catapults and two orders less than laser launch systems. Of course we don’t know for sure how to accelerate even small packages of mass to eleven kilometers per second but if we could, we’d need to operate our system for only a half hour or so. Gravity drops off as we rise higher so under 12,000 Newtons force for 30 minutes our ship would be near Earth escape velocity in an half hour.
In later installments we’ll look at this idea from a variety of perspectives and see if it’s merely a thought experiment or something into which we can really get our engineering teeth. It’s important for now however to keep in mind the difference between energy and power. Energy has to do with the amount of absolute change we can make on a system, how much velocity we can add to it for example. Power is how fast we make that change. Our vertical lofting system uses as much energy and more than a more conventional orbital catapult concept but we can spread the energy out over longer periods of time, thus reducing power levels. Even summing the energy used over the 30 minutes of acceleration however we find it could be generated quite easily, by from one to three tons of rocket fuel, a mass not dissimilar to the vehicle’s own. This is exciting!
|Posted by spacelane on March 14, 2009 at 3:22 AM||comments (0)|
To What Extent Can we Rely Upon Computers?
Yes I do believe star travel is possible someday if very, very difficult and expensive. I doubt however we'd bother to establish colonies on extrasolar planets if those planets weren't a good deal more like earth than most of the real-estate we've found in our own solar system. A fabber (3-D Fabricator) meant to operate on an Earthlike world therefore would be less likely to be used in hermetically-sealed pressure structures then one used on the moon and would more likely turn out agricultural tools, biomass processing equipment, air breathing engines and from whatever the local equivalent of trees might be, structural units. We'd also want simple yet versatile and fairly powerful remote-control or pilotable mobile machines to dig trenches, lift rocks, position beams, transport ore, scout terrain.
Any fabber able to turn out all of these machines either wholly or piecemeal must be able at minimum to build up solid components from electrically conductive elements, electrical insulators and ferro-magnetics, aluminum, silica and iron or steel would be good examples of each, respectively. The fabber would also need to be able to introduce controlled amounts of impurities or do pants into silicon wafers.
Before we go on let's take a look at what kinds of things we'd be likely to need within the first few days, weeks, months after landing on a planet orbiting another star. Right up there with food, water and shelter we'll want energy right away. We might arrive with handheld fusion torches or pocket-sized antimatter reactors but it could happen that such devices would require a larger technical infrastructure to manufacture than could fit inside a starship of a few thousand ton capacity. Photo-voltaic cells are both comparatively simple and within the envelope of a reasonably good fabber. Since we'd be unlikely to mount a colonization expedition on a planet without breathable air, water in quantity and visible light we should be able to use solar cells there. You need some sort of back-up for dark side hours either batteries or some type of heat engine generator operating on stored thermal energy or chemical fuel. In order to get direct use of our solar cells we'll need electric motors. Anything that can fab a motor could also do a good job on generators, piston engines, batteries and the essential parts of wind turbines. It should also be able to manufacture it's own constituent parts.
Besides the economy of sending an all-purpose manufacturing device with a colonization expedition, such a fabber would also provide some cultural security for the descendants of the expedition. Should future generations lose the technical knowledge brought from Sol System by their progenitor, yet retain the skill or lore of turning out copies of established components from fabbers, the culture could retain a level of technological competence which could allow it to conserve resources and avoid the terrible feast-starve annual cycle so common inaboriginal cultures. It's my position that a Native American or an Asian nomad would be able to understand, given the chance, an internal combustion engine or a Stirling cycle and could learn through inspection and experience, how to make use of an electric motor, light or radio. It's less likely at least to me, that the wherewithal to manufacture computer chips and program digital systems could be understood by tribesfolk ignorant of algebra and integers greater than twenty.
What alternative might there be to the digital computer for running something as complex as a fabber? To answer this question we might review the history of television. Before the digital age a great deal of electronic communication went on without anything very much resembling a computer. timing circuits and matrices of photo-electric dots caused moving pictures taken one place to appear on a screen somewhere else and it was all done with technology possible around 1920. You couldn't record a TV show in those days as we do now but you could save the film that was broadcast over the high frequency FM waves.
There is an analogous situation in which solid objects can be copied if not manipulated in all the ways possible with a computer file. Most fabbed artifacts are generated under the direction of a program drawing information from a 3-D CAD file, translating data into substance. The files themselves may be drawn on the computer with graphics programs. They may be generated by scanning a solid object. They may be generated by a combination of the two techniques, a model of some kind which is first scanned then tweaked on the computer to introduce some designer-conceived refinements. We could take a solid object and scan it "destructively," using a laser for instance sweeping back and forth, incrementing from forward to back, using very brief pulses to tick off bits of object. A detector would tell with each laser pulse if some solid has been burned away and if yes, a signal would be sent to a fabber device as a command to deposit an increment on a new build. In this way a new artifact is being built up as another one is destroyed. If we have two fabbers hooked up to the scanner we can produce two copies while one is being destroyed. This seems a bit wasteful of material but it relies upon technology which is fairly macroscopic and much less fragile than modern computers.
Inquiring a bit more deeply into how a system of this sort might work, we'll consider the mass spectrograph. This device is used to analyze the composition of a chemical sample by ionizing it within an electric field and detecting the amount of each element which falls in various regions on a plate or other deposition surface. Each atom when disassociated from others with which it was formerly joined, now existing in the ionized state has a certain charge corresponding to the number of electrons which have been torn away, I.E. One, two, three etc. and a characteristic mass as well. The electric field can pull upon the atom with a force proportional to the charge of the atom and the amount of acceleration thereby imparted to the atom is in turn proportional to the atom's mass. (From knowledge More A) Between the strength of the pull and the inertia of the mass any given type of atom will consistently travel a particular distance and come to rest at a given spot in an electric field of a given strength.
In order to sort out all of the atoms in a large object we'd need to spend a lot of time since atoms are very small and there are so many of them. We could however destructively analyze the composition of a large object by taking a tiny point sample, then burning away a chunk, point sampling again and so-on, throwing most of the mass away. Again this sounds wasteful and hopefully we'll develop ways of recovering streams of vaporized or ionized material to be recycled but there's perhaps an easier way to go about the problem without wasting much valuable material.
Though we need a solid object to break down, one which has as many separate constituents as the object we want to fabricate and use, the model need not be made from the Same constituents. If we're building an object made of copper, iron and silicon for instance we might use a model built up from droplets of molten sodium carbonate, zinc oxide and calcium hydroxide or any of these or other reasonably innocuous compounds with small amounts of different additives in each, to represent distinct materials. As the model is destructed the mass spectrometer would detect the additive molecules while the calcium, sodium potassium zinc, whatever could probably be trapped magnetically or just run through a long narrow metal channel from whence they might later be recovered, reprocessed and separated.
In copying a needed component or device we'd make one or more real working copies and at least one "model" copy from dummy materials. As long as the increments in all of the models are the same size and as long as the deposition units for each fabber uses the same material each time a given material in the real model is laid down, it won't matter to the system if it's making real components or dummy models.
Besides conductor, insulator and ferromagnetic for an electrical device we'd also need a scaffolding material, something to support overhangs as cross sections expand from bottom to top ina given build. We'll need a lubricant material to interface between separate components ina single build should we wish to generate integrated moving parts. We'll need five matter emitters at least and we'll know ahead of time what sorts of materials we'll be using so the model materials can be selected accordingly. I suspect for actual components we'd use something like the fused deposition system the vacuum chamber laser or electron beam devices which might use either wire or beads of molten material so we can build up layers each comprised of two or more elements. Alternatively we might use a powder-based technique with the materials laid down like different inks in a multi-color photo-copier, by means of charged rollers or an inverted pallet.
A destructive master-based fabbing system would differ from present techniques in another important way. In most systems we use today, we have the entire design file available to us so we can build the bottom layer just as it's seen in the computer graphic file. With a destructive technique we'd pretty much need to tick off the top layer on the master letting it become the bottom layer of the copy which will be built upside down with respect to the master or the master must be upside down and suitably supported from above which comes to about the same thing. The point is, the master must be designed to such a way as to be able to render an inverted copy. The most conceptually simple way to do this is to form a structure of some throw-away material around the master so if you turned it upside down it would have a flat surface on which to rest. then we'd arrange for the same or another cheap material to be used as support structure for the copy which would emerge upside down, with other support material as needed, able to be separated from the support structure which material could be used over and over again. In this way a bit of semi-skilled artisanry would allow an essentially blind automaton to copy one artifact from another.
Our automaton must at simplest level move a 3-D positioning system three of them at once actually, master, copy and dummy, increment by increment, along a line then over to the next line and eventually down to the next layer and so on throughout the solid object.
With each increment a signal from a particular region of the mass spectrometer would trigger the appropriate emitter to fire. These are not trivial operations but within the capability of early 20th-century television technology possibly with the exception of laser, electron beam and deposition techniques.
Chief among the things the fabber will turn out early on, will be parts for other fabbers and they will never cease to do so. Over a number of generations the colonists will encounter "drift" meaning the tendency of successive copying from one edition to the next and so to the next and on and on to accumulate mistakes, divergences, change from the original. In order to prevent this I suspect an original computerized fabber will be used to create reference models for as long as possible. Even if this Seed System breaks down entirely or is destroyed; drift can be kept at a hopefully acceptable minimum by hooking a fabber to three or more controller devices. With a fairly simple set of circuitry the replicator could average the distance or time increment dictated by the controllers and deposit a dab of matter or an energy pulse when two or more of the controllers sent simultaneous commands. It makes the electronics a little more complicated but we'll be able to fab capacitors, vacuum tubes, potentiometers, timing circuits, probably transistors.
I suspect we could with 22nd-century technology transplant a self-sustaining self-replicating technology at about the level of 1930 or so using fabbers controlled with sensors and circuitry common in that era and producible with the fabbers described here. In this way a manageable cargo sent across interstellar distances could continue to turn out household utensils, agricultural and carpentry tools, engines, stoves, radios, powered articulated limbs indefinitely. The transplanted technology would be limited in what it could produce but colonists need not build sky scrapers, super tankers and intercontinental ballistic missiles at least not for a few generations after landfall. On one or more continents rich in mineral and biological resources a comfortable way of life could be achieved in less time than it took the English Colonists in Virginia and Massachusetts Bay. Perhaps pioneers to other stars will in time set aside the size-limited design, frozen and admittedly cumbersome fabber-based industry and go after a means of doing business resembling more the industries of the 20th Century than those which took them to the stars. If so, we'd hope they'd build from the ground up with one eye on industrial pollution and the other on overpopulation but we can only hope. It could be however that most of the settlers will embrace the sense of independence a fabber for everyone could impart and they may decide to spread outward at a modest but sophisticated level of technology rather than reaching for the sky or reshaping the face of their new planet. Whether we could realistically expect a band of Lakota or Apache tribespeople to transport fabbers and the mineral extraction equipment needed to feed them across the plains or desert on painted ponies, a band of Gypsies with caravan wagons or a Viking ship plying strange coasts might be believable. A civilization once, starborne might opt for a more pastoral existence than one bound by cities or farmsteads and isn't the urge to explore and seek beyond the next horizon what brought them here in the first place? A nomadic band or agrarian village would require a technical priesthood to carry out the more opaque activities not readily accessible to the average community member but so it his always been to one extent or another from the herbalist or midwife of the Paleolithic Age to the engineers and technicians of today.