It is common for science fiction novels and screenplays to portray starships manned by people, often a rather large number of people. This of course goes back to Jules Verne, where space was seen as something to be explored by people. In the early days of the Soviet and American space programs considerable interest was put forth in piloted spacecraft. The so called race to space was seen as a contest over which side could put astronauts on the moon. It echoed the science fiction screenplays of the 1950s which depicted manned rockets flying to various destinations. Putting humans into space has been seen by many as analogous to the early age of exploration by Europeans. Yet this analogue has its problems.
While the Soviet Union was the first to launch a satellite into orbit and first with a piloted craft in orbit, it was the United States that obtained by first scientific data about space from a spacecraft. Sputnik I went into orbit and sent a repeated beep to indicate to the world its orbital presence. Yuri Gagarin was launched into one orbital cycle of the Earth, but no data about space was obtained. By contrast, Explorer I was launched months after Sputnik and found the Van Allen belts ions trapped in the Earth's magnetic field. So while the popular attention during this time was largely focused on the manned space program, most scientific progress was made in fact by probes.
The success of the Apollo lunar program seemed to suggest that the space frontier was open to humanity. The L — 5 society in the wake of the Apollo program devised grand schemes to construct large habitations positioned at Earth-moon Lagrange points. Yet the post-lunar program reality of manned space programs was less stellar. The Soviet Union lofted space stations, culminating in the MIR space station in the 1980s. The major thrust of this program was the study of human physiology in the weightless environment of Earth orbit. The United States in the 1980s began the space shuttle program, which conducted over one hundred missions. However, of these only a few had much impact on space science. The space shuttle program and the subsequent space station program have largely been very expensive and not very productive on scientific results.
There are current initiatives for putting astronauts back on the moon, and to eventually send a crew of astronauts to Mars. As yet these plans are little more than dreams advanced by the President of the United States. Little has left the drawing board to be seriously considered as a working program, and of course any such plan will have to pass the budgetary scrutiny of Congress. It also has to be mentioned that such programs have a consistent history of huge cost overruns. The ISS space station was first advanced as a 10 billion program, and it ended up costing ten times that. Curiously this program is slated for its end within five years. It is likely to have the same ignominious end the MIR station faced, streaking as fire balls through the upper atmosphere. It is very unclear whether the manned missions to the moon will at all yield any scientific results comparably larger than seen with the space shuttle and ISS space station.
A lunar program might serve scientific ends, but the program has to be designed within a direct mission oriented philosophy. It is possible that scientific facilities could be erected and maintained by a program of intermittent astronaut trips to the moon. The programs could involve astronomical instruments based on the moon, such as optical inteferometers and gravity wave interferometers. The moon would provide a solid platform for such facilities. Also the moon has a history connected to the Earth, and lunar exploration may reveal things about the early Earth. However, probably most of this could be done robotically. It is similarly likely that any facilities on the moon could largely be run robotically as well. The moon is also close enough for some of these robots to be run directly from Earth by telepresent means. So within this framework human intervention on the lunar surface would likely be kept to a minimum.
Current plans call for a permanent lunar outpost, with extensive capabilities. This has some unfortunate similarities to the space station. The lunar environment and geology can probably be very well studied with robotic and telepresent capabilities. If the purpose is purely scientific then there is a question why there should be a permanent human presence. Certainly what ever lunar geology astronauts conduct on the moon could be done with robots. Robots do not also have the environmental requirements that people do, such as breathable air, water, food, living space and others.
The space initiative suffers from some issues of mission orientation.
This initiative also calls for astronauts to be landed on Mars. This would be a very expensive program, with current cost projections in the many hundreds of billions of dollars. Obviously humans on the martian surface can perform a far wider range of activities than robots. However, a large number robotic missions designed for specific missions can be done at the cost of a single mission to send astronauts to the Mars. Currently there are two rovers on the martian surface which have conducted a very wide survey. Since they have no metabolic requirements they can also pursue tasks without a return home time limit. Further programs are envisioned for such missions to Mars. A human mission to Mars would be a huge undertaking, which would put a huge investment towards the success of a single mission. Conversely many robotic missions can be conducted for the same cost, but where a low to moderate failure rate can be tolerated. As seen with the Atlantis and Colombia shuttle crashes such catastrophes are enormous, and such a failure with a piloted mission to Mars would be the same multiplied at least ten times.
Some space enthusiasts argue that the future for space flight will mirror the age of exploration by Europeans in the New World. Of course there are a number of striking dissimilarities. The reasons for these ocean voyages had nothing to do initially with any program for exploration or colonization, but to gain access to the markets of Asia. Asia was a source for many materials that Europeans did not produce, such as silk and refined goods beyond the abilities of European artisans. These goods made their way to Europe by the silk road. The silk road was a long caravan route that traversed central Asia and made its way to Constantinople, which later became Istanbul after the Turks took the city. The silk route was prone to attacks by bandits and warring tribes of Mongols and Turkmen. Further, with the rise of the Turkish Ottoman empire these goods faced a large duty imposed on them. The voyage of Columbus was meant to connect Europe with the Asian markets directly and short circuit the silk road. The American continent got in the way of this. The Spanish colonization was instituted as a way to extract gold from Mexico to be used to barter trade in China. These goods were then sold in the European markets. Colonization was a byproduct of this profiteering.
These voyages were conducted because people were already out there. There is nobody out there in space, at least so far as can be seen. The solar system outside of Earth appears to be a complete void when it comes to these sorts of activities. Another feature with the colonization of the
Americas is that the land provided everything needed. In fact there were people already here who were perfectly culturally adapted to life in the Americas. The moon and Mars are the least hostile of any other of the planets to any attempt at colonization, but even still the environments on these planets are horrendously lethal. Literally everything required for life has to be either carried to the planet, or it has to be manufactured there with what resources might exist. Hence a colony on either of these planetary bodies must be a closed self contained system which is able to produce everything needed for the most basic requirements of life. This is possible in principle, but in practice this may not be feasible. In effect for people on a space colony or city the price of everything would reflect the high degree of fabrication required, including the air breathed. In a space city its citizens would have to pay an air bill, which would be rather considerable. The economic capacity of a space city that is able to sustain itself would on a per capita basis be orders of magnitude larger than what currently exists in any city or many nation states. Energy and prepared material do not come cheap, and in space they come at a premium.
Ideas have been advanced for space mining. It states that a space faring economy can be started with the mining of materials. Yet it has to be realized that the price for such raw material commodities are still moderately low here on Earth. Of course once the easy plums have been picked here on Earth prices will start to climb. However, the price for such materials is not likely to ever reach a height to where it will be economical to use highly fabricated materials required for a large spacecraft, plus the energy required for its navigation through space, in order to mine materials in space at a competitive market price. The lunar rocks returned from the Apollo missions have a tiny market value as a raw material source compared to the cost of the Saturn V rocket, and the materials required to construct it. It is likely that raw materials, such as metals that could be mined from space, are going to be more economically obtained from the Earth for a long time in the future. It is likely to be more economical to get metals from the Earth's mantle than from space. The gravity well of Earth is a serious barrier to schemes of easy access to space.
The economy of space has worked only for information. Comsats and other information gathering space systems have worked to some economic advantage. Of course this is a weightless quantity, well nearly so as information is physical. The next weightless quantity that might be had from space is energy. It is maybe possible to put energy collectors in geosynchronous orbit, or elsewhere in the cis-lunar environment, which beam energy back to Earth. As yet such schemes exist only in principle, but they are possible. Might this be the economic source for the colonization of space? Maybe, but it will not be cheap. Electrical energy from space, which requires an expansion of the the electricity grid off Earth, will not come at cheap me-tered price. Solar photovoltaic energy is still marginally competitive with current energy prices. Expanding this into near Earth space, even there are greater concentrations of solar radiation in space, will not come easily or inexpensively. It is further questionable whether the profit margins, or equivalently the energy surplus, from this will be sufficient to fund or energize a program of human habitation on the moon or elsewhere in the solar system.
So it appears that human expansion into the solar system is problematic. Yet it is still possible in the distant future that humans may step on some planets for a brief period of time. If things continue to progress in a responsible manner it is possible the people will at some time step on the surface of Mars. Of course this assumes that we will not contaminate Earth with any possible martian life form, and visa versa. In order to insure against martian contamination far more robotic missions to Mars are required. Probes capable of returning samples to Earth will be required to put martian material to a rigorous test for biological activity. It is only likely that humans will walk on the surface of Mars only after some of the problems and issues that confront us on Earth are resolved to a measure of sustainability. This puts a "Man on Mars" scenario at best off into the later 21st century.
Putting humans into space is often done with future scenarios of space colonies. A space colony would have to be a mini-Earth capable of supplying all the requirements of its inhabitants. Things that are provided free on Earth, which are being reduced in number as time goes by, must be manufactured. Some schemes involve very large structures with replicas of Earth, complete with forests in some cases. Of course all of this would have to be engineered and maintained in a fail-safe manner. Any failure of a life support system on a space colony could be disastrous. For a large space colony or city the level of complexity would be enormous. Anybody who has maintained a tropical fish tank, or even more a salt water tank, knows that this involves constant intervention and cost. To maintain a terraformed closed system in space would be a vastly expanded version of this.
It is possible that humans will start genetically engineering themselves, which might be required for humanity to colonize space. Again I find this to be a disturbing prospect, yet it has a some possibility or prospect. The economic pressure to have a gene engineered baby with an IQ of 160, or some other attribute, could overwhelm moral principles before long. In such a future children are not born and raised on the basis of unbidden love, but are instead designed commodities. Again something taken for granted becomes a commodity. Indeed those plastic bottles of water so ubiquitous these days illustrates this trend with water. The trends of our current age is that things once considered as "gifts" of nature become later something controlled and commodified. Already preliminary designs for computer-brain implants are being put on the drawing board. It may not be long before parents will have to equip their kids with the latest brain-silicon interface to compete. When it comes to science fiction the movie GATTACA takes a fair look at a future of a genetically modified humanity. The only good thing I can think of with respect to myself is that I will likely be dead before this happens. I would prefer that science be considered more as a sort of liberal art, instead of as a system to design increased control methods. This ideal is broken by the fact that a scientific discovery can result in a working device, while a poem does not.
It has to be noted that hybridized and genetically engineered life forms are weaker than their wild type relatives. The degree of care required for genetically modified or hybridized crops and animals is very high. These crops require intensive amounts of fertilizers and in the case of corn the pollen tassels have to be manually picked in order to fertilize the next seed crop. In the midwest August is detasseling season. Take a look at the hybridized cows these days! They hardly even look like cows. Again these hybridizations and now GMOs are done to increase yields (performance), but these organisms are utterly unable to survive on their own as their wildtype relatives. If humanity begins to design its genome much the same may result.
If economic pressures push us in these directions it implies that some subset of humanity may diverge from the rest. The poor are unlikely to have the option for gene engineered babies, and there are a lot more poor in this world than the wealthy. This divergence might push some of future humanity into space in the distant future. However, at this point these humans may be so different as to be not human in our usual sense. They may well be biologically engineered and integrated into bio-engineered and nanotech systems. In effect these neo-humans would be integrated into a control structure of vast proportions and their activities dictated according to its requirements. Again I am glad I will be dead before this happens.
On the other hand humanity may never realize any of this. The coming energy and resource short falls combined with a possible global eco-spasm due to matters such as global warming could put the kabbosh on much of this, which could also cancel any prospect for interstellar probes as well. Even if we manage to avoid this sort of collapse, we may chose to adopt a different mode of life and thinking, one where we chose not to go down this road. In other words we may find that either there are limits on control structures, or we may find pursuing more control something dystopian and to be avoided.
This does not mean that space colonies are impossible, but they are problematic. In effect we already live on a spaceship, one that evolved naturally, and where we evolved to live within it. In many ways it is a spaceship, for it orbits a G-class star, which orbits in a galaxy, a galaxy within a cluster of galaxies, where these clusters are racing away from each other in an expanding universe. The life support system on Earth is not one we need to manage, though recently in order to extract more from it we have increasingly been managing it. However, we largely breathe air and drink water without too much concern. On a space colony this would not be the case. Everything on a space colony would have to be carefully monitored and maintained with the highest of quality control. Failure to do so would run a risk of a complete disaster. Here on Earth, at least so far, we have none of these immediate concern. The question is whether the economic generator of a space colony is capable of supporting that sort of infrastructure. Further, what happens if the space colony either does not do so, or stops being an economic generator and is no longer self sufficient?
The Earth thought of as a spaceship, with a life support system, is likely to garner far more attention than any space colony. In the 21st century it is likely that the health of the planetary life support system will become a major issue. The damage we have done to it will start to effect issues such as agriculture and health. At some point we may find that we will have to restructure our technological world and be forced to engage in regardening ecosystems back to some state of health. Earth will far more likely be the "spaceship life support" issue of the 21st century than the establishment of a lunar city.
In light of this assessment, which is open to disagreement, and there will be those on the pro-space side who will disagree, we examine the prospects that humans will ever travel to the stars. A look at the charts drawn up indicates the time frames involved. The time on board a spaceship that reaches a 7 = 2 are less than Earth time. Further, once the ship has reached a 7 = 2 the time for the non-thrusted flight will be half that on Earth. A crew on board a starship would then spend up to several decades reaching their destination. This of course would be intolerable for most people. Spending the better part of one's life on a small spaceship is not very attractive for most people. It would also likely lead to a social psychology in its crew, similar to what is seen with prisons. It could easily lead to forms of insanity by some of the crew members. Obviously a small or moderate sized spacecraft designed to take people to the stars at a low gamma is not feasible. An interstellar spaceship would have to be huge.
A way around this problem is to get high gammas. A one-gee photon rocket reaches 7 = 10 rather quickly. The chart for accelerations up to one-gee gives
Thus a hypothetical star 17.42 light years away is reached by the crew on a one-gee rocket in 5.7 years of proper time, if the ship starts to decelerate at one-gee midway in the journey. Of course only 10% of the final craft makes it to y = 10 and 10% of that is left to reach the star. The remnant of the spaceship is reminiscent of the small Apollo space capsules that returned for the moon. So this cold equation indicates that the investment would be very large. This tiny remnant of a spacecraft would itself have to be large enough to supply everything required by the crew over this time frame.
A way out of this problem is with the Bussard ramjet [13.1]. A field of radiation ionizes hydrogen in front of the ship, where this field further collects the ions into the opening of the ramjet. Interstellar space consists of 10~21 kg/m3 of hydrogen. In order to collect one gram of ions per second the ramjet scoop must collect them from an area of 1018 m3. If the ship is travelling close to the speed of light, then in one second it travels near 3.0 x 108 m and so the ramjet scoop field must cover a frontal area of about g (m/sec2) T t d
3.3 x 109 m2, or 32 kilometers in radius. In a year period this would amount to 5.14 x 105 kg or 315 metric tons. Obviously for a spacecraft which is piloted a far larger amount of ions will have to be swept into the ramjet, since the spacecraft must be proportionately larger. The scoop field will have to be several orders of magnitude larger to provide the mass-energy fuel.
The ramjet was not considered for a spaceprobe. The advantage of reaching a high gamma is of limited value if the intention is to receive a signal back on Earth. If this is the intention then a spacecraft travelling at .99c is of little advantage over one travelling at .86c. A high gamma space probe is only of value to a crew on board who take advantage of their contracted proper time. A ramjet with a field capable of sucking in 3.15 x 105 tons per year, which would scoop hydrogen in a cross section of 1800 km, would get a spacecraft of - 3000 tons to its destination by accelerating one-gee to a 7 =10 and decelerating again. A 3000 ton spacecraft could potentially have crew quarters comparable to the ISS space station, with a mass of — 200 tons, where the rest of the ship is devoted to the power system and an extensive life support structure. Things might be scaled up from here. It might also be noted that in this approximate analysis nothing has been said about bringing the crew back to Earth. For a 25 year proper time round trip voyage, if they left after graduate school and training, say at the age of 30 they would return at 55+ years of age to a world that has advanced around 40 years. They would return to find their surviving friends about 15 years older than they are. It is pretty clear that the technological requirements for such a Bussard ramjet are extreme, far beyond those illustrated for a relativistic probe.
The other alternative is the interstellar ark [13.2]. This is a ponderous concept. It would be similar to the Orion concept, with some method of propulsion that pushes a huge spacecraft to high velocity, but far slower than the speed of light. The ship would have a mass in the millions to many billions of metric tons. It would house a population of people numbering from several hundred thousands to into the millions. If one were to assume that a single person's requirements were met with a minimum of a thousand tons of equipment and materials very efficiently recycled, a million populated ark would require a mass of at least billion tons. This behemoth ship would make its way through interstellar space at a small fraction of the speed of light. Given that the most interesting G-class stars are at a distance of 30 lightyears or more it would take this ship centuries to reach its destination. It will be the generations dozens of times removed from the initial generation who reach this destination.
This type of ship has appeared in popular fiction. The very campy science fiction movie Independence Day has us hapless denizens of Earth visited by something of this sort built by another species of intelligent life who have designs on our planet that don't include us. Of course by wit and fortune we defeat the nasty invaders in the end. The reality of this sort of project is of course completely outside of practical considerations. The mass and energy requirements are on the order of the space elevator, which is something that again is not likely to happen any time in the foreseeable future. It costs a billion dollars or more to send a few ton space craft to Jupiter and Saturn. The economic capacity required to construct such a spacecraft would be expanded proportionately, and even more so since it is designed to travel much faster and to survive as a closed system in the cold of interstellar space for centuries.
Of course the purpose of the interstellar ark is to colonize a planet orbiting another star. In the movie Independence Day the aliens came here to live on Earth and to ultimately refurbish their ship or build another one so they could go on to the next biologically active planet. Yet how well does this fiction conform to reality? If we ever identify a biologically active planet around another star, it would be worth sending probe to it. It is presumed we would be precautious and sterilize the probe so as not to contaminate the planet with Earth microbes. In doing so we would accumulate lots of information about the planets's ecology, the molecular structure of its life and other aspects of physiology of organisms. Robots would be deployed on the planetary surface to do the job. Obviously these robots would require a measure of artificial intelligence far beyond current capabilities. On the other hand if you were a space traveller on a landing craft on some life bearing alien surface, would you really open the door and step outside?
Again considering science fiction, the gothic science fiction horror Alien films depict a contact between humans and another life form. Here an intelligent, or at least semi-intelligent, life form is found that is completely vicious and wreaks utter havoc. There are obvious flaws in the science, such as the rapid growth of the aliens after they burst out of people, and in one movie a dog, and some other aspects of the alien fictional biology is also questionable, but there is a message here. Such direct contact between humans, and for that matter life on Earth, with some life on another planet could result in horrid consequences. The consequence could easily go both ways. In the Star Trek screen plays Kirk, Spock, McCoy and others beam down to a planet wearing their uniforms. They don't even wear spacesuits. In fact there are rather comic bits about inter-species mating, such as Spock is a cross between a Human and a Vulcan. Yet to appear on an alien bio-active planet could easily prove to be disastrous. A human being standing on the surface of a biologically active planet has an immune system evolved for Earth microbes. The biochemistry of alien life could be radically different, indeed it is almost guaranteed to be, and our immune system utterly ill-equipped to deal with such an assault. In effect Kirk and others would likely be like loaves of bread left for mould to gobble up. There might well be extraterrestrial microbes that would "see" humans as lumps of biomass to be consumed. The immune system of the hapless astronauts would respond, but likely not in a way capable of managing exposure to microscopic life forms on an alien planet. Conversely the bacteria and viruses carried by Earthly astronauts might prove to be damaging to life on an alien planet.
Astronauts would only be reasonably sent to an extrasolar terrestrial planet to examine its biology. To colonize such a planet would be a far more daunting task. In the first one risks the prospects the crew will die from some infection their immune system can't manage, with the prospect of biological contamination of the planet. When it comes to colonization it can only be said that the follies of human activity here on Earth could pale in comparison to the difficulties and disasters this would present.
Of course there are those who are chomping at the bit with objections here. And it is agreed that "never say never" has a measure of truth to it. Yet it appears that the scale of engineering required for direct human exploration of the stars, in particular with landings on biologically active planets that might be identified around another star, are very daunting. Such things are not likely to occur. Just as the solar system is probably going to be largely explored by probes and robots, where our contact will be largely by virtual reality, the same will most likely be the case with interstellar exploration.
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