Literature Search (Space Colonization)
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Year published Title/authorDepth of readingDocument typeKey quote/ClaimAbstractEvidenceFound by?CommentsLink
Murphy, Tom. Why Not Space?
Prior read
Mainly that space colonization isn't a solution to other woes.
Prior knowledge
Armstrong and Sandberg. Eternity in Six Hours
Prior read
The Fermi paradox is the discrepancy between the strong likelihood of alien intelligent life emerging (under a wide variety of assumptions) and the absence of any visible evidence for such emergence. In this paper, we extend the Fermi paradox to not only life in this galaxy, but to other galaxies as well. We do this by demonstrating that travelling between galaxies – indeed even launching a colonisation project for the entire reachable universe – is a relatively simple task for a star-spanning civilisation, requiring modest amounts of energy and resources. We start by demonstrating that humanity itself could likely accomplish such a colonisation project in the foreseeable future, should we want to. Given certain technological assumptions, such as improved automation, the task of constructing Dyson spheres, designing replicating probes, and launching them at distant galaxies, become quite feasible. We extensively analyse the dynamics of such a project, including issues of deceleration and collision with particles in space. Using similar methods, there are millions of galaxies that could have reached us by now. This results in a considerable sharpening of the Fermi paradox.
Prior knowledge
Hanson, Robin. Burning the Cosmic Commons
Prior read
Prior knowledge
Wikipedia, Space Colonization.
"The distances between galaxies are on the order of a million times further than those between the stars. Because of the speed of light limit on how fast any material objects can travel in space, intergalactic travel would either have to involve voyages lasting millions of years, or a possible faster than light propulsion method based on speculative physics, such as the Alcubierre drive. There are, however, no scientific reasons for stating that intergalactic travel is impossible in principle."

"The Biosphere 2 project in Arizona has shown that a complex, small, enclosed, man-made biosphere can support eight people for at least a year, although there were many problems. A year or so into the two-year mission oxygen had to be replenished, which strongly suggests that they achieved atmospheric closure."

"In 2002, the anthropologist John H. Moore estimated that a population of 150–180 would allow normal reproduction for 60 to 80 generations — equivalent to 2000 years.

A much smaller initial population of as little as two women should be viable as long as human embryos are available from Earth. Use of a sperm bank from Earth also allows a smaller starting base with negligible inbreeding.

Researchers in conservation biology have tended to adopt the "50/500" rule of thumb initially advanced by Franklin and Soule. This rule says a short-term effective population size (Ne) of 50 is needed to prevent an unacceptable rate of inbreeding, whereas a long‐term Ne of 500 is required to maintain overall genetic variability. The Ne = 50 prescription corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders. The Ne = 500 value attempts to balance the rate of gain in genetic variation due to mutation with the rate of loss due to genetic drift."

"Organizations that contribute to space colonization include:

The Space Studies Institute funds the study of space habitats.
The National Space Society is an organization with the vision of people living and working in thriving communities beyond the Earth. The NSS also maintains an extensive library of full-text articles and books on space settlement.[70]
The Space Frontier Foundation performs space advocacy including strong free market, capitalist views about space development.
The Living Universe Foundation has a detailed plan in which the entire galaxy is colonized.
The Colonize the Cosmos site advocates orbital colonies.[71]
The Mars Society promotes Robert Zubrin's Mars Direct plan and the settlement of Mars.
The Planetary Society is the largest space interest group, but has an emphasis on robotic exploration and the search for extraterrestrial life.
The Space Settlement Institute is searching for ways to make space colonization happen in our lifetimes.[72]
Students for the Exploration and Development of Space (SEDS) is a student organization founded in 1980 at MIT and Princeton.[73]
Foresight Nanotechnology Institute – Guiding nanotechnology research to improve fuels, smart materials, uniforms and environments for the pursuit of space exploration and colonization.[74]
The Alliance to Rescue Civilization plans to establish backups of human civilization on the Moon and other locations away from Earth.
The Artemis Project plans to set up a private lunar surface station.[citation needed]
The British Interplanetary Society promotes ideas for the exploration and utilization of space, including a Mars colony, future propulsion systems (see Project Daedalus), terraforming, and locating other habitable worlds.[75][76](registration required)
In June 2013 the BIS began a project [77] to re-examine the space colony studies of the 1970s and revise them in view of advances made since then."
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Conger, Cristen. Will humans be living in space in the next 50 years?
Very partial read
Some people are talking about a lunar base in the next few decades.

"If all goes according to plan, humans will have been living in space for more than 20 years when NASA's centennial celebration rolls around in 2058. As part of President Bush's "Vision for Space Exploration" plan, the agency announced in 2006 that astronauts would break ground on a lunar base settlement no later than 2020 "
Google: space colonization possible
Focused on near-term colonization
NASAish thing. Space Settlement Basics
Quick skim
Focused on within the solar system stuff
Google: space colonization possible
Focused on within the solar system stuff

There are background reading references here

Harris, Philip Robert. Space Enterprise: Living and Working Offworld in the 21st Century. Berlin; New York: Chichester, UK: In association with Praxis Publishing, 2009. ISBN: 9780387776392
TL795.7 .H38 2009 BOOKSTACKS

Krone, Robert M. Beyond Earth: The Future of Humans in Space. Burlington, Ont.: Apogee Books, 2006. ISBN: 1894959418
TL795.7 .B49 2006 BOOKSTACKS

OECD International Futures Programme. Space 2030: Exploring the Future of Space Applications. Paris, France: OECD, 2004. ISBN: 9264020322
T174 .S63 2004 BOOKSTACKS

O'Neill, Gerard K. The High Frontier: Human Colonies in Space. Burlington, Ont.: Apogee Books, 2000. ISBN: 189652267X
TL795.7 .O53 2000 BOOKSTACKS
Note: This edition comes with a CD-ROM of additional resources.

Rouge, Joseph D. Space-based Solar Power as an Opportunity for Strategic Security: Phase O Architecture Feasibility Study: Report to the Director, National Security Space Office, Interim Assessment, release 0.1. Arlington, VA: National Security Space Office, 2007.
TK1545 .S633 2007 BOOKSTACKS

Schmitt, Harrison H. Return to the Moon: Exploration, Enterprise, and Energy in the Human Settlement of Space. New York, NY: Copernicus Books, in association with Praxis Publishing, 2006. ISBN: 9780387242859
TL799 .M6 S34 2006 BOOKSTACKS

Schrunk, David G., et al. The Moon: Resources, Future Development, and Settlement. Berlin; New York: Springer; Chichester, UK: Published in association with Praxis Pub., 2008. ISBN: 9780387360553
QB 582.5 .S37 2008 BOOKSTACKS

Tumlinson, Rick, and Erin Medlicott (eds.). Return to the Moon. Burlington, Ont.: Apogee Books, 2005. ISBN: 1894959329
TL799 .M6 R48 2005 BOOKSTACKS

Wingo, Dennis. Moonrush: Improving Life on Earth with the Moon's Resources. Burlington, Ont.: Apogee Books, 2004. ISBN: 1894959108
QB582.5 .W56 2004 BOOKSTACKS
Wikipedia, 100 Year Starship
Full read$1.1M spent on thinking about how to do space colonization
The 100 Year Starship study is the name of a one year project to assess the attributes of and lay the groundwork for an organization that can carry forward the 100 Year Starship vision.[2][3] Former NASA astronaut Mae Jemison made the winning bid as leader of her own foundation, the Dorothy Jemison Foundation for Excellence.[4] The Dorothy Jemison Foundation for Excellence was partnered on the DARPA project with Icarus Interstellar, a non-profit organisation that is dedicated to interstellar travel,[5] and the Foundation for Enterprise Development.
100 Year Starship Symposium[edit]

Prior to the solicitation for the foundation, the Hundred Year Starship project was initiated with a conference held in Orlando, FL, from September 30 to October 2 2011, co-sponsored by DARPA and NASA, organized by DARPA’s Tactical Technology Office director, David Neyland.[6][7] The conference included presentations on the technology, biology, physics, philosophy, sociology, and economics of interstellar flight.[8][9] Selected papers from the conference were published in the Journal of the British Interplanetary Society.
After naming the Jemison foundation as winner of the solicitation, a second symposium was held in 2012 in Houston. Papers on a number of subjects related to interstellar flight and organization of the foundation were presented,[2] among these a paper by Dr. Harold ("Sonny") White[10] of NASA's Johnson Space Center discussing an attempt to measure the warping of space time using a Michelson interferometer[11] to investigate the possibility of faster-than-light travel.[12]

The Defense Advanced Research Projects Agency (DARPA) is the primary funding agency together with the support of NASA Ames Research Center. So far, NASA has contributed $100,000 while DARPA has contributed $1 million.[1]
100-year starship project referenced by Carl Shulman
NASA Headquarters Library: Space Colonization
First few paragraphs
It has a lot of references.
"We have put men on the Moon. Can people live in space? Can permanent communities be built and inhabited off the Earth? Not long ago these questions would have been dismissed as science fiction, as fantasy or, at best as the wishful thinking of men ahead of their times Now they are asked seriously not only out of human curiosity, but also because circumstances of the times stimulate the thought that space colonization offers large potential benefits and hopes to an increasingly enclosed and circumscribed humanity.
Permanent communities can be built and inhabited off the Earth. The following chapters present a detailed description of a system for the colonization of space. It is not the best system that can be devised; nor is it complete. Not all the important questions about how and why to colonize space have been posed. Of those that have, not all have been answered satisfactorily. Nevertheless, the 10-week summer study is the most thorough and comprehensive one made to date. On its basis space colonization appears to be technically feasible, while the obstacles to further expansion of human frontiers in this way are principally philosophical, political, and social rather than technological."
Google: space colonization possible
R.D. Johnson, C Holbrow, editors, Space Settlements: A Design Study, NASA, SP-413, Scientific and Technical.
First few paragraphs
"Nevertheless, the 10-week summer study is the most thorough and comprehensive one made to date. On its basis space colonization appears to be technically feasible, while the obstacles to further expansion of human frontiers in this way are principally philosophical, political, and social rather than technological"\
Google: space colonization possible
Space Settlements: A Design Study, provides information on space settlement development and education and assists teachers and students in the NASA Ames Space Settlement Design Contest (see the Space Settlement Web Site). The design study was the result of a 10 week program in engineering systems design held at Stanford University and Ames Research Center in the summer of 1975. Participants included professors, technical directors and students in a variety of disciplines from physical science and architecture to engineering and social science. The goal (see preface) was to construct a vision of how people might sustain life in space in a large colony.
The study was copied and placed on the WWW by Bryan Yager with assistance from Hendrick Lee and Gail Felchle. The project was mentored by Al Globus and sponsored by NAS (Numerical Aerodynamic Simulation).

The document (hard copy) is available through NASA/Ames Research Center Library. For further information contact the reference staff at (650) 604-6325.

R.D. Johnson, C Holbrow, editors, Space Settlements: A Design Study, NASA, SP-413, Scientific and Technical.
Wikipedia, Space Habitat
Intro, quick scan
Google: space colonization vs. space settlement
Stross, Charles. HIgh Energy Redux.
Full read and clips (not all comments read)
"I won't rule out the possibility of such seemingly-magical technology appearing at some time in the future in the absence of technology indistinguishable from magic that, interstellar travel for human beings even in the comfort of our own Solar System is near-as-dammit a non-starter."
Referenced by the Daily Galaxy
Daily Galaxy, The. Stephen Hawking on Space Colonization - The Human Future or SciFi Fantasy? (Today's 'Most Popular')
Hawking says it's possible, Charles Stross says it's unlikely to ever happen (but not impossible).

"Stross sums up by saying that while "I won't rule out the possibility of such seemingly-magical technology appearing at some time in the future in the absence of technology indistinguishable from magic that, interstellar travel for human beings even in the comfort of our own Solar System is near-as-dammit a non-starter."

Stross's blog received over 450 comments as of this writing. The most prescient follows:

"First, Stross's analysis fails to take into account future civilization types; I get the sense that he takes a normative view of today's technological and economic realities and projects them into the future. This is surprising, not only because he's an outstanding science fiction visionary, but also because he's a transhumanist who has a very good grasp on what awaits humanity in the future. Specifically, he should be taking into account the possibility of post-Singularity, Drexlerian, Kardashev Type II civilizations. Essentially, we're talking about post-scarcity civilizations with access to molecular assembling nanotechnology, radically advanced materials, artificial superintelligence, and access to most of the energy available in the solar system.

"Stross also too easily dismisses how machine intelligences, uploaded entities and AGI will impact on how space could be colonized. He speculates about biological humans being sent from solar system to solar system, and complains of the psychological and social hardships that could be inflicted on an individual or crew. He even speculates about the presence of extraterrestrial pathogens that undoubtedly awaits our daring explorers. This is a highly unlikely scenario. Biological humans will have no role to play in space. Instead, this work will be done by robots and quite possibly cyborgs (which is how the term 'cyborg' came to exist in the first place).""
Google: space colonization possible
O'Neill, Gerard. The Colonization of Space
Title only
Conference notes?
Referenced by the L5 Society WIkipedia page
Wikipedia, L5 Society
Carl Shulman (prior knowledge)
Wikipedia. The High Frontier: Human Colonies in Space
Partial read
Stross is the main critic listed here.
The High Frontier: Human Colonies in Space is a 1976 book by Gerard K. O'Neill, a road map for what the United States might do in outer space after the Apollo program, the drive to place a man on the Moon. It envisions large manned habitats in the Earth-Moon system, especially near stable Lagrangian points. Three designs are proposed: Island one (a modified Bernal sphere), Island two (a Stanford torus), and Island 3, two O'Neill cylinders. These would be constructed using raw materials from the lunar surface launched into space using a mass driver and from near-Earth asteroids. The habitats were to spin for simulated gravity and be illuminated and powered by the sun. Solar power satellites were proposed as a possible industry to support the habitats.
The book won the 1977 Phi Beta Kappa Award in Science.[1]
Referenced by the L5 Society WIkipedia page
NASAish thing. Space Settlements: spreading life throughout the solar system
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McClellan, Heather. Microgravity Makes Interstellar Travel Impossible, Say Experts.
Full readJournalism
"Giving birth in zero gravity is going to be hell because gravity helps you [on Earth]," said Athena Andreadis, a biologist from the University of Massachusetts Medical School. "You rely on the weight of the baby."

All of this means that we're not going anywhere, perhaps not even Mars, until we master either artificial gravity or some seriously speedy travel methods. Although this news won't come as a surprise to anybody who's put serious thought into interstellar travel, it is humbling to be reminded of these things from time to time. Humans are perfectly adjusted for life on Earth; as Andreadis noted, we'll have to adapt to both the journey and the destination if we're ever to leave.
Google: experts on interstellar travel
Anders Sandberg on Space Colonization
Full readInterviewMIRI blog
Piersma, Theunis. Why space is the impossible frontier
Opinion piece
You can't do long-haul space travel because our bodies don't work well without gravity long-term. (The article does not address any of the proposed solutions to this problem.)
Dreams of long-haul space travel or even colonisation ignore basic biological constraints that anchor us firmly to the Earth, argues Theunis Piersma
Google: space colonization impossible
Finkel, Alan. Forget space travel: it’s just a dream
Full read
Opinion piece?
"HUMAN EXPANSION across the Solar System is an optimist’s fantasy. Why? Because of the clash of two titans: physics versus chemistry.

In the red corner, the laws of physics argue that an enormous amount of energy is required to send a human payload out of Earth’s gravitational field to its deep space destination and back again.

In the blue corner, the laws of chemistry argue that there is a hard limit to how much energy you can extract from the rocket fuel, and that no amount of ingenuity will change that."

I'd summarize the argument as:
1. It would take a very large amount of energy to travel to and from Mars.
2. We can't get that much energy with rocket fuel, no matter how much we optimize it.
3. Therefore, we can't travel to and from Mars.

And then he has some extra stuff to say about why it isn't going to improve.

Lots of energy: "Start with a lightweight payload – a dozen astronauts collectively weighing less than a tonne. Now add the life support systems for a one-year journey, with sufficient food, water, oxygen and an energy source to keep their living quarters warm and bright. Fifty tonnes, perhaps?

Add the rockets and rocket fuel for mid-course corrections, and for landing somewhere interesting then taking off to return to Earth, and the mass spirals to excess.

The laws of physics are immutable. According to these laws, accelerating that large mass and fighting against planetary gravitational fields requires a tremendous amount of energy."

Can't do it with current rocket fuel and not going to improve enough: "Now consider the laws of chemistry. You can’t change them by legislation. The energy content that can be liberated from rocket fuel, and the propulsion force that can be generated, depend on the mass of the fuel, the molecular bond energies and the temperature at which the chemicals burn.

Scientists and rocket engineers have known this for more than a century and have worked hard to optimise all the parameters. But at the end of the day, there is only so much that you can get out of the rocket fuel – and it’s not enough.

SOMEHOW, THE FACT that this clash of the titans restricts our ability to undertake deep space flights doesn’t feel right. Surely the magic of our success in electronics and information systems should apply?

Moore’s law tells us that every two years the number of transistors in an integrated circuit doubles. Futurologists assure us that the total volume of humanity’s knowledge doubles every five years. Why, then, shouldn’t our ability to lift a payload double every five, 10 or even 20 years?

Sadly, the analogy does not apply. In the case of electronics and information systems, we are dealing with soft rules, related to the limits of human ingenuity. In the case of space flight, we are dealing with hard rules, related to the limits of physics and chemistry.

Rocket engineers and scientists have been battling these limits of physics and chemistry for years, with diminishing prospects for further gains."

The clash of two titans - physics and chemistry - are major barriers to human space travel to Mars and beyond, and may well make it impossible ... at least with existing technologies.
Google: space colonization impossible
Doesn't engage with many technological possibilities.

"Alan Finkel is a neuroscientist and entrepreneur, and one of the founders of COSMOS. He is the Chief Technology Officer of Better Place Australia, and the Chancellor of Monash University."
Wikipedia. Interstellar travel
Mostly read
"Given sufficient travel time and engineering work, both unmanned and sleeper ship interstellar travel requires no break-through physics to be achieved, but considerable technological and economic challenges need to be met. NASA, ESA and other space agencies have been engaging in research into these topics for decades, and have accumulated a number of theoretical approaches."

"The energy requirements make interstellar travel very difficult. It has been reported that at the 2008 Joint Propulsion Conference, multiple experts opined that it was improbable that humans would ever explore beyond the Solar System.[3] Brice N. Cassenti, an associate professor with the Department of Engineering and Science at Rensselaer Polytechnic Institute, stated at least the total energy output of the entire world [in a given year] would be required to send a probe to the nearest star.[3]"
"Interstellar space travel is manned or unmanned travel between stars. The concept of interstellar travel via starships is a staple of science fiction. Interstellar travel is conceptually much more difficult than interplanetary travel. The distance between the planets in the Solar System is typically measured in standard astronomical units, while the distance between the stars is hundreds of thousands of AU and often expressed in light years. Intergalactic travel, or travel between different galaxies, would be even more difficult.
A variety of concepts have been discussed in the literature, since the first astronautical pioneers, such as Konstantin Tsiolkovsky, Robert Esnault-Pelterie and Robert Hutchings Goddard. Given sufficient travel time and engineering work, both unmanned and sleeper ship interstellar travel requires no break-through physics to be achieved, but considerable technological and economic challenges need to be met. NASA, ESA and other space agencies have been engaging in research into these topics for decades, and have accumulated a number of theoretical approaches."
Link from Wikpedia: Space Colonization
Wikipedia. Icarus Interstellar.
Link from WIkipedia: interstellar travel
O'Neill, Gerard. Summarization of Conference: The Colonization of Space.
Title only
Conference summary
Google Scholar: space colonization possible
Schrunk, David et al. The Moon: Resources, Future Development and Colonization, by David Schrunk, Burton Sharpe, Bonnie Cooper, Madhu Thangavelu, pp. 466. ISBN 0-471-97635-0. Wiley-VCH , July 1999.
This unique, visionary and innovative book describes how the Moon could be colonised and developed as a platform for science, industrialization and exploration of our Solar System and beyond. Thirty years ago, the world waited with baited breath to watch history in the making, as man finally stepped onto the moon's surface. In the last few years, there has been growing interest in the idea of a return to the moon. This book describes the reasons why we should now start lunar development and settlement, and how this goal may be accomplished. The authors, all of whom are hugely experienced space scientists, consider the rationale and steps necessary for establishing permanent bases on the Moon. Their innovative and scientific-based analysis concludes that the Moon has sufficient resources for large-scale human development. Their case for development includes arguments for a solar-powered electric grid and railroad, creation of a utilities infrastructure, habitable facilities, scientific operations and the involvement of private enterprise with the public sector in the macroproject. By transferring and adapting existing technologies to the lunar environment, the authors argue that it will be possible to use lunar resources and solar power to build a global lunar infrastructure embracing power, communication, transportation, and manufacturing. This will support the migration of increasing numbers of people from Earth, and realization of the Moon's scientific potential. As an inhabited world, the Moon is an ideal site for scientific laboratories dedicated to geosciences, astronomy and life sciences, and most importantly, it would fulfil a role as a proving ground and launch pad for future Solar System exploration. The ten chapters in this book go beyond the theoretical and conceptual. With vision and foresight, the authors offer practical means for establishing permanent bases on the Moon. The book will make fascinating and stimulating reading for students in astronautics, space science, life sciences, space engineering and technology as well as professional space scientists, engineers and technologists in space projects.
Google Scholar: space colonization possible
Tziolas, Andreas. Why I want to make interestellar travel possible
Opinion piece
"A new research program run by my organisation, Icarus Interstellar, is bringing in scientists from around the world to aid in the design, development and construction of the first interstellar spacecraft in our lifetime. The founding members are volunteer scientists, researchers and enthusiasts who understand the incredible magnitude of such an ambitious endeavour and the scientific merit it brings."
My organisation wants to produce the necessary technologies to make interstellar flight possible. In order to do that, we must join forces and continue to invest in space exploration
Google: interstellar travel possible
Cain, Fraser. When Will We Become Interstellar?
Quick read
Interview with
"“I think it is possible for humans to become an interstellar race. I think it’s possible, but not within my lifetime, not the next hundred years without some really transformative technologies in between. The key one on the International Space Station right now we’re testing life support systems, and doing phenomenally well. But the International Space Station is close to earth, so if something breaks down, you can conceivably just hop down and bring something back up, although it is conceivable more complicated than that. As for putting human colonies on other planets, yeah, that’s hard, but you’ve got a gravitational well and you’ve got a base there, you assume that they’ve got some sort of infrastructure working.”
Google: interstellar travel possible
"I’m Dr. Ian O’Neill. I work for Discovery News – I’m their space producer. My background is as a scientist – I’m a solar physicist. I got my PhD in Coronal physics."
MIT Technology Review. Interstellar Travel Not Possible Before 2200AD, Suggests Study
Full readJournalism
A new estimate of the amount of energy needed to visit the stars suggests we won’t have enough for at least another two centuries
Google: interstellar travel possible
The study uses trend extrapolation for available energy (to humanity in total) and the portion of the available energy that gets used on space projects.
Millis, Marc. Energy, incessant obsolescence, and the first interstellar missions
Projections for the earliest interstellar mission possibilities are calculated based on 27 years of data on historic energy trends, societal priorities, required mission energy, and the implications of the Incessant Obsolescence Postulate (Where newer probes pass prior probes). Two sample missions are considered: launching a minimal colony ship where destination is irrelevant, and sending a minimal probe to Alpha Centauri with a 75 year mission duration. The colony ship is assumed to have a mass of 10^7 kg, and the probe 10^4 kg. It is found that the earliest interstellar missions could not begin for roughly another 2 centuries, or 1 century at best. Even when considering only the kinetic energy of the vehicles without any regard for propellant, the colony ship cannot launch until around the year 2200, and the probe cannot launch until around 2500. Examination of the Incessant Obsolesce Postulate shows that it becomes irrelevant under several conditions.
Referenced by MIT Technology Review
Nielsen, Nick. Cosmic loneliness and interstellar travel
Partial skim
I have mentioned inertial confinement fusion above as a possible starship propulsion system, but this example is not necessary to my argument. If there existed only a single propulsion proposal for interstellar travel, and all our hopes for such travel rested on an unknown science and an unknown technology, we would have good reason to be skeptical that interstellar travel would ever be possible under any circumstances. This, however, is not the case. There are a wide variety of potential interstellar propulsion technologies, including inertial confinement fusion, matter-antimatter, quantum vacuum thrusters, and other even more exotic ideas. As long as industrial-technological civilization continues its development, some advanced propulsion idea is likely to prove successful, if only marginally so, but marginally will be enough for the first pioneers who are willing to sacrifice all for the chance at a new world.
Google: interstellar travel possible
Rahls, Chuck. Interstellar Spaceflight: Is It Possible?
Partial skim
"With current space travel limited to just a few robotic probes visiting nearby planets, how realistic is it to think about reaching the nearest stars? For the short term, not very – especially when we speak of manned missions. But the long term - 50 or even 100 years - chances are good mankind will have missions, unmanned to start with, traveling to stars in our galactic neighborhood."

"A study by NASA in 1998 identified 3 potential propulsion technologies that might enable exploration beyond our solar system. Antimatter, fusion and light sails."
Google: interstellar travel possible
NASA. In-Space Propulsion Systems Roadmap
Foreword and title only
Background reading on 100 Year Startship
Seven Sci-Fi Scenarios For Interstellar Space Travel That Could Happen In This Century
7 possible ways of interstellar travel
Background reading on 100 Year Startship
100 Year Starship Symposium Summary
Conference Summary
Background reading on 100 Year Startship
Zubrin, Robert. Entering Space: Creating a Spacefaring Civilization
Amazon page, Wikipedia page (for the book)
Using nuts-and-bolts engineering and a unique grasp of human history, Robert Zubrin takes us to the not-very-distant future, when our global society will branch out into the universe. From the current-day prospect of lunar bases and Mars settlements to the outer reaches of other galaxies, Zubrin delivers the most important and forward-looking work on space and the true possibilities of human exploration since Carl Sagan's Cosmos.

Sagan himself said of Zubrin's humans-to-Mars plan, "Bob Zubrin really, nearly alone, changed our thinking on this issue." With Entering Space, he takes us further, into the prospect of human expansion to the outer planets of our own solar system--and beyond.
Robert Zubrin Wikipedia page
Stross, Charles. The myth of the starship.
Full read and clips (not all comments read)
Note that I'm fairly optimistic about mature diamond-phase nanotechnology (or some cognate thereof). The economic benefits of getting it are huge, and there are no obvious lacunae on the technology road map — unlike, say, fusion or manned interplanetary space travel. I'mless optimistic about mind uploading, because in neuroscience we are just about at the stage of beginning to figure out how ignorant we are. And I'm pessimistic about AGI, because I don't think we stand a hope in hell of working out how to design an artificial general intelligence until we know, at least in outline, what human general intelligence is. (And we don't.) But I suspect some combination of these technologies will show up sooner or later — barring resource-depletion crashes and/or habitable-biosphere-envelope departures on a planetary scale — and once you've got two out of the three, a starwisp-driven expansion starts to look feasible (if energetically expensive...
So, to summarize: yes, I think human interstellar exploration (and yes, maybe even colonization) might be possible, after a fashion. But to get there, we're going to have to master at least two entire technological fields that don't yet exist, even before we start trying to blast compact disc sized machines up to relativistic velocities. And that's without considering the difficulty of how to cram an industrial infrastructure capable of building more of itself, of a machine capable of surviving in deep space — the equivalent of those 300,000 NASA technicians and engineers — into the aforementioned CD-sized machine ...

If we succeed in doing it, it's going to look nothing like the Starship Enterprise. Or even New Horizons. The whole reference frame we instinctively assume when we hear the word "ship" is just so wrong it's beyond wrong-ness: it's on a par with Baron Munchausen's lunar exploitsas seen in light of the Apollo Program. We need a new handle for discussing and analyzing such a venture. And the sooner we consign the "-ship" suffix to the dustbin of failed ideas, the better.
Not available
Carl Shulman
Charles Stross is mildly optimistic about the in-principle feasibility of interstellar travel and colonization.
Landis, Geoffrey. The Colonization of Venus.
Conference paper
Although the surface of Venus is an extremely hostile environment, at about 50 kilometers above the
surface the atmosphere of Venus is the most earthlike environment (other than Earth itself) in the solar
system. It is proposed here that in the near term, human exploration of Venus could take place from
aerostat vehicles in the atmosphere, and that in the long term, permanent settlements could be made in the
form of cities designed to float at about fifty kilometer altitude in the atmosphere of Venus.
Google Scholar: geoffrey landis interstellar
Landis, Geoffrey. Beamed Energy Propulsion for Practical Interstellar Flight
Theory/engineering paper?
At the recent workshop on Robotic Interstellar Exploration, a group was formed to analyze potential beamed power systems for interstellar exploration. Three “strawman” missions were proposed, culminating in a practical interstellar flyby. In addition, a “roadmap” of near-term missions to develop the technology was proposed.
Google Scholar: geoffrey landis interstellar
Landis, Geoffrey. Interstellar flight by particle beam
Theory/engineering paper?
Two difficulties with the use of laser-propelled lightsails for interstellar propulsion are the extremely low energy efficiency, and the extremely large lenses required. The energy efficiency can be greatly increased and the required lens size may be greatly decreased by use of a particle beam, rather than a light beam. The particle beam is reflected by a magnetic field on the spacecraft, for example, by a magnetic sail or a mini-magnetosphere inflated by a plasma current. This results in a net force on the sail with no expenditure of propellant, allowing missions of extremely high delta-V, such as an interstellar probe, to be accomplished. Compared to other beam-pushed propulsion systems, the particle-beam pushed sail has the advantages of light weight, high target area, high thermally limited acceleration, high momentum to energy ratio, high beam energy efficiency, and low beam divergence.
Google Scholar: geoffrey landis interstellar
Mallove and Matloff. The Starflight Handbook: A Pioneer's Guide to Interstellar Travel
Amazon page
Amazon: "The Starflight Handbook A Pioneer's Guide to Interstellar Travel "The Starflight Handbook is an indispensable compendium of the many and varied methods for traversing the vast interstellar gulf--don't leave the Solar System without it!" --Robert Forward "Very sensible, very complete and useful. Its good use of references and technical 'sidebars' adds to the book and allows the nontechnical text to be used by ordinary readers in an easy fashion. I certainly would recommend this book to anyone doing any thinking at all about interstellar flight or the notion of possibilities of contacts between hypothetical civilizations in different stat systems." --Louis Friedman Executive Director, The Planetary Society The Starflight Handbook is the first and only compendium on planet Earth of the radical new technologies now on the drawing boards of some of our smartest and most imaginative space scientists and engineers. Scientists and engineers as well as general readers will be captivated by its:
* In-depth discussions of everything from nuclear pulse propulsion engines to in-flight navigation, in flowing, non-technical language
* Sidebars and appendices cover technical and mathematical concepts in detail
* Seventy-five elegant and enlightening illustrations depicting starships and their hardware"
Recommended by Geoffrey Landis
Mauldin, John. Prospects for Interstellar Travel
Amazon page
Amazon reviewer: "This book presents, in technical terms understandable to most any engineering or science major, the prospects and problems involved with planning an actual interstellar space mission. The bad news, for devotees of Star Trek and others who hope we can easily cross large sections of the Galaxy at will just a few centuries from now, is that the basic laws of physics and engineering as we currently understand them simply rule this out. At best, we are limited to the notion of a relatively slow, multi-generation spacecraft to reach even the closest stars. The author examines, in detail, the different options available for propelling such a ship, and the engineering and human design factors for making it functional. The writing style is a bit dry, but the technical analysis is thorough, yet not overwhelming for one who is not a specialist in the field. Perhaps the ultimate message of this book is that star flight dreamers may have to lower their expectations of "warp drives" and jumps into "hyperspace", or else hope for unexpected breakthroughs in spaceflight technology, ones that will allow us to bypass limits as we currently understand them and someday give us the capability for true, practical high speed travel to the stars."
Amazon review of Mallove and Matloff 1989
Gilster, Paul. Centauri Dreams.
Amazon page
Why, today, would anyone undertake a plan to launch a spacecraft some 30 years in the future, and on a journey that would take some 40 years to complete? Paul Gilster investigates the science, and the spirit, of the NASA and JPL researchers who are actually at work on just such a project.

From the reviews:

"Gilster introduces the challenges of imagining and planning interstellar exploration by leading readers through the difficulties of reaching and exploring the nearest bright star, Alpha Centauri. Seeded by ideas and concepts of the late Robert Forward, the narrative is framed as a learning process undertaken simultaneously by writer and reader. Although Alpha Centauri is astronomically nearby, a postulated trip by robot spacecraft, followed by manned exploration, would take 50 to 1,000 years, depending on the type of spacecraft propulsion used. Various methods for interstellar travel are introduced and discussed, including solar sails that use the power of starlight, nuclear fusion, antimatter hybrid systems, and beamed laser propulsion. One challenge is to get there in a reasonable time so that funding support, public interest, and events on Earth will not divert attention from the mission. Another challenge is timing the mission relative to available technology, because with better technology it might be possible to send a later robot on the same mission in less time. The book has no figures, tables, or illustrations but does include 30 pages of notes and an adequate 14-page index. Though the concepts presented are often fanciful, this book will appeal to readers who wonder about the future of exploration beyond the solar system. Summing Up: Highly recommended. General readers; professionals." (W. E. Howard III, CHOICE, March 2005)
Searching for Mallove and Matloff 1989
Centauri Dreams is also a website with many blogposts and essays related to interstellar colonization. A look at the introduction suggests that Paul spoke with many of the most informed people on these issues. Paul's background is in journalism.
Long, K. F. Deep Space Propulsion: A Roadmap to Interstellar Flight
Amazon page
Amazon: The technology of the next few decades could possibly allow us to explore with robotic probes the closest stars outside our Solar System, and maybe even observe some of the recently discovered planets circling these stars. This book looks at the reasons for exploring our stellar neighbors and at the technologies we are developing to build space probes that can traverse the enormous distances between the stars.

In order to reach the nearest stars, we must first develop a propulsion technology that would take our robotic probes there in a reasonable time. Such propulsion technology has radically different requirements from conventional chemical rockets, because of the enormous distances that must be crossed. Surprisingly, many propulsion schemes for interstellar travel have been suggested and await only practical engineering solutions and the political will to make them a reality. This is a result of the tremendous advances in astrophysics that have been made in recent decades and the perseverance and imagination of tenacious theoretical physicists. This book explores these different propulsion schemes – all based on current physics – and the challenges they present to physicists, engineers, and space exploration entrepreneurs.

This book will be helpful to anyone who really wants to understand the principles behind and likely future course of interstellar travel and who wants to recognizes the distinctions between pure fantasy (such as Star Trek’s ‘warp drive’) and methods that are grounded in real physics and offer practical technological solutions for exploring the stars in the decades to come.
Commonly bought on Amazon with Centauri Dreams
Johnson, Les (ed). Going Interstellar
Amazon page
Edited volume
Amazon: A collection of tales by an all-star assortment of award winning authors including Ben Bova, Mike Resnick, Jack McDevitt, Michael Bishop, Sarah Hoyt and more together with essays on high technology by space scientists and engineers – all taking on new methods of star travel.

Some humans may be content staying in one place, but many of us are curious about what’s beyond the next village, the next ocean, the next horizon. Are there others like us out there? How will we reach them? Others are concerned with the survival of the species. It may be that we have to get out of Dodge before the lights go out on Earth. How can we accomplish this? Wonderful questions. Now get ready for some answers.

Here is the science behind interstellar propulsion: reports from top tier scientists and engineers on starflight propulsion techniques that use only means and methods that we currently know are scientifically possible. Here are in-depth essays on antimatter containment, solar sails, and fusion propulsion. And the human consequences? Here is speculation by a magnificent array of award-winning SF writers on what an interstellar voyage might look like, might feel like—might be like. It’s an all-star cast abounding with Hugo and Nebula award winners: Ben Bova, Mike Resnick, Jack McDevitt, Michael Bishop, Sarah Hoyt and more.

Comprehensive Teacher's Guide available.
Commonly bought on Amazon with Long 2011
Millis and Davis. Frontiers of Propulsion Science
Amazon page
Amazon: "Frontiers of Propulsion Science" is the first-ever compilation of emerging science relevant to such notions as space drives, warp drives, gravity control, and faster-than-light travel - the kind of breakthroughs that would revolutionize spaceflight and enable human voyages to other star systems. Although these concepts might sound like science fiction, they are appearing in growing numbers in reputable scientific journals. This is a nascent field where a variety of concepts and issues are being explored in the scientific literature, beginning in about the early 1990s. The collective status is still in step 1 and 2 of the scientific method, with initial observations being made and initial hypotheses being formulated, but a small number of approaches are already at step 4, with experiments underway. This emerging science, combined with the realization that rockets are fundamentally inadequate for interstellar exploration, led NASA to support the Breakthrough Propulsion Physics Project from 1996 through 2002. "Frontiers of Propulsion Science" covers that project as well as other related work, so as to provide managers, scientists, engineers, and graduate students with enough starting material that they can comprehend the status of this research and decide if and how to pursue it in more depth themselves. Five major sections are included in the book: Understanding the Problem lays the groundwork for the technical details to follow; Propulsion Without Rockets discusses space drives and gravity control, both in general terms and with specific examples; Faster-Than-Light Travel starts with a review of the known relativistic limits, followed by the faster-than-light implications from both general relativity and quantum physics; Energy Considerations deals with spacecraft power systems and summarizes the limits of technology based on accrued science; and, From This Point Forward offers suggestions for how to manage and conduct research on such visionary topics.
Commonly bought on Amazon with Long 2011
Studies at LBL's Bevalac are aimed at resolving uncertainties about radiation risks to space travelers.
Stross's key claim from here: " Cosmic radiation poses a serious risk to long duration interplanetary missions, and unlike solar radiation and radiation from coronal mass ejections the energies of the particles responsible make shielding astronauts extremely difficult."
Not available
Referenced by Stross 2007
Heppenheimer, T.A. Colonies in Space
Amazon page
Book (popular)
Is there life in space? within the solar system, which we can reach and are now beginning to explore, the answer may be: Nothing but spores and bacteria. Perhaps the answer is: Nothing. Beyond our region of space the answer may yet be: Civilizations and cultures of greatness and magnificence untold. But we have not yet learned to detect them or to communicate with them.
As this has become apparent there has been a reaction against many of the more utopian hopes associated with space flight. Less than fifteen years ago John Kennedy could commit the nation to explore "this new ocean," with widespread hope that we were entering a new Age of Discovery. Today it is fashionable to believe that our problems can find solution only on earth and there is nothing in space which can aid us in any way.
This is not so. If we cannot find planets fit for us to live on, or if Mars is not up to our fondest hopes - very well. We can take our own life into space. We can build colonies in space, as pleasant as we want and productive enough to markedly improve humanity's future prospects. And, we can begin to do this anytime we please.
Referenced by Wikipedia, "Space Colonization"
Dyson, M. Hoome on the Moon; Living on a Space Frontier
Amazon page
Book (young adult)
From Booklist: "Gr. 5-8. Dyson, who worked at NASA as a mission controller, makes a solid case for moon exploration and helps readers imagine what it will be like. Recounting the experiences of astronauts who visited the moon, she presents some of the challenges of building a lunar outpost and suggests how to meet them. Detailed captions accompany the colorful illustrations, which include impressive photographs, maps, paintings and digital pictures. Each chapter ends with a suggested activity, such as making an edible moon rock or building a model of a lunar explorer. A glossary and a source bibliography are appended, as well as lists of moon facts, astronauts who visited or orbited the moon, and recommended books and Web sites. Clear writing, vivid images, interesting details, and quotes from astronauts and scientists make this a lively, fact-filled introduction. Carolyn Phelan"
Referenced by Wikipedia, "Space Colonization"
Eckart, Peter. Lunar Base Handbook
Amazon page

Written to cover the technical, economical, historical, management, legal, and even philosophical aspects of lunar base design and development, The Lunar Base Handbook, Second Edition, is a reference on building humankind’s first home on another planetary body. This book provides an overview about the Moon and its environment, the current status of lunar base design, tools needed to design a lunar base, checklists and flow charts that outline the design process, and technological requirements of a lunar base.

The main audience for this book is engineers, but it is also interesting for scientists, managers, undergraduate students, and even interested laymen.
Referenced by Wikipedia, "Space Colonization"
Schmitt, Harrison. Return to the Moon
Amazon page
Former NASA Astronaut Harrison Schmitt advocates a private, investor-based approach to returning humans to the Moon—to extract Helium 3 for energy production, to use the Moon as a platform for science and manufacturing, and to establish permanent human colonies there in a kind of stepping stone community on the way to deeper space. With governments playing a supporting role—just as they have in the development of modern commercial aeronautics and agricultural production—Schmitt believes that a fundamentally private enterprise is the only type of organization capable of sustaining such an effort and, eventually, even making it pay off.
Referenced by Wikipedia, "Space Colonization"
Wikipedia, Effect of Space Flight on the Human Body
"The effects of weightlessness
Following the advent of space stations that can be inhabited for long periods of time, exposure to weightlessness has been demonstrated to have some deleterious effects on human health. Humans are well-adapted to the physical conditions at the surface of the earth, and so in response to weightlessness, various physiological systems begin to change, and in some cases, atrophy. Though these changes are usually temporary, some do have a long-term impact on human health.

Short-term exposure to microgravity causes space adaptation syndrome, a self-limiting nausea caused by derangement of the vestibular system. Long-term exposure causes multiple health problems, one of the most significant being loss of bone and muscle mass. Over time these deconditioning effects can impair astronauts’ performance, increase their risk of injury, reduce their aerobic capacity, and slow down their cardiovascular system.[29] As the human body consists mostly of fluids, gravity tends to force them into the lower half of the body, and our bodies have many systems to balance this situation. When released from the pull of gravity, these systems continue to work, causing a general redistribution of fluids into the upper half of the body. This is the cause of the round-faced 'puffiness' seen in astronauts.[22] Redistributing fluids around the body itself causes balance disorders, distorted vision, and a loss of taste and smell."

Disruption of vision[edit]
Main article: Visual impairment due to intracranial pressure
Because weightlessness increases the amount of fluid in the upper part of the body, astronauts experience increased intracranial pressure. This appears to increase pressure on the backs of the eyeballs, affecting their shape and slightly crushing the optic nerve.[1][49][50][51][52][53] This effect was noticed in 2012 in a study using MRI scans of astronauts who had returned to Earth following at least one month in space.[54] Such eyesight problems may be a major concern for future deep space flight missions, including a manned mission to the planet Mars.[28][49][50][51][52]

Unknown effects: "If off-world colonization someday begins, many types of people will be exposed to these dangers, and the effects on the elderly and on the very young are completely unknown."

Humans are physiologically well-adapted to life on Earth. Consequently, spaceflight has many negative effects on the body.[1] The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton (spaceflight osteopenia).[2] Other significant effects include a slowing of cardiovascular system functions, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include fluid redistribution (causing the "moon-face" appearance typical in pictures of astronauts experiencing weightlessness),[3][4] loss of body mass, nasal congestion, sleep disturbance, and excess flatulence. Most of these effects begin to reverse quickly upon return to Earth.

The engineering problems associated with leaving Earth and developing space propulsion systems have been examined for over a century, and millions of man-hours of research have been spent on them. In recent years there has been an increase in research on the issue of how humans can survive and work in space for extended and possibly indefinite periods of time. This question requires input from the physical and biological sciences and has now become the greatest challenge (other than funding) facing human space exploration. A fundamental step in overcoming this challenge is trying to understand the effects and impact of long-term space travel on the human body.
Browsing from Wikipedia, "Space Colonization"
Landis, Geoffrey. Magnetic Radiation Shielding: An Idea Whose Time Has Returned? Space Manufacturing 8: Energy and Materials from Space, 383-386 (AIAA, 1991)
Journal article
One solution to the problem of shielding crew from particulate radiation in space is to use active electromagnetic shielding. Practical types of shield include the magnetic shield, in which a strong magnetic field diverts charged particles from the crew region, and the magnetic/electrostatic plasma shield, in which an electrostatic field shields the crew from positively charged particles, while a magnetic field confines electrons from the space plasma to provide charge neutrality. Advances in technology include high-strength composite materials, high temperature superconductors, numerical computational solutions to particle transport in electromagnetic fields, and a technology base for construction and operation of large superconducting magnets. These advances make electromagnetic shielding a practical alternative for near-term future missions.
Cited by Wikipedia, "Health Threat from Cosmic Rays"
Wikipedia, Health Threat from Cosmic Rays
"Spacecraft can be constructed out of hydrogen-rich plastics, rather than aluminum.[42] Unfortunately, "[S]ome 'galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them,' cautions Frank Cucinotta, NASA's Chief Radiation Health Officer. 'All materials have this problem, including polyethylene.'"[43]
Material shielding has been considered:
Liquid hydrogen, which would be brought along as fuel in any case, tends to give relatively good shielding, while producing relatively low levels of secondary radiation. Therefore, the fuel could be placed so as to act as a form of shielding around the crew. However, as fuel is consumed by the craft, the crew's shielding decreases.
Water, which is necessary to sustain life, could also contribute to shielding. But it too is consumed during the journey unless waste products are utilized.[43]
Asteroids could serve to provide shielding.[44][45]
Magnetic deflection of charged radiation particles and/or electrostatic repulsion is a hypothetical alternative to pure conventional mass shielding under investigation. In theory, power requirements for the case of a 5 meter torus drop from an excessive 10 GW for a simple pure electrostatic shield (too discharged by space electrons) to a moderate 10 kilowatts (kW) by using a hybrid design.[40] However, such complex active shielding is untried, with workability and practicalities more uncertain than material shielding.[40]"

"None of these strategies currently provides a method of protection that would be known to be sufficient[46] while conforming to likely limitations on the mass of the payload at present (≈ $10,000/kg) launch prices. Scientists such as University of Chicago professor emeritus Eugene Parker are not optimistic it can be solved any time soon.[46] For passive mass shielding, the required amount could be too heavy to be affordably lifted into space without changes in economics (like hypothetical non-rocket spacelaunch or usage of extraterrestrial resources) — many hundreds of metric tons for a reasonably-sized crew compartment. For instance, a NASA design study for an ambitious large spacestation envisioned 4 metric tons per square meter of shielding to drop radiation exposure to 2.5 mSv annually (± a factor of 2 uncertainty), less than the tens of millisieverts or more in some populated high natural background radiation areas on Earth, but the sheer mass for that level of mitigation was considered practical only because it involved first building a lunar mass driver to launch material.[39]

Several active shielding methods have been considered for lesser mass than passive mass shielding, but they remain in the realm of uncertain speculation at the present time.[40][47] Since the segment of space radiation penetrating farthest through thick material shielding, deep in interplanetary space, is gigaelectron-volt-level positively charged nuclei, a repulsive positively charged electrostatic shield has been hypothesized, but issues include plasma instabilities and power needs for an accelerator constantly keeping the charge from being neutralized by deep-space electrons.[48] A more common proposal is magnetic shielding using superconductors (or plasma currents), although, among other complications, if designing a relatively compact system, magnetic fields up to 10–20 teslas could be required around a manned spacecraft higher than the several teslas in MRI machines. The employment of magnetic structures which expose crew to such a high magnetic field may further complicate matters, though, since high-field (5 teslas or more) MRIs have been noted to produce headaches and migraines in MRI patients, and high-duration exposure to such fields has not been studied. Opposing-electromagnet designs might cancel the field in the crew sections of the spacecraft, but such would raise mass. A hybrid of an electrostatic shield and a magnetic shield has also been conceived, charge neutral at large distances and theoretically much reducing the individual weaknesses of each, yet complex to design if doable.[40]"
The health threat from cosmic rays is the danger posed by galactic cosmic rays and Solar energetic particles to astronauts on interplanetary missions.[1][2] Galactic cosmic rays (GCRs) consist of high energy protons (85%), helium (14%) and other high energy nuclei HZE ions.[1] Solar energetic particles consist primarily of protons accelerated by the Sun to high energies via proximity to solar flares and coronal mass ejections. They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.[3][4][5]
Browsing from Wikipedia, "Space Colonization"
Parker, Eugene N. Shielding Space Travellers. Scientific American
Quick scan
Scientific American

Skepticism about magnetic shielding
"Adequate protection for the astronauts means repulsing the very numerous cosmic-ray protons with two billion electron volts (the standard unit of energy used in particle physics). To stop them within the space of a few meters, a shield would have to have a magnetic fi eld of 20 teslas, or about 600,000 times the strength of Earth’s fi eld at the equator. So strong a fi eld requires an electromagnet constructed with superconducting wires, akin to those used in particle accelerators....The astronauts would have to endure a magnetic fi eld of 20 teslas, and no one knows what the biological effects would be. The late John Marshall, a University of Chicago experimental physicist, remarked to me many years ago that when he stuck his head in a 0.5-tesla fi eld in the gap of an old particleaccelerator magnet, any motion of his head produced tiny fl ashes of light in his eyes and an acid taste in his mouth, presumably caused by electrolysis in his saliva." pp. 45-46

Skepticism about regular shielding
"t o m a t c h t h e p ro t e c t io n offered by Earth’s atmosphere takes the same one kilogram of shielding material per square centimeter, although astronauts could comfortably make do with 500 grams, which is equivalent to the air mass above an altitude of 5,500 meters. Any less would begin to be counterproductive, because the shielding material would fail to absorb the shrapnel.

If the material is water, it has to be fi ve meters deep. So a spherical water tank encasing a small capsule would have a mass of about 500 tons. Larger, more comfortable living quar-ters would require even more. By comparison, the space shuttle can carry a maximum payload of about 30 tons. Water is commonly proposed because astronauts would need it anyway and because it is rich in hydrogen. Heavier elements make less effective shields because the extra protons and neutrons in their nuclei fall in one another’s shadows, limiting their ability to interact with an incoming cosmic ray. To increase the hydrogen content, engineers could use ethylene (C2H4), which has the further advantage that it can be poly merized to polyethylene, a solid, thereby avoiding the necessity for a tank to contain it. Even so, the required mass would be at least 400 tons—still not feasible. Pure hydrogen would be lighter but would require a heavy pressurized vessel." pp. 43-44
The galaxy is pervaded with fast-moving particles that
can rip apart DNA and other molecules. Here at the
surface of Earth, we are well protected from this cosmic
radiation by the air mass overhead. Astronauts in near equatorial
orbits are shielded by the planet’s magnetic
field. But those who make long voyages away from
Earth will suffer serious health consequences.
■ A spherical shell of water or plastic could protect space travelers, but it would take a total mass of at least 400 tons—beyond the capacity of heavy-lift rockets. A superconducting magnet would repel cosmic particles and weigh an estimated nine tons, but that is still too much, and the magnetic field itself would pose health risks. No other proposed scheme is even vaguely realistic.
■ Biomedical researchers need to determine more
precisely how much long-term exposure to cosmic rays
a person can tolerate and whether medicines could
stimulate the body’s natural repair mechanisms.
Cited by Wikipedia, "Health Threat from Cosmic Rays"
O'Neill, Ian. Bad News: Interstellar Travel May Remain in Science Fiction.
Full readJournalism
Already there are huge challenges facing the notion of travelling to Proxima Centauri, but in a recent gathering of experts in the field of space propulsion, there are even more insurmountable obstacles to mankind’s spread beyond the Solar System. In response to the idea we might make the Proxima trek in a single lifetime, Paulo Lozano, an assistant professor of aeronautics and astronautics at MIT and conference deligate said, “In those cases, you are talking about a scale of engineering that you can’t even imagine.”
OK, so the speed simply isn’t there for a quick flight over 4.3 light years. But there is an even bigger problem than that. How would these interstellar spaceships be fuelled? According to Brice N. Cassenti, an associate professor with the Department of Engineering and Science at Rensselaer Polytechnic Institute, at least 100 times the total energy output of the entire world would be required for the voyage. “We just can’t extract the resources from the Earth,” Cassenti said during his conference presentation. “They just don’t exist. We would need to mine the outer planets.”

Read more:
Cited by Wikipedia, "Interstellar travel"
Lemos, Robert. Rocket Scientists Say We'll Never Reach the Stars. Wired Magazine.
Full readJournalism
At a recent conference, rocket scientists from NASA, the U.S. Air Force and academia doused humanity's interstellar dreams in cold reality. The scientists, presenting at the Joint Propulsion Conference in Hartford, Connecticut, analyzed many of the designs for advanced propulsion that others have proposed for interstellar travel. The calculations show that, even using the most theoretical of technologies, reaching the nearest star in a human lifetime is nearly impossible.

The major problem is that propulsion -- shooting mass backwards to go forwards -- requires large amounts of both time and fuel. For instance, using the best rocket engines Earth currently has to offer, it would take 50,000 years to travel the 4.3 light years to Alpha Centauri, our solar system's nearest neighbor. Even the most theoretically efficient type of propulsion, an imaginary engine powered by antimatter, would still require decades to reach Alpha Centauri, according to Robert Frisbee, group leader in the Advanced Propulsion Technology Group within NASA's Jet Propulsion Laboratory.
And then there's the issue of fuel. It would take at least the current energy output of the entire world to send a probe to the nearest star, according to Brice N. Cassenti, an associate professor with the Department of Engineering and Science at Rensselaer Polytechnic Institute. That's a generous figure: More likely, Cassenti says, it would be as much as 100 times that.
"We just can't extract the resources from the Earth," Cassenti said during his presentation. "They just don't exist. We would need to mine the outer planets."
Searching for source for O'Neill 2008
Garrett, Henry. “There and Back Again”
A Layman’s Guide to Ultra-
Reliability for Interstellar
Quick read
ppt presentation, may be based on a conference paper
"What are the Key
Reliability Concerns?
1. Environmental Exposure
2. Propulsion Systems
3. Electronic Systems
4. Mechanical Systems
5. Materials
6. Thermal Control
7. Infrastructure
8. Mission Assurance
9. Software
10.Integrated Systems Health Management
11.Navigation and Attitude Control"

"Key Issues:
• We have already reached interstellar space and are capable of at
least 35 year missions
• Propulsion to 10-20% the speed of light may be possible with current
engineering methods… Centauri at 4.3 Ly is a plausible target
• The major natural environment concern will be dust/meteroid
• Will need to re-think our current maintainability procedures in light
of 50 years and autonomous operations (e.g., common parts, inflight
repair/replacement, ability to reconfigure software, etc.)
• Will need to develop robots capable of in-flight repairs—the ultimate
integrated health management system!
• Development of common replacement parts strategy
• Societal issues associated with maintaining a +50 year research
Not available
Searching for reviews of Mallove and Matloff
Garett et al. Interstellar Space Missions: Ultra-Reliability Requirements and Engineering Issues
1st page
Can't copy and paste
Searching for reviews of Mallove and Matloff
IEEE. Robots Pave the Way to Mars
Anders Sandberg
Neal, Megan. Our Best Bet for Colonizing Space May Be Printing Humans on Other Planets
Anders Sandberg
O'Neill, Gerard K. The High Frontier: Human Colonies in Space. Burlington, Ont.: Apogee Books, 2000.
Amazon page, Wikipedia page
In the early 1970s America had proved its leadership in Human Spaceflight but among the nation’s youth an anti-technology mindset was growing. Princeton Physicist and Professor Dr. Gerard K. O’Neill, inventor of the revolutionary Colliding-Beam Storage Ring technology that is now the basis of all high energy particle accelerators, asked his students if they could come up with a working Space Colony system to permanently and happily house tens of thousands of regular people. They dug into the challenge.

Soon his small band of students grew to scores of researchers both young and old, all united in the Big Dream of letting real people have a real choice in their futures.

In 1974, Dr. O’Neill put his three-pronged plan of Space Colonization, Space Solar Power and Large Scale Space Construction into easily accessible form with the release of the book The High Frontier. Fourteen years later, The Space Studies Institute, founded by O’Neill, re-released the original text, unchanged except for the doctor’s addition of the Appendix “A View from 1988.”

Now, The Space Studies Institute makes The High Frontier exclusively available electronically for Amazon Kindle owners.

This is one of the milestone and timeless classics of Space Habitation, Alternative Power and Human Potential, all made possible with technology we already have. A Must-Read.
Prior knowledge
Regis, Ed. "Being told that our destiny is among the stars"
Full text: In 2012 NASA and DARPA jointly funded a "100-Year Starship" program, the goal of which was to achieve human interstellar flight within the next one hundred years. On September 13, 2012, the 100-Year Starship (100YSS) project held the first of its planned annual public symposiums, in Houston, Texas. Here, about a hundred scientists, social scientists, educators, journalists, and miscellaneous others gathered to witness a series of scientific presentations outlining schemes by which human beings could, just possibly, leave planet Earth behind, travel to the stars, and establish a new "Earth 2.0" in another solar system, all within a century.

Traveling to the stars, say many of its advocates, is our preordained destiny as a species. As proponent Cameron Smith puts it in "Starship Humanity" (Scientific American, January 2013): "the concept of a Space Ark, a giant craft carrying thousands of space colonists on a one-way, multigenerational voyage far from Earth" is "technologically inevitable."

Far from being technologically "inevitable," the fact is that such a voyage is not even known to be technologically possible. For one thing, the distances to even the "closest" extrasolar stars are unimaginably vast. The nearest star, Proxima Centauri, is 4.22 light years (24,800,000,000,000 miles), away from Earth. Even if we were to travel as fast as the Voyager I spacecraft, which is now receding from us at 38,698 mph, it would take an interstellar craft more than 73,000 years to reach that destination.

But traveling at significantly faster speeds requires prohibitive amounts of energy. If the starship were propelled by conventional chemical fuels at even ten percent of the speed of light, it would need for the voyage a quantity of propellant equivalent in mass to the planet Jupiter. To overcome this limitation, champions of interstellar travel have proposed "exotic" propulsion systems such as antimatter, pi meson, and space warp propulsion devices. Each of these schemes faces substantial difficulties of its own: for example, since matter and antimatter annihilate each other, an antimatter propulsion system must solve the problem of confining the antimatter and directing the antimatter nozzle in the required direction. Both pi meson and space warp propulsion systems are so very exotic that neither is known to be scientifically feasible.

Indeed, these and other such schemes are really just mathematical abstractions, not working systems: they are major extrapolations from states of matter that exist today only at nano levels (antimatter, for instance, requires huge accelerators to make even tiny amounts of, at stupendous costs). Still other systems depend on wild possibilities such as making use of extra dimensions that are not known to exist, physical forces or influences that are not known to be real, or are sheer flights of the imagination (such as altering the value of Hubble's constant to make the universe smaller).

Even if by some miracle suitable propulsion systems became available, a starship traveling at relativistic speeds would have to be equipped with sophisticated collision detection and avoidance systems, given that a high-speed collision with something as small as a grain of salt would be like encountering an H-bomb. Star voyagers face further existential threats in the form of prolonged exposure to ionizing radiation, boredom, alienation from the natural environment, the possible occurrence of a mass epidemic, the rise of a charismatic leader who might derail the whole project, crew mutiny, religious factionalism, and so on. It is far more likely, therefore, that an interstellar voyage will mean not the survival but rather the death of its crew.

Apart from all of these difficulties, the more important point is that there is no good reason to make the trip in the first place. If we need a new "Earth 2.0," then the Moon, Mars, Europa, or other intra-solar-system bodies are far more likely candidates for human colonization than are planets light years away.

So, however romantic and dreamy it might sound, and however much it might appeal to one's youthful hankerings of "going into space," interstellar flight remains a science-fictional concept—and with any luck it always will be.
Happened to be listening to an audiobook compilation of essays that contained this.
National Research Council. Pathways to Exploration: Rationales and Approaches for a U.S. Program of Human Space Exploration. Washington, DC: The National Academies Press, 2014.
"It is not possible to say whether off-Earth settlements could eventually be developed that would outlive human presence on Earth and lengthen the survival of our species. This is a question that can only be settled by pushing the human frontier in space." S-2
The United States has publicly funded its human spaceflight program on a continuous basis for more than a half-century, through three wars and a half-dozen recessions, from the early Mercury and Gemini suborbital and Earth orbital missions, to the lunar landings, and thence to the first reusable winged crewed spaceplane that the United States operated for three decades. Today the United States is the major partner in a massive orbital facility - the International Space Station - that is becoming the focal point for the first tentative steps in commercial cargo and crewed orbital space flights. And yet, the long-term future of human spaceflight
Happened to see it when glancing at the NYT science page
Project Icarus: A review of local interstellar medium properties of relevance for space missions to the nearest stars
Abstract only
Scientific paper
I review those properties of the interstellar medium within 15 light-years of the Sun, which will be relevant for the planning of future rapid (v≥0.1c) interstellar space missions to the nearest stars. As the detailed properties of the local interstellar medium (LISM) may only become apparent after interstellar probes have been able to make in situ measurements, the first such probes will have to be designed conservatively with respect to what can be learned about the LISM from the immediate environment of the Solar System. It follows that studies of interstellar vehicles should assume the lowest plausible density when considering braking devices, which rely on transferring momentum from the vehicle to the surrounding medium, but the highest plausible densities when considering possible damage caused by the impact of the vehicle with interstellar material. Some suggestions for working values of these parameters are provided. This paper is a submission of the Project Icarus Study Group.
Recommended by Anders Sandberg
A closer look at interstellar dust would want to have look at this paper more closely.
Khan, Razib. Elon Musk Is Wrong About Genetic Diversity
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Carl Shulman
Suggests 1000 people sufficient
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