≡ Menu

How We Get There Matters

Nick Nielsen’s new essay follows up his speculations on interstellar infrastructure with a look at the kind of starships we might one day build. The consequences are profound. What if we master interstellar technologies without needing the Solar System-wide infrastructure many of us assume will precede them? A civilization’s interstellar ‘footprint’ would be radically altered if this is the case, and evidence of mega-engineering among the stars sharply constrained. Then too, how we view what is possible could be transformed by breakthroughs in biology and longevity, all part of the mix as we look at what Nick calls ‘undetermined nodes in future history.”

by J. N. Nielsen


In my previous Centauri Dreams post, The Infrastructure Problem, I sought to make a distinction between fundamentally different forms that a spacefaring civilization might take, one tending toward primarily planetary-based infrastructure, and another tending toward primarily space-based infrastructure. I am always pleased by the insightful comments I receive from Centauri Dreams readers, which never fail to spur me on to further (hopefully improved) formulations. [1] This last post was no exception. I was particularly interested in a comment by William Blight:

“A lot of ifs in this author’s presentation. Large scale industrialization of the moon for power and materials using automation and robotics for rapid bootstrapping is probably the best method for developing a powerful space infrastructure. Colonizing Mars will accelerate the development of propulsion systems. I don’t see how speculation in regard [to] Alcubierre drives has real connection to the development of near-term, space-based industry.”

This comment has helped me to understand the limitations of my exposition. There were a lot of “ifs” in my presentation. Of course what I wrote was highly speculative, as all contemporary writing on interstellar travel must be, but it was speculation with a purpose, and I am concerned that my purpose was not sufficiently clear.

We cannot see the future in detail, but we can distinguish broad patterns of development, just as we can see broad patterns of development in the past, if we look to the past for its overall lessons and not for the ideographic detail that fascinates biographers. Every “if” represents an undetermined node in future history, where under conditions of constraint we may be forced to choose between mutually exclusive alternatives, while given an open future somewhat less subject to constraint (e.g., a future in space where energy and materials are cheaply available, if only we can keep ourselves alive in space long enough to exploit them), an undetermined node represents a point of bifurcation where different communities will take different directions. These are the patterns I am trying to explicate.

Interstellar travel represents an undetermined node in future history, and we do not yet know all the constraints that will bear upon starships once we build them. It would be a mistake to think of interstellar travel in all-or-nothing terms, i.e., either we have the technological capacity or we don’t, because this technological capacity will be developed little-by-little, step-by-step. When an interstellar voyage comes at great personal cost (in time, money, opportunity cost, inconvenience, and discomfort), only a trickle of individuals will possess both the resources and the overwhelming desire to go. As the journey declines in the personal costs it demands, it will appeal to greater numbers of individuals, until the trickle eventually becomes a flood. The relative ease or lack thereof in interstellar travel will be a function of the technologies employed, so that the technologies we will eventually use to travel to the stars will shape the historical structure of that travel, and of the spacefaring civilization that undertakes interstellar travel. In other words, how we get there matters.

There is no more compelling argument for the fact that how we get there matters than the present dependency of the transportation network, and indeed of the whole of industrial-technological civilization, on fossil fuels. We all know that the geopolitics of fossil fuels has decisively shaped the world we live in, and that if some other technology, a non-fossil fuel technology, were the basis of global energy markets, the world today would be a different place.

Future technologies of interstellar flight will shape spacefaring civilization as profoundly as fossil fuels shape our world. Until particular technologies are developed and put into practice, we cannot know which will prove practicable and which will be mere curiosities of little utility, yet by reducing the possibilities for starships down to a few broadly-defined classes, we can sharpen the focus of how we think about the potential niches for spacefaring civilization. Consider this division of potential interstellar transit technologies into four classes:

  • Class 0: Very long term interstellar travel, beyond the practicability of generational starships. Another way to think of this would be in terms of interstellar travel on geological time scales.
  • Class 1: Generational starships, i.e., starships that would require from one to several generations (measured in ordinary human life spans) in order to reach their destination.
  • Class 2: Interstellar transit within the life-span of an individual, measured in months, years, or decades.
  • Class 3: Rapid interstellar transit on the order of global transportation today, measurable in hours or days.

This is a very rough and provisional division, and the reader should place no emphasis on the particular divisions I have made or the particular technologies that I cite, but only on the idea that we can divide potential interstellar transit technologies into broadly distinct classes. (The possibilities for interstellar drives are parallel to the possibility of some other industrial-technological civilization in the galaxy, not identical to us, but differing in terms of countless contingencies. The important point is not the identity of a particular technology or civilization, but the capacity it has to serve a particular role.) In each of these classes we can identify a series of technological developments that could shorten the voyage, but the voyage on the whole would remain roughly within the parameters of the classes sketched above, so that the upper edge of class 0 touches the lower edge of class 1, and so forth.

starship classes

Image: Categories of starships. Credit: Nick Nielsen.

The other variables that enter into the equation of interstellar travel—longevity and destination choice among them—also admit of many possible solutions. Human life might be extended by many different technological means (incremental improvements in the life sciences, regenerative medicine, suspended animation, etc.), or even someday by the simplest of biological means. [2] And once having met the minimum interstellar threshold for a destination, interstellar travelers will have a wide choice of destinations that will affect the length of the trip. A Class 1 starship that would be a generational ship for human beings with an average life-span of today could be considered a Class 2 starship if life spans were considerably lengthened or if suspended animation technology proved to be practicable. The point here is that there is more than one way to approach the problem, and how we solve the problem matters to the kind of spacefaring civilization we eventually build.

Voyager spacecraft

The gravitational slingshot technology employed to send the Voyager spacecraft on interstellar trajectories could be further extrapolated with gravitational slingshots around other star systems, which might raise the velocity of a spacecraft to one percent of the speed of light. [3] This could be much faster than the Voyager spacecraft are traveling at present, but still clearly constituting class 0 interstellar transit. Were we to develop biological reconstitution technology that could remain functional for thousands of years, and we launched this on a class 0 starship (like Voyager, i.e., something that we could build with known technologies), we would then begin the era of human interstellar travel.

Daedalus spacecraft

Image: The Daedalus starship. Credit: Adrian Mann.

A light sail might be at the upper edge of class 0 or the lower edge of class 1 interstellar travel, while a light sail further propelled by a laser might approach the upper edge of class 1. The Daedalus starship design should be considered a class 1 starship, though incremental improvements in fusion technology might boost it to the lower edge of class 2 starships. More exotic drives such as matter-antimatter reaction might qualify as class 2 starships, perhaps attaining the status of a 1G starship (such as I discussed in Stepping Stones Across the Cosmos), which would allow travel throughout our galaxy within an ordinary human lifespan, though relativistic effects would mean that accelerated communities would be temporally disjointed from non-accelerated communities. Even more exotic propulsion systems – whether the Alcubierre drive, the technology to manufacture wormholes at will, or other possibilities not imagined today – would qualify as class 3 starships that would convey us between stars as readily as jet aircraft convey us between continents today.

Bussard ramjet

Image: The Bussard ramjet design. Credit: Adrian Mann.

The technological developments that could shorten the voyage of a particular class of interstellar travel represent technological succession, just as does the sequence of classes itself (which constitutes technological succession on a greater order of magnitude). In many historical cases of technological succession we see the gradual development of improved technologies, as with automobiles or integrated circuits. When technological succession happens in this way it is largely predictable, but technological succession is sometimes disruptive rather than a smooth progression. In the middle of the twentieth century many assumed that human spaceflight would be attained by the gradual improvement in supersonic flight. However, hypersonic flight has proved to be a difficult engineering challenge, and we have not yet mastered it, but chemical rocket technology leapfrogged supersonic flight and put human beings in orbit and on the moon before the gradual technological succession of improving supersonic to hypersonic to escape velocity technology could catch up. It still hasn’t caught up.

Alcubierre drive spacecraft

Image: Conceptualizing the Alcubierre drive. Credit: Anderson Institute.

Gradual technological succession would take place within classes of starships; disruptive technological succession would occur when one class of starship supersedes another. If we launched a class 0 starship with reconstitution technology on board, and a hundred years later (or even a thousand years later) developed class 2 starship technology, the class 2 starships would overtake the class 0 starship in a way not unlike how jet aircraft overtook propeller-driven aircraft, and chemical rockets overtook jet aircraft. If class 2 starship technology disruptively precedes practicable class 0 or class 1 starship technology, the entire era of generational starships, class 0 and class 1, will be bypassed.

We are not in a position to judge the relative success of technologies only now imagined, but once we have in place a way to differentiate between entirely different classes of starships, we can speak in terms of the kind of spacefaring civilization emergent from any technology capable of building a class x starship. What the particular technology will be is indifferent to our problem; any class x starship will do. With these considerations in mind, I can return to the point of my previous post, The Infrastructure Problem.

To restate the infrastructure problem, any sufficiently advanced class 2 starship, or any class 3 starship, that can be constructed exclusively with terrestrial infrastructure would yield a spacefaring civilization that possessed only a minimal space-based infrastructure. A spacefaring civilization with minimal space-based infrastructure would be unlikely to engage in megastructure engineering and would thus have a much more modest “footprint” in the cosmos than a Kardashevian supercivilization.

If contemporary terrestrial industrial-technological civilization continues in its present development (i.e., if it does not stagnate), and if it is not destroyed, our sophistication in science and technology will likely improve to the point at which we can build at least an advanced class 2 starship (if not a class 3 starship) and fly directly from the surface of Earth to other worlds – an SSTS spacecraft (single-stage to stellar), if you will.

Such a trajectory of development creates its own great filter, as the ongoing existential viability of a terrestrial-based industrial-technological civilization is contingent upon passing through an extended window of vulnerability when we have the technological capacity to destroy ourselves (intentionally through warfare or unintentionally through the toxic byproducts of industrialism) without bothering to exploit the technology we also possess to establish a rudimentary spacefaring civilization with multiple independent centers of civilization tolerant of local extinction, where “local” means “terrestrial.”

Ever since the advent of the Space Age in the middle of the twentieth century there have been ambitious plans to rapidly expand the human presence in space, from the “Collier’s” space program (Man Will Conquer Space Soon!) to O’Neill colonies. To date, none of these ambitious plans have come to fruition, although our technology is considerably more advanced than when humanity first entered space. Only superpower competition has proved to be a sufficient spur to a major space effort. It does not appear, then, that humanity is an “early adopter” of existential risk mitigation by way of space settlement; we are not moving in the direction of creating a spacefaring civilization predicated upon a robust space-based infrastructure.

The trajectory of development that humanity has not taken represents a possibility, a niche for spacefaring civilization, that some other intelligent species might have taken, or might yet take, and the result of taking this space-based infrastructure path of development would be a spacefaring civilization of a structure disjoint from that characterizing spacefaring civilization of a primarily Earth-based infrastructure. [4]

If none of the technologies that would make possible advanced class 2 or class 3 starships could be made sufficiently compact that they could be built on Earth and boosted into space, then a civilization would be forced into a choice between remaining stranded within its solar system or eventually building a space-based infrastructure in order to build a starship (this is an instance of “conditions of constraint” resulting in mutually exclusive alternatives mentioned above). For example, a class 1 starship like Daedalus could not be constructed without space-based infrastructure.

I am not an engineer. I will not be designing any starships. Others will design starships, and others will formulate the ideas that are eventually translated into technologies and designs for interstellar flight. As I see it, these technologies are variables in the equation of the large scale structure of any spacefaring civilization. If there is no solution to the equation of spacefaring civilization, given some particular value for the variable of feasible interstellar travel, then we try to solve it again using a different variable. If there are no solutions at all, then we are stuck in our own solar system and the same is true of any other spacefaring civilization that emerges on any other world. [5]

What interests me is the large scale structure of civilization of any possible spacefaring civilization. I assume if a spacefaring civilization emerges more than once in our universe, these multiple spacefaring civilizations may take multiple paths of development (cf. note [4]), or they may converge upon some particular path of development to spaceflight if the parameters of possible spacefaring technologies are quite narrow. Different solutions to the equation for spacefaring civilizations yield different large scale structures of that civilization. If there is only one solution to the problem, i.e., only one technology for practicable interstellar travel, then this will exercise a strongly convergent force on the structure of any spacefaring civilization and is an equally strong condition of constraint.

From these considerations another typology begins to emerge:

    1. There is no solution to the problem of interstellar travel. (Cf. note [5])

    2. There is a single solution to the problem of interstellar travel, where “single solution” means only one practicable class of starships. A single class of practicable starships still admits of the possibility of technological succession within this class, so that interstellar civilizations might admit of different stages of development in their mastery of the single practicable interstellar technology.

    3. There are multiple solutions to the problem of interstellar travel, so that multiple classes of starships are technologically practicable.

In the first case, all spacefaring civilizations are confined to their star system of origin. We already know this to be false, because the Voyager spacecraft are in interstellar space at this moment. However, if one redefines interstellar travel as to exclude class 0 starships, then humanity remains confined within our solar system in this first case. In the second case, spacefaring civilizations are constrained by technology to the choice of becoming an interstellar civilization or not, but all interstellar civilizations will be constrained by the parameters of the single practicable interstellar technology. In the third case, if a spacefaring civilization achieves interstellar travel, it may do so by multiple means, and interstellar civilizations will be differently constrained according to the technology or technologies they develop (in addition to other factors). [6]


[1] All of the comments I have received are greatly appreciated, and I regret that I have not responded to each comment individually, but when the reader sees the extent to which this response to a comment runs, it may perhaps be understandable.

[2] The point I am trying to make in this present argument, how we get there matters, applies equally to the technologies of transhumanism, which will not be separate from interstellar travel but will interact with the human exploration of space. Whether human beings are able to travel to distant stars because of greatly extended life-spans, or suspended animation, or reconstitution, how we get to an extended life-span matters, because each technology interacts differently with the individual life and the socioeconomic structures within which the individual finds a place. Similarly, each interstellar propulsion technology interacts differently with the individual life, making use of such propulsion technologies and the socioeconomic structure within which the individual finds a place.

[3] In a post titled, “Galactic Grand Tours, and strengthening Fermi’s Paradox” on the Well-Bred Insolence blog, Duncan Forgan writes, “…if a probe carries out a series of slingshots as it tours the Galaxy, the probe can be accelerated to approximately 1% of the speed of light without shipping enormous amounts of fuel (bear in mind Voyager 1 is travelling at 0.003% of lightspeed).”

[4] An alien civilization might take a different technological path due to different intellectual endowments. It may be that a science and technology, which remains opaque to the kind of minds that we have, will be readily mastered by an intelligent species with a different kind of mind, and vice versa. Bertrand Russell provided an imaginative example that serves as a kind of thought experiment in this respect:

We are certainly stimulated by our experience to the creation of the concept of number – the connection of the decimal system with our ten fingers is enough to prove this. If one could imagine intelligent beings living on the sun, where everything is gaseous, they would presumably have no concept of number, any more than of “things.” They might have mathematics, but the most elementary branch would be topology. Some solar Einstein might invent arithmetic, and imagine a world to which it would be applicable, but the subject would be considered too difficult for schoolboys. (Bertrand Russell, The Philosophy of Bertrand Russell, edited by Paul Arthur Schilpp, Evanston and Chicago: Northwestern University, 1944, p. 697.)

These considerations apply both to the large-scale structure of a spacefaring civilization as well as the particular technologies any such civilization pursues in the attempt to master interstellar flight.

[5] This is the position of Peter D. Ward and Donald Brownlee (best known for their book Rare Earth: Why Complex Life is Uncommon in the Universe): “The starships of TV, movies, and novels are products of wishful thinking. Interstellar travel will likely never happen, meaning we are stranded in this solar system forever. We are also likely to be permanently stuck on Earth. It is our oasis in space, and the present is our very special place in time. Humans should enjoy and cherish their day in the Sun on a very special planet… Our experience on Earth is probably repeated endlessly in the cosmos. Life develops on planets but it is ultimately destroyed by the light of a slowly brightening star. It is a cruel fact of nature that life-giving stars always go bad.” (The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World, New York: Henry Holt and Company, 2002, pp. 207-208). In this case, the possibility of a large scale spacefaring civilization does not disappear (though Ward and Brownlee explicitly exclude this possibility also), but it takes on a different form, and any communication between advanced industrial-technological civilizations would have to come about by way of SETI and METI. The impossibility of interstellar travel is entirely compatible with megascale engineering within our own solar system, which megastructures could include the building of vast EM spectrum communications antennae capable of communicating across interstellar distances.

[6] A further distinction could be made in the third case between “more than one solution to the problem of interstellar travel exists” (i.e., at least two solutions exist to the problem of interstellar travel), and, “all classes of interstellar travel are technologically practicable.”


Comments on this entry are closed.

  • CharlesJQuarra May 23, 2014, 12:24

    “A light sail might be at the upper edge of class 0 or the lower edge of class 1 interstellar travel, while a light sail further propelled by a laser might approach the upper edge of class 1.”

    This is not accurate. Light sails are not only in class 2, in fact they are the only members in class 2 that we know the physics behind the system is sound. The only thing limiting how fast laser sails go is how much money and resources are we willing to funnel in the orbital laser arrays

  • Glaas May 23, 2014, 13:29

    We should not digress too much on this detail, but how could solar sails be useful for interstellar travel? JUNO is the first probe ever to try to use solar panels at Jupiter. How could the pressure from the Sun work at 1/1000 of Earth insolation and less power at Neptune and beyond, very very far far from any star?

  • Michael May 23, 2014, 14:25

    @CharlesJQuarra May 23, 2014 at 12:24

    ‘Light sails are not only in class 2, in fact they are the only members in class 2 that we know the physics behind the system is sound.’

    Magnetic sails using particle beams are also in Class 2 and the physics is very sound.

  • Leon Froess May 23, 2014, 15:18

    I think your classifications for starships are a good start but have a problem with them. The classification of any given starship, especially class 2 and 3, would change depending on destination. If you are going to Alpha Centuari and can accomplish that in 4 decades (about 1 decade per light year), you would have a class 2 starship. However if you were to take the same starship and aim for Kepler 186f, about 490 light years away, your class 2 starship becomes a class 1 starship or possibly even a class 0 starship as it would take about 4900 years to make the journey. I believe this variable classification depending on distance to the destination would tend to “muddy” the catagories.

    I will offer an alternate suggestion. Rather than basing the catagories on time to get to the destination, which depends on distance, base the catagories on speed. For example, a class 0 starship would be capable of a speed less than 0.01c, class 1 would be capable of between 0.01c and 0.1c, class 2 would be capable of between 0.1c and 0.5c, class 3 would be capable of between 0.5c and c, and possibly an additional class, class 4 would be capable of greater than c.

  • Geoffrey Hillend May 23, 2014, 16:17

    It is important not to be limited to what only seems possible today or today’s technology which is why I like this progressive paper by J. N. Nielsen. We have not even built the telescopes that have the power to detect oxygen and methane in Earth sized planets in other star systems. We might want to find a habitable place to go before we start the journey.

    If we ever develop the technology to build a warp drive all other classes of interstellar spacecraft become completely obsolete. If we knew in the distant future we might have a class three interstellar spacecraft, who would sacrifice their entire life on an interstellar Journey in a class one or two ship? We can use unmanned, computer automated spacecraft for that.

  • Alex Tolley May 23, 2014, 17:22

    A civilization’s interstellar footprint is not really determined by travel technology, but by destinations. Consider, if civilization is terrestrial and has no space infrastructure, just nifty superluminal spaceships, civilization can only develop on other worlds if they are already hospitable, i.e. life bearing with photosynthesis. If these worlds do not exist (and forget about any prime directive in play) and the only worlds are dead rocks or possibly microbial, then they will not make good targets, and new population centers will not arise there.

    If you need to build domes or terraform worlds, you might as well build space colonies. Which means you needn’t leave the solar system. But whether you do or not, the solar system will have these colonies and therefore a space based infrastructure along with them, plus the technology to build similar space cities around other stars.

    The main scenario I see where there is terrestrial infrastructure only, plus interstellar populations living in gravity wells, is where we (or our successors) become non-biological entities.
    Asimov’s early vision of interstellar colonies had humans living on already living worlds, with robots supporting their lives. However, if robots were not just human servants, then it would make more sense for them to populate all possible worlds, living or dead. They would vastly outnumber us in the galaxy. For machines, all the main problems facing biologicals for interstellar travel are moot. They can leave on any class of starship, shut down if necessary, wake up at the destination and do something regardless of the target’s conditions.

    So the question is, is this possible future node more likely than those of human dominated ones in interstellar travel?

  • Samantha Atkins May 23, 2014, 17:44

    If we get FTL first or other starships then how would that make it one whit less important that we know how to live in space itself and how to take advantages of the resources of a solar system or colonize moons and planets? At the least we need a lot of living in space infrastructure down pat just to survive and thrive on the journey. Then once we get somewhere – then what? Either we plant colonies or star wisp production facilities or mine the local systems or what did we make the trip for exactly, photo opportunities? I don’t see how there is any implied either-or here. Being ready for interstellar missions requires mastery of skills that we can only acquire exploiting the local space environment.

    You aren’t going to boost a large generation ship from earth or anything with enough on board resources to deal with anything it encounters on the way that carries human beings.

  • Jer May 23, 2014, 22:44

    I suppose another possibility is that we (or anyone we ever come into contact with) never develop/ engineer/ design beyond Class 0, but instead extend space settlements/ outposts at an outward distance of 0.1 LY every generation. We effectively have numerous branches of exurbs that have contact with their nearest neighbours only, not the ends of each trunk, branch, or twig – certainly not all the way back to our mother Earth by any individual. After 100,000 years we are 500 LY outward from Sol, encompassing any star systems within that sphere, though almost no individual has ‘travelled’ further than the migration jump of 0.1 LY. In this case propulsion has only limited effect on how far we extend. This is greatly enhanced if we say that each migration jump is 0.5 LY at a 0.5 generation step, assuming the archaic definition of a generation of approximately 20 years – a sphere of radius 5000 LY. The factor here is the number of people who migrate rather than the speed. Of course, this requires almost complete resource independence from Earth, including limited cultural and technological contact. What level of technological innovation would this amount of ‘frontiership style’ emigration require as each parent ‘node’ needs to provide initial resources to one or more daughter nodes per generation or less?

  • Marshall Eubanks May 23, 2014, 22:59

    I think that biology is likely to play an important role here, although what that is hard to foretell. Here are two (of many) possible intersections of biology and technology. If generation ships become common, humanity is likely to quickly speciate (small populations sent on long voyages isolated from the rest of humanity will likely turn into separate species). By the time the generation ships reach their destination, the inhabitants may neither need nor want to live on a planet. Conversely, if lifetimes greatly increase, very long voyages may become routine, even at sublight speeds. (If the typical lifetime is “forever,” relativistic voyages taking thousands of years of objective time may seem reasonable.) Not knowing either the biology or the technology to come makes predicting this a difficult proposition.

  • Eniac May 23, 2014, 23:09

    I am not sure I agree with the premise of the article, here: “How we get there matters”. In first order, what really matters is whether we get there at all. It makes the difference between humanity surviving in the long term or not. It also makes the difference between a populated galaxy and one that is not. Arguably, there is nothing that matters more. How this is achieved seems to matter much less, but maybe that is just me?

    Also, regarding your comments on fossil fuel, remember that the colonization of the Earth was achieved before fossil fuel, using ships built from wood and propelled by wind. Renewable resources, all, fossil fuels came much later. They do not really matter very much regarding the spread of humanity.

  • CharlesJQuarra May 23, 2014, 23:57

    @Glaas do not confuse solar light with laser light – the latter is much more focused over long distances

    @Michael, you are right. In that case you need to replace the laser beam with a charged particle beam, which usually have worse divergence. Mag sails are more useful for braking from relativistic velocities up to 0.01c

  • ProjectStudio May 24, 2014, 1:14

    As author Nick has described it — in order to relate to the decision point on space based or earth based infrastructure — the categories should also distinguish starship size/mass so that each technology classification would clearly either allow a single-stage-to-stellar or spaced-based construction/assembly.

    Likely a matrix classification system could map out the classifications for purposes of speculating on why we haven’t detected evidence of extraterrestrial space-fairing civilisations.

    When speculating on humanity’s use of space and potential for interstellar travel, the economics of technological development – the financial ‘infrastructure’ – will have bigger influence I think. Technologies will be developed and ships built as insightful speculations and sound investments. The hair-brained inventor, working in their garage, might conceptualise or even build a limited laboratory proof-of-concept for a star drive, but a practical application won’t be built without a sound business plan. Not in our planetary civilisation at any rate.

  • Michael May 24, 2014, 3:40

    Glaas May 23, 2014 at 13:29

    ‘How could the pressure from the Sun work at 1/1000 of Earth insolation and less power at Neptune and beyond, very very far far from any star?’

    With the use of high powered lasers is what he means. Anyway a light sail can ‘tack’ towards the sun gaining velocity and then on a swing by of the sun orientate itself to use the stronger light from near the sun and then on outwards. Then the high powered lasers could be used.

  • Jer May 24, 2014, 11:43

    After having read this latest instalment, I am seeing issues that may or may not have been intended. How could I have been so slow as to not have considered them? – though I think others mentioned them directly or as a glancing blow – or I could be completely off. Perhaps its the terms used: ‘terrestrial-based ‘ versus ‘space-based’ – that distracted me. When ‘space-based’ was used, I assume that just meant ‘launching point’ and the requisite yards or construction facilities, were off the earth at LEO or otherwise in the earth-moon system. ‘Terrestrial’ therefore meaning launched and constructed from the earth surface.

    This may have been so, but it is not as interesting perhaps, as where the resources and energy are sourced from. Let’s look at the recipe for each of the classes of starship – remembering that I have no space infrastructure/ starship background whatsoever.
    Class 0 – materials, energy, know-how – all from earth mines, earth knowledge institutions, and on-board sources.
    Now this is where it gets interesting… don’t forget we’re talking material and energy sources…
    Class 1 – earth mines and captured asteroids?; earth knowledge institutions?; and on-board -and/or- a certain portion of the sun’s power? (and a string of resources sent or found along the way?).
    Class 2 – earth mines and captured asteroids & other bodies?; earth and extra-solar and AI knowledge institutions?; and on-board -and/or- a significant portion of the sun’s power through a constructed extra-solar array? (and a string of resources sent or found along the way?).
    Class 3+ mobilized materials from earth, sun, solar system bodies, extra-solar ultra exotic resources; earth and extra-solar and AI and alien knowledge institutions?; and on-board -and/or- a significant portion more than our solar system’s power through an exotic multiple-site-source array? (and a string of resources sent or found along the way?).
    It is here that you realize the type of resources and energy that would have to be mobilized would simply be out of the scope of moon-earth systems. It may even be inappropriate to launch some of these ships from within our solar system (unfortunate planting of singularity or such). From that you start to put a connection between starship construction and fuel source and the amount of the solar system’s (or beyond) resources (especially energy) that need to be mobilized and accessed. So, you start to consider Kardashevian numbers. Now that’s interesting – and very difficult to quantify.

  • Michael May 24, 2014, 11:56

    @CharlesJQuarra May 23, 2014 at 23:57

    ‘In that case you need to replace the laser beam with a charged particle beam, which usually have worse divergence.’

    As you increase the velocity of the particles into the relativistic realm they tend towards a collimated beam. Think in terms of the twin paradox, every process takes place normally but at a slower rate in the moving frame of reference. For example if you have two like charged particles next to each other in a stationary frame of reference they will accelerate away from each other very fast. But in the relativistic realm time dilation effects take place, they do not diverge as fast to the stationary observer.

    Now thrash the particles to within an inch of light speed over one year of ‘stationary observer time’ and the particles will hardly move away from each other in their frame of reference. It is possible, provided they do not hit something on the way and the ‘catcher’ can handle it, to keep the divergence to the same size of the ‘catcher’ over very large distances. Particle beams have enormous advantages over lasers and other forms of propulsion.

  • Randy McDonald May 24, 2014, 13:39

    “The trajectory of development that humanity has not taken represents a possibility”

    Is it actually the case that humanity has not taken this trajectory?

    Above, Nielsen notes that even though technology has advanced enormously from the mid-20th century we haven’t gone into space. Might it be that we still don’t have the technology necessary for a viable offworld colonization program? Do we have the ability to build and sustain closed-cycle ecologies such as would be needed for O’Neill habitats, for instance? Or efficient launch technologies that could boost material from Earth?

  • Andrew Palfreyman May 24, 2014, 14:04

    Space progress is far too slow for my taste. When we read about $80 billion spent on military drones, we should wonder what could be done in space with such funds. Perhaps someone has come up with a table of cash available versus possible space milestones?

  • Alex Tolley May 24, 2014, 16:50

    When we read about $80 billion spent on military drones, we should wonder what could be done in space with such funds.

    The costs associated with the Apollo spacecraft and Saturn rockets amounted to about $83 billion in 2005 dollars (Apollo spacecraft cost $28 billion (Command/Service Module $17 billion; Lunar Module $11 billion), Saturn I, Saturn IB, Saturn V costs about $46 billion in 2005 dollars).
    (source: http://en.wikipedia.org/wiki/Budget_of_NASA)

    I feel your frustration. I think the more interesting question is what it might cost if industry was footing the bill for a profitable enterprise, rather than sucking in tax payer dollars. The answer may be quite a bit less. Time will tell. If SpaceX can pull off cheap[er] access to space, encouraging profitable orbital and circum-lunar tourism, we might get a more rapid rate of space utilization than we have historically experienced.

  • hiavatch May 25, 2014, 0:51

    Considering the vast amounts of energy required for any of these options to work, I think information tech will continue to out-pace transportation/energy tech by leaps and bounds.

    For example, AI, and with it, simulated human-like consciousness before practical fusion, say. Given that pacing, I can’t imagine sending fleshy-water sacks to the stars, even very long-lived ones.

    What I can imagine instead, is sending humans in software-form. Putting it bluntly, if brain-uploading is possible, and right now there is nothing we know of that says it is impossible, unlike warp-drive which may truly be impossible, many more options open up.

    Human or AI software running in optimal craft, even if relatively slow, could leave receiving stations en-route, and whoever else wants to travel could then arrive at the speed of light, as all kinds of energy, from lasers, to radio signals.

    IMO, the only thing more game-changing to the whole concept of interstellar travel short of true warp-drive, is humans “traveling” as non-biological beings. I can’t really imagine a future without that being the most significant factor.

  • NS May 25, 2014, 5:15

    Magellan left Spain with five ordinary ships. Only one made it back after three years, but its cargo of spices paid for the entire voyage.

    There doesn’t seem to be anything in space with such quick profit potential to motivate the kind of risks that governments and private enterprises took during the Age of Discovery on Earth. It apparently will require decades of both technological advancement and monetary investment to get any national or monetary return. There is probably enormous potential for political power and financial wealth in space, but the time and effort required to get them are intimidating, with no obvious shorter-term gains to justify them.

  • Alex Tolley May 25, 2014, 16:47

    @hiavatch – it is remarkable how little the idea of humans in software form has been explored. There was Arnold Rimmer in “Red Dwarf”. Arguably the Robert Sawyer’s Mindscan explores a similar idea, but with the software embedded in a machine body.

    Mindscan is particularly relevant here, as the protagonist eventual lives on Mars, oblivious to the lack of air. If we can transfer minds, this would be the way to travel the galaxy, being transferred to a body at the destination using local materials. Failing human mind transfer, then AI’s would fill the same role. This seems far more useful than sending humans in shape or form, including embryos or DNA sequences, only to need major infrastructure to support their biological requirements.

  • Ole Burde May 26, 2014, 4:06

    NS : When Columbus left Spain , he had only vague ideas about what he would find on the other side . Noboddy thought the first voyage should be profitable in it self , it was a wise longterm investment who actually only paid of 50-100 years later . Like president Kennedy , King Ferdinand was a leader of a country who had just won a historicly important and decisive victory , ending the 600 year long war between Christians and Muslims in Spain . Aleader of this kind can unite a whole people behind a project of his choice . You might say that main difference between them was that Ferdinant had better bodygards… Who knows where the space program could have been now ,if Kennedy had lived ? By 1980 we could have lifted a 10.o00 ton spacestation to orbit with a few hundred termonuclear explosions .

  • Abelard Lindsey May 26, 2014, 14:53

    The key issue is if FTL is possible. If it is, it will likely lead to the development of spacecraft that are built on Earth, can lift off under their own power from Earth, and travel to and directly land on planets in other solar systems. This would eliminate the need for space-based industry. Baring any breakthroughs on the part of Woodward and White, I consider this scenario unlikely.

    What is far more likely is that interstellar travel at sublight velocity is possible, but takes several decades to get to the nearest stars. In which case, the future in space will be limited to O’neill style space settlements through out the solar system (as well as the surfaces of Mars and Titan), Interstellar travel will be the outgrowth of a solar system wide civilization, after having built up over a 2-3 century period starting around 2050. In other words, interstellar travel won’t happen till around the 24th century.

  • NS May 26, 2014, 16:24

    Europe already had some idea of what was available in Asia, Columbus’s planned destination. I don’t know if his first voyage made a profit, but it certainly aroused enough interest that he was able to make three subsequent ones, and European efforts in the “New World” expanded rapidly. It was apparent there were profits to be made there. Nothing that our initial space explorations found kindled similar interest in the governments or entrepreneurs of our time. My view is that we’re not any less brave (or less greedy) than our ancestors were, but that it will take much longer, and require much more effort (on a national/international scale), to find and exploit the kind of resources in space that were rather quickly and inexpensively discovered in the past on Earth.

  • ljk May 27, 2014, 9:10

    JFK was looking at peaceful cooperation in space with the Soviet Union, including plans for a joint manned lunar mission. He was not as gung-ho about space exploration as many have been led to believe. He just wanted whatever could defeat the Soviets in a non-military manner on the global stage. JFK also considered an Earth-orbiting station and a manned mission to Mars. Remember he was trying to deflect the bad press from the Bay of Pigs fiasco in 1961; plus Gagarin had just orbited Earth in Vostok 1.

    I wonder if Apollo might have happened at all if JFK had lived as it was partly driven by his memory. If we had gone with a cooperative effort with the Soviets, would it have worked? Was it too early in the Cold War, especially after the Cuban Missile Crisis, to get both sides to trust each other enough to share technology? The Soviets would have been the clear winners there, which I am sure would not have gone over well with the USA. Apollo or its hybrid might have been put off for another decade or even longer, then never happened at all.

    To be optimistic, perhaps if we had gone to the Moon together we might have kept the manned lunar program going to establish bases, rather than the abrupt end with Apollo 17 in 1972 and no humans going back since. Lots of talk, but no new bootprints yet.

  • William Blight May 27, 2014, 11:12

    I note that most of the comments are based on realistic propulsion technology that will require a solar system wide infrastructure.

    I am still not convinced regarding the optimism about disruptive breakthroughs . I don’t see the resources or national energy directed toward fringe science. For example, NASA’s breakthrough propulsion program was shut down. Very few resources are being aimed at either Woodward (none) or White ( a small lab). Elon Musk has the best take on this. Put your own energy and talent into making us a two planet species – and don’t expect much from the government. The massive disruption of colonizing the solar system is the means for going interstellar. Probably, you will need enormous space infrastructure (solar and laser) to propel interstellar craft. Some investment in breakthrough propulsion is wise, but elaborating any plans on this propulsion is not.

  • Alex Tolley May 27, 2014, 15:06

    @William – Nielsen is simply offering scenarios. Most of us are fairly grounded in possible technology. However, we should always be cognizant that we are caught up in our time period. If we were Victorians, we would be taking about steam and muscle power, speculating whether gunpowder/solid rockets or cannons could work as propulsion systems. Another century from now and our descendants may look back at our era as doing much the same, unaware of the impending technology breakthroughs. (Or they may say that it was obvious that no breakthroughs were possible and it was just fanciful thinking.)

  • Geoffrey Hillend May 27, 2014, 17:55

    The NASA Breakthrough Propulsion Physics Program was successful. It generated visionary ideas by scientists which are completely supported by classical and quantum physics. The Alcubierre warp drive is proven possible by general relativity etc. so many things in that program are not “fringe science”, but are not understood by the layman.

    Such ideas are far ahead of their time. I think everyone agrees that the technology of today was once the technology of the future and it was thought to be impossible one hundred years ago.

    The scientific intuition works through progress, and innovation but necessity limits us to keep refining and perfecting the same technology until something new is invented but a risk has to be taken. If something can be supported by even today’s knowledge of physics, we might work out any problems with further understanding or the knowledge of the future and that which has not been discovered yet and that is where new ideas and lines of research and the epiphanies of scientists become game changers.

  • Alex Tolley May 28, 2014, 1:09

    And while we look to the stars, the Guardian’s George Monbiot links to this:


  • ljk May 28, 2014, 8:58

    The conservative comedian Dennis Miller once said this regarding the space program:

    “Let’s dry dock the shuttle and just wait a few decades and I’m sure somewhere down the line a new brainiac kid, the next Einstein, will just scribble something on a legal pad one day and say, “Here Granddad, here’s how to get to Mars using only a shop-vac, a Slinky and a Mennen Speed Stick.”

    The full rant from here:


    This is the kind of attitude which will ensure we do not get back to the Moon or on to Mars any time soon let alone Alpha Centauri. Hoping that some “genius” in the future will solve all out problems, presumably out of the blue one day. Even Einstein did not work in a vacuum. It is thinking like Miller’s which will keep interstellar travel in the fantasy realm indefinitely.

    Our future scientists need concrete support and funding NOW. FTL travel is not going to happen by magic or wishing really hard, assuming it is possible at all. We should also be focusing on the propulsion methods we know are plausible, even if it means we won’t be warping to Vulcan in 15 minutes.

    I am not waiting for the future or aliens or deities to come and “save” us. We can save ourselves. If we want to.

  • ljk May 28, 2014, 10:22

    Geoffrey Hillend said on May 27, 2014 at 17:55:

    “The NASA Breakthrough Propulsion Physics Program was successful. It generated visionary ideas by scientists which are completely supported by classical and quantum physics. The Alcubierre warp drive is proven possible by general relativity etc. so many things in that program are not “fringe science”, but are not understood by the layman.”

    Except that people tend to continually skip over the fact that his warp drive idea requires a chunk of negative matter, which does not exist so far as we know nor would we know where to find any or how to manipulate it for interstellar travel if we did.

    The fact that someone reduced the original size of the required negative matter from the diameter of Jupiter down to the Voyager space probe does not help very much if we still do not know what negative matter is, where it is, how to obtain it, or how to use it.

    Please note, it is negative matter, not dark matter. This is matter with negative mass. Anyone who can figure out how to give matter negative mass will win the Nobel and then the galaxy. But until then, let us focus on the interstellar technologies we can actually work with, please.

  • Michael May 28, 2014, 14:15

    Separating the construction of an interstellar craft and the development of space infrastructure is going to be like separating Space-time, not possible. If we aim for space expansionism we would almost certainly guarantee our species long term survival at least.

    @ljk May 28, 2014 at 8:58

    ‘The conservative comedian Dennis Miller once said this regarding the space program…’

    That is why he is a laughing stock and will remain one…

  • Geoffrey Hillend May 29, 2014, 17:24

    Ljk, I completely agree with you about the improbability of giving matter negative mass which is why I distinguish between negative matter and negative energy. I came to the same conclusion as you have four years ago. I engaged in a little thought experiment where I could not support the idea of negative matter with quantum physics. According to the quantum inequality law, to make negative energy, one must have a little more positive energy than negative energy to make a warp field with negative energy locally. That energy has to come from somewhere and how could you hold together a piece of negative matter when it has a repulsive force? The attractive electro magnetic and nuclear forces inside the atoms would be over powered by a repulsive force which would want to fly apart so how could it hold together or clump together like normal matter? Dark matter like normal matter still has positive energy density or an attractive force which would be the same as normal matter so it is obvious to me that dark matter is not the same as negative matter which has negative energy density.

    I don’t believe there is any such thing as negative matter. It would violate the second law of thermodynamics and energy conservation laws. To get energy from matter E = MC squared you first have over come the electric and nuclear forces in normal matter and even if you did that you would slowly drain away all the positive energy of matter which would vanish or disappear in order to produce a continual field of negative energy. How would it hold together and what would be made out of? Negative energy particles create a repulsive force or create a negative warped field so how could they hold together like particles in normal matter?

    Negative energy and negative mass are different; They are supported by the Casimir effect and Heisenberg uncertainty principle which states that empty space can have both positive and negative energy density due to the wave nature of energy. https://www.google.com/#q=zero+point+energy+wiki

    Virtual particles of negative and positive energy are split apart in the quantum vacuum zero point energy of empty space by black holes. Negative energy falls into the black hole and positive energy is radiated away in the form of Hawking radiation so the idea of negative energy has strong support by quantum physics.

  • Chris W May 31, 2014, 14:25

    Don’t forget the possibility of class 4 – instantaneous travel. “Beaming” people and objects to any desired point in the universe instantaneously. I mean, as long as we’re being speculative. This might be the most culturally/structurally impact full of all. As you could imagine, such tech (terrestrial bound) would be a massive game changer even on Earth bound civilization.

  • Brett Bellmore May 31, 2014, 17:06

    “Europe already had some idea of what was available in Asia, Columbus’s planned destination.”

    I think it needs to be noted that Columbus may very well not have been as ignorant of where he was going to wind up as the usual story has it. Cod fishermen were apparently treating the existence of North America as a commercial secret, and, while it wasn’t “officially” known, it’s quite likely there were rumors.

  • Michael June 1, 2014, 0:35

    @Chris W May 31, 2014 at 14:25

    ‘Don’t forget the possibility of class 4 – instantaneous travel. “Beaming” people and objects to any desired point in the universe instantaneously.’

    Beaming in the sense now is limited to light speed and lower. I am thinking along the lines of FTL is not possible because if an alien race (in the entire universe there must be some) had perfected it they would be everywhere by now, it is that powerful. Perhaps a star-gate setup maybe possible with low velocity initial travel then FTL between those points.

  • Geoffrey Hillend June 1, 2014, 15:50

    I believe it was Carl Segan who said something like “the absence of evidence does not mean evidence is absent. ” There are a lot of reasons why ET’s with FTL could be out there but have not contacted us yet. I don’t want to go into them here.

  • ljk June 2, 2014, 9:10

    No, it was Sir Martin Rees who said that “absence” quote. See here:


  • Aleksandar Volta August 3, 2014, 11:04

    I agree with Geoffrey. There is not one good reason why an extraterrestrial intelligence ‘must’ make itself known or somehow visible to others, even if it can travel the cosmos instantaneously.

    And speaking of such travel speeds – Could wormholes, natural or artificial, provide such journeys and be categorized as Class 4?