All Astronautical Evolution posts in 2011:

The battle for the future (Dec.)

The personal satellite / Olaf Stapledon / Europe needs a strategy (Nov.)

100 Year Starship Symposium / BIS newsletter Odyssey (Oct.)

Development Roadmap for the Worldship (Sept.)

Tumlinson’s challenge for NewSpace / SRI calls for global Apollo day / Poem celebrates Apollo (Aug.)

Dear Mr Dordain… / Mat Irvine: From Imagination to Reality (July)

Society between cosmic growth and utopian dreams / UK Space Conference (June)

Available in any colour so long as it’s black / UK Space Conference and Sir Arthur Clarke awards / David Baker slaying the Space Age myths / Getting involved in the BIS / Cartoon: can Spirit come home now? (May)

Mankind in space: the next fifty years / What future for intelligent life in space? (April)

Does evolution progress? The multi-shell model (March)

Social software for a spacefaring civilisation / Best of the blogs / Space cartoon of the month (Feb.)

2010: Manned spaceflight at the crossroads / 2011: Smoke signals from two dragons (Jan.)

New in 2015:

Short story The Marchioness

AE posts:

2017: Mars…

2016: Stragegic goal for manned spaceflight…

2015: The Pluto Controversy, Mars, SETI…

2014: Skylon, the Great Space Debate, exponential growth, the Fermi “paradox”…

2013: Manned spaceflight, sustainability, the Singularity, Voyager 1, philosophy, ET…

2012: Bulgakov vs. Clarke, starships, the Doomsday Argument…

2011: Manned spaceflight, evolution, worldships, battle for the future…

2010: Views on progress, the Great Sociology Dust-Up…

Chronological index

Subject index

General essays:

Index to essaysincluding:

Talk presented to students at the International Space University, May 2016

Basic concepts of Astronautical Evolution

Options for Growth and Sustainability

Mars on the Interstellar Roadmap (2015)

The Great Sociology Debate (2011)

Building Selenopolis (2008)


Issue 68, 11 April 2011 – 42nd Apollo Anniversary Year

  1. Mankind in space: the next fifty years
  2. What future for intelligent life in space?

All content is by Stephen Ashworth, Oxford, UK,
unless attributed to a different signed author.

=============== AE ===============

(1) Mankind in space: the next fifty years

Will the second half-century of manned spaceflight resemble the first? Apparently not: major changes are in prospect. After 30 years of Shuttle, Soyuz, Mir and ISS, when little seemed to be changing, we have reached a point of reorganisation – look at the current turmoil in the funding and direction of NASA, and the appearance in orbit of new players such as China, with three successful manned flights since 2003, and now SpaceX, with its passenger-capable Dragon capsule successfully test-flown last year.

First let us recall the half-century of spaceflight from Yury Gagarin’s single orbit of Earth in April 1961 up to the end of 2010. Total human activity in orbit over those fifty calendar years comes to 37,216 man-days, or 101.9 man-years, of time logged by men and women in low Earth orbit, flying to and from the Moon and on the lunar surface itself (a paltry 25 man-days).

A total of 276 manned launches to orbit (not including Challenger’s last, tragic, flight, or the Soyuz 18-1 and T-10-1 launch aborts) have carried 1146 people into space, though since many of them have made the journey two or more times, the actual number of individuals who have orbited their home planet stands only at a little over 500. Of those space travellers, 21 have died in flight or in their spacecraft during pre-launch preparations for flight (in Apollo 1, Soyuz 1, Soyuz 11, Challenger and Columbia).

In addition, three people have flown briefly above 100 km altitude without going into orbit (in the X-15 and SpaceShipOne), and a handful of others have flown higher than 80 km (the US Air Force’s criterion for reaching space).

The graph of man-days in space, year by year, shows many precipitous ups and downs. Particularly obvious are the surge forward in 1994-1997, during the heyday of the Shuttle and Mir, and the collapses in activity following Skylab, the Challenger and Columbia disasters, and the onset of problems with the ageing Shuttle fleet during the late 1990s.

Graph of 50 years manned spaceflight

Nevertheless the graph shows overall consistent linear growth from the mid-1960s onwards, adding on average some 48 man-days per year, if very erratically, up to its current peak of 2190 man-days in 2010, representing six people in orbit at any given time.

But the retirement of the remaining Shuttle fleet, and the current practice of returning a three-person crew from the ISS to Earth before their successors are launched, mean that activity has now reached a plateau, and will even fall slightly over the next few years. There is no prospect of further growth from this very low level unless and until new manned spaceflight ventures come into operation.

The fundamental sickness of the government space enterprise becomes clear when considering the number of launches of manned vehicles to orbit, year by year. In 1961 there were two orbital flights, of Vostok 1 and 2. Activity has remained in single figures for 46 out of the past 50 years.

In 2010 there were only seven manned launches – fewer even than the nine which took place 41 years earlier, in the wonder-year of 1969, the climax of the Soviet–American Moon Race. Ten launches in the same calendar year were only achieved at the peak of the Shuttle and Mir era (in 1992, 1994 and 1997), and the current record of eleven launches (nine Shuttle, two Soyuz) carrying a total of 63 crew and passengers to orbit was established back in 1985, the year preceding the Challenger disaster. An average of one launch per calendar month has not yet been achieved (though one can count twelve complete flights in one single 365-day period: between 24 January 1985 and 23 January 1986).

Launch activity, therefore, has been merely marking time over the past quarter century, its further growth prevented both by the failure of the Shuttle to meet its original goals of economic, reliable and frequent operation, and by the collapse of the Soviet economy and political system.

These two factors conspired together in the early 1990s to force a merger of the Russian and American space station plans, which otherwise might have resulted in two six-man stations in orbit by now rather than just the one. Man-days in orbit have benefited, not from any increase in launchings, but from the fact that the ISS now allows each space traveller to spend longer in orbit before returning to Earth.

So much for past history – the legacy of Yury Gagarin’s flight fifty years ago, or rather I should say the legacy of Sergey Pavlovich Korolyov, James Webb and John F. Kennedy, among many others. What happens now?

Let us contemplate three plausible scenarios for the next fifty years.

* * *

(1) Governments in partnership. – This is the paradigm of space exploration and use which is dominant at present, and has been since the end of the Moon Race and the Cold War. It is the world of the ISS and the Global Exploration Strategy.

A new American president, let’s say a Republican, reverses the Obama reversal of George W. Bush’s reversal of NASA’s direction, and reinstates Constellation. China establishes its Tiangong orbital station. Europe develops its ATV capsule into a recoverable manned capsule launched on Ariane 5. Russia introduces the long-awaited successor to Soyuz, a larger capsule launched from its new Vostochny cosmodrome. India too joins the manned spaceflight club with its own capsule and throwaway booster.

Meanwhile attempts to commercialise human passenger spaceflight are frustrated by a tragic accident, or by a crippling burden of red tape imposed on it by a bureaucracy jealous of its monopolistic privilege. Or perhaps the punters simply decide to stay at home.

A decade on, say 2025, and a multinational assortment of astronauts is returning to the Moon. As in the case of the ISS, NASA is merely first among equals, and indispensable roles are filled by vehicles, equipment and personnel from Russia, Canada, Europe, Japan, China, India and elsewhere. While the ISS may have been abandoned and destroyed (too expensive to run two large-scale programmes at once!), a smaller Russian or Chinese or Indian-led station maintains a toehold in low Earth orbit in which astronauts practise for interplanetary flight.

And perhaps by 2040 to 2050 they are setting foot on the surface of Mars – certainly before 2061. Manned activity in space reaches a new plateau perhaps twice or three times as great as today. And levels off, as it must while it remains a net consumer of the world’s treasure.

As our civilisation grows richer, and as new countries climb the development ladder and emulate the economic success of Japan, China and India, so funds for government space exploration gradually increase and it becomes possible to maintain one (just one!) station in low Earth orbit and one (just one!) on the Moon at the same time as launching an expedition to Mars every few years.

Or maybe not…! As the world’s problems multiply – the environment, international development, new technologies (an ageing population thanks to medical advances, nanomachines, computer intelligence) – and as troublemaking nationalist regimes from Russia and China to North Korea and Iran reignite the nuclear arms race, or more probably accelerate higher-tech, lower-cost ways of causing social disruption and mayhem among their perceived enemies, so government space exploration is gradually strangled.

Meanwhile the lack of commercial follow-up deprives exploration of any economic sense, and long before 2061 manned spaceflight has been abandoned altogether.

* * *

(2) Governments in conflict. Of course, another round of global tension offers its own opportunity for manned spaceflight. If Constellation is in many ways a re-run of Apollo, then maybe it will flourish if the world sees a re-run of the Cold War?

While he was still NASA Administrator, Michael Griffin raised the possibility of American–Chinese rivalry on the Moon. Gregory Benford’s novel The Martian Race (Orbit, 1999) extends that rivalry to the Red Planet. Throw a revived Russia and an up-and-coming India into the mix, and there could be a race for the Solar System which turns out to be a marathon in comparison with Apollo’s mere 100-metre sprint.

Or – again – maybe not. From the perspective of a space activist, interplanetary exploration is an obvious economic, technological and prestige multiplier. From the standpoint of a politician with feet firmly planted on the ground and eyes on the next election, it is equally obviously a pointless drain on resources urgently needed elsewhere – for social programmes, for the military, for fighting climate change (whatever that means).

In Kennedy’s day the Moon Race had an earthly payoff: success would demonstrate irrefutable proof of superiority in rocket propulsion and missile guidance – key Cold War technologies. But today a bomb may be delivered to devastating effect by a fanatic carrying a suitcase, or even just a sharp knife, as the 9/11 terrorists showed.

Again, why spend billions on weapons and delivery systems if a guy sitting at a computer can do as much damage in an increasingly nervous, increasingly wired-up world? Racing to be the first on Mars or the first to return to the Moon does not have the political payoff it had half a century ago, and therefore neither is it likely to attract the funding or the sense of national priority.

* * *

(3) The astropreneurial takeover. – But what of a scenario in which government yields its manned spaceflight monopoly to the astronautical entrepreneurs? People such as Sir Richard Branson, Anousheh Ansari, Robert Bigelow or Alan Bond have ambitions even greater than those of any space agency bureaucrat: what if they were to succeed where the government officials failed?

The key point about commercial spaceflight endeavours is that they aim for the largest possible market. Pile ’em high and sell ’em cheap: such is the motto of the supermarket manager, whose maximum profit requires maximum turnover because of the efficiencies of scale.

In astronautics the largest untapped market is that for private space travel – in its 2005 symposium the British Interplanetary Society concluded that space tourism is the key to low-cost access to space. Another barely touched market is for commercial product research in orbit, currently unable to make headway because of the restrictions on access to the ISS.

Launch manned spacecraft at no more than one per month, and reusability makes no sense: the expense of returning a vehicle to Earth and turning it around for the next flight is greater than simply manufacturing a new one from a clean sheet of aluminium. But launch one flight per day – let alone one every working hour of every day – and reusability becomes essential.

With reusability comes the opportunity for repeated testing of a vehicle, as well as incremental testing (fly a little faster and a little higher each time), and hence a quantum leap forward in reliability and abort options. When the Space Shuttle first flew, it had to go all the way into orbit, but a winged vehicle like Skylon does not even have to go supersonic on its first test flight.

With frequent flights comes higher operational safety: a space station like the ISS which must wait months for essential spare parts to arrive is in a completely different orbit to one which receives visiting shuttles on a daily basis. The shuttles themselves are vastly safer, too: if one gets into trouble in space, then no worry – another one will be along in a few hours.

But we cannot get from the situation of one launch every couple of months to daily flights overnight. The problem facing the astropreneur is how to launch the self-stoking cycle of progressively falling costs and rising traffic levels.

With our perspective of the next fifty years, 2011 to 2060, one point at least must be clear: because it cultivates a wide market, large-scale commercial passenger spaceflight must by its very nature drive traffic levels up, reliability up, overall turnover up and unit costs down. But continued government-led spaceflight is not and cannot be aimed at achieving this.

How fast might commercial passenger spaceflight grow? Nobody yet knows. The current rate of about one private passenger per year since Dennis Tito visited the ISS in 2001 is limited by seats available, not by demand, even at the current exorbitant price of some $30 million for a ticket.

The World Tourism Organisation (UNWTO) forecasts that international terrestrial tourism will continue growing at the average annual rate of 4%, equivalent over fifty years to a sevenfold increase. Applying this rate to the current baseline space crew and passenger traffic of about 30 people to orbit and back per year produces an annual turnover of over 200 people by 2061.

But global tourism is long-established, while space tourism is new and may initially expand at a faster rate. There are plenty of rich people out there who might want to buy tickets, even at the multi-million-dollar level. In his talk at the British Interplanetary Society on 24 March 2011, Derek Webber noted that the latest figures from Forbes magazine show there are 1200 dollar billionaires in the world, and over 8 million millionaires.

If we assume a faster rate of growth as more efficient reusable space vehicles start to open up this market, say 10% per annum, then the resulting hundredfold increase per fifty years would lead to 3,000 space travellers per year by the centenary of Yury Gagarin’s solo spin around the planet, and a third of a million a century from today.

Or not. Like the government-led scenarios, the commerce-led one is subject to the same imponderables as any attempt to probe the human future.

But if it succeeds, the thousands of visitors to orbit would create markets in space for water and rocket propellants. The resulting economies of scale and reusability would then drive down the costs of lunar transport and the infrastructure for the permanent human occupation of the Moon, Mars and space itself, leading to large and permanent extraterrestrial populations.

* * *

Finally: would an increase in human activity in space benefit human civilisation in the broadest sense? Clearly there are those who believe it would not, such as the Marxist sociologists Peter Dickens and James Ormrod, whose book Cosmic Society and lecture at the British Interplanetary Society on 8 September 2010 caused major controversy.

Ultimately it comes down to the fundamental facts: space colonisation offers a vast opportunity for sustainable growth to a one-planet technological society, and those societies which seize that opportunity will clearly have far greater prospects of both continued creativity and long-term survival than those which exhaust or stifle growth at the single-planetary level. While the growth of government activity merely consumes wealth, it is commerce which creates new wealth, and the innovative, visionary, self-motivated individual (the “narcissist”, who is suffering from “a kind of personality disorder”, in sociological terminology) who kick-starts commercial enterprise.

Social reformers who wish to improve the workings of our civilisation deserve our wholehearted support: only a prosperous, peaceful and innovative civilisation can muster the considerable resources, material and human, to enable it to make that leap from a planetary to an interplanetary level. This fact was highlighted in the contrast between American success and Soviet failure in the Moon Race.

Talk of a socialist alternative is a red herring: if the vision on offer requires the cessation of growth and the imposition of crippling restrictions on innovation and private wealth in the name of the ideological pursuit of a utopian society or a personal vendetta against the rich, then it is the socialists, not the astronauts and astropreneurs, who aim to frustrate the benefit of human civilisation.

The next fifty years of manned spaceflight will see a complex interplay of national, international, political, economic, competitive and collaborative factors. But in the long term either the profit motive will emerge as the driver, leading to millions of our children first visiting, ultimately establishing themselves permanently in space, or exploration will remain limited to occasional high-cost sorties for a privileged elite of government officers, and such expeditions, like the civilisation which sends them, will prove in the end to be unsustainable.

=============== AE ===============

(2) What future for intelligent life in space?

(Full essay also posted at The Space Review.)

Thirty-five years ago, Gerard K. O’Neill wrote: “We are so used to living on a planetary surface that it is a wrench for us even to consider continuing our normal human activities in another location” (The High Frontier, p.25). He concluded that the best place for a growing industrial society is not on the Earth, or the Moon or Mars, but “somewhere else entirely”: an array of artificially constructed space colonies.

Judging from current attitudes, his fundamental insight is still enough of “a wrench” that it has yet to gain wide acceptance. For example, the material published so far by the DARPA-NASA Ames 100-Year Starship Study ignores colonies in space, despite their obvious relevance, as does Lou Friedman’s report on their recent meeting. Joy Shaffer’s 2004 essay “Better Dreams” at, enthusiastically referenced by one Space Review commenter, explicitly excludes colonies in space: “there is no need to massively industrialize any place in the solar system beyond the elevator terminals and power stations at geosynchronous orbit”. Even the Tau Zero Foundation focuses on “the ultimate goal of reaching other habitable worlds”.

In this essay I want to revisit some of the fundamentals of O’Neill’s concept and demonstrate their continued relevance.

* * *

In order to live and function, multicellular creatures such as ourselves need land area with gravity and an atmosphere. A planet represents a highly inefficient means of providing these basic essential services. Mars, for example, has a mass of 6.42 × 1020 tonnes and a surface area of 1.44 × 108 square km, thus 4.45 trillion tonnes of matter are required for each square km of habitable area.

For comparison, the space colony design Island One has an estimated total mass of about 3.5 million tonnes (including comprehensive radiation shielding) and offers a pressurised surface area of 1.09 square km for a population of 10,000 people (O’Neill, p.57-59). The space colony therefore requires 3.2 million tonnes of structure for each habitable square km, a mass less than that of Mars by a factor of about a million.

The reason is clearly that in the case of the Earth, Mars or any other planetary sized body, almost all the mass of the planet serves no function, from the point of view of its surface life, other than to provide surface gravity, and in some cases also a magnetic field and geothermal heat, though smaller bodies such as the Moon provide little or none of these. Planets are low-tech, compressive structures, as indeed they have to be.

An artificial space colony which provides gravity by rotation, on the other hand, must be maintained in tension, requiring conscious design and high-tech materials. In exchange for the investment of engineering effort, the efficiency in the use of raw materials to provide habitable surface area is increased by about a factor of a million (a factor that varies within an order of magnitude each way depending on the particular sizes of space colony and planet being compared).

The conclusion has to be drawn that, while a planet is a good place for life to get started using unconscious means which can evolve spontaneously from the chemical substrate, once life has reached the stage of industrial development its further growth depends on the use of technology to construct artificial space colonies, which use the material resources of planetary systems at a much higher level of efficiency.

Since, in the O’Neill colony design, about 86% of the mass consists of passive radiation shielding, this conclusion is not strongly dependent on the precise proportions of rocks, metals and volatiles available. Clearly, if adequate protection from cosmic rays can one day be achieved by the use of magnetic fields, the balance swings even further in favour of designed habitats as opposed to natural ones.

In this way, very large future human populations are conceivable; for example John S. Lewis has reckoned that the material resources of the main asteroid belt, together with large-scale use of solar power, would allow at least 10 million billion people to support themselves (Mining the Sky, p.196). When one adds in the Jupiter trojans and the opportunities presented by the outer Solar System, even larger populations become possible. Frank Drake and Dava Sobel have put the overall carrying capacity of our system at “more than a hundred billion billion human beings” (Is Anyone Out There?, p.128), while Marshall Savage suggests an even larger figure (The Millennial Project, p.303).

We do not need to quibble over orders of magnitude in order to make the point that the propensity for economic and population growth characteristic of industrial civilisation is well matched with the opportunities offered by its local environment, provided that the 21st century sees a shift of the focus of industrial and population growth away from Earth and onto large-scale development of the natural resources of near-Earth space.

Clearly the Moon and Mars will remain the main initial targets for astronaut exploration. But the necessity to protect travellers to and from these worlds from solar storm radiation, as well as the advisability of providing them with a safe haven en route, forces a transport architecture based on well-shielded and well-provisioned but consequently heavy cycler stations, and particularly in the case of Mars this drives the designer’s attention towards use of materials from near-Earth asteroids, some of which may be volatile-rich, found in orbits which mimic cycler trajectories.

From there it is a short step towards using asteroidal materials to create and supply space habitats which are independent of the Earth-Mars traffic, leading to a gradual expansion of habitable volume spreading out to the main asteroid belt. The resource limits to growth of this kind will not appear for centuries or millennia to come (depending on growth rates over time).

Other advantages mentioned by O’Neill include full-time, full-strength access to solar power, and the option to choose different or zero gravity levels for different purposes. While transport within a single colony or between two adjacent ones would also be easier than on Earth, colonies in widely differing orbits would not necessarily benefit from cheaper transport, though they would still be mutually accessible without having to climb up out of one steep gravitational well and down into another.

With this picture of space colonisation based on the material resources of the Solar System’s smallest bodies firmly in mind, a number of consequences follow.

* * *

Firstly, the project of sending humans to the stars is absolutely dependent upon prior large-scale space colonisation. To begin with, the passengers on any interstellar mission will be devoting the rest of their lives to the voyage and the explorations at their destination – a return journey within a human lifetime is hardly conceivable (barring some magical new propulsion technology, and even that is hardly likely to come cheap).

This means that no manned starship will be despatched until the viability of a space habitat has been demonstrated for at least one complete human lifetime (including one or more reproductive cycles – unless the starship is conceived as a suicide mission). With space colonisation in progress spurred by general economic and population growth, such a demonstration will be a matter of course, and will be funded by the broader economy. Without it, the demonstration will be an expensive one-off project, and volunteers (together with their yet unborn offspring) will have to renounce all claim to a normal life.

* * *

Again, the practicality of interstellar spaceflight varies enormously between robotic and manned programmes. Travelling to the Moon, the Surveyor robots weighed about a tonne (including descent propellants), as against the 45 tonnes of the complete Apollo spacecraft. But with sights set on Alpha Centauri, a robotic probe could be very much lighter than those of the 1960s (Lou Friedman talks of “masses less than 10 kilograms”), whereas the irreducible need on a manned vehicle for long-term life-support systems and all the equipment, ancillary vehicles and reserves the crew are likely to need for the rest of their working lives, plus an exotic high-energy propulsion system, will surely push the vehicle mass up towards the order of 10,000 tonnes (25 times the mass of the ISS, or the size of a small ocean-going ship).

Thus the step up in scale from a robotic starship to a manned one looks to be on the order of a factor of a million in terms of mass and hence of energy cost. The absolute minimum energy cost for a 10 kg probe with a cruising speed of 0.05c which takes about 80 years to cross to Alpha Centauri is twice its kinetic energy at that speed, or 143 MW years (assuming a perfectly efficient propulsion system!). For even a minimal manned starship weighing say 5,000 tonnes, that energy cost jumps to 71 TW years, equivalent to total current global industrial energy consumption for about five years (in practice a multiple of this, when the inevitable inefficiencies of the propulsion system are factored in).

It is therefore effectively inconceivable that a merely planetary economy would ever be rich enough to afford to fuel a single manned starship – unless it went for a slow, multi-generational approach: travelling at 0.005c, our 5,000 tonne starship would take 800 years to make the crossing, with an energy cost about a twentieth of current annual global consumption (plus inefficiencies). But with the millionfold growth in population, and thus in the overall Solar System economy, made possible by the transformation of our species from a planet-bound to a space-based one, the energy cost of even a fast manned starship programme sinks to a fraction of civilisation’s annual energy budget.

* * *

Thirdly, in the context of interstellar exploration such as that now being contemplated by the 100-Year Starship Study, a consequence of space colonisation within our own Solar System is that all main-sequence stars become targets for colonisation by industrial civilisations, from M dwarfs such as Proxima Centauri to A stars such as Sirius and Altair, provided that those stars are accompanied by asteroidal rubble similar to our own system’s asteroid and Kuiper belts, which according to a well-known astronomer of my acquaintance is indeed very likely.

This acts as a great enabler to manned interstellar spaceflight. Were human star-farers to turn up their noses at any star lacking an Earth analogue planet in a closely earthlike orbit, they might well have to travel tens or hundreds of light-years in order to reach the nearest acceptable destination. (Obviously we cannot yet rule out earthlike worlds orbiting the very nearest stars, but given the unexpected variety of the extrasolar planets which have been discovered so far, does anyone really believe that new Earths are likely to be common?)

* * *

Fourthly, the quest to find earthlike planets becomes a purely scientific one. Should we identify an extrasolar Earth analogue, complete with indigenous life of its own, its value to us as a target of non-invasive scientific study will be far greater than its value for colonisation or resource extraction. The immigrants will be accustomed to living permanently in artificial space structures, and will have no reason to change their lifestyle after arrival, though visits to planetary surfaces for science and recreation will no doubt take place. The scenario of James Cameron’s movie Avatar, which posits human star-travellers coming into conflict with indigenous inhabitants of such a planet, is therefore not a realistic one.

* * *

A fifth consequence is that if space agencies want to promote progress in space development, whether for economic or scientific reasons, or both, they will need to think more carefully about how they coordinate their exploration with commercial ventures which hope to capitalise on those exploratory activities. While it is excellent news that Space Adventures has announced the purchase of more Soyuz seats for fare-paying passengers on trips to the ISS and even around the Moon, this is still happening more in spite of space agency planning than as a result of any coherent strategy to make hardware and technologies purchased at considerable expense with taxpayers’ money useful and profitable in wider society.

Space agencies alone cannot create the complex, dynamic space economy implied by the vision of large, permanent extraterrestrial human populations, which is why NASA and ESA in particular need to pay closer attention to fostering commercial growth in the difficult space environment – starting, obviously, with those companies focused on getting the cost per seat to orbit down, and the traffic level up.

* * *

To the best of current knowledge, almost all the matter and energy in the Galaxy which could in principle be used to support life and civilisation is found in planetary systems which have either no idigenous life at all, or only microbiotic life. Given that space colonisation is undoubtedly technically possible (the unhappy experience of the mismanaged Biosphere 2 project notwithstanding), and that interstellar flight is a logical outlet for the energies of an interplanetary-scale civilisation, it follows that life in the Galaxy will tend over time to become dominated by expansionary, space-based civilisations.

Our own species therefore stands at a unique crossroads in its career: whether to perfect these technologies and move outwards from Earth, effectively making its heritage immortal through a variety of far-flung successor civilisations, each one orders of magnitude larger than that possible on Earth alone, or whether to retreat from a high-tech future and face ultimate decline and extinction on Earth.

Gerard O’Neill’s strategy of economically self-sustaining space colonisation, first published in 1976, is still the touchstone by which future plans for space exploration and development must be judged.

Note: Page references to Gerard K. O’Neill, The High Frontier, are to the expanded 3rd edition published by Apogee Books together with the Space Studies Institute and the Space Frontier Foundation, 2000.