All Astronautical Evolution posts in 2014:

Future growth in space still not being taken seriously (Dec.)

The SpaceShipTwo Crash (Nov.)

To the Rt Hon Greg Clark (Oct.)

Exponential Growth for Another Thousand Years: Growing into an Interstellar Civilisation: Can It Be Done, and If So, How? (Sept.)

Down with the Fermi “Paradox”! (Aug.)

The Great Space Debate – Discussion and Vote (July)

The Great Space Debate: What Should Be the Strategic Goal for Astronautics over the Next 25 Years? (May)

A Four-Point Plan for ESA (April)

Britain’s Major Tim defends the ISS against its critics (March)

Neubrandenburg Thoughts (II): Space for Peace (Jan.)

Creating a Future with Skylon (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 105, 1 September 2014 – 45th Apollo Anniversary Year

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

Exponential Growth for Another Thousand Years:

Growing into an Interstellar Civilisation: Can It Be Done, and If So, How?

Presented at LonCon3, ExCel Centre, Friday 15 August 2014

In association with the British Interplanetary Society

Stephen Ashworth, Oxford, UK

Between the old Limits to Growth argument and the massive but far-flung resources of our Solar System, is it possible to chart a trajectory of growth for human civilisation? How do we answer the critics who say that a technological lifestyle is unsustainable and that exponential growth cannot continue forever?


We’ve all heard the doomsday predictions over and over again. They say there’s just too many damn people, as a result of which:

There’s panicky talk about a “perfect storm” of human-induced disasters, about our civilisation creating a “planetary emergency”, about us humans being the real threat to life on Earth.

How much growth is in fact possible? Consider energy production.

Industrial energy is the foundation for any kind of technological society. What are the basics of energy production? Our universe came into existence some 13.7 billion years ago with an enormous energy imbalance. Almost all the matter in the early universe consisted of hydrogen and helium, and these elements are nowhere near the greatest stability of the atomic nucleus. Had all the matter consisted of atoms of iron, then no energy could have been extracted by nuclear fission or fusion. But hydrogen and helium, when compressed in the interiors of stars, combine to form heavier elements and give off radiant energy when doing so.


It is this radiant energy from the Sun which powers our planet’s climate and biosphere, has done so for billions of years in the past, and is confidently predicted to continue doing so for billions of years in the future. The universe’s total reserves of unburnt hydrogen are sufficient to keep the stars shining for at least trillions of years into the future.

Let’s put some numbers to these facts. The total industrial power demand of human civilisation at present is in the region of 16 TW, or 16 billion kW, a global average of 2.3 kW per person. Actually we use more than that, because of our dependence upon free solar energy to grow food crops for us, and to drive the climatic system which airs and waters those crops. The total solar energy which reaches us on Earth without being immediately reflected back into space comes to about 120,000 TW, 7500 times greater than what we ourselves produce through fossil fuels etc., or a global average of 17 MW per person. But if we’re considering industrial growth alone, we can start from our original figure of 16 TW.

The Sun generates a total of 380 trillion TW, over twenty trillion times greater than our current industrial power budget.

Suppose that in the most expansive vision of the future we’re still only to be able to access one thousandth of the output of our star. Even so, a switch to solar power as the main driver of our civilisation still offers room for growth in industrial energy consumption by a factor of more than ten billion.

But notice the corollary: almost all solar power comes nowhere near planet Earth. The upside is that almost all of it is never obscured by clouds or the day/night cycle. The downside is that we can only harvest it from space. This is necessary in any case because planet Earth could not possibly handle the waste heat from all that extra industrial activity. Therefore if we want to secure our long-term growth, we must start building infrastructure in space.

With exponential growth at two per cent per annum, this gives us over a thousand years of vigorous extraterrestrial growth before we have to start slowing down. Plus what we may also get from constructing artificial nuclear fusion reactors for more power in the outer Solar System, where sunlight is weak. In the end, sure, we have to achieve some sort of zero-growth society. The resources of the Solar System are only finite, the resources of the planetary systems of other stars are isolated by the finite speed of light.

But notice the environmentalist propaganda you constantly hear. Exponential growth cannot go on forever. True! Therefore it must stop today. Wrong, wrong, wrong! We have the resources to hand for another millennium of exponential growth. The society which faces the limits to growth in our Solar System will be very different from our own society of today.

What about the material basis of that society? Certainly, we can colonise Mars, and no doubt also Venus, as Geoffrey Landis proposed, building floating cities suspended high in the venusian atmosphere where we find Earth-like pressures and temperatures. But these are only small worlds, like our Earth.


The asteroids are even smaller. Most of them this side of Jupiter are found in the main asteroid belt; here is Vesta, which was visited last year by the Dawn spaceprobe. Vesta is the second most massive asteroid; the largest, the dwarf planet Ceres, will be visited next year.

Because asteroids are so small, they don’t have much gravity, and so are not much use in themselves for human habitation. But by the same token they can be accessed by mining machines all the way to the core. They offer a source of raw materials consisting of a mixture of useful materials: rocks, metals, ices. Perfect for creating industrial infrastructure.

What human beings basically need for habitable space is simple: surface area with gravity and an atmosphere. Earth supplies these things naturally. But most of the mass of our planet is inaccessible beneath our feet, and supplies only gravity, geothermal heat and the planet’s magnetic field. Supply these services artificially, and a mass saving is possible. What about gravity? If we generate artificial gravity by rotation of a multi-kilometre-sized, hermetically sealed cylinder or torus, then one can provide surface area with gravity and an atmosphere about a million times more efficiently in square metres of floor space per tonne of mass than does our mother planet. One thousandth of the mass of our Earth can be worked into space colonies offering one thousand times greater surface area.

Planets provide surface area inefficiently. They have to: they’re not designed by anybody. They achieve their structural strength by simple compression. A designed space colony is harder to achieve: it requires high-tech alloys or carbon-fibre composites capable of withstanding tension, both from rotation and from internal pressure.


But the reward is that the asteroid belt, currently a region of rubble left over from the creation of the Solar System four and a half billion years ago, now offers the building blocks for the creation of a new Solar System, one hospitable to life not just on planet Earth, but far and wide throughout the system.

Obviously, the same goes for the Jupiter trojans, the Centaurs which orbit between Saturn and Uranus, and even the Edgeworth-Kuiper belt of small icy bodies beyond Neptune. The best-known Kuiper belt object, Pluto, will also be visited by a spacecraft next year.

Considering just the main asteroid belt between Mars and Jupiter: the material present there is sufficient, according to various estimates, to construct space colonies capable of holding somewhere between 100,000 and one million times the number of people currently living on Earth. That’s between one and ten million billion people.

Obviously this is a smaller margin for growth than in industrial energy use. But population growth must proceed slower than industrial growth, because in space industrial processes will need to take over functions such as food production which on Earth are still mostly powered by free sunlight. The industrialisation of our food supply which environmentalists like to complain about needs to proceed to its logical conclusion before large numbers of people can live permanently away from Earth.

Taking one per cent per annum as a reasonable growth rate, exponential population growth can then likewise proceed for a full millennium into the future before things start to get crowded. This is a radically different vision of the human future than the one customarily offered by professional worriers and doomsayers.

The rough estimates above allow a power budget of at least tens of MW per person, double the solar power we currently receive on Earth. Actual per capita consumption will be very much less than this after industrialising the production of food and recycling of air and water more efficiently than currently done on Earth. There will remain a large margin of power to run an extensive network of passenger space transport.

However, when our descendants come to plan the first interstellar voyages, an excess of available power will be good to have.

How might all this exponential growth actually happen?

The space colony designs of Gerard O’Neill from the 1970s are well known. Today, Jerry Stone is leading a new British Interplanetary Society project to update O’Neill’s plans for space colony construction.

But there’s a long way to go from the International Space Station, with a mass of 400 tonnes and a crew of six living six-month shifts, to O’Neill’s Island One, with a mass of several million tonnes and a population of 10,000 people living their entire lives in the space colony. Incidentally, O’Neill’s concept goes back to the Bernal Sphere proposed by J. D. Bernal as long ago as 1929.

If one concept stands out above all others as key to the whole process, it has to be establishing a space economy capable of exponential growth. What are the elements of that space economy that we don’t yet have today?

Many have criticised NASA for merely going round in circles for the past forty years. But NASA did originally have the right idea. After the Apollo missions it was clear that space travel was too expensive relative to the political commitment to going into space per se. Big exploration missions were technically possible, but only achievable in practice if there was something like the Cold War to drum up the political support they needed.

Ever since Neil Armstrong stepped onto the Moon, people have been dreaming of sending astronauts to Mars: the Space Task Group chaired by vice-president Spiro Agnew in 1969, George Bush senior in 1989, George Bush junior in 2004. ESA’s been dreaming, the Russians have been dreaming. They ran a 520-day simulation of a Mars mission in Moscow which ended in November 2011. The Mars Society, inspired by Robert Zubrin’s brilliant designs, have been dreaming. Now the Dutch Mars One group is dreaming, and Dennis Tito’s been dreaming. But nobody has yet seriously started on sending astronauts to Mars. Why not? Because the political support is just not there, relative to the high costs involved.

Even von Braun, architect of the Saturn V moonrocket, recognised that progress inevitably meant opening up space travel to mass markets. In a magazine article in 1966 he wrote:


“We would like to see Earth-to-orbit trips as convenient and inexpensive as a trip from the United States to England, and a flight to the Moon no more expensive than a trip around the world today. To achieve this we must have more economical space transportation systems incorporating launch vehicles that can return to base and be used again. […] It appears feasible to develop an efficient two-stage aeroplane – or aerospace plane – before 1980, if national objectives in space should call for it. […] Men should be living on the moon as a matter of course by the end of this century.”

Yet the Space Shuttle came and went, and launches into space are as expensive as ever. What went wrong? Fundamentally, the purpose behind the Shuttle programme was lost as early as 1982 after the fourth flight of Columbia: STS-4 was assumed to be the final test flight of the Shuttle. President Reagan declared that the system was henceforth operational: the National Space Transportation System.

Yet after the re-entry disaster which destroyed Columbia in 2003, the Columbia Accident Investigation Board stated that the Space Shuttle should never have been declared operational because in fact it was experimental by nature, due to its extremely low flight rate relative to certified commercial aircraft.

The Challenger disaster finally killed the rationale for the Shuttle programme. Instead of studying what was going wrong and moving ahead with new designs, America accepted that the Shuttle system would never make more than nine flights per year instead of the 60 originally intended. The low flight rate was henceforth cemented into the system. From here on, America accepted that the purpose of the Shuttle was to perform occasional missions for government science, not to open up the space frontier for large-scale economic applications, particularly those involving people.

A new mythology appeared: that making access to space “as convenient and inexpensive as a trip from the United States to England”, as von Braun had put it, was physically impossible. As far as people in space went, space could therefore only be reached by a tiny elite of dedicated professionals on occasional, exorbitantly expensive and nail-bitingly dangerous government missions. It would remain off-limits to the non-professional traveller for the foreseeable future. But what if mass market space tourism is indeed the key to low-cost access to space, as argued at a meeting at the BIS nine years ago, led by space engineer David Ashford? Then this mythology is an artificial barrier which must be torn down before progress in space can be restarted.

How plausible is it really that space is so different that access will forever be restricted to that tiny elite? Consider this: at 11 km altitude, higher than the summit of mount Everest, the atmosphere is already too thin to support human life. The pressure is only a quarter of what it is at sea level. The temperature is minus 56 degrees.


Commercial passenger jets fly at 11 km altitude. They carry something like a billion passengers a year on the fringe of space in comfortable pressurised cabin conditions. Sure, getting into orbit is about 100 times more energy intensive per person, and should therefore cost about 100 times more per seat. At present, a trip to orbit and back costs 100,000 times more than a hop across the Atlantic. That extra factor of a thousand is entirely due to the fact that we do not yet have airline-style travel into space. Not to any fundamental physical barrier.

What happens once we can actually get into space? Where will we go? Clearly, the Moon, Mars and Venus are the obvious targets. Mars and Venus both offer, in their very different ways, opportunities to set up bases where explorers can live, which grow into settlements, which grow into new branches of human civilisation.

But how will people travel to and fro across interplanetary space? Possibly the greatest danger threatening them will be the burst of radiation from a solar storm. Another point: consider that you are flying through a vast expanse of complete emptiness in a small vehicle, and something goes wrong. Remember Apollo 13: there’s always the possibility of a breakdown, an accident, an explosion, while you’re months away from the nearest centre of civilisation that could come to your help. Things on the ISS are breaking down and needing to be repaired or replaced all the time.

Ideally, you would want to travel in a ship that had not only plenty of radiation shielding, but sufficient reserves and workshop facilities to maintain itself against mishaps. Something larger than the 400-tonne ISS, in fact. Maybe even something that gave you artificial gravity. But the fuel cost of accelerating this out of orbit at the start of the journey and back into orbit around the destination planet at the end of the journey would be enormous.


The logical solution is the cycler: a large, self-sufficient space station on an orbit which regularly encounters Earth and another planet, and which is served by relatively small, fast shuttle craft, which transport passengers and cargo between the cycler station and a planet as it flies past. Since the cycler is not a vehicle it does not use propulsion for any purpose other than keeping itself on station: it specialises in life support, while the shuttles specialise in crossing the energy gap between the cycler’s orbit and the planets it passes.

The idea goes back to Krafft Ehricke in the 1970s, and even before to Guido von Pirquet in the 1920s. Today, its most prominent advocate is Buzz Aldrin, one of the Apollo 11 astronauts who first walked on the Moon.

Most of the mass of an Earth-Mars cycler station will consist of radiation shielding and stocks of consumables: water, oxygen, rocket propellants. Most of that mass does not need to be launched from Earth because it’s already out there in space! It can come from near-Earth asteroids which are already found in interplanetary space between Earth and Mars. In this way, the construction of a manned base on Mars motivates initial experiments in using asteroidal materials for in-space construction.

The same applies to Venus, and also to the Moon: the first cycler stations could usefully be set up between Earth and the Moon, and again they could benefit hugely from materials brought in from near-Earth asteroids. This sounds like NASA’s proposed Asteroid Redirect Mission, but the joke is that NASA has no idea how practical their proposal really is. Why not? Because they are blinkered by the view that only government science counts in space. They are unable to address any role in supporting exponential growth in space. But in my view, the near-Earth asteroids will play a key role in getting space growth underway.

Planetary surface colonies are easier to build because they rely on buildings under compression in the planetary surface gravity. They will therefore come first. But the transport links to them demand space construction using materials found in space. The habitats for cycler stations are necessarily structures in tension, not compression, and therefore will be more difficult to construct, especially working in space conditions of a dusty vacuum. But in the long term, mastering these technologies opens up the main asteroid belt and beyond to space construction and colonisation.


We first have to get started, and in order to get started we first have to solve the fundamental problem of making access to and from low Earth orbit a thousand times cheaper, safer and more frequent than it is today. Will the new American SLS rocket solve this problem? Will Europe’s Ariane 6? Will the Russians or the Chinese or the Indians do it for us?

Or could the answer be found here in the UK? Skylon: reusable, single-stage, airline-style turnaround and maintenance, capable of carrying a couple of dozen passengers to and from orbit. With a successful experimental programme already under its belt. The new technologies of the dual-function jet/rocket Sabre engine have been validated on the test stand. Support from private investors and from the UK government is gathering momentum. With a vehicle like this a future in space becomes possible.

It cannot be allowed to fall by the wayside as yet another cancelled project.

With Skylon, a future of sustainable exponential growth becomes possible for another millennium.

Therefore we can continue to have a society which values above all human political liberty and economic creativity, as it expands into our Solar System and then to other planetary systems.


Can a global industrial civilisation confined to a single planet survive for long? Can it preserve modern standards of human freedom, or must it adopt an environmentalist-driven tyranny? This is surely the most pressing question facing both academic sociology and practical politics at present. If the answer is no, as seems likely, then we must either ignite a new burst of exponential growth in the Solar System, or accept our inevitable decline and fall back to a new Dark Ages, one which this time continues all the way to the ultimate collapse of civilisation and the disappearance of our species.

As Mark Hempsell wrote in 1989, “We face a choice of the type of future that we leave to posterity: a stone age or a space age. If it is to be a space age there is a need to act now with much greater vigor that is currently being shown.”

For the sake of all those who have suffered from the pains of progress over the past several thousand years, we cannot allow that decline and fall to happen. We must continue to grow, by transferring the focus of that growth to new environments in space and on other planets.


Von Braun quote: “Space Travel – The Breakthrough that Must Come”, Weekend Telegraph, p.19-20, 1966 (exact date not known to me, accompanied by an article by Kenneth Gatland, “Britain Has the Answer – If She’ll Use It”, on the Mustard design).

Mars cycler stations: James Oberg and Buzz Aldrin, “A Bus Between the Planets”, Scientific American, March 2000, p.40-42.