All Astronautical Evolution posts in 2015:

Britain Takes the Wrong Approach to Manned Spaceflight (Dec.) (Comments)

“Drowning in Process” (Nov.)

Does Intergalactic SETI Make Any Sense? (Oct.)

SETI and Sanity (Oct.)

SpaceX, SpaceY, SpaceZ (Sept.)

A Letter to Britain’s New Space Minister (June)

Mars: 25 Years After Mars Direct – Discussion (May)

The Astronist Mars Strategy (May)

Mars: Still So Distant, 25 Years After Mars Direct (May)

The Mariner Anniversary Calendar for Mars (April)

Mars: An Awful or an Awesome Place? (April)

Should We Phone ET? (March)

More Pluto Controversy (Feb.)

The Pluto Controversy (Jan.)

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AE posts:

2022: What’s to do on Mars?…

2021: New space company Planetopolis…

2020: Cruising in Space…

2019: The Doomsday Fallacy, SpaceX successes…

2018: I, Starship, atheism versus religion, the Copernican principle…

2017: Mars, Supercivilisations, METI…

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 113 (continued), 1 May 2015 – 46th Apollo Anniversary Year

26th Mariner Anniversary Annum

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The Astronist Mars Strategy


Let’s begin by setting out six basic axioms of human Mars exploration and settlement.

Mars surface image

(1) The goal is to land people on Mars: initially to explore, ultimately to colonise the planet as we have colonised Earth. The competing goal of preserving Mars free of “contamination” by terrestrial life is rejected, because we take the view that the benefits of colonisation are expected to outweigh the benefits of pure exploration with sterile robots.

As we shall see, the Astronist Mars Strategy would allow a limited period of exploration by orbiting astronauts operating robots on the ground by telepresence, if that is what is decided. But the window of opportunity to do this may last only a few years.

Why Mars? Why a manned base? Not so much as a “backup” to terrestrial civilisation, as some have claimed, nor even primarily for science. The real motivation, in my view, is simply in order to maintain the forward momentum of growth of civilisation. Without taking the analogy with the American frontier too literally, I believe Zubrin is fundamentally correct to assert in The Case for Mars (Epilogue) that continuing growth will be the best guarantee of the survival of liberal, democratic, humanitarian, culturally diverse, free market civilisation.

It is important to demonstrate that humans can embellish their environment, not just damage it. On Earth, the stresses of continuing global development guarantee that those who wish to denigrate their own species will always be able to find black spots of overcrowding and destruction of nature. If humans are to be able to live sustainably on Mars, then beauty spots will have to be engineered: the planet is otherwise a barren desert.

It is important to demonstrate that the growth of civilisation is open-ended. Otherwise its decline and fall within the next 10,000 years at most can be guaranteed, whether from natural environmental stresses, the build-up of industrial pollution, political and economic degeneration, or global war.

(2) Heroic versus systemic: these are the two possible programmatic paradigms, or ways in which something new gets done.

A heroic programme is one like Apollo: a massive effort undertaken by a unitary organisation to achieve a short-term goal, an effort which may collapse at any time due to cultural change or bad management within that organisation, or to achievement of the goal without commitment to any follow-on goal.

A systemic programme is one which arises out of the overall social system, with many organisations pursuing a variety of individual goals which act together to have a particular long-term effect, and not necessarily one consciously planned by any one actor. A good example of the latter is the globalisation of originally European civilisation over the past 500 years.

A heroic programme represents revolutionary change; a systemic one, evolutionary change. History tends to show both acting in concert, thus Columbus’s voyages which opened up the Americas to European colonisation were very much heroic stabs into the unknown, but set the stage for a long, systemic build-up of civilisation in the New World. But revolutions alone tend to restore the status quo under another name. The French Revolution restored the Bourbon monarchy as the Napoleonic dictatorship; the revolutionary Apollo missions restored low Earth orbit as the limit of astronaut travel.

Or, as Napoleon said, explaining his winning strategy for war with Austria, “If you want to take Vienna, take Vienna!” (quoted by Robert Zubrin, via Tom Paine, in The Case for Mars, p.137, in support of his strategy of going to Mars as directly as possible). Today, however, Vienna is not part of France. And when Napoleon applied the same strategy to Moscow, he not only lost Moscow but destroyed his entire army. In terms of distance and its hostile wintry environment, Mars is a lot more like Moscow than Vienna.

Manned spaceflight up to the present has had an overwhelmingly heroic bias, which it inherited from the Cold War. But revolution without a supportive evolutionary environment is no more than a gesture. The Astronist Mars Strategy focuses on the necessary systemic development: evolve the foundations for systemic activity first, then build further on those.

Zubrin has a point: a motivated and well-funded programme begun today could send astronauts to Mars in about 10 years. But that kind of heroic programme would not be sustainable, let alone growth capable. It would certainly be cancelled, just as Apollo was. Why? Because government would be the only customer for such flights, and governments are fundamentally not interested in settling Mars, which possesses neither gold, nor natives in need of a terrestrial master.

(3) The costs of passenger transport to and from low Earth orbit and thence to and from the Moon and planets: at present these are inflated by orders of magnitude over what they would be in a mature space economy. This is demonstrated by a comparison of space transport costs with those of air travel, which is technologically similar but, unlike space, has a highly developed global market.

Therefore before astronauts fly to Mars sustainably, the space economy needs to mature, and while some of that may be driven by government science, by far the largest potential driver at present would be space tourism, with possibly space solar power in the longer term. When 1000 people a month are flying to and from low Earth orbit space hotels at ticket prices 100 times lower than today, the problem of getting to Mars will look very different.

(4) Life support in space: this is as immature as transport. The ISS recycles water and could easily recyle air as well, but closing the cycle between toilet waste and the food supply has not yet been attempted in space. Any serious Mars base (as opposed to one-off visits) would need to develop a complete supporting biosphere, and the example of Biosphere 2 shows how much remains to be done.

Reading Jane Poynter’s account of life in Biosphere 2, two major problems stand out: the splitting of an initially united team into squabbling factions, both within the Biosphere and at Mission Control, and the labour-intensive agriculture. It is unfortunate that no similar project has yet attempted to carry forward the development process and address these problems. The difficulties experienced controlling the oxygen and carbon dioxide levels inside the Biosphere were minor in comparison.

I believe the significance of what we are trying to achieve here is underappreciated. Historically our species has progressed through an evolutionary hierarchy of five distinct life-support modes, with another two modes in prospect:

Life mode 0: The primordial hunter/forager mode shared with all other forms of animal life. Used by all human ancestors and humans up until about 10,000 years ago.

Life mode 1: Village agriculturalist. The first settled way of life, from about 10,000 years ago.

Life mode 2: Nomadic pastorialist. Common in Central Asia before industrialisation. An evolutionary cul-de-sac.

Life mode 3: Pre-industrial cities dependent upon an agricultural hinterland, the majority of the population working on the land as in mode 1, from which mode 3 developed. The characteristic style of the ancient world before industrialisation.

Life mode 4: Industrial cities dependent upon an industrialised agricultural hinterland, the majority of the population working in the cities. The present-day mode in developed countries.

Life mode 5: Industrial self-contained cities, food production totally synthetic, no hinterland, but cities still open to global atmosphere. Expected end-point of evolution of city life on Earth.

Life mode 6: Industrial self-contained cities now hermetically sealed and pressurised independently of the environment, in space and planetary colonies.

Obviously these modes are not mutually exclusive; at present, for example, large populations live in modes 4 and 3, with small scattered communities preserving modes 1 and 0. But as time goes on, progressively more highly developed modes are introduced on top of the previously existing ones.

Human settlements on Mars will have no agricultural hinterland, therefore must be fully self-contained. But in order to get from mode 4 to 6, it would be advisable to develop the intermediate stage of mode 5, particularly as this will contribute towards the long-term sustainability of industrial civilisation on Earth.

Biosphere 2 was overambitious in that it attempted to step directly from mode 4 to mode 6. So no surprise that it was costly and unsustainable.

Cockell’s point was that a Mars base would be so constricted in terms of one’s physical movements and political freedoms that it would not attract large numbers of people. Zubrin’s counter argument is that it would be far enough from Earth that people could evolve new political systems.

As I said before: we accept Cockell’s point, and turn it around. In order to colonise Mars, a new mode of living needs to be developed: the small-scale, completely self-contained urban unit, which produces all its food and recycles all its wastes (mode 6 above). But if we can do that on Mars, then we can also do it more easily on Earth (mode 5), and the environmental rigours of Mars, and the high cost of getting there, require that we do it on Earth first.

This is a programme which a group like the Mars Society, the Mars Foundation or Mars One can adopt. The first step is to build Mars analogue bases, as the Mars Society (as well as NASA) is doing and the Mars Foundation plans to do. But these need to develop towards (a) self-sufficiency, and (b) growth. Essentially we need to colonise Earth first.

To begin with, this can be done, as the Mars Society is already doing, in remote desert locations or on uninhabited islands. But ultimately it needs freedom from existing political units, which is why Marshall Savage’s plan in The Millennial Project for creating floating settlements over the deep tropical oceans needs to be revisited. A research programme into using oceanic resources to create infrastructure in international waters needs to be running in parallel with the first analogue bases.

These projects need to be explicitly designed towards future settlements both on Mars and on Earth.

(5) The physiological response of the human body to long-term exposure to 0.38 gee: this is not yet known. The knowledge needs to be acquired, both in order to make any plans for Mars colonisation, and in order to inform potential emigrants of the hazards they will face. Short of setting up a manned base on Mars itself and operating it for a period of years, there is only one way such information can be obtained: through experience with rotating space stations able to provide any desired gravity level.

Manning a lunar base would provide a clue, but, since the lunar surface gravity is only half that on Mars, a margin of uncertainty would remain.

It is therefore clear that the use of rotating space stations will precede manned landings on Mars, unless an intrepid group of astronauts fly a heroic mission to Mars and accept the risk of ruining their health in the process. This is an example of how a heroic venture might accelerate the systemic evolution of our presence on Mars, provided that the more gradual approach was also in progress.

(6) Extraterrestrial resources: any strategy for sustainable Earth–Mars traffic and Mars settlement needs to take these into account. Zubrin’s Mars Direct plan was the initial theoretical breakthrough that showed how this could be done. But this needs to be extended to include lunar and near-Earth asteroidal resources.

Any Earth–Mars passenger travel will be vastly safer and more resilient if conducted in a large station, heavily constructed with radiation shielding and artificial gravity, and well stocked with reserves of consumables, propellants, tools and spare parts. Therefore a sustainable transport architecture must be based on Earth–Mars cycler stations, with small, high-power shuttles transferring passengers at either end of the journey.

Constructing such stations is greatly facilitated by the fact that most of the mass for radiation shielding and propellants can be sourced from near-Earth asteroids, many of which can be found in similar orbits between the orbits of Earth and Mars. But the precondition for using these resources is that an industry has evolved capable of prospecting for these resources, mining and processing them.

The Moon has one advantage which Mars lacks: its accessibility, allowing it to serve as a destination for short visits lasting a week or two. It would therefore be possible to extend an existing space tourism industry to lunar orbit and to the lunar surface, thus generating income and developing near-Earth asteroidal resources to support that industry.

We need to return to the Moon first in order to build up a cis-lunar space economy capable of supporting flights to Mars.

The strategy

Based on the axioms above, the following strategy emerges.

Each phase may last one or several decades. The price for getting to Mars sustainably is to go more slowly, as constructing firm foundations cannot be hurried.

Phase 1: The starting point has to be to build up private passenger transport to and from low Earth orbit, and accommodation in space hotels while in orbit. Only a virtuous cycle of increasing numbers of travellers and falling costs can raise the traffic volume, reliability and hence safety, and economical viability of space transport to sustainable levels, and make it independent of any one type of customer.

Private visits to the ISS, starting with Dennis Tito’s flight in 2001, have demonstrated a market for private space travel even at current levels of high ticket prices and lack of a suitable destination. This foundation needs to be built upon. While space travel will always be a small, luxury market in comparison with air travel, a future scenario flying thousands of passengers a month is perfectly realistic.

A target of a thousand passengers per month at ticket prices less than a million dollars each would provide a useful mental focus on the scale of the change needed (from today’s dozen or so per year).

Note that self-financed flyers to date have not been space tourists as such, but rather pioneers of private space travel. “Tourism” implies a large-scale activity which people can easily participate in; flights to date, however, have required major commitment and training.

The most important technical innovation required is the transition from throw-away rockets to fully reusable vehicles, whether single stage or two stage to orbit, whether winged or not. In a healthy economy a variety of different systems will emerge, just as it is possible now to get from London to Paris by road, train or air, crossing the Channel through the Tunnel, or by air, or by surface ship or hovercraft.

Meanwhile, on the ground, there needs to be continuous experimentation with sustainable ways of living which can be packaged into small, self-contained urban units able to thrive both in desert and oceanic regions on Earth, and later off Earth. As we saw above, this should be tackled in two stages: for use on Earth, such settlements can be open to the atmosphere, though water and foodstuffs must be fully recycled. Only in the space settlement context does the question of closing the cycle of atmospheric gases arise. Again, settlements do not need initially to be self-sufficient in terms of production of manufactured goods such as clothing, cleaning materials, medicines and hardware items; this must necessarily be approached gradually as their population sizes and economic power increase.

The private Mars societies therefore really need to focus on permanence on Earth before even thinking of attempting permanence on Mars.

Phase 2: Once a low Earth orbit tourist industry has been established, the wealthiest and the most adventurous will want to go further. A lunar flyby is the obvious attraction, for which an Earth–Moon cycler station is the logical architecture, probably in consort with an Earth–Moon L1 station.

Such stations will create a demand for radiation shielding in highly elliptical orbits, and therefore stimulate the growth of near-Earth asteroid water mining as an alternative to lifting the same amount of mass from Earth. Once that supply line is in place, adding stages to deliver the water to low Earth orbit, purify it, split it into hydrogen and oxygen, or add carbon to create methane/oxygen propellants, will develop a commercial in-space refuelling industry.

The self-contained settlements on Earth will need to demonstrate economic self-sufficiency, and also the potential for growth. Considering that Biosphere 2 cost a quarter of a billion dollars and that the eight inhabitants were only too glad to get out at the end of their two-year sojourn, and that small utopian communities in general have not proved wildly successful, some rethinking is required here.

A complementary approach would be to influence mainstream city planning in the direction of greater self-sufficiency at a local level. A key technology would be developing satisfactory synthetic foods which could be manufactured locally near the point of consumption, using locally produced human waste as the input. One can see the small experimental community acting as a test bed for such technologies, developing them for release to the global mass market.

Given present-day emphases upon efficiency and environmental sustainability, such a programme whould work with the grain of present-day culture rather than against it.

Phase 3: We now have a number of Earth–Moon cycler stations and an in-space refuelling network of robotic miners and factories, with a sustainable economic base and a decade or more of experience. The more advanced stations should be able to rotate in order to provide artificial gravity. Placing one or more of these onto Earth–Mars cycler trajectories allows transport to and from Mars in comfort and safety.

If one of these cyclers is fuelled up during its transfer to Mars, on arrival it can drop into Mars orbit, rendezvous with Phobos or Deimos and create a propellant depot and safe haven in Mars orbit. The strategy is to establish permanent safe havens at every step of the way.

This is the period when astronaut observation of Mars from orbit could be carried out via robots on the surface. Note that artificial gravity will be essential for this type of mission, as subjecting astronauts to three years of continuous microgravity would not be acceptable given current medical knowledge. Therefore an experience base using rotating space stations near Earth will also be essential. But the window of opportunity for these missions may not be very long, given that cyclers have made Mars relatively accessible, and there will be entrepreneurs with extensive space experience in the Earth–Moon system who will be strongly tempted to make history by going for that first landing.

Meanwhile, on Earth there should by now be communities with extensive experience living in life mode 5, thus in self-contained cities where food production and waste recycling are carried out locally. Microcosms of life mode 6 will already exist on the Earth–Moon cyclers and even more so on the Earth–Mars cyclers. Thus it will be possible essentially to transfer a working model of a viable long-term self-contained ecological life-support system or biosphere from Earth to the cyclers, and from them to the surface of Mars.

The first Mars colonists will need the assurance of a life-support system that is already known to be reliable and comfortable to live in. They will have enough to do on Mars developing the infrastructure of their base without having to worry about where their food is coming from, or about the buildup of toxins or harmful microflora.

Phase 4: How will the Mars colonists live? Will they in fact be confined to quarters to such an extent that they remain subject to a military style of discipline, or tyranny, as Cockell has suggested?

First, we state that even open terrestrial landscapes are no guarantee against political tyranny. What we regard as normal, democratic, liberal society is an aberration from a historical perspective. Therefore there is not necessarily any direct link between physical freedom of movement and political freedom of thought.

Clearly, both terrestrial and extraterrestrial societies will be strongly affected by continuing development in computer technologies. It is at present impossible to predict how this will turn out, though one can of course construct more or less plausible scenarios. For example, all government might proceed through votes cast by all citizens interested in a particular question, via a Facebook-style interface. Or government might be delegated to some artificially intelligent entity, if it was capable of winning and preserving everybody’s trust.

This sort of question needs to be researched in advance in Mars analogue communities on Earth. While a colonised Mars will undergo its own social evolution, the earliest colonies will need to import a social and political system that has been tried and tested and is known to work reliably in communities as small, isolated and environmentally stressed as the first settlements on Mars. This is another reason why Cockell’s argument must be inverted: sustainable self-sufficient settlements, well organised and attractive to live in, must first be demonstrated in remote, hostile regions on Earth before they can be transplanted to Mars. The foundations of survival on Mars must be laid before attempting to build a colony on them.

What of the longer term prospects? Will Mars ever be terraformed to the point that humans can walk unprotected on its surface?

While this is not part of the Astronist Mars Strategy, I have to express my skepticism about terraforming Mars.

It has been pointed out by Richard Taylor that Mars does not possess enough nitrogen to build an Earthlike atmosphere. But over and above this, there is a general economic question. Altering the surface environment of an entire planet is by any reckoning a massive and long-term project. Who is going to pay for it, and who will persevere for many decades, if not centuries or millennia, until the project is complete? Not any terrestrial government, that’s for sure! Therefore it must be undertaken by the martians themselves.

This implies a substantial martian population in the millions or billions, with a wealthy economic and technological base. But if such large numbers of people are already living their entire lives on Mars in an acceptable manner, why would they have any need for terraforming?

How might they live, and would it in fact be acceptable? Richard Taylor proposed, as an alternative to terraforming, paraterraforming, or construction of a worldhouse: basically a glasshouse with a flat roof raised between one and three kilometres above the martian surface and covering most of the surface area of the planet. The roof performs the function of holding down an oxygen-nitrogen atmosphere at a pressure approximating Earth surface pressure without the need for the large mass of gases that would be necessary to achieve this through gravity alone.

A great advantage of Taylor’s scheme is that it is modular: small areas can be worldhoused at first, and the roofed area extended as economic conditions permit. But his design had one flaw which was pointed out by Ken Roy: the internal air pressure would impose a huge stress on the roof and side walls, trying to blow them outwards, that would be beyond the capacity of any known material to withstand. Roy’s alternative was construction of a shell around the entire planet which would be thick enough to balance the internal air pressure with its own weight, and which because it is a complete sphere would not have any side walls.

I pointed out in an article which was published in JBIS that the shell world concept recovered one of the major disadvantages of terraforming: that one had to engineer an entire planet to hold breathable atmospheric pressure before any one part of the planet could be occupied. This demands engineering success and financial investment on a gargantuan scale, with no intermediate stages at a smaller scale to demonstrate that the engineering concepts have worked or to provide any return on investment. Thus both the terraforming and the shell world concepts, while attractive in theory, are unrealistic on both engineering and financial grounds.

Actually, the only problem with Taylor’s worldhouses was the question of balancing the stress in the roof and walls. The stress in the flat roof is solved by giving it a thickness of several metres (when I first read Taylor’s paper I assumed that this was what he meant, and it was only an e-mail exchange with Ken Roy which alerted me to the fact that he had not included this feature). Assuming glass with a density of 3500 kg per cubic metre, a 3-metre thick roof would in martian gravity balance a breathable internal atmospheric pressure of 210 millibars of oxygen plus 190 of nitrogen (same oxygen partial pressure as on Earth, reduced nitrogen).

This kind of thick roof is demanded in any case in order to screen out high-energy galactic cosmic radiation. The challenge is to make the glass clear enough to allow through as much visible sunlight as possible.

The stress in the side walls may be dealt with in one of two ways. Firstly, large areas of Mars may be roofed over, with a ceiling height of a kilometre or more, with no need for side walls at all. Such natural depressions are quite obvious on the map of Mars, starting of course with the great natural basins of Hellas and Argyre.

The other way is to reduce the ceiling height. Why is an airspace of several kilometres overhead necessary? I don’t think it is. While there are issues of air circulation to consider, from an aesthetic point of view a ceiling height of 50 to 100 metres would be perfectly adequate. For a worldhouse built on a flat plain, one can immediately think of a number of possible wall designs which would be well within the strength of materials such as concrete and glass, particularly as those walls should also be several metres thick. If necessary, the height of the walls can be reduced relative to the ceiling height near the centre of the worldhouse by giving the structure a pyramidal shape.

My conclusion is that the surface of Mars can be progressively enclosed by worldhouses made principally from locally manufactured glass, and with a ceiling height on the order of 100 metres. Small worldhouses can be built at first, and then larger ones, and in greater numbers, as technology progresses and economic conditions develop. It is not necessary to engineer an entire planet before the first immigrant can settle in!

Because of the ever-present danger that a worldhouse might be punctured by a meteor strike, I see no need to fuse adjacent worldhouses into a single building. I would favour a pattern of multiple worldhouses, each say a few tens of kilometres across, joined together by short tunnels which, while normally left open, could be hermetically sealed if necessary.

Living under such conditions should ultimately be hardly distinguishable from living on Earth, apart from the ever-present low gravity. Whether we can adapt successfully to living permanently over multiple generations in martian gravity remains to be seen.

One possibility that has been suggested is that people can live on Mars healthily, but that the formation of the human embryo and the subsequent pregnancy are disrupted by the low gravity, making human reproduction on Mars impossible. This would lead to a scenario in which large rotating stations are built in Mars orbit, and couples who wanted a baby would move to one of these stations for half a martian year or so. This would have the interesting effect of greatly accelerating the development of large-scale orbiting space colonies.

But even without that need, one may expect the Earth–Mars cycler stations to grow towards becoming independent space colonies over time. Once the economic link with Earth–Mars traffic was broken, the entire Solar System, and beyond, would come within the range of settlement.


Marshall T. Savage, The Millennial Project: Colonising the Galaxy in Eight Easy Steps (1992; Little, Brown & Co, 1994).

Richard L.S. Taylor, “Paraterraforming: The Worldhouse Concept”, JBIS, vol.45 (1992), p.341-352, and “The Mars Atmosphere Problem: Paraterraforming – The Worldhouse Solution”, JBIS, vol.54, no.7/8 (July-Aug. 2001), p.236-249.

Ken I. Roy, R.G. Kennedy III and D. Fields, “Shell Worlds: An Approach to Terraforming Moons, Small Planets and Plutoids”, JBIS, vol.62 (2009), p.32-38.

Jane Poynter, The Human Experiment: Two Years and Twenty Minutes inside Biosphere 2 (2006; Basic Books, 2009).

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