Planetopolis: Why Is a New Company Necessary?

Astronautical Evolution, issue 157
Planetopolis – the project

I want to start the New Year by putting into practice a train of thought which has been impressing itself upon me in recent weeks.

Axiom: I wish to see a future of growth and progress for human civilisation, together with all the sciences that enlighten us and the technologies which make our lives so much easier than in the past.

Elon Musk’s SpaceX is the only organisation worldwide which is both devoted to setting up an extraterrestrial human colony, and currently making tangible progress towards that goal. (Image from the SN8 test flight, 9 December 2020) ( / SpaceX)

This means: a future of expansion into the rest of the Solar System, given that the long-term survival of a high-population, high-tech industrial civilisation while confined on its home planet alone is highly dubious (as discussed in an earlier post).

The destination of the human journey after the next few centuries will either look like Star Trek, or it will look like Game of Thrones – this seems to be the unavoidable consequence of the currently unstable state of our civilisation (as discussed in another earlier post).

The most plausible location for the first permanent, self-sustaining extraterrestrial human settlement is Mars, given that surface conditions there are the least extremely dreadful compared with the worst conditions found anywhere on Earth. (It doesn’t matter if it turns out to be somewhere else – the Moon, or an O’Neill colony: we’ll run with Mars for the present, as it’s the focus of attention of the one venture worldwide which has a non-zero chance of actually making something happen.)

People have a pretty good idea by now of what an astronaut exploration mission to Mars would look like, with high-fidelity simulations being conducted in remote locations on Earth by NASA/University of Hawaii, the Mars Society, and others.

A permanent settlement would be a different matter! –

  • Instead of half a dozen astronauts there would need to be thousands.
  • A large-scale closed-cycle ecological life-support system would need to be in place.
  • Recycling of all kinds of waste and discarded equipment and clothing would need to have been brought to a high level of completeness.
  • Local resources would need to be mined and used to build machines and habitable infrastructure.
  • Questions of the political organisation of the colony would become irresistible.
  • Returning everybody to Earth in the event of a malfunction would be impossible.

The question has to be faced: if the supply line from Earth was cut for any reason in the decades after its foundation, would the colony still be able to survive?

The only way to get an answer before committing a huge effort to such a leap into the unknown is, again, through a simulation on Earth. This is why we need a programme of high-tech, progressively more remote, more permanent and more self-sufficient human settlements in desert locations on Earth itself.

I began to toy with this idea in 2016, then under the name Aridopolis. I wrote about it again in issue 18 of Principium (August 2017, p.4-11). But at that time there seemed to be no way ahead for the idea, and I felt resigned to seeing it fall by the wayside, ignored and ultimately forgotten.

Planetopolis – the company

The company header is based on a view of Ares Vallis taken by NASA’s Mars Pathfinder in 1997. (NASA/JPL)

The answer has, of course, been obvious for a number of years. Trust me to be so slow to see it.

What SpaceX is doing is to earn revenue from satellite launches with their Falcon 9 rocket. The profits from doing so in an innovative way (reusable first stage; fast prototyping and development cycle) provide the cash flow to support their more speculative programme aimed at Mars colonisation. The excitement generated by their engagingly presented public relations doubtless helps to attract speculative investment funds. And the profit-making and speculative sides of their business support one another by their shared reliance on big, reusable rocket vehicles.

The question is therefore: can a profit-making company active on Earth support a research programme into making a permanent settlement on Mars a practical proposition?

I’ve long believed that there’s no conflict between improving the ecological sustainability of our cities on Earth and building new cities on Mars. Quite the contrary: the choice which we as a species face is between a high-tech future and a low-tech one.

A high-tech future is one with industrial cities on both Earth and Mars, in both cases using similar technologies to maintain a low-impact lifestyle – on Earth, to save the natural environment, and on Mars, because there is no living natural environment to be parasitic upon, so the low-impact lifestyle is the only one possible. On the other hand, a low-tech future on Earth alone would require a massive reduction in global population size, and would reduce standards of living back to medieval levels. Considering that many countries would resist such a rejection of growth, it could probably only be achieved through world war, or else through some global natural catastrophe.

Star Trek versus Game of Thrones, in fact.

So the technologies we need for life on Mars are the same as those we need to be developing for widespread use on Earth in any case. Let’s set up a company – which I shall call Planetopolis – with two divisions:

  • A profit-making division manufacturing and marketing ecologically improved products for sale to customers living in existing towns and cities on Earth.
  • A research division using those same products to build and operate a series of experimental desert settlements on Earth, aimed at both prototyping new commercial products, and developing a lifestyle that can be transplanted with minimum fuss from Earth to Mars and elsewhere in the Solar System.

When one asks what those products might be, a number of answers suggest themselves –

  • Cultured meat, avoiding the wasteful raising and slaughter of animals.
  • Low-energy construction of buildings, using biofabrication.
  • Clean energy, without the use of fossil fuels.
  • Recycling of human and industrial wastes of all kinds.

When I began to research these things, I found that there’s a massive revolution in a whole range of clean technologies in progress right now. But it’s still at an early enough stage, in most cases, that there’s plenty of room for new start-ups to join in.

I need people who find my logic interesting to join me in defining exactly what this company will do, and thus put together an attractive prospectus to show to potential investors.

Clearly, I’m expecting to receive a lot of negative criticism. I’m not experienced in high technology business management, and there’ll be many difficult hurdles to overcome. Please visit the company website to find what I’ve put together so far, including a prospectus in the form of a modest book (92 pages) on Planetopolis available for free download, and my e-mail contact address:

Thanks, and I look forward to hearing from you!

This post is reblogged from the Astronautical Evolution website.

Stellar Engines

Astronautical Evolution, issue 156

Can one propel an entire solar system?

Small Magellanic Cloud
Part of the Small Magellanic Cloud, from the Hubble Space Telescope. It lies some 200,000 light years away. (NASA/CXC/JPL-Caltech/STScI)

In the previous post we considered intergalactic travel using the planetary system of a rogue star which happened to be going the right way. Here we ask: can we make our own intergalactic star and planetary system?

The Shkadov thruster is the original star-moving engine, the idea dating from 1987. It consists of a giant mirror hovering over the Sun (or another star) – rather than creating an imbalance in radiation pressure, as has been claimed, the real physical process is that it uses the radiation pressure from the Sun to balance the Sun’s gravitational attraction, keeping it in place without being in orbit, and it is the mirror’s own gravitational pull on the Sun which drags the Sun in the desired direction.

Since the acceleration is only enough to impart a speed of something like 20 metres/second to the Sun per million years, the practical value of such a scheme is questionable.

The Svoronos Star Tug

Now Alexander A. Svoronos, a graduate of Yale School of Medicine, has a paper scheduled for publication in Acta Astronautica (Nov. 2020, p.306-12) entitled “The Star Tug: An active stellar engine capable of accelerating a star to relativistic velocities”. Sounds good. But will it work?

His method is to place, not a mirror, but a rocket vehicle – the Star Tug – in suspension above the Sun and close to its surface (or another star, but he uses data for the Sun in all his calculations). A separate piece of infrastructure hovering over the Sun sucks up hydrogen and helium, presumably magnetically, and channels these gases to the Tug. The Tug feeds them into a reaction chamber where the hydrogen undergoes nuclear fusion (the hot CNO cycle), creating an exhaust stream which is directed back past the Sun at greater than solar escape velocity. The rocket thrust balances the Tug’s weight, maintaining its distance from the Sun and allowing its own gravity to drag the Sun behind it.

Svoronov starts with the assumption that the entire output of radiant solar energy (all 3.85 × 1026 watts of it) is harvested by a Dyson sphere and employed to lift gas from the Sun to the Tug. He finds an exhaust velocity for the Tug’s engines of 0.1c.

He then discusses four variants of the design (together with some intermediate cases):

  • The Tug may hover just above the Sun’s surface at a distance of 10,000 km, or it may stand off at a distance of 0.4 AU (the position of Mercury);
  • The three main high-energy processes – capture of solar power; use of that power to lift gases from the solar surface to the Tug; and conversion of nuclear fusion energy to kinetic energy of the exhaust – may proceed with 100% efficiency, or they may proceed with 10% efficiency.

Svoronos’s poster child is the most optimistic case in which a Tug close to the Sun operates at 100% efficiency: in this case he arrives at an acceleration imparted to the Sun of 2.3 × 10–6 m/s2, equivalent to 73 m/s per year. This acceleration begins to fall off after the first thousand years as the Sun’s mass is used up and its luminosity reduced. In order to reach a speed of 1% of the speed of light (3,000 km/s), about 200,000 years of continuous thrusting are required; 10% of light speed (30,000 km/s) is reached after several tens of millions of years of thrusting (as shown in Figure 3 of the paper). Whether these results justify the claim that the Star Tug can usefully accelerate the Sun to relativistic velocities is a moot question.

Clearly, the more realistic assumptions of less than perfect use of energy and standing a little way away from the Sun’s surface reduce the performance of the Star Tug by orders of magnitude.

If, for example, one assigns 10% efficiencies to the uses of fusion energy to create rocket thrust and of solar power to do the work lifting gases from the Sun to the Tug, and if one places the Tug at two solar radii from the Sun’s centre and angles its rockets at 45° to the Tug-Sun line, then an acceleration for the Sun of 1.353 × 10–9 m/s2 is obtained, thus 0.043 m/s per year, or 43 km/s over a period of one million years of thrusting. Given that this requires the Tug’s engines to run at a combined power level of 47 times the power output of the Sun itself, and at a power density of half a gigawatt per kilogram of the Tug’s material structure, I wonder whether even this modest performance is possible.

The paper has an interesting level of detail in some respects and is certainly worth reading for its mind-expanding ideas, but I noticed a couple of obvious errors (which should have been picked up at the review stage). I would also say that the placement of the Tug at only 10,000 km above the Sun’s surface is not a practical possibility. Although Svoronos does not state the dry mass of this Tug, it is easy to calculate that it must be 1.6 × 1022 kg (= 0.22 lunar masses). This is not likely to be enough for a rigid structure that has to stretch across 1.4 million km in order to fire with two engines past opposite limbs of the Sun.

Otherwise, I have only three major reservations about this system.

Problems with the Svoronos Star Tug

globular cluster M13 in Hercules
The globular cluster M13 in Hercules contains several hundred thousand stars. With a galactic latitude of 40° north and a distance from the Sun of 25,000 light years, it is well outside the main disk of the Milky Way, and will therefore need a long-range starship to access.

Certainly, his rocket-propelled Tug is very much more effective than the Shkadov thruster with which this discussion began. Yet the acceleration of the Sun in the desired direction is still achingly slow on a human scale, and the technologies needed to do so – if they are feasible at all – represent capabilities far in advance of those required for interstellar travel using more conventional worldship designs. Therefore I query whether the attempt to move one’s star together with its planetary system accomplishes anything that cannot be attained much more easily and cheaply by other methods?

For example, Svoronos suggests that civilisations more advanced than us might wish to control their star’s motion in order to avoid cataclysmic cosmic events, or to facilitate interstellar and intergalactic colonisation. But there are stars everywhere one looks in the galaxy, and no special reason for preserving the star one is currently resident at. Probably all stars have orbiting matter which can be used to construct habitations, and, due to the constraints on biological evolution, very few of them can have indigenous industrial species. Any organisation in that advanced civilisation which uses vastly smaller worldships to make the necessary journeys would settle suitable unoccupied systems at a much earlier date than those who stayed behind in order to travel with the entire original system.

My second reservation has already been alluded to above. Svoronos’s most effective Tug (10,000 km from the surface of the Sun; all efficiencies at 100%) has a power level of 6.4 × 1031 W, equivalent to 166,000 times the solar luminosity. If we assume that half of the Tug’s dry mass is devoted to propulsion (the other half to structural stiffening), the engine has to handle a power density of 8 GW/kg, or, in the more familiar format used in present-day space engineering, 1.25 × 10–7 kg/kW (the present-day capability is in the region of 50 kg/kW). All one can say is: good luck with that!

Can One Handle the Waste Radiation?

My third question about the Svoronos Star Tug is strongly illustrated even by his most modest proposal: the version in which the Tug hovers at 0.4 AU from the Sun, and has energy efficiencies of 10% in its three major processes.

Again, he does not state the mass, but it works out at 5.22 × 1021 kg, or one fourteenth of a lunar mass. Since it does not have to stretch halfway around the Sun, this version of the star tug can be much more compact, and its entire mass devoted to engines and associated machinery. The propulsive power is 9.2 × 1026 W, or 2.4 times the power of the Sun itself, requiring a more modest power handling capacity of 0.176 MW per kg of engine mass. Note that the requirement for the Daedalus first stage was much higher, at 24 MW/kg, so it appears that we are well into the realm of feasibility here. But the acceleration imparted to the Sun is down to 1.0 × 10–10 m/s2, producing a velocity change of only 3 km/s after a million years of thrusting.

One question which the author skates lightly over is the meaning of 10% efficiency for the fusion engine. He states that this is the efficiency of conversion of gamma rays produced by fusion reactions into thrust, but any sort of combustion, chemical or nuclear, also has an issue in that the fuel is never completely burned, and Svoronos implicitly assumes 100% burnup of his nuclear fuel. If we divide that 10% efficiency equally between gamma ray cleanup and fuel burnup, then, of the theoretical total energy that can be extracted from burning a kilogram of fuel, 68.4% is represented by fuel which does not burn before being ejected into the exhaust stream (still in the form of hydrogen), 21.6% is in the form of gamma rays, and 10% is in the form of the kinetic energy of hydrogen and helium in the exhaust. This generous interpretation of Svoronos’s statement means that, whatever the propulsive power of the engine may be, more than double that power goes into uncontrolled gamma rays.

Even this most modest version of the Tug, then, floods the Solar System with at least five solar luminosity’s worth of gamma rays. Their effect on the habitability of Earth would certainly be severe…

Returning to the design on which the claim of being able to accelerate the Sun to relativistic velocities is based, namely the Star Tug poised 10,000 km above the Sun’s surface and enjoying 100% energy efficiency: we recall that the propulsive power is 166,000 times the solar luminosity. The ambitious target of 100% efficiency in the fusion engine is now an absolute necessity: leakage of only one part in 166,000 of this energy flow would match the power of the Sun itself. Again, on any halfway realistic design assumptions, we have a problem protecting Earth from the intense flux of gamma rays which the engine will produce.

Surrounding the Star Tug with shielding massive enough to absorb that flux does not help much, as it must then radiate away the same amount of power in the form of waste heat. The only way to protect Earth is really to move it into the outer Solar System, but I suppose a civilisation capable of moving a star and with the patience to wait periods on the order of a million years to see results would not have difficulty moving one small planet.

Towards the end of this paper, Svoronos suggests that people, or at least the biological members of the civilisation which built the Star Tug, might prefer to live off-planet, in megastructures (microstructures in comparison with the Star Tug and with the machine that feeds fuel to it!) like O’Neill cylinders. But this of course removes the entire rationale for building a Star Tug in the first place: if living in a space colony is acceptable, then so is living in a worldship. A vast fleet of worldships could be built and flown for a tiny fraction of the effort that would go into constructing even the most modest of Svoronov’s Star Tugs.

The bottom line is this: the power of sunlight by itself is not commensurate with the power needed to accelerate the Sun and planets at a useful rate. Svoronos achieves his results – or apparent results – by adding more power: the nuclear fusion of the hydrogen lifted off the surface of the Sun. That gets him into the realm of power levels orders of magnitude greater than the radiant power of the Sun itself; levels which are able to do the job. But now his power is so high that the slightest deviation from 100% efficiency will be enough to render Earth uninhabitable, making the operation worthless. The game is simply not worth the candle.

An Alternative to the Star Tug

About 150 globular clusters surround the Milky Way
About 150 globular clusters surround the Milky Way. They are thought to contain our galaxy’s oldest stars. (found at, where Deborah Byrd discusses interesting speculations about possible ancient life in globular clusters)

So let us design a worldship for interstellar or intergalactic travel. Let us take Svoronov’s smallest Star Tug, thus with a mass of 5 × 1021 kg (five million trillion tonnes, or one fourteenth of the mass of the Moon). We assign half of this mass to payload, thus the habitable volume occupied by the passengers, and half to the engine, power generators and propellant tanks.

This version of the Star Tug has an exhaust velocity of 9500 km/s. If we give it a mass ratio of 4.0 then its cruising speed will be about 2% of the speed of light. It could make the crossing from our Solar System to the Large Magellanic Cloud, a distance of about 163,000 light years, in a little over eight million years. Over the same period of time, the same version of the Star Tug would manage to accelerate the entire Solar System by a speed of only about 0.01% of the speed of light; the Svoronos Star Tug at 10,000 km from the Sun but with realistic energy efficiencies of 10% would manage 0.2% of the speed of light.

If we assume that the worldship is fuelled by the same supply system as proposed for the Star Tug, the time taken to load it with 15 × 1021 kg of fuel works out at about 24 years. If we allow the total engine burn time, to accelerate the worldship away from the Solar System and decelerate it at a star in the LMC, to be 240 years, then the power level drops by a factor of ten, to 9 × 1025 W = 0.234 sunpower.

The power that goes into waste radiation is double this, if our assumptions above are correct. We would not want to launch this vehicle from anywhere close to Earth, so clearly it needs be moved to the outer Solar System before switching on its main engine. A disk 10 metres thick with a diameter of 2000 km and the density of rock would have a mass of about 1017 kg, which represents 0.00004 of the mass we have allowed for the passenger accommodation, so there’s no problem shielding them from the waste radiation.

Such worldships could basically be launched as fast as they could be built and fuelled. Each would have accommodation for over one trillion passengers, even allowing a very generous one million tonnes per person.

Of course in reality one would not build a single vehicle as large as that. The mass budget for ships and propellant would be spread over a fleet of smaller units in say the tens of millions up to billion-tonne size range (see my discussion of worldship fleets in JBIS). Propulsion would use the easier deuterium/tritium or deuterium/helium-3 reactions, perhaps with lithium deuteride fuel. Deuterium and helium-3 can be mined from the atmospheres of the giant planets (a lot cheaper than trying to lift matter from the surface of the Sun!) and lithium from small rocky worlds. Lithium is needed to breed tritium by fission, as the latter is radioactive and so cannot be stored for the timescales needed. See a paper by Robert Freeland of the Project Icarus Study Group describing a fission-fusion engine using lithium deuteride fuel.

Despite all the verbal handwringing about the difficulties of rocket propulsion and the tyranny of the rocket equation which one so often hears, nuclear fusion is eminently capable of powering massive interstellar vehicles on voyages of a few centuries to the nearest stars, as we discussed earlier. With mature technologies and convoy tactics, the journeys could be extended to thousands, and – who knows? – perhaps even millions of years, given a large enough convoy, allowing access to globular clusters and the nearest galaxies beyond the Milky Way.

While the subject of star tugs and stellar engines is a fascinating intellectual pursuit, I would not advise SETI astronomers to spend much time on making any special searches for them.

This post is reblogged from the Astronautical Evolution website.

Voyage to the Large Magellanic Cloud

Astronautical Evolution, issue 155

Will intergalactic travel ever be possible?

Here’s a question that grabbed my attention recently. Let’s leave to one side fantasy propulsion systems – space warp engines that can supposedly propel a spacecraft faster than light, interstellar ramjets that can accelerate at a constant one gee for decades on end, and suchlike. Let’s dismiss the perpetual motion machines of resonant cavity thrusters and EM drives supposedly pulling energy and momentum for free out of the quantum vacuum, or the intriguing but (to me) incomprehensible theory of quantised inertia, and stick to physics that’s known and tested today.

Would our descendants then be confined forever within the bounds of the Milky Way galaxy plus, looking some billions of years into the future, the other members of the Local Group when they eventually coalesce into one supergalaxy?

The Large Magellanic Cloud, from ESO VISTA
The Large Magellanic Cloud revealed by European Southern Observatory’s VISTA telescope (The European Southern Observatory)

I suggest the Large Magellanic Cloud as our test case. This is the fourth largest member of the Local Group after the Milky Way itself and the Andromeda and Triangulum spiral galaxies.

It’s not the closest to the Milky Way: that honour goes to the disputed Canis Major Overdensity, or to the Sagittarius Dwarf Spheroidal/Elliptical Galaxy. But the distances of these from the centre of the Milky Way, at 42,000 and 50,000 light years respectively, are no greater than the radius of the disk of the Milky Way itself, at around 50,000 light years. Some astronomers have argued that the Canis Major cluster is no more than part of the Milky Way’s own halo, while the Sagittarius Dwarf is, given its distance and direction, clearly more or less in contact with the far edge of the main disk of the Milky Way as seen from our own position.

The Large Magellanic Cloud is therefore the closest external galaxy which is separated from the Milky Way by a clear gulf of intergalactic space, ruling out any chance of star hopping to get there.

A recent paper estimates the motions of the Large Magellanic Cloud and the Andromeda Galaxy relative to the Milky Way for the next seven billion years (see figure below). The LMC is in fact currently moving away from us and will continue to do so for at least a billion years to come. However, on a human timescale these movements are achingly slow (about 120 km/s, or one light year in 2500 years), and over the next few million years its distance will not change by much.

LMC and MW predicted motion
“The predicted future evolution of the distance between the LMC and the centre of our Galaxy (orange lines), and between Andromeda and our Galaxy (blue lines). The solid lines correspond to the orbit of our fiducial model in which the LMC’s total mass is given by the Peñarrubia et al. (2016) measurement and corresponds to roughly one quarter of the MW’s mass; the dashed lines correspond to the orbit for a light LMC halo. The predictions are based on a dynamical model that includes the MW, Andromeda, and the LMC”. (Figure 1 of M. Cautun et al., The Aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud. © 2018. Published by Oxford University Press on behalf of the Royal Astronomical Society.)

It is currently 163,000 light years from the Sun. A little geometry shows that it is 123,000 light years from the rim of the Milky Way’s disk, and since its diameter is 14,000 light years the minimum distance to be crossed, starting from a star in our own galaxy which would be 56,000 light years from the Sun, must be about 116,000 light years. Even taking remote stragglers into account, we are clearly looking at a voyage of at least 100,000 light years through empty intergalactic void.

Crossing that, then, is the challenge!

Travelling in a spacecraft

How fast might an interstellar spacecraft be able to go, and how long would it take to cross 100,000 light years? Due to the limiting speed of light, the absolute minimum time would be somewhat greater than 100,000 years, but that’s galactic time, or star time. In a fast-moving ship, the time will be reduced due to relativistic time dilatation.

The reduction is by a factor of γ (gamma) and is not actually all that impressive. For travel at half the speed of light (c), γ = 1.155, so the journey time, ignoring time spent accelerating at the start of the journey and decelerating at the end, is 200,000/1.155 = 173,000 years ship time.

At 90% of c, we have γ = 2.294 and the journey time is 48,000 years ship time.

At 99% of c, we have γ = 7.089 and the journey time is 14,000 years ship time.

Can such a speed even be reached using known physics? For a rocket-propelled vehicle, the most mass- and energy-efficient propulsion system conceivable is one using matter-antimatter annihilation. Supposing the most energy-efficient mass ratio of 5, and a propellant which is 10% antihydrogen (optimistically high, given the difficulties of containing antimatter so that it does not react prematurely, and of converting its annihilation products to thrust). Then a one-million-tonne ship at departure from the last outpost of the Milky Way will have 200,000 tonnes for payload, engines and tanks, and carry 720,000 tonnes of, presumably, hydrogen, and 80,000 tonnes of antihydrogen.

Assuming an engine which is 100% efficient (!) the exhaust velocity would then be two-thirds of c and the total velocity change, calculated from the relativistic rocket equation, is 0.79 c. Of course half of that is required for deceleration on arrival, giving a cruising speed of around 40% of c, whence γ = 1.091 and the journey time is 229,000 years ship time.

Perhaps the ship might carry a giant sail which is pushed by the beam from a laser installation stationed at the departure star? The ship still has to decelerate without the help of any local infrastructure, so it will need its matter-antimatter engine for that purpose, but at least it can then get its cruising speed up to 80% of c, when γ will be 1.667 and the journey time is 75,000 years ship time.

And unless a million-tonne vehicle (or heavier) can be accelerated or decelerated using the incredibly weak magnetic fields and incredibly tenuous gas found in intergalactic space, that really is the best we can do using known physics. Speeds of 90% of c or over seem unattainable, and any realistic journey time is up in the high tens of thousands of years, or more likely well over 100,000 years.

Is there any alternative means of travel?

Travelling with a hypervelocity star

The random mixing of stars in the galaxy occasionally causes a star to accelerate to galactic escape velocity. This is known to happen if two stars forming a binary system pass close to the supermassive black hole at the centre of a galaxy in such a way that they suffer tidal disruption, one star falling into the black hole, the other being ejected from that region of space at high speed (the Hills mechanism).

Here, for example, is a report on the discovery in 2005 of a massive (8 solar masses) hypervelocity star, B-type spectrum with apparent magnitude 16.3, HE 0437-5439, ejected either from the Milky Way or from the Large Magellanic Cloud. Some discussion in the Wikipedia article gives more details: the star is 200,000 light years away, which puts it well beyond the LMC, and is flying away from both the LMC and the Milky Way at over 700 km/s, greater than galactic escape velocity.

A more recent discovery (2020) describes another massive star (2 solar masses), with A-type spectrum, at a distance of 29,000 light years from the Sunn and travelling out of the Milky Way at over 1700 km/s, ejected from the galactic centre. Clearly, the fact that these stars were spotted at all is due to their intrinsic brightness: both are much hotter and more massive than the Sun.

Might there also be cooler, sunlike hypervelocity stars? Perhaps with planets?

One of my current science fiction projects – working title The Gods of Ultima Landra – is based on the idea that a sunlike star is found leaving the Milky Way in the direction of the Large Magellanic Cloud. If travelling with a speed of 1500 km/s, 0.5% that of light, it will take about 20 million years to cross 100,000 light years of empty intergalactic space.

It is perhaps stretching plausibility a bit to give this star a planetary system, after the gravitational vicissitudes it must have been through to eject it at such a high speed, but it makes for a better story. Ultima Landra itself has Earth-like surface conditions, after a considerable terraforming effort. Also important are the largest satellite of the giant planet, and the asteroid belt: all three locations support human settlement.

The importance of having multiple locations is that, as we discussed in the previous post, history doesn’t stop just because a society becomes industrialised and prosperous. It may be that all civilisations, no matter how technologically advanced, are destined to collapse within a period of time very much less than 20 million years. A single civilisation, then, would not survive the journey to the Large Magellanic Cloud on a hypervelocity star. Even the society on board a single intergalactic starship, which might make the journey in as little as 100,000 years, would be more than likely to die out before arrival.

But in a planetary system there is space and resources to support several independent civilisations. So long as they don’t all go into decline at the same time, then as one falls, another can survive and reboot the collapsed settlement from outside.

But will the inhabitants of even the most prosperous civilisation keep alive the memory of who they are and where they are going over a period of time in the tens of millions of years? And won’t they evolve into new species, or become their machines, or separate out from their machines again, over such a vertiginous timespan?

Meanwhile, some of the more adventurous astronautical thinkers have described systems which they call stellar engines: machines for accelerating a star, together with any planets it may have, in a desired direction. Might this technique get us to the Large Magellanic Cloud any faster? Or perhaps further afield, to its smaller sibling the Small Magellanic Cloud, or to the Andromeda or Triangulum galaxies? I shall address this question in the following post.

This post is reblogged from the Astronautical Evolution website.

Why the Human Exploration of Space?

Astronautical Evolution, issue 154

Adapted from a letter sent to David Baker, editor of Spaceflight magazine, 22 May 2020 – now printed in the August 2020 issue, p.42.

Is it possible to justify the expenditure of large sums on astronaut space exploration when there are so many other priorities on Earth?

Crew Dragon approaching the International Space Station
Crew Dragon approaching the International Space Station, with another cargo Dragon already docked, as it will hopefully appear around the end of this month. (NASA)

David Baker, the editor of Spaceflight, recently commented that our planet is “stressed by an ever-burgeoning tide of human proliferation and the insatiable quest for growth, expansion and consumption”, and he went on to suggest: “perhaps we should be moved more than ever to consider why we are going” into space (Spaceflight, June 2020, p.5). Last month Charles Cockell asked the same question in lecture 36 of the “Life in the Universe Pandemic Series” on his excellent YouTube channel. With a new era of human spaceflight about to start, the question is a timely one.

I want to think a bit about a related question: is it possible for a global industrial civilisation to continue to prosper sustainably for timescales of at least thousands of years?

Clearly, there is a great deal of awareness nowadays of the many threats which could cause societal collapse, including:

  • Climate change (whether natural or induced by industrial pollution);
  • Supervolcano eruption;
  • Asteroid impact;
  • Nuclear war;
  • Ecological breakdown;
  • Runaway robotic or genetic technologies;
  • The takeover of democracies by authoritarian demagogues.

It is also clear that, despite political differences among the governments of the world’s great powers, all countries are linked closer than ever before by ties of economics, finance, media, politics, tourism and trade, so that even a regional setback can stress countries globally. This is now being vividly demonstrated, of course, by the Covid-19 pandemic.

The situation were we to succeed in colonising the Solar System would be different.

Barring the invention of both improbably powerful propulsion systems and improbably cheap energy sources to fuel them, the economies of different worlds would be very much more loosely connected than those of different countries today. Just as in the ancient world the Roman Empire could rise and fall with little effect in China, and none at all in the Americas, so if in that future Solar System, say, civilisation on Earth were to collapse, then that would have little effect on Mars and even less among the satellites of the giant planets. The reason would be the same: the geographical spread of the human diaspora would once again have outrun easy reach of the transport technologies of the day. Of course the pre-industrial human family was still vulnerable to a number of potential global environmental disasters – but on a Solar System scale no such disasters are in sight.

The same would be true – only far more so – of an interstellar human diaspora. If this can be achieved, then the human heritage is secure for as far into the future as one wishes to look. This remains true even if every single colony is doomed to ultimate extinction: in such a population of loosely related civilisations, the overall species prospers so long as each constituent society produces during its lifetime at least one daughter society which creates a new settlement at interplanetary or interstellar distance, either to break virgin ground, or to replace a civilisation which had formerly lived there but had died out.

If therefore we value our human culture and our heritage, we will see expansion of our civilisation into space as essential for its long-term preservation as well as for future growth.

In 1989, Mark Hempsell wrote in Spaceflight that the future facing mankind would be either a space age or a stone age. I believe he was correct. To put it in terms of popular TV serials: the human future will look either like Star Trek, or like Game of Thrones (as I wrote earlier in this post). If certain environmental campaigners and Marxist sociologists do not hold this principle at the forefront of their thinking, if they condemn technological progress and yearn for what they see as a more natural way of living, then it is incumbent upon them to offer a plausible third way for our species in the long term. I have not yet seen any such alternative scenario.

The stresses on Earth’s biosphere and on human society itself caused by continuing economic, population and technology growth now come into focus: they are the growing pains attendant upon the evolution of a new kind of industrial society – one that has never existed before – that can prosper sustainably both on Earth and at extraterrestrial locations. It should be our goal to promote both growth and sustainability and, on Earth itself, environmental responsibility. Where new technologies and new patterns of doing things can contribute to these goals they must be embraced. Commercial passenger spaceflight, nuclear fusion power, artificial intelligence, robotics, artificial meat, farming without soil and under artificial light – these are some of the key factors in our progress at present. Another would be colonising some of Earth’s desert regions – not as a simulation of a Mars expedition for half a dozen people for a few weeks, but building for permanence and long-term growth.

We go into space, therefore, because only through interplanetary and ultimately interstellar growth is the human heritage made secure for the long term. The alternative, sooner or later, is inevitable decline and ultimate extinction.

This post is reblogged from the Astronautical Evolution website.

Artificial Gravity for the Journey to Mars and Return

Astronautical Evolution, issue 153

So, here we are 59 years after Yuri Gagarin’s flight, and there has still not yet been any serious attempt to try out artificial gravity in space, or any serious proposal to do so in the immediate future.

That’s not to say there hasn’t been some serious thinking about it. Watch the video “Artificial Gravity” by Prof. David Kipping at the Cool Worlds YouTube channel for an instructive primer on the subject.

The weirdness of weightlessness

The latest issue of Spaceflight magazine contains an article by space medicine expert Brett Gooden, summarising what we know so far about the response of the human body to microgravity.

Samantha Cristoforetti on the ISS
ESA astronaut Samantha Cristoforetti performs maintenance on a controller panel assembly in the International Space Station’s Tranquility module, late 2014 or early 2015 (ISS exp.43). (NASA)

He asks: could we confidently despatch a crew now on a two-year mission to Mars and expect a successful outcome?

His answer is: no, we could not, because – assuming the interplanetary flights to be carried out in microgravity – the physical resilience of even a crew that was perfectly fit at launch would be likely to be overwhelmed by the biomedical problems encountered:

  • Loss of balance in the inner ear – fortunately the resulting motion sickness usually clears up within 48 hours of entering microgravity;
  • Changes to the heart and blood vessels, leading to faintness (orthostatic hypotension) on return to Earth’s gravity (or presumably also exposure to even partial gravity on Mars);
  • A transfer of blood from the lower to the upper body, which in addition to causing the superficial symptoms of a puffy face and anaemic chicken-legs has a detrimental effect on vision;
  • Loss of muscle and bone mass (the latter leading to dangerous calcification of soft tissues);
  • Increased skin sensitivity, apparently with greater sensitivity to pain in the hands and feet.

The consequences for a group of human explorers of Mars would be severe enough to “court disaster”, according to Dr Gooden. The problem is not really living in microgravity, or even living in one-third Earth gravity. The real show-stoppers are:

  • The astronauts must make abrupt transfers from Earth gravity, to microgravity, to Mars gravity, to microgravity, and finally back to Earth gravity;
  • Each of those changes is accompanied by sudden stresses of multiple-gee loads and vibration for a period of several minutes.

Given time, one’s body can adapt more or less successfully to microgravity, and presumably also to martian gravity, but each adaptation leaves the traveller unfit to face the transfer to the next state. This applies particularly to coming out of microgravity to land on Mars. During the landing itself the astronauts will be especially vulnerable to blacking out, and after landing they will risk falling over and breaking one of their weakened bones, just as elderly people do on Earth.

Dr Gooden mentions the idea of mitigating the problem with artificial gravity. His proposal is to get astronauts to run around the circumference of their habitat like hamsters in an exercise wheel, thus both generating their own gravity and engaging in impact exercise. This was done by the occupants of the 6.6-metre diameter Skylab in the early 1970s, who presumably invented the practice spontaneously.

This is hardly a satisfactory solution to the problem, being little more than a variant on the current obsession with physical exercise on board (two hours per day per astronaut!).

The goodness of gravity

In an article in Spaceflight in 2017, based on a blog post, I suggested a number of guidelines for flights to Mars, one of which was artificial gravity on the interplanetary journeys in both directions. I took the idea up in more detail in a paper which appeared in JBIS in 2018.

Zubrin presents Mars Direct
Robert Zubrin giving a keynote address in 2019 at the fourth annual Project Fibonacci STEAM Leadership Conference for students. (John Clifford for the Rome Sentinel)

Zubrin envisages his spacecraft using its upper rocket stage as a counterweight, and coupling the two together using cables. This design is clearly seen in the photo on the right (in which Zubrin reproduces figure 1.2 from chapter 1 of his book). It has three problems:

  • The spacecraft flies alone, without support, and is therefore vulnerable to an Apollo-13-type accident;
  • The upper rocket stage is discarded just before arrival at Earth or Mars, and lost;
  • Rotation of a long, narrow object is unstable – see the T-handle experiment on the ISS for a vivid demonstration of this.

My JBIS paper fixed the first two of these problems by having two spacecraft fly in tandem. Each spacecraft serves as counterweight to the other for artificial gravity, and each serves as lifeboat to the other in the event of an accident.

Incidentally, Zubrin’s scheme suffers from a further problem in that his Earth return spacecraft is much too small to guarantee the crew’s safety on the Mars to Earth leg of the mission. This can be rectified by making them larger (two flying in tandem, as before), and leaving a rocket stage waiting for them in low Mars orbit. The parking of resources in orbit is described by Zubrin as Mars Semi-Direct; his aversion to any Mars orbit rendezvous manoeuvres seems to be based more on a purist rejection of the official architectures – which resemble Apollo with a massive mother ship left in orbit – than on a dispassionate balancing of risks and benefits.

This leaves the problem of rotational instability.

Surprisingly, the JBIS reviewer of my paper did not pick me up on this. But it is still a loose end which needs to be tidied up.

The Hermes spacecraft from the movie The Martian
The Hermes interplanetary spaceship from the 2015 movie The Martian (dir. Ridley Scott, based on the novel by Andy Weir). (20th Century Fox)

The form which allows for the most stable rotation is a disk or wheel shape, like the living-quarters in the fictional Hermes spacecraft in Andy Weir’s novel The Martian, shown here from the movie. But the wheel on Hermes is on the small side: although exact experiments have not yet been done, it seems probable that in order to avoid motion sickness one needs a lever arm of at least the 85 metres or so that Zubrin allows (giving him Mars-equivalent artificial gravity at a rotation speed of 2 r.p.m.; p.8 of the Touchstone 1997 edition).

The question is therefore whether there is a way of assembling the small spacecraft which are all that an early Mars programme could probably afford into a wheel shape. While having two ships and a tether between them is probably unstable, expanding that to three or more ships spaced equidistantly around the axis of rotation – at the corners of a triangle, a square, a pentagon, etc. – would remove the instability.

Perhaps an ideal system would have four individual spacecraft making the interplanetary crossing together. Rather than using tethers it might be better to have a double rigid truss in the form of a cross, with docking points at all four tips, access tunnels built into the four arms, a large dish antenna, and storage tanks for additional supplies attached near the centre.

This revives a concept which I called a Service Platform when I was sketching Earth-Mars architectures. It would be a relatively light piece of kit that would be parked in Earth orbit or Mars orbit when not being used in interplanetary space. Perhaps it’s time to start thinking about that idea again.


Brett Gooden, “A matter of survival”, Spaceflight, May 2020, p.26-33. Dr Gooden has been involved with space medicine since project Mercury, with articles appearing in Spaceflight as early as March 1964 and again in May 1965.

Stephen Ashworth, “Evaluating Mars programme designs”, Spaceflight, September 2017, p.336-342.

Stephen Ashworth, “An Earth-Moon-Mars Passenger Transport Pyramid”, JBIS, vol.71 no.5 (May 2018), p.165-177.

This post is reblogged from the Astronautical Evolution website.

Cruising in Space

Astronautical Evolution, issue 152

When writing about space colonies or worldships, the go-to picture always seems to be one dating from O’Neill’s studies from the 1970s, or else one closely based on those. Case in point: today’s post on generation ships in Universe Today.

Interior of O’Neill Island Three space colony. (Rick Guidice/NASA)

The image at the head of the article (see left) shows the typical landscape of fields, lakes and rivers imitating a countryside scene in a developed country on Earth, with occasional villages and towns. (The article is unfortunately amateurishly written: it contains nothing new and repeats some well-worn and misleading clichés.)

Incidentally, I found a nice 3-D video animation, by artist Eric Bruneton, of a flythrough of one of these giant cylindrical habitats, again showing very much a late 20th to early 21st century landscape of fields and cities. It is linked to from the National Space Society website where it is described as an animation of Arthur C. Clarke’s fictional Rama – this is incorrect: it is merely “freely inspired” by the famous alien megastucture in Clarke’s novel.

A more recent artist’s impression for Blue Origin. (Sourced from this article critical of the company)

For more of these images, see the collection on the Core 77 design website.

Only problem is: I doubt whether space colonies will ever actually look like this.

In 2012 I wrote:

“Since a space habitat as described by O’Neill and by Bond and Martin has a large interior volume filled with nothing but air, it offers its owners the temptation, or the opportunity, to fill at least part of that volume, working inwards from the rim, with structures in which increased numbers of inhabitants can live, work, and earn money to pay the rent.

“It may be safely anticipated that during at least the first centuries of space colonisation, the cost of a space colony relative to equivalent accommodation on Earth will be high. The economic pressure will therefore be towards efficient utilisation of its interior volume, making it look less like the idyllic pastoral village landscapes of O’Neill’s vision (illustrated in paintings by Pat Rawlings), or the Earth-like diorama envisaged by Bond and Martin, and more like central Tokyo or New York. (The rustic paradise will be provided in the form of virtual reality simulations.)”

I think one can get an insight into likely space colony interiors by looking at modern cruise liners.

The ocean cruising industry carried around 27 million passengers in 2018, with a compound annual growth rate of 6.63% over the period 1990 to 2020. A dozen new ships (listed here) are coming into service every year to serve that demand, the largest of which have berths for 4,000 to over 5,000 passengers. These ships are clearly highly desirable places to spend time, despite their being highly artificial, high-technology, high population density environments.

Cruise liners are therefore good analogues for space colonies, once allowance has been made for a few differences:

  • The lack of a natural outside to a space colony, open to sunshine and to the global air circulation, and the lack of ports of call with green spaces, require the addition of interior park spaces, or what in a skyscraper would be called sky gardens;
  • The presence of a microgravity space close to the axis of rotation creates new opportunities for recreational activities;
  • A space colony needs to provide, in addition to residential and recreational space, working space for those of its inhabitants who are earning a living;
  • A space colony requires a formal political system to govern the lives of its inhabitants;
  • A space colony must bring all life-support loops to a high degree of closure, recycling its air, water, foodstuffs and manufactured products, and maintaining a healthy microbial environment. The loops need not be entirely closed, as Mark Hempsell has pointed out, if a number of space colonies are located closely enough to allow trade between them; for example, this would be the case for colonies orbiting together in cislunar space.
The central arcade on the MSC Meraviglia. (Twitter/emersonpje)

So what would life look like on a glorified cruise liner? Here are a couple of shots of the central arcade on the MSC Meraviglia. Note that the arched ceiling is coated in LED lights, allowing it to display many different patterns.

This particular ship was completed in 2017, and can carry up to 4,500 passengers and 1536 crew. The size is given as 171,598 gross tons; according to the modern definition of gross tons, this represents a total enclosed volume of 545,220 cubic metres. This allows us to get a feel for the amount of space allowed per passenger. Suppose that the crew are removed and replaced with robots, and suppose that the ship’s engines are also removed and replaced with recycling machinery. Assuming a ceiling height of 3 metres, the calculated volume then equates to a deck space of 40 square metres per passenger at full capacity, including utility areas devoted to their life support but not directly accessible by them.

Other modern passenger ships have similar dimensions, between 59 square metres per person on Cunard’s Queen Mary 2 and only 36 square metres per person on what is currently the largest cruise liner in the world, Royal Caribbean’s Symphony of the Seas.

An image of the built-in digital screen on the ceiling of deck 6 of the MSC Meraviglia. (SamHolt6)

If this was the whole story, the resulting population density would be quite large: 25,000 people per square kilometre, comparable with the most densely settled urban districts (such as the municipality of Le Pré-Saint-Gervais in Paris).

But such urban centres on Earth depend upon global agricultural and industrial hinterlands. In a space colony – thinking now of one located in a remote part of the Solar System, and especially if being used as a worldship for interstellar travel, or even for multi-year travel between the inner and outer Solar System – all the functions of these hinterlands – plus also the buffering functions of the global atmosphere and hydrosphere – would have to be replicated on board.

After considering the matter realistically, then, a population density somewhere in the region of 5,000 per square kilometre is probably the greatest that one would want to achieve. (O’Neill proposed 10,000 people occupying a little over one square kilometre in his original Island One design.)

On the other hand, the multi-deck nature of the space colony as I envisage it, filling up between one half and two-thirds of that empty interior space with superstructure, and creating the majority of interior vistas similar to those of cruise ships, would certainly pack a lot more people in per thousand tonnes of construction materials invested into the megastructure.


S. Ashworth, “The Long-Term Growth Prospects for Planetary and Space Colonies”, JBIS, vol.65 no.6 (June 2012), on p.206.

M. Hempsell, “Sky Farm: Feeding a Large Space Population”, JBIS, vol.70 no.1 (January 2017), p.3-11.

G.K. O’Neill, The High Frontier (1977; 3rd edn, Space Studies Institute, 2000).

This post is reblogged from the Astronautical Evolution website.

The Destiny of Civilisations – Fire, Iron and Gold

Astronautical Evolution, issue 151

Civilisation enabled or destroyed by technology?

To continue our train of thought from the previous post: I have seen a similar distinction between dynamic and static models of society in another context, though here they might better be called technocratic versus technophobic.

The natural mindset of anybody who is into technology is to assume that a successful human future must see increasingly powerful technologies coming into use, until humanity merges with its machines. In such a future, our descendants are free to roam the galaxy.

But what of the technophobic mindset, where science and technology are seen as dehumanising and spiritual values of love, religious belief and living in the moment are more important than – and are threatened by – material progress?

Tolkien’s and Lewis’s fictional worlds

One Ring to rule them all, One Ring to find them,
One Ring to bring them all, and in the darkness bind them.

(The inscription on Sauron’s golden ring of power, according to J.R.R. Tolkien, The Fellowship of the Ring, book 1, ch.2.)

The ring of Sauron
The Ring of Tolkien, as visualised in the movies.

A simplistic reading of J.R.R. Tolkien and of his friend and fellow Christian C.S. Lewis might well suggest to the reader that these writers were hostile to technology.

In The Lord of the Rings, Sauron’s ring is both the ultimate technological achievement and the most evil artefact ever forged. It cannot be used for good, but can only be destroyed before it enslaves everybody under the dictatorship of the Dark Lord.

Saruman’s fortress at Isengard is portrayed as a hotbed of dehumanising industrial activity, and is of course overthrown by the protagonists.

In Lewis’s novel The Voyage of the Dawn Treader, part of his history of Narnia, Eustace compares Caspian’s one-masted sailing ship unfavourably with ships on Earth, comparing it with the Queen Mary and pointing out that the Dawn Treader was not much bigger than a lifeboat (diary entry in ch.2). But Lewis’s heart is clearly with the sailing ships of Narnia, and he never allows Narnia (or its southern rival, the evil empire of Calormen) to industrialise.

His anti-technological stance is more explicit in his interplanetary trilogy, where space travel as we understand it today is portrayed as evil, and the evil in the third volume, That Hideous Strength, is a product of perverted science. Lewis is quite clear (in his reply to J.B.S. Haldane’s review of this novel) that he is not opposed to science as such, but that he thinks it is vulnerable to evil tendencies which would use its popularity and effectiveness to insinuate the corruption of mankind and its subjection to the dictatorship of devilish beings.

Although these authors have little interest in talking about technology and industrialisation as such, it is clear that their attitude is highly critical. Of course, a writer such as George R.R. Martin in his A Song of Ice and Fire (a.k.a. Game of Thrones) has so little interest in the topic that he ignores it altogether.

Technology for good and evil

Yet a limited level of technology is clearly indispensable to any kind of life for both human characters and those with human-equivalent intelligence – including the village of Hobbiton in the Shire and the dwarfish, faunish and talking animal settlements of Narnia.

Blacksmiths in the ancient world
Good technology: the iron-age blacksmith at work. (Newegg prints, artwork by Science Source)

Within this limited level we are talking of the ability to make and use fire, the mining and working of metals, construction of buildings of wood and stone, building of sailing ships, production of goods such as swords, coins, jewels, manuscript books, furniture, crockery, candles and oil lamps, fireworks, clothing, and so on.

We are clearly excluding any machine or vehicle powered by fossil fuels, printed books, gunpowder weapons, nuclear power and nuclear weapons, antibiotics, electrical appliances, electronics, radio and television, and so on. Transport is by horse (possibly winged), or indeed by eagle or dragon, as well as on foot, but never by steamship, steam railway or aircraft.

Sometimes high-tech-equivalent capabilities are made available to particular characters. The hermit in Lewis’s The Horse and his Boy has television, as does, if I recall correctly, an elf character in The Lord of the Rings. But in these instances the capability is provided by magic, not industrial technology as we know it. Magic, by its nature, requires a special individual to use it. Unlike technology, it cannot be mass produced or mass marketed (despite Arthur C. Clarke’s famous dictum to the contrary).

So in other words, the technological development in such fantasies is held at a medieval level. It can only legitimately transgress that level in the hands of someone of exceptional spiritual purity, otherwise such advanced capabilities – inevitably seized for selfish ends – become an evil motivating the plot conflict between those who would build a empire based on these higher technologies and those who reject them, with the latter as the heroes of the story who eventually triumph.

Is this dividing line artificial or real? Why should a medieval level be desirable but further development be undesirable? Can one discern any kind of development barrier here?

One writer who can is Sunday Times journalist Bryan Appleyard, who mentioned that ancient peoples did not have modern medicine or electronics, and continued:

“Science and technology have not developed gradually over the whole history of human culture; they have suddenly exploded all about us. Their sheer, profligate effectiveness is something utterly novel. […] It is central to my thesis that […] science is a fundamentally new way of knowing and doing things. I believe that an examination of scientific history makes this point obvious. I find it absurd, almost sentimental, to say, as would Bronowski, that a plough is like a CD-player. They are fundamentally different. The designer of the latter has to have a different way of knowing from the maker of the former.”

Kaiser Wilhelm der Grosse ship
Evil technology: the Kaiser Wilhelm der Grosse (1897) was the first four-funnelled luxury ocean liner.

My own view agrees with Dr Jacob Bronowski: that technological development is a continuous path of progress, from its beginnings in prehistory until some plateau of maximum possible technological capability is reached at some point in our future. Once our ancestors hit on the trick of using one stone to give a sharper edge to another stone, they were launched irrevocably on a course which would lead ultimately to artificial intelligence, genetic engineering and starships – barring catastrophic accidents, of course.

Coming at the question from a very different angle, Bill Joy (cofounder and chief scientist of Sun Microsystems) wrote in Wired magazine:

“The 21st-century technologies – genetics, nanotechnology, and robotics (GNR) – are so powerful that they can spawn whole new classes of accidents and abuses. Most dangerously, for the first time, these accidents and abuses are widely within the reach of individuals or small groups. […] Thus we have the possibility not just of weapons of mass destruction but of knowledge-enabled mass destruction (KMD), this destructiveness hugely amplified by the power of self-replication. I think it is no exaggeration to say we are on the cusp of the further perfection of extreme evil, an evil whose possibility spreads well beyond that which weapons of mass destruction bequeathed to the nation-states, on to a surprising and terrible empowerment of extreme individuals.”

Here we have something very much like what has clearly been working at the backs of the minds of Tolkien and Lewis. It is a risk/benefit calculation.

The idea is that any given technology has potential benefits, and potential risks. When the benefits outweigh the risks, mankind as a whole benefits from introduction of that technology. When the risks outweigh the benefits, then on balance we suffer.

One can see that Tolkien and Lewis are observing a calculation according to which simple technologies provide a net benefit, but as the power of new technologies increases so the risks increase faster than the benefits. Thus improvements in technological level continue until a natural ceiling is encountered, in which the latest technologies to be introduced destroy humanity.

This could be by enslaving people to such an extent that their moral degeneration is complete: this is well symbolised by Sauron’s ring, representing real-world technologies such as mass production and consumerism, or mass surveillance leading to a global dictatorship (like that portrayed in Orwell’s Nineteen Eighty-Four), or genetic modification with the removal of traits open to religious ideas (as in Huxley’s Brave New World).

Alternatively the destruction could be literal physical annihilation, such as that following a global nuclear holocaust, or through more speculative manmade catastrophes such as those raised by Bill Joy: a global pandemic (deliberate or accidental) caused by an engineered virus, or the global extermination of mankind by its own intelligent robots (whether anthropomorphic, purely software, or nanoscale).

The first message from these writers is then that humanity needs the wisdom to develop technology far enough to provide a comfortable level of life, but no further.

And the second message is that, in their view, this optimum situation was arrived at in the middle ages: we have gone too far by now, and must renounce such things as nuclear, genetic and artificial intelligence technologies while we still have time, if we are not to end up destroying ourselves. Even the use of fossil fuels is now condemned by the possibility of disastrous climate change, despite the immense benefits we have gained from these fuels in the past.

Who is right?

Is it in fact the case that the kinds of technologies developed since the beginning of the industrial revolution – including 21st-century technologies of immense power such as genetics, artificial intelligence, nanotech and nuclear fusion – are so dangerous that they will in the end destroy us? Clearly, nobody yet knows.

Controlled nuclear fusion was at first seen as an imminent breakthrough in the supply of clean energy. Although steady progress has been made, it has taken much longer than expected and cost much more. Experimental reactors today still only operate at little better than break-even. Perhaps the replicating technologies that Bill Joy so feared will turn out to be just as intractable in practice?

Regarding the much-invoked need for “wisdom” in our efforts to progress, I believe that wisdom is not a product of spiritual enlightenment before the event, but rather can only be earned through long and painful experience. Whether in transport or energy supply or medicine or computerisation, disasters must always happen because we do not know in advance the safe limits which we should observe. Engineering is never an armchair activity, no matter how ambitious the computer simulations used in advance.

As the two pictures shown above suggest – of the coal-fired iron-working smithy and the coal-fired iron ship from two thousand years later – there is a continuity in science and technology from the earliest beginnings of humankind to the present and to any high-tech future which we may embark upon. To make fire by burning wood is only the first step in a progression of increasingly concentrated sources of energy: coal, oil, gas, nuclear fission and fusion, and perhaps matter-antimatter annihilation. Again, to use a symbolic spoken language leads to writing, then printing, the telegraph, radio and television, computers, and artificial intelligence. And so on. There is no natural boundary between low-tech societies and high-tech ones – though there are quantum leaps in social organisation when new ideas or products come into widespread use, which are what Appleyard, Tolkien and Lewis clearly had in mind.

What about medieval-level technologies being sufficient for a comfortable life? Why not adopt the idyllic rustic life of Hobbiton or Narnia – also dramatised in the ostensibly low-tech forest life of the Na’vi in James Cameron’s Avatar?

No, that would be an illusion. The reality would be the life shown in Martin’s Westeros: dirt, poverty, hard labour and famine for the mass of the population; disease, war, superstition and ignorance, and a liability to torture and summary execution, too, for them and for the aristocracy ruling over them. Without modern medicine, democracy, human rights, education and communications media life would not be tolerable for us – but these are products of a society needing intelligent and discerning consumers for its mass markets. Remove the modern high-tech consumer economy, and the logic of power forces us to inevitably sink back towards serfdom under a ruling class of competing warlords.

As I suggested in a recent paper on the philosophy of the starship, if humanity – or an analogous intelligent species of another star – does succeed in expanding its civilisation into space, then it will be because of a culture in which meeting the challenges of developing new technologies is seen as virtuous. One good reason for such a culture is its consciousness of the horrors of the only alternative model of society we know. Another is the fact that any successful high-tech society will dominate low-tech ones as completely as European colonists dominated indigenous peoples in the rest of the world.

Conversely, any culture which bans progress beyond the medieval level must necessarily remain confined to its planet of origin. But by the same token it will lack radio telescopes – which can only exist as the product of a scientific-industrial civilisation – and so will remain invisible to SETI searches.

A technophobic civilisation will fail to satisfy the characteristics of a static civilisation required for SETI – but so will a technocratic one, as argued in that earlier post.

The terrors of the past are well documented in history books. The terrors of the future are speculative: one possible scenario among several. For my money, virtue clearly lies in braving the future in pursuit of the continued betterment of mankind.


For C.S. Lewis’s reply to Professor Haldane, see Lewis, Of Other Worlds (HarperCollins, 1966), p.117-34, esp. p.123-27.

Bryan Appleyard, Understanding the Present: Science and the Soul of Modern Man (Pan Macmillan, 1992), p.4.

Bill Joy, “Why the Future Doesn’t Need Us”, Wired, April 2000.

Stephen Ashworth, “The Starship Philosophy: Its Heritage and Competitors”, JBIS, vol.67, no.11/12 (Nov./Dec. 2014), p.447-59.

This post is reblogged from the Astronautical Evolution website.

The Destiny of Civilisations – A Problem for SETI

Astronautical Evolution, issue 150

Betting on alien contact

Seth Shostak
Dr Seth Shostak. (Spacefest)

Well-known SETI astronomer Seth Shostak has claimed that he expects the SETI enterprise to succeed very soon in intercepting a message from an extraterrestrial civilisation. In 2017 he bet everyone a cup of coffee that evidence of intelligent aliens would be discovered within 20 years.

I cannot reconcile this claim with the nature of civilisation as we know it from our experience of human life on Earth. Dr Shostak must therefore be using a different model of civilisation. In this post I would like to ask what his reasons might be for choosing a more speculative model.

Even more than low-tech civilisations of the past, present-day industrial civilisation on Earth is clearly in an unstable state. On the one hand, it is under threat from a variety of possible natural disasters, including asteroid impact, supervolcano eruption and solar variations, as well as from artificial disasters, including uncontrolled industrial pollution, world war, economic collapse, political degeneration and, some fear, rogue technologies. The presence of such dangers threatens to cause civilisation to collapse and revert to a pre-industrial stage on a timescale on the order of a thousand years.

On the other hand, the internal collaborative and competitive forces driving industrial civilisation towards further economic growth and technological progress, combined with the large untapped material and energy resources available elsewhere in the solar system, suggest that our currently global civilisation is likely to grow to an interplanetary one within the next thousand years, and an interstellar one within the next few thousand years.

The human future must therefore go one of two ways: it will ultimately settle in a more stable state which is either low-tech or high-tech relative to the present day. Its destiny on a millennial timescale will resemble either Game of Thrones, or Star Trek. I shall refer to this as a dynamic model of civilisation.

Game of Thrones
A low-tech destiny: ‘Game of Thrones’ – pain, dirt and death. The TV show is based on G.R.R. Martin’s still unfinished series of novels, ‘A Song of Ice and Fire’. (HBO)

On this model, interstellar expansion produces a population of related civilisations. It is this multiplicity of offspring that gives the population as a whole its long-term resilience. By natural selection, that population must necessarily become dominated by those cultures which have the greatest expansionist drive, a point which remains true whether a given culture’s decision-making processes are dominated by organic intelligence (brains), or manufactured intelligence (machines), or a symbiosis of the two. The result is therefore that the progeny of the original civilisation spread out and colonise the planetary systems of all main-sequence stars in our galaxy within a period of time no greater than a few tens of millions of years, thus a few per cent of the lifetime of the galaxy to date.

Think of dipping a cup into the ocean: wherever in the world you take a sample, the water will be teeming with microorganisms. The ability of planetary systems to support industrial life is analogous to that of the ocean to support microbes: in both cases, they’ll quickly get everywhere.

Betting on an absence of alien contact

But if this dynamic model is used as a general template for civilisations throughout the galaxy, the probability of SETI detecting a signal is very low.

SETI can only detect a signal if there exists a nearby alien civilisation at a level of development similar to our own at the present day, and which we are able to catch in the window of time between its first developing radio astronomy, and either its subsequent collapse or else its subsequent arrival in colony ships in our own planetary system. This time window is narrow compared with the total time available, and this narrowness forces down the probability of such a coincidence to a low value.

In a recent paper in JBIS I made an estimate of this probability in the context of the METI debate (in which Dr Shostak was also a participant). Based on a dynamic model of societies in the galaxy, I concluded that the maximum defensible probability of finding an interstellar conversation partner (or an interstellar invasion force) anywhere within a 500-light-year radius of the Sun at the present time was around one in a million, if all the factors involved were maximally favourable to their existence, or else less than one in a million.

SETI optimists such as Dr Shostak are clearly using a different model, which I shall refer to as a static model of civilisation.

The cast of Star Trek, the original series
A high-tech destiny: ‘Star Trek’ – culture, politeness, and seeking out new life where no man has gone before. The original series ran from 1966 to 1969. (IMDb)

For example, David Brin – another participant in the METI debate – wrote: “let’s (for now) make standard SETI assumptions – that the Others out there are at least benign, probably altruistic, not engaged in extensive colonization and interested in communicating with newcomer sapient species like us. Posit also that they are very long-lived.”

According to the dynamic model, a civilisation which is long-lived must necessarily be engaged in extensive colonisation; one which is not so engaged must be short-lived, with a duration limited to thousands of years. These conclusions follow from the observed pressures, towards both growth and decline, acting on our own civilisation at the present epoch. Such a picture contradicts Brin’s “standard SETI assumptions”, hence the need for an alternative, more static, model.

A static model would assume that a civilisation can maintain an active interest in its galactic environment through observational astronomy, together with the necessary industrial base, while at the same time refraining from physical access to that environment for scientific work, or for economic use of its resources, on timescales of millions to billions of years. Given the pressures, internal and external, described above, and given the commonality of basic science and technology for both radio astronomy and spaceflight, this would appear to be an unlikely balancing act.

My question to Dr Shostak and his colleagues is therefore this: what grounds, if any, do you have for expecting the static model to apply to extraterrestrial industrial civilisations, rather than the dynamic model?

A clash of concepts

The answer seems to come from an interview a couple of years ago with The questioner asked whether SETI might have missed signals, perhaps ones which more advanced technology might have been able to detect. Dr Shostak replied:

“I’m sure we’ve missed signals. I’m sure there’s signals coming from somebody that we’re totally unaware of because we’re not aiming the big antenna in the right direction, tuned to the right frequency, and all that sort of stuff. I mean we can easily miss that. The universe is 13 billion years old, right? There’s been plenty of time for intelligence to pop up on lots and lots of worlds out there, and there’s lots of them that are older than the Earth, so they may have a tremendous head start. So yeah, I’m sure we’ve missed a lot of clues.”

The implication seems to be clear enough: because there are no signs of extensive alien industrialisation in our part of the galaxy, including our own solar system, some sort of static model of civilisation must apply. After all, surely we know that industrial aliens not only exist, but have existed long before our own species evolved?

But of course we don’t know those things at all! The time taken for life to first emerge from inanimate chemistry and establish itself on Earth-like planets is so far completely unknown (as Paul Davies stresses in chapter 2 of his recent book, The Eerie Silence). If that time turns out to be around nine billion years, then humanity could easily have been first to industrialise in our galaxy or even in the observable universe.

Or it could have been a shorter time, but the likelihood of a species industrialising might be less than would be expected from the single example of which we know. Without science and industry, an extraterrestrial species remains undetectable at the present time. There are simply too many unknowns to be dogmatic: maybe detectable alien civilisations exist in our galaxy, maybe they don’t.

Meanwhile the dynamic model of the destiny of civilisations is firmly based on what we know of our own species and civilisation, and of biological evolution in general. The correct scientific procedure must therefore be to use this knowledge to constrain our speculations about the frequency of industrial life in the galaxy, rather than to use the speculations to set that knowledge aside.


S. Ashworth, “Quantifying the Assumptions Behind the METI Debate”, JBIS, vol.69, no.12, December 2016, p.419-28.

D. Brin, “The Search for Extra-Terrestrial Intelligence (SETI) and Whether to Send ‘Messages’ (METI): A Case for Conversation, Patience and Due Diligence”, JBIS, vol.67, no.1, January 2014, p.8-16, on p.10.

Paul Davies, The Eerie Silence: Searching for Ourselves in the Universe (Penguin, 2010).

This post is reblogged from the Astronautical Evolution website.

The Holy Grail of Space

Astronautical Evolution, issue 149 (originally posted 1 October 2019)

A masterclass in what really matters for spaceflight

From Elon Musk’s latest public presentation at Boca Chica, Texas, on 28 September – the eleventh anniversary of the first time SpaceX reached orbit with its fourth and last Falcon 1:

Elon Musk gives an update on the design and development of “Starship”
Elon Musk gives an update on the design and development of “Starship”. (SpaceX)

“The point of this presentation and this event is really – there are two elements to it. One is to inspire the public, get people excited about our future in space and get people fired up about the future.

(Slide: An Exciting future, full of wonder & possibility, out among the stars.)

“There are so many things to worry about, so many things to be concerned about, there are many troubles in the world, of course, and these are important and we need to solve them.

“But we also need things that make us excited to be alive, that make us glad to wake up in the morning, and be fired up about the future and think, yeah! the future’s gonna be great! – you know, and this – space exploration – is one of those things.

“And becoming a spacefaring civilisation, being out there among the stars, this is one of the things that, I know, makes me glad to be alive, I think it makes many people glad to be alive. It’s one of the best things.

“And we’re faced with a choice: which future do you want? Do you want the future where we become a spacefaring civilisation and are on many worlds and out there among the stars, or one where we are forever confined to Earth? And I say it is the first, and I hope you agree with me!


“The critical breakthrough that’s needed for us to become a spacefaring civilisation is to make space travel like air travel. So with air travel when you fly a plane, you fly that plane many times.

“At the risk of stating the obvious, it really, almost, any mode of transport – whether it’s a plane, a car, a horse, a bicycle – is reusable. You use that mode of transport many times. And if you had to get a new plane every time you flew somewhere, and even get to have two planes for a return journey, very few people could afford to fly. Or if you could use a car only once, very few people could afford to drive a car.

(Slide: Critical breakthrough to make life multiplanetary is for space travel to be like air travel – Requires rapidly reusable rockets.)

“So the critical breakthrough that’s necessary is a rapidly reusable orbital rocket. This is basically the Holy Grail of space, and the fundamental thing that’s required. And it is a very hard thing to do. It’s only barely possible with the physics of Earth. If Earth’s gravity was a little heavier, it would be impossible. And if Earth’s gravity was a little lighter, it would be quite easy.” (1:33-4:10)

And there you have it. What all the mainstream space agencies have been missing ever since Apollo 17 returned from the Moon: we need to –

  • Get fired up about a future in which we become a spacefaring civilisation;
  • Make space travel as economically viable as air travel;
  • Focus on developing rapidly reusable orbital rockets.

The Holy Grail of space, indeed!

This post is reblogged from the Astronautical Evolution website.

Return to the Moon, 50 Years On

Astronautical Evolution, issue 148 (originally posted 1 August 2019)

NASA has learned little

NASA’s attempts to return to the Moon 50 years after Apollo 11 in the form of the Artemis Program are painful to watch.

Orion approaches the Gateway station in lunar orbit
Orion approaches the Gateway station in lunar orbit sometime in the 2020s – maybe. (NASA)

True, NASA has learned a little since Eagle landed. It now expresses an interest in making its spacecraft reusable, and refuelling them in space and on the Moon. It talks of mining lunar water at the South Pole, and building a base with lunar regolith. And it’s inviting contributions from its commercial partners.

All this in support of the goal of Artemis, which is to “send the first woman and the next man to the Moon by 2024 and develop a sustainable human presence on the Moon by 2028.”

Maybe they’ll achieve this? Why not? Isn’t it a noble and worthwhile goal to strive for? Why spoil the party with skeptical comments?

Heroic versus systemic thinking

Ten years ago I discussed the difference between a heroic paradigm of operations and a systemic one. A heroic enterprise is one which requires a particular effort of political will on the part of a monolithic authority. A systemic one is based on the organic growth of a social system comprising a multitude of individual decision-makers. A heroic effort makes a giant leap into the unknown. A systemic one makes small, incremental steps whose cumulative effect is to transform society in a way which is not masterminded by any one actor (not even a government).

Apollo is the quintessential example of a heroic program. Others would include the Manhattan project, the voyages of exploration of 15th-century China, and any war of aggression. Systemic progress, on the other hand, is exemplified by such examples as the agricultural and industrial revolutions, and by the creeping globalisation of the world economy following the industrial revolution, based on key technologies of steam power, the electric telegraph and so on, as well as on mass literacy, mass production, the abolition of slavery and the invention of human rights.

In practice both processes are in play. Columbus’s discovery of the Americas was a heroic mission. But the growing transatlantic traffic that followed in its wake was of a different nature, propelled by the desire on the part of numerous adventurers for gold, land and other resources. Without the systemic growth of that traffic, and without the industrial revolution which greatly accelerated it, America, Europe, Africa, Asia and Australasia would today still be barely in contact.

Apollo needs to be succeeded by the systemic growth of traffic into orbit and to the Moon if NASA’s stated goal of returning to the Moon to stay is ever to be achieved.

Turning space travel from missions into an industry: the transport pyramid

Transport pyramid: thumbnail of first page
An Earth-Moon-Mars Passenger Transport Pyramid. (Journal of the British Interplanetary Society)

My recent article in JBIS, “An Earth-Moon-Mars Passenger Transport Pyramid”, shows how this might be achieved in practice. The key insight studied in this paper is that, in any normal sphere of human activity, easier, cheaper, shorter-range journeys are undertaken more frequently than more difficult, more expensive, longer-range ones.

Thus a typical person makes daily trips within their home town, weekly or monthly trips between cities, and annual international or intercontinental journeys. A voyage around the world or a visit to the North Pole, to the summit of Mount Everest, to the International Space Station or to the wreck of the R.M.S. Titanic is likely to be a once-in-a-lifetime event. The longer-range journeys, requiring greater investments of time, cost and preparation, appear higher up a notional pyramid of travel activity; the shortest-range journeys form the base.

We therefore need to sketch out a similar pyramid of activity for manned spaceflight. The resulting scenario would look roughly like this:

  • 10,000 travellers/year to and from low Earth orbit;
  • 1,000 travellers/year to and from highly eccentric Earth orbit with a sightseeing lunar encounter;
  • 100 travellers/year to and from a lunar surface settlement;
  • 20 travellers per two-year Earth-Mars synodic period to and from Mars.

The Mars travellers would all be professional astronauts; the travellers who go no further than low Earth orbit would be mostly taking a vacation in space.

Compare this scenario with NASA’s plans to see how unrealistic those plans are, and how unlikely it is that NASA will achieve its goal of “a sustainable human presence on the Moon by 2028”.

I believe that Elon Musk, too, will find out in the course of time that he cannot simply send thousands of people to Mars as an activity isolated from other space transport operations. Any such large-scale Mars traffic will need to rest on the technical maturity and economic profitability that can only be provided by a massive base of passenger transport within the Earth-Moon system.

This post is reblogged from the Astronautical Evolution website.