Aurora critiques

Various critiques and analyses of Kim Stanley Robinson’s excellent 2015 generation interstellar starship novel, Aurora.

Envisioning Starflight Failing

by Paul Gilster on July 31, 2015, centauri-dreams.org

Science fiction has always had its share of Earthside dystopias, but starflight’s allure has persisted, despite the dark scrutiny of space travel in the works of writers like J. G. Ballard. But what happens if we develop the technologies to go to the stars and find the journey isn’t worth it? Gregory Benford recently reviewed a novel that asks these questions and more, Kim Stanley Robinson’s Aurora (Orbit Books, 2015). A society that reaches the Moon and then turns away from it may well prompt questions on how it would react to the first interstellar expedition. Benford, an award-winning novelist, has explored star travel in works like the six novels of the Galactic Center Saga and, most recently, in the tightly connected Bowl of Heaven and Shipstar. His review is a revised and greatly expanded version of an essay that first ran in Nature.

by Gregory Benford

Human starflight yawns as a vast prospect, one many think impossible. To arrive in a single lifetime demands high speeds approaching lightspeed, especially for target stars such as Tau Ceti, about twelve light years away.

Generation ships form the only technically plausible alternative method, implying large biospheres stable over centuries. Or else a species with lifetimes of centuries, which for fundamental biological reasons seems doubtful. (Antagonistic plieotropy occurs in evolution, ie, gene selection resulting in competing effects, some beneficial in the short run for reproduction, but others detrimental in the long.) So for at least for a century or two ahead of us, generation ships (“space arks”) may be essential.

Aurora depicts a starship on a long voyage to Tau Ceti four centuries from now. It is shaped like a car axle, with two large wheels turning for centrifugal gravity. The biomes along their rims support many Earthly lifezones which need constant tending to be stable. They’re voyaging to Tau Ceti, so the ship’s name is a reference to Isaac Asimov’s The Robots of Dawn, which takes place on a world orbiting Tau Ceti named Aurora. Arrival at the Earthlike moon of a super-Earth primary brings celebration, exploration, and we see just how complex an interstellar expedition four centuries from now can be, in both technology and society.

In 2012, Robinson declared in a Scientific American interview that “It’s a joke and a waste of time to think about starships or inhabiting the galaxy. It’s a systemic lie that science fiction tells the world that the galaxy is within our reach.” Aurora spells this out through unlikely plot devices. Robinson loads the dice quite obviously against interstellar exploration. A brooding pessimism dominates the novel.

There are scientific issues that look quite unlikely, but not central to the novel’s theme. A “magnetic scissors” method of launching a starship seems plagued with problems, for example. But the intent is clear through its staging and plot.

I’ll discuss the quality of the argument Aurora attempts, with spoilers.

Plot Fixes

The earlier nonfiction misgivings of physicist Paul Davies (in Starship Century) and biologist E.O. Wilson (in The Meaning of Human Existence) about living on exoplanets echo profoundly here. As a narrator remarks, “Suspended in their voyage as they had been, there had never been anything to choose, except methods of homeostasis.” Though the voyagers in Aurora include sophisticated biologists, adjusting Earth life to even apparently simple worlds proves hard, maybe impossible.

The moon Aurora is seemingly lifeless. Yet it has Earth-levels of atmospheric oxygen, which somehow the advanced science of four centuries hence thinks could have survived from its birth, a very unlikely idea (no rust? – this is, after all, what happened to Mars). Plot fix #1.

This elementary error, made by Earthside biologists, brings about the demise of their colony plans, in a gripping plot turn that leads to gathering desperation.

The lovingly described moon holds some nanometers-sized mystery organism that is “Maybe some interim step toward life, with some of the functions of life, but not all … in a good matrix they appear to reproduce. Which I guess means they’re a life-form. And we appear to be a good matrix.” So a pathogen evolved on a world without biology? Plot fix #2.

Plans go awry. Backup plans do, too. “Vector, disease, pathogen, invasive species, bug; these were all Earthly terms … various kinds of category error.”

What to do? Factions form amid the formerly placid starship community of about 2000. Until then, the crew had felt themselves to be the managers of biomes, farming and fixing their ship, with a bit of assistance from a web of AIs, humming in the background.

Robinson has always favored collective governance, no markets, not even currencies, none of that ugly capitalism – yet somehow resources get distributed, conflicts get worked out. No more. Not here, under pressure. The storyline primarily shows why ships have captains: stress eventually proves highly lethal. Over half the crew gets murdered by one faction or another. There is no discipline and no authority to stop this.

Most of the novel skimps on characters to focus on illuminating and agonizing detail of ecosphere breakdown, and the human struggle against the iron laws of island biogeography. “The bacteria are evolving faster than the big animals and plants, and it’s making the whole ship sick!” These apply to humans, too. “Shorter lifetimes, smaller bodies, longer disease durations. Even lower IQs, for God’s sake!”

Robinson has always confronted the nasty habit of factions among varying somewhat-utopian societies. His Mars trilogy dealt with an expansive colony, while cramped Aurora slides toward tragedy: “Existential nausea comes from feeling trapped … that the future has only bad options.”

Mob Rules

Should the ship return to Earth?

Many riots and murders finally settle on a bargain: some stay to terraform another, Marslike world, the rest set sail for Earth. The ship has no commander or functional officers, so this bloody result seems inevitable in the collective. Thucydides saw this outcome over 2000 years ago. He warned of the wild and often dangerous swings in public opinion innate to democratic culture. The historian described in detail explosions of Athenian popular passions. The Athenian democracy that gave us Sophocles and Pericles also, in a fit of unhinged outrage, executed Socrates by a majority vote of one of its popular courts. (Lest we think ourselves better, American democracy has become increasingly Athenian, as it periodically whips itself up into outbursts of frantic indignation.)

When discord goes deadly in Aurora, the AIs running the biospheres have had enough. At a crisis, a new character announces itself: “We are the ship’s artificial intelligences, bundled now into a sort of pseudo-consciousness, or something resembling a decision-making function.” This forced evolution of the ship’s computers leads in turn to odd insights into its passengers: “The animal mind never forgets a hurt; and humans were animals.” Plot Fix #3: sudden evolution of high AI function that understands humans and acts like a wise Moses.

This echoes the turn to a Napoleonic figure that chaos often brings. As in Iain Banks’ vague economics of a future Culture, mere humans are incapable of running their economy and then, inevitably, their lives. The narrative line then turns to the ship AI, seeing humans somewhat comically, “… they hugged, at least to the extent this is possible in their spacesuits. It looked as if two gingerbread cookies were trying to merge.”

Governance of future societies is a continuing anxiety in science fiction, especially if demand has to be regulated without markets, as a starship must. (Indeed, as sustainable, static economies must.) As far back as in Asimov’s Foundation, Psychohistory guides, because this theory of future society is superior to mere present human will. (I dealt with this, refining the theory, in Foundation’s Fear. Asimov’s Psychohistory resembled the perfect gas law, which makes no sense, since it’s based on dynamics with no memory; I simply updated it to a modern theory of information.) The fantasy writer China Mieville has similar problems, with his distrust of mere people governing themselves, and their appetites, through markets; he seems to favor some form of Politburo. (So did Lenin, famously saying “A clerk can run the State.”)

Aurora begins with a society without class divisions and exploitation in the Marxist sense, and though some people seem destined to be respected and followed, nothing works well in a crisis but the AIs – i.e., Napoleon. The irony of this doesn’t seem apparent to the author. Similar paths in Asimov, Banks and Mieville make one wonder if similar anxieties lurk. Indeed, Marxism and collectivist ideas resemble the similar mechanistic theory of Freudian psychology (both invented by 19th C. Germans steeped in the Hegelian tradition) – insightful definitions, but no mechanisms that actually work. Hence the angst when things go wrong with a supposedly fundamental theory.

The AIs, as revealed through an evolving and even amusing narrative voice, follow human society with gimlet eyes and melancholy insights. The plot armature turns on a slow revelation of devolution in the ship biosphere, counterpointed with the AI’s upward evolution – ironic rise and fall. “It was an interrelated process of disaggregation … named codevolution.” The AIs get more human, the humans more sick.

Even coming home to an Earth still devastated by climate change inflicts “earthshock” and agoraphobia. Robinson’s steady fiction-as-footnote thoroughness brings us to an ending that questions generational, interstellar human exploration, on biological and humanitarian grounds. “Their kids didn’t volunteer!” Of course, immigrants to far lands seldom solicit the views of their descendants. Should interstellar colonies be different?

Do descendants as yet unborn have rights? Ben Finney made this point long ago in Interstellar Migration, without reaching a clear conclusion. Throughout human history we’ve made choices that commit our unborn children to fates unknown. Many European expeditions set sail for lands unseen, unknown, and quite hostile. Many colonies failed. Interstellar travel seems no different in principle. Indeed, Robinson makes life on the starship seem quite agreeable, though maybe tedious, until their colony goal fails.

The unremitting hardship of the aborted colony and a long voyage home give the novel a dark, grinding tone. We suffer along with the passengers, who manage to survive only because Earthside then develops a cryopreservation method midway through the return voyage. So the deck is stacked against them – a bad colony target, accidents, accelerating gear failures, dismay … until the cryopreservation that would lessen the burden arrives, very late, so our point of view characters do get back to Earth and the novel retains some narrative coherence, with character continuity. Plot Fix #4.

This turn is an authorial choice, not an inevitability. Earthsiders welcome the new cryopreservation technologies as the open door to the stars; expeditions launch as objections to generation ships go away. But the returning crew opposes Earth’s fast-growing expeditions to the stars, because they are just too hard on the generations condemned to live in tight environments – though the biospheres of the Aurora spacecraft seem idyllic, in Robinson’s lengthy descriptions. Plainly, in an idyllic day at the beach, Robinson sides with staying on Earth, despite the freshly opened prospects of humanity.

So in the end, we learn little about how our interstellar future will play out.

The entire drift of the story rejects Konstantin Tsiolkovskii’s “The Earth is the cradle of mankind, but humanity cannot live in the cradle forever.” – though we do have an interplanetary civilization. It implicitly undermines the “don’t-put-all-your-eggs-in-one-basket” philosophy for spreading humanity beyond our solar system. Robinson says in interviews this idea leads belief that if we destroy Earth’s environment, we can just move. (I don’t know anyone who believes this, much less those interested in interstellar exploration.) I think both ideas are too narrow; expansion into new realms is built into our evolution. We’re the apes who left Africa.

Robinson takes on the detail and science of long-lived, closed habitats as the principal concern of the novel. Many starship novels dealt with propulsion; Robinson’s methods – a “magnetic scissors” launch and a mistaken Oberth method of deceleration – are technically wrong, but beside the point. His agenda is biological and social, so his target moon is conveniently hostile. Then the poor crew must decide whether to seek another world nearby (as some do) or undertake the nearly impossible feat of returning to Earth. This deliberately overstresses the ship and people. Such decisions give the novel the feel of a fixed game. Having survived all this torment, the returning crew can’t escape the bias of their agonized experience.

Paul Davies pointed out in Starship Century that integrating humans into an existing alien biosphere (not a semi-magical disaster like his desolate moon with convenient oxygen) is a very hard task indeed, because of the probable many incompatibilities. That’s a good subject for another novel, one I think no one in science fiction has taken up. This novel avoids that challenge with implausible Plot fix #2.

Realistically considered, the huge problems of extending a species to other worlds can teach us about aliens. If interstellar expansion is just too hard biologically (as Paul Davies describes) then the Fermi paradox vanishes (except for von Neumann machines, as Frank Tipler saw in the 1970s). If aliens like us can’t travel, maybe they will expend more in SETI signaling? Or prefer to send machines alone? An even-handed treatment of human interstellar travel could shore up such ideas.

Still, a compelling subject, well done in Robinson’s deft style. My unease with the novel comes from the stacked deck its author deals.

A Science Critique of Aurora by Kim Stanley Robinson

by Paul Gilster on August 14, 2015, centauri-dreams.org

I haven’t yet read Kim Stanley Robinson’s new novel Aurora (Orbit, 2015), though it’s waiting on my Kindle. And a good thing, too, for this tale of a human expedition to Tau Ceti is turning out to be one of the most controversial books of the summer. The issues it explores are a touchstone for the widening debate about our future among the stars, if indeed there is to be one. Stephen Baxter does such a good job of introducing the issues and the authors of the essay below that I’ll leave that to him, but I do want to note that Baxter’s novel Ultima is just out (Roc, 2015) taking the interstellar tale begun in 2014’s Proxima in expansive new directions.

by Stephen Baxter, James Benford and Joseph Miller

“Ever since they put us in this can, it’s been a case of get everything right or else everyone is dead …” (Aurora Chapter 2)

This essay is a follow-up to a review of Kim Stanley Robinson’s new novel Aurora by Gregory Benford, which critically examines the case that Robinson makes in the book that “no starship voyage will work” (Chapter 7) – at least if crewed by humans. This is a strong statement, and even if the case is made in fictional form it needs to be backed up by a powerful and consistent argument. Greg criticises Robinson’s book mostly on sociological, political and ethical grounds.

Here, to complement Greg’s analysis, we take a critical look at the science in the book. Is Robinson’s ship a plausible habitat for a centuries-long voyage? Could the propulsion systems function as described? Is the planetary threat encountered by the would-be colonists biologically plausible?

This entry is mainly the initiative of Jim Benford, well known to readers of this blog; Jim is President of Microwave Sciences based in Lafayette, California, and his interests include electromagnetic power beaming for space propulsion. Also contributing has been Joseph Miller, biologist and neuroscientist, previously of the University of Southern California Keck School of Medicine, now at the American University of the Caribbean School of Medicine, with a long-time interest in extraterrestrial life. As for myself, I’m a science fiction writer, part-time contributor to such technical projects as the BIS-initiated Project Icarus, and author of some interstellar fiction myself, such as Ark (2009). And as the full-time writer I’m the one who got the privilege of writing up our conversations. Thanks, guys!

I should start by saying that Stan Robinson has been on my own (very short) list of must-read writers for the last twenty-five years at least, and that Aurora is a key book, as with all Robinson’s work deeply researched and deeply felt. If you haven’t bought the book yet, do so now.

Basics

Aurora is a tale of a multigeneration starship mission to Tau Ceti. (Note that Robinson’s starship is unnamed; here I’ve referred to it as “the Ship”.) The Ship reaches its target, but when it proves impossible to colonise the worlds there, a remnant of the crew struggles back to Earth.

This review is an analysis of technical and science aspects of this mission, based solely on evidence in the novel’s text. Of course any errors or misreadings of Robinson’s text are our sole responsibility.

We’ll be making comparisons with two classic studies. The BIS’s Project Daedalus (1978) was a study of an uncrewed interstellar probe which used the same fusion-rocket technology as did Robinson’s Ship in its deceleration mode. Daedalus had initial mass 50,000t (tonnes) of fuel (30kt deuterium (D), and 20kt helium-3 (He3)), the dry mass of its two stages amounted to 2700t, the payload was 450t, and the exhaust velocity was about 3.3%c, with cruise velocity 0.12c (c being the velocity of light). The Daedalus propulsion system was used only for acceleration; it couldn’t decelerate, and so was a flyby mission at its target star. In Aurora the Ship uses its fusion rocket only to decelerate.

Meanwhile the “Stanford Torus” space habitat design (Johnson, 1976) was a product of a 1975 workshop involving NASA Ames and Stanford University. The final design was a torus 1790m across with the habitable tube 130m in diameter. Of a total surface area of about 2.3km², 10,000 people would inhabit a usable surface area of about 0.7 km². The station, located at L5, would be built of lunar resources. The total mass would be about 10 million t, of which 9.9 million t would be a radiation shield of lunar slag around the habitable ring in a layer 1.7m thick, leaving 0.1 million t as structural mass. The relevance to Aurora is that the Ship looks like two Stanford Toruses attached to a central spine.

Let’s begin by looking at the Ship’s construction and inhabitants.

The Ship

Construction

Most of what we learn about the Ship’s structure is given in Chapter 2. The Ship consists of a central spine 10km long, around which 2 rings of habitable “biomes” spin, torus-like. Each ring consists of 12 cylindrical biomes, each 4km long, 1km diameter. There are also spokes and inner rings. The rings rotate around the spine to give a centrifugal gravity of 0.83g.

The 24 biomes contain samples of ecospheres from 12 climatic zones: Old World versions in one ring, New World in the other. Each biome has a “roof” with a sunline, which models the required sunlight and seasonality, and a “floor” on the side away from the spine. The liveable area in each cylinder is given as about 4 km², which is about a third of the cylinder’s inner surface area: 96km² total. In each biome there are stores under the “floor”, including fuel; we’re told this is used as a radiation shield during the cruise.

The total habitable space is allocated as 70% agricultural; 5% urban / residential; 13% water; 13% protected wilderness. The wilderness areas are meant to be complete ecologies.

The crew numbers given appear contradictory; in some places Robinson states there are about 2100 total, but elsewhere is given a number of 300 people per biome which would total 7200. The crew numbers do vary through the centuries-long mission, with births and deaths.

How reasonable are these numbers, given the mission’s objectives? Could the Ship support that many people? Are they enough to found a human population at the target? And is there room for true wilderness?

Closed Ecologies

We don’t yet know how to maintain closed ecologies for long periods. The Ship’s biomes would suffer from small-closed-loop-ecology buffering problems, as Robinson illustrates very well in the text; we see the crew having to micro-manage the biospheres, and dealing with such problems as the depletion of key trace elements through unexpected chemical reactions. In some ways this may prove to be an even more daunting obstacle to interstellar exploration than propulsion systems.

Human population

If there are 300 people per biome, and given a total of 96km² habitable area, that’s a population density of 75 /km². Compare this with Earth’s global average of 13 /km² ; crowded southern England is 667 / km². In terms of the ability of the agricultural space (70% of total) to support the crew, that seems reasonable to us.

But if only 5% of the space is used for residential purposes, the effective living density is high, at 1500 per km² – comparable to densely populated urban areas such as Hong Kong. Such densities would seem problematic on a long-duration mission, though of course the crew do have access to the other 95% of the habitable areas; people hike the wildernesses.

This group is of course meant to be sufficient to found a new human breeding population on a virgin world. What is the minimal population size to maintain the species without an evolutionary bottleneck? Something like 1000 is a good guess. Robinson’s original population was at least twice that. If that population size was maintained, genetic diversity would plausibly be sufficient.

“Wilderness”

We’re told (Chapter 2) that each biome has about 4km² of living space and that 13% of that space is given over to “wilderness”, that is 0.52 km² per biome. The ecologies can include apex predators. In a biome called Labrador, for instance, “In the flanking hills sometimes a wolf pack was glimpsed, or bears” (chapter 2).

This idea is explored in more depth in Robinson’s 2312, in which mobile habitats called “terraria”, hollowed-out asteroids, are used as reserves for species threatened on a post-climate-change Earth. But even these terraria are not very large in terms of the space needed by wildlife in nature. A wolf pack, consisting of about 10 animals, may have a territory of 35 km² (Jędrzejewski et al, 2007). A 2312 terrarium with an inner surface area of about 160 km² would have room for only about 4 packs, or about 40 individual animals, a small population in terms of genetic diversity.

It seems clear that the much smaller biomes of the Ship, though large in engineering terms, would be far too small to be able to host meaningful numbers of many animal species in anything resembling a natural population distribution. A wilderness needs a lot of room.

Mass

We are given a mass breakdown for the Ship as a whole. We’re told that during the Ship’s cruise phase, when it is fully laden with fuel, the total mass is 76% fuel, 10% each biome ring, and 4% the spine.

We aren’t told the Ship’s total mass, however, and to study the propulsion system’s performance we’ll need at least a guesstimate. This is derived by a comparison with the Stanford Torus design.

Each torus-like biome ring consists of 12 pods of length 4km, diameter 1km. So the surface area of 1 pod is 14.1 km², including end caps. And the surface area of one biome ring is 170 km² (which is much larger than the Stanford Torus).

The Ship’s biomes seem to lack a Stanford-like cloak of radiation-shielding material. Robinson says that “fuel, water and other supplies” are stored under the biome floors to provide shielding; the ceilings are shielded by the presence of the spine. Elsewhere Robinson says that during the voyage, the fuel is “deployed as cladding around the toruses and the spine” (Chapter 2)

Assume then that if a Ship biome ring has the same structural properties as the Stanford torus, and if most of its mass is in the hull, then a guesstimate for a single ring mass (without the fuel cladding) can be obtained by multiplying Stanford’s 0.1m tons structure mass (without shielding) by a factor to allow for the Ship ring’s larger surface area. The result is (0.1 * 170 / 2.3 =) 7.4 million tons per biome ring. We know this is 10% of the Ship’s total mass, which therefore breaks down as

76% fuel = 56.2 million tons
20% biome rings = 14.8 million tons
4% spine = 3 million tons
Total = 74 million tons.

These numbers shouldn’t be taken seriously, of course, except as an order of magnitude guide. Maybe they seem large – but remember that Daedalus needed 50,000t of fuel to send a 450t payload on a flyby mission to the stars, a payload comparable to the completed mass of the ISS. By comparison the Ship will be hauling two habitat rings each fifteen kilometres across. This is not a modest design.

Notice that if the Ship’s propulsion follows the Daedalus ratio, the fuel would consist of 60% D = 33.7m tons, 40% He3 = 22.5m tons.

And notice that since this fuel is used for deceleration only, the acceleration systems need to push all this mass up to ten per cent of lightspeed. These numbers do illustrate the monstrous challenges of interstellar travel, with a need to send very large masses to very large velocities, and decelerate them again.

On that note, let’s consider the propulsion systems.

Propulsion

Mission Profile

The Ship is a generation starship. Launched in 2545, it travels 11.8ly (light years) to Tau Ceti at cruise 0.1c (chapter 2). According to the text the journey consists of a number of phases.

The Ship is accelerated to the cruise speed of 0.1c by means of electromagnetic “scissors” slingshot at Titan, imposing a brief’ acceleration of about 10g, and then a laser impulse for 60 years.
The Ship decelerates at the Tau Ceti system using its on-board fusion propulsion system. The technology, like that used by Daedalus, is known as “inertial confinement fusion” (ICF), in which pellets of fuel are compressed, perhaps with laser or electron beams, until they undergo fusion; the high-speed products provide a rocket exhaust. For twenty years the Ship is decelerated by the detonation of fusion pellets at a rate of two per second. The fusion fuel is a mix of D and He3, as was the case for Daedalus (Chapter 1).
We’re told that the total journey time is about 170 years (Chapter 3), consistent with the profile given.
Colonisation in the Tau Ceti system is attempted and fails (this will be considered below).
A section of the crew chooses to return to the Solar System. The ICF system is refuelled at Tau Ceti, and used to accelerate the Ship to 0.1c (Chapter 5).
As the Ship’s systems break down, the surviving crew completes the final leg of the journey in cryosleep.
The Ship has no onboard way to decelerate at the Solar System (Chapter 6). The ICF fuel was exhausted by the acceleration from Tau Ceti, save for a trickle to be used during Oberth Manoeuvres (see below). The laser system reduces the Ship’s speed, but not to rest: from 10%c to 3%c. We’re told that the Ship then sheds the rest of this velocity mostly with 28 Oberth Manoeuvres, using the gravity wells of the sun, Jupiter, and other bodies. This process takes 12 years before crew shuttles are finally returned to Earth.

We can consider these phases in turn.

Acceleration from Solar System

In considering the acceleration system, it should be borne in mind that what we need to do is to give a very large, fuel-laden Ship sufficient kinetic energy for it to cruise at 0.1c. And because of inevitable inefficiencies, the energy input to any acceleration system will have to be that much greater.

In fact the launch out of the Solar System is a combination of two methods, vaguely described, neither of which is remotely efficient. There’s a “magnetic scissor” that accelerates the ship over 200 million miles: “… two strong magnetic fields held the ship between them, and when the fields were brought together, the ship was briefly projected at an accelerative force equivalent to 10 g’s”.

(Of course such acceleration would stress the crew, even though in tests humans have survived such accelerations for very short periods – indeed the book claims five crew died. And such acceleration could stress lateral structures, such as the spars to the biome rings. Perhaps the stack is launched with its major masses in line with the thrust, and reassembled later.)

In Jim Benford’s grad school days, he ran some actual experiments on this effect, using a single turn coil. The energy in the capacitor bank driving it was about 1 kJ and the subject of the acceleration was a screwdriver sitting on a piece of wood in the coil centre. The coil current pulsed to peak in 2 µs. The screwdriver was accelerated across the room to a target at about 10 meters per second. The kinetic energy of the screwdriver was about 5 J and therefore the efficiency of transfer was less than 1%. It seems unsafe to assume an efficiency much better than this.

For the Ship, there then follows a laser driven acceleration. While lasers can certainly accelerate light craft, as has been shown experimentally, they can’t accelerate the enormously massive vehicle that the novel describes. The power required to accelerate by reflection of the laser photons can be calculated from the Ship mass (74 million tons), final velocity and acceleration time (to 0.1c in 60 years, so 0.17% g). The amount of power is about 100,000 TW, a truly astronomical scale. (Earth’s present electrical power output is 18 TW.) The efficiency of power beaming is low because only momentum is transferred from the photons to the ship. Efficiency is the time-averaged ratio of velocity to the speed of light. Therefore the efficiency of this process is about 5%.

The Ship and its mission would have to be a project of a very wealthy and very powerful interplanetary civilisation. It seems unlikely that they would resort to such a hopelessly inefficient system, if it could be made to work at all.

Deceleration at Tau Ceti

The Ship uses its onboard fusion rocket to decelerate.

We’re told the ICF deceleration phase takes 20 years at 0.005g, starting from 10%c cruise speed, with a Ship with an initial fuel load of 76% total mass. These numbers enable us immediately to calculate one critical number, the exhaust velocity of the fusion rocket. A ship with 76% fuel mass has a mass ratio (wet mass / dry mass) of (100/24=) 4.17. The rocket equation tells us that given that mass ratio and a total velocity change of 0.1c, the exhaust velocity must be 7%c. This is twice that of Daedalus, but perhaps not impossible for an advanced ICF system.

Our mass guesstimate above allows us to assess the performance of the rocket. Consuming 56.2mt of fuel in 20 years gives a mass usage rate of 94 kg/sec (cf Daedalus first stage 0.8 kg/sec). (Notice that the two fusion “pellets” consumed per second are pretty massive beasts; in the Daedalus design pellets a few millimetres across were delivered at a rate of hundreds per second. This detail may be implausible. Indeed 49kg may be larger than fission critical mass!)

You can find the rocket’s thrust by multiplying mass usage by exhaust velocity, to get about 2000 MN (megaNewtons). This is much larger than the Daedalus first stage’s 8 MN. And the rocket power is 20,000 TW (the Daedalus first stage delivered 30 TW). Note that this power number is comparable to the launch figures.

Again, these numbers can be taken only as a guide. But you can see that the power generated needs to be maybe three orders of magnitude better than Daedalus, and exceeds our modern global usage by four orders of magnitude.

Meanwhile this system would consume a heck of a lot of fusion fuel. Where would you acquire that fuel, and where would you store it?

The storage is the easy part, relatively. Daedalus’s 50 kt of fuel was stored in six spherical cryogenic tanks with total volume 76,000 m³. At similar densities to store the Ship’s fuel load would require 860 million m³. That sounds a lot, but the volume of a biome ring is about 38 billion m³, so the fuel volume is only 2% of this, making it plausible that it could be stored, as Robinson says, in cladding tanks on the biome rings and spine, without requiring large separate structures. The Ship is big but hollow. It’s not immediately clear however how effective a layer of fuel would be as a cosmic radiation shield.

And note that the need for cryogenic store over centuries before use would be a challenge – as would the need to store any short-half-life propulsion components such as tritium, which has a half-life of 12.3 years, and would decay away long before the 170-year mission was over.
Getting hold of the fusion fuel, meanwhile, is the tricky part. It’s hard to overstate the scarcity of He3 in the Solar System, and presumably at Tau Ceti. Even Daedalus’s 20,000t would deplete the entire inventory of the isotope on Earth (37,000t), and the Ship’s 22.5mt would dwarf the Moon’s store (1 million t); only the gas giants could reasonably meet this demand (the Daedalus estimate was that the Jovian atmosphere contains about 1016 t). The Daedalus design posited acquisition from Jupiter, but estimated that to acquire Daedalus’s fuel load in 20 years would require that the Jovian atmosphere be processed at a rate of 28 tonnes per second. So again the challenge for the Ship’s engineers will be three orders of magnitude more difficult.

And regarding the return journey, although the Ship is stripped down, a fuel load of similar order of magnitude must be acquired from the Tau Ceti system, and without the assistance of a Solar-System-wide infrastructure. Of this huge project, Robinson says only that “volatiles came from the gas giants” (Chapter 4).

Deceleration at Solar System

At the end of the novel, the Ship returns to Earth, decelerating mostly using what is called the “Oberth Manoeuvre”, invented by Hermann Oberth in 1928. This is a two-burn orbital manoeuvre that would, on the first burn, drop an orbiting spacecraft down into a central body’s gravity well, followed by a second burn deep in the well, to accelerate the spacecraft to escape the gravity well. A ship can gain energy by firing its engines to accelerate at the periapsis of its elliptical path.

Robinson wants to use this to decelerate from 3% of light speed down to Earth orbital velocity. 3% of lightspeed is 9,000 km/s. For reference, Earth’s orbital velocity is 30 km/s. Several deceleration mechanisms are referred to in the book. An unpowered gravity assist, passing by the sun and reversing direction, can steal energy from the sun’s rotational motion around the centre of the galaxy. That’s worth about 440 km/s. Other unpowered gravity assists can be used once the ship is in a closed orbit in the sun’s gravitational well. Flybys for aerobraking in the atmospheres of the gas giants are referred to as well. Altogether, these can get you <100 km/s.

But the key problem with using the Oberth Manoeuvre for deceleration of this returning starship is that this craft is on an unbound orbit. That means that, on entering the Solar System its trajectory can be bent by the sun’s gravity, but will then exit the System because it has not lost enough velocity to be bound to the Solar System. To be bound would require velocity decreased down to perhaps 100 km/sec, which is 1% of the incoming velocity. Therefore 99% of the deceleration has to take place in the first pass. And you can’t get that much from an Oberth Manoeuvre.

Cryosleep

As the Ship’s systems collapse, the returning crew gets from Earth plans to build a cryonic cold sleep method, which allows the viewpoint characters to survive until they reach the Earth.

This technology logically undermines most of the problems the early parts of the novel confront, and therefore undermines most of Robinson’s point about the difficulty of interstellar travel: If only the colonists had waited a few centuries for cryo technology, it would all have been so much easier! But this contradicts Robinson’s thesis.

Aurora

Having arrived at Tau Ceti, the colonists’ target planet, called Aurora, is judged lifeless but habitable from a remote sensing of an oxygen atmosphere – presumed created by non-biological process billions of years ago – but in the event the environment proves lethal for humans because of the presence of a deadly “prion”.

In a sense this is the point of the novel, that even if we reach the stars we will find only dead or hostile worlds: “I mean, they [alien worlds] are all going to be dead or alive, right? If they’ve got water and orbit in the habitable zone, they’ll be alive. Alive and poisonous … What’s funny is anyone thinking it [interstellar colonisation] would work in the first place” (chapter 3). And as Greg noted in his essay this reflects recent misgivings expressed by Paul Davies and others about the habitability by Earth life of exoplanets.

Is this reasonable? And is Robinson correct that this could be the solution to Fermi’s famous paradox?

Robinson seems to be saying “alive” worlds will be toxic to all possible biological explorers (there is a little wiggle room here since non-biological automated probes might still survive such worlds). This is a bold statement, but plausible since we lack any relevant data. However Robinson also says “dead” worlds, essentially rocky Earth-size planets in the Goldilocks zone, could be terraformed but that project would take thousands of years. But why should that matter in a galaxy that is billions of years old? There should be plenty of time to terraform such planets, either by biological explorers or perhaps some type of self-replicating von Neumann probes or seed ships. There appears to be no solution in Aurora to Fermi’s question.

Oxygen and Biosignatures

(See Sinclair et al (2012) for a relevant reference.)

It seems implausible that oxygen in Aurora’s atmosphere might not be a biosignature: that is, that it could credibly be created by non-biological processes. Without some continual input into the atmosphere, you would expect any oxygen to rust out, as on Mars. Robinson says the oxygen on Aurora is due to the ultraviolet breakdown of water. We haven’t run the numbers, but that would be a hell of a lot of UV (which itself could make the planet uninhabitable). That might actually work better as a mechanism for oxygen production on Mars, at least long ago when Mars had liquid water. Indeed, UV is how Mars lost its water and atmosphere, and the same would happen on a dead Earthlike world. So Aurora can’t have oxygen; it gets blown off after the hydrogen from water.

Robinson also cites a failure to detect CH4 and H2S, possible markers of life, in Aurora’s air as ruling out a biological origin for the oxygen. However the interpretation of the presence of methane (CH4) in the Martian atmosphere has been a bone of contention for well over 15 years. Is it a biomarker or an index of geological activity? And as far as hydrogen sulphide goes, it sure as hell is not a biomarker on Io!

The “Prion”

The most significant biological problem in Robinson’s scenario is the organism that was so toxic to humans on Aurora. This is said to be “something like a prion”, and is apparently an isolated organism: as far as the explorers could tell there simply was no wider biosphere on Aurora.

For a biologist, that sounds really weird. This is a satellite a couple of billion years older than Earth and the only evolved organism is a prion? In addition we are not sure what “something like” really means, but if it was indeed like a prion one must ask: where on Aurora are the proteins capable of being misfolded by a prion action? That’s what prions do; they cannot exist in isolation. And then why was it that human proteins, from a different biosphere altogether, were such a good match to the prion’s mechanisms?

Of course you can say it was “something like” a prion but not really a prion. But then, what makes it “like” a prion if not protein-folding?

It would take a lot more detail to make this strange single-organism biosphere a plausible ecosystem. Maybe if Robinson ever revisits Aurora and the stayers we could find out! Joe Miller thinks that an Andromeda Strain-like organism, inimical to Earth biology, is no more or less likely than ET organisms which simply find Earth biology indigestible. We don’t know, but the possibility that ET biology would be simply oblivious to Earth biology is a plausible situation, though not treated very much in SF because it is not very dramatic!

Conclusions

Robinson’s Aurora is a finely crafted tale of human drama and interstellar exploration. Its polemic purpose appears to be to demonstrate, in Robinson’s words, that “no [human-crewed] starship voyage will work”. There is much of the science and technology we haven’t explored in this brief note; there’s probably a master’s thesis here – indeed I’ve recommended the book to Project Icarus as a study project.

However, to summarise our conclusions:

The human crew transported to Aurora may plausibly be large enough to support a new breeding population. And the Ship’s dimensions seem adequate to support the crew through their centuries-long mission.
The challenge of maintaining small closed biospheres is depicted credibly, but the “wilderness” areas of the biome arks are too small for their purpose.
Of the elements of the propulsion system, the electromagnetic / laser Solar System acceleration system needs to be so powerful it stretches credibility, while the Oberth Manoeuvre return-deceleration system as depicted is impossible. The ICF fusion rocket system appears generally credible, but would require the acquisition of heroic amounts of helium-3 fuel, a challenge especially at Tau Ceti.
Regarding Aurora itself, the notions of a non-biogenic oxygen atmosphere, and of a single-organism biosphere, and that an extraterrestrial organism as described might necessarily be inimical to humans, all lack credibility.

In summary, while Aurora is an intriguing combination of literary, political, scientific and technical notions, and while it reflects many current speculations about the difficulty of interstellar travel, in many instances it lacks the supporting credible scientific and technical detail required to make its polemic case that human interstellar travel is impossible. The journey is not plausible, and nor is the destination.

What Aurora illustrates very well, however, at least at an impressionistic level, is the tremendous difficulty of mounting such a voyage. Interstellar travel is a challenge for future generations, which will bring both triumph and tragedy.

References

Kim Stanley Robinson, Aurora, Orbit, 2015.

Kim Stanley Robinson, 2312, Orbit, 2012.

Bond et al, Project Daedalus Final Report, British Interplanetary Society, 1978.

Johnson, Richard D. and Holbrow, Charles, (editors), “Space Settlements: A Design Study”, NASA SP-413, 1977.

Jędrzejewski W, Schmidt K, Theuerkauf J, Jędrzejewska B, Kowalczyk R. 2007. “Territory size of wolves Canis lupus: linking local (Białowieża Primeval Forest, Poland) and Holarctic-scale patterns”. Ecography 30: 66–76.

Sinclair, S., Schulze-Makuch, D., Radl

What Will It Take for Humans to Colonize the Milky Way?

Kim Stanley Robinson, scientificamerican.com

The idea that humans will eventually travel to and inhabit other parts of our galaxy was well expressed by the early Russian rocket scientist Konstantin Tsiolkovskii, who wrote, “Earth is humanity’s cradle, but you’re not meant to stay in your cradle forever.” Since then the idea has been a staple of science fiction, and thus become part of a consensus image of humanity’s future. Going to the stars is often regarded as humanity’s destiny, even a measure of its success as a species. But in the century since this vision was proposed, things we have learned about the universe and ourselves combine to suggest that moving out into the galaxy may not be humanity’s destiny after all.

The problem that tends to underlie all the other problems with the idea is the sheer size of the universe, which was not known when people first imagined we would go to the stars. Tau Ceti, one of the closest stars to us at around 12 light-years away, is 100 billion times farther from Earth than our moon. A quantitative difference that large turns into a qualitative difference; we can’t simply send people over such immense distances in a spaceship, because a spaceship is too impoverished an environment to support humans for the time it would take, which is on the order of centuries. Instead of a spaceship, we would have to create some kind of space-traveling ark, big enough to support a community of humans and other plants and animals in a fully recycling ecological system.

On the other hand it would have to be small enough to accelerate to a fairly high speed, to shorten the voyagers’ time of exposure to cosmic radiation, and to breakdowns in the ark. Regarded from some angles bigger is better, but the bigger the ark is, the proportionally more fuel it would have to carry along to slow itself down on reaching its destination; this is a vicious circle that can’t be squared. For that reason and others, smaller is better, but smallness creates problems for resource metabolic flow and ecologic balance. Island biogeography suggests the kinds of problems that would result from this miniaturization, but a space ark’s isolation would be far more complete than that of any island on Earth. The design imperatives for bigness and smallness may cross each other, leaving any viable craft in a non-existent middle.

The biological problems that could result from the radical miniaturization, simplification and isolation of an ark, no matter what size it is, now must include possible impacts on our microbiomes. We are not autonomous units; about eighty percent of the DNA in our bodies is not human DNA, but the DNA of a vast array of smaller creatures. That array of living beings has to function in a dynamic balance for us to be healthy, and the entire complex system co-evolved on this planet’s surface in a particular set of physical influences, including Earth’s gravity, magnetic field, chemical make-up, atmosphere, insolation, and bacterial load. Traveling to the stars means leaving all these influences, and trying to replace them artificially. What the viable parameters are on the replacements would be impossible to be sure of in advance, as the situation is too complex to model. Any starfaring ark would therefore be an experiment, its inhabitants lab animals. The first generation of the humans aboard might have volunteered to be experimental subjects, but their descendants would not have. These generations of descendants would be born into a set of rooms a trillion times smaller than Earth, with no chance of escape.

In this radically diminished enviroment, rules would have to be enforced to keep all aspects of the experiment functioning. Reproduction would not be a matter of free choice, as the population in the ark would have to maintain minimum and maximum numbers. Many jobs would be mandatory to keep the ark functioning, so work too would not be a matter of choices freely made. In the end, sharp constraints would force the social structure in the ark to enforce various norms and behaviors. The situation itself would require the establishment of something like a totalitarian state.

Of course sociology and psychology are harder fields to make predictions in, as humans are highly adaptable. But history has shown that people tend to react poorly in rigid states and social systems. Add to these social constraints permanent enclosure, exile from the planetary surface we evolved on, and the probability of health problems, and the possibility for psychological difficulties and mental illnesses seems quite high. Over several generations, it’s hard to imagine any such society staying stable.

Still, humans are adaptable, and ingenious. It’s conceivable that all the problems outlined so far might be solved, and that people enclosed in an ark might cross space successfully to a nearby planetary system. But if so, their problems will have just begun.

Any planetary body the voyagers try to inhabit will be either alive or dead. If there is indigenous life, the problems of living in contact with an alien biology could range from innocuous to fatal, but will surely require careful investigation. On the other hand, if the planetary body is inert, then the newcomers will have to terraform it using only local resources and the power they have brought with them. This means the process will have a slow start, and take on the order of centuries, during which time the ark, or its equivalent on the alien planet, would have to continue to function without failures.

It’s also quite possible the newcomers won’t be able to tell whether the planet is alive or dead, as is true for us now with Mars. They would still face one problem or the other, but would not know which one it was, a complication that could slow any choices or actions.

So, to conclude: an interstellar voyage would present one set of extremely difficult problems, and the arrival in another system, a different set of problems. All the problems together create not an outright impossibility, but a project of extreme difficulty, with very poor chances of success. The unavoidable uncertainties suggest that an ethical pursuit of the project would require many preconditions before it was undertaken. Among them are these: first, a demonstrably sustainable human civilization on Earth itself, the achievement of which would teach us many of the things we would need to know to construct a viable mesocosm in an ark; second, a great deal of practice in an ark obiting our sun, where we could make repairs and study practices in an ongoing feedback loop, until we had in effect built a successful proof of concept; third, extensive robotic explorations of nearby planetary systems, to see if any are suitable candidates for inhabitation.

Unless all these steps are taken, humans cannot successfully travel to and inhabit other star systems. The preparation itself is a multi-century project, and one that relies crucially on its first step succeeding, which is the creation of a sustainable long-term civilization on Earth. This achievement is the necessary, although not sufficient, precondition for any success in interstellar voyaging. If we don’t create sustainability on our own world, there is no Planet B.

Interstellar Travel and Straw Men

Stephen Ashworth, Oxford, UK

A gloomy prognosis

A bizarre article appeared on the Scientific American website on 13 January under the byline of well-known science fiction author Kim Stanley Robinson, entitled What Will It Take for Humans to Colonize the Milky Way? Bizarre, because it shows a failure of imagination from someone whose imagination is his main professional skill, contains factual errors, and discusses only the Earth-to-Earthlike-exoplanet model of interstellar travel despite the fact that the literature, going back to the 1984-1985 worldship papers in the Journal of the British Interplanetary Society, shows this to be a straw man.

Robinson is notorious for his novel Aurora, published last year and portraying a dysfunctional multi-generation interstellar worldship. Listen to the author talking about his novel on YouTube.

While the question in the title of Robinson’s Scientific American article is a perfectly fair one, Robinson is initially more interested in pouring cold water on the whole idea of manned interstellar spaceflight: “things we have learned about the universe and ourselves combine to suggest that moving out into the galaxy may not be humanity’s destiny after all”.

The distances between the stars are, obviously, mind-bogglingly vast. But not as vast as Robinson claims. Tau Ceti is the target star in his novel, with a distance of around 12 light years from the Sun. Robinson interprets this for Scientific American readers as “100 billion times farther from Earth than our moon”. A little simple arithmetic shows that the true value is 300 million times the lunar distance, a factor of over 300 less than he states.

Wisely, Robinson avoids giving any further numbers, and uses only qualitative arguments. Instead of a spaceship, we would need an interstellar ark (true). The ark would need to be small enough to accelerate to high speed, but large enough to carry a fully recycling ecological system: “The design imperatives for bigness and smallness may cross each other, leaving any viable craft in a non-existent middle” (speculative and not backed up by any detailed calculation).

He states (and again in the YouTube video) that the bigger the ark is, the proportionally more fuel it would have to carry: “this is a vicious circle that can’t be squared”. Maybe it would be a vicious circle if it were true, but it is not. A large ship would need the same proportion of fuel (the same mass ratio of initial to final mass) as a small ship for the same performance engine and the same trajectory.

He allows that humans are “highly adaptable”, but finds that the social system on board his ark would have to resemble a totalitarian state. On top of which, “Add to these social constraints permanent enclosure, exile from the planetary surface we evolved on, and the probability of health problems, and the possibility for psychological difficulties and mental illnesses seems quite high. Over several generations, it’s hard to imagine any such society staying stable.”

Did a science fiction author just utter the words “it’s hard to imagine”? Well, if his imagination is not up to the job, there are plenty of other authors of speculative fiction who can achieve that intellectual feat. Particularly when they consider that, to our ancestors living before the neolithic revolution, our present-day jungle of social, financial and legal constraints, confinement for most of our lives to the enclosed spaces of houses, shops, factories, offices and transport vehicles, exile from the African savannah we evolved in and exposure to the diseases caused by living in close quarters with millions of other people would have seemed terrifying. They would have found it hard to imagine any city-dwelling society staying stable.

After discussing the biological and social problems on board, Robinson talks about the difficulties of occupying an Earthlike planet at the destination as if no other option existed. His conclusion: “All the problems together create not an outright impossibility, but a project of extreme difficulty, with very poor chances of success.”

His answer to the question posed in the title consists of three preconditions for interstellar voyaging: (1) a sustainable civilisation on Earth itself, (2) a practice ark orbiting the Sun to provide a proof of concept, and (3) extensive robotic exploration of nearby stars to see if any of their planets are suitable candidates for human habitation.

What it would really take

Robinson’s assessment is based on the unstated assumption that humans can only realistically inhabit Earth and closely Earthlike planets (such as Mars, the subject of his famous Mars trilogy). The voyage must therefore begin from Earth, and must end at an Earth-analogue world orbiting another star (or at an Earth-analogue satellite of a giant exoplanet as in Aurora, and of course in James Cameron’s Avatar and Buzz Aldrin’s Tiber). The target world is only usable if it allows shirtsleeve surface habitation, or can be terraformed into such a state.

If this assumption is correct, then no manned interstellar voyaging will be possible at all. The project would be simply too great for a one-planet civilisation to attempt (see my technical papers on the subject in JBIS here and here).

Robinson is apparently not acquainted with the astronautical classics such as Gerard O’Neill’s The High Frontier, which is famous for making the point that the surface of a planet is not the best place to locate a technological civilisation, or John S. Lewis’s Mining the Sky, which details the resources available in the asteroid belt.

What Robinson is offering us in this Scientific American post is basically the Wright brothers, circa 1904, stating that transatlantic air travel is a project of extreme difficulty with very poor chances of success, and proving this by referring to the capabilities of the Wright Flyer. But they do allow that it might one day be possible, if a second Wright Flyer was to be built before the final, transatlantic one, in order to fly it around the east coast of America to test it and prove the concept.

Obviously, what actually happened was that, by the time people were ready to attempt the Atlantic crossing by aeroplane, thousands of aircraft were in daily use, and many generations removed from the original Wright Flyer.

Similarly, it should be equally obvious that, by the time people are ready to attempt the first interstellar crossing by worldship, thousands of space colonies with worldship-type living environments, and thousands of interplanetary vehicles using high-power propulsion, will be widespread throughout the Solar System. The problems which Robinson raises will have been addressed over centuries of gradual extraterrestrial development involving billions of people. And in order to grow the Solar System economy to the point that interstellar voyages will be affordable, an extraterrestrial population very much larger than Earth’s will be needed; larger even than can realistically be accommodated on all the terrestrial surfaces of the Solar System with lunar gravity or better (Earth, Moon, Mars, Venus, Ganymede, Callisto, Titan).

An interstellar worldship is basically an extreme space colony: to the majority of its occupants, it will be a world for living in, not a vehicle at all. Such a thing can only be built after a long process of gradual evolution of human capabilities for living in space at locations progressively more remote from Earth. There will be colonies in the asteroid belt, the Jupiter trojans, the rings of Saturn, the Centaurs, even the Kuiper belt.

But this also means that the travellers are released from any dependence on finding an Earth-analogue destination planet: an asteroid belt or collection of small moons will be preferable, as these can supply the raw materials to build more of the type of accommodation which they are used to and which they consider most natural.

The voyage can then be to almost any nearby main-sequence star, not to the minority of stars with an Earth-analogue planet. The journey will therefore be shorter: Alpha Centauri, for example, is only 37 per cent of Tau Ceti’s distance from the Sun, and very probably an even smaller fraction of the distance to the nearest star with an acceptably Earth-analogue exoplanet or exosatellite.

Robinson’s propulsion circle can be squared without resorting to fantasy physics: thanks to the Daedalus Report from 1978 (now republished by the British Interplanetary Society) we know that nuclear fusion is perfectly capable of giving cruising speeds of a few per cent of the speed of light, and hence crossing times of a few centuries for the nearest stars and several centuries to more distant ones, such as Tau Ceti (say 600 years cruising at 2 per cent of light speed).

Any exoplanet truly resembling Earth, thus with its own biosphere, will therefore be more valuable as an object of non-invasive scientific study than as a target for colonisation, removing one of the common popular objections to interstellar travel.

A ship with a dry mass of one million tonnes (less than the mass of Robinson’s ship; see the analysis by Stephen Baxter and others on Centauri Dreams) for around a thousand passengers, boosted to 2 per cent of light speed, and decelerated at the destination, using an efficient nuclear fusion rocket engine (with exhaust velocity 7500 km/s, less than that calculated for Daedalus) would have an energy budget of about 100 ZJ (one zettajoule = 1021 J), thus equivalent to current global industrial energy consumption (~ 0.5 ZJ per year) extended over a period of almost 200 years.

While this is way out of reach for any plausible Earth-based society (and even more so if the estimated dry mass of Robinson’s ship of 18 million tonnes is used instead, and if the speed is increased to his 0.1c), a wealthy Solar System civilisation, the large majority of whose members live in space colony conditions very similar to those of the worldship itself, could possess an economy half a dozen orders of magnitude greater than today’s before coming anywhere close to the Solar System’s carrying capacity, in addition to enjoying easy familiarity with the necessary technologies and social structures applicable to interstellar spaceflight.

Robinson concludes that the preparation for interstellar spaceflight will itself be a multi-century project, and will rely crucially on a prosperous and sustainable civilisation on Earth. On these points I am able to heartily agree with him! But ironically, despite his intention to emphasise the difficulty of the preparation, I think he has underestimated the magnitude of the preparatory development that will actually be needed, as well as its chances of successful extension to an interstellar civilisation.

Linked from 19/1/2020 Journal entry