Still catching up after the recent series on antimatter propulsion, I want to move into some intriguing work on panspermia, the idea that life may spread throughout a Solar System, and perhaps from star to star, because of massive impacts on a planetary surface. Catching up with older stories means leaving some things unsaid about antimatter — in particular, I want to return to the question of antimatter storage, which in my mind is far more significant a problem even than antimatter production. But there’s time for that next week, and as I said yesterday, interesting stories keep accumulating and deserve our attention.

Planetary Ejecta and Trapped Microorganisms

What Tetsuya Hara (Kyoto Sangyo University) and colleagues put forth in a recent paper are their calculations about the ejection of life-bearing rocks and water into space from events like the possible ‘dinosaur killer’ asteroid impact some 65 million years ago, which involved an asteroid 10 kilometers in diameter. It’s a remarkable fact that materials can be knocked off one planetary surface and wind up on another, and in some quantity. Consider, for example, the 100 or so meteorites identified by their isotopic composition as being from Mars. They show marked similarity in chemical composition to Viking’s analysis of Martian surface rocks in 1976, and trapped gases in some closely resemble the Martian atmosphere.

So planets in the same system can exchange materials, and of course the Allan Hills meteorite found in Antarctica (ALH 84001), thought to have been ejected from Mars about 16 million years ago, caused quite a stir back in 1996 when scientists thought they had found evidence for microscopic fossils within it, an analysis that remains controversial. But whether or not ALH 84001 contained life, the discovery of various kinds of extremophiles here on Earth and the possibility that they could survive for long periods trapped in rocky debris leads to the idea that one world can seed another, and as we’ve seen in earlier posts on the topic, the idea goes back as far as the Greek philosopher Anaxagoras, with a revival of interest in the 19th Century.

Image: Would an asteroid impact like this drive life-bearing materials to other planets? Possibly so, but the bigger question is, would microorganisms be able to survive the trip? Credit: NASA.

Fred Hoyle and Chandra Wickramasinghe, who were proponents of continuing panspermia and the idea that life entering Earth’s atmosphere from outside could be a driver for evolution, would doubtless find Hara and team’s work fascinating. While the latter argue that solar storms could eject microbes from the upper atmosphere into space, they concede that bolide impacts would be the major driver:

Naturally, those meteors, asteroids or comets which strike with the strong force, would eject the most material into space. Thus it could be predicted that the asteroid or meteor which struck this planet 65 million years ago, and which created the Chicxulub crater (Alvarez. et al. 1979) would have ejected substantial amount of rock, soil, and water into space, some of which would have fallen onto other planets and moons, including stellar bodies outside our stellar system, Kuiper belt objects, Oort cloud objects, and possibly extrasolar planets…

And there’s the issue — just how much material would actually be transferred not just into the outer Solar System, but to nearby stars? Hara uses the Chicxulub crater event as the model for the kind of collisions that drive Earth materials into space, estimating that about the same amount of mass would be ejected from Earth as arrived in the original asteroid impactor.

Long Journey into the Dark

Remarkably, almost as much of the ejected materials make the journey to Europa as to our own Moon, an interesting outcome explained by Jupiter’s deep gravitational well, which in this case takes possibly biologically-laden material to a moon that contains an under-ice ocean. Another place of high astrobiological interest is Saturn’s moon Enceladus, with an internal body of water of its own, as evidenced by the geysers Cassini continues to monitor around its south pole. Here the numbers drop considerably but as many as 500-2000 Earth rocks may have reached Enceladus. Even distant Eris in the Kuiper Belt scarfs up 4 x 10⁷ Earthly objects in one scenario.

These numbers vary according to which of two models the authors use, but in either case their figures show significant movement of Earth materials into the outer Solar System. Extending the model to Gliese 581 becomes a fascinating exercise because we have reason to believe that the ‘super-Earth’ Gl 581d may orbit in the outer edges of the habitable zone there. The result: As many as 1000 rocks may have made the million year journey to fall upon a planet in the Gl 581 system. Thus we have the possibility, however remote, of dormant microorganisms moving between one stellar system and another, to fall upon a planet that conceivably can support life.

Hara and team acknowledge the uncertainties in their calculations but insist that “…the probability of rocks originated from Earth to reach nearby star system is not so small.” If this is the case, their conclusion points to the possibility that life did not originate on Earth at all:

We estimate the transfer velocity of the microorganisms among the stellar systems. Under some assumptions, it could be estimated that if origin of life has begun 10¹⁰ years ago in one stellar system as estimated by Joseph and Schild (2010a, b), it could propagate throughout our Galaxy by 10¹⁰ years, and could certainly have reached Earth by 4.6 billion years ago (Joseph 2009), thereby explaining the origin of life on Earth.

This assumes that there are 25 sites where life began 10¹⁰ years ago, with biological materials spread through the galaxy by the same kind of impact events that caused the Chicxulub crater. Add to this recent work by Brandon Johnson (Purdue) and colleagues. They’ve been investigating layers of rock droplets called spherules, which may tell us better than craters about ancient impacts, including the size and velocity of the impacting object. An initial reading of their work shows that the Late Heavy Bombardment, thought to have occurred from 4.1 billion to 3.8 billion years ago as huge numbers of asteroids and comets hit the Earth, may have lasted longer than we have previously believed.

Was Chicxulub relatively minor compared to the size of some of these impacts? Evidently so, which would account for even more materials from our planet being pushed out into nearby space. The wild card in all this is the ability of microorganisms to survive not just the impact but the journey, and when it comes to interstellar panspermia, my own credulity is pushed to the breaking point. Although I’m running out of time this morning, I want to return to two papers in Nature that examine the Late Heavy Bombardment and the history of later impacts on our planet. We’ll home in on evidence for a longer bombardment era when Centauri Dreams returns on Monday.

The Hara paper is “Transfer of Life-Bearing Meteorites from Earth to Other Planets,” Journal of Cosmology 7 (2010), p. 1731 (preprint). Thanks to John Kilis for the original pointer to Hara and an update on the Nature work.

One of the joys of writing a site like Centauri Dreams is that I can choose my own topics and devote as much or as little time as I want to each. The downside is that when I’m covering something in greater depth, as with the four articles on antimatter that ran in the last six days, I invariably fall behind on other interesting work. That means a couple of days of catch-up, which is what we’ll now see, starting with some thoughts on a possible planet beyond Neptune, a full-sized world as opposed to an ice dwarf like Pluto or Eris. This story is actually making the rounds right now, but it triggered thoughts on older exoplanet work I’ll describe in a minute.

It’s inevitable that we call such a world Planet X, in my case because of my love for the wonderful Edgar Ulmer film The Man from Planet X (1951), in which a planet from the deeps wanders into the Solar System and all manner of trouble — including the landing of an extraterrestrial on a foggy Scottish moor — breaks out. Of course, Planet X was also the name for the world Percival Lowell was searching for in the 1920s, a hunt that resulted in Clyde Tombaugh’s discovery of Pluto, although the latter occurred more or less by chance since Pluto/Charon isn’t big enough to cause the gravitational effects Lowell was examining.

So is there a real Planet X? Rodney Gomes (National Observatory of Brazil) has run simulations on the ‘scattered disk’ beyond Neptune and, factoring in oddities like the highly elliptical orbit of Sedna and other data points on these distant objects, Gomes believes a Neptune-class planet about four times as massive as Earth may be lurking in the outer system. Sedna, you may recall, has a perihelion of 76 AU but an aphelion fully 975 AU out — it’s on a 12,000 year orbital period! As for Gomes, his team has been looking at what they call ‘true inner Oort cloud objects’ for some time, seeing objects like Sedna as markers for the existence of a planet.

Gomes ran through the results of his simulations at an American Astronomical Society meeting in Oregon in May, keeping the Planet X hunt alive, and it’s worth noting that a Jupiter-class planet at about 5000 AU may also fit the bill (see Finding the Real Planet X). For that matter, the orbits of scattered disk objects may have another explanation besides an undiscovered planet. But thinking about Gomes’ work brought me around to Jason Steffen and team, whose new paper goes to work on a much different kind of gravitational effect, the disruption caused by a ‘hot Jupiter’ as it moves through a young Solar System and scatters smaller planets.

Realm of the Wandering Planets

Steffen (Fermilab Center for Particle Astrophysics) is digging into exactly what makes ‘hot Jupiters’ take up such extreme orbits. These are planets of Jupiter’s size and larger that whip around their stars in periods of just a few days. The question is how they got to their present position, for the assumption is that planets of this size had to form much further out in their system and then move inward. There are two mechanisms that could make this happen, one of which — a slow migration through a gas disk that would allow low-mass planets to likewise migrate inward, where they can be captured into mean-motion resonance with the gas giant — seems benign. These models suggest the presence of smaller worlds near the hot Jupiter.

Image: Artist’s concept of a hot Jupiter, likely a disrupter of any planets that encounter it. Credit: NASA.

The other model is lethal to the inner system. Here, the giant planet’s migration is caused by gravitational interactions with another gas giant that result in one of the worlds being flung into interstellar space, while the other migrates inward and disrupts the orbits of any inner-system worlds. This scenario is what the Steffen paper is suggesting, for the team’s analysis of 63 Kepler planets around solar-type stars in orbits of 6.3 days or less shows no evidence at all for nearby planets. If such worlds were there, they ought to be detectable through transit timing variations (TTV) unless they are smaller than the Earth, or much further out in the system.

To compare and contrast environments, the researchers took another sample of 31 Kepler planets with ‘warm Jupiters’ — planets of Jupiter size around the same kind of star, but with longer orbital periods of between 6.3 and 15.8 days. They also checked 222 Kepler ‘hot Neptunes.’ The result: Three of the 31 ‘warm Jupiter’ systems showed companion planets in the inner system, and fully one-third of the hot Neptune systems showed the presence of inner system planets. Finally, the team looked at 52 ‘hot Earths’ in the Kepler data for TTVs, testing whether hot Jupiters and smaller worlds like these might co-exist in mutually inclined orbits. They found no evidence for high-mass companions on inclined orbits in this scenario.

The authors see this as a boost to the ‘scattering’ model, the study suggesting that hot Jupiters are migrating worlds on initially highly elliptical orbits that scattered other planets out of the inner system before their orbits became circularized close to their stars. Short period, low-mass planets would seem to have a different formation history than hot Jupiters. From the paper:

Hot Jupiter systems where planet-planet scattering is important are unlikely to form or maintain terrestrial planets interior to or within the habitable zone of their parent star. Thus, theories that predict the formation or existence of such planets (Raymond et al. 2006; Mandell et al. 2007) can only apply to a small fraction of systems. Future population studies of planet candidates, such as this, that are enabled by the Kepler mission will yield valuable refinements to planet formation theories — giving important insights into the range of probable contemporary planetary system architectures and the possible existence of habitable planets within them.

If hot Jupiter systems have a different dynamical history than other planetary systems, as this work suggests, then we have a useful filter to apply to exoplanet studies. If it can be firmly established that the presence of a hot Jupiter means no planets in the habitable zone, we know our resources are best focused elsewhere when it comes to looking for terrestrial worlds. It’s too early to make that call now, but the evidence is mounting that in most cases hot Jupiters are killer worlds when it comes to young planets in the warm regions where life may occur.

The paper is Steffen at al., “Kepler constraints on planets near hot Jupiters,” Proceedings of the National Academy of Sciences 109 (21) 7982-7987 (2012). Abstract available.

Long-time Centauri Dreams readers know I love the idea of ‘deep time,’ an interest that cosmology provokes on a regular basis these days. Avi Loeb’s new work at Harvard tweaks these chords nicely as the theorist examines what we know and when we won’t be able to study it any longer. For an accelerating universe means that galaxies are moving outside our light horizon, to become forever unknown to us. Using tools like the Wilkinson Microwave Anisotropy Probe, we’ve been able to learn how density perturbations in the early universe, thought to have been caused by quantum fluctuations writ large by a period of cosmic inflation, emerged as the structures we see today. But are there limits to cosmological surveys?

Start with that period of inflation after the Big Bang, which would have boosted the scale of things by more than 26 orders of magnitude, helping to account for the fact that the cosmic microwave background (CMB) appears so uniform in all directions. We can tease out the irregularities that have grown into galaxies today. Loeb refers to these density perturbations as a ‘Rosetta stone’ that has unlocked our understanding of the largest cosmological parameters.

Even so, he concludes in his new paper that our ability to understand the earliest period of the universe deteriorates over time. In fact, the optimum time to study the cosmos turns out to have been more than 13 billion years ago, with information being lost along the way in the eras since. From the paper:

… the most accurate statistical constraints on the primordial density perturbations are accessible at z ∼ 10, when the age of the Universe was a few percent of its current value (i.e., hundreds of Myr after the Big Bang). The best tool for tracing the matter distribution at this epoch involves intensity mapping of the 21-cm line of atomic hydrogen… Although the present time (a = 1) is still adequate for retrieving cosmological information with sub-percent precision, the prospects for precision cosmology will deteriorate considerably within a few Hubble times into the future.

The era Loeb picks as optimum for observation is just 500 million years after the Big Bang, when cosmic perturbations were still emerging in the form of the first stars and galaxies. Hubble time, as defined by the standard cosmological model, is 13.8 billion years, giving us a sense of the scale he is working with. Today we can use 21-centimeter surveys to map the early distribution of matter, but such observations will be impossible in the far future. We have to reckon with the fact that dark energy is still an open question — does it evolve with time? Loeb’s work assumes a universe with a true cosmological constant, but he notes that the ultimate loss of information will occur whether or not an accelerated expansion varies as the universe ages.

Image: New research finds that the ideal time to study the cosmos was more than 13 billion years ago, just about 500 million years after the Big Bang – the era (shown in this artist’s conception) when the first stars and galaxies began to form. Since information about the early universe is lost when the first galaxies are made, the best time to view cosmic perturbations is right when stars began to form. Modern observers can still access this nascent era from a distance by using surveys designed to detect 21-cm radio emission from hydrogen gas at those early times. Credit: Harvard-Smithsonian Center for Astrophysics.

This work takes us into deep time indeed, with Loeb’s calculations showing that beyond 100 Hubble times (a trillion years in the future), the wavelength of the CMB and other extragalactic photons will be stretched by a factor of 10²⁹ or more, making current cosmological sources unobservable:

While the amount of information available now from observations of our cosmological past at z ∼ 10 is limited by systematic uncertainties that could potentially be circumvented through technological advances, the loss of information in our future is unavoidable as long as cosmic acceleration will persist.

It’s always interesting to speculate about what any observers in this remote future would make of the universe without the ability to recover evidence of the early cosmological perturbations. Clearly our observations have a fundamental limit as a function of cosmic time, and even our existing data, which Loeb sees as far from optimal, will one day be unrecoverable from new observations. If there are future advances that would somehow surmount these limitations to open up the universe’s past, we can only speculate on what they might be, and how they would be developed by a civilization living in this unimaginably remote future cosmos.

The paper is Loeb, “The Optimal Cosmic Epoch for Precision Cosmology,” accepted for publication in the Journal of Cosmology and AstroParticle Physics (preprint).

If you didn’t see this morning’s spectacular launch of the SpaceX Falcon 9, be sure to check out the video (and it would be a good day to follow @elonmusk on Twitter, too). As we open the era of private launches to resupply the International Space Station, it’s humbling to contrast how exhilarating this morning feels with the great distances we have to traverse before missions to another star become a serious possibility. We’ve been talking the last few days about the promise of antimatter, but while the potential for liberating massive amounts of energy is undeniable, the problems of achieving antimatter propulsion are huge.

So we have to make a lot of leaps when speculating about what might happen. But let’s assume just for the sake of argument that the problem analyzed yesterday — how to produce antimatter in quantity — is solved. What kind of antimatter engine would we build? If everything else were optimum, we’d surely try to master a beamed core drive, the pure product of the matter/antimatter annihilation sequence. Protons and antiprotons are injected into a magnetic nozzle, blowing out the back at a substantial percentage of the speed of light. This is the kind of rocket analyzed by Ronan Keane (Western Reserve Academy) and Wei-Ming Zhang (Kent State University) in the paper I’ve been skirting around the edges of these past few days.

Channeling Antimatter’s Energies

The paper, headed for publication in the Journal of the British Interplanetary Society, has the provocative title “Beamed Core Antimatter Propulsion: Engine Design and Optimization,” and it deals with the particle stream emerging from proton/antiproton collisions. What you get when you put the two together are gamma rays and pions, some of the latter charged and some neutral. Almost immediately the pions decay into positrons and electrons, which meet each other and produce gamma rays. But the tens of nanoseconds the pions take to decay gives us long enough to channel the charged pions through a magnetic nozzle to produce the needed thrust.

Image: Antimatter promises fast transportation throughout the Solar System and the opportunity for interstellar probes, but only if we can master its production and storage. New work is explaining how efficient an antimatter engine might be. Credit: Positronics Research, LLC.

The beamed core engine, then, is all about channeling the pions into a focused flow. Get this right and you’ve got a lot of energy to work with. In fact, Keane and Zhang note that the energy released per kilogram of annihilating antimatter and matter is 9 X 10¹⁶ joules, which is two billion times more than the thermal energy from burning a kilogram of hydrocarbon, and over a thousand times larger than burning a kilogram of fuel in a nuclear fission reactor. But while the beamed core engine is attractive because of the high relativistic velocities of the charged particles produced by the annihilation reactions, the situation is not ideal.

For one thing, much of the energy of the reaction goes into producing electrically neutral particles, which are impervious to the workings of a magnetic nozzle and thus cannot contribute to thrust. The other problem is that the nozzles we’ve been able to analyze have efficiency problems of their own in terms of creating the tight beam of thrust we’d like to produce. What Keane and Zhang do is to use software called Geant4 from the CERN accelerator laboratory to produce simulations of the interactions of particles with matter and fields. They want to bring previous studies of beamed core concepts up to date especially in terms of magnetic nozzles.

Robert Frisbee has performed rigorous studies of beamed core concepts in which magnetic nozzle efficiency is only about 36 percent, which means that while you’re dealing with pions that are initially moving at 90 percent of light speed and above, the exhaust velocity of the rocket would be just a third of that amount. Keane and Zhang derive an efficiency that is better than twice that, and manage to reach charged pion exhaust speeds of 69 percent of c. They also show that the initial speed of charged pions in a beamed core engine is actually closer to .81c than Frisbee’s 90 percent-plus. Despite the lower initial speed, the nozzle efficiencies make quite a difference depending on the kind of mission being attempted:

Frisbee’s papers explain in depth the needed generalization to account for emission of uncharged particles… When loss of propellant is taken into account, Frisbee has shown that v_e ~ 0.3c leads to a beamed core rocket facing daunting challenges in reaching a true relativistic cruise speed on a one-way interstellar mission where deceleration at the destination (a “rendezvous” mission) would be involved.

Fuel requirements become critical with lower nozzle efficiencies:

… with a payload of 100 metric tons, a 4-stage beamed core rocket designed for a cruise speed of 0.42c on a 40 light-year rendezvous mission would require 40 million tons of antimatter fuel. If the cruise speed were limited to 0.25c or less, only two stages might be needed, and Frisbee envisaged viable interstellar missions with as few as one beamed core stage; in such scenarios, fuel requirements would be dramatically lower.

All of this at 36 percent nozzle efficiency. The new numbers change the picture, with Keane and Zhang stating “With the new reference point of v_e =0.69c provided by the present Geant-based simulation, true relativistic speeds once more become a possibility using the highest performance beamed core propulsion in the distant future.”

Note the ‘distant future’ caveat, highly significant when you consider our problems in producing antimatter (or harvesting same) and the perhaps even more intractable issues involved in storage.

On Software and Methodology

But even if we can’t put a timeframe on something as futuristic as a beamed core rocket, we can continue to study the concept, and it’s heartening to see Keane and Zhang’s conclusion that the simulation software at CERN has proven robust in meeting this challenge and updating our numbers. Whether or not Keane and Zhang’s methodology is on target may be another issue, as Adam Crowl noted recently in a post to a private mailing list of aerospace engineers. Crowl hastens to add that his computations are provisional, but let me quote (with his permission) where he is right now on the magnetic nozzle efficiency issue:

There’s a problem with using just the exhaust velocity given to *part* of the fuel/propellant. It means the actual mass-ratio for a given delta-vee is quite different to a naive computation using the classic Tsiolkovskii equation. A more useful figure of merit for rockets with mass-loss in addition to reaction mass is specific impulse – momentum change per unit mass of fuel/propellant. Using the equations derived by Shawn Westmoreland and the rather vague particle energies in Zhang & Keane, the effective specific impulse is ~0.28c. Even with a perfect jet efficiency the Isp is just 0.31c.

The antimatter reaction, then, may not offer as much as we hoped:

The 0.81c average particle speed quoted in the paper isn’t as useful as the spread of kinetic energies in the particles produced, or the total kinetic energy in the distribution, but they don’t report either figure. What it does imply is that an antimatter-matter reaction puts about 11% of the mass-energy into the charged particles. Not exactly spectacular.

The chance to go to work on concepts through papers in the preprint process is invaluable, and we’ll see how Crowl’s thinking, as well as Keane and Zhang’s, evolves with further study of the issues in this paper. One thing is for sure: Given the manifest problems of antimatter production and storage, we’ll have no shortage of time in which to consider these matters before the question of actually producing this kind of antimatter rocket becomes pressing.

The paper is Keane and Zhang, “Beamed Core Antimatter Propulsion: Engine Design and Optimization,” accepted by JBIS (preprint).

Antimatter is so tantalizing a prospect for propulsion that every time a new slant on using it appears, I try to figure out its implications for long-haul missions. But the news, however interesting, is inevitably balanced by the reality of production problems. There’s no question that antimatter is potent stuff, with the potential for dealing out a thousand times the energy of a nuclear fission reaction. Use hydrogen as a working fluid heated up by antimatter and 10 milligrams of antimatter can give you the kick of 120 tonnes of conventional rocket fuel. If we could get the cost down to $10 million per milligram, antimatter propulsion would be less expensive than nuclear fission methods, depending on the efficiency of the design.

But how to reduce the cost? Current estimates show that producing antimatter in today’s accelerator laboratories runs the total up to $100 trillion per gram. But when I was researching my Centauri Dreams book, I spent some time going through the collection of Robert Forward’s papers at the University of Alabama-Huntsville, where several boxes of materials are stored in Salmon Library. Forward was constantly working in a number of different fields, always keeping his eye on the latest research, and as part of that effort he produced a series of newsletters on antimatter developments that he circulated among colleagues.

Image: A Penn State artist’s concept of an antimatter-powered Mars ship with equipment and crew landers at the right, and the engine, with magnetic nozzles, at left. Credit: PSU.

Reading through these materials, I came to see that when we quote the $100 trillion per gram figure, we’re talking about antimatter as produced more or less as a byproduct. Forward understood and appreciated the science requirements of particle accelerator labs but also saw that they were hardly the most efficient place to produce antimatter in any quantity. They were not, after all, in the propulsion business. He proceeded to do a study for the US Air Force looking at what might happen if an antimatter facility were actually designed for no other purpose than the creation of antiprotons, finding that the energy efficiency could be raised from one part in 60 million to a part in 10,000, or 0.01 percent.

The cost of building the factory, meanwhile, could be lowered dramatically, to the point where Forward believed our $10 million per milligram would be within reach. This is an interesting figure in several ways. As noted above, it makes antimatter feasible for certain kinds of space missions (assuming equivalent advances in our methods of antimatter storage. But as the price begins to drop, we can expect to find new applications in other areas of research, which should drive demand and spur further work on efficient production. It’s worth remembering that even at today’s prices, antimatter has proven its worth in scientific research and medical uses.

What about other ways of lowering the cost? One possibility is to look beyond slamming high-energy protons into heavy-nuclei targets. Writing with Joel Davis in a book called Mirror Matter: Pioneering Antimatter Physics (Wiley, 1988), Forward looked at options like heavy ion beam colliders, in which beams of heavy ions like uranium could be collided to produce 10¹⁸ antiprotons per second (with acknowledged problems in creating large amounts of nuclear debris). He also considered new generations of superconducting magnets to create magnetic focusing fields near the region where the beams collide, which should make tighter beams and greater antimatter production possible.

I bring all this up because the possibility of harvesting antimatter from natural sources in space, which we talked about last week, has to be weighed against boosting production here on Earth. But Forward’s ideas actually coupled the two notions. He wanted to move antimatter production by humans into space in the form of huge factories. Here’s what he has to say on this in an essay in his book Indistinguishable from Magic (Baen, 1995):

Where will we get the energy to run these magic matter factories? Some of the prototype factories will be built on Earth, but for large scale production we certainly don’t want to power these machines by burning fossil fuels on Earth. There is plenty of energy in space. At the distance of the Earth from the Sun, the Sun delivers over a kilowatt of energy for each square meter of collector, or a gigawatt (1,000,000,000 watts) per square kilometer. A collector array of one hundred kilometers on a side would provide a power input of ten terawatts (10,000,000,000,000), enough to run a number of antimatter factories at full power, producing a gram of antimatter a day.

We’re a long, long way from producing a gram of antimatter a day, of course, which is why studies like the recent one performed by Ronan Keane (Western Reserve Academy) and Wei-Ming Zhang (Kent State University) have such a futuristic air. But it’s important to learn the theoretical constraints on propulsion systems even if the required antimatter isn’t available, and on that score, Keane and Zhang are thinking ahead to the most advanced kind of antimatter of them all, a beamed core drive. To make it work, assuming you have the antimatter available, you need to inject protons and antiprotons into a magnetic nozzle, one that channels charged pions from the matter/antimatter annihilation into a focused beam of powerful thrust.

Although charged pions decay quickly, they can start out at 90 percent of the speed of light. Unfortunately, earlier magnetic nozzle calculations have proven inefficient at channeling these energies, dropping the exhaust velocity down to a third of this value. Tomorrow we’ll look at how a more efficient magnetic nozzle can produce better results, as Keane and Zhang have analyzed using CERN software to simulate what would go on in the hellish interior of a beamed core antimatter engine. But we also need to consider other ways of using antimatter for propulsion, assuming that Forward’s space-borne factories aren’t going to be coming online any time soon.

Today was to have been devoted to antimatter, continuing the discussion not only of how to produce the stuff on Earth or harvest it in nearby space, but how to create the kind of propulsion system that could tap its enormous energies. But the Dorothy Jemison Foundation for Excellence released its first public announcement about the 100 Year Starship yesterday, and I want to go right to that story given the interest that grew out of last year’s starship symposium in Orlando. I’ll get back to antimatter, then, and particularly the provocative work of Ronan Keane and Wei-Ming Zhang on magnetic nozzles for propulsion systems, on Monday.

For today, though, let’s talk about pushing out into the galaxy. The Tau Zero Foundation has a particular interest in the 100 Year Starship organization because our friends at Icarus Interstellar, who are re-thinking the 1970s Project Daedalus design, were partners in the winning proposal, which was called “An Inclusive, Audacious Journey Transforms Life Here on Earth and Beyond.” I have no experience with the Dorothy Jemison Foundation or, for that matter, the third partner in the winning proposal, the Foundation for Enterprise Development, but our long relationship with Icarus Interstellar has demonstrated the expertise and commitment this band of scientists, engineers and enthusiasts brings to the task.

You’ll recall that the Defense Advanced Research Projects Agency (DARPA) put up the seed funding for what was to become a non-government entity with a focus on the long term, one that is designed to promote advanced capabilities for interstellar flight over the next hundred years. The 100 Year Starship name refers, then, not to a mission that lasts a hundred years but to an entity robust enough to grow the interstellar idea through the coming century, the hope being that somewhere around the early part of the 22nd Century, our technologies may have reached the point where we can launch a mission to another star.

Mae Jemison, a former astronaut who flew aboard the Space Shuttle Endeavour, puts it this way:

“Yes, it can be done. Our current technology arc is sufficient. 100 Year Starship is about building the tools we need to travel to another star system in the next hundred years. We’re embarking on a journey across time and space. If my language is dramatic, it is because this project is monumental. This is a global aspiration. And each step of the way, its progress will benefit life on earth. Our team is both invigorated and sobered by the confidence DARPA has in us to start an independent, private initiative to help make interstellar travel a reality.”

Whether you were able to get to the 100 Year Starship symposium last year in Orlando or not, be aware that a second symposium is in the works for Houston on September 13-16 of this year. The organization’s press release says that the symposium will from here on out be an annual event that will examine not only the scientific and engineering challenges of starflight but the multidisciplinary questions starflight raises in economics, philosophy and culture. You can sign up to be notified about further symposium news here. And the call for papers has just gone out as well.

I’m pleased in particular to see that the 100 Year Starship is to include a scientific research institute called The Way which will place an emphasis on long-term science and technology issues. Readers of Centauri Dreams know that long-term thinking is an obsession of mine, as the necessity of looking beyond immediate material and financial returns to the kind of future we can build through sacrifice and dedication has never been more clear. On that score, I appreciate the quote from columnist and critic John Mason Brown that’s found on the organization’s website: “The only true happiness comes from squandering ourselves for a purpose.”

Indeed, and what a purpose it is. A starship is the ultimate in long-term thinking, a challenge to our science, our engineering, our conception of ourselves. What interstellar flight asks of us is whether we are prepared to make a commitment that reaches well beyond our own generation, to take the first steps forward on a journey whose end most, if not all of us, will never see. It is gratifying to see the idea moving forward, and the Tau Zero Foundation sends congratulations to all involved in the new organization.

Related: 100-Year Starship: Mae Jemison reaches for the stars, in BBC Future. From which this quote from Mae Jemison:

We are not saying our organization, is going to be the one that necessarily launches a mission to the stars in a next 100 years. We want to be the little piece that crystalizes out, the effort, the energy, and the capacity to make sure that the capabilities exist within in the next 100 years in case somebody wants to launch a mission.

And this:

I think that people need an adrenalin rush. Folks need something aspirational, they need to do something that is hard. That’s what ignites the imagination. I grew up during the Apollo-era, in the 1960s. When I was a little girl: I thought when I had an opportunity to go into space, I thought I would at a minimum be working on Mars, or another large planet because we were doing all of these incredible things. But we stagnated, because we didn’t continue that push. We started to get a little bit timid. Timidity does not inspire bold acts.

In Stephen Baxter’s wonderful novel Ark (Roc, 2010), a team of scientists works desperately to come up with an interstellar spacecraft while epic floods threaten the Earth. The backdrop gives Baxter the chance to work through many of our current ideas about propulsion, from starships riding a wave of nuclear explosions (Orion) to antimatter possibilities and on into Alcubierre warp drive territory. I won’t give away the solution, but will say that it partly involves antimatter used in an unorthodox way, and because Baxter’s is a near-term Earth, there simply isn’t enough antimatter to go around. That means getting to Jupiter first to harvest it.

Antimatter in space is an idea that James Bickford (Draper Laboratory) analyzed in a Phase II study for NASA’s Institute for Advanced Concepts, for he had realized that high-energy galactic cosmic rays interacting with the interstellar medium (and also with the upper atmospheres of planets in the Solar System) produce antimatter. In fact, Bickford’s calculations showed that about a kilogram of antiprotons enter the Solar System every second, though little of this reaches the Earth. To harvest some of this incoming antimatter, you need a planet with a strong magnetic field, so Jupiter is a natural bet for Baxter’s scientists, who go there to forage.

The odd thing, though, is that Saturn is actually a better source of antimatter than Jupiter, with 250 micrograms produced by reactions in the rings and injected into the magnetosphere every year. Bickford’s work showed that the process by which galactic cosmic rays produce antimatter isn’t as effective around Jupiter because its magnetic field shields the Jovian atmosphere and lowers the flux. A much larger flux reaches the atmosphere of Saturn. But Bickford also believed that our own Earth would be a good antimatter source, leading to the idea of using a plasma magnet — the scientist discusses using high temperature superconductors to form two pairs of 100-meter RF coils to manage this. The result is a kind of magnetic scoop that could trap antiparticles found in our planet’s radiation belts.

Image: Among sources of naturally occurring antimatter in our Solar System, Saturn may be the most useful. Credit: James Bickford.

Why go to the trouble of collecting antimatter from space? Because antimatter production on the order of one-trillionth of a gram per year, which is about what we can get out of today’s accelerator labs through high-energy particle collisions, isn’t enough to power up a lightbulb for more than a few seconds. Moreover, at today’s prices the stuff costs about $100 trillion per gram. This is why Robert Forward, who used to circulate an antimatter newsletter among colleagues and wrote extensively about its possibilities, proposed that one day we would build antimatter factories in space. Build a large enough solar-powered array and you could, he thought, come up with something on the order of a gram of antimatter per day.

Remember that as little as ten micrograms of antimatter might power a 100-ton payload on a one-year mission to Jupiter and you can see that one gram of antimatter a day is a bountiful supply. But Forward’s antimatter collector array was huge, 100 kilometers to the side, and well beyond today’s engineering. Thus the interest generated by the PAMELA satellite (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) last year when it picked up more antiprotons in the region known as the South Atlantic Anomaly than had been expected.

This South Atlantic Anomaly is where the inner Van Allen radiation belt makes its closest approach to the Earth’s surface, which in turn creates a higher flux of energetic particles there. The PAMELA work showed that Bickford’s original NIAC analysis was correct — antimatter is indeed being produced near the Earth. Bickford went on to suggest that we could collect some 25 nanograms per day using his magnetic scoop, a process that if successful would prove orders of magnitude more cost effective than creating antimatter here on Earth.

So would Baxter’s doughty crew be able to harvest their antimatter much closer to home than Jupiter or Saturn? Maybe not. A new paper by Ronan Keane (Western Reserve Academy) and Wei-Ming Zhang (Kent State University) comes into play here. The authors have developed new thinking on antimatter propulsion, specifically on the magnetic nozzles that would be required to make it work. It’s important work and tomorrow I want to get into the propulsion aspects of it, but for today I note their comment on the PAMELA findings and antimatter. Here’s a quote:

The recent PAMELA discovery, in which the observed antiproton flux is three orders of magnitude above the antiproton background from cosmic rays, paves the way for possible harvesting of antimatter in space. Theoretical studies suggest that the magnetosphere of much larger planets like Jupiter would be even better for this purpose. If feasible, harvesting antimatter in space would completely bypass the obstacle of low energy efficiency when an accelerator is used to produce antimatter, and thus could offer a solution to the main difficulties stressed by the skeptics.

The problem with this — and this has been noted by The Physics arXiv Blog and Jennifer Ouellette in recent days — is that PAMELA could come up with only 28 antiprotons over the course of 850 days of data acquisition. There is no question that Bickford is right in seeing how antimatter can be produced locally. In fact, the paper on the PAMELA work says this: “The flux exceeds the galactic CR antiproton flux by three orders of magnitude at the current solar minimum, thereby constituting the most abundant antiproton source near the Earth.” But does the process produce enough antimatter to make local harvesting a serious possibility?

We need to learn more, obviously, and it’s worth noting, as Keane and Zhang do in their paper, that the Alpha Magnetic Spectrometer was installed on the International Space Station in mid-2011, giving us a much enhanced ability to detect and measure antiparticles in Earth orbit. Antimatter harvesting within the Solar System appears to be a workable concept, but if we’re going to need to go to the gas giants to make it happen, we’re obviously pushing back the time frame on collecting significant quantities that could be used in future propulsion systems.

More on this tomorrow, when we’ll look further at Keane and Zhang’s ideas on antimatter engines and what could make them possible. Their paper is “Beamed Core Antimatter Propulsion: Engine Design and Optimization,” submitted to the Journal of the British Interplanetary Society (preprint). The PAMELA work is Adriani et al., “The discovery of geomagnetically trapped cosmic ray antiprotons,” Astrophysical Journal Letters Vol. 37, No. 2, L29 (abstract / preprint). For a cluster of Bickford references, see Antimatter Source Near the Earth, published here last August.

As we continue to think about the implications of Planetary Resources and its plans for asteroid mining, I was interested to see exoplanet hunter Sara Seager (MIT) make a rousing case for the company’s ideas and for commercial space ventures in general. Seager, who works with Planetary Resources as a science advisor, tells The Atlantic’s Ross Andersen in a May 14 interview that one reason for optimism is the progress we’re making with robotics. Mining operations currently being managed beneath the seas are being handled by robotics. Couple that with our ability to get to and orbit an asteroid as well as to scoop up surface materials and you have all the ingredients for a workable mining operation in a low-gravity environment.

Seager explains that asteroids are attractive mining targets because unlike fully formed planets like the Earth, their heavier elements have not largely sunk inside through planetary differentiation in the early days of the planet’s existence. Asteroids are either fragments of bigger objects or building blocks that were never fully formed, meaning that high-value platinum metals should be readily accessible on the right kind of object. Their low gravity and, in the case of NEA’s, proximity mean that they are attractive targets from which to return materials.

Image: All the technologies may be falling into place for asteroid mining. But is a move to commercial operations a story with even bigger implications? Credit: NASA.

Planetary Resources is intriguing not only because of potential mining returns but because it involves a different model of detail and risk than would be acceptable in a government-created program. Here Seager invokes the Mars Science Laboratory, a $2 billion mission that will land a rover on Mars this summer. MSL became a huge operation because it is a general science mission that demands the 10 different science instruments aboard the craft, making it a heavier rover and demanding a landing system far more complicated than the air-bag methods we’ve used successfully in our last several Mars landings. A private firm, on the other hand, can focus tightly on a specialized goal rather than aiming for a multi-purpose mission from the start.

But there’s a bigger difference, adds Seager:

In the private spaceflight world there are focused goals with profit and new capability as priorities. At NASA the motivation for space missions is different. In addition to big and general science goals, the main goal appears to be not to fail. In this sort of culture the bigger space companies and academia are taught that it, the mission, has to work.

Even the large space companies like Lockheed and Northrop Grumman can become trapped inside this paradigm, for they are not creating long-term, sustainable businesses with the work they perform for the government. Instead, they are operating within a culture riddled with bureaucracy and plagued with high costs. Seager likes the look of young and lean space companies:

…at small space companies, things can fail. Risk is part of developing new technology. Also, for the big space companies the whole competition is just getting the government contract. The competition is not about making something awesomely cool, first to market, and making a ton of money out of it. So in my opinion, the motivation factor and the risk aversion factor make it basically impossible for these larger companies to shift gears. The question that is on the minds of a lot of people is “Can America continue to be competitive in space with the current paradigm?” And the answer is no. That is the reason we have seen the rise of the commercial space flight world—they’re trying to start a new paradigm for spaceflight with a sustainable business that doesn’t just rely on government contracts.

The Seager interview is well worth your time as she discusses not only the Planetary Resources business model but the implications involved in getting a new generation of small and inexpensive technology into space. It’s no surprise that the Arkyd series of spacecraft should catch her eye, since Seager is also involved in a project called ExoplanetSat, a prototype ‘nanosatellite’ that can monitor a single, Sun-like star for two years. This gets seriously interesting when you start talking about producing a large number of such satellites, because while we have the Kepler mission monitoring planetary transits in a fixed field, we have no mission in the works to hunt for planets around the nearest and brightest stars.

So instead of a single space telescope fixated on tens of thousands of stars, most of them distant from the Sun, we invert the model to produce a fleet of tiny telescopes with a single target each, with the detailed properties of each star under observation programmed into each instrument. You can see why Planetary Resources’ plan to launch a large number of small space telescopes would appeal to Seager. The Arkyd series (based on the company’s original name) would allow small institutions to buy a space telescope for a price ranging from $1-10 million, opening space-based observations to universities or even wealthy individuals.

Image: ExoPlanetSat is just 10 centimeters tall, 10 cm wide and 30 cm long, and will complement existing planet-hunters like NASA’s Kepler space telescope and ground-based assets. It gives NASA the ability to dedicate relatively inexpensive assets to stare at a star for long periods of time to look for transits. Credit: MIT/Draper Laboratory.

Here again Seager sees Planetary Resources tweaking the basic model of how science gets done. A telescope specifically designed for a unique science goal can produce superb results, as we’ve learned from Hubble, CoRoT, Kepler and other missions. But bring a commercial interest into the mix and a new flexibility emerges. Planetary Resources can sell small space telescopes into a new market, while also using the product for its asteroid characterization work. The mix of motivations provided by commercial space drives the enterprise. Adds Seager, “If you’re part and parcel of the commercial space flight world, it appears you can get a lot of interesting things done. I think that in academia we could learn a lot from the business world.”

It’s too bad we don’t already have a workable Enterprise, that vast near-term rendition of the Star Trek vehicle that a systems engineer named ‘Dan’ has been talking about on BuildTheEnterprise.org (a site which has been so heavily trafficked in the last 48 hours that it has proven almost inaccessible). What Dan has in mind is the design, down to the smallest level of detail, of a ship powered by three ion propulsion engines that tap on-board nuclear reactors to remain operational. It may not be an antimatter-powered Enterprise, but it’s a faithful simulacrum, reflecting its creator’s long-lasting interest in the ship that William Shatner once commanded.

Dan thinks the new Enterprise could get us to Mars in 90 days, but getting nuclear reactors into low Earth orbit in the first place will be a challenge not only technically but politically, and shielding the crew will also involve a serious amount of mass that has to get lifted. One of the fascinations of this highly detailed site is that many of these objections are anticipated:

NASA is developing a heavy lifter, the Space Launch System (SLS), that will be able to carry a payload of 280,000 pounds, about the same as a Saturn 5 rocket. Unfortunately this is about a factor of four too low for what the Enterprise will optimally need. Because the Enterprise’s wet mass will be around 187 million pounds, a suitable heavy lifter should carry a payload of at least 1 million pounds to keep down the total number of launches needed. This is a payload similar to the Nova rocket designs from the 1960s that were never taken to production. So, in general, if the Enterprise program is someday funded, NASA will have to start a new heavy lifter rocket program that can carry much bigger payloads than their current plans.

And what about radiators to remove excess heat? Dan’s design better factor those in. An informal peer review of the concept is already beginning, as witness Adam Crowl’s take on the radiator problem on Crowlspace and back-channel discussions among aerospace engineers and designers in various places. If you want to track the new Enterprise beyond its own site, Dan’s Twitter handle is @BTE-Dan, and I’ll plan to have a report on some of the informal peer review in these pages before long.

Dan is a man with a long-term plan — he’s proposing not only building a huge ship but making it the first of a series, with three new ships per century, each keying on advances made during the intervals between construction. Early missions could involve the Moon, Mars, Venus and perhaps the moons of Jupiter, for while we’re a long way from Star Trek’s warp drive, Dan claims the new Enterprise’s ion propulsion would allow a constant .002g acceleration for planetary exploration. A rotating wheel within the ship’s saucer section would provide an artificial 1g of gravity. The latter is one case of reworking the original Enterprise design to fit the requirements of a technology far less sophisticated than what was proposed in the TV series.

Image: A new Enterprise engineered around current and near-future technologies. Credit: BuildTheEnterprise.org.

The Daily Mail looks at the new Enterprise in a May 15 story, quoting its creator on his changes to the ship, one of which was made to keep the ship’s officers in workable conditions:

“Another example of a change is that the bridge is not at the top center of the saucer hull as it is shown in the figure above. If it was there in the Gen1 Enterprise then there would be no gravity on the bridge. Having the ship’s captain and crew floating around inside the bridge just makes no sense. Thus, in the Gen1 Enterprise the bridge is in a dedicated section of the gravity wheel so that they will work in 1g gravity.

“While things get moved around quite a bit inside the Gen1 Enterprise when compared to the ships from Star Trek, they are not moved around upon a whim. They are moved around because the Gen1 ship’s technological capabilities demand certain changes.”

The gung-ho spirit of Dan’s vision is engaging, especially his belief that all this can be achieved in 20 years, and the man who describes himself as a systems and electrical engineer in his day job tells the Daily Mail his BuildTheEnterprise site grew naturally out of the same kind of thinking he brings to bear at his high-tech firm, built on exploring new ideas and pushing technologies. I’m glad to see that he’s also hoping that young people find inspiration in his site, for it’s this kind of brainstorming, so often found in science fiction, that can motivate young minds into engineering or scientific careers. “…this may still be a long way from warp drives powered by anti-matter,” he tells the Daily Mail, “but it will be a respectable start.”

I love thinking big, but if we did have the technological means to build the first generation Enterprise in the short term, what about the needed economic and political environment? Is Congress likely to fund NASA to embark on a project of this magnitude — while continuing its funding for robotic missions to planets and elsewhere — given the size of the budget deficit and an environment of overwhelming debt? Surely that idea is more fantastic than the actual construction of a ship that can accommodate 1000 people within the next 20 years.

No, let’s take a longer perspective, with all due respect for energetic thinkers like Dan who want it done tomorrow. Ideas grow in their own time, and something along the lines of the new Enterprise design in terms of propulsion — i.e., large scale ion propulsion fed by nuclear reactors — may emerge as a working concept for our future Solar System-wide infrastructure, one that not a few scientists and engineers are now examining to weigh its merits and ponder its implications. In any case, Dan has a backup plan of his own in case his schedule is too optimistic. Once his site stabilizes under the current traffic load, have a look at it to see his proposed way forward.

I’ve been thinking all weekend about Dandridge Cole, the aerospace engineer and futurist whose death at age 44 deprived interstellar studies of one of its most insightful advocates. Cole died in 1965, just five years before a deadline he himself set (in 1953!) for a manned landing on the Moon. But then, the former paratrooper from Ohio thought a lot about the future and the need for a kind of ‘future studies’ that would look at current technological trends and project going forward just as conventional historical studies reconstruct what happened to us in centuries past.

The heart attack that struck Cole down in his office at General Electric’s Space Technology Center in Valley Forge, PA deprived us of much, but we do have the substantial legacy of a number of articles and monographs, along with three books, among which Islands in Space: The Challenge of the Planetoids, written with Donald Cox (Chilton Books, 1964) may stand out as the most influential. Andreas Hein, who is heading up the Project Hyperion worldship study for Icarus Interstellar, harks back to the inspiration of Cole in The Hollow Asteroid Starship: Dissemination of an Idea, published on the Icarus blog late last week.

Image: Dandridge Cole, who coined the term ‘macro-life’ to refer to human colonies in space and their evolution. Credit: Wikimedia Commons.

The idea is now a familiar one to science fiction fans, especially after its appropriation by George Zebrowski in his 1979 novel Macrolife, but in the mid-60s, the notion of hollowing out an asteroid to create an interstellar vehicle would hardly have been common currency. As Hein comments in his article, what Cole was doing was creating a bridge between the kind of space colonies that Gerard O’Neill would make famous and the worldships that might one day take a large human colony, a self-contained society, to a distant star.

The idea has resonance because star journeys may turn out to be multi-generational affairs that evolve naturally out of our eventually mastered skills at creating self-contained habitats in nearby space. If you can build a ship large enough and comfortable enough to re-create a planet-like environment within it, then living there might become so natural that future generations born aboard the craft would see no need for planetary living. A colony world like that might eventually disengage from the stellar system that created it and begin a voyage that would have no other aim than continuing exploration, taking ‘home’ with the crew wherever it went.

Artist and futurist Roy Scarfo provided the artwork in Cole’s 1965 book Beyond Tomorrow. On his site, Scarfo recalls going with Cole in the ambulance and being in the hospital at the time of his death. A futurist to the end, Cole had planned to have his body frozen and had made a serious study of cryogenics:

When we got to the hospital, the hospital personnel took him to a room. When they informed me that Dan was dead, and knowing that Dan wanted to be frozen, I called Ettinger, who I believe was in Chicago and who was the authority on cryogenics at the time. He knew Dan and instructed me to get in touch with a hospital and make arrangements for freezing. I believe it was the University of Pennsylvania hospital. I was racing against time as every second counted to preserve the body.

Personal and legal issues persuaded the family not to proceed with the arrangements, and Cole was buried conventionally, with Scarfo serving as one of the pallbearers.

Scarfo also wrote an appreciation of Cole on Alex Michael Bonnici’s Discovery Enterprise site in which he recalls working with Cole on Beyond Tomorrow in the evenings after work in Scarfo’s office at GE, where they would go over the chapters word by word. Says Scarfo:

Our work together gave us a handle as “the weird couple” because of the way-out material we were producing together. Today many of those concepts are as common as soap. The majority of our work together was done outside our regular responsibilities at GE, although sometimes they overlapped. We would meet almost daily for lunch at the cafeteria and afterward walk and talk during the rest of our lunch hour. This went on for years.

We’re surely due for a renewed look at Cole’s contribution and his ideas, especially as attention now turns to mining and the other possibilities the asteroids represent. Alex Michael Bonnici wrote his own tribute to Cole in 2007, one that encapsulates the asteroid-as-habitat idea:

In 1963, Cole wrote Exploring the Secrets of Space: Astronautics for the Layman with I. M. Levitt. In this book they suggested hollowing out an ellipsoidal asteroid about 30 km long, and rotating it about its major axis to simulate gravity. By reflecting sunlight inside with mirrors, and creating, on its inner surface, a pastoral setting an asteroid could be transformed into a permanent space colony. Cole and Cox also envisioned that asteroids would provide the raw materials to form the basis of a spacefaring civilization. And, that asteroidal materials would also serve terrestrial needs. In their view these materials could be transported using mass drivers or linear motors. Cole’s work largely presages that of Gerard K. O’Neill by more than a decade.

Extend the notion to an interstellar journey and you get what Cole would call a ‘nomadic pseudo-Earth’ that would be the seeding ground for so-called ‘macro-life.’ Cole’s view was that future human evolution inside such habitats, which includes synchrony between humans, their environment, and their technology, creates a ‘new large-scale life form.’ It was one he felt we must become, for in the years not long before his death, he had become extremely worried about our species not only in terms of population pressure but also weapons proliferation. Moving into space would be the chance to give humanity a progressing series of new and better starts.

Image: The populated asteroid from without and within. Credit: Roy Scarfo.

Here’s TIME’s take on Cole’s macro-life views in a January 27, 1961 article:

Cole proposes the development of giant spaceships, each of which would contain at least 10,000 individual humans who would function rather like the cells of a multicelled animal; collectively, they would constitute what Cole calls a unit of “macrolife.” Stowed along with the humans in the vast body of the macroorganism would be domestic animals, plants, raw materials, machines and computers, as well as microfilms of all the books in the Library of Congress. A fully developed unit of macrolife would have rocket propulsion to enable it to move at will around the solar system. It would be able to live independently almost anywhere in space, but its normal habitat would be the asteroid belt between Mars and Jupiter where it could feed upon the mineral riches of the asteroids.

Macrolife in space would be self-adjusting, spinning off new units aboard new asteroids as necessary, but Cole freely acknowledged the difficulties in creating self-sustaining biospheres, urging that underwater bases or other sealed environments would need to become experimental testbeds for his ideas. A spacefaring species aboard a hollowed-out world, spun up for artificial gravity and provided with many of the amenities of planetary life, could well take to the stars one day. But in any case, Cole’s legacy of insightful probings of the human future will endure, the work of a man whose all too short life yielded much and has inspired interstellar theorists ever since.

For more on Cole, see Joseph Friedlander’s In Praise of Large Payloads for Space.