Paul Gilster's Blog, page 229

The British Interplanetary Society at 80 Years

by Kelvin F.Long

Centauri Dreams readers will know Kelvin Long as the Chief Editor for the Journal of the British Interplanetary Society, but the résumé hardly stops there. He is also the Deputy Chair of the BIS Technical Committee and a member of the governing council. Long is the co-founder of Project Icarus, co-founder of the non-profit Icarus Interstellar (formerly serving as the Vice President European Operations) and is the co-founder of the pending Institute for Interstellar Studies. He is the managing Director of the aerospace company Stellar Engines Ltd. Here Kelvin begins a two-part article (to be completed on Monday) highlighting the British Interplanetary Society and its numerous contributions to spaceflight concepts both interplanetary and interstellar.

Liverpool is a unique location in British history. Not just because of the Beatles or Olaf Stapledon, but because this is where the British Interplanetary Society (BIS) was founded in 1933 by a Cheshire-born engineer, Philip E.Cleator. Impressed with the rocketry efforts in the US and Germany, he took the initiative to form a UK based rocket society and he published his article “The Possibilities of Interplanetary Travel” in Chambers Journal in January 1933. This was subsequently picked up by the Editor of the Liverpool Echo and eventually by the national press in the form of the Daily Express. This led to a front page feature and the gathering of a small collection of local people at his home.

The decision was then made to set up the British Interplanetary Society. The inaugural meeting of the society took place at the office of H.C.Binns on the second floor of No.81 Dale Street, Liverpool, on Friday 13th October 1933. It was not until the end of 1945 that the articles of the reformed BIS were drafted (the society was suspended during the war) and the society registered as a limited company. It was in 1936 that the London section was formed and this eventually became the main headquarters the following year. For the record, the Journal of the British Interplanetary Society was founded in 1934 and is the oldest astronautical journal in the world. The society’s popular space magazine Spaceflight (now edited by David Baker) was founded in 1956 (a year before Sputnik 1), and remains at least one of the oldest space magazines still in existence (today the BIS also publishes the space history journal Space Chronicles (1980), edited by John Becklake, and the science fiction based e-magazine Odyssey (2011), edited by Mark Stewart.

Image: Current headquarters of the British Interplanetary Society at 27/29 South Lambeth Road, London. Credit: Kelvin Long.

The society grew from those early foundations and some of the earlier members included people like Arthur C. Clarke, Les Shepherd, Eric Burgess, Ralph Smith, Harry Ross, Ken Gatland, Val Cleaver and later on Patrick Moore. For anyone who knows their space history, all of these people have had huge impacts on the development of space technology or in helping to communicate and advocate for the exploration of space. Clarke pioneered the idea of the telecommunications satellite as well as writing world class science fiction; Eric Burgess was the first to suggest to Carl Sagan that a message for ET could be included on the Pioneer spacecraft; Val Cleaver was the inventor of the British rocket engine that went into the Blue Streak missile; Gatland, Smith and Ross were all pioneers of rocketry, satellite payloads and space architectures; Les Shepherd was a pioneer of nuclear propulsion and eventually went on to be the president of the International Astronautical Federation (IAF), an organization that included the BIS as one of its founding members in 1951.

According to the Memorandum of Association:

“The objects for which the British Interplanetary Society is established are to promote the advancement of knowledge and the spread of education and particularly to promote the advancement and dissemination of knowledge relating to the science, engineering and technology of Astronautics and to support and engage in research studies and to disseminate the useful results thereof and in furtherance thereof…to hold meetings, promote exhibitions, publish reports, make awards, medals or grants, to provide funds for educational and academic activities in furtherance of its objects”.

In order to understand the crucial role that the British Interplanetary Society has played in the history of space exploration, it’s worth looking at some examples from the society’s rich technical history.

The BIS Moonship

For years people had dreamed about visiting the Moon and some even wrote about it. Jules Verne originally wrote From the Earth to the Moon in 1865. This is a fascinating tale of a group of people who build an enormous space gun and launch themselves in a projectile spaceship all the way to the Moon. Verne had apparently done some calculations for the mission, although the particular method lacked the safety we have come to expect for man-rated vehicles – it is not likely the crew would have survived the trip. H.G.Wells made an interesting attempt at lunar flight in his 1901 story The First Men in the Moon. The vehicle would use a mysterious substance called “Cavorite” which would negate the force of gravity to effectively give the vehicle its required lift properties and allow a visit to the extraterrestrial civilization of insect-like creatures inhabiting the Moon known as the Selenites.

These were wonderful works of the imagination but could we come up with anything that resembled reality? So it was that in 1938, the BIS Technical Committee decided to go the full distance and produce a conceptual design of a vessel that would carry a crew of three safely to the Moon, permit them to land for a stay of fourteen days, and provide for a safe return to the Earth with a final payload of half a ton. The object of the exercise was to demonstrate that, within the capabilities of propellants that could be specified (at least theoretically) at the time, such a mission was not merely possible but would be economically viable – insofar as the vehicle lift-off mass from the Earth would be no more than one thousand tons. The conceptual design that resulted came to be known as the BIS Lunar Spaceship, and for all its flaws and misconceptions it must be regarded as one of the classical pioneering studies in the history of astronautics.

Image: BIS Moonship and Lander. Credit: British Interplanetary Society.

The mission proposed for the Lunar Spaceship would involve total velocity changes in excess of 16 km/s, a figure that would be significantly increased by certain losses. The best available propellants were not expected to achieve rocket motor efflux velocities of one quarter of that figure. This enormous disparity implied that, if one attempted to achieve the entire mission with a simple single-stage vessel, 99% or more of its initial lift-off mass would have to consist of the propellant. (In the more common parlance of rocketry this required a mass ratio exceeding 100.) The most enthusiastic proponents of space flight were at one with their critics in dismissing this as inconceivable. To circumvent the problems, the pioneers of astronautics invented the Step Rocket, in which the vessel consisted of a series of stages of diminishing size, fired in sequence. As each successive stage completed firing, its engines and other redundant structure would be discarded leaving the higher stages to continue the flight.

In this way it would be possible to obtain a high mass ratio without invoking the need to achieve impossible structural factors. Looked at in another way, the total velocity change required of the overall vessel would be shared between the stages. In this case, four equal stages would each need to contribute little more than 4 km/sec to the total velocity change. That would be possible with the performance of known propellants. The proportion of the stage mass taken up by propellant would assume a reasonable level (say, 75%, corresponding to a mass ratio of 4). However, a penalty would be incurred in the final payload, which would be reduced in inverse proportion to some number raised to the power of the number of stages. Optimistically, at the time, that number might have been taken as 10. Thus, with four stages, the final payload might be expected to be only one ten-thousandth of the lift-off mass. The nub of the argument of the more informed critics of such a lunar flight would have been that such a mission would probably have required as many as five stages, perhaps more, so that the initial vessel would have had to match an ocean liner in size to carry an ultimate payload of one ton. Such a mission could not be viable.

In 1919 Robert Goddard, in his classic paper “A Method of Reaching Extreme Altitudes”, went a stage further than the step rocket principle in suggesting a firing procedure that amounted to the continuous discarding of redundant structure. This procedure, in principle, could result in a significant improvement in payload ratio compared to the step rocket. The BIS, in its design concept, adopted a cellular construction that, in essence, conformed to Goddard’s suggestion.

The BIS Space Ship was described in the January 1939 Journal by H.E. Ross. The vessel was divided into six tiers (steps) of equal hexagonal cross-section and the six sections were made up of an array of tubes each consisting of separate rocket motors. Each of the lowest 5 steps was made up of 168 motors, intended to impart sufficient velocity to achieve escape from the Earth’s gravitation. The remaining stage consisted of 45 medium motors and 1200 smaller tubes intended to land the remainder of the vessel on the Moon, allow for subsequent escape from the latter (leaving redundant structure on the surface of our satellite), and for reduction in velocity prior to entering Earth’s atmosphere. Perhaps the most important lasting achievement of the Lunar Spaceship study, however, came from its conclusions regarding the landing upon, and lift-off from, the lunar surface. R.A. Smith developed the concept after World War II in an article – “Landing on an Airless World” – published in the August 1947 BIS Journal, accurately depicting the procedure that was to be adopted with the Apollo Lunar Excursion Module. The only notable difference between the two cases was, perhaps, that Smith’s design was more elegant than the actual LEM.

The Technical Committee decided that its activities should embrace an experimental programme to support its Lunar Spaceship concept. From the outset, it rejected the experimental “firing of free rockets” as valueless on account of their small scale and lack of control over the many parameters involved in such flights. It made no attempt, therefore, to emulate the VfR [the German Verein für Raumschiffahrt, or Society for Space Travel] or later American groups. The BIS workers considered that the development of rocket motors for their proposed lunar mission would have to proceed in stages, beginning with literature and experimental studies of possible propellants, followed by the design of chambers and nozzles on the best theoretical basis – the work of Sänger was cited as noteworthy in this respect.

The resulting motors and selected propellants would then be brought together in static proving stand firings in which all the variables could be systematically controlled and measured. The intention was correct and logical, but even the over-optimistic members of the Technical Committee were bound to note that such a program was far beyond their resources. Nevertheless, largely under the supervision of Janser, who was a research chemist, they embarked on the preliminary stages of the propellant survey hoping that eventually they would solicit sufficient support from public benefactors, convinced by the evidence emerging from the Lunar Spaceship study, to proceed with serious development. Undaunted, R.A. Smith designed a basic test stand that was actually constructed. Despite some shortcomings, the program of the Technical Committee was a laudable endeavor.

The BIS Space Suit

In a November 1949 symposium, Harry Ross presented a paper on the “Lunar Space-Suit”. Ross had examined the problem of a 68 kg lunar space suit (equivalent to 11 kg on the Moon) which could be worn for up to 12 hours, within the temperature range of 120 degrees to minus 150 degrees Celsius, representing night and day. The suit design was 4-ply, made up of a thin exterior skin of closely woven cloth. It had a 1 cm layer of cellular heat-resisting material (Kapok, wool, felt et cetera) and a 1-2 mm main airtight sheath of fabric-backed natural or synthetic rubber. It also had an interior lining of non-hygroscopic material, mainly for comfort and to manage contact between the rubber and skin and absorption of the water-vapor.

Image: The BIS Space Suit. Credit: British Interplanetary Society.

The exterior of the lunar space suit was to be a highly burnished metallic film, designed to reflect as much heat as possible. The chest and thigh areas were to be given an external matt-black finish to manage heat loss. Operation of the suit during the lunar day would require further cooling through the use of a low boiling liquid such as ammonia or water – which would vaporize to space through a thermostatic valve. The helmet was to be a light, rigid double-shell structure, with the inner a bright alloy metal and the outer a plastic with burnished metal coating. Lateral vision of 180 degrees was proposed with a minimal vertical extension in order to minimize heat gain or loss. A special glass to prevent heat and actinic ultraviolet rays would be employed. There would be further precautions, including providing the helmet with a shading peak and an external moveable visor made either of darkened glass or bright metal pierced with cross-slits in front of the eyes. The suit was to be a good fit to ensure maximum comfort and the shoulders would be internally padded.

Considerable thought went into the problem of air-conditioning, as discussed by Bob Parkinson in his book Interplanetary:

“Compressed (bottled) oxygen was regarded as simplest, and Ross recognized that a skin-tight suit with bottled oxygen flushing to waste might be sufficient, the weight of even a 12-hr supply not being excessive. However, a pure liquid oxygen supply was suggested, with the atmosphere maintained at about 160 mm Hg (21 kPa). The suit’s atmosphere was to be circulated through the conditioning units and throughout the dress by an electric fan-pump driven by the electric battery. Respired carbon dioxide was to be removed by chemical means – sodium peroxide being preferred because the reaction yielded oxygen, reducing the generous allowance of 0.78 litres per min by as much as 43% – as against, for example, sodium hydroxide, where there is no regain. The sodium peroxide would also absorb water, of which it was assumed the lungs and skin would yield some 108 gm/hr”.

The space suits that were eventually worn by the Project Apollo astronauts are a far cry from this original 1940s design. But the work started out by Harry Ross led to credible thinking on how humans could survive in a self-contained, mobile habitat. The original paper by Harry Ross is titled “Lunar Space Suit,” Journal of the British Interplanetary Society, Vol.9, No.1, pp.23-37, January 1950

Project Megaroc

The “Megaroc” man-carrying rocket proposal had been put forward by R.A. Smith in 1946 after H.E. Ross observed that the V-2 was “nearly big enough to carry a man.” The objective was to provide manned ascents to a maximum of 304 km (one million feet). During flight, it was proposed that scientific observations could be made of the Earth and the Sun, that radio communication through the ionosphere could be tested, and that data should be collected on human performance over a wide range of g-conditions. The project was submitted to the Ministry of Supply on 23rd December 1946, but rejected. The proposal has remarkable similarities to the subsequent American Mercury project. Where differences do occur, they generally arise from the fact that Megaroc was much less ambitious, not being designed for orbital flight.

The Ross and Smith Megaroc was a modified, enlarged and strengthened V-2. The normal motor was retained but the tank diameter was increased and the end walls strengthened to accommodate enough propellant for 110 sec at full thrust, and a further 38 sec at constant acceleration. This brought the maximum hull diameter up to 2.18 m. The graphite efflux control vanes were retained, enlarged, and given the extra duty of imparting a slow stabilizing spin to the rocket. On the other hand, the big aerodynamic fins and associated controls were omitted, saving some 320 kg of weight. This was, indeed, one of the first big rocket designs in which aerodynamic fins were omitted – a feature not generally adopted in practice for another ten years.

Image: The BIS Project Megaroc. Credit: British Interplanetary Society.

The standard turbo-pump was retained but turned through 90°, rotating about the major axis of the rocket to prevent the turbine promoting tumbling after fuel cut-off. In place of the instrument bay and warhead there was a pressurized cabin, enclosed in a streamlined, jettisonable nose cone. This brought the overall length of the rocket up to 17.5 m. The launch weight was 21.2 tons. The cabin, with a return weight of 586 kg, had two large side-ports for access, observation and egress.

There was also a “strobo-periscope” (a modified form of the BIS’ pre-War coelosat, which was an experimental device to examine the possibilities of interstellar navigation) for rearward viewing after the rotating cabin had separated from the hull. Mercury’s one-ton double-walled titanium cabin started off with a topside escape hatch, two small ports and a periscope. However, the hatch was later more conveniently situated, like Megaroc’s, in the side of the cabin and arrangements were made for picture-window visibility. Megaroc’s observer was to wear a standard high-altitude g-suit, with its own air-conditioning unit and personal parachute. No other air-conditioning was proposed owing to the short duration of the flight. Although both used a cradle-type seat with integral controls, the Mercury cradle was fixed while Megaroc’s was counterbalanced and designed to tilt. The cabins of both rockets were attitude-stabilized by hydrogen peroxide jets, and both were fitted with automatic, manual and emergency controls, differing mainly in that the Megaroc was designed for a less hazardous mission.

Mercury’s cabin was provided with a heat shield against frictional heating upon re-entry to the atmosphere, retro-rockets and parachutes for braking and descent. Megaroc needed no special heat shield and relied on a reefing parachute ejected by spring flaps and a compressed air charge to provide constant drag irrespective of air-density and velocity of descent. Megaroc’s cabin was suitable for either sea or land impact and was fitted with a crumple skirt to absorb some of the shock and avoid bounce with a quick-release mechanism for the parachute. The maximum ascent acceleration imposed on the Megaroc observer was 3 g (for Mercury the figure was 9 g).

Megaroc would be launched from a tower inclined at an angle of 2° from the vertical with an initial acceleration of 9.8 m/sec2. Constant thrust would be maintained for 110 sec when the rocket would have reached 46,000 m, and the effective acceleration would have become about 20 m/s2. At this point the pilot would be experiencing 3 g, the limit at which it was thought that operational duties could be satisfactorily discharged. The pilot would actuate the fuel controls at this point to progressively reduce thrust and keep the g-meter reading constant. In case of emergency at any stage of the flight, relaxation of the pilot’s grip would switch the rocket from manual operation to automatic radio-telecontrol from the ground.

When the air-density had reduced to a point where drag was negligible, a pressure operated release mechanism would unlatch the nose-cone sections ready for jettisoning. At some subsequent moment the pilot would operate a compressed-air charge to drive the cabin and hull apart. This would also initiate operation of a delay mechanism for ejection of the hull-recovery parachute.

The control connections between cabin and hull would uncouple automatically on separation and the communication system would be switched from the four-dipole arrays arranged in blisters near the stem of the hull to arrays situated under the floor of the cabin. Cabin attitude and rate of spin would be controlled by hydrogen peroxide jets. It was thought that the pilot would therefore be able to carry out experiments with various values of g, down to zero, including free movement inside the cabin, and would be able to turn the cabin stern-down for re-entry into the atmosphere. The apex of the trajectory would be attained about 6 min 16 sec after launch and the cabin’s constant-drag parachute was to be ejected in descent at an altitude of about 113 km, the maximum deceleration imposed on the pilot being calculated as 3.3 g. The parachute would be fully extended on approaching touchdown, when it would be released to prevent the cabin from being dragged along.

It was appreciated that the Megaroc project would need to progress through a series of preliminary experiments to test the practicality of the design. For example, the modifications to the turbine and fuel control, and the endurance and reliability of the motor under the prolonged running conditions would need to be verified. The efficiency of other special innovations, such as the crumple skirt, variable-area parachutes and strobo-periscope were also to be tested. An operational mock-up of the cabin was proposed, to be suspended by a cable so that the pilot could be trained in control of orientation and spin. The pilot would also be trained in the telecontrol of an unmanned rocket and cabin assembly in free flight. Manned ascents to progressively increased altitudes were to be undertaken before attempting the maximum terminal altitude of over 1,000,000 ft (304 km).

End of part one. Part two follows on Monday.

Voyager: Looking Backward and Forward

The Voyager spacecraft have run into their share of problems as they move toward true interstellar space, but on the whole their continued operations have been a testament to what well designed equipment can do. Voyager 2’s camera platform locked for a time not long after the Saturn flyby but controllers were able to restore the system by experimenting with similar actuators on Earth. Three years ago the craft began having data problems resulting from a flipped bit in an onboard computer but a reset from Earth corrected the fault. Even the failure of the primary radio receiver not long after launch was resolved by the use of the onboard backup.

Obviously both craft are living on borrowed time as the power output of their radioisotope thermoelectric generators (RTGs) continues to decline, but we should still be getting signals for another decade or so. With the Voyagers now on what is designated their ‘interstellar mission,’ it’s pleasing to note that Alpha Centauri is the guide star that Voyager 1 used to reorient itself to resume transmissions to Earth following 2011 maneuvering to allow better detection of the solar wind. We continue to push deeper into a region of space that is now little understood.

Leaving the Solar System

Yesterday’s brief skirmish over Voyager 1’s true situation tells us how much we have to learn about the Solar System’s edge. A paper by William Webber (New Mexico State) and the late Frank McDonald (University of Maryland) reported that a sudden change in cosmic rays detected by Voyager 1 last summer showed that the spacecraft was in a new region of the Solar System they called the ‘heliocliff.’ What evidently confused matters was that the American Geophysical Union, publisher of Geophysical Review Letters — the publication at which the paper had been accepted — sent out a news release saying the craft had left the Solar System.

While the cosmic ray changes were marked, with galactic cosmic ray intensity suddenly doubling last August, Caltech’s Ed Stone issued a statement saying that a change in the magnetic field will be the true indication of Voyager 1’s arrival in interstellar space. No such change has yet been detected, and the AGU soon revised the news release headline to say that the spacecraft had ‘entered a new region of space.’ The ‘heliocliff,’ in other words, is apparently the same region that NASA scientists had already noted as a previously unknown ‘highway’ of magnetic particles. Nancy Atkinson straightened all this out quickly on Universe Today.

So Voyager 1 hasn’t yet left the Solar System, even if it is in a curious boundary region we’re still learning about. Stone said last December that he believes true interstellar space may be months or at most a couple of years away. Whenever the transition does occur, it will mark our species’ first penetration of the realm beyond the heliosphere, and we’re fortunate indeed to have two spacecraft still functional enough to report back their findings as it occurs. After all, the Voyagers were never designed to be interstellar craft and have far exceeded our expectations.

Image: The launch of Voyager 1 on September 5, 1977. Credit: NASA.

Voyager and the Archaeological Record

Meanwhile, another take on the Voyagers was offered up last January at the World Archaeology Conference in Jordan, where the spacecraft were treated as artifacts of our civilization. Colleen Beck (Desert Research Institute) and Ben McGee (Astrowright Spaceflight Consulting LLC) looked at the probes as meaning-bearing objects with or without their famous ‘Golden Records,’ markers of the culture that made them. Their presentation was titled “The bottle as the message: Solar System escape trajectory artifacts.” Matthew Battles uses Beck and McGee’s work as a launching pad for his own insights into the Voyagers in The Ache for Immortality.

Surely the Golden Records will never be snared by an extraterrestrial civilization, but compiling them taught us much about ourselves and our need to be remembered. Carl Sagan wrote about the Golden Record project in Murmurs of Earth (1978) where, Battles reminds us, he invoked the name of Esarhaddon, a 7th C. BC Assyrian king who saw to it that plaques were placed in the foundations of monuments in his kingdom as messages to the future. Thus the idea of a votive impulse focused not on the gods but rather posterity, an impulse to connect with successor generations that appears to be hard-wired in the species.

It turns out that another probe designed for our descendants is already in space. The Laser Geodynamic Satellite (LAGEOS) was launched in 1976 and joined by a second LAGEOS in 1992, both designed to study continental drift. Battles describes the satellite as a ball of brass more than half a meter in diameter, weighing 450 kg and carrying no instrumentation. The working principle is that ground-based lasers use the satellites to measure accurate distances, allowing scientists to detect tiny movements in the Earth’s crust. LAGEOS is in an orbit that will take over 8 million years to decay. It, too, contains a plaque, this one showing Earth’s continents over 16 million years of projected continental drift, a kind of time capsule in its own right.

What to make of gestures like this? From the essay:

There is a peculiar quality in these plaques and golden records — a compound of the Quixotic and the Ozymandian; an acknowledgement of our cosmic insignificance, paired with pride in the craft that pries that knowledge loose from the world — which is deeply characteristic of science in the late 20th century. Sagan stated as much when he wrote of the first Voyager mission, ‘the launching of this “bottle” into the cosmic “ocean” says something very hopeful about life on this planet’ — a hope that, however slim, was still vastly greater than the chance that one of the Voyagers would ever encounter life elsewhere. These messages in a bottle were among the more telling transmissions in a mythology of wonder that American science generated in the mid-20th century — an attempt, through science itself, to preserve a record of life on Earth, in light of destructive powers unleashed by science in the atomic age.

But an archaeological look at human monuments scattered throughout the Solar System — probes in long orbits, abandoned equipment on the Moon, networks of communications satellites — might see them in the same light that we now examine Esarhaddon’s works, for, as Battles puts it, “…like the monuments of ancient Mesopotamia, they embody our wonder tales as well.” I think any future archaeologist, human or otherwise, would read into the Voyager spacecraft the desire of a species to transcend itself, hopeful of finding a bridge to other intelligence but pressing on regardless as a way of building meaning into the cosmos.

Keeping the Probe Alive

Talking about issues of long-term maintenance and repair, as we have been for the past two days, raises the question of what we mean by ‘self-healing.’ As some commenters have noted, the recent Caltech work on computer chips that can recover from damage isn’t really healing at all. Caltech’s researchers zap the chip with a laser, but there is no frantic nanobot repair activity that follows. What happens instead is that sensors on the chip detect the drop in performance and go to work to route around the damage so the system as a whole can keep performing.

So the analogy with biological systems is far-fetched, and we might think instead of Internet traffic routing around localized disruptions. It’s still tremendously useful because CMOS (complementary metal–oxide–semiconductor) chips can start acting flaky depending on factors like temperature and power variations. Problems deep inside a chip generally force us to replace an entire piece of equipment — think cell phones — whereas a chip that can smooth out disruptions and continue to perform more or less as before would add to product life.

Restoring Function Inside the Chip

While the Caltech work proceeds, researchers at the University of Illinois at Urbana-Champaign have taken a different approach to electronic chips. They put tiny microcapsules filled with eutectic gallium-indium — chosen because it is highly conductive — into experimental circuits so that when the circuits were broken (the voltage falling to zero) the ruptured microcapsules ‘healed’ them within a millisecond. The voltage measured prior to the break was quickly restored. The team worked with microcapsules of different sizes to measure their effects, learning that a mixture of 0.01 mm and 0.2 mm capsules produced the best result.

The implications of this kind of work for future space missions were not lost on aerospace engineering professor Scott White, who told the BBC:

“The only avenue one has right now is to simply remove that circuitry when it fails and replace it — there is no way to manually go in and fix something like this… I think the real application area that you’ll see for something like this is in electronics which are incredibly difficult to repair or replace — think about satellites or interplanetary travel where it’s physically impossible to swap out something.”

Image: Self-healing electronics. Microcapsules full of liquid metal sit atop a gold circuit. When the circuit is broken, the microcapsules rupture, filling in the crack and restoring the circuit. Credit: UIUC/Scott White.

All of this comes out of work into extending the lifetime of rechargeable batteries (see Self-healing electronic chip tests may aid space travel for more). White said that physically building new circuits every time we need new functionality may give way to circuits that last longer, circuits whose redesign is keyed more to software upgrades than constant hardware changes. Imagine cell phones rendered more sustainable by the presence of ‘self-healing’ circuitry that can repair tiny cracks that would otherwise cause the device to stop working.

Healing Spacecraft Composites

We’ll see how the electronics industry reacts to these ideas when the technology becomes generally available. Meanwhile, the implications for deep space and other environments where chips are hard to replace are clear. This in turn reminds me of a study funded by the European Space Agency back in 2006. Carried out at the University of Bristol, it involved materials that could be used on the superstructure of space vehicles. Cracks caused by temperature extremes or the impact of dust grains traveling at several kilometers per second can build up over the lifetime of a mission, weakening the structure and threatening catastrophic failure.

The Bristol team, led by Christopher Semprimoschnig (ESTEC) inserted hollow fibers filled with adhesive materials into a resinous composite similar to that used in spacecraft components. The glass fibers were designed to break when any damage to the spacecraft ‘skin’ occurred, releasing the liquids needed to fill the cracks. Semprimoschnig likened the process to what happens when humans cut themselves and their blood hardens to form a protective seal that allows new skin to form underneath. This ESA news release provides more background.

Image: Hollow fibers just 30 micrometres in diameter thread the new material. When damage occurs, the fibers break releasing liquids that seep into the cracks and harden, repairing the damage. Credit: ESA.

My assumption is that advances in both biology and nanotechnology are going to provide startling breakthroughs in materials that will make autonomous repair — whether we call it true ‘healing’ or not — possible in settings where no human intervention is possible. The worldships we talked about last week would be repaired and maintained by their inhabitants, but robotic probes on century-long journeys will need every tool in our arsenal to keep themselves functional. A truly autonomous spacecraft really does mimic biological systems in its ability to repair and adapt. Learning how to build it is a priority for future starship design.

Autonomy and the Interstellar Probe

Yesterday’s thoughts on self-repairing chips, as demonstrated by recent work at Caltech, inevitably called Project Daedalus to mind. The span between the creation of the Daedalus design in the 1970s and today covers the development of the personal computer and the emergence of global networking, so it’s understandable that the way we view autonomy has changed. Self-repair is also a reminder that a re-design like Project Icarus is a good way to move the ball forward. Imagine a series of design iterations each about 35 years apart, each upgrading the original with current technology, until a working craft is feasible.

My copy of the Project Daedalus Final Report is spread all over my desk this morning, the result of a marathon copying session at a nearby university library many years ago. These days you can skip the copy machine and buy directly from the British Interplanetary Society, where a new edition that includes a post-project review by Alan Bond and Tony Martin is available. The key paper on robotic repair is T. J. Grant’s “Project Daedalus: The Need for Onboard Repair.”

Staying Functional Until Mission’s End

Grant runs through the entire computer system including the idea of ‘wardens,’ conceived as a subsystem of the network that maintains the ship under a strategy of self-test and repair. You’ll recall that Daedalus, despite its size, was an unmanned mission, so all issues that arose during its fifty year journey would have to be handled by onboard systems. The wardens carried a variety of tools and manipulators, and it’s interesting to see that they were also designed to be an active part of the mission’s science, conducting experiments thousands of kilometers away from the vehicle, where contamination from the ship’s fusion drive would not be a factor.

Even so, I’d hate to chance one of the two Daedalus wardens in that role given their importance to the success of the mission. Each would weigh about five tonnes, with access to extensive repair facilities along with replacement and spare parts. Replacing parts, however, is not the best overall strategy, as it requires a huge increase in mass — up to 739 tonnes, in Grant’s calculations! So the Daedalus report settled on a strategy of repair instead of replacement wherever possible, with full onboard facilities to ensure that components could be recovered and returned to duty. Here again the need for autonomy is paramount.

In a second paper, “Project Daedalus: The Computers,” Grant outlines the wardens’ job:

…the wardens’ tasks would involve much adaptive learning throughout the complete mission. For example, the wardens may have to learn how to gain access to a component which has never failed before, they may have to diagnose a rare type of defect, or they may have to devise a new repair procedure to recover the defective component. Even when the failure mode of a particular, unreliable component is well known, any one specific failure may have special features or involve unusual complications; simple failures are rare.

Running through the options in the context of a ship-wide computing infrastructure, Grant recommends that the wardens be given full autonomy, although the main ship computer would still have the ability to override its actions if needed. The image is of mobile robotic repair units in constant motion, adjusting, tweaking and repairing failed parts as needed. Grant again:

…a development in Daedalus’s software may be best implemented in conjunction with a change in the starship’s hardware… In practice, the modification process will be recursive. For example the discovery of a crack in a structural member might be initially repaired by welding a strengthening plate over the weakened part. However, the plate might restrict clearance between the cracked members and other parts, so denying the wardens access to unreliable LRUs (Line Replacement Units) beyond the member. Daedalus’s computer system must be capable of assessing the likely consequences of its intended actions. It must be able to choose an alternative access path to the LRUs (requiring a suitable change in its software), or to choose an alternative method of repairing the crack, or some acceptable combination.

Image: Project Daedalus was the first detailed study of an interstellar probe, and the first serious attempt to study the vexing issue of onboard autonomy and repair. Credit: Adrian Mann.

The Probe Beyond Daedalus

Robert Freitas would follow up Daedalus with his own study of a probe called REPRO, a gigantic Daedalus capable of self-reproduction from resources it found in destination planetary systems. Another major difference between the two concepts was that REPRO was capable of deceleration, whereas Daedalus was a flyby probe. Freitas stretched the warden concept out into thirteen different species of robots who would serve as chemists, metallurgists, fabricators, assemblers, repairmen and miners. Each would have a role to play in the creation of a new probe as self-replication allowed our robotic emissaries to spread into the galaxy.

Freitas would later move past REPRO into the world of the tiny as he envisioned nanotechnology going to work on interstellar voyages, and indeed, the promise of nanotech to manipulate individual atoms and molecules could eventually be a game-changer when it comes to self-repair. After all, we’d like to move past the relatively inflexible design of the warden into a system that adapts to circumstances in ways closer to biological evolution. So-called ‘genetic algorithms’ that can test different solutions to a problem by generating variations in their own code and then running through generations of mutations are also steps in this direction.

One thing is for sure: We have to assume failures along the way as we journey to another star. Grant sets a goal of 99.99% of all components aboard Daedalus being able to survive to the end of the mission. This was basically the goal of the Apollo missions, though one of those missions suffered only two defects, equivalent to a 99.9999% component survival rate. Even so, given the need for repair facilities and wardens onboard to fix failing parts, Grants figures show that a mass of spare components amounting to some 20 tonnes needs to be factored into the design.

It will be fascinating to see how Project Icarus manages the repair question. After all, Daedalus was set up as an exercise to determine whether a star mission was feasible using current or foreseeable science and technology. With the rapid pace of digital change, how far can we see ahead? If we’re aiming at about 35 years, do we assume breakthroughs in nanotechnology and materials science that will make self-healing components a standard part of space missions? Couple them with advances in artificial intelligence and the successor to Daedalus would be smaller and far more nimble than the original, a worthwhile goal for today’s starship design.

The two papers by T.J. Grant are “Project Daedalus: The Need for Onboard Repair,” Project Daedalus Final Report (1978), pp. S172-S179; and “Project Daedalus: The Computers,” Project Daedalus Final Report (1978), pp. S130-S142.

Self-Healing Circuits for Deep Space

Computer failures can happen any time, but it’s been so long since I’ve had a hard disk failure that I rarely worry about such problems. Part of my relaxed stance has to do with backups, which I always keep in triplicate, so when I discovered Friday afternoon that one of my hard disks had failed — quickly and catastrophically — it was more of a nuisance than anything else. It meant taking out the old disk, going out to buy a new one and installing same, and then loading an operating system on it. Because I do 90 percent of my work in Linux, I opted for Linux Mint as a change of pace from Ubuntu, making it the tenth version of Linux I’ve used over the years.

My weekend was mildly affected, but the new disk went in swiftly and the operating system load went without incident, so I was still able to get to two concerts, one of them an absolutely brilliant handling of Elgar’s ‘Enigma Variations,’ and to see the new Tommy Lee Jones movie ‘Emperor.’ Hardware failures in the midst of an urban environment, and with adequate backups on hand, are thus easily handled. But then I started thinking about robotics and deep space. Ponder the hardware failures that are inevitable on missions lasting decades or even centuries. An unexpected failure in a key circuit could wreck a lot more than a weekend on such a probe.

From Wardens to Self-Healing

Remember the ‘wardens’ that were built into the Project Daedalus plan? They were designed to take care of the vessel on its 50-year run to Barnard’s Star, an acknowledgment of what happens to complex systems over time. These days we’re focusing in on self-healing electronics that can repair themselves in microseconds, integrated chips that spring back from potential disaster, rebuilding themselves faster than any human intervention could manage. Members of the High-Speed Integrated Circuits laboratory at Caltech have been experimenting with self-healing integrated chips that can recover all but instantaneously from serious levels of damage.

Image: Some of the damage Caltech engineers intentionally inflicted on their self-healing power amplifier using a high-power laser. The chip was able to recover from complete transistor destruction. This image was captured with a scanning electron microscope. Credit: Caltech.

The chips in question are high-frequency power amplifiers useful for communications, imaging, sensing and other applications. Each of these chips holds more than 100,000 transistors along with a custom-made application-specific integrated-circuit (ASIC) that monitors the amplifier’s performance and adjusts the system’s actuators when changes are called for. The idea is to let the system itself determine the need to use the actuators without humans overseeing the process. Researchers therefore target the chips with a high-power laser over and over again, observing the chips as they come up with split-second workarounds to the damage.

“It was incredible the first time the system kicked in and healed itself. It felt like we were witnessing the next step in the evolution of integrated circuits,” says Ali Hajimiri (Caltech). “We had literally just blasted half the amplifier and vaporized many of its components, such as transistors, and it was able to recover to nearly its ideal performance.”

This Caltech news release compares the healing properties of these integrated-circuit chips to the human immune system, which can likewise respond quickly to a wide range of attacks. Interestingly, the team discovered that the amplifiers with self-healing capacity consumed about half the amount of power as standard amplifiers, while their overall performance was more predictable. By demonstrating self-healing in a highly complex system like this one, the Caltech researchers have shown that it can be extended to many other electronic systems.

All this is good news for our starship. We naturally think about catastrophic problems that damage parts of the circuits, but when we’re thinking long-term, the issues are likely to be more subtle. Problems can emerge as continual load stresses the system and causes changes to its internal properties, while variations in temperature and supply voltage can also degrade operations. For that matter, variation across components can play a role, making an electronic system with a built-in immune function an insurance policy for deep space robotic missions.

Meanwhile, my own computer operations continue with extensive human intervention, though I’m pleased to see that the new hard disk I installed checks out perfectly. We are all learning through experience how our lives are supplemented and changed by digital technologies. But robotic probes operating at the edge of the Solar System and beyond have no repair team on staff to open up a housing and plug in a new chip, We’re now learning that beyond redundancy and backups a new set of tools are emerging that will keep long-haul missions healthy.

The paper is Bowers et al., “Integrated Self-Healing for mm-Wave Power Amplifiers,” IEEE Transactions on Microwave Theory and Techniques Vol. 61, Issue 3 (2013), pp. 1301-1315 (abstract). Thanks to Eric Davis for the pointer to this work.

Biological Evolution in Interstellar Human Migration

Centauri Dreams is happy to welcome Dr. Cameron M. Smith, a prehistorian at Portland State University’s Department of Anthropology in Portland, OR, with an essay that is the capstone of this week’s worldship theme. Dr. Smith began his career excavating million-year-old stone tools in Africa and today combines his archaeological interests with a consideration of human evolution and space colonization. He is applying this interest in his collaboration with the scientists at Icarus Interstellar’s Project Hyperion, a reference study for an interstellar craft capable of voyaging to a distant star. Recently Dr. Smith presented a paper at the NASA/DARPA ’100 Year Starship Study’ conference in Houston, Texas. His recent popular science publications in this field include “Starship Humanity” (Scientific American 2013) and the book Emigrating Beyond Earth: Human Adaptation and Space Colonization (Springer-Praxis, 2013). We can look forward to a follow-up article to this one in coming weeks.

by Cameron M. Smith

1. Interstellar Migration: An Insurance Policy for the genus Homo

Planets orbiting distant stars are now being discovered at a rapid pace, with hundreds known and countless worlds implied. As an anthropologist, I take a wide and long-term look at human evolution, and this development is very exciting to me; those almost unimaginably-distant planets are where humanity is headed, in the longer or shorter term. Humanity has been characterized by spreading itself wide across the Earth, and after first colonizing Mars we will surely wish to go farther, just as, in Polynesian legend, the siblings Ru and Hina—having explored the whole Pacific—chose to build a special vessel for a trip to the moon. Although civilization as practiced so far is perhaps its own worst enemy, I am optimistic that humanity’s better side will generally prevail, and that our species will invest in space colonization as an insurance policy for our lineage. Figure 1 indicates the five most recent mass-extinction events in Earth history, and Figure 2 indicates that even in recent times, civilizations have repeatedly collapsed and disintegrated, with no guarantee of recovery [click on figures to enlarge as needed]. In the larger picture, over long time, space migration is the best means of surviving such disasters.

Recently humanity has spent just over a generation exploring the solar system just beyond our atmosphere, sometimes with robotic voyagers, and sometimes with our own bodies; for the past 23 continuous years human beings have already lived off of the surface of the Earth in various orbital stations; cosmonaut Sergei Krikalev has spent over 800 days in space, and his colleague Valeri Polyakov once remained continuously in orbit for well over a year. Despite some close calls, nobody has died in this nearly quarter-century of continuous space habitation, which has taught us some basics of space biology. Clearly, our species’ technical capacities are superb, and the essential technologies for long-term stays in space are being sketched out. We also have realistic destinations in view, and highly-focused, forward-thinking physicists and mathematicians working on how to reach those destinations with unique propulsion systems.

Will developing space technology be enough, however, to pave a way to space colonization? It will be part of the equation, but the equation is not complete. Space colonization will be about humans living off of Earth, but human biology off of Earth is only barely understood, and only in the cases of the individual physiology of adults, for short periods of the entire life course. Space colonization, however, will be about humans living out entire lifetimes—from fertilization to embryo development and so on through adulthood—and in populations (rather than just individuals) and populations over multiple generations, not short stints in Earth orbit. For these reasons, at least, we need an anthropology of human space colonization. Anthropology studies the biocultural evolution of our lineage and some of our closest relatives. In this article I would like to introduce some of the biological issues involved in space migration, specifically among multigenerational, interstellar voyages. In a second article I will introduce cultural evolution in such vessels.

2. Where to Begin?

Space colonization will be a continuation of human evolution. I don’t mean this in the shallow sense of a ‘March of Progress’, but in a deeper, more mature and more useful way. Humans are life forms, and thus we change through time, both biologically and culturally. When such change allows us to live in new places—for example, the Canadian Arctic (over 5,000 years ago), the islands of the Pacific (over 3,000 years ago), or Earth orbit—it is called adaptation. Space colonization, then, will be an attempt at adaptation, and if we want to succeed in this adaptive endeavor we should be informed with everything we know about evolution in general and adaptation in particular.

Generally speaking, while it is clear that humanity has adapted to many ecological niches over time, it is equally clear that our adaptation differs significantly from that of most other life forms. This is because humanity adapts more culturally and technologically than biologically; witness our essential biological similarity across the globe, despite a few regional variations in skin color, hair texture and so on. Rather than adapting largely by body, then, we adapt largely by mind, which generates complex behavior (such as adjusting our kinship rules and sex taboos to match our distribution across landscapes) and complex technologies (including everything from inventing sailing vessels and stellar navigation in the Pacific to walrus-hunting watercraft and harpoons in the Arctic) allowing our species to flourish in places never dreamed of by our earliest bipedal ancestors. Having said this, humanity continues to evolve biologically even today, and will continue beyond Earth, and that evolution must be considered.

While technology is a cultural invention, in this article I will leave the technologies of space colonization to the engineers, and focus on the biological issues involved in interstellar voyages. These have been sketched out before in disparate literature; here I would like to update the material and consider it specifically in the case of current draft studies of interstellar vessels.

3. A Thoughtscape for Planning Interstellar Voyages

Current plans for interstellar voyaging essentially envision a gargantuan starship hurtling on a one-way voyage from Earth towards a distant star system. Interstellar craft would have to be very large—perhaps kilometers on a side—to house populations in the thousands, as I will discuss below. The most distinctive characteristic of these colony ships is that they would essentially be closed systems, with no opportunity for bringing in new genes, maintenance or repair materials, or consumables, such as water or breathing gases. These ‘Space Arks’ would have to be regenerable and self-contained, a fascinating challenge not just in engineering but also concerning biology and culture.

Presuming that we could build such vessels, the main engineering challenge is going to be propulsion (an issue being tackled right now by the scientists at Icarus Interstellar). Our galaxy, the milky way, contains an average density of .004 stars per cubic light year, and the closest star to Earth, Proxima Centauri, is 4.2 light years away. At light speed that is 4.2 years of travel time, but today, attaining that speed (or, technically, something very close to it, as light speed is not thought to actually be attainable by anything other than individual photons or similar particles) is unrealistic. How fast can we go? The fastest humans have moved is about 24,790mph (just over .00003% the speed of light), on Apollo X in 1969. At that pace, Proxima Centauri is about 140,000 years away. Maybe we can do much better, though. In the last 150 years we have increased human travel speeds almost a thousandfold up from the locomotive’s 30mph (the Voyager spacecraft speed along at about 1,000 times the speed of a locomotive). If we can do something similar in the near future, travel times become significantly more manageable. A 100-fold increase in speed from Apollo X (bringing us to just under 3,000,000 miles per hour) would take us to Proxima Centauri in something under 1,400 years. This is getting manageable, but is still a long time; imagine launching the ship during the Dark Ages (just after the collapse of Rome, about 1,400 years ago) and having it arrive at its destination in the time of such oddities as desktop computers. If, however, we manage to make a 1,000-fold increase in speed (bringing us to about 30,000,000mph) in the next century or so, then the heavenly wonders of Proxima Centauri (actually we don’t know what it is like there, yet, but I am being optimistic) could be achieved in about 140 years (see Figure 3). This is a very manageable timescale, a distance only that from today’s world to that of 1872–less than five generations distant and essentially comprehensible.

This, then, is the thoughtscape I am exploring in this article; voyages on the order of under two centuries, carrying some thousands of people (a number discussed below) before reaching another solar system. What biological and cultural issues need to be addressed on such voyages? While the answer will be some time coming (I’m currently investigating it in research for my forthcoming textbook on the anthropology of space colonization), I can sketch out some below.

4. The Biology of Interstellar Voyaging

While evolutionary biology is currently undergoing significant revision in the light of new genomic data, the principles of evolution are largely intact. These include the four main processes (genetic mutation, selection, migration and drift) that change the properties of the gene pool over time. Each is discussed below.

4.1 The Biology of Interstellar Voyaging: Mutation

Mutation is ultimate source of new variations, such as coarser hair, or darker skin than one’s fellows. In common speech a mutation is thought of as being deleterious, but scientifically speaking mutations could be advantageous, disadvantageous or neutral. Some mutation is a result of radiation, and interstellar voyage designs will have to consider trapped particles, radiation energy near Earth and constrained within the Van Allen belt (and presumably about other planets with analogs of the Van Allen belt; cosmic rays derived from many sources outside this region, and solar radiation blasts out of suns. Radiation can degrade biological tissues and cell functions, and it can also be a powerful mutagen, altering DNA; recently it has been suggested that cosmic radiation could increase the incidence of brain disorders.

Certainly radiation is an issue to be addressed, but it does not seem to be a showstopper for human space colonization. First, many shielding schemes have been devised. In interstellar craft some kind of radiation shielding will be necessary, but because shielding is heavy, designers will probably try to get away with as little as possible. How thin is too thin? This is difficult to answer; aside from clear cases of lethal exposure to high doses of radiation, its long-term effects are mysterious. One 1995 study tracked the health of over 70,000 children of parents who were within a kilometer of the nuclear bombings at Hiroshima and Nagasaki, Japan, during World War II. Surprisingly, there was no statistically significant difference between the study population and populations of children of non-irradiated parents, in terms of malignant tumors in early age, differences in sex of offspring, chromosomal abnormalities and other mutations. On the other hand, recent studies have shown highly elevated mutation rates in people living near the Chernobyl disaster site. We have plenty to learn.

The second reason that radiation will not be a deal-breaker for interstellar voyaging is that mutagenesis itself has recently been found not to be largely the result of such ‘one-off’ ‘zaps’ from space, but rather more the result of the failure of DNA-repair mechanisms on the molecular level itself (over 300 such mechanisms and processes have been identified in the human genome alone). Thus, DNA repair therapy will probably be a large part of mitigating radiation issues in interstellar voyages.

In short, anywhere beyond Earth’s natural radiation shielding, under which we have evolved for millions of years, the mutagenic environment will be new and therefore a candidate for affecting our genome. Obviously we will use technology to mitigate such effects, including shielding and management of DNA repair, but we must remember that we do not know everything and that it will take time to adjust—both biologically and culturally–to new environments.

4.2 The Biology of Interstellar Voyaging: Selection

Natural selection occurs when life forms are prevented from reproducing—or simply have less offspring than others of their generation—due to their genetic characteristics. For example, a fly born without wings is unlikely to have offspring, or at least less offspring than its cohort (because of its reduced health and reduced ability to find mates) such that ‘wingless’ genes are likely to be ‘selected out’. Concomitant to most ‘selection against’ certain characteristics is selection ‘for’ alternatives. It’s often thought that humanity has halted natural selection with modern medicine and technology, but this is an illusion; many people continue to die before giving birth because of their genetic properties, particularly in populations without access to modern health care; and several recent studies have shown natural selection to be underway in modern populations. Even so, by the time of interstellar travel health technology will be much advanced…and yet selection will continue, for at least three reasons.

First, conditions off of Earth will differ from the conditions on Earth, where a relatively narrow environmental envelope of temperatures, atmospheric pressures and elemental compositions, nutrient supply and gravity have prevailed. The conditions in interstellar craft might well approximate these conditions, but much experimental data indicates that even small alterations in such variables as breathing gas composition and pressure can negatively effect gene expression (the switching on and off of genes on very complex schedules) and development of vertebrate embryos during the critical phases of early formation (e.g. gastrulation). We will of course try to control such variables, but it is unlikely that we will be able to anticipate everything. It seems certain that there will be a degree of increased infant mortality as the human genome adjusts to new conditions in interstellar colony craft, however carefully we design them. I am currently researching the genetic aspects of human development and the life course in environments slightly different from those on Earth.

Second, selection will likely play out in the cases of sweeps of novel diseases through interstellar craft populations. Again, we will be very careful, but it is impossible to anticipate all biological change, and in smallish populations (e.g. the 10,000+ that I suggest for interstellar craft; see below) inhabiting closed environments, sweeps of new disease, I believe, might well occur. Whether such sweeps structure the interstellar craft genome structurally is impossible to know, but we must be prepared for this possibility.

Finally, most interstellar voyage plans head not for other stars per se, but for their planets, where the resources and landscapes of alien worlds will allow humans to once again take to a planetary surface. In such a case, it is certain that new environmental conditions will be encountered. We will use technology to mitigate environmental selection, of course, but we must remember that we are only just appreciating the significance of epigenetics, the throwing of genetic switches by environmental factors. How will new planetary conditions shape the human genome? We simply can’t say, but we can be sure that it will occur. For example, even the Apollo lunar walkers commented on the lunar soil they inadvertently tracked into their lunar modules; you can bet that they breathed it in. They stayed on the moon only for days…but what would be the effect of such close contact of the human body with new chemistries of different worlds over the course of a lifetime? What genetic switches could be activated in such conditions? We don’t and can’t know; we can estimate and model, but we can’t be certain, and it is likely that selection will occur on our genome again in new planetary environments, at least until we control it with technology.

To succeed in migrating from Earth we are going to have to accept some risk. We do this on a daily basis; in the U.S. many of us take a daily commuting gamble, with nearly a hundred losing that bet—dying in car crashes—daily. If we can take that risk, surely we can adjust to the return of a degree of selection in our dream to colonize space and supply our genus with an insurance policy against extinction or even ‘just’ civilization collapse.

Ultimately, natural selection can be strongly mitigated with technology and is unlikely to strongly structure our genome in the 140-year ‘thoughtscape’ I am currently exploring. But natural selection should not be discounted in plans for interstellar colonization, particularly because it will ultimately involve generations of humanity adapting to new environments.

4.3 The Biology of Interstellar Voyaging: Migration and Drift

Migration is the flow of genes into and out of gene pools (populations) and it is a major factor on Earth, where humans have vast travel networks and today mate even across different hemispheres of the globe. However, in interstellar voyaging craft populations will be relatively fixed (rather than expanding, until new planets are reached), and migration will be between rather small sub-populations of the interstellar craft, an issue returned to below.

Drift, on the other hand, is the result of chance events in the history of a species; a good example, and one most suitable here, is the founder effect in which the genetic composition of a population is strongly conditioned by its founding members. This factor will be of critical importance in interstellar colony voyages because they will be closed genetic systems—as just mentioned—whose genetic structure will be largely established by the founding populations.

Regarding populations, we should take a minute to consider the size of interstellar colony groups. Should we send tens, thousands, millions of people? One way to tackle this issue is to consider our species’ MVP or ‘minimum viable population’, the figure required to avoid the deleterious effects of inbreeding. This figure has been much debated; anthropologist John Moore has suggested a figure of about 150, while others have suggested closer to 500. Such small populations, however, are highly vulnerable to single catastrophes, and my own calculations have suggested an MVP of about 3,000, multiplied by a ‘safety factor’ of 4 to 6 for an interstellar colonization population ‘reference figure’ of 12,000-18,000, which I consider significantly capable of surviving both biological disasters such as disease sweeps and a number of significant technological failures, over the low-centuries figure to reach, for example, Proxima Centauri.

From 12,000 to 18,000 people, then, as a ballpark figure for a founding population for interstellar migration; how do we pick them from the human population? Evolutionary ecologists measure s species’ health by its genetic diversity because a diverse gene pool allows for adaptation to new, unexpected conditions; thus our colonists should be biologically diverse, representing the human genome worldwide (which includes variations adapted to low and high altitudes, for example). However, an over-inclusive approach could endanger future populations if certain genetic maladies are allowed among the founding population. The screening process—determining that certain humans should not and could not participate in off-Earth colonies—seems to go against the very Enlightenment values of equality and freedom at the heart of Western Civilization, but if we are going to succeed in human space colonization we cannot ignore genetics. This is nothing new: over thousands of years human cultures have already devised many and elaborate kinship systems and sexual regulations that prevent the genetic disorders associated with close inbreeding; a survey of Yale’s Human Resources Area Files ethnographic database indicates that most cultures ban marrying or mating between parents and siblings of parents, siblings themselves, grandparents, and first cousins. Humanity has been looking after our genome for a very long time.

The main issue in genetic screening is the detection of genetic disorders that might send a biological ‘time bomb’ into future populations, particularly small and closed populations. But even this ‘simple’ issue includes moral and practical hurdles. In practical terms, this is evident in a depressing poster generated by the federal Genomic Science Program, a rather gruesome document pointing out the location–on each of our chromosomes–of many hundreds of genetically-controlled disorders, from cancers to deafness (we should remember that genes don’t exist simply to cause problems, and that in most cases they build healthy individuals!). Screening for interstellar suitability here seems simple enough: people carrying certain genes would have to remain Earthbound. The significant complication, though, is that while many genetic disorders are known to be simply correlated with certain genes—these are called Mendelian traits—modern genetics finds that more disorders are not so easily ‘pinned’ onto just one easily-spotted genetic marker. Indeed, in a recent paper Professor Aravinda Chakravarti of the Johns Hopkins School of Medicine noted that the textbook concept of simple Mendelian inheritance—‘evolution basics’ that I teach in my own classes—seems to be melting away in light of his ‘genetic dissections’ of the real mechanisms of genetic disease, replaced by far more complex models. For example, many disorders are polygenic, the complex result of the interactions of many genes. And, single genes can be pleiotropic, affecting multiple characteristics of the individual organism! To further complicate matters, even though one might carry the gene or genes ‘for’ a certain disorder, environmental factors encountered during the course of life can determine whether or not those genes are activated in such a way as to ‘express’ the genetic disorder.

We must address such issues because, as geneticist David Altshuler of the Harvard Medical School recently noted in the New York Times, “Even if you know everything about genetics, prediction will remain probabilistic and not deterministic.”

And what if we could identify, say, a ‘gene’ for deafness? Just after thirty years of age, Beethoven became deaf; it this were due to a genetic disorder, should he have been ‘selected out’? Should Beethoven’s deafness have been ‘pre-emptively corrected’? He completed much fine music even after his deafness. And what about Stephen Hawking’s genetic disorder, amyotrophic lateral sclerosis? Would screening out someone carrying a certain likelihood of expressing that disorder be a good idea? We already make mate choices, some based on actual or perceived health and future of our partners, and even the fates of some of our embryos. For the health of off-Earth populations, we must be willing engage in these complex discussions to determine what levels of probability we are comfortable with in terms of deciding whether or not a given person can participate in space colonization. Philosophers of morality could be of great help in clarifying the issues in a secular way, and designing real-world solutions.

On the surface, we might think that a solution to these issues would be to encourage the breeding of a master ‘Space Race’, as in the science fiction film Gatacca. But this idea is counter to nature and all of population genetics. If all are identical, all are subject to the same evolutionary ‘sweep’–for example, a single devastating disease. This is why ecologists measure—as mentioned–the health of a species not by its sameness, but by its genetic diversity, which is a well of untapped variation that might provide for a changed future. Any ‘super-race’, then, would be genetically imperiled in the manner of the closely-inbred royal families of Europe, who, according to Dr. Alan Rushton, author of Royal Maladies: Inherited Diseases in the Royal Houses of Europe, have suffered statistically more than their share of genetic disorders.

All in all, from a genetic perspective we have plenty of both moral and genetic reasons to begin studying the genetics of space colonization today. And, critically, we will have to ensure the genetic health of our domesticates and symbionts as well: we will be taking many domesticated plant and animal species off of Earth, some as food, some as companions, some as providers of such things as fibers. A good way to proceed would be to set clear milestones for what we want to know before we can leave the Earth, and work towards meeting them; otherwise, the endless, question-generating process at the heart of science might keep us here too long–and it is only a matter of time before a civilization- or species-destroying event will occur again on Earth.

In the end, if we are going to migrate from the Earth we are going to have to grapple with the probabilistic world of the genome in order to make smart—and moral—choices about the genetic health of our descendants. Regarding the important issue of preserving genetic variability, this could be maintained by ensuing gene flow among sub-populations of the interstellar craft as well as such technological means as carrying along from Earth ‘novel’ genetic material in the form of stored sperm and egg, as well as artificial mutagenesis. All of these measures are under investigation.

5. The Biology of Interstellar Voyaging: Final Comments

Over the course of several generations, as on voyages to nearby stars with propulsion systems that are beginning to seem reasonable, interstellar voyaging is entirely possible from a genetic perspective, with two provisions. First, we will have to ensure the genetic health of the colonist population as it will be under strong founder effect. Gene therapies, carrying genes from Earth in the form of stored eggs and sperm, and even the artificial induction of mutations can all be used to mitigate such effects, but at some point it will cease to be desirable to keep ‘pushing’ a human Earth genome into interstellar space. This brings us to the second proviso, and that is that natural selection will in fact return as a significant concern in human evolution, particularly when the unknowns of new planetary environments are encountered (even if they are surveyed by reconnaissance vehicles first).

We should note that, in the currently-considered timelines and populations, according to what we know about human biology it is unlikely that humanity will undergo speciation in less than a few thousand years (Figure 1, lower right).

These lessons remind us that adaptation is a continual process of the adjustment of the genome to environmental conditions. In non-humans that evolve reactively, with no conscious effort, this equilibriating process is slow and uncentralized and results in many extinctions over time. In humanity, consciousness can be used to help proactively shape our evolution, but we must remember that the only way to stop evolution is by extinction. We should accept and learn from the fact that if things live, they evolve and adapt. We should plan our adaptation to space as students of evolution. We must internalize the truth that the nature of the universe is change, not fixity, and allow this truth to condition our plans for the human colonization of space.

In the next article I will address cultural evolution, and some issues in the coevolution of DNA and culture, in biocultural evolution.

Habitable Zone Planets: Upping the Numbers

Whether we’re planning to go to the stars on a worldship or with faster transportation, the choice of targets is still evolving, and will be for some time. Indeed, events are moving almost faster than I can keep up with them. It was in early February that Courtney Dressing and David Charbonneau (Harvard-Smithsonian Center for Astrophysics) presented results of their study of 3897 dwarf stars with temperatures cooler than 4000 K, revising their temperatures downward and reducing their size by 31 percent. The scientists culled the stars from the Kepler catalog, and their revisions had the effect of lowering the size of the 95 detected planets in their data.

They went on to deduce that about 15 percent of all red dwarf stars have an Earth-sized planet in the habitable zone. [PG note: The 15% figure is a revised estimate that I've just learned about from Ravi kumar Kopparapu. Dressing and Charbonneau call attention to this change at the end of their paper. See citation below].

That would make the nearest Earth-like planet in the habitable zone about 13 light years away (I’m still holding out for the much closer Proxima Centauri when it comes to M-dwarfs). But Ravi kumar Kopparapu (Penn State) has revisited Dressing and Charbonneau’s work because of a key fact: The latter used habitable zone limits based on a 1993 study by James Kasting which Kopparapu believes are not valid for stars with effective temperatures less than 3700 K. The scientist was in the news almost as recently as Dressing and Charbonneau with his study of habitable zones around main sequence stars, where he presented an improved climate model developed with Kasting and other colleagues that allowed him to move the habitable zone boundaries out a bit further from their stars than they had been before (see Habitable Zones: A Moving Target for more).

Rory Barnes (University of Washington) called the work of Kopparapu and colleagues ‘the new gold standard for the habitable zone,’ and in a paper just accepted by Astrophysical Journal Letters, Kopparapu now uses his habitable zone revisions to estimate the rate of occurrence of terrestrial-sized planets in the habitable zone of M-dwarfs. His new paper was based on the Harvard team’s data and used the same calculation method. But with the new habitable zone parameters worked in, the number of habitable planets is greater than previously thought. Four out of ten of the nearest small stars should have potentially habitable planets.

Image: The graphic shows optimistic and conservative habitable zone boundaries around cool, low mass stars. The numbers indicate the names of known Kepler planet candidates. Yellow color represents candidates with less than 1.4 times Earth-radius. Green color represents planet candidates between 1.4 and 2 Earth radius. Planets with “+” are not in the habitable zone. Credit: Penn State.

Kopparapu’s new work would place the average distance to the nearest habitable planet at around 7 light years. Given that there are eight stars within 10 light years of the Sun that fit this model, we could expect to find perhaps three Earth-sized planets in the habitable zones there.

M-dwarfs are becoming increasingly important in the search for terrestrial-class worlds. Because their orbits are close to the parent star, habitable worlds in such systems would transit often and produce a stronger transit signal than a similar planet around a G-class star like the Sun. That makes M-dwarfs good Kepler targets and also suggests that future space-based missions may find this class of star an extremely useful target. Given that M-dwarfs may comprise as much as 80 percent of all stars in the galaxy, it could turn out that most life-bearing planets orbit small red stars, assuming life can indeed develop around them.

The paper is Kopparapu, “A revised estimate of the occurrence rate of terrestrial planets in the habitable zones around kepler m-dwarfs,” accepted at Astrophysical Journal Letters (preprint). The Dressing and Charbonneau paper is “The Occurrence Rate of Small Planets Around Small Stars,” to be published in The Astrophysical Journal (draft version online).

Life Aboard the Worldship

Konstantin Tsiolkovsky is the first person I know of to talk about worldships and their ramifications, which he did in an essay originally published in 1928. “The Future of Earth and Mankind” was the rocket pioneer’s take on the need for enormous ships that could reach the stars in journeys taking thousands of years. The notion percolated quickly through science fiction, and by 1940 we have Don Wilcox’s “The Voyage that Lasted 600 Years,” which ran in Amazing Stories. Wilcox, who taught creative writing at Northwestern University, imagined a ship’s captain who, though kept in hibernation, wakes up every 100 years to check on his ship, watching the gradual degeneration of the successive generations of the crew.

It’s a bleak take on worldship travel that has often been echoed in later science fiction. But would a worldship actually be this horrific, a cruise from hell that lasted entire lifetimes? See Ken MacLeod’s Learning the World: A Novel of First Contact (2005) for the worldship as a place of unlimited opportunity, and consider reading some of the many worldship stories covering the entire range of possibility that SF has produced, from Lawrence Manning’s “The Living Galaxy” (Wonder Stories, 1934) all the way forward to Gregory Benford and Larry Niven’s Bowl of Heaven (2012), which depicts what might be described as a traveling Dyson Sphere, though one with unusual design parameters.

Population Density Enroute to the Stars

Stephen Ashworth’s papers on worldships, recently published in the Journal of the British Interplanetary Society contain his speculation that reasons of economic efficiency will produce colony vessels and then worldships with high population densities, supporting thousands of inhabitants per square kilometer. What to do with a human spirit in need of open spaces? One solution is virtual entertainment in which the crew — or colonists, or whatever we choose to call them — could tap into the experience of their choice, perhaps mixing Earth-like desert, jungle and ocean adventures with customized fantasy according to whim.

When Gerard O’Neill wrote about colony worlds in The High Frontier (1976), he imagined a different outcome. Huge communities like his Island Three would not necessarily need to be space-going versions of Manhattan, but might take advantage of the abundant resources of the Solar System to provide living room in a variety of settings:

…as colonists from various countries of Earth arrive to settle the many communities in space, there will be a great variety in the ways in which land area will be used. Some immigrants may choose to arrange their land area in small villages, with single-family homes, the villages being separated by forests. Others may prefer to build small, intimate towns of high population density, to enjoy for example the color and excitement and human interaction that is so much a feature of small villages in Italy. With many new communities to choose from, the emigrants from Earth will settle in those they like best.

Of course, O’Neill was not talking about worldships but what might be their predecessors, the kind of colony worlds that would define a truly system-wide economy. Even so, we can imagine scenarios where the inhabitants of such a colony, having produced several generations of space-adapted descendants, may decide that long journeys are not a problem if their entire world goes with them. Imagine, then, a truly sylvan setting like O’Neill’s:

I would have a preference, I think, for one rather appealing arrangement: to leave the valleys free for small villages, forests and parks, to have lakes in the valley ends, at the foot of the mountains, and to have small cities rising into the foothills from the lakeshores. Even at the high-population density that might characterize an early habitat, that arrangement would seem rather pleasant: a house in a small village where life could be relaxed and children could be raised with room to play; and just five or ten miles away, a small city, with a population somewhat smaller than San Francisco’s, to which one could go for theaters, museums, and concerts.

Image: The vast interior of an O’Neill cylinder presents a more spacious view of what a worldship might become. Credit: Rick Guidice/NASA.

Requirements for the Journey

The idea that we might one day build such artificial worlds, whether or not we translate them into star-voyaging worldships, seems fantastic. And for a bit of sobering up, Ashworth’s papers are just the ticket. In “The Emergence of the Worldship (II): A Development Scenario,” he looks at the requirements for sustaining human life on a vessel whose travel time might be measured in millennia. Space precludes running through all of these, but many are obvious:

Closed cycle production and recycling of food, water and oxygen;
A source of electrical power independent of Sun or planets and sustainable over the course of the journey;
Thermal management through radiation of waste heat to space;
Full control over the microbiological environment;
Viability of all food and ornamental species in functional reproductive health at stable population sizes over an indefinite number of generations

and so on. The list is understandably extensive, and includes factors like ensuring social and psychological stability, the need for continuing maintenance of all systems, and the long-term stability of the gene pool. None of these are factors that could be resolved in short time frames, and Ashworth believes they may emerge through a series of colonies set up at progressively greater distances from the Earth. Eventually such colonies learn how to operate independent of planetary surfaces and a manned starship — the worldship — may emerge, seen here as the logical endpoint of a lengthy period of technological and social growth. From the paper:

Viewed as a government research programme such a demonstration seems implausible, due to both its complexity and the timescales required to achieve operational maturity. Viewed as a gradual evolution of humanity into space, however, aimed not at starflight as such but at space colonisation within our own Solar System, and motivated by the large energy and material resources available for expansion, it seems likely that after a timescale on the order of centuries the preconditions listed above may be fulfilled in the course of normal economic growth.

We’ve come a long way in our conception of worldships from Robert Heinlein’s “Universe” (Astounding, 1941) and its sequel the following month, “Common Sense.” Published in book form as Orphans of the Sky, the story follows a ship’s crew that has long forgotten the nature of the voyage and no longer realizes that its world is a ship. The result is social deterioration and a rigidly stratified society of the sort Brian Aldiss explored to much greater effect in his 1956 novel Non-Stop. One can only imagine how the inhabitants of a worldship structured more or less along O’Neill lines might fare over the course of a similar journey, and we can assume that science fiction isn’t yet through exploring the ramifications of this intriguing concept.

The citation for Stephen Ashworth’s paper is “The Emergence of the Worldship (II): A Development Scenario,” JBIS Vol. 65, No. 4,5 (2012), pp. 155-175.

Space Habitats and Nearby Resources

If humans go out into the Solar System and beyond drawing on the resources they find along the way, they don’t necessarily have to do it on worldships of the kind we talked about yesterday. But it’s a reasonable assumption that creating large space habitats would make engineering projects in deep space easier to implement, housing workers and providing a base for operations. Ken Roy presented ideas about habitats in the Kuiper Belt at Huntsville, including the possibility of a large colony being created inside objects like Pluto. If we choose to go that route, we’ll have the kind of space expertise to create artificial objects similar to worldships to help ourselves along.

Of course, we hardly need to limit ourselves to the Kuiper Belt for this kind of thinking. Whatever the design of the ships we use, we can also consider expansion into the vast cometary resources of the Oort Cloud and any other objects that may lurk there, including so-called rogue planets. For years we’ve kicked around the idea of a possible brown dwarf closer than the Sun, and it seemed the WISE mission was putting the idea to rest. But maybe not. Yesterday we got word of the closest star system found in a century, a brown dwarf binary 6.5 light years out.

Image: This diagram illustrates the locations of the star systems that are closest to the Sun. The year when each star was discovered to be a neighbor of the Sun is indicated. The binary system WISE J104915.57-531906 is the third nearest system to the Sun, and the closest one found in a century. Credit: Janella Williams, Penn State University.

The Closest Brown Dwarfs Yet

You have to go back to 1916 to find another discovery this close, and that was Barnard’s Star — E. E. Barnard was not the actual discoverer of the star, but he was the first to measure its proper motion, thus pegging it as a near neighbor. Proxima Centauri was itself discovered just the year before by Robert Innes at Union Observatory in Johannesburg. The new system, WISE J104915.57-531906, reminds us that brown dwarfs may become a potential source of raw materials that facilitates outward expansion. We also know that some brown dwarfs have planetary systems while others have disks that may indicate planet formation has begun.

The new brown dwarf binary comes from WISE data and leads to the speculation that there are other interesting small systems yet to be discovered within 10 light years or so of Earth. The discoverer, Kevin Luhman (Penn State) spotted the signs of rapid motion in the WISE images and then looked for the object in older sky surveys, finding it in the Digitized Sky Survey as well as the Two Micron All-Sky Survey and the Deep Near Infrared Survey. All of this led the astronomer to work out the distance of the binary by parallax, with follow-up from the Gemini South telescope.

This exciting new find gives us a sense of how much we may yet discover. Says Luhman: “There are billions of infrared points of light across the sky, and the mystery is which one — if any of them — could be a star that is very close to our solar system.”

Meanwhile, Closer to Home…

We are a long way from operating so far from Earth, but the presence of resources between the stars may re-shape our expectations about small, fast expeditions, and lead to the slower, staged approach implicit in worldships. But whether it leads to this outcome or not, Stephen Ashworth makes a case in his recent JBIS paper for exploiting resources here in our own system that could lead to what he calls an ‘astro-civilization,’ in which the construction of large space habitats and the ability to mine the needed resources leads inevitably to a culture more at home in space than on a planet.

John Lewis considered the potential of asteroid mining some time ago in Mining the Sky, a book now on the must-read list for admirers of the asteroid mining operations like Planetary Resources and Deep Space Industries that are now emerging. Lewis believed that freely orbiting space colonies built from raw materials extracted from the asteroids would allow for huge increases in the human population. He suggested an increase by a factor of 106, though Ashworth, working the numbers anew, comes up with a more conservative figure of 2 X 1015 humans, which works out to a factor of 286,000 over the current planetary population.

Whichever figure we go with, we are talking about vast increases in living space for our species. Note, too, that both Lewis and Ashworth are talking about a population model that applies to artificial habitats constructed in the inner Solar System, meaning out to and including the main belt asteroids. Neither writer is including the moons and Trojans of the gas giants, nor the abundant resources of the Kuiper Belt and the Oort Cloud, and of course neither works into his calculations the possibility of rogue planets without stars or potentially nearby brown dwarfs.

But a space-based civilization living in the inner Solar System could be the staging area for further expansion. Ashworth thinks the extensive development of the main belt asteroids and exploitation of resources closer in would produce an energy economy throughout the Solar System in the region of 2.5 X 106 zeta joules (ZJ) per year. A zeta joule is 1021 joules, the joule being a standard unit of energy equal to 0.2389 calories.

Ashworth’s figures show that a program consuming 1 percent of the Solar System GDP annually over a ten year period would demand 2.5 X 105 ZJ. At this level of energy production, the construction of a worldship designed for 107 passengers is 28 percent of the amount, meaning that a space-based civilization at this level would find it within its means to build such a vehicle.

Any culture building vast artificial structures in space is one capable of a long-term interstellar crossing, but it is clear that a worldship is not an object that can be completed and then left alone to function. Indeed, the humans aboard the vessel will be spending a great deal of time maintaining and improving their world. From Ashworth’s paper:

These trends involve an increasing reliance upon engineered control systems in order to maintain the correct temperatures, air composition, water purity, food supply, and biological and microbiological health. Space colonies are to be understood, not as small artificial self-regulating planets, but as large self-contained buildings requiring continual maintenance. An astro-civilisation must be constantly active in order to survive: repairing space colonies, scrapping superannuated ones, recycling their materials and constructing new ones, just as an urban civilisation on Earth today is constantly renewing its built infrastructure, or as the human body is constantly renewing the cells of which it is composed.

There too is the sense of purpose which some have speculated might be lost by the numerous generations on their way to another star. For constantly improving and upgrading conditions aboard a space habitat offers a challenge upon which the survival of all aboard depend. Learning to live off the resources that proliferate throughout the outer system and beyond — and the Oort Cloud may extend out a light year or more — the worldship inhabitants will be interested in where their next resource collection will be. Habitable planets in a destination star system will be of fascinating astrobiological interest, but asteroids and small moons may be where the action is.

I haven’t yet gotten to the reflections on Gerard O’Neill and the internal conditions on a worldship that I promised yesterday, but time draws short this morning. More on all this tomorrow. Repeating the Ashworth citation, it’s “The Emergence of the Worldship (I): The Shift from Planet-Based to Space-Based Civilisation,” in JBIS 65, No. 4-5 (2012), pp. 140-154. You might also want to check out the JBIS website, which is being revised and updated.

Toward a Space-Based Civilization

The assumptions we bring to interstellar flight shape the futures we can imagine. It’s useful, then, to question those assumptions at every turn, particularly the one that says the reason we will go to the stars is to find other planets like the Earth. The thought is natural enough, and it’s built into the exoplanet enterprise, for the one thing we get excited about more than any other is the prospect of finding small, rocky worlds at about Earth’s distance from a Sun-like star. This is what Kepler is all about. From an astrobiological perspective, this focus makes sense, as we want to know whether there is other life — particularly intelligent life — in the universe.

But interstellar expansion may not involve terrestrial-class worlds at all, though they would still remain the subject of intense study. Let’s assume for a moment that a future human civilization expands to the stars in worldships that take hundreds or even thousands of years to reach their destination. The occupants of these enormous vessels might travel in a tightly packed urban environment or perhaps in a much more ‘rural’ setting with Earth-like amenities. Many of them would live out their lives in transit, without the ability to be there at journey’s end. We can only speculate what kind of social structures might emerge around the ultimate mission imperative.

Moving Beyond a Planetary Surface

Humans who have grown up in a place that has effectively become their world are going to find its norms prevail, and the idea of living on a planetary surface may hold little interest. Isaac Asimov once wrote about what he called ‘planetary chauvinism,’ which falls back on something Eric M. Jones wrote back in the 1980s. Jones believed that people traveling to another star will be far more intent on mining asteroids and the moons of planets to help them build new habitats for their own expanding population. Stephen Ashworth, a familiar figure on Centauri Dreams, writes about what he calls ‘astro-civilizations,’ space-based cultures that focus on the material and energy resources of whatever system they are in rather than planets.

Ashworth’s twin essays appear in a 2012 issue of the Journal of the British Interplanetary Society (citation below) that grew out of a worldship symposium held in 2011 at BIS headquarters in London. The entire issue is a wonderful contribution to the growing body of research on worldships and their uses. Ashworth points out that a planetary civilization like our own thinks in terms of planetary resources and, when looking toward interstellar options, naturally assumes the primary goal will be to locate new ‘Earths.’ A corollary is the assumption of rapid transport that mirrors the kind of missions used to explore our own Solar System.

Image: A worldship kilometers in length as envisioned by space artist Adrian Mann.

An astro-civilization is built on different premises, and evolves naturally enough from the space efforts of its forebears. Let me quote Ashworth on this:

“A space-based or astro-civilisation…is based on technologies which are an extension of those required on planetary surfaces, most importantly the design of structures which provide artificial gravity by rotation, and the ability to mine and process raw materials in microgravity conditions. In fact a hierarchical progression of technology development can be traced, in which each new departure depends upon all the previous ones, which leads ultimately to an astro-civilisation.

The technology development Ashworth is talking about is a natural extension of planetary methods, moving through agriculture and industrialization into a focus on the recovery of materials that have not been concentrated on a planetary surface, and on human adaptation not only to lower levels of gravity but to life in pressurized structures beginning with outposts on the Moon, Mars and out into the system. Assume sufficient expertise with microgravity environments — and this will come in due course — and the human reliance upon 1 g, and for that matter upon planetary surfaces, begins to diminish. Power sources move away from fossil fuels and gravitate toward nuclear and solar power sources usable anywhere in the galaxy.

Agriculture likewise moves from industrialized methods on planetary surfaces to hydroponic agriculture in artificial environments. Ashworth sees this as a progression taking our adaptable species from the African Savannah to the land surface of the entire Earth and on to the planets, from which we begin, as we master the wide range of new habitats becoming available, to adapt to living in space itself. He sees a continuation in the increase of population densities that took us from nomadic life to villages to cities, finally being extended into a fully urbanized existence that will flourish inside large space colonies and, eventually, worldships.

An interstellar worldship is, after all, a simple extension from a colony world that remains in orbit around our own star. That colony world, within which people can sustain their lives over generations, is itself an outgrowth of earlier technologies like the Space Station, where residence is temporary but within which new skills for adapting to space are gradually learned. Where I might disagree with Ashworth is on a point he himself raises, that the kind of habitats Gerard O’Neill envisioned didn’t assume high population densities at all, but rather an abundance of energy and resources that would make life far more comfortable than on a planet.

Tomorrow I’ll want to take a look at O’Neill’s thoughts on how human society might conduct itself in space, and then return to Ashworth’s ideas on a natural progression to worldships. For now, though, let me give you the reference on Ashworth’s paper. It’s “The Emergence of the Worldship (I): The Shift from Planet-Based to Space-Based Civilisation,” in JBIS 65, No. 4-5 (2012), pp. 140-154. As you can see, the paper puts worldships in the far broader context of humanity’s future in space as we tap new sources of energy and materials. See Astronautical Evolution for more of Ashworth’s extensive contributions to the field.