Habitability: The Case for F-Class Stars

by Paul Gilster on March 27, 2014

When it comes to habitable planets, we focus naturally enough on stars like our own. But increasing attention has been paid to stars smaller and cooler than the Sun. M-class dwarfs have small but interesting habitable zones of their own and certain advantages when it comes to detecting terrestrial planets. K-class stars are also interesting, with a prominent candidate, Alpha Centauri B, existing in our stellar back yard. What we haven’t examined with the same intensity, though, are stars a bit more massive and hotter than the Sun, and new work suggests that this is a mistake.

Manfred Cuntz (University of Texas at Arlington), working with grad student Satoko Sato, has been leading work on F-class stars of the kind normally thought problematic for life because of their high levels of ultraviolet radiation. Along with researchers from the University of Guanajuato (Mexico), Cuntz and Sato suggest that we take a closer look at F stars, particularly considering that they offer a wider habitable zone where life-sustaining planets might flourish.

Cuntz thinks the case is a strong one:

“F-type stars are not hopeless. There is a gap in attention from the scientific community when it comes to knowledge about F-type stars and that is what our research is working to fill. It appears they may indeed be a good place to look for habitable planets.”


Image: The habitable zone as visualized around different types of star. Credit: NASA.

The team’s paper in the International Journal of Astrobiology makes this argument based on its studies of the damage that ultraviolet radiation can cause to the carbon-based macro-molecules necessary for life. Its estimates of the damage that would accrue to DNA on planets in F-class star systems covered calculations for F-type stars at various points in their evolution. Planets in the outermost regions of the habitable zone experience much lower levels of radiation. This UT-Arlington news release quotes the paper:

“Our study is a further contribution toward the exploration of the exobiological suitability of stars hotter and, by implication, more massive than the Sun…at least in the outer portions of F-star habitable zones, UV radiation should not be viewed as an insurmountable hindrance to the existence and evolution of life.”

F-type stars represent 3 percent of the stars in the Milky Way, as compared with G-class at about 7 percent and K-class at approximately 12. And then there are M-dwarfs, which may account for over 75 percent of all main sequence stars. In any event, the more we widen the prospects for astrobiology beyond stars like the Sun, the more we address the possibility of a galaxy suffused with life, even if we still have no direct evidence. Just as intriguing: If it turns out life is abundant, is intelligence abundant as well?

The paper is Sato et al., “Habitability around F-type Stars,” International Journal of Astrobiology, published online 25 March 2014 (abstract).



A Dwarf Planet Beyond Sedna (and Its Implications)

by Paul Gilster on March 26, 2014

Most Centauri Dreams readers are hardly going to be surprised by the idea that a large number of objects exist well outside the orbit of Pluto and, indeed, outside the Kuiper Belt itself. The search for unknown planets or even a brown dwarf that might perturb cometary orbits in the Oort Cloud has occupied us for some time, with the latest analysis of WISE findings showing that nothing larger than Jupiter exists out to a distance of 26,000 AU. Objects of Saturn size or larger are ruled out within 10,000 AU, according to the work of Kevin Luhman (Penn State) and team, whose study probed deeply into the Wide-field Infrared Survey Explorer’s results. For more on all this, see WISE: New Stars and Brown Dwarfs.

But the evidence for objects big enough to perturb the local neighborhood does persist, even if we have to scale down our expectations as to its size. A new paper in Nature reports the discovery of 2012 VP113, a dwarf planet that joins Sedna in orbiting entirely beyond the Kuiper Belt’s outer edge, which is normally defined at 50 AU. The object at perihelion does not approach closer than 80 AU, making it more distant than Sedna itself. The work of Scott Sheppard and Chadwick Trujillo (Carnegie Institution for Science, Washington), the paper goes on to suggest a larger inner Oort Cloud population and the possibility of perturbed orbits there. Are the orbits of objects like 2012 VP113 and Sedna telling us something about larger bodies in this region?

The researchers used the NOAO 4-meter telescope in Chile in conjunction with the Dark Energy Camera (DECam), a high-performance, wide-field CCD imager, a combination that offers a wide field of view in the search for faint objects in large areas of sky. They also used the Magellan 6.5-meter instrument at Las Campanas Observatory to help determine the orbit of the newfound object. As with Sedna, we find that the orbit of 2012 VP113 takes it well outside the Kuiper Belt. In fact, given that their orbits extend at aphelion out to hundreds of AU, it is only the fact that both are currently near their closest approach to the Sun that has made them detectable.


Image: Artist’s rendering of the Oort cloud and the Kuiper belt. Credit: NASA.

Sedna, it appears, is not unique, and we can continue to infer from this the existence of the so-called inner Oort Cloud, extending out to about 1500 AU, where numerous objects with sizes larger than 1000 kilometers may exist. Sheppard and Trujillo, basing their estimate on the amount of sky searched, believe that 900 objects in this category may be found there, with a total inner Oort Cloud population probably larger than both the Kuiper Belt and the main asteroid belt.

The problem of distance is such that most would not be visible with current technology. However, says Sheppard, “Some of these inner Oort cloud objects could rival the size of Mars or even Earth. The search for these distant… objects beyond Sedna and 2012 VP113 should continue, as they could tell us a lot about how our solar system formed and evolved.”

2012 VP113’s orbit brings it to as close as 80 AU, outside Sedna’s perihelion. Interestingly, this finding indicates at least the possibility of a much larger planet, perhaps ten times the size of the Earth, orbiting in the inner Oort and influencing the orbits of both Sedna and the newfound object. The possibility remains that a ‘super-Earth’ or somewhat larger object at hundreds of AU, and thus well within the inner Oort, could be influencing the orbital configurations of objects like 2012 VP113 and Sedna. And based on Kevin Luhman’s WISE data studies, the existence of such a planet would not be inconsistent with what WISE is capable of telling us. If this unseen world is just several Earth masses in size, it’s going to be tricky to find, although locating more small objects being gravitationally influenced by it could eventually help us pin its orbit down.


Image: This is an orbit diagram for the outer solar system. The Sun and Terrestrial planets are at the center. The orbits of the four giant planets, Jupiter, Saturn, Uranus and Neptune, are shown by purple solid circles. The Kuiper Belt, including Pluto, is shown by the dotted light blue region just beyond the giant planets. Sedna’s orbit is shown in orange while 2012 VP113′s orbit is shown in red. Both objects are currently near their closest approach to the Sun (perihelion). They would be too faint to detect when in the outer parts of their orbits. Notice that both orbits have similar perihelion locations on the sky and both are far away from the giant planet and Kuiper Belt regions. Credit: Scott Sheppard / Carnegie Institution for Science.

Meanwhile, the inner edge of the Oort Cloud seems to be fairly well defined. From the paper:

Although our survey was sensitive to objects from 50 AU to beyond 300 AU, no objects were found with perihelion distances between 50 AU and 75 AU, where objects are brightest and easiest to detect. This was true for the original survey that found Sedna and the deeper follow-up survey… If the inner Oort cloud objects had a minimum perihelion of 50 AU and followed a size distribution like that of the large end of all known small-body reservoir distributions…, there would be only a 1% chance of finding 2012 VP113 and Sedna with perihelion greater than 75 AU and no objects with perihelion less than 75 AU. Therefore, we conclude that there are few (although probably not zero) inner Oort cloud objects in the 50-75 AU region. Some stellar encounter models that include the capture of extrasolar material predict a strong inner edge to the perihelion distribution of objects, which is consistent with our observations.

A few words about this: Sheppard and Trujillo distinguish between the inner Oort out to 1500 AU and an outer Oort Cloud, assuming that beyond 1500 AU objects are more subject to interstellar influences. One theory of inner Oort Cloud object formation is that Sedna and its ilk are captured extrasolar planetesimals lost in encounters with stars in the Sun’s birth cluster. Primordial close encounters with other stars may be implicated, but only further discovery of other inner Oort Cloud objects will provide the information needed to make this call about our system’s evolution.

The paper is Sheppard and Trujillo, “A Sedna-like body with a perihelion of 80 astronomical units,” Nature 507 (27 March, 2014), 471-474..



Imaging Beta Pictoris b

by Paul Gilster on March 25, 2014

This morning I want to circle around to a story I had planned to write about a couple of weeks ago. One thing writing Centauri Dreams has taught me is that there is never a shortage of material, and I occasionally find myself trying to catch up with stories long planned. In this case, the imaging of an exoplanet around the star Beta Pictoris demands our attention because of the methods used, which involve charge-coupled devices and wavelengths close to visible light. The detection marks real progress in visible light imaging of exoplanets.

The work, which is slated to appear in The Astrophysical Journal, was conducted by researchers from the University of Arizona led by Laird Close. Charge-coupled devices (CCD) are the same kind of technology we find in digital camera imaging sensors, used here in a setting where we’d normally expect an infrared detector. But using infrared means viewing massive young planets hot enough to put out considerable heat. As the exoplanet hunt develops and we push the search for life in the cosmos, we’re after much trickier game, says Close:

“[W]e now are a small step closer to being able to image planets outside our solar system in visible light. Our ultimate goal is to be able to image what we call pale blue dots. After all, the Earth is blue. And that’s where you want to look for other planets: in reflected blue light.”

beta_Pic_VisAO_v3 (1)

Image: An image of the exoplanet Beta Pictoris b taken with the Magellan Adaptive Optics VisAO camera. This image was made using a CCD camera, which is essentially the same technology as a digital camera. The planet is nearly 100,000 times fainter than its star, and orbits its star at roughly the same distance as Saturn from our Sun. (Image: Jared Males/UA).

Beyond young, hot planets, we’d like to image planets that have long since cooled, the kind of worlds where the passage of time has allowed for the development of life. Beta Pictoris b certainly does not fit that bill, but the technology points in the right direction. Now deployed at the Magellan 6.5-meter instrument in Chile, the system Close and team have developed — Magellan Adaptive Optics — can manipulate a deformable mirror so that its shape changes a thousand times a second in real time, overcoming atmospheric distortion. The team used the MagAO system in tandem with VisAO, a visible wavelength camera. The detection points toward future space-based observatories that can ‘drill down’ to the detection of cooler terrestrial worlds.

“[W]e were able to record the planet’s own glow because it is still young and hot enough so that its signal stood out against the noise introduced by atmospheric blurring,” added lead author Jared Males. “But when you go yet another 100,000 times fainter to spot much cooler and truly earthlike planets, we reach a situation in which the residual blurring from the atmosphere is too large and we may have to resort to a specialized space telescope instead.”

The imaged planet orbits at 9 AU from the host star, a bit closer than Saturn in our own Solar System, and appears 100,000 times fainter than the star. Males describes the image as having the highest contrast ever achieved on an exoplanet this close to its star. That the image was actually that of Beta Pictoris b, an object about twelve times the mass of Jupiter with an atmospheric temperature in the range of 1700 Kelvin, was confirmed using a second MagAO image taken in the infrared spectrum, where the giant world shines much more brightly.

So we’re a long way from directly imaging Earth-like planets around other stars, but tuning up our methods in visible light will eventually pay off with future space-based planet finders. The paper is Males et al., “Magellan Adaptive Optics first-light observations of the exoplanet β Pic b. I. Direct imaging in the far-red optical with MagAO+VisAO and in the near-IR with NICI,” accepted at The Astrophysical Journal (preprint). A University of Arizona news release is also available.



A Glassy Sea on Titan

by Paul Gilster on March 24, 2014

The second largest sea on Titan is Ligeia Mare, made up of methane and ethane in a body of liquid that is larger than Lake Superior. Now we have word that the surface of Ligeia Mare is so utterly still that it would appear like glass. The news comes from Stanford University, where geophysicist Howard Zebker had led a new study based on Cassini measurements made in 2013. “If you could look out on this sea,” said Zebker, “it would be really still. It would just be a totally glassy surface.”

Titan seizes the imagination not only because it is planet-like, with seas and a thick atmosphere, but because we know of no other body in the Solar System besides Earth that has a complex cycle involving solid, liquid and gas. Because the thickness of Titan’s atmosphere compromises optical observations, Cassini bounced radio waves off the surface and analyzed the resulting echo. Wave action could be measured by the strength of the returning echo. Zebker explains in this Stanford news release that the echo is analogous to an Earthly lake which, if completely still, would reflect an extremely bright image of the Sun, while a surface in motion would produce a much dimmer reflection.


Image: This false-color image of the surface of Titan was made using radar measurements made by NASA’s Cassini spacecraft. The spacecraft revealed that the surface of Ligeia Mare, Titan’s second largest lake, is unusually still, most likely due to a lack of winds at the time of observation. Credit: Howard Zebker.

Given that Cassini’s radar sensitivity is one millimeter in this study, any waves on Ligeia Mare would have to be smaller than one millimeter, which makes for a smooth surface indeed. Cassini’s only comparable observation occurred in a late 2008 Titan flyby that studied Ontario Lacus, with both studies indicating an equally smooth surface. Lack of winds during the time of observation is one explanation for the calm seas, but a layer of material could also suppress any waves. Says Zebker: “[O]n Earth, if you put oil on top of a sea, you suppress a lot of small waves.”

Also interesting here is that radiometry measurements of the terrain surrounding Ligeia Mare show little surface water ice. Instead, the area seems to be made up of solid organic materials, probably the same methane and ethane constituents that make up the sea itself.

Talking about Titan’s seas reminds me inevitably of Michael Swanwick’s Hugo winning novelette “Slow Life,” which ran in Analog in 2002. In it, astronaut Lizzie O’Brien finds herself landing at the shore of one such sea. This snippet gives you the flavor of the story:

“Chemically, the conditions here resemble the anoxic atmosphere on Earth in which life first arose,” Consuelo said. “Further, we believe that such prebiotic chemistry has been going on here for four and a half billion years. For an organic chemist like me, it’s the best toy box in the Universe. But that lack of heat is a problem. Chemical reactions that occur quickly back home would take thousands of years here. It’s hard to see how life could arise under such a handicap.”

“It would have to be slow life,” Lizzie said thoughtfully. “Something vegetative. ‘Vaster than empires, and more slow.’ It would take millions of years to reach maturity. A single thought might require centuries . . .”

What happens next involves unusual dreams, robotic exploratory ‘fish’ and a plunge into liquid ethane. You can track this one down in Swanwick’s short story collection The Dog Said Bow-Wow (Tachyon, 2007). We’re going to get a lot of interesting science fiction as the exploration of Titan continues. Meanwhile, the Zebker paper is “Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis,” published online by Geophysical Research Letters 30 January 2014 (abstract).



What Kardashev Really Said

by Paul Gilster on March 21, 2014

Whenever we’re audacious enough to categorize far future civilizations, we turn to the work of Nikolai Kardashev. Nick Nielsen today looks at the well known Kardashev scale in the light of a curious fact: While many use Kardashev’s rankings in their own speculations, few have gone back and dug into his original paper. In Kardashev’s terms, our planet is close to attaining Type I status, which would surprise many commentators. And doesn’t the ambiguity over what constitutes the energy of a star — red dwarf? red giant? — play havoc with cut and dried ‘type’ definitions? How subsequent writers have adapted and modified the Kardashev scale makes for a cautionary tale about mastering our sources before using them for further extrapolation. For that matter, are there better gauges of a civilization than its use of particular energy resources? Answering the question deepens the debate that Kardashev so fruitfully began.

by J. N. Nielsen


The name of Nikolai S. Kardashev is synonymous with the Kardashev ranking of civilizations according to their energy profile, and probably will be so synonymous as long as human civilization (or some successor institution) endures. Perhaps someday the term “Kardashevian” will be an adjective like “Copernican” and Kardashev’s name will join the select group of cosmologists who have given their name to an entire cosmological theory.

Kardashev is a radio astronomer and among the pioneers of SETI, and his idea of classifying civilizations according to their ability to harness energy was directly related to his experience in radio telescopy (thus I find myself again in this post verging into the territory of SETI, METI, and Existential Risk). Kardashev asked himself how powerful an extraterrestrial radio signal would have to be in order to be detected, “by conventional radio astronomical techniques.” [1] The numbers he came up with were quite high, and this furnished the basis of his tripartite division of civilizations into Type I, Type II, and Type III.

If a civilization could radiate EM spectrum emissions at the energy levels of naturally-occurring astronomical radio sources, such a civilization could be detected as easily as we detect pulsars, radio galaxies, and the like. For a civilization to radiate at such levels of energy, however, would require technological capacities beyond our current abilities. Kardashev notes his Type II and Type III civilizations could radiate at such high energy levels, and although we could not match these levels, we could receive these signals. He also suggests that known astronomical radio sources could have an artificial origin. Thus from a Kardashevian perspective, the existential risk of METI is negligible, as only very advanced and powerful civilizations would be able to transmit to the universe at large, while younger, less advanced, and therefore more vulnerable civilizations are restricted to passive listening, for all practical purposes.

Kardashev’s rankings of civilization have become widely known – so widely known that it is not uncommon to hear others toss off casual references to “K1” or “K2” or “K3” – and the terminology of Kardashev rankings has been generalized and extrapolated so that now one may speak in terms of Type 0 and Type IV civilizations and anticipate being understood. [2]

Sometimes the discussion of Kardashev civilization types seems to become a little too casual, and, like the sailors on the Pequod who each look into the gold doubloon nailed to the mast and see themselves and their personal concerns mirrored within, writers on the possibility of extraterrestrial civilizations (and especially speculation on supercivilizations) tend to read their preoccupations into Kardashev’s types without being much concerned with what Kardashev himself actually wrote about this. While many writers have parsed the Drake equation with painstaking attention to detail, I find it remarkable that no one seems to have done this for Kardashev, instead seeming to prefer impressionistic renderings of Kardashev’s civilization types.

Here is Kardashev’s original formulation of the three types of civilizations he recognized:

I – technological level close to the level presently attained on the earth, with energy consumption at ~4 x 1019 erg/sec.

II – a civilization capable of harnessing the energy radiated by its own star (for example, the stage of successful construction of a “Dyson sphere”); energy consumption at ~4 x 1033 erg/sec.

III – a civilization in possession of energy on the scale of its own galaxy, with energy consumption at ~4 x 1044 erg/sec. [1]


Note that there is an ambiguity of the Kardashev metric in terms of actual vs. comparable energy usage. A carefully constructivist account of Kardashev would insist that a Type II civilization is “a civilization capable of harnessing the energy radiated by its own star,” and that all of this energy must in fact come from that particular star and from no other source. In other words, given a strict conception of a Type II civilization, a civilization utilizing energy quantitatively equivalent to but not identical to the actual energy produced by a single star would not constitute a Type II civilization. Actual and equivalent energy use are very different measures, and Kardashev himself uses both formulations (type II is “energy radiated by its own star” while type III is “energy on the scale of its own galaxy”).

Image: Russian radio astronomer and SETI theorist Nikolai Kardashev.

Moreover, in defining a type II civilization as, “harnessing the energy radiated by its own star” (a definition which is, I must observe, impredicative, because it defines an individual in terms of a whole of which it is a part) [3], Kardashev introduces an ambiguity due to the fact that there are stars of many different luminosities and temperatures. Generally speaking, the largest stars burn very hot, are very bright, and burn themselves out relatively quickly, while small stars are much dimmer and endure much longer. Brown dwarfs will likely outlast almost all other stars.

Presumably a “standard” measure of a star would lie along the main sequence of stellar evolution (cf. the Hertzsprung–Russell diagram), but this still isn’t very helpful as a quantitative measure, not least because it falls far short of the precision that we could bring to question. If we take our own sun as the standard measure (as it is commonplace in astronomy to speak of “solar masses”), this would significantly distort any measure of a civilization that happened to emerge, for example, orbiting a supergiant or a red dwarf star. [4] Such a measure might still be useful, but we could do much better simply by stipulating a measure of energy not relative to the star of a civilization’s homeworld. Kardashev does this when he cites specific energy levels, and he departs from this when he presents his formulations in terms of, “its own star” and “its own galaxy.”

One of the persistent themes we find in commentaries on Kardashev’s civilization types is that our terrestrial civilization is not yet a type I civilization, but this isn’t at all what Kardashev said. In fact, it is the opposite of what Kardashev said, as he specified for a Type I civilization a, “technological level close to the level presently attained on the earth.” Kardashev did not say what “close” means in this context.

For the past decade, global energy consumption has been increasing at an average rate of 2.3 percent per year – more growth in years of economic growth or difficult winters, less in years of recession and mild winters. Roughly, this means that global energy consumption will double every thirty years, so that since the time Kardashev wrote his paper, global energy consumption is well on its way to quadrupling. So for those who say that we are still short of what Kardashev called a Type I civilization in 1964, even if we were a little short of the mark at that time, we ought to be well past the mark by now.

But this only scratches the surface of the kind of impressionistic readings of Kardashev that are common. Here is an example from George Basalla:

“A Type I Kardashev civilization is similar to the modern technological societies found on Earth. It draws upon the energy falling upon a planet from its sun. Kardashev estimated the Earth’s energy consumption at about 4 x 1019 ergs per second. The Earth has not quite reached Type I status because its inhabitants are unable to capture all of the radiant energy streaming down upon it. For this reason, Carl Sagan said that the Earth was more accurately called a Type .7 civilization.” [5]

This is an entirely reasonable extrapolation of Kardashev, but it is an imaginative reconstruction of Kardashev rather than an explication and application of the principles implicit in the exposition of his civilization types. The passage to which Basalla alludes in from Sagan’s The Cosmic Connection: An Extraterrestrial Perspective:

“The energy gap between a Type I and a Type II civilization or between a Type II and a Type III civilization is enormous – a factor of about ten billion in each instance. It seems useful, if the matter is to be considered seriously, to have a finer degree of discrimination. I would suggest Type 1.0 as a civilization using 1016 watts for interstellar communication; Type 1.1, 1017 watts; Type 1.2, 1018 watts, and so on. Our present civilization would be classed as something like Type 0.7.” [6]

Sagan’s interpretation provided a template for many other interpretations. Here is another example, from David Lamb:

“Type I would have a similar technological level to Earth, using 6.6 × 1012 watts. This civilization could engage in something akin to the present power output of Earth for the purpose of interstellar communication. Type I civilizations would have the power to restructure entire planets.” [7]

This is closer to the spirit of Kardashev’s original exposition, since it focuses on the use of energy for interstellar radio communication, but, again, this is not how Kardashev formulated his types. Kardashev wrote of a civilization in possession of energy levels of, “4 x 1033 erg/sec. or more, which it is capable of transmitting in a coded isotropic radio-frequency signal, may be detected by conventional radio astronomical technique,” which is the energy he attributes to Type II civilizations, and he is clear in the body of his paper that it would be Type II and Type III civilizations that would be transmitting, and Type I civilizations, like ourselves, who would be listening.

Michio Kaku is even more imaginative than Sagan and others in drawing out the implications of Kardashev’s civilization types as he sees them. For example, here is how Kaku defines a Type I civilization:

“Type I civilizations: those that harvest planetary power, utilizing all the sunlight that strikes their planet. They can, perhaps, harness the power of volcanoes, manipulate the weather, control earthquakes, and build cities on the ocean. All planetary power is within their control.” [8]

Kaku goes into much more detail in Chapter 8, “The Future of Humanity,” in his book Physics of the Future [9], most of which chapter is an exposition of Kaku’s interpretation and extrapolation of Kardashev civilization types.

There is something intuitively attractive and plausible about equating a type I civilization with planetary energy resources, a type II civilization with stellar energy resources, and a type III civilization with galactic energy resources, and it would further be intuitively attractive and plausible to equate planetary energy resources with the burning of fossil fuels that are the result of a planetary biosphere (and are not to be derived from stars and are not found in space). This is Kaku’s approach. But this is not what Kardashev said.

The ideas of Sagan, Kaku and others for a typology of civilizations are worthwhile, but they aren’t what Kardashev said. Nevertheless, as the idea of Kardashev civilization types becomes further elaborated, many writers routinely refer to Kardashev types, but this only compounds the ambiguity because one never knows if they are referring to what Kardashev actually said, or to subsequent embroidering upon what Kardashev said. And it is a different that makes a difference. If we cannot be clear about what we mean, we will only engender more confusion the more we say.

The kind of elaboration of Kardashev we find in Sagan and Kaku has owes much more to Constantinos Doxiadis’ (Κωνσταντίνου Α. Δοξιάδη) vision of Ecumenopolis – the world city or universal city (which I wrote about in Civilization and the Technium) [10] – than to Kardashev’s scientifically-inspired quantification of civilization. If you read Sagan and Kaku next to Doxiadis you will immediate see the resemblance, whereas these visions of a harmonious planetary civilization have no place in Kardashev’s text.

Kardashev concluded his famous paper with this reflection:

“…we should like to note that the estimates arrived at here are unquestionably of no more than a tentative nature. But all of them bear witness to the fact that, if terrestrial civilization is not a unique phenomenon in the entire universe, then the possibility of establishing contacts with other civilizations by means of present-day radio physics capabilities is entirely realistic.” [1]

These are the sage words of a scientist who expects (or at least hopes) that others will take up his work and expand upon it. Tentative formulations invite others to revise and extend them, and certainly many have sought to do this with Kardashev’s civilization types. I don’t wish to suggest that the extrapolations and extensions of Kardashev’s idea are illegitimate, only that they aren’t at all what Kardashev said, and we ought to be clear about this.

If we take up Kardashev’s idea in the spirit in which he initially proposed it, then other quantitative measures that have been suggested, such as measures of information processing [11], or even Kaku’s suggestion of measuring civilizations by entropy [12], would be appropriate extrapolations of the idea. Indeed, we might use several quantitative measures of civilization to define a parameter space, and be well on our way to mathematically modeling civilization. In Kardashev’s later paper, “On the inevitability and the possible structures of supercivilizations” [13], he mentions the parameters of “mass of constructions,” “power consumed,” and “information volume which describes the program activity and memory,” and suggests an argument from mathematical induction to arrive at arbitrary large civilizational activity. These suggestions seem to me more in line with what Kardashev had in mind than the persistent idea of planetary civilizations that have reached a stage of totality in harnessing some particular energy resource.

You needn’t take my word for what constitutes an extrapolation of Kardashev’s civilization types in the spirit of its initial formulation. As of this writing, Kardashev is still alive, and I am sure that someone with the right connections could ask him what his intentions were in formulating his civilization types; it is Kardashev who could provide the definitive insight into what is and what is not in the spirit of his original (and tentative) exposition of the idea.

However we choose to interpret and extrapolate Kardashev, we need to accustom ourselves to thinking as rigorously about civilization as we do about science (or, at least, make the attempt to do so) so that all those who think about SETI, METI, extraterrestrial civilizations, and astrobiology, inter alia, will not be derisively dismissed as being in the realm of “science fiction” – and I trust a good many of my readers have felt the sting of this charge when trying to discuss such matters in a careful and rational manner.

This rigor is eminently within our grasp, but in order to do justice to it (and therefore to do justice to the ideas of extraterrestrial civilizations and supercivilizations) we must take care in our formulations to refine them to the fullest extent possible. Aristotle famously began his Nicomachean Ethics with the observation that, “…it is the mark of an educated man to require, in each kind of inquiry, just so much exactness as the subject admits of: it is equally absurd to accept probable reasoning from a mathematician, and to demand scientific proof from an orator.” [14] The study of extraterrestrial civilization, and of civilization simpliciter, does not yet admit of the degree of exactness of mathematics, but it is to be hoped that it admits to a greater degree of exactness than oratory. It is our responsibility to make it so.


[1] Kardashev, N. S., “Transmission of information by extraterrestrial civilizations,” Soviet Astronomy, Vol. 8, No. 2, Sept.-Oct. 1964.

[2] Carl Sagan wrote, “There is no provision for a Type IV civilization, which by definition talks only to itself.” (The Cosmic Connection: An Extraterrestrial Perspective, p. 234) Others, however, have sought to give content to the idea of a Type IV civilization and beyond. (Cf. Kardashev scale) John D. Barrow extrapolated a negative Kardashev scale to quantify the technological ability to manage ever smaller structures, in contradiction to the ever larger structures obtained by extending the Kardashev scale. Barrow’s formulation of Types I-III is interesting for its use of the idea of “restructuring” (i.e., a civilization capable of restructuring a planet, solar system, or galaxy, respectively) – an interesting idea, but not something to be found in Kardashev’s definitions of the types.

[3] Self-reference is a common feature of many paradoxes. Roughly, impredicativity is that form of self-reference derived from the violation of the vicious circle principle. (Cf. Chihara, Charles S., Ontology and the Vicious-Circle Principle, Ithaca and London: Cornell University Press, 1973.) Most big picture conceptions are impredicative; any definition of humanity that involves a reference to the universe of which we are a part is essentially impredicative.

[4] Of course, we would expect to find peer civilizations in cosmological circumstances similar to our own, i.e., on a planet orbiting a sun-like star. If we construe peer civilizations very narrowly, we could limit ourselves to the sun as a standard measure, but this strikes me as the arbitrary and the cosmological equivalent of Lakatosian “monster barring.”

[5] Basalla, George, Civilized Life in the Universe: Scientists on Intelligent Extraterrestrials, Oxford: Oxford University Press, 2006, p. 148. If anyone knows the source of the 1981 interview with Kardashev referenced by Basalla, I would appreciate it if you would make the reference known to me.

[6] Sagan, Carl, The Cosmic Connection: An Extraterrestrial Perspective, Cambridge University Press, 2000, Part Three, Chapter 34, “Twenty Questions: A Classification of Cosmic Civilizations”

[7] Lamb, David, The Search for Extraterrestrial Intelligence: A Philosophical Inquiry, London and New York: Routledge, 2001, p. 182. (I previously discussed this book in Is astrobiology discrediting the possibility of directed panspermia?) Note that Lamb employs the locution of “restructuring planets” which is a formulation due to John D. Barrow (cf. note 2 above).

[8] Kaku, Michio, The Physics of the Impossible, New York, et al.: Doubleday, 2008, p. 145.

[9] Kaku, Michio, Physics of the Future, New York, et al.: Doubleday, 2011.

[10] Doxiadis defined Ecumenpolis as follows: “Ecumenopolis: the coming city that will, together with the corresponding open land which is indispensable for Man, cover the entire Earth as a continuous system forming a universal settlement. Term coined by the author and first used in the October 1961 issue of Ekistics. (Constantinos A. Doxiadis, Ekistics: An Introduction to the Science of Human Settlements, New York: Oxford University Press, 1968, p. 516.)

[11] Quantifying civilizations in measures of information processing power is due to Sagan:

“If we have used numbers to describe energy, we should perhaps use letters to describe information. There are twenty-six letters in the English alphabet. If each corresponds to a factor of ten in the number of bits, there is the possibility of characterizing with the English alphabet a range of information contents over a factor of 1026 – a very large range, which seems adequate for our purposes. I propose calling a Type A civilization one at the ‘Twenty Questions’ level, characterized by 106 bits. In practice this is an extremely primitive society – more primitive than any human society that we know well – and a good beginning point. The amount of information we have acquired from Greek civilization would characterize that civilization as Type C, although the actual amount of information that characterized Periclean Athens is probably equivalent to Type E or so. By these standards, our contemporary civilization, if characterized by 1014 bits of information, corresponds to a Type H civilization.” (Sagan, Carl, The Cosmic Connection: An Extraterrestrial Perspective, Cambridge University Press, 2000, Part Three, Chapter 34, “Twenty Questions: A Classification of Cosmic Civilizations”)

[12] I don’t know if Kaku originated this idea of measuring civilizations by entropy, but he gives a brief exposition of this in his Physics of the Future (Chapter 8, in which he discusses Kardashev civilization types) and provides no reference to a source in his notes, so I assume the idea is Kaku’s.

[13] Kardashev, N. S., “On the inevitability and the possible structures of supercivilizations,” The Search for Extraterrestrial Life: Recent Developments; Proceedings of the Symposium, Boston, MA, June 18-21, 1984 (A86-38126 17-88). Dordrecht, D. Reidel Publishing Co., 1985, p. 497-504.

[14] Aristotle, The Nicomachean Ethics of Aristotle, Translated by F. H. Peters, M.A., London: Kegan Paul, 1893, p. 4.



Solar Probe Plus: Prelude to ‘Sundiver’?

by Paul Gilster on March 20, 2014

‘Sundiver’ maneuvers are surely the most extreme events to which we could subject a solar sail. To my knowledge, it was Gregory Benford who first came up with the term — he mentions in Fantasy & Science Fiction that he passed the coinage on to David Brin when Brin was working on the book that would bear its name (Sundiver, published in 1985, would be the first volume in Brin’s Uplift Saga). But Benford credits Brin with the actual concept, which he needed to make his plot work, so it seems best to give credit to both writers for an idea both went on to explore, Benford not only in fiction but in scientific papers as well.

The maneuver is straightforward if breathtaking. Benford explains it in terms of a carbon sail being deployed in low Earth orbit and then launched into deep space by microwave beam:

Consider the sundiving sail. Approaching the Sun turned edge-on (to prevent the increasing flux of sunlight from pushing against its fall), the carbon sail heats up. At closest approach, the craft could turn to absorb the full glare of the intense Sun, gaining a high velocity as it accelerates strongly, under desorption. It exhausts the store of molecules lodged in its fibers, losing mass while gaining velocity. It then sails away as a conventional, reflecting solar sail. Its final speed could be high enough to take it beyond Pluto within five years. There it could do a high velocity mapping of the outer solar system, the heliopause and beyond, to the interstellar medium—the precursor to true interstellar exploration.

So there you are, a fast, propellantless way to do missions to the outer Solar System. But how likely is it that a craft like this would survive a close approach to the solar furnace? To find out just what the parameters would have to be, we need more data from this extreme environment. It’s interesting to note, then, that the Johns Hopkins University Applied Physics Laboratory (APL) is engaged in the advanced stages of design, development and testing of Solar Probe Plus now that its work has received a thumbs up from an independent assessment board.

With a launch set for 2018, the spacecraft is intended to orbit the sun 24 times, assisted by seven flybys of Venus along the way. The craft is going to be moving at extraordinary speeds at its closest approaches, some 190 kilometers per second. Contrast that with Voyager 1’s 17.1 kilometers per second, or the previous record-holder, the two Helios probes, that reached up to 70 kilometers per second. In terms of distance, Solar Probe Plus will take its ten scientific instruments a little more than 6 million kilometers from the Sun’s surface.


Image: Artist’s impression of NASA’s Solar Probe Plus spacecraft on approach to the sun. Set to launch in 2018, Solar Probe Plus will orbit the sun 24 times, closing in with the help of seven Venus flybys. The spacecraft will carry 10 science instruments specifically designed to solve two key puzzles of solar physics: why the sun’s outer atmosphere is so much hotter than the sun’s visible surface, and what accelerates the solar wind that affects Earth and our solar system. The Johns Hopkins University Applied Physics Laboratory manages the Solar Probe Plus mission for NASA and leads the spacecraft fabrication, integration and testing effort. Credit: NASA/Johns Hopkins University Applied Physics Laboratory.

An extreme environment indeed, with temperatures exceeding 1370 degrees Celsius (2500 degrees Fahrenheit). Solar Probe Plus is equipped with a carbon-carbon composite heat shield designed to withstand these temperatures, not to mention the impacts of hypervelocity dust particles, and the spacecraft’s liquid-cooled system should keep its solar arrays at survivable temperatures through all 24 solar passes. We’ll learn much about the Sun’s outer atmosphere and the solar wind from all this, but I like what NASA’s Lika Guhathakurta threw into the mix:

“Solar Probe Plus is a pathfinder for voyages to other stars and will explore one of the last unexplored regions of the solar system, the solar corona, where space weather is born.”

Guhathakurta is a program scientist at NASA headquarters in Washington who is aware of just how challenging this mission is going to be. As this APL news release notes, we’re talking about going ten times closer to the Sun than the planet Mercury. Amidst everything else we learn, we will have data that can assist in any future sundiver missions. In their book Solar Sails: A Novel Approach to Interplanetary Travel (Copernicus, 2008), Greg Matloff, Les Johnson and Giovanni Vulpetti make the case that a sundiver could reach outbound speeds of at least 120 kilometers per second.

Solar Probe Plus will achieve high speeds as well, of course, but only within the context of operations near the Sun. A true sundiver that used the Sun for a massive gravity assist would attain speeds going outward that could allow it not only to explore the outer planets but reach the Sun’s gravitational focus. “[W]e may view these early efforts as humanity’s first true starships,” the authors write, the beginning of what we can hope is an extended era of exploration.



From Cosmism to the Znamya Experiments

by Paul Gilster on March 19, 2014

What got me thinking about French influences on early solar sail work in Russia yesterday was the realization that science fiction was much stronger in Europe, and particularly France, in the latter part of the 19th Century than we Americans might realize. Hugo Gernsback to the contrary, the genre did not emerge in 1926 with the appearance of Amazing Stories, nor did key early texts like Mary Shelley’s Frankenstein launch the genre in England. Brian Aldiss would probably argue with this (see his Trillion Year Spree, 1973), but I agree with Brian Stableford in seeing a true genre emerging first on French soil.


Whether you agree or not, have a look at Stableford’s essay The French Origin of the Science Fiction Genre, where I find this in reference not only to Verne but writers like George Sand (Laura: voyages et impressions, 1865) and Camille Flammarion (Récits de l’infini, 1872):

These works were sometimes referred to by contemporary commentators as examples of roman scientifique — a phrase that can be translated, because of the flexibility of the first word’s range of reference, as “scientific fiction,” “scientific romance,” or “the scientific novel.” Verne’s work in particular attracted numerous imitators because of its enormous popularity, and eventually inspired the founding of a specialist periodical, the Journal des Voyages, in 1877, dedicated to fiction in that vein.

Novelist Stableford is, in addition to being a critic, a fine translator of numerous French works from this period. Much of this work remains little read in our time, and I suspect some enterprising historian of science will one day mine further connections between French scientific romances and the early history of astronautics, particularly their influence on Tsiolkovsky, Fridrikh Tsander and the evolving philosophical movement known as Cosmism, that emerged as a way of integrating natural history with a human future in space. Tsiolkovsky believed that colonizing space would transform Earthly human life into an existence blessed with immortality.

Image: Novelist and translator Brian Stableford. Credit: Brian and Jane Stableford.

The whole interplay with cosmism and Russian space exploration is a vast topic — for more, I’d recommend George Young’s The Russian Cosmists (Oxford University Press, 2012), which focuses on life extension advocate Nikolai Fyodorovich Fyodorov but examines the work of all his followers as well. Thinkers who believed that humanity was evolving into a space-going species, these people were fascinated with technology’s potential, and it’s not surprising to me that early rocketry and sail advances should be associated with them.

Znamya: Testing Deployment Technologies


When it came to practical sail experiments, though, that work would have to wait until the end of the 20th Century when Russia performed the first demonstrations of sail technologies in space. The Znamya project involved mirrors rather than sails, but learning how to spin up a 20-meter mirror in Earth orbit involves many of the same methods that sails would demand. The idea was to test whether it would be practical to brighten remote polar and sub-arctic settlements after dark, the first deployment occurring on February 4, 1993 from a Progress supply ship.

Image: The deployed Znamya mirror attached to the Progress spacecraft after deployment in 1993.

After a successful deployment, the Znamya mirror illuminated a spot on Earth five kilometers in diameter that had the intensity of a full moon. Traveling at approximately eight kilometers per second, the beam swept through Europe and into western Russia, but Europe was covered with clouds that day and the beam could be seen by only a few. More to the point in terms of sail technologies, though, the use of centripetal acceleration of the spinning canister proved a viable way to deploy the film.

Znamya was de-orbited after several hours and burned up upon re-entry, giving way to the larger Znamya 2.5 mission, whose deployment in February of 1999 was a failure, as the mirror film caught on an antenna on the Mir space station and became tangled. Unable to free the material for full deployment, controllers de-orbited the Znamya 2.5, and it too burned up upon re-entry. An even larger Znamya 3 was never built as interest in the space mirror project waned.

Fifteen years later, we have seen successful deployments of free-flying solar sails in space, and are getting closer to bringing some of Tsiolkovsky and Tsander’s notions to fruition, with the launch of NASA’s Sunjammer sail scheduled for next year. The 38 X 38 meter sail, like IKAROS, will doubtless have much to tell us about deployment issues and performance as it moves toward the L1 Lagrangian point. I, for one, love the science fiction reference in its name, a nod not only to Arthur C. Clarke’s 1964 story but also to a Poul Anderson tale that ran under the pseudonym Winston P. Sanders in Analog in 1964. Both brought science fictional methods to bear on a promising technology that has taken all too long to begin active space testing.



SF Influences: A Solar Sail Theory

by Paul Gilster on March 18, 2014

Last week I looked at three figures who put solar sails on the map in the 1950s — Carl Wiley, who wrote the concept up in Astounding, Ted Cotter, who analyzed it for colleagues at Los Alamos, and Richard Garwin, who brought solar sailing into the academic journals. It was not long after Garwin’s work that science fiction pounced on solar sails through a cluster of memorable stories beginning with Cordwainer Smith (Paul Linebarger) and “The Lady Who Sailed the Soul.” More about that story and its era soon, including work by Poul Anderson, Jack Vance, and perhaps the best known of all from that era, Arthur C. Clarke’s “Sunjammer.”

But today let’s go way back to what is I think the first story that ever dealt with raw light as a propulsive mechanism. Georges Le Faure and Henri de Graffigny published Aventures extraordinaires d’un savant russe (The Extraordinary Adventures of a Russian Scientist) in three volumes beginning in 1889, with a fourth volume coming out under the promising title Les mondes stellaires (Stellar Worlds) in 1896. This last volume was from a different publisher, which affected its circulation. Let me know if you ever run across a copy — from a collector’s standpoint, it’s by far the hardest of the four to find.


Image: A look inside The Extraordinary Adventures of a Russian Scientist. The illustrations are by the French astronomer Camille Flammarion, who also wrote a preface to each volume. Credit: http://www.livre-rare-book.com/.

It’s fair enough to say that Le Faure and de Graffigny worked in the shadow of Jules Verne, whose From the Earth to the Moon first appeared in 1865, and our authors divide their characters’ exploits into sections on the Moon, the Sun and inner planets, and the outer planets and comets. Like Verne, they imagine sending humans into space using enormous cannons. But unlike Verne, they carry out at least some of their explorations in a hollow sphere that is pushed by the pressure of sunlight concentrated by a huge reflecting dish. Here we might be reminded of something Johannes Kepler said: “Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes.”

We’re getting into interesting if speculative history. For around the same time that Jules Verne was finishing up Autour de la lune (Around the Moon), first published in 1870, James Clerk Maxwell was developing equations that would show the existence of light pressure. In 1900, the Russian physicist Peter Lebedev, experimenting with beams of light focused on metals of different reflectivity, made the first precision laboratory tests that demonstrated the phenomenon, verifying Maxwell’s predictions. Lebedev’s work is obviously key in the development of solar sails in Russian scientific thinking, but it’s also worth noting that science fiction may have played a role.

I have no hard evidence that Konstantin Tsiolkovsky ever read Le Faure and de Graffigny, but it’s at least a possibility, the major argument against it being lack of access to books, for Tsiolkovsky lived in an isolated town some 200 kilometers southwest of Moscow, and was a deeply reclusive individual. On the other hand, he was well acquainted with Nikolai Fyodorov, a proponent of the Russian space philosophy known as Cosmism, and may well have been exposed to the French writers’ works during time in his youth spent in Moscow. It seems apparent that he knew his Jules Verne, so it’s not too large a leap to Le Faure and de Graffigny’s space travel tales.


Did the latter influence Tsiolkovsky’s interest in solar sails? For by the 1920s, working with a Latvian colleague named Fridrikh Arturovich Tsander, he began talking about using enormous mirrors crafted into thin sheets that would gather sunlight for propulsion. Tsander was writing about solar sailing as early as 1924, a heritage that may explain the Russian interest in sail technologies that manifested itself in the 1990s Znamya deployments (about which more later).

Tsander is one of those figures who is not as widely known in the West as he deserves to be. He was active in the development of liquid fueled rockets and a founder of GIRD (Group for the Investigation of Reaction Propulsion). It was the GIRD-10, a liquid fueled rocket of his own design, that became the first Russian rocket of its type, although he died before he could see its launch. Early in his life he had become a passionate advocate of space travel, developing equations for a Mars mission while still in Latvia at the Riga Polytechnic Institute.

Image: Astronautics pioneer Fridrikh Tsander.

The young spaceflight engineer would move to Moscow in 1915. Just how energetic he was about space may be gauged by the names of his two children, a daughter named Astra and a son named Mercury. He would found the Society for Studies of Interplanetary Travel, would examine aerobraking to slow returning spacecraft, and be granted a patent for a winged rocket he designed as an interplanetary vehicle. He explored gravity assists for acceleration as early as 1925. The solar sail, it is clear, was but one of Tsander’s many astronautical interests.

I suspect that the French science fiction writers of the second half of the 19th Century were a continuing inspiration for men like Tsiolkovsky and Tsander, even if their job was to translate tales of adventure into concepts in accord with known physics. It’s an intriguing thought that Le Faure and de Graffigny may have spurred the early investigation into properties of light we now know can propel a spacecraft. We can only imagine with what interest both Tsiolkovsky and Tsander would have followed the IKAROS sail, and the upcoming launch of Sunjammer.



Creative Constraints and Starflight

by Paul Gilster on March 14, 2014

I discovered Karl Schroeder’s work when I was researching brown dwarfs some years ago. Who knew that somebody was writing novels about civilizations around these dim objects? Permanence (Tor, 2003) was a real eye-opener, as were the deep-space cultures it described. Schroeder hooked me again with his latest book — he’s dealing with a preoccupation of mine, a human presence in the deep space regions between ourselves and the nearest stars, where resources are abundant and dark worlds move far from any sun. How to maintain such a society and allow it to grow into something like an empire? Karl explains the mechanism below. Science fiction fans, of which there are many on Centauri Dreams, will know Karl as the author of many other novels, including Ventus (2000), Lady of Mazes (2005) and Sun of Suns (2006).

by Karl Schroeder


My newest science fiction novel, Lockstep, has just finished its serialization in Analog magazine, and Tor Books will have it on the bookshelves March 24. Reactions have been pretty favourable—except that I’ve managed to offend a small but vocal group of my readers. It seems that some people are outraged that I’ve written an SF story in which faster than light travel is impossible.

I did write Lockstep because I understood that it’s not actual starflight that interests most people—it’s the romance of a Star Trek or Star Wars-type interstellar civilization they want. Not the reality, but the fantasy. Even so, I misjudged the, well, the fervor with which some people cling to the belief that the lightspeed limit will just somehow, magically and handwavingly, get engineered around.

This is ironic, because the whole point of Lockstep was to find a way to have that Star Wars-like interstellar civilization in reality and not just fantasy. As an artist, I’m familiar with the power of creative constraint to generate ideas, and for Lockstep I put two constraints on myself: 1) No FTL or unknown science would be allowed in the novel. 2) The novel would contain a full-blown interstellar civilization exactly like those you find in books with FTL.

Creativity under constraint is the best kind of creativity; it’s the kind that really may take us to the stars someday. In this case, by placing such mutually contradictory — even impossible — restrictions on myself, I was forced into a solution that, in hindsight, is obvious. It is simply this: everyone I know of who has thought about interstellar civilization has thought that the big problem to be solved is the problem of speed. The issue, though (as opposed to the problem), is how to travel to an interstellar destination, spend some time there, and return to the same home you left. Near-c travel solves this problem for you, but not for those you left at home. FTL solves the problem for both you and home, but with the caveat that it’s impossible. (Okay, okay, for the outraged among you: as far as we know. To put it more exactly, we can’t prove that FTL is impossible any more than we can prove that Santa Claus doesn’t exist. I’ll concede that.)


Generations of thinkers have doubled down on trying to solve the problem, unaware that the problem is not the same as the issue. The problem — of generating enough speed to enable an interstellar civilization — may be insoluble; but that doesn’t mean the issue of how to have a thriving interstellar civilization can’t be overcome. You just have to overcome it by solving a different problem.

The problem to solve doesn’t have to do with speed (or velocity, for you purists), but rather with duration.

Enter Lockstep. In the novel, all worlds, all spacecraft and all habitats participating in a particular civilization use cold-sleep technology “in lockstep:” the entire civilization sleeps for thirty years, then simultaneously wakes for a month, then sleeps for another thirty years, etc. All citizens of the lockstep experience the same passage of time; what’s changed is that the duration of one night per month is stretched out to allow time for star travel at sublight speeds. In the novel I don’t bother with interstellar travel, actually; the Empire of 70,000 Worlds consists almost entirely of nomad planets, wanderers populating deep space between Earth and Alpha Centauri. Average long-distance travel velocity is about 3% lightspeed, and ships are driven by fission-fragment rockets or ‘simple’ nuclear fusion engines.

The result is a classic space opera universe, with private starships, explorers and despots and rogues, and more accessible worlds than can be explored in one lifetime. There are locksteppers, realtimers preying on them while they sleep, and countermeasures against those, and on and on. In short, it’s the kind of setting for a space adventure that we’ve always dreamt of, and yet, it might all be possible.

Cold sleep technology is theoretical, but unlike FTL, it’s not considered out of the question that we could develop human hibernation. It’s a bio-engineering problem, and probably admits of more than one solution. It’s an easier problem to solve than FTL, in other words. And by solving it, and using locksteps, we have a universe where travelers can go to sleep at their home port, wake up the next day at a world that could be light-years away, spend some time there and, when they return, find that exactly the same amount of time has passed at home. Locksteps give you the effect of FTL, without requiring FTL.

I won’t go into all the implications—that’s what the novel’s for. But, to circle back to the idea of creative constraint, by requiring an FTL-like civilization without FTL, I stumbled into a whole new universe. In the world of Lockstep, there are Sleeping Beauty-like tales, a version of the Twin Paradox, and an even stranger paradox in which the newest immigrants to the lockstep have the longest history with it… It’s no exaggeration to say that many books could be written in this world without exhausting its possibilities. Maybe I’ll write more of them myself.

Meanwhile, the idea’s out there. It’s a bit crazy, but it’s a possible solution to an issue, that avoids having to solve an impossible problem.

A constraint that gives us a way to reach the stars.



Solar Sailing Moves into the Journals

by Paul Gilster on March 13, 2014

I’m just getting started with Chris Impey and Holly Henry’s Dreams of Other Worlds (Princeton University Press, 2013), but glancing through it yesterday reminded me how long it has taken sail hardware to get into space. While Ted Cotter and Carl Wiley hoped for early experiments with sail ideas, we never got them until much later. Interesting mission concepts like JPL’s ‘gyro’ sail to Halley’s Comet did develop (although it never flew), and the Soviet Znamya deployments gave us some experience with thin membranes in space (I’ll talk about those soon), but by and large we left interplanetary exploration for the rockets.

The deep space probes and near-Earth observatories Impey and Henry cover — Viking, Voyager, Stardust, Chandra, Hubble and their ilk — gave us outstanding results but were not, until IKAROS, joined in space by alternative sail technologies. I’ll review this book in some detail as soon as I finish it, but for today let’s go back to the late 1950s, a time when Carl Wiley had already introduced solar sailing to a science fiction audience and Ted Cotter had apprised his colleagues at Los Alamos about the possibilities of a spinning sail.


For sails were about to make their debut in the technical journals. At the IBM Watson laboratory at Columbia University, physicist Richard Garwin, although deeply involved in nuclear weapons issues at a time of serious Cold War tensions, had become taken with the advantages of traveling between planets without propellant, not to mention the continuous acceleration that would allow the minute ‘push’ of photon momentum transfer to build up to high speeds when given enough time. In a March 1958 paper in the journal Jet Propulsion, Garwin published an analysis that ends on a note of genuine optimism: “There are considerable difficulties connected with space travel, but those connected with the sail appear relatively small.”

Image: Physicist Richard Garwin in 1980. Credit: Wikimedia Commons.

Garwin’s paper surely served as the stimulus for the detailed studies that would soon emerge, many of them covered in these pages, from the likes of Robert Forward, who would be talking about not just solar sails but sails propelled by laser in short order. Carl Wiley’s 1951 article in Astounding had been surprisingly technical, showing that sails could be maneuvered by ‘tacking’, thus allowing them to move inward toward the Sun, but it would be Garwin who put the term ‘solar sailing’ into wide use in the scientific community. By 1973, NASA would be funding solar sail studies at Battelle laboratories in Ohio, and Jerome Wright’s work on sail trajectories would lead to the Halley’s Comet mission concept, a spin stabilized heliogyro configuration using twelve 7.5 kilometer long blades of thin film.

Solar-electric propulsion won out over the heliogyro, but sharply rising cost estimates ultimately killed the entire rendezvous mission. It’s worth mentioning, since we’ve been looking at early sail pioneers this week, that the heliogyro concept itself had been developed in the 1960s by Richard MacNeal (Astro Research Corporation). The design was particularly interesting in this timeframe because it seemed to solve the challenging issues of deployment — a heliogyro would simply unroll each individual blade, as Colin McInnes explains in his Solar Sailing: Technology, Dynamics and Mission Applications (Springer, 2004). The work also led to the characterization of a wide range of thin sail films as we began to develop sail expertise.

If you’re interested in the Halley’s Comet mission, Louis Friedman’s Starsailing: Solar Sails and Interstellar Travel should be on your shelf. As to Richard Garwin, something that Enrico Fermi said surely resonates. Working with Garwin at the University of Chicago in the late 1940s, Fermi described him as the only true genius he had ever met, as recalled by fellow Fermi student Marvin Goldberger, who would himself become the head of both Caltech and the Institute for Advanced Study in Princeton. Garwin worked on nuclear arms design and in particular on the world’s first hydrogen bomb.

By 1958, the year of the solar sail paper, he was immersed in his work with IBM but also consulting for Los Alamos as well as Washington and holding down a physics appointment at Columbia. His work on how underground nuclear tests could be detected grew out of Dwight Eisenhower’s proposal of a Comprehensive Test Ban Treaty, one that failed but did lead to a partial ban in 1963.

Garwin’s later efforts on behalf of test ban issues during the Clinton administration are admirably summed up in this 1999 article by William Broad, who refers to him as a ‘onetime boy wonder’ who went on to become a celebrated physicist and passionate advocate of nuclear test bans. By then he had become chairman of the State Department’s advisory board on arms control, taking on the job with a ‘famously sharp tongue’ and bulldog tenacity. Garwin’s interests were wide, and we can be happy that one of them included a then novel way of propelling a spacecraft, a still visionary concept in 1958 but one about which research momentum was beginning to build.

Garwin’s solar sail paper is “Solar sailing — a practical method of propulsion within the solar system,” Jet Propulsion 28.3 (1958): 188-190.