The serious study of flight to the stars is a comparatively recent phenomenon. One of the early papers to take interstellar travel to a new level — and to my knowledge the first technical article on manned interstellar missions — was Leslie Shepherd’s ‘Interstellar Flight,’ which appeared in the Journal of the British Interplanetary Society in 1952. These days we all tinker with sociology and psychology, musing about what drives a society spaceward, but Shepherd, a British physicist and one of the godfathers of today’s interstellar work, thought the reasons were obvious. We’ll go to the stars out of scientific curiosity and the pure love of adventure.
Thus the view from a somewhat more optimistic 1952, at least where space was concerned. It was an era when what seemed possible far outweighed the budgetary and political concerns that would silence efforts like Project Orion and, eventually, Apollo itself. But Shepherd, who at the time he wrote the paper was technical director for the BIS, recognized other motives as well, including the need to communicate with the other species he assumed must inhabit other star systems, and the imperative to disperse humankind over many worlds to ensure its survival.
Image: The April, 1953 issue of Hugo Gernsback’s Science Fiction Plus, which contained a version of Leslie Shepherd’s ‘Interstellar Flight’ for a broad audience. The image shows what appears to be a hollowed out asteroid being used as a massive generation ship.
For all these reasons, the view from 1952 was startling to many who read Shepherd in JBIS or, in more popular form, in Hugo Gernsback’s Science Fiction Plus, where he wrote on the subject in 1953. Shepherd wasn’t much interested in probes in that era. He wanted to get not just a few humans but entire colonies of them across the interstellar gulfs. And after going to great pains to address the problems of distance and energy, and to explain them with the relevant mathematics, he went on to take a science fictional concept into the realm of the possible:
…the explorer or colonist setting out for some distant system may do so in the knowledge, not only that he will never again see his native planet, but that he will not even see the planet of his destination – a privilege reserved for his descendants. Thus the philosophy of the explorer may be that of the soldier or airman setting out on a suicide raid, doing so in the knowledge that for him there can be no personal gain, only the dying knowledge that some will survive to benefit from his action. Indeed, interstellar colonization may call for the sacrifice of whole generations in the lonely reaches of space. Colonies once established may have to exist for generations in a state of complete isolation and such communications as exists between systems may be a very tenuous and precarious matter.
When Starflight Becomes Possible
This is bracing talk because it assumes, as Robert Forward would do a decade later, that despite its incredible hardships, an interstellar journey is possible within the bounds of known physics. When would we begin to take the idea seriously? In Shepherd’s view, a journey to Alpha Centauri would start to resonate when we could reach velocities of up to 10,000 kilometers per second, a speed that gets you to the Centauri stars in a bit less than 130 years. The figures and mathematics he provides in his paper show how severe the power requirements would be with conventional rocketry, and why systems with low thrust and high exhaust velocity (an ‘ion rocket’) would be optimal.
Remember, this is in the pre-laser days, when the idea of a solar sail was just beginning to go from a theoretical fancy to a real possibility for space missions — here we think back to Carl Wiley (writing as ‘Russell Saunders’), who published ‘Clipper Ships of Space’ in the May, 1951 issue of Astounding Science Fiction. So sail configurations and in particular Forward’s ‘lightsails,’ with their laser beam push, have no place in Shepherd’s thinking. Nor did he have the benefit of our catalog of over 500 exoplanets to work with, though he did note the necessity of such observations before any interstellar departure.
And, of course, he captured the essence of the drama that various science fiction authors, including most recently Greg Bear in his novel Hull Zero Three (2010), have worked with. The ‘slowship’ to the stars becomes a sociological experiment on a grand scale, particularly when the destinations are so distant that travel times of a thousand years can be anticipated:
In the normal way, some thirty generations would be born and would die upon the ship. It would be as though the vessel had set out for its final destination under the command of King Canute and arrived with President Truman in control. The original crew would be legendary figures in the minds of those who finally came to the new world. Between them would lie the drama of perhaps ten thousand souls who had been born and had lived and died in an alien world without knowing a natural home.
Shepherd saw this ship as a kind of Noah’s Ark, one carrying everything, including the vast variety of Earthly life forms, that colonists would need to set up shop on another world. The vehicle would of course be gigantic, a small planetoid in its own right weighing at least a million tons excluding the weight of propellants and fuel. He recognized that on a journey of many generations even a million tons makes for a tiny living space, but assumed that sufficient care to design could make it bearable. All along the route, his crew would work to preserve order:
The community would be subjected to a degree of discipline not maintained in any existing community. This isolated group would need to preserve its civilization, hand on precious knowledge and culture from generation to generation and even add to the store of science and art, since stagnation would probably be the first step to degradation.
The Hope for Relativistic Flight
And if we could reach much faster speeds? Shepherd’s section on relativistic flight works through the benefits of time dilation and ponders the possibilities of antimatter to generate the energies required. But he also introduces, in one of the earliest discussions of the question, the consequences of the ship’s interactions with interstellar gas and dust, noting what the designers of Project Daedalus would wrestle with much more extensively 25 years later, that any spacecraft moving at a significant fraction of lightspeed would have to be well shielded.
Shepherd’s conclusion is straightforward, like his entire paper:
There does not appear to be any fundamental reason why human communities should not be transported to planets around neighbouring stars, always assuming that such planets can be discovered. However, it may transpire that the time of transit from one system to another is so great that many generations must live and die in space, in order that a group may eventually reach the given destination. There is no reason why interstellar exploration should not proceed along such lines, though it is quite natural that we should hope for something better. To achieve a more satisfactory performance, however, we should need sources of energy far more powerful than any utilized or known today.
Shepherd remains a seminal figure in the development of interstellar studies, and I notice that he is honorary symposium chairman for the 2011 interstellar sessions in Aosta, to be held this July. His sober analysis of generational starflight foreshadows Robert Forward’s attempts to ramp up velocities while remaining, as Shepherd did, within the realm of known physics and technologies that could be extrapolated from what we use today. His paper is well worth reading for its historical value in placing our dreams of the stars on a solidly scientific foundation.
Thanks to Kelvin Long for passing along a copy of this paper. The reference is Shepherd, “Interstellar Flight,” JBIS Vol. 11 (1952), pp. 149-167.
A new image from WISE is always of interest, given our hopes that the Wide-field Infrared Survey Explorer will help us understand the distribution of nearby brown dwarfs. This image of the Triangulum Galaxy (M33) is at the other end of WISE’s charter, which covers objects both near and inconceivably remote. But it’s too gorgeous not to run, and it demonstrates how effective the four infrared detectors aboard the spacecraft are at pushing into this region of the electromagnetic spectrum with greater sensitivity than ever before. Here, the blue and cyan colors represent infrared at wavelengths of 3.4 and 4.6 microns — this is largely starlight. The green and red show light at 12 and 22 microns, most of which is light emitted from warm dust.
Image: One of our closest neighboring galaxies, Messier 33. Also named the Triangulum Galaxy (after the constellation it’s found in), M33 is one of largest members in our small neighborhood of galaxies — the Local Group. The Local Group consists of about 30 galaxies that are gravitationally bound and travel together through the Universe. M33 is the third largest member of the Local Group, dwarfed only by the Andromeda Galaxy (M31) and our own Milky Way. Credit: NASA/JPL-Caltech/WISE Team.
Notice the bright orange objects, which are areas of intense star formation — NGC 604, in the spiral arm at the upper left, is roughly forty times larger than the Orion Nebula. The WISE mission, however, may tell us about star formation in objects that are more distant still. Back in the 1980s, the IRAS (Infrared Astronomical Satellite) spacecraft showed us galaxies that were a hundred times more luminous in the infrared than in visible light, galaxies like Arp 220, which have earned their own acronym — Ultra-Luminous InfarRed Galaxies (ULIRGs). The fact that these galaxies are more plentiful at larger distances indicates they were more common in the early universe, perhaps the result of galactic collisions and mergers. WISE should give us a handle on the ULIRG population back to a time when the universe was just 3 billion years old.
M33 doesn’t fit into the ULIRG category, but WISE’s ability to peer through areas hidden behind dust in visible light shows us where clouds of cool gas are to be found. Normal star-forming regions stand out in this image in green and red. The benefits of infrared are clear: Little star formation is occurring in the core of this galaxy in the WISE view, but a visible light image would mask that effect, with the core appearing as the brightest feature. We can also see through infrared that the galaxy is larger than it appears in visible light, with dust extending farther from the core than expected.
And now I’m brought back to Gott and Vanderbei’s book Sizing Up the Universe, recently reviewed here, which talks in its first chapter about our perception of astronomical objects from the surface of the Earth. M33 is roughly half the size of the Milky Way, some 50,000 light years across, but at three million light years it’s close enough to us to cover an area of sky four times larger than the full Moon. Low surface brightness nonetheless makes it a very tricky catch for the naked eye. Somewhat easier is the Andromeda galaxy (M31), a full 2.5 degrees across, making it five times as wide as the Moon. It’s just a smudge with the unaided eye, and all we can really see is the bright core, but with both M31 and M33, we’re looking at some of the few objects that can be seen without a telescope that are not inside our own Milky Way galaxy.
The asteroid that crashed into the Nubian desert in the fall of 2008 turns out to be more interesting than we first realized. You’ll recall that the 59-ton object was first detected by the Catalina Sky Survey (another reassuring instance of the CSS doing its job, as discussed in a recent post). That allowed astronomers to track the asteroid immediately before its plunge into the Earth’s atmosphere, a first for this kind of observation. In addition, it was possible to create a search grid that Peter Jenniskens (NASA Ames) was able to use in guiding a recovery team in the Sudanese desert. Four expeditions later, 600 meteorite fragments are now at our disposal. This short film was made during the effort, giving an idea of conditions in the search field.
A close examination of these fragments reveals the interesting fact that the asteroid (2008 TC3) contained at least ten different kinds of meteorites, some containing chemicals that form life’s building blocks. Researchers have identified amino acids and polycyclic aromatic hydrocarbons (PAHs), the latter being complex organic molecules that are widely distributed in the galaxy. But the fact that 2008 TC3 was unusual became obvious long before its fragments made their way into a laboratory. “ Right from the start,” says Muawia Shaddad (University of Khartoum), “the students were surprised to find so much diversity in meteorite texture and hue.”
Growth After an Ancient Collision
Shaddad led the search effort, which included 150 students from the university. Approximately 23 pounds of asteroid debris were recovered by the team, and scientists have been able to identify most of the fragments as ureilites, a kind of meteorite so uncommon that fewer than 10 of the nearly 1,000 known meteorites fall into this category. The team was also able to identify a mixed-composition, or polymict ureilite. The remaining fragments are similar to the far more common kind of meteorites called chondrites, but it’s the ureilite fragments that have center stage at the moment. They contain varying amounts of the minerals olivine and pyroxene.
Researchers at the Carnegie Institute of Washington have found that the olivine and pyroxene have the full range of oxygen atom signatures detected in previous ureilites. This argues for all known ureilites having an origin in a common source. Such a parent body might have been fragmented in a collision 4.5 billion years ago that caused iron-rich minerals to smelt into metallic iron, while the olivine and pyroxene failed to melt, allowing the oxygen atoms in them to remain in the same arrangement as when the object first formed. 2008 TC3 was, then, one of a number of fragments of the parent body that underwent a series of subsequent collisions and impacts.
These later impacts account for the incorporation of non-ureilite types of meteorites in the asteroid, an indication that mixing and reassembly may not be unusual among asteroids. Says Jenniskens:
“Asteroids have just become a lot more interesting. We were surprised to find that not all of the meteorites we recovered were the same, even though we are certain they came from the same asteroid.”
Interesting indeed, and a reminder that our knowledge of asteroids down to their basic composition is more than a little incomplete. Asteroids are intriguing objects in their own right — we know they could play a role in providing raw materials in the development of a future infrastructure in space — but we also need to know enough about them to know how they would behave if it ever becomes necessary to nudge one out of an Earth-crossing trajectory. Along the way, gaining much good data about the early Solar System is a not inconsiderable bonus.
A series of papers flow from this work, but see Jenniskens and Shaddad, “2008 TC3: The small asteroid with an impact,” Meteoritics & Planetary Science Vol. 45, Issue 10-11, pp. 1553-1556 (abstract). Links to the other papers on 2008 TC3 in the same journal issue are here. An excellent SETI Institute talk by Jenniskens is also available on YouTube.
Although Jane Smiley has made the haunting story of the Viking settlement of Greenland widely known in her novel The Greenlanders (Knopf, 1988), we have few modern accounts that parallel what happened in remote places like Brattahlið and Garðar, where Erik the Red’s settlements, which had lasted for 500 years, eventually fell victim to climate and lack of external supplies. But local extinctions and near-misses are important because, as John Hickman explains in his new book Reopening the Space Frontier (Technology and Society, 2010), they promote the kind of story-telling that Smiley is so skillful at, advancing the case that not just settlements but entire species can fail when conditions turn ugly.
Image: A reproduction of a Norse church in Greenland, with Eriksfjord in the background. Credit: Hamish Laird/Wikimedia Commons.
In this excerpt from the book, Hickman writes about three modern parallels to 15th Century Greenland, the first being the Sable Island mutiny, where provisioning ships to a French penal colony in the north Atlantic stopped arriving in 1602. The demise of the Sadlermiut Inuit is another case in point, the 58 remaining members of this Dorset culture population expiring due to the effect of infectious disease after a Scottish whaling ship reached Hudson Bay. And then there is Clipperton Island, an eastern Pacific atoll that collapsed when provisioning ships stopped bringing supplies during the Mexican Revolution.
Why write about this in the context of space exploration? Because Hickman wants to understand why we pay so little heed to the technologies that could save our planet from extinction from the likes of a rogue asteroid. We see small catastrophes and large around us, from the 100 million who died at the hands of war, genocide and famine in the twentieth century to the hundreds of millions affected each decade by earthquakes, floods and hurricanes. But our own survival is assumed. Writes Hickman:
Recent events such as the 2005 Indian Ocean tsunami, the 2008 tropical cyclone in the Irrawaddy River Delta, and the 2010 earthquake in Haiti which each killed more than 200,000 people provide powerful reminders of the vulnerability of our species to natural disasters. What they have not done is increase awareness of human vulnerability to extinction. Interviews with people who had managed to cheat fate by surviving catastrophes do not incline viewers to consider the possibility of a global catastrophe without human survivors. News audiences around the planet learned about each of these events via television news coverage, which means that the emotional impact of each event was cushioned by the medium’s entertaining and anesthetizing unreality. If these tragedies were rendered to that degree unreal then the possibility of human extinction must seem impossible.
Thus it is that, while we know about the risk of impacts from space and have funded efforts to detect incoming debris, we have yet to devise a well-funded solution to prevent such an impact. Having little experience with truly existential threats, and having seen nothing but the excavations at scattered sites like those above to remind us how a culture can collapse and disappear, we fail to accept the severity of long-term risk. Hickman thinks we’re hard-wired to recognizing only the immediate, a consequence of evolving in environments that did not demand a longer perspective.
Rather than evolve a general perception of risk and a rational calculation of relative risk, our 150 millennia living as hunter-gatherers and the most recent 2 millennia living as farmers prepared us to deal with only some kinds of risk. We respond strongly to those with a high probability of occurring rather than to those with a low or unknown probability of occurring. Warfare, subsistence failure and cooperation failure have produced an animal that is equipped with “specific cognitive adaptations for perceiving cues regarding the likelihood and magnitude of adverse events” and for making rapid decisions based on “risk-risk” trade-off calculations.
And so it is that three million Italians continue to live around the Bay of Naples near Mt. Vesuvius, the consequences of whose historical eruptions are available for all to see in the ruins of Pompeii. People live by the millions along fault lines in California that could spawn catastrophic earthquakes, coping with a threat of extinction that is, in many ways, too abstract to visualize. We get on with daily life. Our perception is deeply human and understandable, and it offers a recipe for playing down security for future generations in favor of proceeding with today and stressing how infrequently catastrophes occur. Short-term means getting through a finite lifespan, and it doesn’t extend to the kind of lapidary effort that builds a safer future for generations beyond.
It’s a difficult truth to acknowledge, but it seems to be part of human nature. Our innate assessment of risk means we have a steep wall to climb to promote the well-being of our distant descendants, and that makes even the most basic attempts to survey the population of near-Earth objects a matter of constant watchfulness to ensure the continuation of funding. Getting into space to prevent an asteroid strike that might not occur for millennia is a hard sell, and so is establishing a space presence to ensure species survival in case anything happens to our planet. Read the excerpt from Hickman’s book and you’ll understand why it may take a near-fatal event (think of the survivable asteroid strike in Clarke’s Rendezvous with Rama) to make long-term danger immediate and reinvigorate our will to master space technologies.
I just have time this morning to get off one more post before Christmas, although it’s a close call. I’ve got family coming over at mid-day for the first of two holiday gatherings and, because I’m an inveterate baker, I have sourdough bread to attend to. Sourdough (or as my guru Peter Reinhart likes to call it, ‘wild yeast bread’) appeals to me because of its slow rhythms, multiple builds and lengthy rise times, and I’ve enjoyed cultivating local yeasts for both a white and rye starter that I use constantly. Sometimes breadmaking is a wonderful change of pace from keyboarding — you put the mind in neutral for a while and start kneading a mass of dough, a wonderfully Zen-like experience.
The story I wrote this morning is below, but let me take this chance to wish all of you a happy holiday! Centauri Dreams relies on a reader base that has been active and engaged from the start, and I’ve found my thoughts on interstellar issues challenged, shaped and stimulated by our continuing discussions. Looking back, it’s been over six years and 2,000 posts (this is actually the 2,023rd) since I began this site, thinking to turn it into nothing more than a personal database to keep up with news on interstellar issues. It’s now become a career of its own, and I owe that to its readership.
Asteroid or Comet?
And now to business, and the fortunes of the curious object known as (596) Scheila, long thought to be an asteroid but now showing distinct cometary symptoms. Discovered in 1906, Scheila is out of the ecliptic plane and was, in fact, mistakenly identified as a new comet by Steve Larson, senior staff scientist with the Catalina Sky Survey. Long-time Centauri Dreams readers know that the CSS is all about searching for potentially hazardous asteroids, which is what Larson was doing when he ran across the mutable object. The comet identification seemed a natural, says Larson:
“Its brightness of a total magnitude of 13.4 visual, which is about 900 times fainter than the faintest star you can see in a clear, dark sky, led me to suspect that it was a known comet, but I checked the comet database and got nothing.”
Once identified as an asteroid, Scheila was found in the CSS archives, revealing a December 3 image that showed a slightly diffuse object, but not quite the distinctly cometary bright core with faint tail that Larson saw eight days later. Scheila has been analyzed before and found to be made of carbonaceous material left over from the earliest days of the Solar System. Is Scheila, then, an extinct comet that has somehow come back to life? Sorting that out demands the closer look now being given, to determine whether that ‘tail’ is made up of cometary gas and ice or simply dust associated with a collision with another asteroid. Results so far are inconclusive.
Image: The International Space Station is a streak behind the CSS’ 60” dome operated by Steward Observatory (University of Arizona) in the Catalina Mountains north of Tucson. Credit: CSS/UA/Full Moon Photography.
An asteroid collision is interesting, to be sure, but a comet would stand out, as Larson notes:
“Most asteroids are collision fragments from larger asteroids and display a range of mineral composition. But a fraction are thought to be former comets whose volatile ices have been driven off by the sun. If the activity in Scheila proves to be cometary in nature, this will be only the sixth known main-belt comet, and about 100 times larger than previously identified main belt comets.”
Meanwhile, it’s reassuring to know that the Catalina Sky Survey, with telescopes in Arizona and Australia, is out there doing its job. CSS says that it is discovering 70 percent of the near-Earth objects that might pose a threat. Remember the background: A 1998 congressional directive instructed NASA to identify objects 1 kilometer and larger to an estimated confidence level of 90 percent or better. In June of 2006, that mandate was extended to include 140-meter or larger bodies at the same confidence level. The CSS works with the separate Mt. Lemmon and Siding Springs Surveys — all three operating under the name of the Catalina Sky Survey — to sustain the investigation.
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
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