by Paul Gilster | Jul 17, 2012 | Culture and Society |
Galileo Galilei makes a brief appearance in the news this morning with word that several copies of his books, including two examples of the Sidereus Nuncius, have turned out to be forgeries. The latter, whose title is usually translated as Starry Messenger, was the first scientific presentation on observations made with a telescope, and contains Galileo’s early work on the Moon and the moons of Jupiter, among other things. One Marino Massimo De Caro, currently under arrest for massive thefts from the Girolamini Library in Naples, may have had connections with the forgeries, which are worrisome news for those of us who like to poke around in ancient manuscripts and for anyone interested in the history of science.
News of the manuscripts also puts me in mind of a paper by Danielle Briot (Observatoire de Paris), which uses Galileo in quite a different context. Briot became interested in the life and work of Ary Sternfeld (1905-1980), a prolific writer on science and a researcher who may have been the first to have used the word ‘astrobiology,’ although his work is all too little known today. Sternfeld’s 1935 article “La vie dans l’Univers” in the French science magazine La Nature looked at beliefs and hypotheses about life in the cosmos and reached conclusions remarkably similar to those under active investigation in today’s journals.
In fact, in discussing the state of the art in research into these matters, Sternfeld wrote as follows: “The development of both the natural and astronomical sciences has led to birth of a new science whose main objective is to assess the habitability of the other worlds… this science is called astrobiology.” Briot believes this is the first time the word ‘astrobiology’ appears, and it is followed up — just two years after Hitler assumed power in Germany and the German military buildup was just beginning — with a review of theories on the origin of life and even considerations about how it might be transported through space. Sternfeld thought extraterrestrial life was likely and wondered how we would discover planets around other stars.
Image: Ary Sternfeld at work, an astronautical pioneer whose work is only now being rediscovered in the west.
Galileo swings back into the discussion because the 77 years that have passed between the publication of Sternfeld’s paper and today is roughly the same interval between the publication of the Sidereus Nuncius (1610) and Fontenelle’s Entretiens sur la pluralité des mondes (Conversations on the Plurality of Worlds) in 1686. What’s striking about this is that between Galileo and Fontenelle there is a world of new thinking as an observation-enriched view of the cosmos emerged, whereas the Sternfeld paper offers a view of the universe that, with the exception of its model of planet formation, is one that could have come out of a recent science magazine.
Bernard Le Bovier de Fontenelle (1657-1757, a remarkable lifetime!) spoke to the general public in his Conversations, drawing on not just Galileo but also Copernicus, whose De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres) had appeared in 1543. The language, significant in a scientific work at the time, was not Latin but French, presenting the conversations between a philosopher and a nobleman as they study the stars on a late-night walk. Between the time of Galileo and Fontenelle we have moved into a world keen to know more about the immensity of the universe and actively speculating on life around other stars.
If Fontenelle was a man of his time, Briot gives the impression that Sternfeld was very much ahead of his, at least where ideas about extraterrestrial life are concerned. His own life was a good deal more restricted. Born in Poland in 1905 of Jewish parents, he was unable to attend the Polytechnical School in Warsaw because of his religion and moved to France in 1924, although his application to do a doctorate in astronautics at the Sorbonne was rejected. Even so, by 1933 he had written a book on the discipline he called ‘cosmonautics,’ presenting calculations on spacecraft trajectories that proved accurate though written 25 years before Sputnik.
Briot has the rest about this remarkable man who published in both popular and professional periodicals in France and speculated actively on SETI methods using optical and radio technologies as early as 1935. It was later in that year that he and his wife moved to the Soviet Union, where he narrowly survived Stalin’s purge of Russian scientists in 1938, going on to write some 30 books and over 400 articles in a wide variety of venues. Sadly, he was not allowed a visa to return to France even when he received an honorary doctorate there in 1961. Sternfeld died in 1980 and his name is engraved on a small plaque aboard the New Horizons spacecraft honoring the pioneers of astronautics. A crater on the far side of the Moon also bears his name.
In 2010 the Space Research Center of the Polish Academy of Science (CBK PAN) organized a conference to commemorate the work of Ary Sternfeld. Although he could not attend in person, Mike Gruntman (USC) produced a video that was played at the meeting and can be seen online. The Briot paper is “Is it the first use of the word Astrobiology?” (preprint). Be aware, too, of Gruntman’s From Astronautics to Cosmonautics (2007), which describes the work of Sternfeld as well as Robert Esnault-Pelterie, another figure we’ll need to talk about soon in these pages.
by Paul Gilster | Jul 16, 2012 | Exoplanetary Science |
Is the discovery of oceans on planets orbiting distant stars within our reach? Finding such an ocean would be of immense interest from an astrobiological perspective because water on the surface is the traditional marker for a habitable zone. Astrobiology Magazine has just written up work by Nicholas Cowan (Northwestern University) and colleagues, who have been looking at the ways we might detect such oceans. The researchers are thinking ahead to a time when we have an actual image of a terrestrial world to look at, even if that image is little more than the ‘pale blue dot’ Voyager saw in its famous portrait of the Solar System. When we have identified that ‘dot,’ we can do a lot with it by studying the way its light varies as it orbits its star.
Let’s assume we deploy a starshade and use it in conjunction with the James Webb Space Telescope to block the light of the star and reveal the faint signature of the planet. A disk tens of meters wide with petal-like extensions, the starshade would be placed between the telescope and the star under observation, its shape designed to prevent the rings and refractions that would be created by a circularly shaped shade. One option under consideration is to place the starshade about 160,000 kilometers away from the telescope, which will orbit at the L2 Lagrangian point. Such a configuration could yield the image of a terrestrial world in the habitable zone, a planet whose variations in light can tell us something about what is on its surface.
Finding oceans then becomes a major first step in characterizing the planet. The Cowan paper presents the three methods that have so far been proposed for detecting alien oceans:
Variations in the color of the planet are useful because oceans are darker and have different colors than the surface features of continents. Watching the planet over time should reveal these changes.
Oceans polarize light, whose phase variations can flag the presence of water. The trick is that light also scatters off molecules in the atmosphere (‘Rayleigh scattering’), masking the effect, but rotational variation in polarization may allow us to infer the presence of an ocean.
Oceans can throw bright reflections, especially when the planet is in its crescent phase, making the planet appear brighter than would otherwise be expected. Variations in reflectivity (albedo) as the planet circles its star can thus be markers for an ocean if properly interpreted.
Image: Glinting sunlight off Lake Erie. Can we use this kind of specular reflection to identify the oceans of an alien world? Credit: Image Science and Analysis Laboratory/NASA JSC.
Cowan and team focus largely on the specular reflection method, noting that all three techniques have been studied in terms of cloud cover and changes in albedo due to seasonal changes on the surface. But they also identify what they call the ‘latitude-albedo’ effect, which can play havoc with these observations by mimicking the glint of an ocean when none actually exists. The reason: A planet in the habitable zone with low axial tilt (obliquity) would tend to have highly reflective snow and ice in the regions least illuminated by sunlight. A false positive for ocean glint is thus produced.
In other words, the polar regions will make the apparent reflectivity of a planet with low axial tilt increase when the planet is seen in its crescent phase, an effect that will diminish in the gibbous phase. The latitude-albedo effect thus limits our ability to use ocean ‘glint’ as a marker for water on the surface, though the authors note there are some ways around the problem. It will be necessary to study the color variations of the planet during its own rotation and during the entirety of its orbit to develop an estimate for the planet’s obliquity. The rotational albedo map that can be generated out of this should allow better interpretation of the variations in light observed. The JWST/starshade combination may be powerful enough to monitor these tiny changes.
If you’re wondering how significant the ‘glint’ effect could be, consider that Tyler Robinson (University of Washington), modeling the Earth as it would appear to a distant observer back in 2010, was able to show that the Earth would be as much as 100 percent brighter at crescent phases when modeled with the glint effect than without it. Thus specular reflection can be a major player in characterizing an exoplanet, but only if we learn how to interpret it properly.
The Cowan team’s simulation worked with a planet whose obliquity is 23.5 degrees, the same as the Earth’s, calculating light curves as they would appear to a distant observer. Subtracting out the kind of reflection that would produce an ocean glint, they still found the false positive, phase variations that mimic the glint. Planets like the Earth have enough axial tilt that the methods above can correct for the latitude-albedo effect, but the authors note that zero-obliquity planets will be extremely hard to investigate. It’s worth noting that planets like these should be fairly common around red dwarf stars, where the planet has become tidally locked to the primary.
The paper is Cowan, Abbot and Voigt, “A False Positive For Ocean Glint on Exoplanets: the Latitude-Albedo Effect,” accepted at Astrophysical Journal Letters (preprint). Thanks to Antonio Tavani for the pointer to this paper.
by Paul Gilster | Jul 13, 2012 | Outer Solar System |
When I was a boy, I became fascinated early on with the outer planets. The further out, the better as far as I was concerned, and as you might imagine, I had a special fascination with Pluto. In the summer, I used to haunt the library in the nearby suburb of Kirkwood (in St. Louis, where I grew up), working my way through all the books on astronomy and space I could find. Because I was reading all of them, I would encounter older volumes, some pre-dating the discovery of Pluto, and more recent tomes with details about the planet I didn’t know. It didn’t matter; I just kept reading.
What was fun about all this was that I kept expecting to find something new each time I opened a book, and was sometimes rewarded with a fact that brought this distant realm into perspective. The news that Hubble has now found a fifth moon orbiting Pluto awakens that same sense of satisfaction, for as we keep tuning up our observing skills, we’re learning much about the outer system that surprises us. The fact that this tiny dwarf planet — I would prefer to think of it as a ‘double planet’ more than a ‘dwarf’ — has such an elaborate set of moons is unexpected.
Image: Pluto’s newly discovered moon P5 (circled). Researchers are intrigued that such a small planet can have such a complex collection of satellites. The new discovery provides additional clues for unraveling how the Pluto system formed and evolved. The favored theory is that all the moons are relics of a collision between Pluto and another large Kuiper belt object billions of years ago. Credit: NASA, ESA, and M. Showalter (SETI Institute).
The existence of P5 is another useful piece of information for the New Horizons team as their spacecraft streaks toward its 2015 encounter at Pluto/Charon. The moon, currently designated P5, looks to be between 10 and 25 kilometers across, residing in a 93000 kilometer circular orbit that is evidently co-planar with the other four satellites. With five moons, Pluto is likely home to a good deal more debris that we haven’t yet found, a factor in working out the safest trajectory for the spacecraft. We’ll be watching Pluto carefully up to and beyond the New Horizons encounter.
A Not So Quiet Hibernation
Meanwhile, New Horizons, the hero of this piece, continues its relentless journey, now almost 24 times as far from the Sun as our own planet and once again in a state of hibernation. The ‘deep cruise’ phase of the mission lasts until the encounter operations begin to accelerate in the summer of 2014, with closest approach to Pluto on July 14, 2015. Even though most of its subsystems, including science instruments and flight electronics, are turned off, the Student Dust Counter (SDC) is to be left on during the hibernation period, measuring dust impacts as the spacecraft pushes deeper into the system than any dust detector has ever been sent before.
Yes, the Voyagers can measure dust impacts, but they do so with their plasma wave instrument rather than through an actual dust detector. Both spacecraft have been detecting micron-sized impacts for years, noted because the impact of a dust particle causes it to be vaporized and heated to a plasma of electrons and ions. The resulting plasma cloud creates a voltage pulse in the plasma wave receiver. Researchers can count the impacts over a period of time and learn much about the density of the impacting particles in the outer interplanetary medium.
We need to learn about dust in the outer system, of course, because as we push deeper and move faster small impacts become much larger factors, risking the very life of the mission if we’re talking about interstellar flight speeds. Interestingly, the Voyager dust measurements show the number density of impact particles to be more or less the same for both Voyager 1 and 2, a noteworthy item given that Voyager 2 is much closer to the ecliptic than Voyager 1. That suggests the outer system dust both spacecraft are running into is likely cometary in origin, or at least that it does not originate from a planetary source.
But back to New Horizons. The latest report from the spacecraft team now tells us that the Solar Wind Around Pluto (SWAP) and Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instruments will also remain active during hibernation, representing a major upgrade from the instruments on the Pioneer and Voyager spacecraft. The report quotes Matthew Hill (JHU/APL) on their ability to measure charged particle radiation from the solar wind and elsewhere:
“It’s been more than 30 years since we’ve had a spacecraft venture beyond Saturn, and it’s the first time we’ve had observations from this region while having supporting measurements both farther out [from Voyager 1 and 2] and closer to the Sun [missions at Mercury, Earth and Saturn]. Events associated with solar flares and coronal mass ejections that propagate through the solar wind plasma can now be observed throughout the heliosphere as never before. With solar activity on the rise, the timing is great to have these state-of-the-art New Horizons instruments observing the heliosphere.”
The report is calling the new observations ‘enhanced science’ — the use of SWAP and PEPSSI during hibernation had not been part of the original mission schedule — and the hope is that it will provide a welcome additional dataset as we continue our study of the heliosphere. With the Pluto/Charon encounter ahead, we have much to look forward to, but even after the encounter, we’ll eventually be using the James Webb Space Telescope’s infrared capabilities to probe this icy realm. Who knows how many more moons of Pluto, or Kuiper Belt bodies beyond, we’ll have uncovered by then?
by Paul Gilster | Jul 12, 2012 | Culture and Society |
Paging back through Kelvin Long’s book Deep Space Propulsion (Springer, 2011) last night, I was reminded that Freeman Dyson had written about his disillusionment with nuclear pulse propulsion methods long after Project Orion was terminated. The passage is in his autobiographical account Disturbing the Universe (Basic, 1981), which caught Long’s attention and led him to reprint it. Here’s a snippet of Dyson’s reflections:
Sometimes I am asked by friends who shared the joys and sorrows of Orion whether I would revise the project if by some miracle the necessary funds were suddenly to become available. The answer is an emphatic no… By its very nature, the Orion ship is a filthy creature and leaves its radioactive mess behind it wherever it goes… Many things that were acceptable in 1958 are no longer acceptable today. My own standards have changed, too. History has passed Orion by. There will be no going back.
Long speculates that Dyson may simply have been referring to Orion as an Earth-launch vehicle, leaving open options for construction and deployment in deep space, but my own sense is that the passage above means just what it says. When I interviewed Dyson for Centauri Dreams (the book) back in 2003, he made it abundantly clear that he considered the matter closed. He criticized nuclear methods because they could use no more than one percent of the mass with any nuclear reaction, and said he was much more enthusiastic about laser and microwave beaming and pellet propulsion concepts like those first developed by Clifford Singer back in the ‘70s and later expanded significantly by Gerald Nordley.
Interstellar Flight in the Public Eye
Long covers the Orion concept in detail as well as Medusa, a remarkable attempt to fuse pulsed propulsion with sail technologies (we need to talk more about Medusa soon). But I was really digging into his book in relation to Robert Bussard, whose 1960 paper “Galactic Matter and Interstellar Flight” (citation below) is in my view the real marker for the emergence of interstellar studies. To be sure, there were key papers before this, including the significant contributions of Leslie Shepherd and Eugen Sänger, both of whom I want to talk about in coming days. But what you get with Bussard is an idea published in an academic journal that is found and brought emphatically into the public consciousness in ways that transform public thinking.
If the beauty of beamed propulsion is that it removes the need to carry huge stores of propellant, the advantage of Bussard’s ramjet concept was that it harvested what it needed from the medium. Bussard announced his intention to speed up interstellar travel times enormously:
… by abandoning the interstellar rocket entirely, turning to the concept of an interstellar vehicle which does not carry any of the nuclear fuel or propellant mass needed for propulsion, but makes use of the matter spread diffusely throughout our galaxy for these purposes. By rough analogy with its atmospheric counterpart we call this an interstellar ramjet. Other possible types might include, vehicles which carry all of the nuclear fuel on board and only use swept-up galactic matter as inert diluent added to the propellant stream analogous to the operation of ducted rockets in atmospheric ?ight and all variations between these two extremes. Study of the performance of these fuel-carrying vehicles is deferred to a future paper.
To my knowledge, Bussard never wrote this future paper — if I’m wrong about that, I hope someone will correct me. His ideas, of course, generated an influx of new concepts tweaking the ramjet and taking the idea of matter collection in deep space in entirely new directions.
We’ve looked at problems with the original Bussard design in these pages before, focusing especially on the proton/proton fusion reaction and the power needed to exploit it. A number of theorists have suggested workarounds, including Centauri Dreams regular Al Jackson, who in several papers explored a laser-powered ramjet design that I want to talk about next week. For today, though, the focus is on reaction to the Bussard paper of 1960, for it was quickly seized upon by science fiction writers and scientists alike. The book Intelligent Life in the Universe, co-authored by Carl Sagan and Iosif S. Shklovskii, focused on time dilation at relativistic velocities and the way to the stars seemed to open.
Time Dilation Takes Center Stage
Intelligent Life in the Universe came out in 1966, a greatly expanded version of Shklovskii’s original Russian text of 1962. It is the coupling of relativistic time dilation and the Bussard ramjet idea that seized the imagination of science fiction writers. Sagan and Shklovskii could show that at an acceleration of 1 g, only a few years (ship-time) is required to reach the nearest stars, while (as experienced again aboard the ship) only 21 years takes you to the galactic center, and 28 years to the Andromeda galaxy. There being no time dilation on the home planet, the elapsed time there as the star mission proceeds, for distances beyond about 10 light years, roughly equals the distance of the destination in light years. In other words:
…for a round-trip with a several-year stopover to the nearest stars, the elapsed time on Earth would be a few decades; to Deneb, a few centuries; to the Vela cloud complex, a few millennia; to the Galactic center, a few tens of thousands of years; to M 31, the great galaxy in Andromeda, a few million years; to the Virgo cluster of galaxies, a few tens of millions of years; and to the immensely distant Coma cluster of galaxies, a few hundreds of millions of years. Nevertheless, each of these enormous journeys could be performed within the lifetimes of a human crew, because of time dilation on board the spacecraft.
Einsteinian time dilation had been considered long before this, of course, and it shows up in science fiction in early stories like Robert H. Wilson’s “Out Around Rigel,” which ran in Astounding Stories in December of 1931. But when Sagan and Shklovskii combined time dilation with a serious discussion of communications between galactic civilizations as enabled by Bussard-style ramjets, the notion went from utterly theoretical to a matter that mixed science with engineering. Bussard’s ideas went on to inspire a wave of ramjet-related studies, as we’ve already seen, and also inadvertently triggered the study of magnetic sails as braking devices.
Image: The Bussard ramjet, which opened serious speculation about attaining speeds close to c. Credit: Adrian Mann.
The Ramjet in Science Fiction
Meanwhile, we can think about the later science fiction that flowed from the Bussard ramjet. I usually cite Poul Anderson’s Tau Zero in that regard, a 1970 novel that grew out of a 1967 short story (“To Outlive Eternity,” which ran in Galaxy a year after Sagan and Shklovskii). But we can add to Anderson’s tale of a runaway starship the work of Larry Niven, who described Bussard vessels in his 1976 novel A World Out of Time:
The starships were Bussard ramjets. They caught interstellar hydrogen in immaterial nets of electromagnetic force, compressed and guided it into a ring of pinched force fields, and there burned it in fusion fire. Potentially there was no limit at all on the speed of a Bussard ramjet. The ships were enormously powerful, enormously complex, enormously expensive.
I pulled this quote from Technovelgy.com, which routinely looks at the intersection of science and science fiction. The first part of Niven’s novel appeared in Galaxy in 1971 as a short story called “Rammer,” another indication that Bussard’s notions were quickly embraced. Gregory Benford uses a greatly modified Bussard design in his Galactic Center novels, dodging the proton-proton fusion problem in well-vetted ways we’ll discuss next week. Sagan went on to refer to the ramjet in the popular television series Cosmos and the book that accompanied it, but the ultimate sign of Bussard’s ideas reaching full public awareness may have been the ‘Bussard collector’ used in the Star Trek universe as part of StarFleet’s propulsion paraphernalia.
It could be argued that much was coming together anyway by the early 1960s, and two years after Bussard described the ramjet, Robert Forward would put the idea of a laser-propelled lightsail into the public consciousness in an article in Missiles and Rockets. But I’ll give the nod to Robert Bussard, with a major assist from Sagan and Shklovskii, for turning the interstellar idea into public currency by suggesting that although the engineering was far beyond our skills, the basic physics did not rule out human travel to the stars. And if you’re a science fiction writer with a need to get around the galaxy quickly, Bussard will always be a contender.
The Bussard paper is “Galactic Matter and Interstellar Flight,” Astronautica Acta Vol. 6 (1960), pp. 179–94 (available online).
by Paul Gilster | Jul 11, 2012 | Culture and Society |
It had never occurred to me that there was something the Graf Zeppelin and the Saturn V had in common. Nonetheless, a re-reading of Freeman Dyson’s paper “Interstellar Transport” confirms the obvious connection: Like the great airships of the 1930s, the Saturn V was huge and carried a payload that was absurdly small. Dyson, writing in 1968 fresh off the end of Project Orion, the rise of Apollo, and the triumph of chemical propulsion, had thought at one time that the US could bypass the Saturn V and its ilk, offering a fast track to the planets at a fraction of Apollo’s cost. The Atmospheric Test Ban Treaty of 1963 was a major factor in putting an end to that speculation.
I mentioned yesterday that I thought Dyson set about to be deliberately provocative in this piece, that he hoped to reach people who would have been unaware that interstellar distances could conceivably be crossed (thus his choice of Physics Today as his venue). To do that, he had to show that even reaching the Moon was a stretch for chemical methods, which he characterized as “…not bad for pottering around near the Earth, but… very uneconomic for anything beyond that.” While an Apollo mission to the Moon demanded staging and a huge mass ratio, an Orion vessel was built with only one stage, its mass ratio well under 10 even for long journeys out and around the Solar System.
Image: Dyson’s largest concept, a ‘super-Orion’ carrying colonists on an 1800 year journey. Credit: Adrian Mann.
Orion could have managed this because the exhaust velocity of the debris from its nuclear explosions would be in the thousands of kilometers per second range instead of what the chemical rocket could offer with its paltry 3 kilometers per second. Dyson assumed the use of hydrogen bombs (“the only way we know to burn the cheapest fuel we have, deuterium”) and a conservative energy yield of one megaton per ton, going on to say this:
These numbers represent the absolute lower limit of what could be done with our present resources and technology if we were forced by some astronomical catastrophe to send a Noah’s ark out of the wreckage of the solar system. With about 1 Gross National Product we could send a payload of a few million tons (for example a small town like Princeton with about 20,000 people) on a trip at about 1000 km/sec or 1 parsec per 1000 years. As a voyage of colonization a trip as slow as this does not make much sense on a human time scale. A nonhuman species, longer lived or accustomed to thinking in terms of millenia rather than years, might find the conditions acceptable.
Anyone who has spent time in the absurdly pretty town of Princeton NJ, where Dyson has lived for years while pursuing his work at the Institute for Advanced Studies, knows why he coupled a familiar scene with something as joltingly unfamiliar as a starship. The choice is reflective of his method: Dyson expresses the results of his calculations in tableaux that are both publicly accessible and mind-jarring, as a look through almost any of his books will demonstrate (think, for example, of his idea of a life-form that might poke out from an inner sea onto the surface ice of a Kuiper Belt object, a kelp-like, mirrored being he christened a ‘sunflower’). Root one end of an idea in the everyday, the other in a mind-bending direction, and you make your point memorable, which is one reason Dyson has inspired so many young people to be scientists.
Remember, the intent here was to get the Orion idea into the public discussion, along with an interstellar implication that Orion’s original designers had never built into their thinking. Dyson always knew that if you put the idea out there, the next step is to get to work on the specifics, detail after patient detail, work that on the interstellar level would presumably involve many generations. When remembering Dyson’s involvement with Project Orion, I think about something he once told Stewart Brand (in a Wired interview):
You can’t possibly get a good technology going without an enormous number of failures. It’s a universal rule. If you look at bicycles, there were thousands of weird models built and tried before they found the one that really worked. You could never design a bicycle theoretically. Even now, after we’ve been building them for 100 years, it’s very difficult to understand just why a bicycle works—it’s even difficult to formulate it as a mathematical problem. But just by trial and error, we found out how to do it, and the error was essential.
It’s the same method we would have used for Orion if the project had proceeded, but the number of factors working against it proved insurmountable, and here one of Dyson’s greatest strengths — his ability to engage the public — was running up against a growing public distrust of nuclear technologies. But the point is that theory always couples with engineering practice, hammering on a problem until the best solution is reached. Unless, of course, the kind of bureaucracy that Dyson so disliked steps in to muzzle the research early on. A bit of that dislike comes across in the conclusion of “Interstellar Transport,” as he ponders what a starship would achieve:
By the time the first interstellar colonists go out they will know a great deal that we do not know about the places to which they are going, about their own biological makeup, about the art of living in strange environments. They will certainly achieve two things at the end of their century-long voyages. One is assurance of the survival of the human species, assurance against even the worst imaginable of natural or manmade catastrophes that may overwhelm mankind within the solar system. The other is total independence from any possible interference by the home government. In my opinion these objectives would make such an enterprise worthwhile, and I am confident that it will appear even more worthwhile to the inhabitants of our overcrowded and vulnerable planet in the 22nd century.
Dyson looked at questions of cost and energy production and assumed a continued economic growth of what today seems like a sizzling 4% per year. Working out the cost of the Orion starship (he figured 1011 dollars), he concluded that such a mission would be as economically feasible in the future some 200 years off as a Saturn V was in 1968. We can argue about such numbers (and be sure to check the comments from yesterday, where a fruitful discussion on the implications of exponential economic growth is continuing) but I suspect they are the first instance of a methodical prediction on when starflight will occur that most readers of Physics Today had ever encountered.
The paper thus comes into focus as a landmark in introducing a pulsed fusion concept to a wide audience, explaining its deep space potential, and calculating when an interstellar future might be possible. I can see why Greg Matloff considers it a key factor in the growth of the interstellar movement because of its broad audience and energizing effect. But tomorrow I’ll make the case for a slightly earlier paper’s even more profound effect on the public perception of interstellar flight, one that has played into our media imaginings of traveling among the stars ever since its publication.
Dyson’s paper “Interstellar Transport,” ran in Physics Today October 1968, pp. 41-45, and is available online.
