Interstellar Studies: Surveying the Landscape

by Paul Gilster on February 12, 2013

One of the things I love about writing Centauri Dreams is that I learn something new every day. Often this comes from the research needed for individual stories, but just as often it comes from readers suggesting new directions or seeing nuances in an earlier story that I had missed. Yesterday’s post on long-term thinking led to an exchange with Centauri Dreams regular NS, who questioned my ideas on longevity in the Middle Ages, and before long we were both digging up data to try to discover what the numbers really are. It’s an ongoing process, and if you’re interested in such arcana, you can follow it in yesterday’s comments thread.

If you’re just joining us and wondering why we’re discussing medieval longevity, it ties into what I was saying about long-haul construction projects like cathedrals, and the question of what a worker on one of these projects might have thought of his chances of seeing its completion. You can also chalk it up to a fascination with the Middle Ages that has always preoccupied me.

Of course, my interest in long-haul projects doesn’t mean I wouldn’t welcome much faster transportation methods to get to the stars than the worldships I sometimes write about. My friends at Icarus Interstellar have their own worldship study, Project Hyperion, in progress in the capable hands of Andreas Hein, but they also have as their centerpiece Project Icarus, which is an attempt to design a fusion starship that some of their members believe can fly in this century. This seems wildly optimistic to me but I would love to be proven wrong. Icarus Interstellar president Richard Obousy discussed all these matters at the recent workshop in Huntsville.

An Eye on Breakthrough Propulsion

“Interstellar Flight from Conception to Reality” was the title of his talk, and in it Obousy made the case that one of the drivers for the new enthusiasm for interstellar flight is the wildly accelerating pace of exoplanet discovery. He sees exploration as the ‘expression of a curious and energetic species,’ one also becoming aware of the need for planetary defense and the imperative for developing skills in deep space. But one of his key points — and I’ve heard him say this before — is that we tend to overestimate what we can do on a short time-frame, and underestimate what we can do over longer periods.

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It’s a heartening thought for me because it means interstellar flight might take place sooner than the several centuries ahead I normally consign it to. Obousy ran through key discoveries at the atomic level, pointing out that it was no more than 70 years after we refined the model of the atom through the discovery of electrons, protons and neutrons that we developed the first nuclear thermal rocket. The history of flight tells the same tale. We have gone from theory to experiment to useful technology in a numbingly short time, from Kitty Hawk to the Moon landings.

Image: I don’t know why Richard Obousy would be difficult to photograph, but my shots of him from the conference all had one or another thing wrong with them, so I’m pulling this one from the Icarus Interstellar site.

While running through interstellar options from fusion to antimatter, Obousy told the Huntsville audience that he had a deep interest in breakthrough propulsion ideas, the kind of thing once actively studied at NASA through the Breakthrough Propulsion Physics project under Marc Millis. If we can go from Maxwell’s equations on electromagnetism to the world we see today in so short a time, what might we pull out of the theoretical physics of dark energy in another hundred years? In a way, it could be said that the Victorian era was the birthplace of the nuclear rocket, and Obousy wonders what string theory, supersymmetry, dark energy and dark matter may ultimately lead to as we take a similar path from theory to experiment to technology.

“Theoretical physics is the key to a future interstellar civilization,” Obousy said, suggesting that a world-class technical team could grow up around these ideas working one day with a breakthrough propulsion physics research lab. Icarus Interstellar obviously has such a project in mind as Obousy charts its future direction, and the beauty of the approach is that in gathering momentum, such an effort need not be costly, for the emphasis right now remains on theory rather than experiment as we chart the early stages of some of these concepts. We have much to learn. What constraints do the laws of physics place on advanced civilizations? What exactly is the dark energy field that evidently exerts negative pressure on spacetime?

Beginning of Interstellar Studies

Kelvin Long, president of the Institute for Interstellar Studies and editor of the Journal of the British Interplanetary Society, noted in his talk that a 2007 BIS conference had worked through many of the issues raised by Miguel Alcubierre in an often-referenced 1994 paper. It was Alcubierre who studied how spacetime could be warped to accelerate a spacecraft, identifying the basic physics problems that would have to be solved if such a thing were to happen (the conference identified nineteen of these, a daunting figure). The premise here is that while no object can move through spacetime faster than light, spacetime itself has no such restriction, as assumed through theories of cosmic inflation in the early moments of the universe.

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But Long paused only briefly on Alcubierre. His intent was to offer an overview of interstellar concepts, and in doing so he ran through the contribution made by the BIS not only with an early Moon mission design but also through Project Daedalus, the fusion starship that came out of late-night sessions in various London pubs back in the 1970s (particularly the Mason’s Arms, I’m told — is it still there?). At the party before the conference, Kelvin talked to me about his view that interstellar studies really began with Les Shepherd’s 1952 paper “Interstellar Flight” (JBIS, Vol. 11, pp. 149-167). I think it’s a reasonable assumption, because Shepherd’s was the first paper I know of to approach the question with true scientific rigor.

In fact, Shepherd did a little worldship building of his own, as I noted in an obituary of the man written about a year ago. I’ll run the same quote I did then to make the point:

It is obvious that a vehicle carrying a colony of men to a new system should be a veritable Noah’s Ark. Many other creatures besides man might be needed to colonize the other world. Similarly, a wide range of flora would need to be carried. A very careful control of population would be required, particularly in view of the large number of generations involved. This would apply alike to humankind and all creatures transported. Life would go on in the vehicle in a closed cycle, it would be a completely self-contained world. For this and many other obvious reasons the vehicle would assume huge proportions: it would, in fact, be a very small planetoid, weighing perhaps a million tons excluding the dead weight of propellants and fuel. Even this would be pitifully small, but clever design might make it a sufficiently varied world to make living bearable.

But the paper goes on to look at antimatter options that could take starships up to relativistic speeds and considers not only time dilation but also the problems of running into stray gas and dust along the way. It’s a classic that’s well worth re-reading today. And it’s worth remembering that the JBIS ‘red cover’ issues devoted to interstellar studies set the standard for innovative thinking on the topic for many years. Although the British Interplanetary Society has run into a host of problems in the past few years, it’s heartening to see how much Kelvin has achieved as the new editor of JBIS in getting the publication back on schedule. Well done, sir.

I won’t go through all the interstellar propulsion concepts that Long and Obousy presented because they’re already part of our continuing discussion in these pages. Instead, I’ve asked both for a Centauri Dreams contribution, Obousy to talk about where Icarus Interstellar now stands and Long to give us more about JBIS and its history, including the fascinating fact that Project Daedalus came about largely to make a point about the Fermi paradox. Calling Daedalus ‘a balance between being credible and being bold,’ Long noted that even the most improbable starship design — if it could be shown to be feasible for future engineering — would have ramifications for Fermi’s ‘where are they’? question.

More on this in coming days, along with a series of stories on a space power concept that would constitute an essential early step in our building of a system-wide infrastructure. I’m also hoping to discuss an idea that is making a comeback, the colony starships of Robert Enzmann. Consolidating ideas from the Huntsville conference should keep me busy for quite some time.

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{ 17 comments }

GaryChurch February 12, 2013 at 14:48

“For this and many other obvious reasons the vehicle would assume huge proportions: it would, in fact, be a very small planetoid, ”

My vision of the first starship is a sphere several miles in diameter, ore melted and inflated like blown glass at the lunar lagrange. Spin it for earth gravity at the equator on the inner surface. Send it out bound by way of a Lunar Solar Power generated beam of tremendous power. Load it with H-bombs to slow it down on arrival.

I am not a big fan of the idea of a generation ship; I think freezing people will become a common procedure that will change the human condition permanently- and also make star travel practical.

Wojciech J February 12, 2013 at 16:17

If you are interested in life expectancy in the past, you will be probably surprised that rise of civilization led to decrease of living age. Hunter gatherers lived up to 60s with relatively healthy bodies.

Rob Henry February 12, 2013 at 22:05

How appropriate that we have just covered the influence of religion on society and next we are mentioning that breakthrough propulsion is a possibility. My point is NOT that the eternal hope of such a possibility is becoming a religion in the scientific community. Quite the opposite.

Scientists are gradually shifting focus from increasing the predictive power of their models to increasing their explanatory power (as religions do), lead by string theory and the multiverse.

To me a prime example of this was that many predictions for the detailed structure of the CMB were published before the launch of WMAP. At first I marvelled at their diversity, then I noticed that not one of them modelled with superluminal neutrinos even or even mentioned as an aside what effect that might have. Considering that experimental evidence always indicated an imaginary rest mass for them, that seemed amazing.

If we have moved so far away from allowing breakthrough possibilities to make predictions, then how are we ever going to ever be convinced of such a possibility if we find a model that allows a better fit after the data is acquired and known. That would never convince me, so I can’t see how the increasingly close-minded physic community could currently progress to new physics.

See you all, I’m on holiday and offline for the next few days.

Alex Tolley February 13, 2013 at 1:38

“The history of flight tells the same tale. We have gone from theory to experiment to useful technology in a numbingly short time, from Kitty Hawk to the Moon landings.”

That is 66 years. 43 years later and how much has aviation developed since? The first 747 flew in 1971. We are still flying them 40+ years later. We have backed off from commercial supersonic flight. 30+ years after Reagan suggested development of a “Orient Express” we have no vehicle meeting that vision. Arguably aviation is now well beyond the s-curve inflection point.

For star flight to become a reality, either the economy will have to be vastly larger, or the costs must drastically fall. The former probably requires extra-terrestrial expansion. The latter, inexpensive, new techniques of space travel.

GaryChurch February 13, 2013 at 15:22

“For star flight to become a reality, either the economy will have to be vastly larger, or the costs must drastically fall.”

The economy is plenty large enough. As for costs- nobody knows what the cost is Alex.

Alex Tolley February 13, 2013 at 17:34

@GaryChurch – if you recall, we had this discussion on costs and timing. The idea was that even with sustained C20th economic growth, it would be centuries before we could attempt a human crewed star ship with current design concepts. I personally am doubtful the earth can sustain this economic growth rate, so I assume that it will mean off planet economic growth if that is to happen.

Your own ideas for star flight – beamed power from the moon – is not going to happen with the current economy, even if you could divert all that military spending to the project.

I don’t have to prove that we can’t fund the star ship program with the current economy, it is you that has to show you can. So less hand waving and wishful thinking, and explain how it can be done.

GaryChurch February 14, 2013 at 0:17

“- beamed power from the moon – is not going to happen with the current economy, even if you could divert all that military spending to the project.
I don’t have to prove that we can’t fund the star ship program with the current economy, it is you that has to show you can.”

Lunar Solar Power certainly could happen if DOD funds were diverted. And why do I have to show you anything? If you are going to accuse someone of handwavium peddling you better be able to prove they are wrong instead of just naysaying.

If we spend the next thirty years on the Moon instead of continuing to go in circles in low earth orbit then the energy will be available to melt ore at the Lunar Lagrange and also power a beam propulsion system. Prove me wrong.

Astronist February 14, 2013 at 14:16

GaryChurch: your proposed starship “several miles in diameter” might have a mass on the order of a billion tonnes. You do not state on this comments thread what speed you would give it, but let’s say a modest 0.5% of c, leading to millennial or multi-millennial interstellar crossings. Its energy consumption (assuming rocket propulsion at maximum efficiency; beam propulsion would be less efficient, as would propulsion by “H bombs”) for acceleration and deceleration would then be about 7 x 10^24 J, or about 14,000 times greater than present-day annual global industrial energy production (at its current rate of 16 TW).

Alex Tolley’s point would therefore appear to be a sound one, unless you can produce convincing reasons why 30 years of lunar development, starting today, could realistically be expected to result in a power source some four orders of magnitude greater than that of the entire developed world (or three orders of magnitude for acceleration and fuelling periods on the order of ten years). I agree with Alex that the onus is on you to develop this concept, not for others to disprove it!

Stephen
Oxford, UK

GaryChurch February 14, 2013 at 20:39

“Its energy consumption (assuming rocket propulsion at maximum efficiency; beam propulsion would be less efficient, as would propulsion by “H bombs”

It is not rocket propulsion and beam propulsion would be far more efficient. I do not think you understand what I am talking about concerning Lunar Solar Power; “20 Terrawatts (TW) of power. The Moon receives 13,000 TW of power from the sun. Criswell suggests that harnessing just 1% of the solar power and directing it toward Earth could replace fossil fuel power plants on Earth.”

http://www.sciencedaily.com/releases/2002/04/020416073334.htm

http://nextbigfuture.com/2011/02/nasa-researcher-kevin-parkin-discusses.html

As for H-bombs not being efficient….. puh-leez.
They are the most powerful devices ever made and well over a trillion dollars, probably several trillion (classified), has been spent perfecting them.

GaryChurch February 14, 2013 at 20:56

The most efficient rocket propellents give an isp of about 450 seconds. While a microwave rocket would double that, a system that does not use a heat exchanger but instead uses a form of plasma drive like VASIMR would give far higher numbers. ISP numbers for bomb systems this large (the larger the bomb system the more efficient) would probably be over a million.

http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket

Tarmen February 15, 2013 at 17:20

Thirty or fifty years is over hasty for this type of project. Although Luna is a stepping stone to the stars, regardless of our overall vision. The near-Earth asteroids are another step, likely for the mining companies. And then Mars. Militaries of the USA and China, others will be ‘out there’ too, trying to one-up each other as they do today in Earth orbit. Private ‘missionary’ groups may then lead out ahead of the miners and the militaries. I could imagine a Gates Foundation type of group building a slow boat colonial ship for a band of true believers. Although that might not end well. Further attempts would be staged in following centuries. As the Inner System economy grows, our civilization grows ever more capable.

Thomas Hackney February 15, 2013 at 17:25

My vision of the first starship is a home-made job — a small ship with just enough space for a few smart and independent people to make a reasonable life for themselves while simultaneously expanding the envelope. The only stumbling blocks are the expense of getting the massive components and a smart breeding pair up in space. Bone mass increasing excercizes (machine?), some hydoponics, a nice tight Heinleinesque ship. Plenty of books and DVDs.

Astronist February 15, 2013 at 21:10

GaryChurch, the energy efficiency of space propulsion concerns the efficiency with which energy released is converted into useful kinetic energy of the payload, and is different from the exhaust velocity (or equivalently the specific impulse). For a rocket, it depends on the mass ratio, and for non-relativistic speeds reaches a maximum of about 64% when the mass ratio is 4.9. For a beam pressing against a light-sail which accelerates from zero speed relative to the transmitting station, the efficiency approximately equals the final speed divided by c, until relativistic speeds of around 0.5 c are reached. If my calculations are correct (and I would be grateful if you could check them for me; see JBIS, April/May 2012, p.173-174), if accelerating a vehicle from rest by a directed laser beam, a final speed of about 0.7 c must be reached before its energy efficiency overtakes that of a conventional rocket operated at maximum rocket efficiency (assuming that the exhaust velocity requirement for such a rocket can be met).

Clearly, H bombs release a lot of energy, but I wonder what fraction of that energy is converted to useful kinetic energy of the vehicle, and what fraction is dissipated into space as radiation and as kinetic energy of the bomb fragments and reaction products?

However, regardless of figures for energy efficiency, even a highly efficient system still requires the use of an industrial power source whose capacity is a large multiple of the energy production of present-day annual global civilisation for each individual starship launch.

Alex Tolley and I are saying that this is not economically feasible without major industrial growth, and that no realistic starship programme can absorb more than a small fraction of a civilisation’s total energy output. You seem to be saying that a starship programme can produce energy at a rate which is a large multiple of a civilisation’s power production for all other purposes combined. The question is how you would answer your critics who point out on economic grounds that this is unlikely ever to happen!

Stephen

GaryChurch February 16, 2013 at 11:36

“The question is how you would answer your critics who point out on economic grounds that this is unlikely ever to happen!”

“Economic grounds” has nothing to do with reality. Money is magic and makes the world go round is what everyone believes is true- but it is the big lie.
Those meteors yesterday prove me right. Survival trumps economics.

James Jason Wentworth February 17, 2013 at 5:20

GaryChurch wrote:

[“Economic grounds” has nothing to do with reality. Money is magic and makes the world go round is what everyone believes is true- but it is the big lie. Those meteors yesterday prove me right. Survival trumps economics.]

Indeed, money’s reality as a store of value depends upon belief that it is–but the yet-again-demonstrated (as of yesterday) threat from cosmic impacts could lead to, as Dave Bowman said in “2010,” “Something wonderful!” Two quotations from a Space Daily report on the meteor incident in Russia (see: http://www.spacedaily.com/reports/Divers_scour_Russian_lake_after_meteor_strike_injures_1200_999.html ) might just be the beginning of “family humanity.” Here are the quotes:

“Instead of fighting on Earth, people should be creating a joint system of asteroid defence,” the Russian parliament’s foreign affairs committee chief Alexei Pushkov wrote on his Twitter account late Friday.

“Instead of creating a (military) European space defence system, the United States should join us and China in creating the AADS — the Anti-Asteroid Defence System,” the close ally of President Vladimir Putin wrote.

Eniac February 17, 2013 at 13:32

Astronist:

for acceleration and deceleration would then be about 7 x 10^24 J, or about 14,000 times greater than present-day annual global industrial energy production (at its current rate of 16 TW)

Gary Church:

The Moon receives 13,000 TW of power from the sun

It seems, then, that the entire insolation of the moon is still one order of magnitude short of the energy needed to propel Gary’s Bernal sphere to 0.5% of c. Shucks, it seemed like such a good idea while it lasted.

Anyone want to calculate the number of H-bombs needed to decelerate that sphere?

GaryChurch February 18, 2013 at 22:18

“the moon is still one order of magnitude short of the energy needed to propel Gary’s Bernal sphere to 0.5% of c.”

I do not think so- it is not a light sail.

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