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Monday, November 25, 2013

Reading List: Starship Century

Benford, James and Gregory Benford, eds. Starship Century. Reno, NV: Lucky Bat Books, 2013. ISBN 978-1-939051-29-5.
“Is this the century when we begin to build starships?” So begins the book, produced in conjunction with the Starship Century Symposium held in May of 2013 at the University of California San Diego. Now, in a sense, we built and launched starships in the last century. Indeed, at this writing, eight objects launched from Earth are on interstellar trajectories. These are the two Pioneer spacecraft, the two Voyagers, the New Horizons Pluto flyby spacecraft, and its inert upper stage and two spin-down masses. But these objects are not aimed at any particular stars; they're simply flying outward from the solar system following whatever trajectory they were on when they completed their missions, and even if they were aimed at the nearest stars, it would take them tens of thousands of years to get there, by which time their radioactive power sources would be long exhausted and they would be inert space junk.

As long as they are built and launched by beings like humans (all bets are off should we pass the baton to immortal machines), starships or interstellar probes will probably need to complete their mission within the time scale of a human lifetime to be interesting. One can imagine multi-generation colony ships (and they are discussed here), but such ships are unlikely to be launched without confidence the destination is habitable, which can only be obtained by direct investigation by robotic probes launched previously. The closest star is around 4.3 light years from Earth. This is a daunting distance. To cross it in a human-scale time (say, within the career of a research scientist), you'd need to accelerate your probe to something on the order of 1/10 the speed of light. At this speed, each kilogram of the probe would have a kinetic energy of around 100 kilotons of TNT. A colony ship with a dry mass of 1,000 tonnes would, travelling at a tenth of the speed of light, have kinetic energy which, at a cost of USD 0.10 per kilowatt-hour, would be worth USD 12.5 trillion, which is impressive even by U.S. budget deficit standards. But you can't transmit energy to a spacecraft with 100% efficiency (the power cord is a killer!), and so the cost of a realistic mission might be ten times this.

Is it then, silly, to talk about starships? Well, not so fast. Ever since the Enlightenment, the GDP per capita has been rising rapidly. When I was a kid, millionaires were exotic creatures, while today people who bought houses in coastal California in the 1970s are all millionaires. Now it's billionaires who are the movers and shakers, and some of them are using their wealth to try to reduce the cost of access to space. (Yes, currency depreciation has accounted for a substantial part of the millionaire to billionaire transition, but the scope of what one can accomplish with a billion dollar grubstake today is still much greater than with a million dollars fifty years ago.) If this growth continues, might it not be possible that before this century is out there will be trillionaires who, perhaps in a consortium, have the ambition to expand the human presence to other stars?

This book collects contributions from those who have thought in great detail about the challenges of travel to the stars, both in nuts and bolts hardware and economic calculations and in science fictional explorations of what it will mean for the individuals involved and the societies which attempt that giant leap. There are any number of “Aha!” moments here. Freeman Dyson points out that the void between the stars is not as empty as many imagine it to be, but filled with Oort cloud objects which may extend so far as to overlap the clouds of neighbouring stars. Dyson imagines engineered organisms which could render these bodies habitable to (perhaps engineered) humans, which would expand toward the stars much like the Polynesians in the Pacific: from island to island, with a population which would dwarf both in numbers and productivity that of the inner system rock where they originated.

We will not go to the stars with rockets like we use today. The most rudimentary working of the numbers shows how absurd that would be. And yet nuclear thermal rockets, a technology developed and tested in the 1960s and 1970s, are more than adequate to develop a solar system wide economy which could support interstellar missions. Many different approaches to building starships are explored here: some defy the constraints of the rocket equation by keeping the power source in the solar system, as in “sailships” driven by laser or microwave radiation. A chapter explores “exotic propulsion”, beyond our present understanding of physics, which might change the game. (And before you dismiss such speculations, recall that according to the consensus model of cosmology, around 95% of the universe is made up of “dark matter” and “dark energy” whose nature is entirely unknown. Might it be possible that a vacuum propeller could be discovered which works against these pervasive media just as a submarine's propeller acts upon the ocean?)

Leavening the technical articles are science fiction stories exploring the transition from a planetary species to the stars. Science fiction provides the dreams which are then turned into equations and eventually hardware, and it has a place at this table. Indeed, many of the scientists who spoke at the conference and authored chapters in this book also write science fiction. We are far from being able to build starships or even interstellar probes but, being human, we're always looking beyond the horizon and not just imagining what's there but figuring out how we'll go and see it for ourselves. To date, humans haven't even learned how to live in space: our space stations are about camping in space, with extensive support from the Earth. We have no idea what it takes to create a self-sustaining closed ecosystem (consider that around 90% of the cells in your body are not human but rather symbiotic microbes: wouldn't you just hate it to be half way to Alpha Centauri and discover you'd left some single-celled critter behind?). If somebody waved a magic wand and handed us a propulsion module that could take us to the nearest stars within a human lifetime, there are many things we'd still need to know in order to expect to survive the journey and establish ourselves when we arrived. And, humans being humans, we'd go anyway, regardless. Gotta love this species!

This is an excellent survey of current thinking about interstellar missions. If you're interested in this subject, be sure to view the complete video archive of the conference, which includes some presentations which do not figure in this volume, including the magnificent galaxy garden.

Posted at November 25, 2013 23:35