Original URL: http://www.theregister.co.uk/2007/07/26/grow_your_own/
A handy guide to growing your own spaceship
Terran life-forms need not apply
Column If you were one of the SETI at home crowd - three million PC owners worldwide, all trying to scan radio signals from space to find alien transmissions - you may have missed the news that gives us (yes, I was one!) hope of really reaching the stars. I'm thinking of building a living starship.
The news came from a report  on The Limits of Organic Life in Planetary Systems suggesting that we're daft to limit ourselves to searching for protoplasmic life with a taste for watching Big Brother TV signals.
OK, it doesn't say that. What it says is:
As the search for life in the solar system expands, it is important to know what exactly to search for. Previous life-detection experiments have been criticised for being too geocentric. This study aims to inform research programme managers, policymakers, and mission designers about the possibilities for life on other solar system bodies. Further, during planetary protection exercises at the National Aeronautics and Space Administration (NASA), questions concerning the possibility of non-terran life recur repeatedly. Remarkably little knowledge is organised that might shed light on the plausibility of bizarre life as a concern for planetary protection.
The heck with that. I'm interested in bizarre life as a way of reaching other planetary systems.
I'm entirely with Charlie Stross  on this: the way we're thinking about it now is obviously nonsense.
"This is not to say that interstellar travel is impossible; quite the contrary. But to do so effectively you need either (a) outrageous amounts of cheap energy, or (b) highly efficient robot probes, or (c) a magic wand. And in the absence of (c) you're not going to get any news back from the other end in less than decades. Even if (a) is achievable, or by means of (b) we can send self-replicating factories and have them turn distant solar systems into hives of industry, and more speculatively find some way to transmit human beings there, they are going to have zero net economic impact on our circumstances (except insofar as sending them out costs us money)."
If you haven't read his analysis, you'll be wasting a lot of everybody's time commenting to this. I'm going to assume much of what he says is true, because it so obviously is. Actually, I think he is vastly over-optimistic.
It's one of the dreams of SF writers to produce a convincing interstellar space opera and, as Charlie says, most of them involve c - a magic wand - in some way or other. The main reason for saying that is that nothing the human race has ever done can prepare for the designing of starships.
Larry Niven was fond of saying that his Ringworld was "just" a very big suspension bridge. It's odd he should say that; this month we discovered that nearly all the UK's existing suspension bridges - from the Forth to the Severn and including the Humber - are coming apart. The individual wires are breaking, because it turns out that water can get into the cables, and you can actually hear the "ping" as they break. The Forth road bridge will be out of commission in less than a decade, unless someone can find a way of rebuilding it while using it.
It doesn't matter what materials you build out of - nothing we have ever used for making houses, pyramids, bridges, tunnels, or ships can be expected to last the sort of time-scales a starship will have to endure - and endure with a 100 per cent non-failure record. But suppose we could grow the thing?
It was that thought, coupled with the report from National Academies, which reminded me of a wonderful SF trilogy by John Varley: Titan, Wizard and Demon. The three books are one story, describing humanity's discovery of a giant wheel near Saturn, which contained a biosphere.
The "wheel" is both hollow, and alive - sentient. At its hub is the main intelligence, controlling several subordinate intelligences around the circumference, all operating to maintain an environment which supports several intelligent life forms, and millions of vegetable, insect, animal, and bacterial ones. And the intelligence in the centre is a bit loopy, but even in its old age and short quite a few marbles, it is capable of maintaining the biosphere.
That's the one bit of technology which, so far, no human engineer has been able to develop - a way of avoiding the disaster of evolution.
People travelling across the stars (check Stross for the sums) have to find a way of keeping their civilisation stable (another trick we haven't managed) for not just decades, but centuries, and probably millennia. To quote Douglas Adams: "You may think it's a long way down to the chemist shop..." but interstellar space is, literally, beyond imagination. We have to retreat into arithmetic - actually finding a place to visit might take millions of years. During that time, nothing at all can prevent the life-forms inside the spaceship from mutating - and eventually, changing.
Varley's story gives us an idea of how to deal with this.
OK, he doesn't deal with trivial engineering problems like "how do we take the Sun with us?" and "how does the thing move?" because his story discovers the giant wheel simply orbiting the planet. It's been there for thousands of years, and it's potty, and doesn't remember, or want to tell, how it got there. But if you read the book with this thought in mind, it becomes clear that it would make a great starship. It has the ability to design life-forms and balance ecologies.
In other words, it can do the equivalent of spotting cancers spreading inside its own body and fix them.
Now, you don't have to be a rocket scientist to see that you aren't going to build such a being out of hide and bone. But why limit your definition of life to "carbon-based, water-powered" biologies?
Actually, there are lots of good answers to that, but the Academies report lists them in full. Chief among them is the need for biosolvents. Water is about as good as it gets, for lots of reasons - but it's hardly unique. Others you might look into: Ammonia, Dihydrogen, Dinitrogen, Ethane, Formamide, Helium, Hydrazine, Hydrogen cyanide, Hydrogen fluoride, Hydrogen sulphide, Methane and even Neon are all possible candidates. Some of them might work as life even in interstellar cold. Others might work at ferociously high temperatures of the sort you find in fission plants.
In other words, it's possible to conceive of a living being capable of growing and healing itself in space.
Varley's solution to the intelligence problem is another one which is ideal for interstellar travel - making sure the motivation of the spaceship is in some way governed by the desires of the passengers. He has a kind of "elevation to God" process whereby the consciousness of a human (or something else) can take over as the consciousness of the spaceship - which would be handy if the people decided to change their itinerary, for example, and the spaceship was programmed not to.
OK, the technology doesn't exist. It's not going to solve any sort of problem with today's blue, cloudy Terran planet any century soon (we do have to solve global climate change on our own), and it certainly isn't going to provide remote colonies to trade with. But it might allow a human being, many centuries from now, to watch a different star rise as the sun above a different planet.
In the meanwhile, forget SETI@home. It won't find anything, and it uses masses of mains electricity (roughly, doubling the power used by your PC when just sitting there). And the reason it won't find anything is simply that as a civilisation gets sophisticated with wireless (like, within a century or two) it quickly discovers cellular radio and stops shining its transmitters wastefully out into the sky. It uses techniques like ultra-wide band (UWB), which are indistinguishable from background noise if you don't have the key. Actually, UWB is not only the same as noise, but quieter.
And the most likely source of interstellar invaders is ourselves. Just suppose some idiot did manage to build a light-speed drive and set out to explore the galaxy. After 60, 200 or so years, they'd come back home, to where a couple of million years would have gone by - only to discover a civilisation of alien monsters had apparently conquered Earth. And Earth's newly evolved master race would find this weird group of hostile bipeds trying to claim they owned the place. ®