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Notes & Queries 3/5/10

Nuclear Cannon A Descendant of Orion

The new Carnival of Space is now out, from which I’ll focus on Brian Wang’s interesting notions on nuclear propulsion. The power behind the indispensable Next Big Future site, Brian has been writing about an Orion variant for some time now, one that should be able to get around the nuclear testing restrictions that put Orion itself into mothballs. A 1963 treaty effectively ended Orion’s prospects, and in 1974 the Threshold Test Ban Treaty was signed, prohibiting the testing of nuclear devices with a yield exceeding 150 kilotons. What can we do with a 150 kiloton upper limit for underground devices, and how does it relate to pulsed propulsion?

Wang envisions building what he calls a ‘nuclear cannon,’ capable of launching heavy payloads into Earth orbit. A 150 kiloton nuclear device is placed at the bottom of a two-mile shaft, packed with boron and other elements that will be converted to plasma. The 3500 ton launch projectile is placed on top. The explosion of the nuke launches it, with a chemical charge being used to quickly fill in the shaft as soon as the projectile clears it, the idea being to contain contamination. Figuring $10 million for the projectile and the propellant to launch it, plus another $20 million for construction of the shaft, Wang calculates launch costs in the neighborhood of $10 per pound, far cheaper than current launch options including the low-ball Russian Dnepr, a three-stage converted ICBM.

We’re not talking human missions here (not at 5000 G’s!) but heavy lift of the basic supplies for industrialization, with our standard launch systems being reserved for more fragile supplies and astronauts. Here’s Wang’s summation of the project’s cost and potential savings:

…100,000 tons of cargo delivered to the moon would be worth $5 trillion at the best prices today. 200,000 tons delivered to orbit would be worth $1 trillion @$5000/kg. If this could be done at one tenth the cost it is still worth $100 billion to orbit and $500 billion to the moon. Getting to one tenth of current costs is an optimistic ten years away and billions in development. The cost is to find a location like another remote island to sacrifice the underground area for nuclear launch similar to the areas sacrificed for underground nuclear testing. However, with proper preparation and a dome with a door and charges to speed the collapse of the shaft, there would be no radiation into the atmosphere.

It’s an intriguing notion, and not out of line with other industrial activities:

Other industries like oil, gas and coal regularly contaminate salt domes and underground and above ground locations. This would be safer and cleaner than those continuing operations. We would use nuclear bombs that are costing money to be maintained in storage and have a risk non-peaceful use. There is no risk of damaging EMP because damaging EMP occurs when a nuclear device is exploded at high altitude.

Interesting concept! Read more about the details here. And be aware that the regular postings of the Carnival of Space, which Brian handled this past week, are a good place to keep up with insights from space bloggers. This week you’ll find, in addition to the nuclear cannon and related links, a mind-boggling look at a Martian avalanche, a discussion of bad science in the movies (Apollo 13 and Contact stand out as exceptions to the rule that Hollywood invariably botches the science in the service of dubious plot lines), and Russia’s allocation of about $16 million for nuclear space projects this year, with plans to increase to $580 million over the next nine. Is the Russian initiative a keeper, and will it inspire new nuclear technologies from the West?

An Eerie Silence Indeed

Prolific author and physicist Paul Davies (Arizona State) will be offering an online lecture on March 31 covering our current SETI work and the prospects for extending it in new directions. His new book The Eerie Silence: Are We Alone in the Universe is just out this month from Penguin. Davies offers up an overview of our quest for extraterrestrial intelligence in a thoughtful piece on physicsworld.com, one that encapsulates the history of the discipline and asks whether we shouldn’t be thinking of expanding our horizons. It’s always interesting to note that current SETI research is almost all privately funded, with the 350-dish Allen Telescope Array now under construction growing from the philanthropy of Microsoft co-founder Paul Allen, and numerous activities coordinated by the SETI Institute and other sources working the sky on a regular basis.

Davies has his doubts that a scenario like Carl Sagan’s Contact, in which a civilization elsewhere in the galaxy beams messages to establish dialogue and provide wisdom, is really credible:

A major problem with Sagan’s thesis is that if there are any aliens out there, they almost certainly have no idea that the Earth hosts a radio-savvy civilization. Suppose there is an advanced alien community 500 light-years away – close even by optimistic SETI standards – then however fancy their technology might be, the aliens will see the Earth today as it was in the year 1510, long before the industrial revolution. In principle they could detect signs of agriculture and construction works such as the Great Wall of China, and they might predict that we would go on to develop radio astronomy after a few centuries or millennia, but it would be pointless for them to start signalling us until they obtained positive evidence that we were on the air. This would come when our first radio signals reached them, which will not be for another 400 years. It would then take a further 500 years for their first messages to arrive. So Sagan’s scenario might be conceivable in another millennium or so.

More likely that we pick up a beacon, one designed to sweep the plane of the galaxy, one sending out a civilization’s last wishes, perhaps, or calling attention to anyone who receives it that there are others who have survived their technological infancy. Even so, Davies doubts we would find the brief ping of a beacon amidst the sea of incoming data from our antennae. Better, perhaps, to look for signs of technology like Dyson spheres or other large-scale astroengineering projects which might change the spectral character of a host star.

Even changes confined to a planet’s surface may be detectable in the not-too-distant future in the form of industrial pollutants or other weird molecules in the spectrum of the planet’s atmosphere. The Kepler mission should soon produce a tally of Earth-like extrasolar planets that would be a natural target list for a future space-based optical system with this capability. We must also be alert to the possibility that an alien community might produce very different by-products than humanity – perhaps ultra-energetic neutrinos in the peta-electron-volt (1015 eV) range or intense bursts of gamma-ray photons from matter–antimatter annihilation that would be too concentrated to come from any plausible natural source.

So many questions arise from all of this and Davies works over them all, from extraterrestrial artifacts (and how to discover them if they exist in our own Solar System) to post-biological intelligence and the dangerous trap of anthropocentrism, in which we use our own civilization as a model for what an extraterrestrial culture must be like. Davies wonders whether biological intelligence won’t give way to new kinds of ‘thinking systems,’ artificial intelligence and genetically modified neural networks merging to create a new kind of sentience. Physicist Frank Wilczek calls such a development ‘quintelligence,’ and Davies thinks it might be found in intergalactic space, exploiting low temperatures and all but impossible to spot via SETI.

And what about right here on Earth?

As a final example of what we might look for, an alien expedition or migration wave may have tampered with terrestrial microbiology, perhaps creating its own shadow biosphere to assist with mineral processing, terraforming or energy production. Also, if the aliens really wanted to leave a message for posterity, implanting it in the genomes of micro-organisms might be a better strategy than sending out radio signals from a beacon. Using viruses or living cells as information repositories has many advantages: biological nanosystems are self-replicating and self-repairing, and have the potential to conserve information for millions of years. Some genes, for example, have remained largely unchanged for more than a billion years.

In any case, it’s hard to disagree with Davies’ notion that we now need to widen the search beyond radio and optical methods in the new hunt for astroengineering and technological footprints beyond our own. We’ve come a long way since the 1959 paper in Nature by Giuseppe Cocconi and Philip Morrison that first advocated a systematic search for alien radio signals. Frank Drake’s use of the 26-meter dish at Green Bank (West Virginia) was the start of a hunt that may well occupy us for decades more and perhaps centuries. My guess is that it’s the longest of long-shots, but then I think intelligent life is uncommon in the galaxy. My hope, though, is that we do find it — nothing would please me more than being proven wrong by a solid SETI detection.


Comments on this entry are closed.

  • Athena Andreadis March 5, 2010, 12:50

    “Biological nanosystems are self-replicating and self-repairing, and have the potential to conserve information for millions of years. Some genes, for example, have remained largely unchanged for more than a billion years.”

    I do wish, for the zillionth time, that physicists would bother becoming familiar with basic biological facts before making statements like that last sentence. The function of some genes has remained unchanged for a billion years at the molecular level. That is, a gene product that started as a kinase generally remains a kinase (although they may gain new functions or finetune the one they started with by various means, from alternative splicing to gene duplication).

    However, both the gene sequence and the cellular function of a given gene product diverge widely from one organism to the next. Most pertinent to Davies’ statement, no embedded “message” in a genome would long survive this drift. That scenario works well in science fiction and can become a gripping story; but it makes for crappy science, crappy popular science and crappy predictions.

  • T_U_T March 5, 2010, 14:02

    what about making the shaft not vertical but a diagonal tunnel ?

    If a human immersed in fluid could withstand 100 G for 8 seconds
    you would get v = 8kms^-1 a = 10 G
    s = v^2 / 2a = 32.6 km long tunnel

  • Michael T. March 5, 2010, 15:38

    @Athena – Interesting post and I do lean towards your analysis of the improbability of encoding a message in a given genome due to changes over time. However, could we not use a “lossy compression” analogy here? Yes, there are errors in the data but useful information may be teased out?

  • Kenneth Harmon March 5, 2010, 16:06

    Kenneth Harmon,

    Personally, I suspect that the Universe is filled with Intelligent life. Unfortunately, we may live in a very very remote part of the Milky Way Galaxay. Furthermore, we also appear to be riding in a local bubble (along with Alpha Centauri and a few other close star systems) that may further mask our presence and make it hard to detect and communicate with us. In essence, we seem to be tucked away in a local bubble that is part of a larger bubble in a remote part of the Milky Way. More attention should be paid to the Galactic position and local “Geographical conditions” of Sol/Terra and also Alpha Centauri (not originally from our Galactic neighborhood) as we conduct various types of SETI searches and speculate on why we have not had obvious contact. Perhaps, where we sit is a major driver or as the saying goes location, location, location.

    Finally, a question for Athena from a previous string which is now defunct. Based on your previous writings you are obviously skeptical about major advances in life extension from where we are today, at least for the next Century or so. One of the obvious apparent deal breakers is going to be in extending the Human Brain. However, how do you feel about getting to an average life span of 150 for people being born in the 21st Century? A 150 year average life span seems to be a relatively modest goal, and we should be able to keep a Human Brain going that long with the right drugs, nano-medicine and Gene therapy once we have a much better understanding of how brains age in the next `30 years. I am not one of those who believes in radical life extension, 200+years, but it seems to the untrained eye that roughly doubling the average Human life span from where we are now, and doing this by 2100 seems to be an achievable goal provided one lives in a fully developed country. With average life spans of 150 years travel to local star systems becomes much more practical provided that the propulsion and protection challenges can be solved.

  • Athena Andreadis March 5, 2010, 16:20

    Michael, lossy compression fails rather miserably if you want to decode a drifted message of the type “Zrukumfpt from Epsilon Eridani was here when all of yous were lowly amoebae”. Also, regardless of scale, what information can you tease out that shows a past footprint if you don’t have a Rosetta Stone equivalent? We can’t decipher earth scripts and languages that lack such aids, how are we going to do that with an info fragment from an alien mindset?

  • Eniac March 5, 2010, 16:48


    However, both the gene sequence and the cellular function of a given gene product diverge widely from one organism to the next.

    While this is true for most genes, there are quite a few which are conserved well across all phyla, all the way down from mammals to bacteria. These sequences are billions of years old, just as Davies has said. The ribosomal proteins and RNA they encode co-originate with the peptide synthesis mechanism which is universal to life.

    See for example I-Tsuen Chen et al., PNAS, Vol. 83, pp. 6907-6911, 1986:
    ( http://www.pnas.org/content/83/18/6907.full.pdf )

    ABSTRACT We describe sequences of two human ribosomal
    proteins, S14 and S17, and messenger RNAs that encode
    them. cDNAs were used as molecular hybridization probes to
    recognize complementary genes in rodent, Drosophila, and
    yeast chromosomal DNAs. Human ribosomal protein sequences
    are compared to analogous Chinese hamster, yeast,
    and bacterial genes. Our observations suggest that some
    ribosomal protein genes have been conserved stringently in the
    several phylogenetic lines examined. These genes apparently
    were established early in evolution and encode products that
    are fundamental to the translational apparatus. Other ribosomal
    protein genes examined, although similar enough to
    heterologous DNA sequences to indicate their structural relationships,
    appear to have diverged substantially during evolution,
    probably reflecting adaptations to different genetic environments.

    RNA structure is based on nucleotide pairing. That means you can mutate paired nucleotides by switching them, or even substitute an alternate matched pair, without affecting function in most cases. Because the simultaneous natural mutation of two specific nucleotides in the just right way is exceedingly unlikely, and mutation of only one of them leads to loss of function, any such changes you make will not revert. You can thus encode quite a lot of information by switching around nucleotide pairs in conserved RNA structures, such as the 20 different transfer RNAs. My guess would be that there is tens of kilobases of strictly conserved information to play with in ribosomal and transfer RNAs that will last billions of years if artificially mutated this way.

    Another thing you can do, which is absolutely permanent, is to modify the genetic code. There is no way the code can change by itself, except for very minor modifications, but it IS arbitrary. A concerted intervention can switch around the meanings of the code positions. That gives you perhaps a few dozen bits worth of information. Not much to work with, but if cleverly arranged it could probably be made to spell “artifact!”.

  • Adam March 5, 2010, 17:22

    Hi Athena

    What about the ultra-conserved sequences in mammalian genomes? They’re not exons and yet somehow they’re being protected from mutation. Why? Any theories of your own? They’re a counter-example to the general rule of endless molecular drift. There’s also those very recent discoveries of convergence at a molecular level in certain genes across quite an evolutionary span. Molecular biologists are still scratching their heads over that one.

  • bigdan201 March 5, 2010, 18:44

    an intriguing idea. whether its nuclear cannons or launch loops, making it more economical to reach orbit will be a major step forward.

    Its hard to say how aliens will react to us, or whether theyll try to communicate. the idea of us getting a random beacon is reminiscent of the Wow! signal. In any case, anything outside of about 100 light years at the most hasnt heard any radio signals from us.

    I read eniacs post about encoding information into dna/rna, but are you sure that there wont be any mutation or information loss through the generations? Biology tends to be fuzzy. Physical artifacts are more likely, which reminds me of the m-arc discs designed to last for the very long term.

  • Eniac March 5, 2010, 19:09

    Also, regardless of scale, what information can you tease out that shows a past footprint if you don’t have a Rosetta Stone equivalent? We can’t decipher earth scripts and languages that lack such aids, how are we going to do that with an info fragment from an alien mindset?

    Now here is an interesting question. You could, for example, spell out the binary digits of a sequence of prime numbers. That would be quite easily decoded, and the meaning would be very clear without any Rosetta Stone: “someone from some other planet was here when all of you were lowly amoebae”. The problem of sending more complex decodable messages has been well discussed among METI researchers, I believe.

    Dealing with noise is an additional difficulty, but the simple prime number sequence, for example, would still be intelligible if half the numbers were knocked out, which well within the degree of conservation suggested by the sequence alignments in the aforementioned PNAS paper.

  • Athena Andreadis March 5, 2010, 19:15

    Adam, I’m not familiar with what you’re describing. What ultra-conserved sequences are you referring to? If you point out a reference or link, I may be able to answer your question.

    Eniac, what do you do in real life? I’ve worked on RNA throughout my scientific career, starting with tRNA and rRNA, then on to alternative splicing of mRNA. If you want to go into nitty gritty, there are several factual errors in your post. There are 20 commonly used amino acids but many more than 20 tRNAs. Theoretically, the absolute minimum is about 30 for unambiguous translation, but they are far more redundant than that. Their number varies across organisms and so do their details, although most of them do fold into a similar higher order structure when fully mature (2-D cloverleaf, 3-D L-shape to fit in the ribosome groove).

    If you read that 1986 PNAS paper that you linked to, you will find out that there are actually many differences between the rRNAs they compare. Even between human and mouse the divergence is 10%. With yeast, it’s more than 30% and they’re no longer colinear. If you mutate paired nucleotides in a structural RNA you may leave structure unaffected but you may well influence function, because they interact with other RNAs and proteins (and usually unfold to do so). When this happens “in real life”, you get diseases, gain or loss of function, etc.

    The code can change by mutation and has done so: mitochondria, archaea and several bacteria have differences in their codes. What hasn’t changed is the general mechanism (tRNAs, ribosomes, triplets). Which — as I said in an earlier post in Centauri Dreams — is powerful proof that extant terrestrial life arose from a single source. It doesn’t preclude early alternatives. We just ended up with this one, through chance circumstances that allowed it to thrive.

  • Eniac March 5, 2010, 19:17

    I read eniacs post about encoding information into dna/rna, but are you sure t
    hat there wont be any mutation or information loss through the generations?

    Well, yes, I am quite sure there are sequences that are preserved over billions of years with only minor information loss. I explained why in my post and cited a publication for reference.

  • Eniac March 5, 2010, 19:20

    I think in the contrary, physical artifacts are much more destructible than DNA sequences. Where are you going to put it without having it subducted into the Earth’s mantle over millions or billions of years?

  • Athena Andreadis March 5, 2010, 19:25

    I wanted to emphasize the following linked points regarding “embedding” information in a genome:

    — Structural RNAs undergo drift like all other genes, although they are subject to conservation pressure (but then, so do the mRNA coding portions); they deal with this by redundancy.
    — If aliens embedded such information, they did so when terrestrial life was at the bacterial stage at most. We know this because all terrestrial life is based on a single plan (with variations of course).
    — Hence, at this point such information has become scrambled beyond recognition.

  • justcorbly March 5, 2010, 19:54

    Wouldn’t a 5000g ride pose a problem for at least some kinds of cargo?

  • Athena Andreadis March 5, 2010, 21:59

    Kenneth, somehow I missed your earlier comment on this thread. It seems that the natural human lifespan hovers around 100 years. Until now, first world countries have managed to increase the average life expectancy and the major causes were relatively low tech: clean water, antibiotics and vaccines. The lifespan high end remains stubbornly fixed at 100, and it’s clear that few humans are equipped to attain it, as is obvious from the proliferation of degenerative diseases in developed countries (cancer, diabetes, dementia).

    A lifespan of 150 is only a 1.5 fold increase on our starting number, even if we manage to stave off those problems — which won’t happen by 2100, although we may understand a lot more about the brain by then. What we really need is a 10-fold increase, as long as we don’t get bored to death or run out of room. Most people argue that disease-free longevity is a prerequisite for crewed space travel. I think it’s actually the reverse: radical longevity will make space travel an absolute necessity, for both pragmatic and existential reasons.

  • Eniac March 5, 2010, 23:07


    If you read that 1986 PNAS paper that you linked to, you will find out that there are actually many differences between the rRNAs they compare.

    Many differences, yes, but more importantly, many similarities as well. Between mammalian S14 and E. coli S11, 43% identical in amino acids, and 44% identical in nucleotides. This similarity is highly statistically significant, and it completely substantiates Davies’ (and my) assertion that information has been preserved for billions of years. It is not much information, and noisy, but far from zero, as you have asserted, IIRC.

    If you mutate paired nucleotides in a structural RNA you may leave structure unaffected but you may well influence function, because they interact with other RNAs and proteins (and usually unfold to do so)

    Yes, you may, but not always. Mutating some pairs will disrupt function, but most will not. You are the engineer, you chose which you mutate, so no problem, you just have somewhat less “storage space”. The key is to understand that every functional structure has not one, but an enormous number of possible sequences. The sequence->structure->function mappings are many-to-one, in the extreme.

    I found homology data between human and bacteria only on ribosomal protein genes (the PNAS paper), I am still searching for data on tRNA genes. They may or may not be similarly conserved, at this point I just don’t know. It sounds like you might, given your extensive RNA experience?

    tRNA sequence can be engineered much more easily, because the dominant interaction is base-pairing, which is much simpler to model than 3-d protein structure. Still, it is possible create a functionally equivalent protein with a completely different sequence. Protein engineers are starting to do that today, for real.

    The code can change by mutation and has done so: mitochondria, archaea and several bacteria have differences in their codes. What hasn’t changed is the general mechanism (tRNAs, ribosomes, triplets).

    Substantially more hasn’t changed. The thing that counts most, the mapping between codons and amino acid, has not changed, with very few exceptions. And it never will, by itself. This mapping is arbitrary, i.e. life would work just as well if the same amino acids were coded for by different codons. Anything that is constant, but arbitrary, can be used to persistently encode information.

    Bring in the RNA engineer, and it is a fairly straightforward task to reshuffle the tRNAs by creating hybrids, i.e. splicing together the anticodon of one with the body of another. The hard part is to resynthesize every single coding sequence in the genome without forgetting a few or messing up the splicing and various overlapping signal sequences. Not at all easy, but we are talking super-humans here, are we not? Venter will do it before breakfast.


  • Eniac March 5, 2010, 23:26

    – Hence, at this point such information has become scrambled beyond recognition.

    This “Hence” here comes out of nowhere, and the substantial homology between bacterial and mammalian sequences disproves your point. If it was “beyond recognition”, you would not see homology.

  • Michael T. March 6, 2010, 0:31

    Nice discussion folks and thanks Athena for engaging, really informative. But I am still bewildered. You say that some things haven’t changed like the general mechanism (tRNAs, ribosomes, triplets), could that not be the what encodes this so-called alien message? (I don’t actually buy into it but it’s fun to think about.)

    I would think that if any intelligence could encode a message in a biological scheme would have the wherewithal to leave a clue, your “Rosetta Stone”. The mystery deepens, now sounds like a bad episode of Lost ;)

  • Tulse March 6, 2010, 1:01

    I would think that a major problem with any cannon-style launcher is that the launch vehicle travels at maximum speed in the densest part of the atmosphere. Unlike rockets which accelerate as they liftoff, and thus only reach final escape velocity where the atmosphere is relatively thin, a cannon-launched vehicle has to be going faster than escape velocity when it leaves the cannon muzzle, as it gets no further acceleration. This means that such a vehicle will need extensive heat shielding on its nose, shielding that would have to be heavier than it would use for re-entry, where the drag of the upper atmosphere would slow it down to lower velocity compared to its speed out of the muzzle. (It will of course need shielding on its tail, where it is in contact with the blast, which also ups the weight and complexity of the vehicle.) It also means that the launch velocity will have to compensate for the drag, and thus the velocity out of the muzzle will have to be much higher than the final desired speed (which in turn exacerbates the problem of heat shielding).

  • Adam March 6, 2010, 2:29

    Hi All

    Athena, one of the first papers on the ultra-conserved sequences was this one…


    Science 28 May 2004:
    Vol. 304. no. 5675, pp. 1321 – 1325
    DOI: 10.1126/science.1098119

    Ultraconserved Elements in the Human Genome
    Gill Bejerano,1* Michael Pheasant,3 Igor Makunin,3 Stuart Stephen,3 W. James Kent,1 John S. Mattick,3 David Haussler2*

    There are 481 segments longer than 200 base pairs (bp) that are absolutely conserved (100% identity with no insertions or deletions) between orthologous regions of the human, rat, and mouse genomes. Nearly all of these segments are also conserved in the chicken and dog genomes, with an average of 95 and 99% identity, respectively. Many are also significantly conserved in fish. These ultraconserved elements of the human genome are most often located either overlapping exons in genes involved in RNA processing or in introns or nearby genes involved in the regulation of transcription and development. Along with more than 5000 sequences of over 100 bp that are absolutely conserved among the three sequenced mammals, these represent a class of genetic elements whose functions and evolutionary origins are yet to be determined, but which are more highly conserved between these species than are proteins and appear to be essential for the ontogeny of mammals and other vertebrates.

  • Adam March 6, 2010, 4:27

    Hi again

    Brian & Joe’s Verne-Gun is a BIG idea, but is it very useful? Just what do they want to throw into space and for what purpose? The whole idea is to boot-strap industry in space, thus throw bulk materials into a suitable orbit then extract at leisure to build facilities on the Moon or at Lagrangia. But the 5,000 gee launch gives me pause – what industrial material will survive and be worth launching?

  • Eniac March 6, 2010, 10:30


    The atmospheric ablation problem seems solvable. Warren Smith writes in some detail on it in his magnetic catapult paper (a good read otherwise, too):



    Pretty much any bulk material will survive such launchings, and even some more complicated devices, such as “smart” artillery shells, which remain functional despite similar g-forces. See here for an interesting table:


  • Athena Andreadis March 6, 2010, 10:47

    Eniac, Venter will say (loudly and often) that he can do it before breakfast. For the rest, suffice it to say that we’ll have to agree to disagree on several points. My bottom line is that whereas conservation is obvious in the genome on several scales, it will not retain “Kilroy was here” messages. If the aliens wanted to leave an obvious message, they should engineer a single life form that differs crucially from all others — at whatever level. However, that’s not at easy at it seems for several reasons (I leave this part to you as an exercise).

    Adam, I will take a look at the Science article and get back to you!

  • philw1776 March 6, 2010, 12:31

    Water would survive launch. I’m not convinced that lunar water is that reaily extractable. Water, nitrogen and other bulk compounds would bootstrap a cislunar space industrial society using lunar soil and solar energy. Water in huge quanties doubles as a rad shield.

    Later once cislunar is well established, the asteroids could supply such elements and compounds.

  • Jim Vincent March 6, 2010, 15:31

    SETI searches also face the limit,as we see in our own society of “how long might they be broadcasting?”, and not just in terms of civilization survival. Cable TV, focussed satellite radio, etc….how detectable are *we* compared to 20 years ago?
    It is interesting to see ‘2001’ and ‘Andromeda Strain’ ideas come back again as places we might legitimately start looking (at last).

    One thing that bothers me about the VerneGun is the disposibility – the charges that collapse the gun after it makes a shot. Continually making and sealing such shafts sounds highly ineffcicent, and wasteful.

  • NS March 6, 2010, 20:24

    The idea of using a cannon to launch satellites has been worked on before, most notably by Gerald Bull:


    His concept actually involved launching a rocket out of a cannon, rather than a pure cannon design. Unfortunately the idea had enough potential military applications (and Bull himself too cavalier about them) that it got the ultimate wrong sort of attention — Bull was murdered in 1990.

  • T_U_T March 7, 2010, 13:15

    just a question only tangentially related to he topic. Is a ground launch orion type spacecraft simpler, or more complicated than a multistage cryogenic fuel rocket ? Could an orion spaceship be launched not by solid state boosters but directly from water surface or from above a deep shaft ?
    Given that all you need (apart from nuclear explosives ) is a pusher plate and a sturdy frame resistant enough to not to fall apart from repeated jolts, and one cannon to launch the nukes, it seems that it could be relatively easy to construct. As opposed to a rocket engine that is extremely complicated and works at the edge of physical possibility.

  • Elon March 8, 2010, 17:57

    The first nuclear cannon? FYI, http://nuclearweaponarchive.org/Usa/Tests/Plumbob.html is fun, it describes how Dr. Robert Brownlee is occasionally credited with launching a “man-hole cover” into space during pre-Sputnik underground-*+ nuclear testing, though Brownlee himself doesn’t appear to go along for the whole ride, so to speak: http://nuclearweaponarchive.org/Usa/Tests/Brownlee.html. Probably due to the ablation problem Tulse and others mention above?

  • Athena Andreadis March 8, 2010, 18:32

    Adam, I promised you an answer about ultra-conserved elements. Not surprisingly, the paper indicates that such elements are conserved only in related species (in this case, vertebrates) and that they appear to be under constraint for functional reasons other than protein coding (which is often the sole thing people know about the genome). Many appear to code for distal enhancers, several are involved in transcriptional or splicing regulation. Others may be coding for miRNAs. So they sound exotic enough to the non-biologist, but they’re nothing a molecular biologist doesn’t already know and, at some level, understand.

  • Greg March 10, 2010, 22:28


    Even if we have extended lifetimes , reaching 150 years. I seriously doubt people will spend a good fraction of their life in a small, cramp vessel for that matter more than 3 years at a time, very most 5. We would most likely go with extremely large “world ships” or very fast transit times.

  • Adam March 11, 2010, 6:16

    Hi Athena

    At that sort of fidelity their exact specification must have a lot of down stream functionality – yet knock-out mice without the UCS appeared to show no ill-effects. Very odd if it’s selection keeping them stable against mutational rewriting.

  • Eniac March 12, 2010, 0:17

    One (speculative) possibility for ultra-conserved sites is that they may be functional as hybridization nucleation sites for the alignment of paired chromosomes during meiosis. Mutations would be strongly suppressed in such areas, because they would create a mismatched base pair and substantially weaken the hybridization rate. This would interfere with proper alignment, causing sterility. Perhaps the knock-out mice Adam mentions were not tested for reproductive function.

    There is an interesting similar hybridization phenomenon going on in the Y-chromosome, which is unpaired: The Y-chromosome has eight large palindromic regions, containing most of its genes, which are thought to hybridize in a hairpin fashion to make up for the lack of a paired chromosome during meiosis. See this section from http://txtwriter.com/Onscience/Articles/ychromosome.html:

    A palindrome has a very neat property: it can bend back on itself, forming a hairpin in which the two strands are aligned with nearly identical DNA sequences. This is the same sort of situation — alignment of nearly identical stretches of chromosomes — which permits the copy-edit of the X chromosome during meiosis. Thus in the Y chromosome, mutations can be “corrected” by conversion to the undamaged sequence preserved on the other arm of the palindrome. Damage does not accumulate, Muller’s ratchet is avoided, and males persist.

    The Y-chromosome is an interesting beast, with many peculiar properties. It is thought to contain the gene for map-reading, for example, and those for couch-sitting, beer-swilling and football-watching.

  • Mike Prather March 21, 2010, 4:42

    Paul Davies seems to have misread Contact. The premise is actually that the galactic community has unmanned radio outposts stationed throughout the galaxy (in this case, 75ly away at Vega) which are capable of picking up nearby signals from early radio blasts, such as we have produced, and then sending a generic message which only gives instructions for building a one-shot delivery device so we can visit and get the briefest of introductions. The aliens in Contact didn’t do all this to open a dialog – they admitted that we currently didn’t have anything significant to offer – they did this just to let us know that the community was there when we’re ready to join it and to tell us that survivability of a technological species is possible. That’s really the best message we could ever get.