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Posted by: tacitus Jan 23 2006, 04:36 AM

Hi, I've just written the first draft of a science fiction short story and I need little help with the plausibility factor . Since many highly educated people hang out in this forum (flattery will get me everywhere... I hope!) I thought this might be a good place to ask a few questions.

The story is about a colossal creature (think Titan-sized, as in the moon Titan) that lives amongst the stars, travelling from solar system to solar system, hibernating while in between. (Hey, I didn't claim it was original .) I'm not so concerned about the plausibility of such a species evolving as I am about how the creature is powered.

The creature's internal systems are powered (for want of a better word) by a fission reactor, which I think is okay. But its propulsion is powered by the burning of hydrogen and oxygen (i.e. as in rocket fuel) extracted from water - and this is the bit I'm unsure about.

I know hydrogen and oxygen can be extracted from water, and with a colossal nuclear reactor at its core there is enough energy for the creature to do so, but I just don't know how plausible this whole propulsion set up it. (I guess I can live with "unlikely", I just don't want to base the story on something that's "impossible".

An important aspect of the story as it is written is that the creature needs to stock up on its water supply and has to munch on moon-sized objects to do so (think Europa-sized or smaller in this instance). So its critical for the story that water, and the need to replenish its supply of water, plays a very large factor in the creature's life. I know we are talking colossal sizes and amounts of water here, but that's part of the nature of the story.

So, what do you think? Am I on the right track or careening off the rails?

Any help at all would be greatly appreciated.

Thanks,

Mike

Posted by: exobioquest Jan 23 2006, 03:32 PM

Well I'm not educated but a several thousand Km wide planet eating space monster that is fusion powered yet is propelled by H2+O2 is like a nuclear submarine propelled by paddles! You got fusion power, just us it to plasmify a propellant (H2O, H2, heck any materially eaten) and vector it out, it should give you many times the specific impulse of H2+O2 combustion. The creature will likely have a preference for hydrogen for its fusion reactor(s) thus planets with water (planets with gaseous hydrogen will likely be too big to eat)

Posted by: tacitus Jan 23 2006, 03:52 PM

Good point - but the way the story stands the creature has an internal fission reactor, not fusion. Does that make any difference? (Probably not, I guess). Thanks for the tip.

Posted by: ljk4-1 Jan 23 2006, 04:14 PM

Have you read Gregory Benford's 2000 SF novel, Eater?

http://www.space.com/sciencefiction/books/eater_000317.html

http://www.sfsite.com/05a/eat80.htm

http://www.scifi.com/sfw/issue152/books.html

http://en.wikipedia.org/wiki/Eater_%28novel%29

And knock my socks off - I just discovered that someone has written a screenplay of the novel and it is online here:

http://www.lasttemplar.com/PDF/EATER.pdf

Posted by: tacitus Jan 23 2006, 06:03 PM

No, I haven't... looks interesting. I'm sure that Benford, being a scientist, has thought out the technical nature of his beast in great detail.

In my case, since it's a short story, I don't really have the time to delve too deep into the nature of my beast, I just want it to be possible, if not plausible. I wanted to come up with something that is so alien, so different that it would not even comprehend that other life, particularly on our scale, could exist. So something that simply sees the solar system as a feeding ground is going to cause major problems - especially if the planet we happen to be living on is seen as a "Tasty Morsel" (the name of the story).

Posted by: ljk4-1 Jan 23 2006, 06:36 PM

I know you know your story is not original, but note that there was an animated Star Trek episode from 1973 titled "One of Our Planets is Missing" about an immense intelligent cloud that consumes planets but has no idea that there is intelligent life on those worlds (they are too small for the cloud to detect).

http://en.wikipedia.org/wiki/One_of_Our_Planets_is_Missing_%28TAS_episode%29

There is also Fritz Leiber's classic SF novel from 1964, The Wanderer, about an artificial planet that suddenly appears out of hyperspace near Earth and causes havoc to humanity.

http://www.sfsite.com/03b/wan100.htm

I am not presenting these earlier stories to you to discourage you; rather, I hope you can take from these examples (I am sure there are others, these are just the two that most prominently spring to my mind, along with Eater) and make your being and story even more different and original, along with giving you more data to work on.

Posted by: exobioquest Jan 23 2006, 07:18 PM

Fission, didn't see that, but as long as the power levels are high enough the reactor can produce plasma directly (see gas core reactor) or indirectly by generating electricity and that would be used to plasmify a working fluid. But I got to ask were this creature gets all of its uranium from?, small moon size worlds are lacking in heavy metals.

Posted by: tty Jan 23 2006, 07:29 PM

Fred Hoyle's classic "The Black Cloud" (1957) also comes to mind.

If You have a fission reactor in mind, then there is another plausible reason for such a creature to need water: for use as a moderator.
Unless the creature has an internal enrichment plant it will need water to increase the fission cross section enough to start a chain reaction. Even so it will need uranium from an appreciably younger solar system than ours to work (unless it can use deuterium as a moderator, which also requires enrichment).

A "natural" fission reactor is actually possible and has even happened here on Earth at Oklo in central Africa, see:

http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml

and

http://presolar.wustl.edu/ref/Meshik2004PRL.pdf

There are material for several plot twists there I think.

Incidentally such a creature might want to conserve the water as a moderator, using other volatiles as reaction mass. The water would be circulated, in order to cool it down, and also keeping the interior of the creature at a comfy temperature during those long, cold hauls between solar systems.

tty

Posted by: RedSky Jan 23 2006, 08:08 PM

Reminds me of the old Star Trek "Planet Killer" episode.

A more recent TV example, the SciFi channel series from a couple of years ago, Lexx... about a huge dragonfly-looking ship that blew up planets and "fed" on the biological debris and water. The show was pretty bizarre, mainly about the wacky passengers. I didn't watch it often, but when the series ended after a few years, I saw the final episodes where Lexx was stranded in the Solar System, too low on power (i.e., hungry) to escape... so it blew up and ate the earth!

Posted by: ljk4-1 Jan 23 2006, 08:14 PM

Since your being is the size of a planet, why not give it a magnetic field so it can attract and scoop up interstellar hydrogen to fuel a fusion reactor to power itself through space ala the Bussard Ramjet.

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

http://www.itsf.org/brochure/ramscoop.html

If it gets enough fuel this way, it might not even have to eat planets, but then that might diminish the dramatic possibilities. Or it might make your story even more original.

Of course let us not forget the ultimate consumer of worlds:

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

Posted by: Bob Shaw Jan 23 2006, 11:32 PM

There have been even larger, though non-biological, entities in fiction.

Marvin the Paranoid Android, for example, had a brain the size of a planet, giving rise to some questions (such as: was it a very small planet, and: how big was the rest of him?). Or then there's mice, which are simply the extrusions into what we are pleased to call 'normal' space of pan-dimensional mega-beings.

As for propulsion, presumably something squid-like might have evolved, with material being ejected from the rear of the creature, resulting in it being propelled forward. A fairly crude system, I realise, and prone to all sorts of high losses and general wear and tear (if you were to try to consider what it might be like to be such a creature, then think about the strange black rings around Uranus, and weep).

On a more serious note, try reading John Varley's 'Titan'. And, did you know that to base 13, 6 x 9 = 42 after all?

Bob Shaw

Posted by: Bob Shaw Jan 24 2006, 12:06 AM

Oh, and I nearly forgot: it's SF (prounounced 'Ess Eff') not Sci-Fi (pronounced 'Skiffy').

Ess Eff makes you think, while Skiffy makes you cringe...

Bob Shaw

Posted by: ljk4-1 Jan 24 2006, 02:09 PM

No, no - now it is being called Speculative Fiction, which still retains the SF abbreviation.

God forbid the literary types have to learn any "science", even in entertainment.

Posted by: tacitus Feb 1 2006, 08:09 PM

Sorry I've been away for a while - that was not my intent!

Anyway, thanks for all the suggestions and pointers. It seems that superheated plasma is the way to go as far as a propulsion system is concerned, and since getting such a large mass moving at speeds that will get it from star to star in at least a few hundred years would need a huge amount of fuel (mass) to accerelate it.

Yes, I think a fission reactor is more plausible since they do occur (abeit in a limited way) in nature, and water could be used as a regulator as well as mass for the accelerant. In fact, since heavy water reactors can be used (along with natural uranium) to power the fission, perhaps there's another need for water (heavy water is present in sea water - 1 in 3200).

Of course a fission reactor would, as you point out, need nuclear fuel. My assumption was that perhaps the creature would not need to refuel its uranium at every stop, but would have to restock its reaction mass, so bypassing (conveniently) the need to worry about that .

The story is told from the creature's (fairly limited) POV, with the point being that if and when alien life encounters us (or vice versa) they might be so alien that they might not even recognize what we are, much to our detriment!

Since this is a short story I don't want to get too bogged down with the details (as long as they don't beggar belief). If I was writing a novel then I would certainly have to nail down the details since there would be more time in which to do so.

If I ever get it published (a long shot, for sure) I'll let you guys know!

Mike