Science: Spacecraft: Propulsion
Autophagic Heavy-Pykrete Starship   (+8, -3)  [vote for, against]
A big blob of frozen heavy water with a human colony inside it


A huge ball of frozen heavy water reinforced with random carbon fibres is built from one of the ice moons, asteroids or comets. This is hollowed out, and spun to create artificial gravity on the inside surface as per your standard generation ship. The deuterium is used to drive a fusion rocket and/or nuclear mass driver.

Ice is thus the structure, the fuel, the reaction mass, the air supply, and the rad shielding.


After reading [link 1] which shoots down the prospects for human interstellar colonization and [2] I propose the following.

Problem space:

The technical trifles which negative nellies throw in the way of our manifest destiny to populate the universe may be summed up as follows:

a/ Energy
b/ Time
c/ Microgravity effects on the human organism
d/ Radiation ditto
e/ Launch costs

I leave such piffling matters as economic justification and political and public will to others.

The traditional scifi way of dealing with a/ and b/ without magic has been to build a humungous ship, fill it with lots of people and push it slowly through space as they have babies, die, etc.

This is known as a generation ship. Pushing slowly lowers the energy required, and making babies as you go buys you time.

The most promising ways of dealing with c/ and d/ seem to be c/ spinning a (large) craft to simulate ~0.3 to 0.5 G through centripetal acceleration, and d/ putting masses of Stuff between the squishy meat monkeys and all those high energy particles.

The extra Stuff required for rad shielding poses a weight problem, unless the Stuff is Stuff that is needed for other purposes. Amongst proposals I've seen are using trash, other equipment, or the fuel as absorption mass, surrounding the habitable space.

e/ is best dealt with in all serious proposals such as this by building as much Stuff as possible off-Earth.


On or below the surface of Triton [3], an automated deuterium enrichment plant produces heavy water. A mass driver - basically a whopping great fire hose - shoots it off the surface to a Lagrange point.

Another automated plant is deployed on a carbonaceous asteroid to create fluffy, porous carbon fibre strands. Note these are not exotic fullerene strands, just your bog standard carbon fibre. These are also mass-driven to the appropriate Lagrange point, where they collide with the steam/water/ice streaming up from Triton, and mingle randomly amongst.

There it re-freezes and coalesces under self-gravity into a huge lump of carbon-fibre Pykrete [4].

When said lump reaches a certain size, the Giant Space Laser and/or robots are deployed to shape it in certain ways, to whit:

Deep beneath a kilometer or so of ice, at the center of the new body, a hydrolysis plant cracks the water into oxygen and deuterium. The deuterium is used to power a fusion drive [5] on the surface, either inertially or magnetically contained.

Part of the helium created in the fusion reaction is captured, and mixed with the O2 to create a breathable atmosphere.

A small percentage of the energy from the fusion drive is bled off to power onboard systems.

As the core of the planetoid is consumed, it is progressively spun up to create an artificial gravity effect on the inside of the cavity thus created. This also helps to prevent collapse of the cavity due to self-gravity. This core is filled with the O2/He atmosphere.

The initial orbit of the planetoid takes it to a near Earth encounter, where the colonists board, along with any other heavy equipment needed.

The kilometer of ice provides more than adequate shielding from the hard radiation of space, as well as from the fusion drive.

Tunnels are dug from the core to observation/agriculture decks near the surface, where short visits to view the wonders of the universe (and to prevent mass solipsism) are allowed.

Coolant channels are run near the surface for the massive, fusion-powered refrigeration system needed for the Earth approach, and the slingshot orbit around the Sun. All the illegal Freon seized by the Ozone Police is sent to meet the iceship on its way to Earth. Once out of >0C space, the Freon is fed into the drive as reaction mass.

As the fusion drive consumes the bulk of the ship, the internal cavity and its atmosphere increase in size. This allows progressively more habitable space over the course of the journey, which allows the colony population to increase, rather than being strictly limited by a fixed infrastructure ceiling.

Thus you can start your journey with a minimum genetically viable population (~200) and arrive with a small nation in tow (10k-100k).

Admittedly, the radiation protection is also being consumed, but by timing this right, your distant descendants arrive at the destination star just as their vessel vanishes in a puff of steam. By then they have built their many smaller transfer craft and are decelerating towards insertion orbits around the target planet or planets.

Where they are all amazed to find their voices drop an octave.


If fusion propulsion proves a pipe dream, then one of the other proposed or existing nuclear propulsions systems [6] can be used.

If fullerene toughness is desired and feasible, long strands (at least, Space Elevator long) are not needed. Short, fluffy bundles of randomly varying length should do nicely.
-- BunsenHoneydew, Jul 18 2007

[1] Why we won't colonise the universe http://www.antipope...ier_redux.html#more
SF writer Charles Stross shoots the galactic fantasy down with hard numbers [BunsenHoneydew, Jul 18 2007]

[2] D2 Ice Spaceship http://magicdragon....lications/STAR.html
Autophagic, yes, but frozen hydrogen?? That's non-trivial. Let's use D2O (heavy water) ice instead. NB borked HTML [BunsenHoneydew, Jul 18 2007]

[3] Triton http://en.wikipedia...i/Triton_%28moon%29
"... is probably about 25% water ice ..." [BunsenHoneydew, Jul 18 2007]

Your competitor Low_20budget_20spacecraft
We specialize in cost savings [normzone, Jul 18 2007]

Ice Tire Spaceship
first hit on Google [baconbrain, Jul 18 2007]

[4] Pykrete
"... water and any porous and fibrous material ... crush resistance of greater than 21 megapascals (3,000 psi)" [BunsenHoneydew, Jul 18 2007]

[5] Fusion Propulsion http://en.wikipedia.../wiki/Fusion_rocket
[BunsenHoneydew, Jul 18 2007]

[6] Nuclear Propulsion http://en.wikipedia...ine#Nuclear_heating
alternatives to [5] [BunsenHoneydew, Jul 18 2007]

Starflight without Warp Drive http://magicdragon....Nonfiction/STL.html
Another reference to the autophagic H2 ice ship [BunsenHoneydew, Jul 18 2007]

A series of computer adventure games first released in 1983 by Level 9 - linked is the background story/instructions, which pretty closely resembles the idea (except they used frozen ammonia, rather than deuterium) [zen_tom, Jul 18 2007]

I like Stross's writing, and it's easy to point out why it can't happen. The hard work is figuring out how to make it happen.
-- normzone, Jul 18 2007

I Googled for "ice spaceship" and found the linked item.

I'm sure I read this in a science-fiction book. I know I sketched it for a while.

A good thing about an ice-ball ship is that the front end cushions high-speed impacts.

Oh, heavy water! That's a new twist, at least to me. [+]
-- baconbrain, Jul 18 2007

Nice link, [baconbrain]. What does it say that I only searched here for prior art before posting?

Yes, it uses ice as a structural material ... but it's not an autophagous carbon-fibre heavy-Pykrete ship.
-- BunsenHoneydew, Jul 18 2007

Visits to the rad-vulnerable observation decks probably don't require time limits enforced by regulation or religious taboo.

They'll most likely be self-limiting - it should be fairly disconcerting to stand (or slump) on the transparent floor, at several times your accustomed weight, watching the stars whizz by under your feet.
-- BunsenHoneydew, Jul 18 2007

Looks good. A close variant on the ships I am reading about in Ken McCloud's "Learning the World" Also autophagic, but a different drive technology lets them use anything as reaction mass. One extro phagic croissant
-- Galbinus_Caeli, Jul 18 2007

//your distant ancestors arrive at the destination star //
So, it goes faster than light?
-- AbsintheWithoutLeave, Jul 18 2007

I think s/he is assuming powerful anti geriatrics. Every generation arrives at the destination simultaneously.
-- Galbinus_Caeli, Jul 18 2007

// ancestors // fixed, ta.

Another correction: the agricultural decks won't be on the outer surface, as there's no usable sunlight in interstellar space. They'll be on the inner surface, where the plentiful nuclear powered grow lights are.

// by timing this right, your distant descendants arrive at the destination star just as their vessel vanishes in a puff of steam. //

Which, as a friend points out, rather neatly takes care of the problem of loss of mission focus which plagues fictional generation ships.

"Well, son, the Council Of Elders Inter-Tribal Steering Group On The Sky Falling In has determined that we will all be exposed to the Void Beyond Knowing in 3 generations. By the strangest coincidence, we will be passing a habitable star system right about then ..."
-- BunsenHoneydew, Jul 23 2007

[Bunsen] Ken MacLeod deals with that issue nicely in the book I just finished reading. (No, not that one, I have no interest in that one.) The title is "Learning the World: A scientific romance." In it you can also see him using the idea that is the genesis of my username.

Anyway, what he has done is separate "The Crew" from the rest of "The Complement" of the starship. After delivery of Colonists to a new system, the ship reconfigures and refits to travel on to another system.
-- Galbinus_Caeli, Jul 23 2007

Are we sure that 200 is enough to avoid ending up at the destination star with the last remaining vestiges of a dying society of inbred hillbillies and hicks?

That Arizona fundie mormon group that has that rare disease had a couple of hundred at one point, as I recall, which I am too lazy to look up before I click the "OK" button below to ensure that I'm not making an idiot of myself...
-- globaltourniquet, Jul 23 2007

Your living complement does not have to be your total genetic complement. A freezer full of thousands of frozen embryos would not take up much room at all.
-- Galbinus_Caeli, Jul 23 2007

// Are we sure that 200 is enough //

People that study these things seem to think that's a bare minimum. More is better
-- BunsenHoneydew, Jul 25 2007

A new wrinkle that just occurred to me: buried in the ice a couple of hundred meters in from the outer surface are the preassembled, vacuum-packed re-entry craft, complete with manuals and embedded simulator training software. They will automagically appear to the inhabitants when the inner ice floor melts around them, a few years before planetfall, giving the colonists enough time to familiarise themselves with them and take them out for a few flights.
-- BunsenHoneydew, May 18 2011

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