Ice Rocket

[mike alexander]

For a story I'm working on I need to send mined lunar water up to a Mars spacecraft being built in lunar orbit. The concept I've designed is a rocket made out of ice (strictly speaking, hollow-cast ice fuel tanks holding the LOX/LH2) on top of an engine akin to the original Rocketdyne RL-10. All-up mass at launch around 50,000 lbs. Very roughly, imagine a rocket the size of a V2 made mostly from frozen water. The (alternate) timeline is the late 70's - early 80's, using materials/concepts of the time or those that were being developed and discussed.

Anyone ever heard of such a thing, even as a paper concept? As fiction, accuracy would be nice, but verisimilitude is adequate.

[antoniseb]

I'm picturing that you'd be building and launching it at night. Visually this is a compelling item for your story.
I think the things you'd want to check on are the various material strength of LOx temperature water ice, and perhaps its solubility in your fuels.

[Jeff Root]

That's insane.

I prefer nuclear-powered mud rockets.

-- Jeff, in Minneapolis

[pzkpfw]

Are they also mining asbestos or something on the Moon? I'd suspect there's a need for something fibrous in the ice to add some tensile strength.

[mike alexander]

I'm picturing that you'd be building and launching it at night. Visually this is a compelling item for your story.
I think the things you'd want to check on are the various material strength of LOx temperature water ice, and perhaps its solubility in your fuels.

Launch will be from inside a shadowed polar crater. Water mined there and cast, tank two half cylinders melted together. Probably separate LOX and LH2 tanks due to differential shrinkage of ice at different cryo temperatures.

I would expect the ice to be very clear (no dissolved air to cause bubbles) but casting imperfections should give an uneven surface, which should look very pretty when it hits sunlight. Wall thickness on the order of 8-10 inches depending on final design. Minimal tank pressurization, fuel feed from small turbopump.

[mike alexander]

Are they also mining asbestos or something on the Moon? I'd suspect there's a need for something fibrous in the ice to add some tensile strength.

I just don't know. Ice is strong in compression but I have no idea how much internal pressure a cylindrical tank made of ice at cryo temperatures could stand.

[mike alexander]

That's insane.

I prefer nuclear-powered mud rockets.

-- Jeff, in Minneapolis

Well, the Mars rocket is a NERVA using water as the working fluid. Lower efficiency than LH2, but no worries about cryogenic storage.

[Van Rijn]

Are they also mining asbestos or something on the Moon? I'd suspect there's a need for something fibrous in the ice to add some tensile strength.

A bit like pykrete. I was thinking the same thing - ice isn't that strong. A composite could be much stronger.

I can't recall any real examples of ice rockets. The only things I've ever heard of that are vaguely similar is an idea for a deep space rocket using hydrogen (deuterium actually) ice composite for a fusion rocket and an Asimov story returning Saturnian ice to a (very dry) Mars. In that case, water was heated to steam by a nuclear rocket engine.

[Jeff Root]

Asimov's story is 'The Martian Way'.

The nuclear-powered mud rocket is a design by Anthony Zuppero
from the Idaho National Engineering Laboratory. Put a nuclear
reactor on an icy body like a comet nucleus, surround it with
something to capture water vapor (put it in a body bag), and
produce superheated mud for propulsion.

I didn't realize you were going to launch the ice rockets from
the Moon's surface. I thought you were transporting the water
from the Moon to lunar orbit, and building the rockets there,
where you could have low acceleration to leave lunar orbit and
go into Mars orbit. I thought that was insane. Expecting the
ice to hold together during launch from the surface is insanely
insane. But it explains why your rockets are so small.

Peter Kokh, in Milwaukee, publisher of the 'Moon Miner's
Manifesto', who essentially *is* the Lunar Reclamation Society,
and is allied with the Moon Society, has put an enormous
amount of thought over the last three decades or so into using
lunar resources to do anything you can imagine. He has made
simulated lunar concrete and has ground up simulated lunar rock
to make pigments for paints to be used on the Moon. I've seen
paintings he made with them, on substrate which could be made
on the Moon from indiginous material. I ate a meal he designed
which consisted entirely of foods which could be grown on the
Moon. A lot of what he has written could go into any story
involving the Moon.

-- Jeff, in Minneapolis

[mike alexander]

Jeff,

The rockets are small so they can use extant 70's technology (sic). The story is set in an alternate timeline where both the US and USSR get to the moon and cold war pressures drive a first-to-Mars race. That's just the backdrop for a murder mystery, though. 95% of the background work never shows in the story, anyway.

[Noclevername]

Fiberglass might make a suitable strengthening agent for the ice. I remember reading a book in the 70's by Gerard O'Neill where he talks about making fiberglass from slag tailings from regolith aluminum processing, or maybe it was directly from regolith, but I'm fuzzy on the details. Maybe the ice miners could take a suitable material from their shelters or worksite and "rebar" the ice with it.

[caveman1917]

Wasn't there a plan/idea to build aircraft carriers out of ice during WW2? I think they were planning on using pykrete, but on the other hand that wasn't at cryo temperatures so might not be necessary. Either way, perhaps you might find something relevant there.

ETA: It was project habakkuk

[mike alexander]

The problem with putting stuff in the ice to strengthen it is that you have to then filter it out to use it. And then before that you have to make the additive and figure out how to keep a uniform suspension during freezing. Et cet. And, we're talking relatively low accelerations here; I'd be more concerned with vibrations. And it is assumed that any such system would be working on the edge of practicability, with some failures (such a rocket getting up into the sunlight and then disintegrating would be another nice image).

Looking back, Apollo was an engineering triumph. Other than that, it was nuttier than a good fruitcake. This just takes the premise and stretches it closer to insanity.

As to why not just do the whole thing in LEO and ship the water up from earth instead... there are economic-political considerations at work.

[orionjim]

Maybe you could invent something like a Ranque-Hilsch vortex rocket. Use the hot end for lift and the cold end to keep the ice frozen.

See: http://en.wikipedia.org/wiki/Vortex_tube

Jim

[Buttercup]

All you have to do is switch on the ignition, put it in drive, and keep the object in direct sight -- heading straight for it continually.

Does that help?

[mike alexander]

orionjim, the vortex tube is amazingly cool (yet another device I never heard of before). I will keep it in mind for future speculations.