Habitats
Blow the Rock Like Glass
My father's answer to how you build something big enough to spin, and the man who worked it out in 1963
In the last piece I said the only answer to gravity that we know works is a structure hundreds of meters across, turning slowly. Then I said the honest problem with that answer is mass. You will never lift a building that size out of Earth's gravity well, and I left it there.
This is the other half. How do you actually build the thing?
The version I am going to lay out came to me from my father, at the kitchen table, when I was young enough to take it as fact. He did not invent it. I am nearly certain he read it somewhere and carried it around for years the way he carried a lot of things, and then handed it to me. I have since found where it came from, and I will get to that. But I want to give it to you the way I got it first, because the way he told it is still the clearest version I know.
The way my father told it
Find a metal asteroid. Not a rubble pile, not a ball of ice and dust. A solid nickel-iron body, the kind that used to be the core of something bigger before it got smashed apart.
Drill into it. Mine out the center, the way you would drive a shaft and then open a room at the bottom of it. Take out as much as you can and keep the ore, because that is feedstock and you will want it later.
Now pack the cavity full of ice. Water ice, from wherever you can get it, and in the belt that is not hard. Fill it. Then weld the door shut. Seal the whole thing up so it is a solid rock again with a core of ice.
Then heat it. Get the outside red hot — with lasers, with mirrors, with concentrated sunlight, with whatever you have. The rock softens. It does not have to melt through; it has to get plastic, the way a bar of steel goes soft in a forge before it goes to liquid.
And when the heat reaches the ice, the ice turns to steam, and the steam has nowhere to go.
So it pushes. It pushes outward against a shell that is now soft enough to move, and the asteroid balloons. It swells up like a bottle on the end of a glassblower's pipe, and what was a solid rock with a small chamber in the middle becomes a hollow shell with an enormous chamber in the middle.
Let it cool. Now you have your ship. Now you spin it.
And the part he always ended on, which is the part I think matters most: when you are done, you have three or four feet of solid rock all the way around you. Every direction. Radiation shielding you never had to launch, never had to bolt on, never had to think about, because it is the hull.
Where it actually came from
The idea is Dandridge Cole's. He was an aerospace engineer at General Electric, a former paratrooper, and one of the real visionaries of the early space age, and he died of a heart attack in his office in 1965 at forty-four.1 Most people have never heard of him. I had not, until I went looking for where my father got this.
In 1963, in a book written with I. M. Levitt, Cole proposed hollowing out an asteroid something like thirty kilometers long, spinning it on its long axis for gravity, bouncing sunlight in with mirrors, and building a countryside on the inner wall.2 The next year, with Donald Cox, he went further in a book called Islands in Space and described how you would make the hollow. Heat from solar mirrors. The rock fused and shaped from the inside, he wrote, the way a glassblower turns a small lump of molten glass into a large empty bottle.3
That is the sentence my father carried. I recognized it the moment I read it. He had the mirrors, he had the glassblower, he had the whole picture. What he added, or what somebody added between Cole and him, was the ice. Cole's version relies on the volatiles already inside the rock boiling off when the heat gets to them. The version I was given packs the ice in on purpose, so you are not gambling on what the asteroid happens to contain. I think that is the better version, and I do not know whose it is.
So Cole gets the credit. He was drawing this thirteen years before O'Neill drew his cylinder, and O'Neill's cylinder is the one everybody remembers, because O'Neill's was a metal structure you could imagine somebody building, and Cole's asked you to believe you could blow up a mountain like a balloon.
Why I think Cole was right and O'Neill was practical
O'Neill's answer to the mass problem was a mass driver on the moon, throwing lunar material up to a construction site. It is a good answer and I have written that I believe in it. But look at what it asks you to do. Mine the moon. Refine the material. Fling it into space. Catch it. Refine it again. Roll or print it into structure. Assemble a cylinder miles long out of pieces, in vacuum, with people or robots doing the assembly. Then pile more material on the outside for shielding, because the structure itself is thin.
Now look at what Cole asks. Go to the rock. Dig one hole. Fill it. Seal it. Heat it. Wait.
Every one of those steps is enormous, and I am not pretending otherwise. But there is no assembly. There are no pieces. There is no shielding to add, because the shielding is what is left over. The material never gets lifted anywhere; it stays exactly where it already was and just changes shape. That is the thing about this idea that has never let go of me. It does not fight the mass problem. It uses the mass.
The parts I cannot answer
I am a builder, and I have spent forty years watching good drawings meet real materials, so I am going to be honest about what I do not know.
I do not know whether a nickel-iron body heated to plastic will swell evenly. A glassblower turns the pipe, constantly, because glass sags and thins where it is hottest. A rock the size of a town does not get turned. You would need heat that is very even, or a way to spin the whole thing while it is soft, and I do not know what that looks like.
I do not know what the shell does when it thins. Three or four feet of rock is the number I was given, and I have kept it because it is the right kind of number, but it is a hope, not a calculation. Somebody has to work out how much ice, how much heat, how big a rock, and what the wall ends up being.
I do not know if there is a metal asteroid of the right size in the right place. The belt is a big place and metal bodies are the minority. That is a survey problem, and it is the kind that a robot can do long before a person gets there.
And I do not know what the inside of the chamber looks like when it cools. Smooth like the inside of a bottle, or torn and cracked like slag. That decides whether you have a hull or a cave.
Any one of those could kill the idea. I am putting it in the magazine anyway, because the reason we have not answered those questions is not that they are unanswerable. It is that almost nobody has asked them since 1964.
One idea among many
I said in the gravity piece that spin is the only answer we know works. I want to be careful not to say the same thing here about how you build it. This is one way. O'Neill's is another. There will be others that neither of them thought of, and some of them will be better, and I hope some of them show up in this magazine written by somebody who knows more than I do.
But if you had asked my father, he would have told you this was how it gets done. Find the rock. Fill it with ice. Seal the door. Heat it up and let it grow.
I still think he might have been right.
From one explorer to another, we appreciate you reading this far. We are excited about what this endeavor brings, and we would like you along for the rest of it.
Come join us. Because we are Star Bound.
John LangEditor
Ideas in Star Bound are published open — take them, build them better. Our open proposal.
A note on where this comes from. I am not a metallurgist, a spacecraft engineer, or a degreed engineer of any kind. But I am a practical one, with more than forty years in heavy industrial construction: welding, millwright work, hydraulics, mining, and thirty-three years of electrical construction and commissioning on the North Slope of Alaska, in a place that punishes anything built wrong. Much of that time I have worked as a field engineer, which means I am the one standing in front of the equipment when the drawing turns out to be wrong, and the fix has to be made on the spot, with what is on hand, and has to work the first time. Anyone who has done that long enough learns that a lot of engineering gets corrected in the field by people with more experience than the people who drew it. That is the eye I bring to these subjects: not what should work on paper, but what actually gets built, and what breaks. The facts I take from other people are footnoted so you can check them and read further. The ideas built on top of those facts are my own, and I would rather see them knocked down by somebody who knows better than left standing because nobody looked.
Sources
- Paul Gilster, Remembering Dandridge Cole, Centauri Dreams, 2012 — Cole died of a heart attack in his office at General Electric's Space Technology Center in Valley Forge, Pennsylvania, in 1965, at forty-four; he also coined the term “macro-life” for human colonies in space. ↩
- Alex Michael Bonnici, Islands in Space: The Challenge of the Planetoids, the Pioneering Work of Dandridge M. Cole, National Space Society — the 1963 proposal, with I. M. Levitt in Exploring the Secrets of Space, to hollow an ellipsoidal asteroid about 30 km long and spin it on its major axis for gravity. ↩
- David Darling, Cole, Dandridge MacFarland (1921–1965) — the “nomadic pseudo-earth” of Cole and Cox's Islands in Space: The Challenge of the Planetoids (Chilton, 1964), hollowed by “fusing and sculpting” with “heat from solar mirrors,” producing a “gigantic geodesic interior chamber” the way a glassblower shapes a lump of molten glass into an empty bottle. ↩
The packed-ice variation is the version I was given by my father; I have not found it in Cole's own writing and do not know where it originated. The behavior of a plastic nickel-iron shell under internal steam pressure is a question I am raising, not answering, and nothing in this article should be read as a calculation.
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