Trade-offs
Cast It or Print It
Three ways to make a hundred thousand habitat panels. What each one buys you, what each one costs you, and where each one belongs. The first entry in a department that exists to write both columns down.
Every idea in this magazine buys you something and costs you something. Most articles argue for the idea, and the cost gets a sentence near the end. This department is where the cost gets the same space as the idea. Each entry takes one decision, lays out the options, and writes down what you gain and what you give up with each. No winner is declared unless the arithmetic declares one.
The first decision is the one that came out of One Press or Ten Thousand: how do you make a hundred thousand ten-inch panels?
Option one: cast aluminum in a giant press
This is the Giga Press route. Molten aluminum is injected into a die with dozens of panel cavities, the clamp holds it shut, and every few seconds the die opens on a full tray of panels.1
You gain: volume that nothing else touches. Tens of thousands of panels a week from one plant. Every panel identical, because they all came out of the same die. Cheap per part once the die is paid for.
You give up: the material. It has to be aluminum, because no die survives molten stainless. Aluminum is lighter and weaker, and it does not have the fatigue life for a wall that cycles under load for fifty years. You also give up the network: one plant, one die, one supplier, and if the plant stops, everything stops.
Where it belongs: the outer wall. The bumper. The one that gets hit and is supposed to be cheap to replace.
Option two: print stainless in the garages, sinter at the yard
This is the A Thousand Garages route as corrected in Cold, Vacuum, and a Hundred Thousand Joints: a garage printer makes a green part from steel powder in a binder, and the yard furnace, press, and coupon test make the strength.
You gain: stainless, with the strength and fatigue life the structural walls need. A supply chain with ten thousand nodes that no single failure can stop. A part that anyone with a six-hundred-dollar printer can make, which means anyone can also test one.
You give up: speed and consistency. Ten thousand printers means ten thousand slightly different printers, and the scatter in the parts has to be found and driven out by testing rather than designed out by the die.2 The part comes out of the furnace porous and needs hot isostatic pressing to close it, and it shrinks twenty percent on the way, which every drawing has to allow for. The yard does more work than the parent article admitted.
Where it belongs: the structural walls. The ones that carry the spin and the air.
Option three: press dry powder
The century-old route: steel powder pressed in a die at up to fifty tons per square inch, then sintered.3
You gain: no binder, no debinding step, a denser green part than printing gives you, and a process every powder-metal shop on Earth already runs.
You give up: almost everything else. The pressure is per square inch of part, so a ten-inch panel wants thirteen hundred to twenty-two hundred tons all by itself, and even the biggest press ever built only makes three to five of them a stroke.4 It does not scale with the machine. It is not a garage process and it is not a mass-production process either. It is a good way to make a bushing.
Where it belongs: possibly nowhere in this design. Possibly in the yard, for test coupons, where a dense pressed reference part is useful to compare the printed ones against.
Where it lands
The decision is not one press or ten thousand. It is one press for the aluminum wall and ten thousand garages for the stainless walls, and the two are not competing. The cost of that answer is that the habitat now has at least two supply chains, two qualification programs, and two kinds of joint, one cast and one printed, that have to meet somewhere at an edge. That edge is a design problem nobody has drawn yet.
The other cost is that this whole table rests on a number nobody has measured: what a printed stainless joint actually holds, and how much it varies. Until fifty of them have been broken, every line above is an argument. That is why the press test comes before the wall drawings, and not after.
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
- IDRA Giga Press: 5,600 to 6,200 tons clamping force; a single casting replacing an assembly of up to 70 parts. InsideEVs, Learn About Tesla's Giga Press From IDRA, January 2022. ↩
- Binder-jetted 316L: about 3 percent initial porosity, pores clustered in layers perpendicular to the build direction. Roth et al., Rate-dependent strength and ductility of binder jetting 3D-printed stainless steel 316L, International Journal of Mechanical Sciences, 2021. ↩
- Powder compacted in a rigid die at up to 50 tons per square inch. Metal Powder Industries Federation, Industry Facts. ↩
- Editor's arithmetic, laid out in note 9 of One Press or Ten Thousand: 43.3 sq in × 30 to 50 tsi = 1,300 to 2,165 tons per panel; 2.8 to 4.6 panels per stroke at 6,000 tons. ↩
The assignment of each process to a wall is my own proposal, built on the four-wall stack described in One Press or Ten Thousand. The gains and costs listed are the ones I could see; the ones I could not are exactly what this department is for. If you know a cost I left off the table, that is the letter I want.
More from Star Bound
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- Commission It FirstWe have already run phase one. It cost one man 150 million dollars of his own money, and it very nearly killed the people inside.
- Life in the BarrelO’Neill gave us the barrel in 1976 and got very little of it wrong. What he did not finish was the inside — and the standard the inside has to meet isn’t twenty years. It’s forever.
- Worms: The Backbone of CivilizationWhy the first Martians will need a bucket of worms more than another rocket
- Send the Robots FirstWhy the road to Mars runs through the moon, and why the first lunar miners will never leave Earth
- Wet the Ground and WaitA passive water generator for the desert, and why we should build one before we need one on Mars
- Fish, Salt, or DirtThree ways to feed a habitat, what each one costs you, what each one can't survive, and a question for the reader.
- The Box Nobody TestedIn 1991 eight people were sealed inside three acres of glass to prove a closed world could keep them alive. It nearly didn't, and the reason was sitting in the walls the whole time.
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- A Message in a Bottle, Thrown HardEvery article in this magazine is about how to build something. This one is about how to pay for it.
- Grind the Asteroid, Print the PartWhy there will never be a steel mill in space, and what replaces it
- Powder or WireThe two ways to print metal, why neither one is ready for the Belt, and the questions somebody has to answer first
- Bones Don't Travel WellThe one problem no rocket solves, and why Gerard O'Neill worked out the answer in 1976
- Blow the Rock Like GlassMy father's answer to how you build something big enough to spin, and the man who worked it out in 1963
- Sixteen Inches of SteelThe number that breaks the mile-wide barrel, four ways around it, the one we would bet on, and a file you can print tonight
- Launch the Parts, Not the ShipYou cannot launch a habitat big enough to spin. So you launch a shipyard, and you let the robots build it.
- Built for Earth, or Built for Something Bigger?The tools a colony needs are being perfected right now, by people who say they are building them for us
- A Thousand GaragesBefore there is a printer in space, there has to be a shipyard on the ground, and the shipyard does not have to be in one place
- Thirty Thousand Volts and a Piece of Tin FoilI drove an hour and a half to call a man a liar. He turned on a computer monitor instead, and I have been thinking about it for twenty years.
- Out the Side of the MountainTwenty miles of vacuum tube under a Hawaiian volcano, and a freight train that never comes back down. What a ground-based mass driver would actually take, and why it exits the flank instead of the summit.
- That’s Not a Rocket, It’s a Freight TrainHow I wired the one on my bench in 1994, the one I drew and never built, and why a mass driver runs on railroad logic, not rocket logic.
- Cold, Vacuum, and a Hundred Thousand JointsWhat geosynchronous orbit does to the ten-inch panels in "A Thousand Garages," starting with the question every steel man asks first — and one thing that article got wrong.
- Mission Watch: September 2026What private enterprise and the agencies actually did this summer, in the order that matters
- The Question I Asked Buzz AldrinIn 1996 I asked the second man on the Moon what part private enterprise would play in space. Thirty years later, the answer is checkable
- One Press or Ten ThousandElon Musk casts a car underbody in one shot with a machine the size of a house. We proposed ten thousand garages. It turns out we may both be right, on different walls — but nobody knows until somebody breaks fifty panels on purpose.
- Powder or PlateThe garages stay. What's in them changes.
- Refuel It or Strip ItThe graveyard belt is the closest junkyard we've got.
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