I shrugged. Maybe Alexei thought this was exciting, but I didn't. We'd grown up in a tube‑town–which is really just a polite way of saying we lived in a giant sewer. No kidding. Any tube that failed the structural integrity tests for piping sewage was still considered strong enough for housing. They all came out of the same factory. So I didn't see that a used shipping box was all that much of an improvement, especially not one with 450,000 kilometers on it.
On the other hand, if you had to live in a used shipping box, you could do a lot worse than a Lunar cargo pod. Alexei showed us how the hull of the pod was made out of six simple pieces: four identical curved hull sections, each describing a 90‑degree arc, and two identical circular end pieces. Each piece was designed to fit into every other piece, and each panel had its own hatch and window.
Also, each hull unit had two survival cabinets, one at each end. Each cabinet contained the minimum basic life‑support supplies necessary for one person for three days; so the pod had eight total. Alexei showed us how each of the survival cabinets held food, water for drinking and ballast, oxygen‑recyclers, self‑heating blanket‑ponchos, first‑aid kits, plastic toilet bags, and personal survival bubbles because you can't pack space suits in enough different sizes. And please read the instructions before opening anything.
Mickey explained that the pods were essentially the spacegoing version of an Antarctic explorer's travel‑hut. A onetime pod doesn't need the same kind of precision machinery as a reusable vehicle, and it's unnecessary to build a whole lander for the delivery of cargo, so the steering and braking systems were the cheapest brute‑force method possible.
"Is the engines that are most clever," Alexei said, glancing at his wrist. "Nyet–not to worry. We are fine for another ninety minutes. Time enough for lesson. I explain fuel rods. Is really quite simple. How do you fire rocket in space? No oxygen in vacuum, da?So you put oxygen in fuel mix. Make whole thing one solid tube of fuel. Ignite at one end, it burns until fuel is gone. Is very efficient booster system. But one big problem with solid‑fuel booster. Timing. Once burn starts, you cannot turn it off. So is not good for precision burns, da? Nyet,we find a way. Is much simpler than you think–we use Palmer tubes. Invented by engineer with too much time on hands. Name of John Palmer. Playing with his poker chips at Las Vegas. Very famous story, I share with you.
"Dr. John Palmer, famous engineer, sits at roulette table, thinks of mathematics of chaos and order. How good luck, bad luck both run in streaks. How random numbers cluster up. Thinks about composition of solid‑fuel boosters. Meanwhile, he stacks chips, red and black, red and black, red and black. Then he runs out of blacks, so he stacks two red, one black, two red, one black. Suddenly light goes on in head. He pushes everything onto double zero and gets up from table. Wins eleventy‑thousand plastic‑dollars anyway–almost forgets to collect winnings, he is so excited.
"He rushes back to laboratory and invents Palmer tube. I explain. He slices solid‑fuel rod of metallized hydrogen into little flat poker chips. Very thin. In between, he puts little polycarbonate separators, even thinner. Separating disks are made of several layers, perforated and corrugated and shaped to be strong on one side but weak on the other; crisscrossed with grooves so that weak side looks like business side of nail file. Strong side looks like mirror. Very clever, da?
"Then Palmer gets even more clever idea. When he makes separator chips, he paints circumference with liquid conductor. When he makes rod, he glues insulatedwires down each side. He makes whole thing in polyceramic tube, holds fuel rod like gun barrel.
"Works like this. Turn on current, juice goes down wires, da?All the way to end of tube, to bare ends of wires–last separator in line has shiny side out, grooved side in. Conductive ring around separator chip completes circuit, ignites fuel chip in front of it. Creates ring‑shaped ignition. Most efficient explosion. Fuel slice vaporizes, separator vaporizes– bing!Next separating disk in line is shiny side out, strong enough to protect next fuel slice–remember, separator only weak on grooved side, not shiny side; so when force of explosion hitsshiny side, next separator works like back wall of combustion chamber for just that moment. Da?So you get one little poof of thrust. Only one.
"But explosion also heats ignition wires, melts insulation off–enough so that bare wires now touch next separator disk. If there is still current, that disk completes circuit and ignites fuel slice behind it–and whole process happens again. Fuel slice explodes and vaporizes separator disk that ignites it, but does not ignite nextdisk again. And just like before, next separator is back wall of combustion chamber and you get next little poof of thrust. And process starts again. Wires melt a little more, and if there is still current, next disk goes bingtoo. Everything happens very fast– bing, bing, bing, bing, bing, bing, bing, bing–like so.
"As long as current flows through wire, disks blow off the end of the tube, one after other. Is like packing whole bunch of bullets in same barrel, but no bullets, only charges. When you burn enough fuel, you turn off current. Explosions stop. Thrust stops. Is beautiful clever, da? Da?
"But firing tubes like this– bing, bing, bing, bing, bing–makes very unpleasant pulsing effect. Not a fun ride. Like sitting on machine gun. Not a problem. You bundle tubes together. Tubes not work in sync, all the little bing‑bingsaverage out. Instead of machine‑gun feeling, you get corrugated road. More tubes, more average, more smooth–but smooth not needed for cargo, packages don't complain, so is still rough ride, but tolerable, da?Never mind. We get there. Palmer bundles guarantee delivery. Is simple brute‑force brilliant. If one tube in bundle fails, no problem; others make up difference. Thrust monitor in bundle manages everything. You need this much thrust? Fire tubes until. Da!
"Here is more brilliance. Palmer tubes can be any size. As thin as paper clip, as thick as elephant leg–we have elephant on Luna, you know, baby female; you must come to our zoo, see baby elephant bounce–much funny. Anyway, Palmer tubes and Palmer bundles can be made all sizes. Use different size bundles of tubes for all different purposes. Heavy lifting, braking, steering, attitude adjustment, lots of useful boost. Launch to orbit from Luna or Mars. Very efficient. Bring asteroids home for mining. Deliver cargo pods anywhere. Fling them off Line, steer them to destination, brake to match orbit.
"This is why Palmer tube is so brilliant. Volume manufacture makes space travel cheap. Palmer tubes as easy to make as pencils. Put in red goop here, blue goop there, black goop over there, run the machine, stack the firing tubes here. Bundle together, plug in timing caps and thrust monitor. Da?Very cheap. You can put three sets of boosters and a thrust monitor on a pod for less than a thousand plastic‑dollars. And whatever part of tubes are left over at destination can be used for other things.
"You know story of Crazyman Tucker? He lived in old cargo pod. Very nice pod too. Much fancy. He collected unburned ends of tubes for years, he finally bundle them into big cluster, launch his pod into Lunar orbit. Another cluster of tubes sends him off to rendezvous with Whirlaway rock. He almost makes it too. What some people won't do to avoid export taxes, da?But rescue costs more than taxes. So he lose entire fortune anyway. He should have used Palmer tubes for more mining. Get more rich. But he say, 'What good is money on Luna? Nothing to do but throw rocks at tin cans. And you have to bring your own rocks.' Is very forbidding planet. But you will like, I promise. I teach you to fly at Heinlein Dome. You will have so much fun, you will never want to leave."