I recently inherited my wife’s father’s old slide rule, which he used when he went to the (now gone) Royal Roads Military College. It is stamped “Made in Occupied Japan.” World War II was still recent history.
I already had one that I had bought for myself way-y-y-y back in the day when these new-fangled electronic calculators were beyond the means of a struggling country boy. It’s a Versalog, pretty much the Rolls-Royce of slide rules. I’ve been knocking the pretty thick layer of dust off my skills with them, and that got me thinking.
“What’s a slide rule?” There will be a lot of people asking, to the accompaniment of puzzled looks. Well, the world wasn’t always awash in cheap computer power. By the way, I don’t disdain that, at all. I’m writing this on a medium serious Linux workstation.
They look like this. They’re simple, rugged, don’t need batteries or electricity, and can be hand-crafted with 18th century technology. Until calculators put them out of business, they were the mark, and the indispensable working tool, of the engineer and scientist.
It is instructive to look at what can be done with such simple and easy to make tools, and there are some literary situations where your characters can’t just whip a smart phone out of their pocket. I’ll get to that a little later.
A very science fictional equation is the rocket equation, which basically determines the performance of your rocket ship. It goes like this.
ΔV=Ve * ln(Mw/Md)
Where ΔV is the change in velocity the rocket engine(s) can give you, Mw is the mass of the spacecraft fully fuelled, Md is the empty mass of the spacecraft and Ve is the velocity of the rocket exhaust.
That short equation is the rod across the back of anyone who wants to build a rocket of any size. It covers the fact that you need to carry the fuel to carry the fuel to get you to where you’re going. Then, you have to decelerate again, unless you’re building a missile or re-entering into an atmosphere, so at a minimum you need twice that \Delta VΔV. Then, pilots like to have a margin of fuel for whatever the mission is.
The saving grace is how good the rocket engine is, measured by how fast it spits the fuel out the back. The Space Shuttle Main Engine is about the best chemical rocket engine ever built, and it gets 3400 m/sec. Plug that into the rocket equation and start looking at mass ratios, and very quickly you discover why the Shuttle External Tank was so darned big.
A slide rule can tackle this problem just fine. Divide the masses, move the cursor to get the natural log, multiply by the Ve, don’t like the answer and add more fuel until you get to the amount of fuel needed to get to orbit.
The size and mass of the tanks needed to carry all that fuel are simple enough, too. Area and volume of a sphere are quick to do, then multiply by the thickness of tank walls and the density of the material to get the mass, and don’t like that answer either.
Okay, point made. For those who want more on this subject, there is lots more at the incredibly useful Atomic Rockets web site run by Winchell Chung. It’s on my bookmarks toolbar.
So, in a post-collapse world where the resurgent civilisation is heading back to space, they aren’t going to have all those computers. They can still build spacecraft. They may not be quite as elegant, but they’ll get there. They might not even be interested in rebuilding the advanced computer networks of our day if they failed spectacularly enough.
In my novel Spymaster’s World, the fallen Galactic Empire left behind a lot of virtually immortal FTL starships. Problem was, the AI’s that ran them failed or went insane over the centuries, so the resurgent civilisation led by the Dux Avalonis winds up using slide rules and telescopes to navigate among the stars. The Apollo astronauts did just that. It was a backup to the primitive computers in the spacecraft.
An offshoot of technology is steampunk, where Victorian level technology is central to the whole genre. Now, most of the books I’ve read in this genre are more about dashing adventurers riding airships rather than the engineers who build them and the crews who navigate them, but both will very likely be putting a lot of wear on their slide rules to determine the answers to questions like, “Do we have enough fuel to make port?”
How about fantasy? I’m pretty sure I’ve never seen anything like that in any fantasy world. If magic requires mathematical computations instead of just pointing a wand and doing an incantation, then a wizard might tote a slide rule.
Duke Hardcastle glared down at the elven wizard, wondering why he was fiddling with this computing device instead of getting on with casting the spells which would end the siege of the rebel stronghold at long last. “Why are you wasting my time?”
The elf looked up at him, twitching his ears disdainfully and setting his slide rule aside. “Your Grace, if you wish my blasting spells to hit the gates of the castle instead of your own troops, I will trouble you to let me complete my calculations uninterrupted.”
Here and there in the modern world, slide rules still survive. A lot of pilots use the E6B flight computer to do a lot of the calculations required for flight. It’s a specialised slide rule that’s rugged, simple and doesn’t need batteries. There are other examples, as well.
I’ll end with a personal anecdote. When I worked in an operations centre whose business was tracking nuclear capable bombers, we did indeed use a lot of computers. When I was reporting to the Senior Ops Officer and I wasn’t at my computer, it was very helpful to be able to glance at my watch, set the circular slide rule built into it, and give him a good-enough ETA to our own airspace right away when minutes mattered.
Simple, rugged and reliable technologies have their place, even in future worlds.
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