Those are from Expanse? I believe those are fusion drives, which aren't quite as terrifying as photon drives. Although you still don't want one touching down at your local airport.
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Yeah the Expanse. Hmm I need to read up on power calculations more.
aug 31, 2025, 4:05 pm • 0 0 • view
One way to look at it is to consider how much mass at what velocity one is hucking out the back. Again, 100 tonne rocket, 2 g acceleration, V exhaust is 5,000 km/s. Yes, mixing units is Satan's work. MV = mv, where M is ship mass, V ship velocity, m reaction mass, v reaction mass velocity.
aug 31, 2025, 4:16 pm • 2 0 • view
We want MV/v = m. If we want to add 20 m/s in one direction, then (100,000 kg x 20 m)/5,000,000 m/s = 0.4 kg get thrown out the back. Ek = 1/2mv^2, so .2 x (5,000,000 x 5,000,000) ... 5 trillion watts? I think. My coffee is broken and my calculation is downstairs.
aug 31, 2025, 4:21 pm • 3 0 • view
yeah over the years i’ve learned that “physics calculations on my phone” tend to go awry.
aug 31, 2025, 4:22 pm • 0 0 • view
This ignores mass ratios, which is OK because so do most SF novels.
aug 31, 2025, 4:22 pm • 3 0 • view
I've got a product that gives authors easy lookup tables for mass ratios...$3! Cheaper than a cup of coffee! Or a bottle of dihydrogen monoxide at an airport or concert venue!
aug 31, 2025, 4:33 pm • 1 0 • view
Oh, I can do mass ratios. It's just that in this case, it's an unwanted complication.
aug 31, 2025, 4:44 pm • 1 0 • view
Heinlein had a odd quirk, which is that he could do mass ratios as long the power source was moderately shitty (chemical, single-H, NTR) but he seemed to think they didn't apply to total conversion drives.
aug 31, 2025, 4:25 pm • 3 0 • view
This is actually an area where slide rules would probably be pretty useful.
aug 31, 2025, 4:27 pm • 0 0 • view
My slide rule is upstairs. On average, my computing devices are where I need them.
aug 31, 2025, 4:28 pm • 2 0 • view
The Kzinti Lesson. tvtropes.org/pmwiki/pmwik...
aug 31, 2025, 4:24 pm • 3 0 • view
Niven also had a story about why handing random people Bussard ramjets might be a bad idea, unless you don't mind the occasional lunatic using one to express his displeasure.
aug 31, 2025, 4:27 pm • 4 0 • view
yeah the math on those magnetic fields would involve a lot of digits somewhere. (KSR’s version, basically an Orion drive with a reverse ramjet pushing particles out of the way, made a lot more sense)
aug 31, 2025, 4:30 pm • 1 0 • view
Any narratively interesting drive has outputs measured in war crimes per second. If you want to get a feel for flying one of those things, boy have I got boardgames for you... @adastragames.com has the deets.
aug 31, 2025, 4:32 pm • 2 0 • view