Assume a 100 tonne ship, 20 m/s/s acceleration. 100,000 kg x 20 m/s/s x 300,000,000 m/s = 30 trillion watts or about a Hiroshima per second. Given the captain is nearly broke, do you want him to have a 1 H/s drive as a negotiating tool?
Replies
The danger would be mitigated by using a graviton drive (same power/force relations, but very little environmental impact), but one still has to consider what energy source is providing all that power to the drive....
aug 31, 2025, 3:27 pm • 1 0 • view
Good math! The Rocinante would be an order of magnitude bigger (5g max acceleration, and 3-5x the weight seems to be the best guess) so ~10 H/s. The Donnager and the like seem to be in the 100kton range so even assuming 2G max, that’s ~1000 H/s.
aug 31, 2025, 3:33 pm • 2 0 • view
Seems like an optimal battle tactic would be “come in fast and decelerate at your enemy”.
aug 31, 2025, 3:34 pm • 1 0 • view
This is basically Larry Niven's Kzinti Lesson: "A reaction drive is a weapon, powerful in direct ratio to its efficiency."
aug 31, 2025, 4:02 pm • 2 0 • view
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.
aug 31, 2025, 3:37 pm • 4 0 • view
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
this is one of the main reasons I restrict my tramp freighters to the moons of Saturn, where the equivalent of a space shuttle main engine is more than sufficient
aug 31, 2025, 3:57 pm • 0 0 • view
Oh, hey. Hi there, basic math error. Forgot to multiply by 20. Make that 600 trillion watts or about 20 Hiroshimas per second or maybe 10 Tsarbombas per day.
aug 31, 2025, 3:54 pm • 1 0 • view
"20 Hiroshimas Per Second" would also be a great name for a band
aug 31, 2025, 3:58 pm • 3 0 • view
I wonder if H Beam Piper's Hellburners were an unintentional by-product of fusion drive research?
aug 31, 2025, 4:02 pm • 1 0 • view
Don't know that, but the Niven short Story, The Warriors has entered the chat.
aug 31, 2025, 4:11 pm • 2 0 • view