Knights of Sidonia aka Shidonia no Kishi - Misunderstood physics in Mecha Anime

[RedPine]

Knights of Sidonia is the sort of anime where when the characters say "All 256 pilots are deployed" there are actually 256 mecha on screen and 256 pilot pictures in the command center. Rifles have recoil and limited ammo, halfway to your destination you turn around to decelerate, and spacesuits have catheters. Sadly, like most fiction, this attention to detail does not extend to basic physics.

"Clasp Hand Formation" - In the show, it is shown that if you want to make a mecha fly fast in space, give it a big jetpack. So far so good. Next, if you want to make a mecha fly even faster in space, have it hold hands with another mecha with a jetpack. Keep in mind that both mecha fire their jetpacks and run out of fuel at the same time. Then if you want go REALLY REALLY fast, have 256 Mecha with jetpacks hold hands... and fire their engines at the same time, thus running out of fuel at the same time. (Keep in mind that the jetpacks are heavy and can be ejected.)

Railgun Mecha Launcher - At the same time as the "try not to run out of fuel" speech, the Mecha's are being launched out of the FRONT of the ship when the enemy they are fighting is BEHIND the ship.

Spacecraft Turn in Wide Circles - No comment. Clearly spacecraft have the maneuverability of oil tankers.

Accelerating at 5g's - To escape, the Sidonia fires the right engine while keeping the left engine off, in order to accelerate and turn rapidly. So far so good. If you do this while the engines are firing at 5g's, you get 5g's worth of structural damage inside the spacecraft due to "perceived" gravity coming from a 90 degree angle from where it normally does. Wait a sec - if you have a craft approx 30km long and 5km wide, the center of mass is near the center, and you accelerate from a single engine at the rear of your craft... here's a diagram:

XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

XOOOOX????????????????????XMMMMEngine Firing This Way ---->

XOOOOX????????????????????XMMMMX

XOOOOX????????????????????XMMMMEngine Turned Off

XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

X=Hull

O=Ocean (heavy)

?=Open air and hollow structures (light)

M=Engine Stuff(heavy)

Obviously, firing only one engine will cause gravity to come from a up to a 90 degree angle relative to the rest of the craft from the perspective of the people in the area labelled "??????". Clearly, firing only a single engine at 5g's imparts imparts 5g's worth of apparent gravity at a 90 to 45 degree angle... Note that the craft only turns about 45 degrees, so centrifugal force is not an issue. Anyway, the resulting trajectory is at a 45 degree angle compared to the original vector. The original vector was the result of periodically firing the engines over a thousand years, and the new trajectory was obtained after just a few minutes.

[T-Bouw]

And in spite of all of this, I still enjoyed Knights of Sidonia. Both seasons.

Maybe it's because I like mecha's even more and those are hardly realistic...

Planetes does the physics even better for an anime. I watched and enjoyed that one after a recommendation on this forum.

[problemecium]

If possible, could a mod merge this into http://forum.kerbalspaceprogram.com/threads/123458-Knights-of-Sidonia please? Just so we have one nice big place to talk about this without having to sort between physics discussions and general comments.

So anyway, here's my answers to OP's comments:

- Last I checked, the clasp formation isn't really to boost speed so much as keep the Guardians together. I suppose also it ensures that if one engine underperforms, that guy doesn't get left behind.

- I don't think that Kidonia's engines are capable of producing more than 1 G (I may be wrong). My thinking is that the artificial gravity is running parallel to the engine. Assuming they don't have a way to flip it to negative, then as the engines power up, the artificial gravity can power down to maintain roughly 1 G. At full throttle, the engines' acceleration would provide all the artificial gravity - but if they went above that, yeah, people would get pancaked and buildings would collapse. Of course this only applies when both engines are firing symmetrically; fire one or the other and yeah, you'll get sideways gravity as shown in the manga / anime and the OP here.

- I think they launched Guardians out of the front because they didn't have launchers in the back. Guardians can just fly around to the back anyway.

- I have a bigger problem with the fact that the center of thrust on the Guardians seems to be way off center.

- So they tried to save resources by making humans photosynthetic. But we still have the law of conservation of mass. Humans will still need to consume the same amount of matter to stay alive - it's just changed from conventional food to uh, other chemicals.

'Course I still loved the anime and the manga. I'm not a mecha person, but fortunately it's not overly heavy on the mecha motif.

[vger]

Gotta say, even if it were realistic, I find the concept of a bunch of Mecha in such a formation to be rather silly.

"I'm scared. I've never done an escape burn before."

"It'll be alright. Here. Hold my hand."