My current movie bugbear: Non-rotating with a large rotating section for the human habitat. Bonus points if the habitable part spans both the rotating and non-rotating portions and the crew can move freely between them.

It's an absurdly complex challenge to build it this way, it introduces an open set of failure modes that would not otherwise exist and there's no good reason for any of it that I can think of.

Instead, rotate the whole ship, and if there are a few things which for some reason must not be rotated (scopes, antennae and cameras, perhaps?) place them in the smallest and simplest possible unpressurised nonrotating segment at the axis.

(If you're using solar collectors and your path isn't radial to the sun, then you don't want the solar collectors to be mounted to the rotating part either. But we've already established that you'll want some minimal nonrotating section with power and comm links, so that's covered.)

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(2001: A Space Odyssey got one thing right, at least: the rotating section was fully contained within the pressurised hull, so you didn't need to build and worry about atmospheric and life-support couplings. 2010 and The Martian, etc, didn't even have this mitigation.)

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By contrast, 2001's Discovery centrifugal habitat ring, thanks to being wholly contained within the pressure hull, was not different in any important way from having a hamster wheel in an Apollo command module. You could plan it in such a way that you could avoid the need for much in the way of crazy-robust and complicated couplings. A single -- admittedly probably pretty elaborate -- coaxial power and data link, some WiFi (1968 version) and simple package transfer of solids and liquids and you're all set. In principle.

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@pieist cinematically it should also make sense to do this, have the camera stabilised on the ships main section, the antennae/solar panels mount rotating majestically with the stars in the backdrop.

I can see it looking like a small propellor on the spindle of the ship, as less velocity than if they were on a rail outside of the main ring.

@pieist Seems like you'd be spinning up a lot of mass that doesn't need it, like fuel and propulsion systems. Doing solar power would be harder. Depending on the ship's mission you might want zero-G labs and workspaces, and there is also the question of auxiliary craft docking (think Discovery's pods in 2001).

@chris Doesn't seem like the same scale of problem. The energy cost of spinning the ship is vanishingly small compared to that of sending it many light minutes outward into the Solar System, and if your fuel tanks or whatever don't want pseudogravity, put them at the axis. That's ideal anyway because it helps with the balancing issue as they are depleted.

@chris (Oh, 2001 depicts docking at the hub, because the space station in Act II is wholly rotating. Also, the Discovery's rotating section is wholly enclosed within the pressure hull, unlike say the one in The Martian or 2010, so they didn't have the massively problematic environmental coupling problem.)

@pieist You're quite right, the delta-v to spin up/down is fairly small. I think Discovery's spinning section probably has 75% or so of the environmental coupling needs even if enclosed in the sphere (power, water, ventilation, networking).

The PanAm docking sequence always struck me as an overly complex maneuver, as you have to map translations to a spinning reference and execute thruster burns accordingly. Hmm, wonder if I could try that in KSP...


Agreed. Stationary core and rotating ring is insanity.

Bridging the rotating/ non-rotating interface with power cables is difficult (slip rings or a Canfield Joint).
Bridging the interface with sewage lines is freaking impossible.

Just spin the entire ship already.

@nyrath Yep. The worst part is the atmospheric seals. One or multiple rotating rings that have to keep air in? Nutjobbery.

(2001: A Space Odyssey, unlike say The Martian or 2010, didn't have that problem: the rotating ring was fully enclosed within the pressure hull, which at least avoids that huge problem. Putting the toilets in the nonrotating portion solves the sewage issue as well, though they don't depict that.)

@nyrath @pieist Stationary core and rotating ring was the defacto standard for comm sats (particularly from Hughes) for many decades. The electronics and antennas were on a despun core, surrounded by a rotating "drum" that provided solar power, thermal regulation, and stability as a giant flywheel.

You'd never build a satellite like that today, but it was a very clever and robust design for the time.

@simonbp @nyrath Awesome. Thanks for that. The biggest part of my complaint-slash-incredulity is to do with the transfer couplings that have to retain atmosphere, resist torsional strain, be low friction and reliable. Not a job I would even want as an engineer. ("How about giving me a non-stupid problem to solve, please.")

No habitat involved in what you're talking about so it's mostly a "how much power and data complexity can we put into a coaxial link" problem.

@pieist @nyrath

The NASA Nautilus X ISS demonstrator was supposedly going to test that out, but they never got proper funding. It ended up being downscoped to the BEAM (non rotating) demonstrator, which launched shortly before Bigelow went under (but is still attached and functional on ISS).

@simonbp @nyrath Again, thanks for this. I f-ing love NASA; one of human civilisation's most unalloyed goodnesses. I'll read up on this more closely as I have time.

@simonbp @pieist @nyrath Inverting things; the never-launched ISS Centrifuge Accommodations Module had a rotating core and a stationary shell. But that had the problem of the spinning section being entirely surrounded by air, increasing drag and angular momentum transfer to the shell.

@michael_w_busch @simonbp @nyrath

2001's Discovery was comparable: the spinning ring portion of the habitat was wholly enclosed within the pressure vessel. It solved a lot of problems re pressure couplings but yeah, you had friction losses and as you say, angular momentum to compensate for as a result.

While in principle you've reduced the complications to, say, putting a hamster wheel in an Apollo command module, you still had data and power transfer issues. And a f---load of mechanical load etc.

@pieist @simonbp @nyrath When I was involved with the Asteroid Redirect Mission proposal a decade ago; one variation was to have a non-spinning spacecraft surround a spinning asteroid without touching it, seal the bag, and then very slowly despin the thing by pumping in nitrogen to create air drag and transfer the angular momentum to the shell to be canceled by thrusters.

That was quite complicated enough.


I have one better for you - spacecraft with rotating sections for artificial gravity with windows for occupants to look out of. The problem appears when you see them through the window and their feet are pointed at the center of the spinning mass instead of the opposite direction.

Caught that one on "The Ark" on the SyFy cable station, which was awful for a whole host of other additional reasons.

@chris Eek. Yes. What killed me about the 2009 Star Trek film was seeing the Enterprise being built on the surface of the Earth. That'd be absurd, it's meant to spend its life in space, why build it down here and only to hoick it up there? Somehow I don't think the original ST developers would have made that mistake. (Though having everybody's feet pointing in the same direction still seems like a pointless requirement, even if you have artificial gravity.


I'm sure that planet-side construction was intended to so that they'd be sure it would be robust enough to also function as a submersible.

That's my head-canon at least.

Books, do that too. The otherwise delightful (and quite enjoyable) novel "Braking Day" featured a generation ship with a pressurized, nonrotating central core and multiple rotating habitat wheels, one of which had suffered catastrophic failure and atmosphere loss and thus was no longer rotating.

The problems of pressure sealing gigantic rotating joints to last for centuries (not to mention bearing wear and atmosphere loss) never got a mention.

It was never very clear to me why the whole ship wasn't just rotated as a unit.

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