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Comment by Hemospectrum | Hacker News Reader

The result screenshots are pretty cool-looking... and I personally wouldn’t board any of these spacecraft! The decks should be stacked along the main engines’ thrust vector, so the acceleration doubles as a source of artificial gravity.

Maybe I should open an issue...

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If you’ve got a magically efficient drive that’s unrealistically fuel efficient to sustain long term high thrust like in The Expanse that’s one option. But if we’re waving our magic wands anyway, why not just wish up artificial gravity instead?

It would be much harder to maintain homogeneous artificial gravity so I imagine if/when it is invented, it will look like waves creating centers of higher gravity and lower gravity underneath each deck, making you feel like you're riding on a bumpy road instead of walking straight.

    ``'-.,_,.-'``'-.,_,.='``'-.,_,.-'``'-.,_,.='``

In other words, it'll feel like a boat.

Another model is that each mobile object worth keeping held down gets its own gravity well which moves with it via an array of pads in the floor. They feel a constant acceleration, but gravity is uneven where they aren't.

why have engines at all in that case? :)

Good question. In Larry Niven's Known Space stories a common drive system is the Gravity Planar, which simply tilts the gravity field around a vehicle so it 'falls' in the desired direction.

That’s what the inertial dampeners are for :)

I think it was the first "Expanse" book that referenced that... and it rocked my world. Never able to willfully suspend it since.

The problem with that is that you'd have to be always thrusting in order to maintain that artificial gravity, which doesn't sound feasible.

I'd argue a more practical design would be to include centrifugal rings (even number, paired up in opposite rotational directions, so that they offset each others' torque). That way you still get artificial gravity, even while the ship's hanging out in orbit. As a bonus, the habitats might be able to double as reaction wheels (though I don't know if this is exactly feasible; reaction wheels usually spin much faster, IIUC, though maybe bigger wheels don't need such high speeds to control the attitude of a spacecraft).

It depends on how long, and how often, you burn those engines. If you’ve got a big torch that can sustain a large fraction of one gee for weeks or months, and your fuel is cheap enough, why turn it off at all? On the other hand, if it’s only good for a big push at the beginning and end of your trip, and you’ll spend the whole time coasting, spin is absolutely the way to go.

The Expanse, as mentioned in other comments, showcases both these designs. Most ships fly a brachistochrone trajectory with a mid-point “flip and burn,” but the Mormons’ giant colony ship has a drum.

> why turn it off at all?

Because once I get into an orbit I'd generally prefer to stay there :)

I mean, I guess you could just keep spinning around to constantly counteract nudging yourself out of orbit, but that just seems like a centrifugal habitat with extra steps.

On another note, though, today I learned the word "brachistochrone", so thanks!

> Because once I get into an orbit I'd generally prefer to stay there :)

Or you can just be geostationary at 100 km with the engine on.

I loved The Expanse. But you just made me wonder how the colony ship could possibly be practical, because it has to function in both those modes and I don't know how you'd design the interior spaces for that. Unless you had spaces that could only be used in one mode or another, which seems like a big waste.

It was built as an interstellar colony ship - even with the ridiculously powerful and efficient drive technology they have in the Expanse it would take many years, possibly decades after reaching cruise speed before it would break at the destination. So I assume the colonists would just wait in a part of the ship perpendicular to the thrust axis during the acceleration burn and then move from that section (which would be now in micro gravity) to the rotating section. Then in reverse for the deceleration.

Pointy end being front on ascent, blunt end being front on descent, interior wise pointy end being top, floor be round, exterior wise celestial body be down and velocity vector be either where engines face or not face, is kind of norm for spacecrafts though.

Manufacturability, spaceship designs, and space-gun designs are where norms of this sort aren’t very well understood among designers, time to time I’d think “how on Moon are you going to 3D print it” or “this is going to quite spectacularly flip and kaboom in KSP” or “just no way this gun feeds”

I think the best places to have centrifugal gravity would be the toilet, the shower, and the gym. As for the kitchen, I want someone to make a spherical pizza pressed along the inside or the outside of a heated sphere to bake. So we still need an area of zero-g there.

You're missing the point of zero gravity pizza, Moebius strip pizza. Think about it, it'd be infinite pizza!

Regular pizza already has just one edge, which has no beginning or end. It has two sides, though.

You're right, I edged my way to this joke the wrong way. A regular pizza has two sides and one edge, Moebius pizzas would just have one of each. It might not be infinite, but it would be bottomless.

When you slice a Moebius pizza, it'll have cheese on both sides and two edges.

I'm sold.

When you slice a Moebius pizza, you can tell your friend he's getting a half, and slice it down the middle of the strip. Or else promise a third, and slice it a third of the way from the edge.

Either way, your friend isn't getting anything; in the first case, you end up with one pizza with a double twist; in the second, the piece your friend ought to be getting is a chain link connected to yours.

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