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Because it’s way more expensive impractical and error prone I assume

In The Martian, the hermes ship used to go between Mars and the Earth used this method. In the hail Mary Project the ship split in two halves joined by cables to replicate earth gravity, by separating the two halves by large distance.

It's a Sci fi concept so far, there must be a reson it's not implemented.

damn a whole shitload of people answered this question

Because it's expensive.

You have to build equipment to withstand constant load, which is much heavier, which means more launches and launches are more expensive.

Suddenly there is a greatly reduced working and living area. You go from being able to work in any surface to only surfaces near the "floor". So you need to build more areas, and the architecture becomes more complex, both requiring many more launches.

A lot of the things you want to do in space, like science experiments, have to do with micro gravity, so introducing artificial gravity would make space stations kind of pointless.

To make the structure big enough to spin comfortably would require a very large structure, which means a lot of material, and a lot of launches. And more places for things to go wrong, so a lot more engineering and safety assurance is required.

As some have already mentioned - coriolis forces. But why not build bigger so coriolis forces aren’t an issue? Because spinning up anything of sufficient diameter to even come close to 1G would need some kind of unobtainium to be strong enough to keep the spinning object intact. Say 5 tons of mass at 0 G is just mass, but now accelerate it and you need to figure out how to support 5 tons.

1 rpm for 1 G is going to need almost 1km radius. 2 rpm is ~400m.

You can see that the numbers, size, and engineering get pretty ridiculous to keep people from being sick when spun.

Basically, the spinning diameter has to be really long so the spinning doesn't make you puke long-term (Coriolis force is a bitch). There were NASA tests and studies about it, which range between a 100 and a 1000 meter diameter.
So, the ship has to be built for it from the design phase, be it with a rotating ring or a tether approach. Which we didn't have yet a usecase for (for only a few days or months):

• For a future Mars mission, would slow acceleration and deceleration be more viable.
• Only real fitting usecase is a orbital space station with permanent crew.

lol did you just watch Project Hail Mary?

Because it would be less fun

Because the constant rotation complicates things a lot.

Specifically talking about the International Space Station, its main mission is a microgravity laboratory. We put it up there so we can learn about microgravity. Why go through all the expense of putting it up there and then spinning it to make gravity when we get it for free down here on the surface?

As for other craft? We have yet to develop manned spacecraft that can do the duration where it would be worth doing. Even the longer Apollo missions were in space for a whopping two weeks and 2/3 of the crew still landed, got out and stretched their legs. It hasn't been worth the engineering hassle to do it.

And it is an engineering hassle, because...

1. The ship has to be designed to handle it. It's under additional stresses, so it's got to be built tougher to handle it. That's added weight, and just typing that sentence made at least three rocket scientists cringe to death.

2. Humans actually aren't great at living in a spin gravity environment. The smaller the radius of the spin, the worse it gets. For one thing, in a centrifuge, there's a pretty steep gradient in centrifugal/centripetal/pedantic force, the farther toward the rim you are the greater the gravity. For very small distances that can be significant enough to cause problems on its own. But also, spinning humans isn't good for their vestibular systems. Each of your inner ears has three semi-circular canals filled with fluid, and little hairs that can detect the movement of that fluid. This allows you to sense rotation around three axes, kind of like a gyroscope sensor. This evolved in an environment that rotates a 1 rotation per day, functionally stationary. Spin a human at several RPM and that constant rotation is enough to start throwing off balance, causing nausea etc. So the bigger the radius of the spin, and the slower, the better. That takes more weight, and there go three more rocket scientists.

3. It makes the spacecraft a pain to handle. You need to be able to orient spacecraft in space to point engines, windows, instruments, docking adapters etc. in various stable directions. A constant roll complicates that. "point in this direction and fire the engines" becomes a pain because, say you're constantly rolling, and you need to change the direction your long axis points. What thrusters do you fire in what combination to steer the ship? Or do you stop the roll, maneuver/use your telescope/dock/whatever, then start rolling again? So now you've got to deal with gravity starting and stopping variously throughout the journey. Or, do you design the ship to have sections that do roll and sections that don't? First, look up "gyroscopic precession" on Wikipedia. Second, wiring, plumbing etc. is a pain in the ass to handle via slip ring, let alone crew access. Third, that adds weight, which...I should probably stop saying that, rocket scientists aren't cheap to train and that's nine we've killed just in this list.

In conclusion, look what you made me do.

The ISS is primarily designed to research the effects of microgravity and other space environment issues. Hard to study zero g manufacturing when your station has artificial gravity.

Small ships would have to rotate really fast to make 1G, and it’s not worth the trouble if nobody lives there permanently.

size

We haven't done anything worthy of the effort to build a ship that's capable yet, basically.

Here is a great video on spin gravity. It covers an important detail that another comment mentions but most over look. Spinning fast enough to create gravity-like centrifugal force causes real dizziness at small diameters. 5 or 6 rpm is about the maximum we can stand.

You would need a pretty large radius to generate stable rotational gravity. If the radius is too small, the speed of rotation would make standing or walking nearly impossible. The larger the radius, the more imperceptible the rotational effects would be.

It helps reduce the problems mentioned if you lessen the target goal. We don't need 1 G of force just like we don't need a full 1 atm or pressure or 80% of nitrogen mix in the air to breathe. Less gravity force, less RPMs for the same diameter.

But scale is still the better option, making something a few kilometers wide and with only 0.7 G means less stress, less effects from the rotation, etc. That's still in the category of megastructures though, so while not impossible to build, not going to happen at our current level.

the one in space odyssey did.