# How far are we away from (rotational) artificial gravity in spacecraft? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [October 18, 2022, 12:28pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427 "2022-10-18T12:28:36Z")\ **Posts on this page:** 11\ **Page:** 3
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [October 21, 2022, 12:23am UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/41 "2022-10-21T00:23:25Z")
> [@Dr.Strangelove](#): > > The separate crews will grow apart and come to despise each other. This, on the other hand, wouldn’t be a cheesy sci fi movie. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 21, 2022, 2:56pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/42 "2022-10-21T14:56:30Z")
okay… good chat. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [October 21, 2022, 3:09pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/43 "2022-10-21T15:09:25Z")
> [@Dr.Strangelove](#): > > > [@Just\_Asking\_Questions](#): > > > > The bad part is you have two crew halves that can’t interact for a year. > > The separate crews will grow apart and come to despise each other. Eventually, they will realize they can’t share the same planet. One of them has anticipated this set of events, and saved all of its waste products onboard, ending up with a higher mass than the other module. They concoct a plan to spin up the bola as they approach Mars, just to the point where the heavy module will have a barely low enough velocity to make it back to the lander with its maneuvering thrusters (discarding the trash at that point), and then cut the cable. The light module, traveling faster, simply won’t have enough delta V to make it back. > > What they didn’t anticipate is not only had the other module mostly faked their own waste disposal, they had already turned on themselves. Those who were simply killed were the lucky ones. The rest were eaten alive. Less than a tenth of the crew remained. > > The handful of psychotics remaining discarded the corpses and excess equipment once the bola was cut. They had more than enough delta V to make it back to the lander first and lock the doors. But burning up in the Martian atmosphere instead of encountering whatever the other crew had turned into was a blessing in disguise. I’ll greenlight it. But you’ll have to add a Romeo & Juliet subplot, where the lovers illicitly spacewalk to the hub for their zero-g trysts. It’ll end in tears, of course. I’m thinking Zendaya and Caleb McLaughlin. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [October 21, 2022, 3:18pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/44 "2022-10-21T15:18:33Z")
> [@Just\_Asking\_Questions](#): > > The crew module thrusters are used to spin the assembly up to maybe 2 rpm I was think about this: how about a flywheel in the drive module that is set spinning before the ship leaves Earth, and the rotational energy is transferred to the crew modules? If you design it right, you can eliminate the fuel required for spin up and slow down, or at least reduce the amount required. Of course, the trouble with a Bola ship is if something happens to knock the drive module cattywompus, the whole thing is going to spin in some weird three dimensional wobble and the crew modules will end up slamming into each other like clacker balls. Now _there’s_ a sci fi movie visual! It occurs to me that the crew modules don’t actually have to be attached at all time to the drive module. Since they are all already going at 24K mph or whatever to Mars for 8 months, they crew module bolas can be detatched from the drive module and just spin along next to the drive module. With my first deign of spinning the whole thing, you get the benefit of solar panels on the drive module to power everything. I guess trade studies would have to be done to see which design has the greater risk. Computer spin models could be created. Either way, I’d spin the (inhabited) bolas in earth orbit for two years to see what happens, what problems come up. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 21, 2022, 3:21pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/45 "2022-10-21T15:21:12Z")
> [@Sam\_Stone](#): > > We’ve put peoole in the ISS for longer than a Mars trip and they come back to Earth with minimal rehab. Mars would only be 1/3g, so the travelers should be able to get around fine. We put people in top physical health into the ISS, give them hours a day of exercises to do, and they still need rehabilitation when they get back to Earth. > [@Just\_Asking\_Questions](#): > > And does anyone think that we can’t make a cable (and it’s multiple redundancies) that can last two years of spinning? The only time it would break is in cheesy sci fi movies. Especially if it turns out that we don’t need full Earth’s gravity for the trip. Mars gravity would be useful, as that would acclimate the crew to their destination. But less may be fine as well, and the less gravity the crew needs, the simpler both the craft and the cable can be. > [@Just\_Asking\_Questions](#): > > The bad part is you have two crew halves that can’t interact for a year. But you do have full crew redundancy should some catastrophe happen. They _can_, it’s just a bit of a trek. Probably something that should be possible to do in an emergency, but not something that would be done regularly. > [@Chronos](#): > > Why would this be any more difficult than a suspension bridge? You say that almost as though suspension bridges are easy. 😉 It’s certainly doable, but it will require some pretty smart people to think about things and perform some experiments before we should be trusting people’s lives to it. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 22, 2022, 2:19pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/46 "2022-10-22T14:19:09Z")
I mean, sure, you want a team of highly-competent engineers to do a thorough job designing a suspension bridge, and do tests of all of their materials, and so on. It’s still a big job. But nobody ever says “What, a suspension bridge? That’s far beyond our capability, and nobody should ever try it, because it’s too dangerous”. > [@Just\_Asking\_Questions](#): > > I was think about this: how about a flywheel in the drive module that is set spinning before the ship leaves Earth, and the rotational energy is transferred to the crew modules? If you design it right, you can eliminate the fuel required for spin up and slow down, or at least reduce the amount required. You definitely don’t want to launch something with an already-spinning flywheel in it. But it takes only a trivial amount of propellant to get the spacecraft spinning (in fact, it can be done with an arbitrarily small amount). Propellant to spin up (and later spin down) the spacecraft is not a major concern. ---
**Author:** ![Just\_Asking\_Questions](https://avatars.discourse-cdn.com/v4/letter/j/ba9def/32.png) [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)\ **Post date:** [October 22, 2022, 4:45pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/47 "2022-10-22T16:45:02Z")
> [@Chronos](#): > > You definitely don’t want to launch something with an already-spinning flywheel in it. That one’s on me. I meant, launched static, but spinning the flywheel up to speed before it leaves earth orbit. And then top off the fuel before it leaves. But even so, just using rockets to spin it is probably better. I’m generally expecting that, if the spacecraft I’m proposing was built, that we would have some more advanced in-orbit assembly capability, maybe even some sort of “space tanker” in-orbit refueling capability. I figure like this is 1961 and my mars mission is 1969. A lot of little things to work out. I wouldn’t propose launching the whole thing at one go. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [October 22, 2022, 5:53pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/48 "2022-10-22T17:53:13Z")
> [@Chronos](#): > > It’s still a big job. But nobody ever says “What, a suspension bridge? That’s far beyond our capability, and nobody should ever try it, because it’s too dangerous”. Yeah, but it’s still news when someone opens the longest or tallest new suspension bridge. And this would be both. I see no reason it can’t be done, just that it _would_ be quite the megaproject. I look forward to Simon Whistler’s video about it. The one thing that I do think should be done first is to determine what kind of gravity humans need for long term duration stays. > [@Just\_Asking\_Questions](#): > > I meant, launched static, but spinning the flywheel up to speed before it leaves earth orbit. And then top off the fuel before it leaves. But even so, just using rockets to spin it is probably better. Using the flywheel to spin it up isn’t a bad idea, but you wouldn’t need to spin it up ahead of time. Spinning up the habitat would cause the flywheel to spin up in the opposite direction. You probably _want_ that in order to mitigate precession. (I think, I’m not an orbital surgeon.) > [@Just\_Asking\_Questions](#): > > if the spacecraft I’m proposing was built, that we would have some more advanced in-orbit assembly capability, maybe even some sort of “space tanker” in-orbit refueling capability. I figure like this is 1961 and my mars mission is 1969. A lot of little things to work out. I wouldn’t propose launching the whole thing at one go. Getting at least the fuel, if not some of the superstructure, from in-situ-resources from the Moon would also help immensely. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 22, 2022, 8:42pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/49 "2022-10-22T20:42:23Z")
About using the flywheel to spin up the spacecraft, unless you plan to let go of that flywheel, wouldn’t it need to keep spinning for as long as you wanted to keep the spacecraft spinning? Is there some trick one could do with 2 of them by spinning them both in the same direction turning them 180 degrees against each other, then decelerating them to further increase the spacecraft spin? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 22, 2022, 11:25pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/50 "2022-10-22T23:25:24Z")
> [@kanicbird](#): > > Is there some trick one could do with 2 of them by spinning them both in the same direction turning them 180 degrees against each other, then decelerating them to further increase the spacecraft spin? In short, no. Angular momentum is conserved. The act of turning one of them around would undo what you’re trying to do, and would put all sorts of interesting internal stresses on your apparatus in the process, possibly resulting in similarly-interesting failure modes. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [October 23, 2022, 4:25pm UTC](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427/51 "2022-10-23T16:25:53Z")
Many speculative designs of spacecraft that include a rotating segment to generate gravity also include a (larger) non-rotating segment, that includes the drive system, fuel and propellant reserves, communications system and radiators/thermal regulation system. In practice even this ‘non-rotating’ segment might be required to rotate slowly, to maintain thermal equilibrium in the sunlight. So this means there are at least two large sections of this spacecraft rotating at different rates (even if one of those rates might be zero). If there is any friction at all between these two segments, the spacecraft as a whole might start to precess and rotate chaotically. To avoid this you’d need some way to control the rotation of both segments independently, a process which would require power. I wonder if the best design might be two counter-rotating wheel segments, which make the overall angular momentum of the vessel as close to zero as possible. These counter-rotating segments could be sped up and slowed down as necessary, to maintain balance. [Previous page](https://boards.straightdope.com/t/how-far-are-we-away-from-rotational-artificial-gravity-in-spacecraft/973427.md?page=2)