We all know the pictures of the astronauts on the ISS floating around. We also suspect that a lack of gravity is bad for the body as the muscles go weak and such.

Why don’t spaceships just rotate to cause the effect of artificial gravity through centrifugal forces?

  • BorgDrone@feddit.nl
    60·
    18 hours ago

    Even if a small ship rotates fast that would ‘t work. If you have a small diameter then there would a huge difference between the perceived ‘gravity’ at your head vs at your feet.

          • 4am@lemmy.zip
            3·
            15 hours ago

            Elevators don’t cause a pressure differential within your body.

              • Luminous5481 "Lawless Heathen" [they/them]@anarchist.nexusEnglish
                8·
                16 hours ago

                https://ntrs.nasa.gov/api/citations/20070001008/downloads/20070001008.pdf

                At body motions or centrifuge rotation rates that are small in magnitude, the effects of the Coriolis force are negligible, as on Earth. However, in a centrifuge rotating at several rpm, there can be disconcerting effects. Simple movements become complex and eye-head movements can be altered: turning the head can make stationary objects appear to rotate and continue to move once the head has stopped. This is because Coriolis forces also create cross-coupled angular accelerations in the semicircular canals of the inner ear (see Figure 4-01) when the head is turned out of the plane of rotation. Consequently, motion sickness can result even at low rotation rates (<3 rpm), although people can eventually adapt to higher rates after incremented, prolonged exposure (see Chapter 3, Section 3.1).

            • deegeese@sopuli.xyz
              54·
              17 hours ago

              You said force of rotation but the chart is talking about RPM.

              Still only 1G.

              • Windex007@lemmy.world
                4·
                14 hours ago

                Everyone is doing a terrible job of explaining, but they’re right.

                Gravity, 1G, is described on terms of an acceleration. 9.81m/s2.

                What is an acceleration? Is is the rate of change of a velocity. If a velocity changes slowly, it means the acceleration is low. If the velocity changes quickly, the acceleration is high.

                Now, imagining a record player. Or cd player. Or your spinning wheel of choice:

                You know that points farther away from the center are moving faster in absolute terms compared to points closer to the center.

                Because the points farther from the center have a larger velocity, that means after some rotation, the total change of velocity for the outer points must be larger than the change of velocity for inner points. So, points farther away must have greater acceleration.

                So, the apparent acceleration changes according to how far things are from the center point. This is why it really isn’t the case that it would be 1G everywhere. 1G is a specific acceleration, if if we’ve established that acceleration isn’t constant across the radius, then it can be 1 G only at one spot, not all.

              • Luminous5481 "Lawless Heathen" [they/them]@anarchist.nexusEnglish
                61·
                16 hours ago

                You said force of rotation but the chart is talking about RPM.

                yes, you have forgotten to take into account the Coriolis force and the effect it would have on your astronauts.

                https://ntrs.nasa.gov/api/citations/20070001008/downloads/20070001008.pdf

                At body motions or centrifuge rotation rates that are small in magnitude, the effects of the Coriolis force are negligible, as on Earth. However, in a centrifuge rotating at several rpm, there can be disconcerting effects. Simple movements become complex and eye-head movements can be altered: turning the head can make stationary objects appear to rotate and continue to move once the head has stopped. This is because Coriolis forces also create cross-coupled angular accelerations in the semicircular canals of the inner ear (see Figure 4-01) when the head is turned out of the plane of rotation. Consequently, motion sickness can result even at low rotation rates (<3 rpm), although people can eventually adapt to higher rates after incremented, prolonged exposure (see Chapter 3, Section 3.1).

                in other words, the higher the RPM needed to generate 1g, the worse the effect of the Coriolis force on the astronauts.

      • fizzle@quokk.auEnglish
        3·
        17 hours ago

        Im not really sure what you mean by lying down? You’re not always lying down. Surely gravity is less relevant when you’re lying down anyway.

        … I dont have a good understanding of physics but sci-fi novels suggest a few problems on small ships.

        The first problem is the difference in gravity between your feet and your head. In a small command capsule like Artemis 2, your head might be near the centre at 0g while your feet are at the outside at 1g or even 2g. How hard does your heart need to pump blood? Would this create some kind of blood pressure problem?

        The next problem is how it would “feel”. Is it called the Coriolis effect?

        In a small ship you might experience 1g, but it would feel like you’re being spun around in a washing machine. Your ears would tell you that you’re constantly changing direction and it would 100% fuck you up. In sci-fi the spinning thing needs to be large enough that some g-force is produced without you feeling that sense of motion, or at least for ot to be small enough that you get used to it.

        Another problem I just made up is that if there’s no gravity then 100% of the inner surface area can be terminals and readouts and equipment. If you create gravity then you need a floor to walk on which will use a heap of surface area.

        • Windex007@lemmy.world
          3·
          15 hours ago

          There was recently a “design proposal” (more of a published thought experiment) I read (posted on lemmy) where the authors had figured out the diameter required such that the gravity differential from feet to head wouldn’t be weird. It was quite large if I recall.

          • fizzle@quokk.auEnglish
            1·
            5 hours ago

            I guess thats why, in sci fi it’s only used on ring shaped objects. A ship with a ring around its mid section, or a space station, or the expanse has a barrel shaped ship.