# Tag Info

54

Constant acceleration requires energy. Our current rocket engines need to use propellant to provide that energy. And there just cannot be enough propellant to generate artificial gravity for any meaningful duration. We would need a new type of space drive to be able to use acceleration that way. The concept is well known from (science-)fiction (sometimes ...

46

jkavalik gives the right answer. But to put this in perspective, let me add some numbers. Let's say, we use a battery of state-of-the-art ion drives to retain a semi-comfortable, Martian level of gravity, of 3.73 m/s2 for a period of 24 hours. 24 h is 86400 seconds. At 3.73 m/s2 this gives 322,272 m/s of delta-V. Let's use a large number of VASIMIR ...

37

What radius and rotation would be needed to produce 1g consistently from the floor to a height of about 6ft (2m)? Infinity. Technically there will always be a vertical gradient of artificial gravity. Realistically, people will not care. Even with a radius of 224 m the difference isn't much. The acceleration for anything attached to the structure will be:...

35

First off, it really isn't artificial gravity, it is radial acceleration (often known as centripetal force) - AlanSE's answer on the 'Size and rotation of a station' question describes how radial acceleration is very different to gravity. The major reason this is unlikely for some time is that in order for radial acceleration to feel like gravity, you need ...

31

It is worse than that. In order to really plan for future human habitation elsewhere, you do not want just 1G fields, you want 1/6th to mimic the Moon, and 1/3 to mimic Mars. You need to be able to run long term studies comparing similar samples at 0G, and other G levels. There was planned to be a Centrifuge Accomodations Module, on the sky facing port ...

27

I feel like the other answers are missing one fundamental design driver of the ISS. Unlike space stations like the rotating von Braun station or the Stanford Torus, the ISS was primary designed as a scientific space station and not as a leisure outpost in space. Microgravity (in fact there are not absolute zero-G on the ISS, but a very small force ...

27

There are several reasons not to do this: Artificial gravity in such a small space is not very pleasant. You'll get a noticeable difference in gravity in different places, which makes it difficult to move around without banging into the walls. You also get coriolis forces (thrown objects don't move in a straight line) which makes moving around non-...

27

First, I'll adopt terminology from Ringworld: "spinward" is in the direction of spin, and "antispinward" is opposite the direction of spin. And I'll say a bit about the Coriolis equation, but then go into qualitative effects. Basically, anything that involves "up", "down", spinward or antispinward motion (which captures the fraternity-party activities in ...

27

The presence of gravity simplifies a number of common processes. Some examples: Separating liquids from gasses, eg. getting the water out of the air after you take a shower, or removing the hydrogen bubbles from water produced in a fuel cell. Cooling hot objects: you can use radiator fins and convective airflow rather than needing to stick cooling fans or ...

25

Thrust won't generate gravity, but it will produce acceleration which may be indistinguishable from gravity to an occupant. Yes, it's possible to simulate gravity by having a spaceship constantly thrusting to travel in a circle, but it would be an awful waste of fuel. Rotating a large object, or pair of objects connected by a tether, to simulate gravity is ...

23

It would help you to learn which plants can grow properly in a greenhouse on the moon or Mars. When a seed germinates, the root starts growing downward with gravity, and the shoot grows upward to the surface of the soil. Light also helps to orient the plant, but it only works once the shoot has breached the surface of the soil. The angle of sunlight is ...

19

That is an excellent thought experiment to consider for a spinning vehicle. You are correct that if you simply enter the open space inside the rotating cylinder, somehow not following the rotation yourself, you will not experience a force to pull you to the outside. You could just hang there and watch the "floor" rotate below you. However you probably won'...

17

The power and data part is easy. The Galileo spacecraft that went to Jupiter was a "dual spinner", which had spun and stationary sections. The rotating joint had 48 slip-rings over which power and data were transmitted between the sections. As for connecting pressure vessels with a rotating joint, there are similar industrial applications ...

16

What hasn't been mentioned so far are the extra problems caused by gravity: it's not just that gravity is an expensive and inconvenient luxury, it also brings problems. (In this answer I will just say "gravity" to refer to a constant force along one axis, whether that's real or simulated.) Accessibility In zero-g, you can get anywhere on the ship by ...

16

The highest rotational rate ever achieved by a shuttle in orbit was only 3 degrees/second (approximate). This was inadvertently caused when Mission Control uplinked a bad state vector during crew sleep* and caused the vehicle to go out of control. This rotation rate was not nearly enough to induce artifical gravity. *incident is described on pages 2-4 ...

15

If you can have dissipation of energy by any means, i.e. the body is not completely rigid (and there will be plenty of stuff moving around inside a space station, making it not rigid), then the angular energy will be minimized by shifting the angular momentum axis to the principal axis that has the greatest moment of inertia. The axis of a long cylinder has ...

15

Yes, as far as the ISS is concerned, there were at least two such projects in the past that I know of: ISS centrifuge demonstration as part of the Nautilus-X (Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration) Centrifuge Accommodations Module that was designed for NASA by JAXA None of these seem to be going anywhere, for ...

14

NASA did research on Feasibility of liquid-metal vacuum seals, the article was published in 1963 and is accessible here (please look up section B, page 29). Here is quote of the articles conclusion sections. A procedure was found for using a liquid-metal seal in an ultrahigh-vacuum system. Leak reates through a $5.5$ inch-diameter seal were so small that, ...

14

"Artificial" gravity is the name given to techniques to create acceleration that mimics gravitational force. There are two major ways to do this -- both of which are very feasible: Rotation -- in this case, the acceleration is created by centripetal force. The rotating structure accelerates the crew by forcing them to follow a curved (usually circular) ...

14

It is entirely correct to replace "artificial" with "simulated" or even "emulated" or "imitated". Simulated can be defined as "imitating the conditions of something". In that vain, simulated gravity would in no way imply that we are somehow creating actual gravity. It simply means that we are creating conditions similar to gravity. Replacing "gravity" with ...

13

Your intuition is correct. So-called centrifugal force is a product of mass and acceleration in a rotating frame. If you're in a centrifuge, and you let go of the rotating frame, you're no longer accelerated radially, but merely keep the momentum imparted onto you by it and your own force as you let go of it. If this centrifuge was setup in zero gravity, ...

11

Having a facility to investigate the effect of variable gravity levels would be very interesting from a scientific perspective. Some of the questions that might be worth finding the answers to are: How do various plants and bacteria respond to different gravity fields? How does this effect how they grow and the crop yields for plants? How does Lunar or ...

10

Contrary to small animals, now that the human being has stand up on their feet, their brain is located much higher than their heart, but the brain still continuously needs blood. Under increased vertical acceleration, the blood pressure must be increased to maintain brain irrigation. This has been studied in the past: The Biology of Human Survival: Life ...

10

The correct term is centrifugal force. It's correct that centrifugal forces does not exist in an inertial reference frame, but the inside of the station is not inertial. Hence when you are using that as your reference frame you would see centrifugal forces. If you are using an inertial reference frame the physically correct term for what is pulling you ...

10

The problem is about a so called 'comfort zone'. In fact it is not radius but a ratio of radius and angular velocity. Nausea or motion sickness is caused mostly by Coriolis acceleration which makes 'artificial gravity' different form nearly homogeneous earth gravity. There is a real expert on topic Theodore W. Hall. Among a lot of staff about artificial ...

10

Basically, we just don't have engines that can accelerate at 1G, or anywhere near that, for more than a few minutes. Not only do we not currently have such engines, we aren't even sure when we will. Nuclear-thermal designs can get at least twice the $I_{SP}$ of chemical rockets, meaning the same amount of thrust can be maintained for twice as long for the ...

10

You're forgetting about the air. Thanks to drag, the air inside the cylinder will have essentially the same reference frame as the cylinder itself. So a bird (or plane) flying parallel to the axis will experience something close to normal gravity (modulo the usual gyroscopic distortions that all rotational artificial gravity has) as it rotates around the ...

9

Roman aqueduct engineers used a typical gradient of 1:4800, which is about 20cm per km. The equivalent acceleration is about $2 mm/s^2$. So not very much is required to keep the water flowing.

9

We must remember that there is no spoon gravity here and that as soon as our astronaut is no longer in contact with the floor they must have an essentially straight line trajectory. Below is a simulation in an inertial frame moving towards Jupiter along with Discovery 1. Let's assume that the astronaut is initiall standing and has a tangential velocity equal ...

8

Yes. Centrifugal force acts on everything, just like gravity.

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