# Is an artificial gravity room on a modern spacecraft or space station feasible?

I'd like a gravity room on my space vessel for long space stays to avoid osteoporosis. They would spend a few hours each day in this room, reading or doing paper work, to maintain bone-mass.

I'm imagining a chamber (it doesn't need to be large) where the astronauts stand against a wall as the room rotates, like the classic carnival ride.

Image By Lzcracker - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4531120

I imagine that I would need some kind of counter-weight (spinning in the opposite direction) to maintain net-zero rotational momentum.

My question is whether a room like this is feasible on a spacecraft that would be built today. Or whether I'm overlooking some other factors that would make this undesirable.

Edit: I am imagining a very small centrifuge. Not large enough to run around in (as in 2001 or the Martian).

• 2015's "The Martian" ?
– Karl
Commented Dec 14, 2016 at 21:28
• Oh man, I threw up every single year the Gravitron visited our base. I nearly threw up seeing the picture. I suspect it needs to be a larger structure for proper gravity sensation. Keep in mind as well the connectivity of a non-rotating structure to a rotating structure. (That's why this is a comment, not an answer: just a suggestion) Commented Dec 16, 2016 at 6:35

## It's possible...

As the other answers suggest, your science and reasoning are sound. Such a room, if spun at the right rate, could simulate gravity, and perhaps negate some of the effects of prolonged exposure to microgravity. This is also fully possible with modern technology.

## But for what it actually does, no one will pay for it.

### Expensive to fuel

Moving a pound of material into orbit costs on average between 2,000 and 20,000 dollars. To keep this room spinning relative to the rest of the station, you would need to constantly burn fuel (or sacrifice most of your solar input). Electricity is valuable, and fuel costs too much to move up, so such an endeavor may not be accepted.

The difference between this approach and entire stations that spin is that the "one-room" approach involves friction. The friction between the spinning room and the rest of the station will slow it down, requiring more motion to combat, and thus more fuel. Meanwhile, if you spin the entire ship, it will keep spinning unless acted upon by another force - requiring significantly less energy.

### Expensive to build

As noted above, moving mass into space is expensive. I'm not going to make any assumptions about the size of this room but if you want something large I wish you luck finding an investor. It's just cheaper to move the whole station.

### Not very effective

• A few hours each day will not help significantly. Spending the rest of their hours without gravity will reverse most of the positive changes you make, if not all.
• Bone density is lost in space because bones no longer need to stay strong enough to fight gravity; that material is better used elsewhere. By lying on their backs, or with their backs to the wall, bones will act as if humans are sleeping; there is not much work that they need to do, so density will not increase by much.
• Other problems, such as impaired vision, occur in space because internal fluid is not restrained by gravity. By pulling from the front of the individual to the back, you will simply change where the fluid pools - in the back - and drain it from the wrong places - as opposed to pulling it down from the brain.
• Bed sores will occur from astronauts constantly lying down (as opposed to standing up produced by upright motion).

## Consider spinning the whole ship, indefinitely, and having people stand upright.

• Fun theoretical twist: It's possible that quantum foam interactions can rob an item of it's angular momentum, eventually causing even a fully spinning ship to stop spinning. However it would take so long that you'd see the end of the universe before measuring a noticeable effect on even a rotating screw in space. :D Commented Dec 15, 2016 at 9:05
• A couple of your points seem to assume that the astronauts would use the room the same way we would - that is, with their backs to the wall and the noticeable pressure front to back. On earth that's necessary because actual gravity is perpendicular to the spinning of the room - but in microgravity, I think the room's force would be primary, turning that "wall" into the floor - on which they might sit "upright", stand, or walk without gravity pulling them off the side. Commented Jan 11, 2017 at 4:02
• @Megha the OP specified on their backs - I agree, that's not ideal. Commented Jan 11, 2017 at 4:26

While the idea of having artificial gravity is sound, there are several issues with the idea of having a room or "Hamster wheel" for artificial gravity inside your spaceship:

1. It is heavy. The cost of bring ing objects or even inert mass into orbit is enormous, and will be so for the foreseeable future (even with SpaceX). A separate rotating structure isn't just the wheel, but the bearings and support structure, motors to spin and despin it, rotating slip joints and seals, slip rings for passage of electrical power and data etc. You will also need a set of flywheels or perhaps another ring spinning in the opposite direction to cancel out torques, and possibly some sort of counterweight system so your moving around in the room won't destabilize the system.

2. It is complex. Looking at the list of items in 1 above, this thing is going to be a maintenance hog and nightmare for your crew to keep going. Just ensuring the flow of electricity and data to the rotating cabin is going to be difficult enough, much less airlocks, pressure seals and so on.

3. It is dangerous. Can you imagine if your slip ring has to transmit kilowatts of energy, either by design or because of an accident? What happens if the wheel becomes unbalanced? Will the vibrations damage important systems on your ship? is there some means to brake the system in an emergency and deal with the sudden change in rotational energy?

4. It isn't healthy. If your room is too small, the corals force of the rotation could induce nausea and disorient the people inside. The calculations can be found on the ever helpful Atomic Rockets site. In general terms, rotating at faster than 7RPM can cause problems for the people inside. Either the room has to be unreasonably large or you will have to settle for less than one "G" if you rotate the room more slowly. While Atomic Rockets has lots of caveats, much of this has to do with training and also with gradually upping or reducing the rotational speed. This may or may not be practical.

However, there is a solution: turn the entire spaceship into the centrifuge. No slip joints or moving parts, the ship can spin at any arbitrary rate and the "room" is the size of the entire habitat portion. This fan art version of the "Hermes" from the novel "The Martian" shows how its done:

The nuclear reactor is facing the viewer in this picture, and the habitat is on the far end of the boom. The ion engines are in the centre of the boom, and can be rotated to provide course adjustments and corrections. A .gif of the ship in rotation is here

So by some clever design, you can make the entire ship rotate and provide the crew with 100% gravity inside the crew quarters for as long as you like. Rotating the ship and despinning do have issues (and you need to take this slowly in order to prevent over stressing the central truss), but overall, this is a much more robust solution than a spinning room inside the ship.

• I like your first four points. Spinning the whole spaceship is a solution I'm aware of as it comes up in many many many novels, but I was specifically looking for reasons not to spin just part of the ship. Your first four points address this nicely. Commented Dec 15, 2016 at 19:02

The concept is certainly workable, and is being actively investigated by a number of different groups. It's also been depicted in science fiction many, many times.

A recent high-profile proposal for a vessel using such a system was the Nautilus X, a proposed multi-role spaceship that would use a centrifuge to provide around 0.5 - 0.6 g for the crew.

A version of the same concept was also tried on Gemini 11. The crew capsule and its Agena target vehicle were connected by a tether and spun around their common centre. The experiment was not a total success, for various reasons, but they did generate a small amount of artificial gravity.

To my knowledge, nobody has actually flown another mission to test the concept in space, despite many proposals. The Soviets experimented extensively with centrifuges as a habitat on Earth, but never in orbit. A module called the Centrifuge Accommodation Module was partially built for the ISS, but was cancelled before completion.

Generally speaking, the idea should be workable. For 2016, the problem is that we don't have many spacecraft or space stations, and those were launched in many small parts. Assembling this room in orbit would be difficult.

• Something similar was shown in the movie 2001.
• Variant: The spacecraft has two (or four) pods rotating on arms. The Leonov from 2010 or some Earth Force ships from Babylon 5.
• Variant: The spacecraft has a ring rather than separate pods.
• Ah, I forgot that only one part of the 2001 Discovery One spun. In my memory, the whole ship rotated. Commented Dec 14, 2016 at 21:13

It doesn't really make much sense to have only a room. If you can build it it would be better for it to represent all (or almost all) of the living space available.

If the room available is limited for any reason then you could still have a very small centrifuge, maybe divided in a few bunks, so that people can rest there and maybe sleep.

The reasons such a space would be used for sleeping and resting are two: first if the centrifuge is small, moving inside is difficult and you will experience different levels of acceleration within you body and also a very strong coriolis effect every time you turn around; second, sleeping in space is actually very difficult! Astronauts on the ISS can hardly sleep a few hours, so if you have a gravity room available only at times sleeping in there is one of the best thing you can do probably.

Oh, also, if the space is limited better do something in there that requires limited movements and room.

• That's actually why I imagined them reading in the room, but sleeping makes even more sense. Commented Dec 14, 2016 at 21:43