Artificial Gravity Via Rotation

[Wayne Mack]

Need to determine how big and how fast a space ship needs to rotate to generate gravity? I found this calculator online. Hint, set the fourth value units to 'g' with a value of '1' to get one gee of gravity.

SpinCalc

 

[Ori Vandewalle]

Fun fact: as a quick rule of thumb to remember, you get ~1 gee of gravity whenever the period squared (in seconds) is 4 times the radius (in meters). So, for example, with radius=100m, period=20s (20^2=400), you get 1.006 gees.

 

[farntfar]

That's a very nice rule. Thank you Ori.

 

[Mon0Zer0]

How big? Big enough to avoid this kind of effect:

 

[farntfar]

The tricky part with that room has to be that the spin is creating an artificial gravity toward the outside of the spin, but they haven't cut off the actual earth gravity towards the floor. So you end up with a slightly greater than normal force at about 45° (ish) to the horizontal.
They could possibly design a room with a tilting floor to create a resultant force which is apparently downwards. (More problems presumably follow.

 

[Ursa major]

With a ship (or part of a ship) providing artificial gravity by rotation, changes in its vector (altering course, accelerating, decelerating) would have a similar effect to that which gravity has in the spinning room, except that they would not be constant**, so the adjustments the body was making to them in that room might be more difficult to achieve if there were a series (and variety) of changes over a short period of time...

...so even on a relatively large ship (to get near to normal gravitation without involving too big an adverse coriolis effect) having close to a 400m diameter, you'd still need to be careful about its manoeuvrability and range of acceptable rates of acceleration/deceleration (and with, say, warships, other means of keeping the crew safe if those rates had to be exceeded).


** - In a ship that was either constantly accelerating or constantly decelerating, there would be a second source of artificial gravity. IIRC, the lighthuggers in Alastair Reynolds's Revelation Space universe use that constant acceleration/deceleration to provide the artificial gravity, with no spinning used at all. The only issue this has (other than when the ship isn't on a journey) is at the point in a journey where the switch is made from one to the other, i.e. the acceleration ceases and deceleration begins. (This change is described in one of the books, possibly Redemption Ark.)

 

[JunkMonkey]

The only issue this has (other than when the ship isn't on a journey) is at the point in a journey where the switch is made from one to the other, i.e. the acceleration ceases and deceleration begins.

And, presumably, getting your maths right so you make the changeover at EXACTLY the half way point - otherwise you will have to adjust the deceleration to compensate and end up with a lower or higher than 1G on the second leg.

EDIT: Though 'exact' when you are dealing in light years still gives you a huge amount of distance to play with before any compensation would become apparent to humans. At a guess the level of difference between being at sea level and on top of a mountain on Earth. Measurable but not discernable.

 

[Mon0Zer0]

Btw - Scott Manley helped design this craft which spins with the crew in just one side of the vessel in "Stowaway". I thought it was an interesting 'spin' on artificial gravity.

 

[DrStrangelove]

While experimenting with the concept myself I always found it hard to create a realistic ship that relies on a centrifuge or other way to create artificial gravity without compromising it's combat viability (as many of the ways which we use for hard depictions of gravity in spacecreate structural weaknesses in the ship/craft).

One site I cannot recommend enough for people interested in writing a harder SF story is Atomic Rockets - Atomic Rockets.

It is an amazing resource not only for general info and calculations, but also a ton of info on the history of the genre.

 

[KiraAnn]

Two things to remember about rotating spaceships:

(1) Current thinking is that more than 2 rpm can cause dizziness and nausea until the crew adjusts. The higher the rpm, the longer that takes. There is no consensus on whether anything more than 2 rpm would cause long-term damage.

(2) The rotation would also create gyroscopic effects on the control of the spaceship.