how fast does a space station have to spin to generate gravity?

[Omegachi]

how fast does a space station have to spin to simulate earthlike gravity? say... the space station is in either a ring or spherical shape.

 

[brentkiosk]

It depends on the size. The centripetal acceleration is v^2/r at a distance r from the center of rotation. For example, to get 1 g at 100 meters, you would have to go about 30 m/s. That would amount to about 3 rpm!

 

[BitByBit]

If you're referring to the ring-shaped stations as seen in the film 2001, then it depends on the radius of the ring.
To generate a force equal to one 'g', the station would have to spin sufficiently quickly to cause an acceleration of 9.8ms^-2.
The velocity necessary at any point within the ring is given by:

9.8 = v^2 / r
9.8 = v^2 / 100 =>
v = 980^0.5
v = 31m/s

To calculate the angular velocity in radians/sec, use the equation:
W = v/r (Let W represent angular velocity)
W = 31 / 100
W = 0.31 rad/s

If you want this in RPM, we must first express 1 rad/s in RPM:
1 rad/s = 60 / 2pi = 30 / pi RPM
0.31 rad/s = 30 X 0.31 / pi RPM
0.31 rad/s ~ 2.96 RPM.
This may seem slow, but don't forget that I set the radius equal to 100m.

For such a system to work, the centre of mass would have to be directly at the centre of the station. If this isn't the case, then you'd get a wobble.

 

[BitByBit]

Wow, we both went for 100m!

 

[brentkiosk]

Well -

It's a pretty round number and I didn't have a calculator within reach.

 

[Hacp]

Doesn't need to be 9.8.... could easily be a slightly lower number! Ya he mentioned earthlike, but who would know the difference if it were 9.8 Vs. 8? You'd only feel 20% lighter.

 

[Omegachi]

so... do you guys think it is possible to create such a function station in space? with the abillity to dock space shuttles?

 

[PowerEngineer]

Originally posted by: Omegachi
so... do you guys think it is possible to create such a function station in space? with the abillity to dock space shuttles?

Already worked out a few years back...

 

[The Boston Dangler]

Occupying the area along the rotational axis could be tricky, and a docking bay would be a nightmare.

 

[glorygunk]

First keep in mind that constructing anything in space is a huge undertaking. Just look at the ISS. Every part needs to be ferried into orbit...a huge cost. Then it needs to be assembled. Assembling a huge diameter rotating space station would require international resources and decades of planning.

To create a space station that simulates natural gravity via a centrifuge would require a very large diameter indeed. If you're thinking ferris wheel, forget about it It should be large enough that the difference in centrifugal acceleration between head and toe is negligible (otherwise the astronauts would get nauseous.)

A cool idea that had been broached before was instead of a wheel, you create a "slingshot" with the space station on one end, and a counterweight on the other, with a tether between the two. This substantially saves on material cost, but operating it would be difficult. Drag still exists in LEO (Low Earth Orbit) so the slingshot station would have to expend extra fuel to keep itself in rotation, on top of the fuel required to maintain the whole thing in orbit. Oh, and docking with a slingshot would be VERY difficult indeed.

 

[Calin]

Originally posted by: The Boston Dangler
Occupying the area along the rotational axis could be tricky, and a docking bay would be a nightmare.

No it won't - a docking bay on the center of rotation (on the axle of rotation) and looking away from the station could be easy to construct, and the shuttles will start a rotation (roll) to synchronize with the station.

This "slingshot" idea could be a very good thing - but instead of having a counterweight on one end, move all the power generation on that "counterweight". You could then use a nuclear reactor shielded only on the side to the rest of the space station, saving on shielding weight. Or for the same weight you could have a bigger reactor, better protection for the crew and so on.
For docking you could have a docking place - like some kind of an elevator, having just some hooks for the space station. You could move the docking place from one end of the slingshot to the other (keep it at the counterweight end to increase the radius of rotation of the human module during normal operation, move it at the center of mass so the shuttle will have a rotating (but not moving in other directions) place to "land", and move it to the human module to dock the shuttle when a shuttle is on the space station.

 

[Bona Fide]

Some of you guys should be working at NASA

But seriously, if we're able to make it work in theory, shouldn't NASA be pursuing a way to make it work in practice?

 

[Jeff7]

Originally posted by: Bona Fide
Some of you guys should be working at NASA

But seriously, if we're able to make it work in theory, shouldn't NASA be pursuing a way to make it work in practice?

They can hardly keep the ISS working, and that's right here in low Earth orbit. A large spinning station might need a higher orbit to avoid excessive atmospheric drag, as Glorygunk hinted at. That translates to more time and energy needed to get that massive load of materials up there in the first place. Maybe it could have a processing bay to collect orbital debris and process it for raw materials for repairs? That's dreaming now...

Doesn't need to be 9.8.... could easily be a slightly lower number! Ya he mentioned earthlike, but who would know the difference if it were 9.8 Vs. 8? You'd only feel 20% lighter.

Yeah, but when they get back to Earth, their muscles will be weaker, and it'll still be a strain to get used to it again. So either full gravity, or else they'd need some strict exercise regiment.

 

[Calin]

Yes, it would be great to have a system to collect orbital debris moving at speeds in the range of several kilometers per second. However, collecting orbital debris moving "in counterflow" would slow down the space station, and it would need to regenerate that energy (speed or altitude) using rocket engines. I suppose it would be cheaper to get mass orbited from Earth than to get mass from those fast-moving against the space station's direction orbital debris.
And about the weaker muscles - total imponderability has a great negative effect on muscle strength. However, living long time at half Earth gravity would be absolutely enough for even a year in space, combined with exercises.

 

[Calin]

Why they don't use the system? It was used (if I remember correctly) with two modules (russian I think) that were rotating around each other (around the docking ring). However, I don't know how successful was the experiment, the cosmonauts might have been dizzy.

 

[The Boston Dangler]

Or, you could have people living in a >1G environment. With this kind of training, we could have a sweep in the Olympics.

 

[Tiamat]

Originally posted by: The Boston Dangler
Or, you could have people living in a >1G environment. With this kind of training, we could have a sweep in the Olympics.

LOL, i smell a DBZ reference coming ;p

 

[Ronf56]

They can hardly keep the ISS working, and that's right here in low Earth orbit. A large spinning station might need a higher orbit to avoid excessive atmospheric drag, as Glorygunk hinted at. That translates to more time and energy needed to get that massive load of materials up there in the first place. Maybe it could have a processing bay to collect orbital debris and process it for raw materials for repairs? That's dreaming now...



Yeah, but when they get back to Earth, their muscles will be weaker, and it'll still be a strain to get used to it again. So either full gravity, or else they'd need some strict exercise regiment.

Your comments are appreciated...fyi, the word which best fits your context is "regimen" rather than "regiment". Thanks.

 

[Paperdoc]

A couple notes to add. You can see from the math above that the actual "gravity" force generated from the spinning space station depends on how far from the centre you are. The closer to the centre, the less the simulated gravity force is, and at the very centre there is none. That is why those science fiction movies so often show a large ring structure with a few spokes and a small central hub, so that most of the occupants' time is spent in the periphery where the "gravity" is highest.

Consider docking an approaching craft. If the station is spinning, to dock at the periphery or somewhere along a "spoke", the craft would have to be travelling in a circle at the same speed as the docking hatch. A circle is NOT an easy path, and requires constant use of propulsion engines to keep the circular path - very difficult and a huge waste of energy. So by far the best practise in such a case would be to have a single docking station right at the central hub (or maybe two - one on either side) and use the idea Calin mentioned above. In preparation for docking the approaching craft first lines up with the port, then established a rotation of itself exactly matching the rotation of the station AND positioning itself angularly so its docking clamp mechanism is aligned with the mating part of the port mechanism, and then moves forward. Then of course, ALL transfers of people and goods at the docking station are done under zero gravity conditions, because they are at zero distance from the centre of rotation.

Such an arrangement would be a real problem for some activites on the space station. Any attempts at observation of anything else in space - earth, moon, sun, other stars / galaxies, etc - would be carried out from a platform rotating in space at a VASTLY faster rate than the rotation of earth.

 

[Red Squirrel]

Nah you can just do a "no time for caution" style docking. Not really that ideal in real life though... I mean, it's doable, but it's quite risky. You would also need counter weights that can move the centre of mass to make sure the docking port is 100% centred mass wise or it would wobble. (ex: more people on one side of the station).

I'm thinking the best bet would be to have a separate ring and only that part rotates while the rest of the station is stationary. That is also tricky on it's own to do, technically you need to rotate the entire station the opposite way, then rotate the ring until the rest of the station stops rotating. Such ring could be useful though so astronauts can get back to a normal gravity so they don't lose bone density as much etc. Could do more standard exercises and even eat, sleep, clean etc more normally in that section of the station.

 

[Iron Woode]

I see no mention of Babylon 5 in which this concept is used. It is also used for the Earth Alliance warships.

 

[serpretetsky]

THREAD NECRO!!! (I'm okay with it )

I figure this thread would benefit from having a table of different radii and what speed would be needed to achieve 1G.


ISS orbit matched pretty well when i plugged in 0.89g for gravity acceleration at ISS orbit. Assuming the calculations are correct, I'm surprised a circular orbit at earth's distance to sun would need to finish a full orbit in 8.96 hours to achieve 1G. Seems kind of fast.

 

[Red Squirrel]

This just gave me a random thought, does the Earth's rotation have an effect on gravity by creating centrifugal force to cancel out some of the gravity? Ex: if it stopped spinning would the gravity be stronger? Could a planet spin fast enough that it essentially cancels out it's own gravity? Like it would still have gravity, but if you try to land on it at same rate as it's spin (so ground under you is not moving) you would basically be floating.

 

[serpretetsky]

does the Earth's rotation have an effect on gravity by creating centrifugal force to cancel out some of the gravity? Ex: if it stopped spinning would the gravity be stronger?

Effectively yes.

http://curious.astro.cornell.edu/ab...etween-the-poles-and-the-equator-intermediate

"Taking into account both of the above effects, the gravitational acceleration is 9.78 m/s2 at the equator and 9.83 m/s2 at the poles, so you weigh about 0.5% more at the poles than at the equator. "

 

[Paperdoc]

Interesting thought by Red Squirrel. But consider the many disatrous consequences of having a planet spin so rapidly that it has effectively zero gravitational pull at its surface. EVERYTHING wound have NO attraction to the surface, and most would drift away into space until the remaining material had a small enough radius to reduce the effect substantially. Planet? What planet?