We build a space station that produces localised gravity.





If we had space station wit gravity that would be a important development, the cost to breech this mile stone must be a lot less than even the recent reduced moon costs (down from 300billions to 30b).

The logistics of docking with rotating mass large enough to produce 1g would be interesting.

Just slow down the rotation while docking.

Easier and cheaper (fuel) to just have the docking craft match the rotation.

Yep. In orbiter most spinning space stations have a docking port in the center of the station, you line up with the port and begin rotating the craft at the same speed then go in for docking.

Not as hard as it sounds.

Who said the middle of the station needs to rotate where docking. Its the middle after all. Spinning or not it will be zero G in the center. And that is actually useful to load and unload things. I find much of the thinking on these things filled with ground based biased. But also not that hard to match a slow spin of a station. center on where you want to dock and a bit of thrust to impart spin and then forward until dock. Just don't screw it up. But less fuel to spin a docking ship than a station.

And why a ring for a station? Its zero G in a vacuum. You could simply impart a wacky rotation on anything you want to generate something resembling gravity. Heck, shape it like a slice of pie. Zero G and Newtons laws don't care. Simply need to consider where to stick a source of thrust and how much in what direction. And why 1 G? You simply need something to help with atrophy. .9 G or heck, even .3 is better than 0. Will slow that down somewhat. How cool would it be to say you can bench press 1200 pounds? My only question is how does the inner ear perceive the rotation? If you feel like your spinning all the time that could make you grumpy.

But spinning up and down is not an answer. To much fuel would be needed to stop and start the spin. And any mild error could screw things up. Like increase or decrease the orbit. Although might be decades before that caused any problems but makes it harder to fix when the station is fully built. Suddenly you need way more fuel to correct even a mild error.

One argument offered up against it is that one
of the purposes of the current space station is
to study things that only occur in zero gravity,
but that seems to me to be a pretty feeble point:
considering the problems that 0g causes, one ought
to be able to conjure a habitat that has both
conditions, to preserve the occupants' health.

More relevant I think is just the mass-cost of
building such a thing. The orbiting section would
have to be much more structurally sound than
the structures we have up there now, which don't
have to bear any weight. And of course the thing,
once spinning, would a permanent safety hazard,
there'd always be the the potential for things
to get flung off, including people. Suggestions for
lower cost structures, like dumbbell designs, would
be even more of a hazard, in that regard.

It will be done eventually, but I've come to think
that it will only occur when we've got the infrastructure
to source its material from the moon, or a small
asteroid we've toted into near space as a resource.

...this reminds me of reading a SF story from the
late 40s which imagined a very large rotating space
station made from steel girders in the manner of
construction then used for buildings on earth.
The author seemed oblivious to the quantity of
fuel it would require, and the number of launches.
Some serious math deficiency there, both the author
and his editor/publisher who let that go by.

How do you propose people are going to make a non-rotating, air-tight axle in space? It seems like a huge waste of time and resources, excessively complicated. Conversely, creating a simple, one piece structure could be done very easily using expended staging sections for creating the outer parts of the station without any need of bearings or other heavy and/or expensive parts.

The reason most designs for a 1g space station look like a ring is because that is the simplest way to create a relatively flat surface that experiences the same gravity. If you shape it like a pie you have a whole bunch of useless space near the narrow end that doesn't experience 1g. It might be useful during the construction of the station (building in pie segments) but as a completed design it doesn't make sense.

A space station does not need to rotate that quickly for the sections on a ring to experience 1g or near 1g. Spinning a spacecraft up to the correct RPM's does not take much fuel at all - a small burst, maybe 1 second long from thrusters would be far more than enough power to do the job. This is stuff that has already been done for many decades.

An centrifugal artificial gravity station doesn't have to be a full circle either. Picture a "butterfly" steering wheel (google if you've never seen one). Nor do the spokes of the wheel have to be rigid, they could be cables. Then you could have 2 arch shaped modules, connected by mile long cables circling their barycenter at a relatively low rate of revolution but still creating as much as a full G of artificial gravity.

Such a station would only be really needed in long trips such as to Mars and back with dockings only occurring a few times in Earth or Mars orbit, you wouldn't be needing to spin up or stop the spin very often.

That is entirely dependant upon the radius you're spinning around, make it short and you have to spin fast to achieve 1 G, make it long and not so much.




And that is entirely dependant upon the mass of the ship, 100 tons will require more 100x fuel to spin up than 1 ton will.

I think you should take a trip in a space or microgravity simulator and play around with things to see how things actually work in space. There are a few good ones. Orbiter is the best overall IMO and it is free, but there is also Kerbal, and a number of others that offer higher fidelity but less user friendliness. I think you're severely overestimating how much energy is needed to set a weightless object into motion (especially rotation about an axis), and underestimating the complexity and expense of getting materials up there in the first place.

I've spent more time than I can count in Orbiter / Kerbal and I am very aware of how these things work thank you very much. And every word of what I previously posted is factual.

http://www.calctool.org/CALC/phys/newtonian/centrifugal


A spinning station with a radius of 100 meters will have to spin at 3 rpm to achieve 1 g.

One with a radius of 1000 meters will only have to spin at 0.95 rpm to achieve 1 g.


Also the larger the radius the smaller the difference in g experienced between a person's feet / head. With a 100 meter radius the head experiences 98.5% the g as the feet but with a 1000 meter radius the head experiences 99.8% as much g as the feet. This difference could determine how much one's vestibular system would be affected.

Examples of rotating tethered stations:

I thought those numbers were a bit low (100 metres, 3 rpm) but it's quite correct. That's a lot smaller/slower than what I would have guessed.

Why aren't we doing this?? We also don't need 1G, why not simulate around 0.5 G's so we can get acclimated/more data on what it's like to spend more time on low gravity objects, like the Moon & Mars.

Gemini 11 conducted the only (as far as I know) artificial gravity tether experiment in orbit using a 100 ft tether between the Gemini spacecraft and an Agena docking target. They generated something like 0.0002g.

Here's an interesting question though - say you have a space station with areas of rotationally generated gravity (nevermind exactly what G level).

And some zero G environment in the center (or wherever).

What does that do to the astronauts? Do they spend months in the "Vomit Comet" logging in hundreds of hours to deal with that?

They acclimate to zero G, and have to do that again upon returning to Earth. Now expand that process to "every day" or whatever...

There has to be a biological challenge there....

I don't think it's that big a problem, the body seems to be able to adapt to short term weightlessness relatively well, perhaps with some people experiencing motion sickness. The vomit comet is still an important part of training because some people just get too sick or disoriented from weightlessness.

I would think a permanently manned station would have living quarters somewhere out at the fringes of the station where G's are highest, and stuff like storage, tankage, etc could be kept in the center.

There are definitely challenges to a station like this, I think specifically things like gravitational perturbation and localized gravity differences due to large masses of water or sewage or whatever, they would all act on the craft to destabilize it from its rotation.

But I still think we should have built a spinning station years ago.

We should probably have a whole whack of them running like the old ships of sail used to do. Have a space station do a complete orbit around Mars and earth every 12 months and have 6 or 12 of them doing the same trip. Refuel rockets sent up constantly to handle refueling. If we had kept up the pace of the 50's and 60's we'd probably have this stuff by now

An object spinning to generate 1g is going to have
its outer surface experience the force equivalent
to its weight on earth. Whatever it supporting it
from the axis will also experience that force, it
will be like having the object hanging from it on
earth. So, everything will have to be built, basically
as if it was a suspension bridge deck on earth.
A lot more strength, and weight, required.

The longer the distance from the axis, the slower the
rotation required, but the more mass under large force
in the beams/cables holding up the outer spinning
surface, which means the fatter the structure must be
to support it. Your suspension bridge gets much longer
cables. Steel breaks under its own weight in 1g at
around 10 km, or 1km of steel cable can only safely
hold up about the equivalent of 6km weight worth of the
same mass cable, to have a safety margin.

It is correct you don't need 1g, 1/3g may be sufficient,
which allows for a more massive "bridge deck" to cable
ratio.

Regardless of g force, studied have found rotation rate
determines motion nausea, and most people can't cope
with 3 rpm; things are much improved at 1 rpm, and much
less than that, there are rarely problems for anyone.

...A possible solution for docking is to have a "can", with
airlocks at each end, one facing the docking ship, the
other toward the station. The can is supported in concentric
orientation at the axis of the station by powered wheels
against its outer surface. These wheels can be driven to
spin the can relative to the station's motion. The can can
then be spun to exactly counteract the station's spin,
at which point a visiting ship can dock with it without
having to spin up. Cargo transfer then occurs, then the
ship undocks. The wheels then slow to a stop, causing the
can to be fixed relative to the station. Then the station-
side airlock can be extended to mate with the station, and
cargo exits into the station. The can will be quite light,
so not a lot of energy is required for the manoeuvre.

Rotating bodies precess as they rotate. Wouldn't this potentially create some issues for a body in low Earth orbit?

Good point, NavyNuke99, but I'm too tired to "brain" that hard now! I'm sure the ol' boys at NASA have considered it, though.

I just came to say, in case someone else didn't, that you don't have to spin the ship that is docking to a spinning station. You have the docking collar on a bearing, and once you dock up, it will spin the supply/transfer ship up itself when you pull it up tight. You don't want to have to match angular speeds in order to dock successfully, in addition to everything else that it takes.

Precession requires an unequal force on the
spinning object, such as with a top if it
is not perfectly vertical, or a not perfectly
symmetrical object (I mean symmetrical along
the spin axis, not around it) passing through a
trace of residual atmosphere. For a symmetrical
object in orbit, this should not be much of a
problem. The object must be wider than long
(like a plate, not a pencil) in order to be
stable, but meeting that criterion it shouldn't
have further issues, except what might be generated
by the shifting of weight caused by people
moving around inside. I suppose that could result
in some shifting over time, but a very small
thruster adjustment every few months should
be able to correct for what might build up,
if anything.