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View Full Version : Space Station "Artificial" Gravity

DyerWolf
2009-Aug-18, 09:35 PM
Not a 'mysterious unknown tech' type of question; should be feasible without breaking the laws of physics (if, alas, not fuel-efficient...).

Would it be possible to place a space station in Jupiter's orbit around the sun in a location that could provide the crew with 1g (Earth nominal), while maintaining the same distance (i.e. station-keeping) from Jupiter?

I presume the station (ship?) would have to be under constant acceleration of some sort, but have no idea how to figure this out.

If possible, how far from Jupiter would the station have to be?

ETA:
<clarification>
What I'm trying to do is get the station to orbit the SUN (= zero gravity from the sun / object being orbited) - but use Jupiter's gravity to keep the crew's feet on the deck.

What I meant by 'under constant acceleration ' was due to my anticipation that the ship/station would need to maintain a constant distance from Jupiter to gain the benefit of the gravity, as without the acceleration, big bad J would either gobble them up or fling them from it's orbit...
<from below...>

ShinAce
2009-Aug-18, 09:37 PM
Since when does an object in orbit feel weight?

I must have misread your question, but the answer I'm finding is 'no'. You'll need to rotate the station or tether it to something for a gravitational field to yield weight.

kleindoofy
2009-Aug-18, 09:42 PM
... maintaining the same distance ... be under constant acceleration ...
A contradiction which would be hard to over come.

m74z00219
2009-Aug-18, 09:48 PM
You'll find a very interesting example in Robert Forward's Rocheworld.

There is a space station that hovers over Mercury. It is held up purely by light pressure and it balanced within the planet's shadow: catching only the right of sunlight to hold it aloft. I think this would turn out to be woefully impractical at Jupiter's distance. This situation keeps you at the same distance from the planet while still allowing them to feel weight.

DyerWolf
2009-Aug-18, 09:51 PM
Since when does an object in orbit feel weight?

I must have misread your question, but the answer I'm finding is 'no'. You'll need to rotate the station or tether it to something for a gravitational field to yield weight.

Ah... seems I should have been more specific.

What I'm trying to do is get the station to orbit the SUN (= zero gravity from the sun / object being orbited) - but use Jupiter's gravity to keep the crew's feet on the deck.

What I meant by 'under constant acceleration ' was due to my anticipation that the ship/station would need to maintain a constant distance from Jupiter to gain the benefit of the gravity, as without the acceleration, big bad J would either gobble them up or fling them from it's orbit...

astromark
2009-Aug-18, 10:06 PM
If I understand you it would work like; Using just enough energy to hold you at a position where the crew would feel just 1g. While the craft orbited Jupiter. YES. it could work but, NO. The energy required would be constant and costly. Accelerating against gravity at 1g would consume vast energies calculable by the mass and distance. Yes its not impossible but yes it is...:) The Small Mass Black Hole held just under the craft would do it. So would rotating around a central point. Your idea could work but it would require to much cost.

Rhaedas
2009-Aug-18, 10:13 PM
Another factor to consider. Without doing the math, I'd assume you'd have to be close to Jupiter to have a 1 g pull. The radiation from Jupiter would be a much bigger problem than anything else.

I'm assuming there's a reason for such a thought experiment, but it seems much, much simpler to just rotate a station and be able to put it anywhere with much less energy expenditure.

kleindoofy
2009-Aug-18, 10:17 PM
... orbit the SUN ... but use Jupiter's gravity to keep the crew's feet on the deck.

... the ship/station would need to maintain a constant distance from Jupiter to gain the benefit of the gravity, ...
The acceleration would be needed to provide the benefit of the gravity. Jupiter would be pulling on both the space station and on the people within it with the same force and both would "fall" towards Jupiter with the same speed, resulting in the same pesky weightlessness.

Accelerating the station would cause the movable objects within it to feel their own mass inertia as "gravity."

You would have to park somewhere within the close range of Jupiter's pull and the "ride the clutch," so to say.

cjameshuff
2009-Aug-18, 11:23 PM
Use stationkeeping thrusters to provide gravity, while using Jupiter to maintain position? You really don't need a planet at all, just travel in a circle, applying outward thrust and rotating to circle a point in space. Hovering over any planet would involve the risk of falling into the planet if thrust failed.

And if you're flying in a circle around empty space, you're just spending energy and propellant to do what can easily be achieved without either, using a counterweight on the end of a tether.

matthewota
2009-Aug-18, 11:52 PM
What we have here from the original poster is a lack of understanding of celestial mechanics. When you orbit the sun the sun's gravity is no 'zero'. If this were so you would not be in orbit, you would travel in a straight line. If you wanted to maintain 1G on any spacecraft you would have to do it by either creating artificial gravity by spinning it, or somehow maintaining constant acceleration at 1G.

The only spacecraft that have accelerated fast enough to escape the sun's gravity are the Pioneer 10 and 11, the Voyager 1 and 2 and the New Horizons spacecraft. But they are travelling in arcs not in straight lines.

Sam5
2009-Aug-19, 02:50 AM
Well, what happened to the old idea of a circular space station that rotates and provides an artificial gravity via centrifugal force, like in the movie 2001?

http://discaircraft.greyfalcon.us/picturesf/nor207.jpg

Jens
2009-Aug-19, 03:55 AM
What I'm trying to do is get the station to orbit the SUN (= zero gravity from the sun / object being orbited) - but use Jupiter's gravity to keep the crew's feet on the deck.

Other people may have said this already, but what you are thinking of doing is impossible. There is no way that the gravity of Jupiter could pull the crew without pulling the station itself. Same with the gravity of the sun. Whatever gravity the station feels, the crew will feel as well. You are somehow thinking that with the station in orbit around the sun, that Jupiter could pull on the crew inside without pulling on the station. But that can't happen.

hhEb09'1
2009-Aug-19, 04:47 AM
Ah... seems I should have been more specific.

What I'm trying to do is get the station to orbit the SUN (= zero gravity from the sun / object being orbited) - but use Jupiter's gravity to keep the crew's feet on the deck.

What I meant by 'under constant acceleration ' was due to my anticipation that the ship/station would need to maintain a constant distance from Jupiter to gain the benefit of the gravity, as without the acceleration, big bad J would either gobble them up or fling them from it's orbit...Make a space platform that orbits Jupiter so that its center of mass is at about 7 earth radii from its surface. Place a crew habitat on a tether so that it is about one earth radius above the surface of Jupiter. The crew should experience about one earth gravity. No other constant acceleration needed. :)

Jens
2009-Aug-19, 06:22 AM
Make a space platform that orbits Jupiter so that its center of mass is at about 7 earth radii from its surface. Place a crew habitat on a tether so that it is about one earth radius above the surface of Jupiter. The crew should experience about one earth gravity. No other constant acceleration needed. :)

Interesting idea. But wouldn't that end up pulling the whole space station toward Jupiter?

NorthernBoy
2009-Aug-19, 09:53 AM
It's worth pointing out that this scheme will use just as much fuel/thrust as simply setting the ship on any arbitrary course with 1g acceleration. Basically, you are hovering above the surface of jupiter, and will use fuel commensurate with this.

Ronald Brak
2009-Aug-19, 01:02 PM
You could put a ring around jupiter and walk around on the outside of it. But hhEB09'1's suggestion would be a lot easier.

How far would it the ring have to be from Jupiter? Well, some crazy English dude who was brain damaged by an apple came up with some theory or other on this, but using that would require, like, maths. The equation is:

F=G m1m2/rr (Note rr is r squared. I don't know how to type exponents.)

Now we need the gravitational constant and Jupiters mass and... and I think I want to cry now. I blame my parents for not buying me lego when I was younger. I had to play with my sister's Barbie dolls instead and they didn't like maths.

Grashtel
2009-Aug-19, 01:19 PM
Interesting idea. But wouldn't that end up pulling the whole space station toward Jupiter?
No, or rather yes but the large counterweight that is keeping the station's centre of mass out at 7 Earth radii1 will be pulling the station away from Jupiter with equal and opposite force cancelling the inward pull out. its basically a space elevator (http://en.wikipedia.org/wiki/Space_elevator) that only goes part way to the planet.

1: I suspect that hhEb09'1 is underestimating the distances involved, but this doesn't change the general concept.

hhEb09'1
2009-Aug-19, 01:26 PM
Interesting idea. But wouldn't that end up pulling the whole space station toward Jupiter?The main object would be in orbit, the crew would be experiencing a tidal force more or less--so there would be a balance.

It's worth pointing out that this scheme will use just as much fuel/thrust as simply setting the ship on any arbitrary course with 1g acceleration. Basically, you are hovering above the surface of jupiter, and will use fuel commensurate with this.Which scheme? Not mine, right?

You could put a ring around jupiter and walk around on the outside of it. But hhEB09'1's suggestion would be a lot easier.

How far would it the ring have to be from Jupiter? Well, some crazy English dude who was brain damaged by an apple came up with some theory or other on this, but using that would require, like, maths. The equation is:

F=G m1m2/rr (Note rr is r squared. I don't know how to type exponents.)

Now we need the gravitational constant and Jupiters mass and... and I think I want to cry now. I blame my parents for not buying me lego when I was younger. I had to play with my sister's Barbie dolls instead and they didn't like maths.The reason I chose 1 earth radius and 7 earth radii in my scheme, is that at 1 earth radius the gravity of Jupiter is about two earth gravities and at 7 it is about one earth gravity.

If I didn't screw it up. :)

Let's see, Jupiter has about 318 the mass of earth, and 11 times the radius. So at 7 earth radius above the surface, it would be 18 earth radius from the center. Since gravity is proportional to mass over radius squared, that gives us 318/182, which is .98 earth gravity. So, put your ring at about the same place as my station.

At 12 earth radii it's 318/122, or 2.2 earth gravity. 13 radii gives 318/132, or 1.88 earth gravity. So, it's approximate. :)

1: I suspect that hhEb09'1 is underestimating the distances involved, but this doesn't change the general concept.
I didn't estimate, I calculated. :)

But it was the middle of the night...

DyerWolf
2009-Aug-19, 01:27 PM
...1g acceleration. Basically, you are hovering above the surface of jupiter, and will use fuel commensurate with this.

This part of your response gets as close to what I was thinking as any other description... (and thanks to the others for your responses / alternatives / pointing out the problems:)).

I presume that since gravity decreases with distance, there is a 'balance point' (*) some distance from Jupiter where Jupiter's pull on the station & crew is 1g & the ship could accelerate away from the planet at 1g, thereby station keeping with Jupiter and providing the ship & crew with 1g apparent gravity.

I'm simply wondering whether an efficient engine (like an an electric rocket (http://www.scientificamerican.com/article.cfm?id=the-efficient-future-of-deep-space) could be used to put the station / ship (**) at a point where its in a stable predictable & routinely reachable (visitable) place in space that - without having to rotate the station - gives the crew an almost earth-normal working environment as well as flat decks.

The problem I see with the typical 'ship accelerating at 1g' scenario is that, relative to the rest of the solar system, because the ship & crew is constantly going faster & faster there is no way to reach them - they effectively take themselves out of our frame of reference, and ultimately out of the solar system. So, my thought was that by using Jupiter as a 'counter-weight' (***), we could have a space station where the crew could live almost normally (no weightlessness) and it could be a place where folks from Earth could travel to and from, conduct business, scientific experiments, etc...

*Spherical distance?

** I guess 'ship' is the correct word for anything with onboard propulsion, while 'station' presumes the structure has no self-propulsion capabilities - however 'station' intimates the size of the structure I envisioned better than 'ship'...

*** for lack of a better term

DyerWolf
2009-Aug-19, 01:51 PM
Wow... cross posting. Didn't see hhEb09'1's post. So, the ship / station would have to be at 7 earth radii from Jupiter to do this? That's closer than I'd thought.

<calculating & googling>

So that would place the ship / station only about 27,713 miles above Jupiter's surface? That's closer than the geostationary orbit of satellites above the Earth. Which makes Rhaedas's concern regarding radiation worth noting...

hhEb09'1
2009-Aug-19, 02:11 PM
Wow... cross posting. Didn't see hhEb09'1's post. So, the ship / station would have to be at 7 earth radii from Jupiter to do this? That's closer than I'd thought.
No, the platform where the crew would experience one earth gravity would be at only a little more than one earth radius from Jupiter. You can go farther out (up to 7) with this, but the tether gets longer.

DyerWolf
2009-Aug-19, 02:22 PM
No, the platform where the crew would experience one earth gravity would be at only a little more than one earth radius from Jupiter. You can go farther out (up to 7) with this, but the tether gets longer.

I modified your answer to fit my scenario. Perhaps I did this incorrectly - I read your response as 'at 7 Earth radii, the effective gravitational pull of Jupiter is 1g'; so my constantly accelerating (i.e. flying) ship would have to thrust away from Jupiter at 1g at an average distance of 27,713 miles above Jupiter's surface to give the crew a flat deck and the feel of Earth nominal gravity... if I worked this out correctly.

Clearly your tether idea is much more fuel-efficient.

hhEb09'1
2009-Aug-19, 02:51 PM
I modified your answer to fit my scenario. Perhaps I did this incorrectly - I read your response as 'at 7 Earth radii, the effective gravitational pull of Jupiter is 1g'; so my constantly accelerating (i.e. flying) ship would have to thrust away from Jupiter at 1g at an average distance of 27,713 miles above Jupiter's surface to give the crew a flat deck and the feel of Earth nominal gravity... if I worked this out correctly.

Clearly your tether idea is much more fuel-efficient.Ah :)

But as long as you're willing to expend the fuel, you can position your ship virtually anywhere, above that. The acceleration takes care of the induced gravity, you just have to continually steer the ship to keep it in the vicinity of Jupiter. The crew might have to react to the course adjustments, depending upon how gentle they are.

cjameshuff
2009-Aug-19, 03:04 PM
The problem I see with the typical 'ship accelerating at 1g' scenario is that, relative to the rest of the solar system, because the ship & crew is constantly going faster & faster there is no way to reach them - they effectively take themselves out of our frame of reference, and ultimately out of the solar system.

Only if they never change direction. As I mentioned before, they can just fly in circles in empty space, and they wouldn't have to worry about falling into a gas giant if their engines failed. And the rotating tether and counterweight (or tidal station, as hhEb09'1 describes) arrangement lets you accomplish this without using any fuel or energy.

So, my thought was that by using Jupiter as a 'counter-weight' (***), we could have a space station where the crew could live almost normally (no weightlessness) and it could be a place where folks from Earth could travel to and from, conduct business, scientific experiments, etc...

Accelerating a large structure at 1g with a high-Isp engine would take a horrific amount of energy. And an object hovering at orbital altitudes above a gas giant is less accessible than one that is in orbit and rotating. You're going through massive effort to avoid a minor inconvenience that doesn't even really qualify as a problem...with a large radius of rotation, Coriolis forces and floor curvature would be unnoticeable.

mugaliens
2009-Aug-20, 06:00 AM
Ah... seems I should have been more specific.

What I'm trying to do is get the station to orbit the SUN (= zero gravity from the sun / object being orbited) - but use Jupiter's gravity to keep the crew's feet on the deck.

What I meant by 'under constant acceleration ' was due to my anticipation that the ship/station would need to maintain a constant distance from Jupiter to gain the benefit of the gravity, as without the acceleration, big bad J would either gobble them up or fling them from it's orbit...

That's certainly possible, but only for a short time, as 1 G of acceleration would rapidly use up their fuel.

Assuming it's large enough (it would have to be incredibly large at Jupiter's distance from the Sun), a solar sail would also work.

cjameshuff
2009-Aug-20, 02:33 PM
That's certainly possible, but only for a short time, as 1 G of acceleration would rapidly use up their fuel.

Assuming it's large enough (it would have to be incredibly large at Jupiter's distance from the Sun), a solar sail would also work.

Go further out to one of the smaller gas giants, or inward to Venus, and you can use buoyant structures to do the same job. ~0.9g for Saturn and Venus, a little less for Uranus, and 1.14g for Neptune. Need large balloons for lift on the gas giants (less so for Venus), but it'd be a lot easier than achieving 1g of acceleration at the distance of Jupiter using a solar sail.

ravens_cry
2009-Aug-20, 03:02 PM
Go further out to one of the smaller gas giants, or inward to Venus, and you can use buoyant structures to do the same job. ~0.9g for Saturn and Venus, a little less for Uranus, and 1.14g for Neptune. Need large balloons for lift on the gas giants (less so for Venus), but it'd be a lot easier than achieving 1g of acceleration at the distance of Jupiter using a solar sail.
Hmm, hot hydrogen balloons would likely help. With no free oxygen, there's no danger of combustion. They would still have to be quite large, but it would help.

danscope
2009-Aug-21, 03:50 AM
Hi Dyerwolf, You really should consider 2001:space odysee . Although quite large,
this design is quite practical in that it provides the gravity we seek and is balanced by simply pumping the water supply from tank to tank in a computer controled
program which accounts for the movement of individuals within the space station.
Accelerometers can detect with extraordinary accuracy the total stability of the station, and the design provides for a large living environment as well as being built in stages while occupied. But..... everything costs money.
Dan

GoneToPlaid
2009-Aug-21, 03:58 AM
What I meant by 'under constant acceleration ' was due to my anticipation that the ship/station would need to maintain a constant distance from Jupiter to gain the benefit of the gravity, as without the acceleration, big bad J would either gobble them up or fling them from it's orbit...

Um...no, since both the station and its occupants would be pulled on by Jupiter at 1G. There is one way to do it, although impossible in practice. Place the space station on a giant stick coming up from the "surface" of Jupiter. The stick needs to be long enough such that the space station at the end of the stick feels 1G of tug from Jupiter beneath it. But, unfortunately, this solution doesn't have the space station in orbit -- just merely suspended above Jupiter atop a really long stick. Oh, and this only would work at Jupiter's equator due to Jupiter's rotational velocity.