Ring Around Jupiter

[RandalThor66]

OK, so I am a pretty-advanced society and I want to build a ring around a Jupiter-like planet that could serve as a living space - lots of living space. Lets say I want it to be about 5K miles wide and have roughly 1G gravity. Questions*:

 

1. How far above the "surface" of the gas giant do I need to be to have an Earth-like gravity?

2. What would be the circumference of the ring?

3. How much surface area would it have? (Rated in living space equal to the Earth's, i.e. it has the surface area of 350 Earths.)

4. What would be the best way to maintain atmosphere? Just high side-walls + gravity? A "force-field" technology? A thick, clear glass-like cover. (It should have the high side-walls anyway, I imagine.)

 

Some assumptions: The builders were very advanced (obviously), but would also try to use as many natural features as possible (like using the planet's own gravity field to generate gravity instead of using an artificial gravity). They would tap the gas giant itself for as a power source (not sure exactly how) but still have other sources as back-ups. The living space will be on the side facing away from the planet.

 

I assume that there are tons of things I am not thinking of, so if you do please feel free to mention them, including any specific problems they would have had to deal with (other than all the regular ones like building a huge ring around a gas giant). I am looking for this information for a possible RPG campaign I would like to run, so it isn't anything really important - I just like to have some level of the "reality" attatched to my games. I appreciate  any/all constructive input. (Plus, I just find this sort of thing facinating to think and learn about. )

 

 

*Not looking for exacts here, just some possibilities.

[CraigD]

Since the force of gravity varies inversely with radius² (the only physic principle we need for the calculation) the ring would need a radius of

[math]r = \sqrt{ \frac{M_{\mbox{Jupiter}}}{M_{\mbox{Earth}}} } \cdot r_{\mbox{Earth}} \dot= \, 113607507 \,\mbox{m}[/math]

 

Its height above Jupiter’s gassy surface, then, is

[math]h = r - r_{\mbox{Jupiter}} \dot= \, 42116000 \,\mbox{m}[/math]

 

Its circumference is

[math]c = 2 \pi r \dot= \, 713817021 \, \mbox{m}[/math]

 

So given a 8046720 m (5000 mile) width w, the area of one side of it is

[math]a = c \cdot w \dot= \, 5743885697890369 \, \mbox{m}^2[/math]

 

That’s about 11.3 times the surface area of Earth, or about 38.6 times its land area - a lot of space, indeed.

[RandalThor66]

Very nice, thank you.

[CraigD]

It's easier to visualize with a quick sketch than with numbers:

[Moontanman]

So we are talking about a Niven ring around Jupiter? 

[AuraNightheart]

So we are talking about a Niven ring around Jupiter?

 

It would seem so, yes, except this Niven Ring actually is around Jupiter, rather then orbiting as in the original book.

[CraigD]

So we are talking about a Niven ring around Jupiter?

It would seem so, yes, except this Niven Ring actually is around Jupiter, rather then orbiting as in the original book.

There are some extreme differences between the AuraNightheart’s ringworld and the one in Niven’s famous 1970 novel:

• A Niven ring is much (about 262000 times) bigger
• Up is inward, toward the sun at the center of a Niven ring. Up is outward, away from Jupiter, on an AuraNightheart ring.
• The downward force on a Niven ring from the centrifugal pseudoforce of its rotation. On an ANh ring, which doesn’t rotate very fast or at all, it’s from the gravitational attraction of Jupiter.
• The structural forces on a Niven ring are tensional, like on a long hanging rope, tending to tear it apart. On an AHh ring, they’re compressional, like an arch, tending to crush it together.

and perhaps most significant

• A Niven ring is 1AU from a Sol-like sun, so has an Earth-like climate. An ANh ring is 5 to 5.5 AU from the Sun, so without artificial heating, has an icy climate like a moon of Jupiter.

So if your goal is to have a place terrestrials can live much like on the surface of Earth, you’ve got a temperature problem to solve!

 

As with any world, planet or planet-emulating, the usual and obvious solution to temperature is sunlight. At ~5 AU, the Sunlight flux is about 1/25th Earth normal. Given an ANh ring’s surface area, which is 45 times the disk of the Earth (for incoming solar flux, a planet’s [math]\pi r^2[/math] disk rather than its [math]4 \pi r^2[/math] surface area is used), this would require lenses or mirrors with a total area of 3187902949436175 m², about 1125 times the Earth’s disk, of a collection of 302 circular disks as wide as the ring.

 

You could reduce the required sunlight by having a more effective greenhouse effect – up its atmosphere’s CO₂ and CH₄ concentration, or even cover it in a heat-reflective transparent film, like an actual greenhouse – and heating it from beneath via gravitational kneading (this is how Jupiter’s natural moons, like Europa, manage to have some liquid water), but as you need sunlight for more than just heat, I imagine a AHh ringworld would still need to need an array of gigantic, precisely aimed and focused Jupiter orbiting Fresnel lenses or mirrors.

[Moontanman]

How does it stay suspended? 

[CraigD]

How does it stay suspended?

It’s not suspended, like a bridge surface hanging from cables, but supported, like an arch. It’s different from the kinds of arches humans have been building since antiquity, because ideally, each of its sections have the same load, unlike an ordinary arch, the segments have different loads depending on where they are in the arch. In essence, every section of an AuraNightheart ring is a “keystone”.

 

It wouldn’t be an unassistedly stable structure, but would tend to have one section “fall” toward Jupiter while others are lifted away from it, the downward force on its lowered sections increasing while those on the lifted sections decreases. It could do this either while remaining rigid and undeformed, or while being “flattened”. It would need a precisely dynamic system, such as one using position sensors and rocket motors, to remain stable.

 

More complicated forces could cause runaway wavy oscillations, so the control system would need to be sophisticated, detecting and dampening such movement before it became uncontrollable.

[Moontanman]

I know this is an old thread but could the temp problem be solved by a thicker atmosphere than Earth normal? 

[Darky]

Hi,

 

You don't need cables if you can use the star (*our star)'s gravity. I am not experienced at this so take it as an opinion.

 

Regards,

Darky.

[A-wal]

Hi,

 

You don't need cables if you can use the star (*our star)'s gravity. I am not experienced at this so take it as an opinion.

 

Regards,

Darky.

:huh: How could the sun's gravity be used to suspend something around Jupiter?

[Darky]

:huh: How could the sun's gravity be used to suspend something around Jupiter?

The sun's gravity would cancel out (not cancel out but decrease it enough for no drastic movements) Jupitar's; trapping it into an orbit. The same way the ISS is in the orbit around Earth. Surely, that would work.

[A-wal]

Jupiter itself is under the same gravitational influence. For the purpose of anything within a system that's experiencing uniform gravitational free-fall from an object that's external to the system it's basically like that system is on its own in deep space.

 

There will be a slight difference in gravitational acceleration due to tidal force (the difference in the amount of gravity felt because of the difference in proximity to the mass, in this case the sun) but it's negligible.

Edited April 21, 2017 by A-wal

[Darky]

Jupiter itself is under the same gravitational influence. For the purpose of anything within a system that's experiencing uniform gravitational free-fall from an object that's external to the system it's basically like that system is on its own in deep space.

 

There will be a slight difference in gravitational acceleration due to tidal force (the difference in the amount of gravity felt because of the difference in proximity to the mass, in this case the sun) but it's negligible.

Hi,

 

So, there would be no need for cables. The only problem would be to get such a massive structure into orbit. Something of such mass (more than earth) would essentially have its own gravitational field. For this to work, you can do two things.

 

One being you send it up in parts in which case you'd need to send one to one of Jupiter's angles and another one at it's exact opposite. If you start filling up one side, it would cause Jupiter to lose it's current orbit creating future problems. As it is, Jupiter is quite spaced out from all the other planets, but even a slight change could possibly bring Jupiter to crash into an asteroid field/commet/one of its moons or if we're looking at a bigger picture, another planet.

 

The second option being to send it up at once. This will decrease if not clear the chances of gravitational re-adjustments. However, we'll be back at step 1; how to get such a massive structure into space.