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I'm working with the idea of a 'ring station' encircling a planet, as a tightly connected belt of structures that connect in orbit around the planet's equator. I'm curious to know what would happen if a portion of that structure were destroyed (say, 10-20% of the structure), in particular what effect it might have on the surviving majority of the station.

Would the remaining structure continue to orbit relatively undisrupted? Alternatively, would there be some stresses introduced to the structure, or some decay introduced to the structure's orbit?

EDIT: Thanks so much for the great responses, this has given me a lot to think about! I appreciate I haven't offered much in the way of detail (orbital distance, mass, structural details) however at this stage I'm still just rolling the idea around a little to see what's viable for my story.

As I picture it, the structure would be a rigid or semi-rigid, continuous man-made 'belt' around the planet, equidistant from the surface on all sides. Much like the structures in the Halo game series, though on a scale that would comfortably encircle a planet. The belt would be perhaps 100-200 metres wide/deep - enough to allow inhabitants to set up habitation and other facilities, and traverse the circumference via some means of transportation, such as a rapid transit rail network.

I'm more than happy to hear of any obvious or significant limitations on whether this is remotely possible, and make the call from there on whether it's still hand-wavingly plausible to proceed with in my setting.

Thanks again!

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    $\begingroup$ Does 20% magically disappear or is there some kind of explosion or something else which might give the rest of your station a bit of a push in a certain direction? $\endgroup$ – Raditz_35 Jul 10 '17 at 13:53
  • $\begingroup$ Welcome to WorldBuilding nish! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun $\endgroup$ – Sec SE - clear Monica's name Jul 10 '17 at 13:55
  • $\begingroup$ A ring can't be in orbit -- see for example Larry Niven's problem with the dynamic stability of the Ringworld. $\endgroup$ – Mike Scott Jul 10 '17 at 13:57
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    $\begingroup$ Naturally occuring ring systems are formed by gazillions of objects of varying sizes, each in their own orbit. Magically removing some of those should have relatively little effect on the other objects in the ring system. Just to be clear: you are talking here about an artificial, somewhat rigid construct encircling the planet, correct? If so, please edit and elaborate a bit on how that structure maintains the correct orbit during normal operation, as that may very well have a large impact on what happens if a portion of it disappears. $\endgroup$ – a CVn Jul 10 '17 at 13:58
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    $\begingroup$ I don't have enough knowledge to answer this question, but I think there are a lot of details that need to be added before this becomes answerable. For instance: what is the orbital distance of the structure? What is its mass? The gravitic attraction between the structure and the planet is what will determine the stability of it's orbit, and these two factors are critical for determining that... $\endgroup$ – Isaac Kotlicky Jul 10 '17 at 14:19
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I think it depends on what orbit it is at. For instance if it is at a low orbit and spun up to create artificial gravity, then once the ring is broken the remaining pieces will fly away by their own momentum.
This wouldn't be the case if they are at the right speed for their orbit.

Another thing to consider is how the ring is broken. If a large explosive is used, then the shock wave through the rest of the ring could cause problems; the part of the ring "after" the blast will be given more acceleration, and the part of the ring "before" the blast will be given a push backward. This would cause the ring to flex, part would slow down and fall further into the atmosphere, part would speed up and be pushed away. More twisting would happen as wave propagated around the ring, and could cause the whole thing to fly apart.
Assuming that the ring has some big stability thrusters in place to keep it in a proper orbit due to the instability of a solid ring (as others have pointed out) you might be able to cancel out the wave and save the rest of the station.

You could actually solve both problems by not having it be a solid ring, but instead a series of stations in the same orbit. Take a bunch of O'Neill cylinders or other rotating ring stations and build them in the same orbit a couple hundred KM apart, with shuttles to transfer between them, and you could have a few blow up without disrupting the stability of the ring as a whole. You'd still have other stations damaged by debris, but at least the whole thing wouldn't come crashing down.

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The station's orbit will destabilize.

There are several underlying principles to keeping a ring-station in a stable orbit around its parent:

  1. Aligned center of mass with parent.
  2. Matched rotational spin (specifically the precessional angular speed of the ring to Earth’s rotational angular speed).
  3. artificial gravity induced by centripetal acceleration.
  4. Stabilizers to prevent precession of the ring.

    Since the station is uniformly circular, its center of mass lies at the geometric center of the ring. Gravitational problems, when applied to uniform objects, simplify down to the gravitational forces acting upon the center of mass of each object. If the ring's center of mass aligns with the parent, then it will not experience a net gravitational pull from the parent. If, however, the the point is misaligned, then the ring will experience a gravitational force from the parent. Since the misaligned center of mass of the ring lies well outside of the ring, the entire ring will move as the center of mass orbits the parent's center of mass. This induces an external spin upon the station which introduces precession beyond what the stabilizers may have been designed for.

what would happen if a portion of that structure were destroyed (say, 10-20% of the structure),

The station's center of mass will move from the ring's center to a point off center opposite of the destruction (assuming the destruction uniformly affect a single area of the ring). This will cause the parent to induce a net gravitational force on the structure's center of mass which now orbits the parent several miles off the parent's center of mass. This force will induce angular momentum and precession of the entire station and cause the entire station to spin and orbit around the parent without stability.

Example:

Your station is built around Earth, but well below The Moon's orbit. Bombs destroy 10-20% of the station's ring closest to The Moon. The ring's center of mass moves from the center of Earth, to miles off center but opposite of the moon. Earth's gravitational force will then pull the entire station towards the moon, throwing it off its original orbit. The parts of the station opposite of the closest to the destruction will lift to a higher orbit while parts of the station on the opposite side (where destruction was the least or nonexistent) will drop closer to Earth. But, the ring already has a spin, so this center of mass will also spin around the Earth's center of mass. As a result, the parts of the station closest to the destruction will swing about a higher orbit while the parts of the station farthest from the destruction swings about lower orbits. Without quick action to combat the introduced precession, the station runs the risk of brushing to close to the atmosphere and causing permanent destruction.

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  • $\begingroup$ Thanks for that visualization of the center of masses. Very neat. $\endgroup$ – Mad Physicist Jul 10 '17 at 18:18
  • $\begingroup$ Why does the station's rotational spin need to match that of the parent? To me, "orbit" means that the station is spinning at the speed necessary to keep its parts in microgravity. $\endgroup$ – Bergi Jul 10 '17 at 21:03
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    $\begingroup$ I wasn't specific enough. Specfically, you want to match the precessional angular speed of the ring to Earth’s rotational angular speed. This prevents the ring from preccessing due to the gravitational effects of earth's angular momentum. $\endgroup$ – KareemElashmawy Jul 10 '17 at 21:11
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If they are in orbit.. then essentially, nothing. The rest of the ring will just stay in orbit. Unless it is so big that it has its own gravity.

At least if you just remove a chunk in a surgical fashion. The problem comes if you have an explosion. This will push lots of big fragments into similar but not identical orbits to your ring, with everything going around 6-8 km/second. Those chunks pushed into elliptical orbits will be crossing the orbit of your ring at considerable relative velocities.. hundreds of meters per second at least. There will be secondary collisions, each increasing the amount of debris and the chance of more collisions. Eventually your ring will be entirely destroyed.

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    $\begingroup$ ... everything has it's own gravity, by definition. the larger and slower it is the faster it's orbit will decay. $\endgroup$ – Isaac Kotlicky Jul 10 '17 at 14:20
  • $\begingroup$ Depends if the self-gravity is enough to be worth considering. Orbital decay should not be a problem (actually worse for lighter and faster objects), if your ring is close enough to the planet for orbital decay to be a serious problem then you'd have plenty of problems before this situation ever arose.. $\endgroup$ – Andrew Dodds Jul 10 '17 at 14:24
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    $\begingroup$ Which is why we need more information about the scenario before a meaningful answer can be given. See the comment by @MikeScott - a ringworld isn't necessarily stable anyhow, so the answer may as well be "your question is wrong." But that's not fair to the OP. $\endgroup$ – Isaac Kotlicky Jul 10 '17 at 14:29
  • $\begingroup$ The speed of an object in orbit is only relevant to a collision when it is colliding with an object in a different orbit. If parts of a large orbiting object are separated in an explosion, then the average velocity of the resulting debris is still identical to the main object (assuming the explosion did not push the debris all out in only one direction, in which case there would be a small difference). A subsequent collision between the original object and its own debris should occur at relative velocities no greater than those produced by the explosion. $\endgroup$ – David Scarlett Jul 11 '17 at 6:01
  • $\begingroup$ Following from my previous comment, if you're driving in a car at 100km/h and you throw a rock directly upwards, the rock does not impact the vehicle at a relative speed of 100km/h when it comes back down. It impacts at whatever speed you launched it at. $\endgroup$ – David Scarlett Jul 11 '17 at 6:02
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I can think of two way of making a ring arround a planet

On orbit

The probleme is that it must match orbital speed witch is higly unpractical. Because the lower the altitude the faster it goes the much fuel it requier to reach and the higher altitude the farther you need to go and the much fuel it requier

Depanding on the altitude it can differ but if destroyed it wont affect structural stability that mutch but fragment can causes damage

Orbiting 'inner' ring supporting a tidely locked 'outer' ring

If this a part of this one is destroyed it depend if the inner ring is to.

If not then except the debries of the part destroyed and the part of the inner ring exposed then there isn't much disrupt

If the inner part is affect then because the inner part goes beyond orbital speed to compensat outer part mass then the inner ring will go at an orbit higher until his speed match the orbital speed and the outer part wich is no longer supported will crash onto the planet

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Suppose a uniform ring (of any width) around a spherical mass. In such a situation, the ring's positioning around the center point would be unstable. In order for the ring to be in "orbit", it could not be a single rigid body, but a series of loosely connected pieces; and in such a case there would be none of the centrifugal "gravity" normally desired from such a configuration. The ring would in fact need to be spinning faster than the velocity of circularly orbiting objects at that altitude. If perfectly centered, the net forces acting on it would be null, but any perturbation would result the closer side of the ring being drawn toward the central body. In the sequel to Niven's Ringworld, he addresses this oversight by supposing the existence of massive thrusters to compensate for such perturbations. Let's then suppose this is the situation on your ring, as otherwise it wouldn't have been stable in the first place. If a portion of the ring's mass from one side is instantly missing, it would begin to be drawn toward the central body from the opposite side, which the thrusters would attempt to compensate. If the removal is explosive, the situation becomes more complex, but once again falls upon the thrusters to compensate. However, suppose your ring is spinning to generate centrifugal "gravity". The missing, low mass portion would be spinning around the center at a high rate of speed, which would lead to the perturbations to be very chaotic. The exact result would depend heavily on the initial conditions. Furthermore, a spinning ring would be under immense tensile stress, and would likely be thrown open instantly if a portion were removed.

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Here's a different way of thinking about it: If your ring station is made up of segments, what are the forces between adjacent segment?

If the ring is spinning slower than the velocity that an object in orbit at the same height would, then the segments must be pushing against each other to prevent them falling towards the Earth. The contents of the station will experience a gravitational pull towards Earth, which, for example, would be equivalent to 90% of surface gravity if the station were nonrotating and at the height of the international space station. The gravitational pull felt would decrease if either rotation speed or height increased. If a segment of the station were removed or destroyed, the remainder of the station would collapse towards the gap and fall to Earth.

If the ring is spinning at the same velocity that an object in orbit at the same height would, then it's just as if the segments are all in orbit independent of each other. The contents of the station will experience weightlessness. The removal or destruction of a segment will have no effect on the remainder of the station (assuming it can remain airtight).

If the ring is spinning faster than the velocity that an object in orbit at the same height would, then the segments must be pulling together to prevent them shooting out into wider, elliptical orbits. The contents of the station will experience a gravitational-like pull away from Earth, dependent on how fast the spin was. If a segment of the station were removed or destroyed, the remainder of the station would peel outwards away from the gap, and would probably whip out into a horrible, spinning, wide elliptical orbit, or just tear apart and fire off into a bunch of different and potentially intersecting elliptical orbits.

Edit: Actually, as an interesting addition, it is quite conceivable that in the case of a ring spinning slower than orbital speed, the same engines used to perform adjustments to hold the station in position could also be used to close any gap that was created by the removal, destruction, or ejection of a segment. I.e. Any damaged segments are ejected, then the entire ring shifts marginally closer to Earth, rejoining and resealing to form a very slightly smaller ring.

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