Effect of a destroyed orbital ring falling down on the planet [duplicate]

Question

I'm working on a story where an orbital ring situated in LEO above the equator of an earth-like planet is destroyed which is a calamity for the species that used it. The ring is essential for them and most of their settlements are along the equator where they have easy access to it.

The ring is composed on an inner part that spins at the speed necessary to keep it in orbit and a geostationary part levitated over the spinning part that is connected to the surface with tethers/ space elevators. It is as heavy as needed to wreck appropriate havoc.

Edit: Quick sketch (not to scale) I had envisioned that it gets destroyed or damaged in a manner that de-orbits the ring, resulting in most of the material falling down and destroying the settlements below it. I also imagined that some of the material remained in orbit and continuously rained down as meteors, making the equator region inhabitable and hazardous to cross. Is that at all realistic?

Edit 2: Not sure if this is allowed since it's technically a different question, but on a order of magnitude how quickly would this thing come down? If you know someone who works up on the ring station and they phone you when they notice it's breaking, do you have time to pack up your car and leave? Do you have time to jump in your car and leave?

Answer 1

Probably not much damage

After watching the linked video, there are two main points to consider (which are both noted in the video):

1. The "geostationary bits" are not actually "geo" stationary, they are just plain stationary, being supported by "upwards" force from the inner ring. If something goes wrong and these parts are separated from the orbital ring then they will fall straight down to the point directly beneath them on the planet. There may be some deviation due to atmospheric effects (so the population centre on the surface would sensibly be built about 50-100 km north or south of the connection point) but the damage will be from an object falling at terminal velocity in the atmosphere. Note that terminal velocity in an atmosphere is very different to orbital velocity - the damage these things will do if no safety measures operate (see below) will be equivalent to an object of the same size being dropped from an aircraft. Time from failure until impact will be effectively instantaneous for the section closest to the ground and a few minutes for the section that was up in space if the safety equipment fails. If the safety equipment (big parachutes) work then the larger sections will descend at human-survivable speeds over maybe 30-60 minutes, longer with proportionally larger parachutes. Exact timing will depend on lots of variables - density of atmosphere, depth of atmosphere, density and aerodynamic profile of each component.
2. In order to support the stationary parts, the inner ring is a thin wire moving at more than orbital speed. An intelligently designed ring from a safety viewpoint will be made of a wire with a thickness and composition such that if it re-enters the atmosphere it will burn up rather than survive re-entry and impact the ground. However, it will not be re-entering in a hurry as it is being spun at greater speed than is required for its orbital height in order to support the stationary elements. Assuming that the ring fragments, most sections of cable will move into a higher, albeit unstable, orbit. Expect them to re-enter individually over the next few years unless they are collected up for re-use by then.

The only way to create the level of catastrophe you have in mind is to have a civilisation completely fail to consider failure modes at all. I seriously question how anyone could survive the initial construction process if they did not consider this - something always goes wrong at some point during a major construction such as this - but if the plot demands it then...

• Put the major population centres directly under the terminus of the cable - basically like building a really compact city and then building a major airport on a roof on top of all the buildings in terms of common sense.
• Do not include any parachutes on stationary elements. (If the destruction is due to sabotage then this one can be made believable by having the terrorists sabotage the parachutes.)
• Make the inner ring really thick and heat resistant so it can survive re-entry to do the maximum damage - heat tiles surrounding a tungsten / depleted uranium core a few metres in diameter should do the trick.

You may be interested in reading The Sundering - Book Two of Dread Empire's Fall by Walter Jon Williams. The construction and emergency measures of the Zanshaa ring are described in detail and are a significant plot element.

Answer 2

Yes that's fairly realistic.

The level of damage and devastation would depend on the mass of the fragments dropping from orbit. I don't have the calculations on hand but i'm sure they've been done. However the general theory is sound - a shredded or exploded ring would lead to fragments in decaying orbits, and interaction between fragments would potentially lead to further decaying orbits as time went on. This kind of 'orbital debris cloud' is something that is generally considered to be Incredibly Bad and is actually a major worry for space exploration as we clutter our own LEO with random stuff.

One note is that if most of the debris falls down initially, you might not have enough left in orbit to produce the 'constant meteor danger'. You need a fair amount of stuff in orbit to produce the decaying orbits (unless there's other factors involved like Weird Gravity or Malicious Intervention) required for constant meteor danger, and if most of the material fell initially and you still had enough left in orbit to do that, the initial fall would be an extinction event (unless the initial fall was reduced to quite fine chunks).

You can solve this fairly simply - just have only 'some' of the debris fall initially, leaving enough in orbit for meteors and still enough dropping on people to make the initial fall (the Fall?) notable and cataclysmic.