If a generations ship was destroyed while in low Eath orbit (LEO), would debris fall to the surface?

Question

I understand there are a lot of factors to consider here, but would it be possible for material from the ship's destruction to fall to earth and cause significant damage to a city? What is a reasonable amount of time to pass for the debris from the destruction to hit the Earth's surface?

It is relevant that the ship was built by humans and in the far future, but the material, size, and manner of destruction are irrelevant as long as it is possible for debris from its destruction to hit Earth. Basically I need to know if it is possible for the ship to be destroyed in some way and in a fairly tight time frame (minutes to days, not months to years) have debris hit the Earth's surface.

Material, Size, manner of destruction, as well as orbital altitude can all be modified to achieve the desired outcome.

Answer 1

Let us consider what happened when a large man-made orbiter did fall to earth.

http://www.history.com/news/the-day-skylab-crashed-to-earth-facts-about-the-first-u-s-space-stations-re-entry

On July 11, 1979, with Skylab rapidly descending from orbit, engineers fired the station’s booster rockets, sending it into a tumble they hoped would bring it down in the Indian Ocean. They were close. While large chunks did go into the ocean, parts of the space station also littered populated areas of western Australia. Fortunately, no one was injured....

Mocking NASA’s inability to say precisely where Skylab would land, entrepreneurs across the country sold T-shirts emblazoned with large bullseyes. Another enterprising individual took a different tack and sold cans of “Skylab repellent.” Few people felt reassured by NASA’s statement that the risk of human injury from the event was just “one in 152.”

A lot of Skylab pieces showered Australia. Some are collected in a museum there. Here is the biggest piece: an oxygen tank weighing about a ton.

from https://www.space.com/21122-skylab-space-station-remains-museum.html

So: if little Skylab can shower the earth with 1 ton pieces, your huge ship could definitely do the same.

A caveat as regards destruction: Having a big wad of metal fall on you will mush you, but your falling ship will not wreak dinosaur-killer scale havoc. Pieces falling out of orbit are moving at approximately 270 miles per hour when they hit: that is terminal velocity and will be true regardless of the mass of the falling piece, That is true also for meteorites less than 10 tons which slow down in the atmosphere then fall at terminal velocity.

Big 10 ton+ meterorites have too much kinetic energy to slow all the way down. They can hit at speeds of 5000 miles per hour or (much) more. F = mv^2 and so these things are what make the huge craters. https://www.amsmeteors.org/fireballs/faqf/#12

Answer 2

Strictly speaking, the answer is "Yes, that can happen." However, there are so many ways that it could happen that the full scope of "how" would be too broad.

Since you don't need the full scope, but rather need only a few good ideas, I will offer some.

1. During an explosion, pieces are going to be generally accelerated in all directions. If the explosion is strong enough, you can decide that sufficient acceleration has occurred on the debris to make it go in whatever direction you want.

2. During the explosion, perhaps one of the rockets was actively thrusting at that moment, or maybe it is thrusting in reaction to the explosion to help stabilize; either way, that rocket, and any arbitrarily large chunk(s) of the ship attached to it, break away because of the reduced structural integrity. This piece(s) could now be essentially a missile and could happen to randomly land wherever you want. This might be your best bet.

3. You said "in low earth orbit," but is it actually orbiting at that height? Similar to the answer from @AndreiROM if this is a new ship, or not new but is currently being moved from planet-to-orbit or orbit-to-planet, and it is being hauled up or down on a space elevator then all you need is for an accident where the elevator breaks or the ship breaks off it or similar. This would allow the entire structure to fall almost straight down if it's only at LEO altitude. A little bit more altitude and you could have it fall in an arc away from the elevator location. This would probably be the fastest option and would provide you with whatever time frame you wanted depending on the altitude the accident happened at: minutes, hours, days, even months or years... whatever you want, just change the altitude accordingly.

Of course, you can combine multiple ideas together. Perhaps a large shower of debris over a large area and a rocketing piece or two to specific locations.

Answer 3

Unless it has additional force added, anything in LEO will eventually fall back to earth. There is enough atmospheric drag to cause it to slow down.

For a really good description of Low Earth Orbit, see What’s So Special About Low Earth Orbit?

The question is, where and when will it eventually fall?

See this for a discussion on de-orbiting time frames.

If you want it AIMED at a city, then the applied force to de-orbit it would have to be precisely calculated and methodically applied. It would have to be a controlled reentry. And even then, it would not be a sure thing. However, the time frame could be in hours, if enough thrust were applied to slow it sufficiently. The orbit would effectively be changed from that of an orbiting object to that of a ballistic object - that is, a parabola, as if it were shot like an ICBM from earth. Their targeting can be very precise, but the applied maneuvering thrusts are very carefully controlled.

In point of fact, when vehicles are returning from the ISS, they are sometimes deliberately placed into a steep parabolic ballistic trajectory from their orbital trajectory. See this very technical description, complete with graphs, from NASA, for re-entry trajectories. See particularly figure 2 for a 'Skipping reentry trajectory' - basically, puting it into a parabolic trajectory.

However, if you wanted it to accidentally hit a city, then introduce fate into your story. It is highly unpredictable as to where something will fall. The upper atmosphere is highly unpredictable. But the steeper the descent (the more velocity it looses) the quicker and more predictable the impact point. The more like a ballistic (parabolic) trajectory and less like an orbiting (circular) trajectory. The time frame can be anything from a week to decades, depending on the initial orbit and how much atmospheric drag it comes under.

As for the damage it would cause, it also depends on the impact trajectory and angle of approach. However, if it started from a stable low earth orbit, it would not have gained enough energy to be anything greater than a very big accidental localized collision. It would be similar to a similar sized airplane falling to the ground. It might take out several city blocks, and even leave a trail of destruction if the angle of impact were really shallow, but it would not be a city-buster.

TL;DR

Think of the impact damage of the planes that hit the World Trade Center. They hit under full throttle, and the towers survived initial impact. Scale up the size of the aircraft to match the size of your generation ship, and you have some idea of the scale of the collision. The speed of the falling space ship would actually be somewhat less than the speed of these planes, since the ship would be under free fall, and the planes were under powered flight. And given that generational ships would probably not be aerodynamically shaped, atmospheric drag would be significantly greater than a plane.

Answer 4

A generation ship is, by its very nature, going to be very big.

Assuming that its structure was largely complete, yes, it would most likely fall to the ground in a giant heap of twisted metal which would cause terrible destruction and devastation.

Of course the manner of its destruction is also very important. If it gets blown into a million pieces its impact on the ground is going to be much smaller, with only a few pieces being large enough to do any real damage (the debris would, however, cause untold chaos in our orbit, perhaps taking out every satellite we have).

If, however, the shipyard somehow lost control of the behemoth while towing it to a new location, for example, and it somehow "slipped" into Earths atmosphere, it would impact the ground like nothing that has ever hit the Earth before.

Depending on the size, it could be capable of causing, if not an extinction level event, at least global devastation (tsunamis, earthquakes, massive fires, not to mention nuclear fuel spills, etc.)