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So I've got a colony ship crashing onto a world, and I want to reality check its effects on ship, crew and landscape.

Firstly the ship is fairly large. Its job is to seed human colonies on alien worlds, and while it can move faster than light, its journey time length it still expected to be decades and thus it carries families and extensive facilities with it to cover every expected need.

However, on its final approach to the earth-like planet, it was planning to colonise, things go very wrong, and it loses the ability to properly slow down as it enters the atmosphere and crashes into the planet.

Couple of key points that need to be true for the sake of the story.

  1. Most of the crew need to die, but I need to be able technobable my way how a small number didn't. So I need to avoid a 100% fatality rate crash.
  2. I need some of the ship systems to still be repairable, the ship can -mostly- be a wreck, but not annihilated.

Now here come the bit where I'm wondering about the details.

Would it be reasonable to assume that a large ship would likely create a new canyon-like effect if it crashed at the right angle and slide across the surface?

What kind of damage would a mostly metallic hull likely suffer and what would it look like? Crumpling, discolouration?

I'm going to assume the main causes of death would likely be g-force related and fire.. so broken bones and people being smashed against walls? Along with people being burned alive and smoke inhalation?

Another factor that's important, is the crash site been left for a few hundred years in a earth like climate. Besides the obvious rotting, are there other factors I need to be aware of?

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    $\begingroup$ How large is "fairly large"? Are we working with normal physics, or do we have superluminal drives and inertial dampeners? What was the ship made of? (Most space craft don't crash well because you don't need to build a spaceship to be as tough as vehicles that undergo non-space stresses.) $\endgroup$
    – jdunlop
    Feb 12 at 22:56
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    $\begingroup$ Also, as a side note, without inertial dampeners, it is safe to say that you would not see a "new canyon" because anything carrying enough energy to gouge granite would definitely kill everyone inside on impact. $\endgroup$
    – jdunlop
    Feb 12 at 22:58
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    $\begingroup$ What type of deceleration/landing profile is the ship planning to use? If its plan is to enter orbit and have people shuttle/drop pod down, that's going to result in a very different ship design than if it's intended for terminal aero/lithobraking. $\endgroup$
    – Cadence
    Feb 13 at 1:14
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    $\begingroup$ Regarding "the crash site been left for a few hundred years in a earth like climate", everything that's still there will be subject to moisture and atmospheric reactions/corrosion, sunlight UV damage, bacteria feeding off it, etc. Even in a sealed container, thermal cycling because of seasons, natural material aging and natural chemical decomposition (e.g. plastic/rubber embrittlement, lubricant polymerization), natural corrosion / migration, and other processes. In short, nothing more complex than, say, a hammer will still be usable condition. $\endgroup$ Feb 13 at 2:47
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    $\begingroup$ Basically, the only way it can work is that if the ship will be trying to make a controlled landing but fail at that in some moment AFTER it entered the atmosphere. Else you'll get something more along the lines of an asteroid impact rather than a ship crash - not many things will be left unvaporized, let alone ship systems that can be salvageable. $\endgroup$ Feb 13 at 16:16
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The ship breaks into pieces in high atmosphere, each with separate aerodynamic properties

I'm assuming the failure comes pretty late in the entry sequence, after a heat shield has slowed the craft considerably - otherwise, this will be a short story.

A big generation ship wont be built for high G loads like tumbling through the atmosphere, when air resistance hits the wrong parts of it (probably for the first time ever if it was built in space), it will rip into pieces.

This is the key to your story. Big light chunks fall slowly as they get air resistance. Small dense chunks fall quickly. Imperfect chunks tumble. Chunks deform on impact, decelerating survivors slowly enough that they survive.

The chunks will be spread over hundreds or thousands of km; eg this is where from the space shuttle Columbia ended up: enter image description here

It's not only plausible for there to be a small number of survivors after an event like this - it's happened multiple times. Wikipedia list 5 people who have fallen to the planet's surface at terminal velocity without a parachute and survived, 2 of which were able to walk away from their impact with minor injuries, and 3 who needed immediate medical attention but survived:

  • Vesna Vulović, 10.1km. Pinned between an airline food cart and a chunk of the aircraft cabin. Major injuries and needed first aid on the ground
  • Alan Magee, 6.7km. Slowed down by a glass roof of a train station. Broken bones and organ damage but recovered in POW camp.
  • Juliane_Koepcke, 3km. Still strapped in her seat and seat rows were joined together, and they deformed optimally on impact. Walked away and was found next morning.
  • Ivan_Chisov, 7km. Hit the edge of a snowy ravine. Needed major surgery.
  • Nicholas Alkemade, 5.5km. Hit pine trees and snow cover. Only injury was a leg sprain.

Will it create a canyon?

Only if it's made of unobtainium. When big metal things impact the ground at high speed the ground tends to win. Look at aviation crashes for example.

enter image description here

It depends exactly on how its constructed - but I'd expect each individual chunk that reaches the ground to be about the same size, composition, and velocity of the worst aviation disasters. They may scratch the ground, but they're not going to create a massive geological feature like a canyon.

What's the most common cause of death?

Someone's actually published a paper on this. Head injury is the most common single cause of death.

Multiple injuries were listed as the immediate cause of death in 42% of the fatalities, followed by head injury (22%); internal injury of thorax, abdomen, or pelvis (12%); burns (4%); and drowning (3%). Head injuries were most common among children. The majority (86%) died at the scene or were dead on arrival at the hospital. Eighteen percent of the victims were reported to have sustained a single injury, with head injury being the cause of death in nearly a third of these fatalities. Blunt injuries resulting from deceleration forces, in particular head injury, are still the most important hazard threatening occupants' survival in aviation crashes.

Are there any other factors? Yes - nudity

The corpses will be naked. Very little clothing (including underwear) will survive free fall from these altitude. Eg In MH17:

the New York Times’ Sabrina Tavernise took a grim inventory of the victims, noting that they included a woman “naked except for a black bra,” a man lying “still in his socks but without pants,” and a boy in “blue shorts, wearing red Nike sneakers but no pants,” who “lay with his arms and legs splayed outward, an iPhone by his side.”

The sudden exposure to 500km/hr+ wind of an inflight breakup will rip most clothes at the seams.

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    $\begingroup$ This is a splendid answer - I never saw that chart of the Columbia debris. But I do think a generation ship would leave a much bigger mark than an airplane. Maybe you're not picturing a hollowed out or rebuilt asteroid, but there needs to be a tremendous amount of living space, farms, a massive (though not tremendously reliable) propulsion system. It is still hollow and should break up, but with much larger chunks of debris. $\endgroup$ Feb 13 at 14:14
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    $\begingroup$ @MikeSerfas I wasn't picturing an asteroid (which would impact like... an asteroid I guess), more thousands of chunks - each no larger than a 747, hence the comparison. I'm guessing two different large chunks of thin shells of metal hitting the ground at high speed are going to be roughly equivalent. Individual parts can get buried in the impact (I remember one MayDay episode explained they found the black box about 30m underground), but the ground as a whole fights back. $\endgroup$
    – Ash
    Feb 13 at 14:28
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    $\begingroup$ This is an excellent answer; I shan't bother to write one myself as it would have little to add! I will note that people surviving falls from aircraft will be rather different from people surviving falls from a re-entering spacecraft which will be at least one order of magnitude more energetic. Surviving an uncontrolled re-entry seems implausible; the failure of the craft would have to come after the vessel had slowed to subsonic speeds for people to bounce rather than splat when they hit the ground. $\endgroup$ Feb 13 at 14:37
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    $\begingroup$ In addition to the higher energy of a spacecraft crash, spacecraft are even more optimized to minimize mass than aircraft are. This is especially true of the part of a generation ship that actually gets braked into orbit at the destination...it's likely to discard any heavy impact/radiation shielding that will no longer be needed after arrival, instead of waste propellant braking all that mass. What reaches the surface is going to be shredded on impact unless it very, very nearly makes a soft landing, and in that case it's not carving any canyons, or even knocking down many substantial trees. $\endgroup$ Feb 13 at 18:16
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Bail out.

Some of the people in the crashing ship see what is going on. They are close enough to the shuttlecraft equivalents to get aboard and get out.

The big ship goes down and people inside are asphyxiated as the big ship breaks apart from air resistance entering the atmosphere. The broken apart pieces are slowed by atmosphere (and heated up) then they all fall at terminal velocity. Big pieces will leave a dent in the ground. As in a plane crash the bodies inside are smashed up when they hit. No-one is burned alive. If gory specifics are needed for your story I am sure you can find online exactly what happens to people in a plane crash.

The shuttlecraft free of the big ship try to shed velocity thru various improvised maneuvers of varying success. Some of these craft make it to the surface more or less intact. They would probably be able to find pieces of the big ship large enough to salvage for repairs although parts would likely be spread over a huge area and possibly nowhere near where the shuttlecraft come down.

Maybe there were other last minute launces besides the shuttlecrafts. I like the idea of the shuttlecraft parties later finding a lady and a cat that got into her gas giant atmosphere probe that then methodically lowered itself and its cargo down into the atmosphere. To make sure of the methodical part she tweaked the program from the inside on the way down.

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    $\begingroup$ Escape by shuttle seems a good way to handwave how a few made it to the surface, totally using that now. $\endgroup$ Feb 12 at 23:55
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    $\begingroup$ Big pieces are likely to break up. Only small-ish, or very tough pieces are likely to survive to make dents. Look at the debris that came out of eg. the skylab re-entry... pressurised gas tanks hit the ground hard, but not much else. $\endgroup$ Feb 13 at 14:39
  • $\begingroup$ Plane crashes are a little different because fuel is stored in the wings and they can ignite on impact. A large spaceship will probably behave a little differently. $\endgroup$
    – forest
    Feb 13 at 22:51
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    $\begingroup$ @StarfishPrime, dense structural members tend to also survive. For example, in the Columbia breakup, the nose landing gear and the engine thrust structures landed reasonably intact. $\endgroup$
    – Mark
    Feb 14 at 0:19
  • $\begingroup$ Not just asphyxiated but exposed to depressurization, high Gs, exposure to high temperatures, etc. See: en.wikipedia.org/wiki/… Also, most likely the old lady did it! ;) $\endgroup$
    – stux
    Feb 14 at 5:22
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You want a big ship crashed from orbital+speeds, with a nice canyon dug out by the ship, and you want some, but few survivors. Many systems intact-ish, but broken.

Canyon: Requires high impact inertia, huge mass, and something harder than unobtanium. But not extremely high impact speeds, as otherwise you just get nice round impact craters.

Survivors: Normally speaking, forget about it. Human bodies will turned to a bowl of soup-with-bone-shards at impact energies way below the "canyon-forming" levels.

Only practical solution: Limited range and location

Stasis Fields

Your travelers have the means to set up a complete motion stasis field, wherein nothing moves. At all. Effectively, time is suspended within the sphere.
These stasis spheres cannot be too large, otherwise they would have just covered the whole ship with it and landed like a brick. Say the stasis field is a bubble 5m in radius, max. It will completely protect its contents in perfect condition, unless the field collapses under enormous stresses. In which case, the field fails and it crumples like a tin can.
Shield bubbles cannot touch, cannot overlap. They must be discrete.

When the ship tries landing, it is like a bag full of walnuts. The guidance, propulsion and navigation cannot be inside the spheres, as being frozen would prevent them from working. Nor, unfortunately, can the crew who are manning these emergency systems. Nonvital crew and passengers and sections of the ship that are not required to do a landing, are suitably protected. Mostly. Some of the protective fields fail, most survive.

End result: The ship lands 80% or so intact, but the engines and computers and bridge crew and engineering are completely wiped out.
The ship gouges a huge canyon in the ground as it impacts. Quite destroying the exposed segments, but leaving many of the passengers and stores and non-ship equipment intact.
Ship structure on unshielded segments between stasis bubbles is crumpled, bent and generally badly damaged. Ship structure and mechanisms that were inside stasis bubbles that survived are in pristine shape.

You could even make a plotline out of having some of these stasis fields survive the landing, only to fail to switch off after the event. So there's this metallic-looking sphere sitting in the wreckage. It is an active field. What is inside? Maybe some other crew, maybe food, maybe those repair robots we so desperately want.

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    $\begingroup$ I was thinking something along these lines too: that the canyon cannot be dug with currently known physics, but could happen if the ship was held together with extremely powerful Start Trek style force fields. $\endgroup$
    – Robyn
    Feb 14 at 2:15
  • $\begingroup$ @Robyn Yep. The scales of energies are just too huge. But if you have a force field that covers the whole ship, how do you match the criteria that it still crashed, digs the canyon, yet allow most of the crew to die while leaving some crew and much equipment salvageable? that's a very fine knife-edge to balance on between too much damage and too much protection. My solution gives(much) more protection to those parts of the ship that are not really "ship" but more "cargo" when crashing. $\endgroup$
    – PcMan
    Feb 14 at 12:12
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You have your solution right there: it loses the ability to properly slow down.

This doesn't mean it can't improperly slow down. Things went very wrong, but it didn't just crash into the planet.

Sliding is possible, and it may do some damage to the surface, but a full-blown canyon is improbable, because the earth being tossed aside will dampen its forward motion, and the harder the earth, the less damage the ship will be able to do, and the softer the earth, the more quickly the damage can erode away.

Damage to the ship is likely to look very like the damage to a car when it collides with rock: crumpling of the metal, breaking of fragile parts, people tossed about. Note that unlike today's cars, it will not have crumple zones.

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Some replicators survive. The ship can't decelerate, but the atmosphere slows it down a little. It comes down as a flaming half-kilometer ball at twenty times the speed of sound, tearing branches off the trees a hundred miles away. But the computers enact one of their worst case scenarios and use maneuvering thrusters and aerodynamics to spin it up as it moves into the atmosphere until it breaks apart, and one of the pieces thrown backwards suffers comparatively little damage. That means that a few of the myriad solid state replicators, built from solid blocks of patterned silicon, are still able to produce expert technicians with portable equipment from the rapidly dwindling chemical feedstocks embedded in their microfluidic architecture.

The crash site is essentially a large meteor impact, decorated with blocks of alien stone (actually sophisticated electronics/microfluidics). The diversity of feedstocks present, and the centralized nature of some of them used for particularly specialized equipment, means that miners may occasionally tap a wondrous lode of silver or gold hidden within these ancient stones.

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  • $\begingroup$ What are the replicators powered by? Given that the querent used the reality-check tag, rearranging matter takes a lot of energy and the reactors and any batteries are long dead after a couple hundred years. $\endgroup$ Feb 13 at 13:47
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    $\begingroup$ Well, YWMV, but I'd say either metatope power (induced gamma emission with a cascade of meta-isotopes that break down the energy into manageable photons), or neutrino pair production to create a cold sink for a heat engine (works like perpetual motion but not against physics - problem is, I think you need some rather intricate infrastructure working to make the halo nucleus catalyst) $\endgroup$ Feb 13 at 14:06
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    $\begingroup$ Not sure that the replicators will fit your plot, but the idea of spinning it so that a few bits are thrown backwards and thus survive sounds good to me. The occupants are going to endure some massive G-forces but they and local equipment could survive. Nice story btw. $\endgroup$
    – NL_Derek
    Feb 13 at 22:10
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Crumple zones.

The centre of the biggest pieces remain mostly intact as the bits in front of it take the impact.

The ESA Schiaparelli used an analogous mechanism for the final landing. Though obviously the mechanism wasn't proven given the failure of the landing.

The touchdown speed will be a few metres per second, with the impact absorbed by a crushable structure similar to the crumple zone in a car, on the underside of the lander, preventing damage to the rest of the module.

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