This was an idea loosely inspired by a Sci-fi movie that I will not name here. But the relevant part is that it involves an interstellar colony ship landing on a planet and the crew learning that the ship had been submerged in an ocean.

Now there is something that kind of bugged me at the time of seeing it, that I thought would be a rather interesting set piece that I myself would like to work with. To illustrate this, here is a rough cross-section of a spin gravity spaceship in space.

enter image description here

Now, this set up works because the only gravity is generated by the spin of the ship. Up and down are meaningless terms in space but the passengers need some way to orient themselves, so down is always towards the floor and outside the ship while up is always towards the center of the ship. Now here is the cross-section of the ship when it is submerged. enter image description here

This changes things because now there is a definite down that no longer corresponds to the floor. The bottom of the ship would be unaffected the top of the ship would be completely upside-down while the sides would be...well on their sides. Where once there was a gently sloping hallway now it’s a really long curved shaft going up and an equally deep pit going down. Which personally I find much more interesting topography than what we got in the film where the deck plan was always nice and flat. Poseidon adventure on steroids. But this new orientation of the ship creates a rather interesting problem that I admittedly can’t think through. How on (insert planet name or designation here) can you get around?

So here is the riddle: How can human adventurers navigate and maneuver around a submerged spin gravity ship to salvage from it?

Edit: I have decided to pivot the original hard science tag with the more accurate science-based tag which doesn't require the strenuous citations. As was pointed out this question is harder to come up with hard science answer to, and I really don't want any of your wonderful comments to be deleted because you didn't include equations that I can't make head nor tail of. Thank you for enjoying this post.

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    $\begingroup$ .... This ship is 1) Almost certainly not going to survive reentry. 2) Not going to survive landing on the water. 3) Not going to survive resting on the seabed. 4) Not going to survive the water pressure (built for at best -1 ATM difference, is now experiencing a gradient +1/+2 to... depends on buoyancy). 5) Not built to withstand wave action (stresses are in the wrong direction, and will be worse if near shore, or in storm). Realistically, everybody dies (even if they get in an escape pod, since those likely don't have enough supplies for long term survival). $\endgroup$ Aug 10, 2020 at 16:30
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    $\begingroup$ Frame challenge – a ship large enough to bother with spin gravity to work seems unlikely to be capable of surviving reentry. Certainly anything with an exposed ring like that seems unlikely. $\endgroup$
    – Dan W
    Aug 10, 2020 at 17:05
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    $\begingroup$ This is from Pandorum, isn't it? $\endgroup$
    – user73910
    Aug 10, 2020 at 18:25
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    $\begingroup$ A riot gun with a load that can actually hole the ship? It's been 800 years... there's still food? The ship has crew that can't speak the same language? 800 years is long enough for mutations to occur? Who taught the cook? How did the cook know what happened? This is the one and only ship of what remains of Earth, heading to a single solar system and there's no rescue coming, so why are there escape pods? There's a big difference between the internal and external pressures of outer-space and half-submerged on a planet... how did the ship survive crashing without completely coming apart... $\endgroup$
    – CGCampbell
    Aug 10, 2020 at 23:30
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    $\begingroup$ in water shallower than the ship's diameter? It's the rest of humanity, yet there are only 3 bridge crewmen at a time? They've got weapon's enough to kill most of the zombies in the bridge, so why didn't they kill most of the zombies from the bridge? The crew are in stasis, and there are zombies aboard... vent the zombies to space... except then water. The sensors can work to understand where they are in space, and yet don't know they aren't anymore? $\endgroup$
    – CGCampbell
    Aug 10, 2020 at 23:34

10 Answers 10


Need some dimensions to work on this :

enter image description here

From the referenced show, which shall not be named: the crew, when they became aware of their situation, escaped in pods to the surface where they could see the coastline in the distance.

According to this article, that puts the crew, at most, 2.65 miles away from the shore (of course, it's relying on Earthlike geometry). The characters are able to swim to land, which would cause me to believe they are much closer. Maybe 1 mile or less.

enter image description here

Again, relying on Earthlike geometry, the continental shelf is no more than about 100 meters deep.

Assuming the spin was 1 whole g (9.8 $m \over {s^2}$) : $a = \omega^2 r, {\delta{a} \over {\delta{r}}} \approx 0 = \omega^2$. $9.8 = $So, what all that means is that I don't want some sort of strange blood-pooling effect because the "gravity" at your head is too much lower than the "gravity" at your feet. A ship diameter of 100 meters (50 meters radius) would spin at 0.442 ${radians} \over {sec}$, and ${\delta{a} \over {\delta{r}}}$ for a ship this size is about 2% of "g". That seems low enough.

So, I'd guess these dimensions :

  • Ship diameter : 100 m
  • Bottom depth : 100 m
  • Top depth : surface (light blue in the image); or just beneath surface at tide.

At the top:

Everything is upside down. You can stand on the roof and walk with some safety. The grade of the "roof" starts to increase as you approach the sides :

You can refer to this image for grade, or here are some high points -

  • 20 degrees : 35% grade (difficult walking) - this grade kicks in at $+ \over -$ 20 meters from the highest point (so about 40% of the top and bottom can be walked)
  • 90 degrees : $\infty$ grade (vertical climb) (about 60% of the station).

You'd need up to 60 meter long ropes to navigate to the bottom. Many typical climbing ropes are 100 meters or 200 meters long.

Ropes will have to be secured to some fixture on the ship. It might also be possible to climb some distance from fixture-to-fixture.

enter image description here

Although the ship has open access to the air, some airtight seal is keeping water pressure out below the surface, or the flooded sections are sealed. In the later (and more likely) case of the flooded sections being sealed, no special diving equipment is required on the inside. Pressure on the bottom is roughly the same, in this case, as it is on the top. No special equipment would be required.

It may be possible to reach flooded sections through airlocks that were meant for space, but can be used for this purpose. There also may be environmental seals between parts of the ship.

** At the bottom **

All moisture, dust, and dirt is working it's way to collect at the bottom, under the guidance of gravity. I'd expect the floors to at least be wet, unless an environmental control system is still working to remove humidity from the ship.

As said above, if the flooded sections are sealed, the pressure down here is 1 atmosphere. The air may be stale, if oxygen scrubbers aren't still working. And you may need light, depending on the state of the power and lighting systems.

As on the top, at the bottom, you get a nice $+ \over -$ 20 meters (40 meters total) of walkable surface. Which is about 40% of the ship. In this case, the floor is the floor and everything is "rightside up".

  • $\begingroup$ Alright, I like what I am seeing and I see that you have certainly done your homework. Sorry for the Hard-Science Tag, I had no idea the baggage that came with until too late. But congratulations you are in the running for that bounty, now let's see how the rest of the week plays out. $\endgroup$ Aug 12, 2020 at 23:10

Climbing/Caving Equipment

Humans have been maneuvering through tight, awkward, occasionally-vertical spaces for centuries, if not millennia. Climbing and caving gear is well-established and well-developed, and would work just as well in an artificial environment like you're describing as it would in a natural cave.

For flooded portions of the interior, cave-diving is also a well-established discipline, so that also wouldn't be anything too novel. It's definitely a specialty, though, as it's one of the most dangerous types of diving.

Outside the ship, normal scuba/submersible equipment could be used, just like any other underwater salvage work.

  • 2
    $\begingroup$ Also, if the ship isn't too badly damaged, diving through the submerged sections wouldn't be anywhere near as hazardous as real cave diving. You'd just be swimming through the corridors, not unlike astronauts moving around on the ISS - after all, if they were big enough for people to walk through (presumably multiple people passing each other), they're more than big enough to swim through. $\endgroup$
    – Kayndarr
    Aug 11, 2020 at 2:34
  • $\begingroup$ @Kayndarr I'd suspect that all kinds of things got ripped out of the walls and any furniture available will block your way. If it's floating it's even more dangerous. You might get stuck. Gravity still applies so if you loosen anything previously stuck, it will sink and it might have enough weight to kill you. $\endgroup$
    – kaiser
    Aug 11, 2020 at 9:43


First off, rule number one in space or on planets is never board a derelict ship. it's never safe. Even on the ocean, boarding derelict ships are unsafe. hundreds of shipbreakers in Alang India die every year inside these hulks due to workplace accidents involving these ships. Like a man looses his footing to an oil patch and falls all the way down from the top deck to the ship's keel. One time this happened, and a man broke his back. He was one of the lucky ones.

But, with most ships, if it has been submerged for that long in water, it's beyond salvage, so as dangerous as it is, the best course of action is for the flightless hulk to become scrap. A floating crane would be what you'd want for this task. just cut apart the ship, and take it up piece by piece.

enter image description here

Because the ship being rendered into scrap will be less cost intensive than restoring it--which will in all likelihood never be possible. And the ship turning into scrap will proved much needed building material for starting the colony.

  • $\begingroup$ As far as I knew this film - this is not a derelict ship. Crew just were sleeping in cryostasis for too long in that ocean. So it is there ship (still there is some danger there). They know itquite good. And they are more like Robinsons - they have really little other choise. $\endgroup$
    – ksbes
    Aug 10, 2020 at 11:07
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    $\begingroup$ Agree, especially if wave/tidal action starts the thing rolling. Imagine that happening as you're exploring what a second ago was the top of the ring... $\endgroup$ Aug 11, 2020 at 5:18
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    $\begingroup$ also, most colony ships like the one one he thinks of would actually be designed to be deconstructed into a settlement. $\endgroup$ Aug 11, 2020 at 5:47

If the ship lands on a planet deliberately under human or computer control, instead of crashing, then landing should be a process the ship is designed for.

In that cases, the ship would be designed so that nobody would be upside down when on the planet. Presumably the ship would stop rotating while still in outer space, so that it wouldn't have any gravity from spinning. Everyone would be in weightlessness during the landing, except for acceleration and deceleration and the planet's gravity getting stronger and stronger.

So if the ship deliberately lands on a planet instead of crashing, it should be designed to stop spinning and descend without spinning. And presumably the crew quarters would be designed to turn so that the former down direction to the exterior of the ship, was now pointing d toward the planet. Thus after they landed on the planet the decks would be underneath instead of upside down or vertical.

So the crew quarters would have to be in several parts that could separate and move to a new orientation and then reattach.

Thus I suspect that the ship would land, if it landed deliberately, with its long axis pointed down at the planet's surface, and the crew quarters would be swung around at right angles from their previous orientation so that their decks now pointed down toward the planet, instead of pointing outward perpendicular to the long axis of the ship.

  • 3
    $\begingroup$ And if the ship wasn't designed to land deliberately on a planet, then crashing won't leave the ship in any recognizable shape. It will be a giant crater (and many many smaller craters) with burned pieces of material scattered over a huge area, there will be nothing there which even remotely resembles a ship. $\endgroup$
    – vsz
    Aug 11, 2020 at 11:15
  • $\begingroup$ I think it might make even more sense that they'd leave the "ring" in space, and move to the central rocket for landing. There are probably seats there that they strap in to every time they use the engines. $\endgroup$
    – workerjoe
    Aug 11, 2020 at 14:53

Cut internal power and flood the ship.

This is likely to be one of the safest ways you can actually explore the interior of the ship. It solves a number of potential issues, namely:

  • Gravity becomes mostly irrelevant because you can easily move in three dimensions.
  • You don't have to deal with the otherwise complicated process of entering and exiting the ship.
  • The equalized pressure inside and outside the ship will make it less likely that structural damage will cause it to crumple like an aluminum can.
  • Because of the uniform environment inside and outside, it becomes much easier to use drones and robots to do the exploration instead of actual people.

The downsides are that for safety reasons, everything inside has to be unpowered (you're not likely to get shocked, but it could still happen), and the submerged environment brings some interesting engineering challenges (mostly due to pressure/temperature/salinity differentials screwing with buoyancy).

Of course, some of this also depends on the design of the ship itself. If it was properly designed to allow easy traversal in zero gravity (that is, without the ring spinning), then regular climbing becomes much easier, but so does navigating underwater. OTOH, if it's a smooth design like the stuff seen in a lot of sci-fi (think like the inside of the Death Star in Star Wars, or the inside of the USS Enterprise in Star Trek), then the only practical option is going to be flooding the ship.

  • 1
    $\begingroup$ Although note that doing this would make it cave diving on steroids, or really dangerous for human divers. $\endgroup$ Aug 10, 2020 at 16:15
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    $\begingroup$ This seems like a bad idea – lots of stuff inside the ship would not b expected to get wet. Not just electronics (including every battery, even if you cut internal power), but everything from food to clothing to chemicals in air systems. $\endgroup$
    – Dan W
    Aug 10, 2020 at 16:59
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    $\begingroup$ @Clockwork-Muse It's going to be really dangerous regardless simply because you're in a structure that was designed for a positive pressure differential from the inside to the outside in a situation with a negative pressure differential and filled with a highly compressible gas (air). Despite how dangerous cave diving is, it's still almost certainly going to be statistically safer than just hoping the whole thing won't suddenly collapse under the weight of the water outside. $\endgroup$ Aug 10, 2020 at 17:10
  • $\begingroup$ @DanW Whether that matters really depends on what you care about salvaging. Chances are in a situation like this you aren't going to care about stuff like clothing or food (electronics maybe, but even then it's not certain). $\endgroup$ Aug 10, 2020 at 17:11
  • $\begingroup$ @AustinHemmelgarn it’s entirely down to plot what they’re trying to recover. It might be a McGuffin, but otherwise for a crash on an inhabited planet, abandoning it would be best, and leave recovering any nuclear material or nasty chemicals to robots. On an uninhabited planet, comms (and this power), and survival gear would presumably be top choice - all of which at risk from water. $\endgroup$
    – Dan W
    Aug 10, 2020 at 17:45

One seldom sees a rolling tire come to rest standing up. If the ship is being retrieved as salvage... and assuming it survived reentry (somehow), it seems its most likely final orientation would be lying on its side, more like a disc than a ferris wheel. In that case, none of the issues you mention would apply.

If it somehow it DID land upright, I would think the easiest way to get around inside would be to simply knock it over first. If its frame could somehow survive reentry and the incredible water pressure toward the "deep end," it could surely survive being knocked over, too.

  • 2
    $\begingroup$ Although I had the same thought, you're assuming that the ship does actually resemble a disk and not a cigar. If it's rotational axis is the longest dimension of the ship (hello, Rama! ...or most things based on an O'Neill cylinder, in fact), it is very likely it will end up with its rotational axis horizontal. $\endgroup$
    – Matthew
    Aug 10, 2020 at 19:24
  • 1
    $\begingroup$ The picture is a cross section, the ship would probably be tube shaped, less like a tire and more like a pipe like the ship from Rendezvous with Rama or the Behemoth from the Expanse. $\endgroup$ Aug 10, 2020 at 19:26

FLOAT the ship

Especially if the ship is in an awkward position like shown (you say we’re looking endwise upon a cylinder like Rama, not a torus like the 2001 space station).

The way you float a ship like this is by welding tanks to it, to the outside. You then selectively flood or evacuate those tanks to change the bouyancy of the entire structure. You saw this done with the Costa Concordia recovery, and it’s being done again (with an un-sunken ship) with the Texas restoration. In Texas’ case, they want permanent bouyancy, so they are filling those voids with foam. But you would certainly want to have them under control so you could rotate the ship.

In fact, you would attach the first few tanks, some underwater (filled with water) and then fill them with air to lift the ship off the bottom and rotate it for attaching more tanks.

Get it away from the shore!

The biggest threat to the ship, sitting on the bottom and exposed to air, is that sea and wind forces will move it back and forth repeatedly. It happens at least once a decade that a US destroyer or other Navy ship finds itself aground, and is torn apart by sea forces dragging it across the bottom, before the Navy can respond. In fact, it’s all the Navy can do to get the fuel drained (to prevent an oil spill). The ship is a total write-off.

Now, if the ship is deeply embedded so it can carry the sea loads, this may not be a problem. But it will become critical to move the ship from “solidly not floating” to “solidly floating” in one calm day, much like the Costa Concordia lift.

And then get it into a deep, calm harbor

Once you can get it independently floating, you will get it away from shore and float it in deeper water. (But not so deep as to be unrecoverable if it sinks).

Meanwhile, you’ll be preparing a deep harbor capable of taking it. Because you’ll want to be able to effectively “dry-dock” it. That probably means using a natural deep harbor like San Francisco Bay and dredging out parts of it so it can be moved farther from sea action.


Handwaving all the factors that allow the ship to survive being sunk in the ocean, there's a really simple answer: you build a salvage vessel capable of raising the spaceship.

This has actually been done, semi-successfully. In the mid-70s, the US CIA funded the construction of just such a ship, the Hughes Glomar Explorer, in order to recover a sunken Soviet nuclear submarine: https://en.wikipedia.org/wiki/Project_Azorian


Ship is sealed below the water line, buoyant, and you want to salvage every gram?

Go to the section above water, take every intact peice of equipment, then cut the ship just above the water line. Remove that peice and process the metal. The ship is now lighter as its mass is lower, and will rise in the water. Allowing another section to be processed.

Cut the ship and lift it up

Ship has inertial dampeners still intact?

Recovery team goes in with a generator, powers up the inertial dampeners, and tweaks them to maximum dampening (minimal mass). Lower mass and higher volume will make the ship float very high in the water. That ring shape will rise, and flop onto its side. Gravity will still be the wrong way, but there wont be any long drops.

No flooding, and you need to salvage only a few key items?

Rock climbing equipment. Drills, ropes, pulleys. Team of people belaying each other down the curved shafts bulkhead to bulkhead.

Flooding, and you need to salvage only a few key things?

Scuba gear. Underwater lights. Rope to find your way back. If it's partially flooded, a mix of scuba and rockclimbing gear.

The entire ship is worth salvaging with aims to repair and re-use?

The technique used to recover a sunken space ship is the same as used to recover a sunken water ship - use buoyancy to lift it. Lifting the entire ship can be done using compressed air and parachutes: Lifting a 6tn block of concrete from the ocean floor

The ship is a radioactivity hazard?

If the reactor has melted down, and the ship is resting on the ocean floor, the ocean is keeping the radioactivity contained (every 7cm of water stops 50% of the radioactivity). You can't lift the ship. You can't walk through it. You can't cut it above water as that may raise the reactor above the waterline.

Get a pressurised diving bell for divers to live in during the process (so they dont need to decompress between shifts), and salvage the ship bottom up. Cut parts of the ship, let the ship sink further, and lift bits up when they've been confirmed to be safe. That's slower and more expensive, but contains the radioactivity.


Spaceships might be big and strong but you're forgetting one thing. A spaceship is built for space. In space the pressure exerted on the Hull of a spaceship would be a problem the ship was designed to handle.

This same spaceship will most likely be full of air or another mix of gasses suitable to the users of the ship.

But that same ship underwater will not have a Hull capable to handle the immense pressures that the ocean brings down on it. Here on Earth those same pressures demand a special sub to get into the Mariana trench (and they're not very big) .

So either the ship will be incredibly strong (a fancy super material) to resist the immense pressure that is exerted by the water. Or it will be a collapsed semi-imploded graveyard of the crew that went down with it.

  • 1
    $\begingroup$ I can understand the reasoning behind your answer, nicely summed up in this clip (m.youtube.com/watch?v=Ewu-zHH5Qwg) but I don’t think this ship is under 150 atmospheres of pressure, after some calculations I think the ship is under 11, so I don’t think the implosion possibility is a problem in this case especially since I’m firmly of the belief ships need to be built for an environment where “being hit by a 'sugar-cube' of space debris is the equivalent of an exploding hand-grenade.” $\endgroup$ Aug 12, 2020 at 2:01

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