I need a way to get two men from the inside of a submarine to the inside of a sunken rocket 3000 feet under the water without

  • killing the men
  • flooding the rocket
  • flooding the submarine

Does anybody have any ideas? The two men in question are manning the submarine and need to get inside the rocket.


  • the rocket contains 4 men who need to be alive, so it is imperative that the rocket is not flooded.
  • the rocket has been underwater for ~20 years.

Now is there any way under the sun that such a situation would be possible?

  • 3
    $\begingroup$ What kind of rocket are you referring to? If it has a "port" for docking in space you could rig something up to mate with it. $\endgroup$
    – Razmode
    Apr 12, 2018 at 21:59
  • 20
    $\begingroup$ Reminds me of the book Sphere. Also... rockets are designed to be as light as possible. Not only that, but it's pressure is internal. There's no way a rocket is strong enough to withstand that much external pressure pressure. $\endgroup$
    – RonJohn
    Apr 12, 2018 at 22:01
  • 5
    $\begingroup$ You say "rocket" but a rocket is just a propulsion unit. I suspect you mean some kind of craft with rockets, but we need to know the nature of the craft. Is the craft even designed for humans ? Internal pressure and atmosphere ? Any airlocks with external controls ? E.g. if it was a strange alien craft it might not be possible to even figure out how an airlock worked or recognize one. $\endgroup$ Apr 12, 2018 at 22:28
  • 9
    $\begingroup$ @StephenG You also need to decide if the rocket is flooded or not. If it isn't then you need to explain what's keeping it on the bottom and what's keeping it from imploding. Rockets are necessarily very light devices and would be buoyant if there's air-filled living space. If it's flooded, then the transfer problem is actually pretty straight-forward. But what then? $\endgroup$
    – Mark Olson
    Apr 12, 2018 at 22:48
  • 3
    $\begingroup$ Leaving the entire crashed rocket bit out, 4 people surviving without food and resources for 20 years at the bottom of the ocean is simply not believable. Unless, as @Theraot suggested, you have cryo capsules, but that makes the non-recovery for 20 years unbelievable. You need to flesh out the background a lot more before anyone can provide a useful answer. $\endgroup$
    – nzaman
    Apr 13, 2018 at 7:01

5 Answers 5


I am a former submariner from the U.S Navy. I'm certainly not going to say this cannot be done, but I am going to give you a list of problems.

First, let's clear up a common misconception - differential pressure crushes hulls, NOT absolute pressure. The effects of absolute pressure on substances is important in terms of determining things like whether or not your atmosphere is currently in liquid form, but that shouldn't be a concern here either. If you can pressurize the interior of your hull to about 1320 psi absolute, the differential pressure on the cabin will be about zero. That means no crushing.

"Why aren't all submarines pressurized like this?", you are probably asking. The answer is that this would be very difficult to do without killing all the sailors. High partial pressures of oxygen are toxic to the human body. Getting the mixture exactly right is hard enough during saturation dives. At 1320 psi, the amount of oxygen has to be less than 1% by volume, and the rest of the atmosphere has to be hydrogen, helium or neon. At these ratios the hydrogen won't even be flammable. Any more oxygen and people will definitely start having seizures, and even this is probably too much for 20 years.

Another brief anecdote about pressure - an instantaneous change in pressure of 55 pounds or more should, theoretically, kill basically everyone, and that's just less than 5 percent of the pressure the cabin will have to be raised just to keep from being crushed. The pressurization will either have to be done automatically, or manually through some very carefully designed valves that were basically designed for this exact purpose. A mistake can kill everybody on board, and that's not even accounting for the fact that it could pop the cabin outright.

Now let's assume you have the facilities necessary to feed these people for the requisite amount of time. Fine. The moon has essentially no atmosphere, and it is exposed to sunlight periodically. Vacuum is a terrific insulator. The sea floor is COLD, and hasn't seen sunlight since some monstrous astronomical event deposited water on this planet. Water loves to suck heat out of things. I'm not saying no - I'm saying on top of having highly specialized pressurizing and mixing equipment to prevent being crushed, you also need a seriously robust energy source to prevent your people from succumbing to exposure. People are known to wear jackets in the enginerooms of nuclear submarines when they're deep, because the seawater piping cooling everything works really well.

Now I have great news. Once you have these problems solved, the rest is actually pretty easy in comparison. Your scenario makes it pretty clear that rescuers have time on their side - there is not an immediate need to rush into things. This gives them the opportunity to do everything they would have to do - like building a deep dive vessel capable of interfacing with another pressurized vessel. DSRVs don't have a way to raise their internal pressure to 1320 psi, and it is highly unlikely that the airlock will conform to the aspect of a standard submarine escape trunk. These obstacles can be overcome - it will take a budget, and it will set records, but it's significantly more possible than the set up on the rocket itself.

As long as the DSRV takes precautions to prevent incompatibilities with the atmosphere on the rocket, can depressurize at controlled intervals, maintain partial pressure of oxygen on the way up, and stay deployed long enough to get the divers into a proper diver's bell or hyperbaric chamber to finish depressurizing, you should be all set.

  • $\begingroup$ Answer might be a bit on the scientific/realistic side of things for the OP, but is very informative and interesting none the less. $\endgroup$
    – r41n
    Apr 13, 2018 at 13:41

In the movie, "The Hunt for Red October" men were moved between two submarines using a DSRV, or "Deep Sea Rescue Vehicle." You're going to use something similar.

But, your biggest problem is that the rocket won't have an underwater airlock that a DSRV would expect to find. This would require outfitting the DSRV (as they had to do in the movie, oddly enough), to permit access.

Note that from the standpoint of believability, rockets are designed to hold pressure in, not keep it out. At 3,000ft it would likely crush like a beer can. I'm going to assume you addressed this issue in your story.

  • $\begingroup$ Greatest possible depth without collapsing, then? Give me an estimate. $\endgroup$ Apr 12, 2018 at 22:34
  • 12
    $\begingroup$ If it is like an ICBM, not much. One collapsed in Arkansas under normal atmosphere simply because the oxider and fuel leaked. And then it exploded. $\endgroup$
    – Razmode
    Apr 12, 2018 at 22:55
  • 1
    $\begingroup$ @godsaveuseveryone 3000 feet is more or less the 20th century depth record for military submarines (link). "One atmosphere" of pressure is approx 35 feet (so e.g. "2 atmospheres" is 65 feet). $\endgroup$
    – ChrisW
    Apr 12, 2018 at 23:40
  • 7
    $\begingroup$ @godsaveuseveryone Greatest possible depth was answered in this Futurama episode. $\endgroup$
    – user535733
    Apr 13, 2018 at 2:02
  • 2
    $\begingroup$ @Raznarok Did I just hear that [it] turned inside out, and then it EXPLODED? $\endgroup$ Apr 13, 2018 at 13:51

You need an airlock. Simply have one on the sub with some sort of watertight gasket around it, then have a matching hatch airlock assembly thing on the rocket. Once the seal with the rocket's hatch is made, lock onto it somehow, then pump the water out of the airlock area.

  • 3
    $\begingroup$ But what's the likelihood that there's a compatible airlock on the rocket? $\endgroup$
    – RonJohn
    Apr 12, 2018 at 21:59
  • 6
    $\begingroup$ It's the OP's rocket, isn't it? So it had to have a compatible airlock, because reasons. $\endgroup$ Apr 12, 2018 at 22:08
  • $\begingroup$ how do you equalize the pressure at such depth? usually body of submarines are designed as one piece whole or they wielded the pieces together flawlessly. unless you can find a heavy duty gasket that the dwarves used in their pressure cooker when baking mjolnir ;D $\endgroup$
    – user6760
    Apr 13, 2018 at 3:27
  • $\begingroup$ @RobertColumbia Or OP's submarine could just so happen to be transporting some parts for OP's rocket's country's secret space program, which are exactly the ones needed... Or the submarine could just have lots of duct tape. $\endgroup$
    – Nic
    Apr 13, 2018 at 5:21
  • 2
    $\begingroup$ @RonJohn the sub could be custom-built to salvage that particular rocket, and be compatible to the rocket's space docking infrastructure. After we've handwaved the rocket preserving air inside for four survivors at 3000 ft without being crushed, repurposing space docking for undewater use is very mild in comparison. $\endgroup$ Apr 13, 2018 at 7:46

deep sea diving suit https://en.wikipedia.org/wiki/Atmospheric_diving_suit#/media/File:Deep_Sea_Diving_Suit.jpg

  1. Sub comes along side rocket at chosen point of entry. Sub aligns exit hatch or (better) moon pool with chosen point of entry.

(A moon pool) is an opening in the floor or base of the hull, platform, or chamber giving access to the water below, allowing technicians or researchers to lower tools and instruments into the sea... A moon pool also allows divers or small submersible craft to enter or leave the water easily and in a more protected environment.

  1. Crewman leaves sub in diving suit. Sub is firmly affixed to outside of rocket with straps, bolts, etc. Juncture between sub and rocket is made water tight. One could swath the area with some sort of tough fabric or plastic which will be forced into the crack when the water pressure difference is great.

  2. Diver returns to sub. Water is pumped out of moon pool until rocket side shows. Water does not flow in because of #2 above.

  3. Men cut through side of rocket with appropriate tools.

Re rocket not getting crushed: air filled nonpressurized spaces will probably get crushed. Fluid filled spaces will not get crushed. You could have the rocket area have flooded and then the men pump it out via the sub. You could have it partly crushed but still accessible. You could assert it was a rocket intended for a Venus surface mission and so crushproof.

But the coolest of all: on sinking, the rocket tanks rupture internally. The liquid hydrogen and oxygen propellant vaporizes, filling the rocket with a highly pressurized hydrogen and oxygen gas atmosphere. This high internal pressure prevents the rocket from being crushed and in fact it is bubbling from the outside. This atmosphere is breathable. But no smoking please.

"We're breathing rocket fuel."

"It would be Chuck Norris manly if our voices weren't so squeaky".

  • $\begingroup$ "The ADS can be used for very deep dives of up to 2,300 feet" but the OP wants 3000 feet. $\endgroup$
    – ChrisW
    Apr 12, 2018 at 23:34
  • 3
    $\begingroup$ @ChrisW - "cap'n shes only rated to 2300 feet! she canna take the pressure!" "She's going to have to take it, ChrisW. Move fast out there." $\endgroup$
    – Willk
    Apr 12, 2018 at 23:50
  • $\begingroup$ Okay, it seems like I need to clear some things up here. 1) The rocket was going to the moon. 2) There are 4 people inside the rocket and 3) These four people need to still be alive after having been in this sunken rocket for ~20 years. Definitely kind of far-fetched, maybe stupid, and highly, highly unlikely, but IS THERE a small chance that it could be possible? Or should I just scrap the whole idea? $\endgroup$ Apr 12, 2018 at 23:56
  • 2
    $\begingroup$ @godsaveuseveryone 20 years! 20 minutes yes (if it doesn't get crushed), 20 hours sure, 20 days - pushing the limits for a moon rocket with a typical trip time (even 50 years ago) of just a few days, but we could argue that the rocket had plenty of extra supplies, backup CO2 scrubbers, etc. 20 years! No way, unless this was designed as a long-term habitat - i.e., an explore the galaxy ship, not a quick moon rocket for the band. By the way, is it a yellow submarine? $\endgroup$ Apr 13, 2018 at 0:50
  • 1
    $\begingroup$ @godsaveuseveryone vehicles are designed to survive the environments they are expected to operate in. A space vehicle is designed to resist 1 atmosphere of internal pressure, not hundreds (?) of atmospheres of external pressure. And what will these people eat? Drink? Breathe? How much room is there inside? What will they do with all the poo? How will they avoid going mad? Getting rickets? Just psychologically speaking they would need to "crash" in a large B&B with a gym, lots of books, or videos, or games, working phones, kitchen, (internet?) and sewers. $\endgroup$ Apr 13, 2018 at 9:46

The space vessel doesn't stand a chance of preserving normal atmospheric pressure inside its fragile hull. The only way this works is if they slowly pressurized the spaceship to equal the water pressure (30 feet ~= 1 atmosphere of pressure, so 100 atmospheres of pressure) -- in a way that didn't harm the crew. It helps to be breathing pure oxygen and not nitrogen (of course, oxygen at 100 atmospheres pressure is a real fire hazard!)

The humans don't need to stay at 1 atmosphere of pressure. Sudden transitions are bad, but humans can adapt to changing pressures. That is how diving works. The trick is managing the transition between 1 atmosphere and much higher pressures.

If they are equipped for space EVA, they possess SCBA equipment, and it may be possible to adapt it for 100 atmospheres. If that's the case, they can take their sweet time getting to the sub!

Regardless, if the spaceship is pressure-equalized with the ocean, it may be as simple as opening a door (preferably on the bottom) and swim to the sub. Do this when the sub is right alongside, obviously.

It's not a problem getting people in and out of the sub at depth, they all have airlocks, not least for Kursk style evacuation.

The hard part is coming back to 1 atmosphere of pressure, as we presume will be inside the submarine (which is built for the external pressure). Doing this is well-understood, but can be a very long, slow recuperation that must be done inside a controlled-pressure vessel. Which a submarine airlock is. Again it helps to have been breathing pure oxygen for awhile.

If the sub has enough notice, they can send out divers to aid in the evac. Some submarines are especially equipped to move large numbers of divers in and out, so if there's time to dispatch the right sub, this can go easier still.

  • 2
    $\begingroup$ Oxygen toxicity at 100 atmospheres would kill all of the astronauts pretty quickly, $\endgroup$ Apr 13, 2018 at 3:14
  • 1
    $\begingroup$ Humans can adapt to changes in pressure within limits. 100 atmospheres is well outside those limits, even with special atmospheres like heliox, which wouldn't be present in a spacecraft atmosphere. You'd have to reduce the percentage of oxygen to eliminate oxygen toxicity, which would make it basically unbreathable at normal atmospheric pressure. $\endgroup$
    – jamesqf
    Apr 13, 2018 at 5:05

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