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Set in the near future Space tourism is a thing, all commercial and non-military spaceships must come equipped with multiple escape pods. The minimum specs for each escape pod are as follows:

  • min capacity of 1pax
  • oxygen tank lasts for 72hrs
  • 2 litres of consumable water
  • medium size first aid kit
  • solar powered torchlight
  • radio beacon
  • fire extinguisher
  • heater with thermostat
  • 1000w rechargeable battery
  • 200w solar powered panels

Basically the design of the escape pods should ensure the survivability of the crew from imminent danger such as a spaceship is about to explode, etc. During an emergency the crew and passengers must attend the nearest available escape pod and manually launch themselves away from the doomed spaceship. These manned escape pods will accelerate away from the spaceship to a safe distance or until the thruster is completely depleted. Some newer designs come with a heat shield and a parachute which comes in handy during an atmospheric entry, but nonetheless none of them can be opened from the inside. Is there a good explanation for all escape pods to follow such a design?

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    $\begingroup$ it makes a lot of sense for a space pod NOT designed for reentry but absolutely no sense for one that is. there is little reason to be able to open a pod to vacuum. $\endgroup$
    – John
    Jan 13 at 12:32
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    $\begingroup$ do you need this to be a one off or rare event or true of all escape pods? a vacuum only pod cheaply upgraded for reentry might not have the exit feature but making it standard design practice would make no sense $\endgroup$
    – John
    Jan 13 at 12:46
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    $\begingroup$ Unless your story is about a political debate about escape pod safety reform, I can't imagine why you need all escape pods on all ships to be sealed metal coffins, as opposed to just these escape pods from this ship, which is a much easier narrative lift. $\endgroup$
    – g s
    Jan 13 at 16:44
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    $\begingroup$ 2 L of water is insufficient unless you’re assuming one person per pod. It might be enough if you were dealing with a lifeboat on an ocean liner and had a compact desalination system to supplement it, but for a case where you have no water you didn’t bring with you it’s not going to cut it. And single-person pods are almost certainly economically infeasible (compare real life cruise ships, their lifeboats are usually designed to accommodate at least 100 people each). $\endgroup$ Jan 13 at 20:36
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    $\begingroup$ Fire extinguisher? The only remotely viable extinguisher I'm aware of for enclosed space use is water. Your normal extinguishers are going to kill the occupants because of inhaling the dust. And Halon systems kill the occupants even on Earth. $\endgroup$ Jan 14 at 4:16

22 Answers 22

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Mass-produced civilian hardware

Your escape pods are mass-produced, cheapest-source products. Escape pods are one of those things that, ideally, are never used and need a long shelf-life. Nobody wants to spend expensive man-hours constantly inspecting and, if necessary, maintaining an enormous numbers of pods.

Because of this, three factors emerge as priorities in escape pod design: reliability, simplicity, and cost.

Now, with this in mind:

No operable door simplifies the mechanism. If you have a door that can be opened and closed at will, you need hinges, locking bolts, gaskets, etc. These need to be lubricated and add cost and complexity to the design. These also make the pods more expensive, which nobody wants.

No operable door keeps the inhabitant safe from themselves. Statistically, half of all people have less-than-average intelligence. In an emergency situation, this gets even worse. If the doors were made so that they could open at will, there would be people who'd simply open them in space, which would kill them. Especially considering that most users of these pods might be completely untrained tourists, who have no clue what they are doing.

There is no reason for the inhabitant to ever open the door. Excepting the rare, rare case where an emergency pod ends up not only on the surface of a planet, but also one that has a breathable atmosphere, there will basically never be a survivable atmosphere outside of an escape pod. In >99.99 percent of cases, the emergency pod will be floating around in vacuum, until a rescue ship comes by who have the requisite can-opener that they can use to open the pod.

Un-openable pods

With these factors in mind, I suggest a (civilian) pod design that seals once and then can't be opened without a "can opener" type tool or some sort of cutter. In order to seal the pod, a one-time reaction occurs: maybe the pods all have a lid that closes, and then a powerful two-part adhesive seals it or some pyrotechnic automatic welding line quickly welds the escape pod airtight.

This has multiple advantages. For example, a chemical-energy solution would work regardless of power failure or even consciousness of capsule inhabitant. Hypothetically, a crew member could toss an unconscious passenger in one and then close the lid or pull some sort of tab to automatically start the chemical welding or gluing process. They don't need to fiddle with levers, handles, or wheels and it seals completely unattended.

I think that "non-civilian" grade escape pods would be different though, because you need far less of them, you can make sure the crew are trained to use them, and there might be cases where someone who's wearing a sealed suit is inside one, so they could hypothetically open it without being killed immediately.

Extra

Personally, I'm skeptical that a single-occupant life-pod makes much sense in most spaceship scenarios. If you look at similar equipment today, you'll almost never find a single-person life-boat: most are designed for many passengers at the same time. The main reason behind this is because the "threshold of effort" between making a one-person system and making one which can hold multiple people is not that high.

Specifically, to expand your escape pod from a one-person solution to one designed for two people, hardly any changes need to be made. A bit more volume, and maybe a bit more food/water/o2, but you don't need an entirely new craft's worth of material and supply.

I think a better solution would be something analogous to life vests today: something unobtrusive that everyone can wear at all times, that, while not a permanent solution, will save you for long enough to be rescued if your suddenly thrown into space. For example, this could be a shipboard jumpsuit that, in a pinch, has a hood you can zip up and a small gas-canister that will pressurize it and keep you safe for an hour or two.

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    $\begingroup$ Note that your shipboard suit will go basically totally rigid if you seal it and throw it into space. The issue is that bending your joints compresses the air volume and that takes energy. For something that approximates clothing, it takes too much energy. That's why spacesuits have big, complex joints--to keep the volume constant as the joint flexes. The fingers are small enough this is neither feasible nor essential but it makes using your fingers EVA tiring. $\endgroup$ Jan 14 at 3:56
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    $\begingroup$ @LorenPechtel I don't care to be trapped inside a rigid inflatable doll as long as I stay alive. I don't need to move, the goal is to be rescueable (and stay rescue-worthy). $\endgroup$
    – Bergi
    Jan 14 at 23:48
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    $\begingroup$ @MikeB By "door" I mean a device that is designed to be used many times and that can be opened and closed at will. What I'm describing is more like a hole or opening that can be sealed once, and then is permanently closed, so not really a door. $\endgroup$
    – Dragongeek
    Jan 15 at 9:59
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    $\begingroup$ @Limey: And indeed, the vast majority of people have more than the average [mean] number of legs! $\endgroup$
    – psmears
    Jan 15 at 14:34
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    $\begingroup$ I can't believe that this throwaway line triggered such an argument. That said, I think it's pretty safe to say that intelligence, no matter how it's measured, falls on a bell curve. On this bell curve, half the population will be below the halfway point. $\endgroup$
    – Dragongeek
    Jan 15 at 20:58
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A Vessel that doesn't allow the doors to be opened from the Inside fundamentally is a bad idea. In terms of Space Flight - the example that immediately comes to mind is:

The Apollo 1 Fire

One of the causal factors was that the Air pressure inside prevented the Escape door from being opened. So you've got some precedent to overcome.

I'm going to make the assumption that for Story reasons you need the Doors not to be openable from the Inside. There's 2 scenarios that immediately spring to mind where you could have this (and be somewhat believable):

Scenario 1: The Escape Pod has a number of sensors that scan the outside environment and will only release the doors when safe to do so. The problem here is that for such a system to be believable, you are going to have to have a lot more food/water/Oxygen/Provisions - otherwise the Escape Pod is basically a Death Trap or a really great way to have a Survival Cannibalism episode. Now, depending on the speed of Travel and Rescue within your world, 72 hours might be sufficient. E.g. an emergency signal is sent when the Pod is launched and there's a 24 hours maximum time for help to arrive (hypothetically) then 72 hours could be justified, but I would still add more time.

Scenario 2 - This one I think you can weave into a world and have be more realistic - The Vessels used are re-purposed Prison/Military vessels and the Escape pods are of a specific design to prevent unauthorized opening from inside. No one bothered to check this as the ship had Escape Pods and the authorization was retained by the Prison/Military entity that the ship came from and so no one has it.

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    $\begingroup$ To be fair, if it automatically opened by a system it isn't opened by the people inside. That means it isn't opened from the inside. $\endgroup$
    – Trioxidane
    Jan 13 at 11:17
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    $\begingroup$ +1. The Titan submersible wasn't openable from the inside. And it was also a bad idea. $\endgroup$ Jan 14 at 4:37
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    $\begingroup$ @KevinKostlan but the problems of Titan had nothing to do with it not being openable from the inside, on the contrary. $\endgroup$ Jan 14 at 15:28
  • $\begingroup$ @leftaroundabout - You are correct in that statement - however, a number of people after the accident commented that the hatch being only openable from the outside was a bad idea. $\endgroup$ Jan 14 at 20:08
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    $\begingroup$ @TheDemonLord: Was a bad idea for what reasons. A submersible is expected to surface on its own, and there it makes sense for occupants to be able to open the hatch. An escape pod is not supposed to be able to execute atmospheric reentry on its own -- not that there's many planets available where it would even make sense -- so in which conditions would people inside be in a position to open the hatch without killing themselves? As mentioned per Dragongeek, there seems to more risks of accidents, ie deaths, in making it possible to open it from the inside. $\endgroup$ Jan 16 at 15:44
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I'll disagree with the existing answers, and say that an escape pod that can't be opened from the inside is a good idea.

Why? This is the principle of reducing potential points of failure. The person escaping the ship enters a pod and it is activated. The pod closes itself and launches. If the pod is able to be controlled by the occupant, that would require some way of determining if the occupant is competent to operate the pod. If the occupant is able to open the pod, that would require some way of determining if the occupant is competent to do so safely.

Since determining the competence of the occupant is a very difficult task that relies not only upon the occupant being in possession of relevant knowledge, but determining if the occupant is or is not traumatised by the events to the point of being suicidal or homicidal, it is safest to simply deem that no occupant of such a pod is more competent to make the best decisions for their personal safety than the pod's software.

So, it makes perfect sense to me that the occupant of an escape pod could not open the pod to vacuum by themselves, that it would take an outside agency to move the pod to a safe environment or the pod arriving in a habitable environment and deciding for itself to unlock the hatch before the occupant could exit.

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    $\begingroup$ The problem is that sometimes what is inside the pod is a more immediate threat to life/limb than what is outside. Like Fire, flood, oxygen starvation, food starvation etc. $\endgroup$ Jan 13 at 8:26
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    $\begingroup$ This produces another potential point of failure - there is nobody outside to open the pod. Thus the occupant expires inside. If the options are "possibly vacuum themselves in space or survive" or "remove the small chance of vacuuming themselves but introduce a larger chance of dying trapped inside", I'd always go for option 1. $\endgroup$
    – VLAZ
    Jan 13 at 8:32
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    $\begingroup$ @VLAZ In safety design people cannot be trusted. Fire doors are designed in most cases so a throng of people can run into it, as they cannot be trusted to open the door normally. If the chances that someone opens the escape hatch and puts everyone in more danger are substantially higher than edge cases where they legitimately need to escape the pod on their own, you keep them in. Save more lives by having a theoretically less safe design is a tried and tested method. $\endgroup$
    – Trioxidane
    Jan 13 at 9:37
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    $\begingroup$ except there is something outside the pod, the OP specifically includes pods designed for reentry, not just space. there are lots of places on a planet were staying put is very dangerous. $\endgroup$
    – John
    Jan 13 at 12:44
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    $\begingroup$ The last sentence is key here, and I think makes this answer's proposed design to be contrary to the OP's design desire. It's trivial (and standard) to make a door that can't be opened against a negative pressure difference. All commercial airliners have them. However, commercial airliners can be opened from the inside by any reasonably fit passenger once the pressure is normalized, even if all the crew are incapacitated and none of the electronics are working. People don't like locking themselves into metal coffins. $\endgroup$
    – g s
    Jan 13 at 16:39
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Because the spread of disease or alien organisms is a very real threat. On earth we have multiple historical instances where an infected shipload of people has gone on to infect and decimate populations.

My locale lost 1/4 of its population to such an event when a New Zealand ship discharged sick passengers in 1908.

So it makes sense not to always trust the pod's inhabitants and investigate before opening the pod.

It's not a spaceship you can navigate and fly to a habitable planet a few light years away and survive a crash landing. It's an escape pod, it just gets away from danger, send out mayday signals and hopes for rescue before its life support and supplies run out. So if it isn't rescued then you'll die anyway. Opening the door won't keep you alive.

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  • $\begingroup$ An escape pod like that would guarantee you die when there is nobody to infect. I fail to see how this is a good idea. It's throwing the baby with the bathwater at this point. $\endgroup$
    – VLAZ
    Jan 13 at 9:28
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    $\begingroup$ @VLAZ Life is full of trade-offs. they think the risk of your dying when you could escape is not worth the risk of your dying because someone shot down your pod as a threat. $\endgroup$
    – Mary
    Jan 13 at 18:50
  • $\begingroup$ No, just no. In a stricken spaceship in deep space you stay with your ship, using the escape pod systems to survive but not even detaching. You retain the ability to open the door so that once you collect your wits and your spacesuit you can reenter your ship and see if the problem is something you can fix. Only if the pod can reach an inhabitable planet (presumably Earth in this near future) would you ever detach. $\endgroup$
    – Joshua
    Feb 13 at 3:43
  • $\begingroup$ Thats like leaving the lifeboat on the deck of the burning ship $\endgroup$
    – Kilisi
    Feb 13 at 4:09
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Safety first

Elevators have escape hatches. Interestingly, many cannot be opened. Why would you add in an escape mechanism, but not allow it to be opened? The reasoning is simple. Because in 99% of the cases, people will put themselves into more danger than staying put. That is why many can only be opened from the outside.

The elevator example isn't fool proof, as there's plenty of countries that allow it to be opened from the inside. However, the philosophy is sound.

Now put that philosophy to escape pods. People in an escape pod will generally be at their safest. Opening the hatch can mean exposure to the vacuum of space, and there are precious few advantages for people to be outside the pod in space. There's little chance they need to repair it, and if they should, with what tools, materials and knowledge? There's only edge cases we can imagine where opening the pod is safer in space. You save more lives by preventing it from being opened.

What about after reentry? From your question I do not know if this is sci-fi with artificial gravity or the like, but let's assume two scenarios. One is with current technology, the other sci-fi.

With current technology we already see the astronauts stay put and let the hatch be opened by a rescue team. They are often in inhospitable environments like the middle of an ocean or desert. This is by design, but an ocean is pretty likely for a crash anyway. Not to mention that a 'normal' environment can already be dangerous for people in heavy space suits after some time in microgravity. Stay put is safest until a rescue team arrives.

If it's more sci-fi with artificial gravity and such it isn't too different. The environment can be dangerous on Earth, but much more so on other planets or rocks of dirt.

Again, there are of course legitimate reasons why you do want to open the pod. Oxygen running out, a fire, a psychopath on board, cannot take a leak with others watching. But making things less safe to protect people is a tried and tested method. People can become irrational and stupid in stressful situations. Giving them the option to go outside is theoretically more safe, but in reality people cannot be trusted to do the safe thing.

Save lives. Prevent it from being opened from the inside.

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  • $\begingroup$ Escape pods are used in an emergency. How do you guarantee there would be somebody who can get to the pod in time? With elevators it's easy - an elevator doesn't stray away from civilisation. Even astronauts are not randomly ejecting to other unknown locations. $\endgroup$
    – VLAZ
    Jan 13 at 9:31
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    $\begingroup$ in the ocean getting out before it sinks would be essential, sinking to the deep ocean only for the pod to be crushed by the pressure or land near an active volcano are real possibilities. $\endgroup$
    – John
    Jan 13 at 12:39
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    $\begingroup$ @John why wouldn't you design them to float? They do so already in case the astronauts need to land in water. We can think up ways that you need to escape the pod, but those we call acceptable casualties. If you save more lives by not allowing them to open the pod, we accept that a few will die in fringe scenarios. This is a basic principle of emergency design, not some outlandish theory. Like the elevator, some might be saved when the elevator gets stuck and a fire breaks out. But this happening both is less likely than someone falling down the elevator shaft when just being stuck. $\endgroup$
    – Trioxidane
    Jan 13 at 13:07
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    $\begingroup$ @John That's not how the physics works though. With a sealed tin can full of air, it'll always bob to the surface. The only way to get it to sink is to make a hole in the capsule - for example by opening the hatch! This actually happened to Gus Grissom. He nearly drowned, directly because of the misconception that astronauts should be able to exit when they wanted. The hatch mechanism malfunctioned and fired on its own, and the capsule filled up with water. $\endgroup$
    – Graham
    Jan 13 at 15:56
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    $\begingroup$ @John A space capsule able to withstand durect sunlight in space while barely able to radiate heat, able to reenter the atmosphere at 1650°C (3000F) bakes in the sahara desert? But again, it doesn't matter. The question requests for a reason not to open the pod. I give a tried and tested method. You can argue edge cases all you want, it does not change the fact we sacrifice some people with our emergency design to save more people in other ways. $\endgroup$
    – Trioxidane
    Jan 15 at 7:27
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They carry prisoners

I agree with the current top answer that this is a fundamentally bad idea. The basic principles of safe design just don't justify it.

However, in some cases, those basic principles are overridden. The transport of prisoners is one example. We're happy to shackle people into a fast moving truck, and to take the risk that the truck becomes submerged or catches fire. In this case, the risk of the prisoner getting free overrides some of our notions of design for safety.

Of course, in your setting, the occupants may not be prisoners, but there the narrative can help out. For example:

  • The space station is a repurposed prison, and when the disaster strikes, the systems need to be rebooted, resetting to factory defaults.
  • The space station has a prison section, and the protagonist is a lawyer visiting their client. In the chaos of the disaster they get stuck in a prisoner's escape pod. Maybe together with their dangerous client for extra jeopardy.
  • The space station is not a prison, but due to the dystopian nature of the setting, the workers really need to be treated a bit like prisoners, for their own good. They keep trying to escape, and the space station director has a quota to fill.
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Because They are Stoned out of Their Minds:

Your escape pods are theoretically openable from the inside. But after you get in, precedent says your odds of survival are slim-to-none. Inevitably, the person in a pod is panicking, and not in their right mind. Now they are left in the vastness of space with little hope of rescue. The hours tick by, and sanity begins to erode as you sit trapped in a tiny, tiny space.

The solution? Tranquilize your survivor into unconsciousness. There is nothing they can do to better the situation. Any situation where they survive involves an outside agency saving them. All they can do is dwell on their likely death. The statistics say that most survivors given a choice go mad in the vastness of space, open their pods, and die. So they are given no choice. A nutrient IV starts automatically, they are drugged, the doors lock (to prevent accidental release) and they fall into blissful unconsciousness - or a drugged state similar enough not to matter.

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    $\begingroup$ Yeah, being drugged would also probably save a lot of oxygen and other critical resources to survive longer $\endgroup$
    – Piro
    Jan 15 at 7:50
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Environmental Protection

The answers I read seem to suggest that the only thing that matters is the pod and the person inside the pod. Even today, we live in a world where you aren't allowed to launch something into space without filing an environmental impact statement. What might happen if that philosophy were extended to new biospheres.

Perhaps, in their zeal to prevent strange new worlds from becoming contaminated, the Environmental Protectorate requires that all escape pods perform a review of the environment outside the pod, and determine that opening the pod will not cause damage that exceeds the value of the life inside it. In the absence of such a review, the pod stays locked.

After all, we don't want people releasing a deadly plague in order to save their own skins. I'm sure precedence can be set in your history.

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Escape pods are intended for use under specific circumstances.

The real reason why escape pods are mandatory is because of the times when a ship which can help is right nearby, but has no way to get people into the safe ship before the other ship succumbs to its damage. Escape pods are really only meant to be used as a method to quickly get people off a ship, so that another ship can be right there to catch them, and extra provisions are there so that if it takes a bit longer to round up every escape pod, they don’t die.

If you are just alone and shoot off an escape pod, well, the escape pod isn’t designed to help you at all.

Creating a door which can be opened from the inside, adds additional failure points, and these failure points are on the same side as the thing you are escaping from. So almost every designer of an escape pod decided to just have the door permanently and solidly closed, requiring the rescuer to open it. Some manufacturers use thermite charges to weld the metal together, or arcs, some use large clamps which lock into place irreversibly, there are a lot of different methods, but they all keep the door more secure at the expense of it being impossible to open the door without destructive tools from the outside. Sure, a very select few escape pods do have the ability to open the door, as it’s not a requirement for doors to be unopenable, but they are incredibly uncommon.

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  • $\begingroup$ that would make sense in space but not for a pod designed to land on a planet, there are way to many places on a planet where exiting the pod is a timely fashion is essential so survival of reentry. $\endgroup$
    – John
    Jan 13 at 12:34
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What is the function of an escape pod?

Presumably, something bad is happening to the main ship. This should have the deltaV to get you to your destination. A large fraction of the main ship, and certainly a large fraction of the stored energy within the ship may be the propulsion system.

It is unlikely that your escape pod will carry enough deltaV to get you to land on a planet. That would make it impossibly heavy. If staying with the main ship is not good, your best chance might be to get into some small 'lifeboat' with all the essentials for your immediate survival, and hope someone will come looking for you. You will put yourself into some deep sleep or suspended animation to minimise your resources and maximise your survival time. That is probably the answer to your question: you will not open it from the inside because you are asleep. You could have a door you can open from the inside, but you would be better off using glue to seal the door and using the mass allowance on extra life support consumables.

You make be in deep space. Perhaps no-one can come for you. You may have to stay awake and try and pilot yourself to safety like Interstellar Captain Bligh, making an epic voyage using just the ion drive. In this case, we may have to reconsider what an 'escape pod' is.

In Apollo 13, they had the Lunar Module with its own air and power system. It could not get them back to Earth, but it did provide them with resources that let them survive long enough to get back. A ship probably has some redundancy in the life-support system, and several propulsion systems. Soo, instead of launching a lifeboat, you may jettison parts of the main ship, or at least isolate the part you are living in. Your 'lifeboat' may be the whole living quarters of the ship. This gives you more options, which would be vital in deep space, where a timely rescue from outside is unlikely. But it is part of the original ship, so the doors probably open from the inside.

IMHO an 'escape pod' only works if you are close to other craft that could rescue you, or you are in some remote part of your craft away from the main life support and the other crew come to rescue you. It might well have a door that you cannot open from the inside.

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The pod is ejected while the ship being far from Earth and there is no habitable planet, or a planet with an unbreathable atmosphere. Will you just open the pod and exit?

The pod is too small to have a sophisticated airlock with a double gate system, a pressurization chamber and a space suit. The solution: Build a small and simple gate which allows you to dock and clamp to another ship. When you dock your pod, you can leave it and enter the ship.

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If an escape pod cannot be opened from inside, then they are probably escaping a oppressing power. Even if that was not the imminent, intended cause, it is at least the suspected cause. Everyone is suspected to defect.

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    $\begingroup$ This could work, if there was a rationale for why people in the countries they're escaping to, would be less likely to open the pod from the outside than people within the oppressing power. $\endgroup$ Jan 13 at 16:41
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    $\begingroup$ @DewiMorgan Good point. That is why the escape pods had better be equipped with locks that only the power can open, and if someone else tries it, they explode. $\endgroup$ Jan 13 at 20:29
  • $\begingroup$ That works for me! $\endgroup$ Jan 13 at 20:40
  • $\begingroup$ Putting a mechanism in that blows up the pod if it's attempted to be opened by anyone else seems very easy to accidentally trip through damage. Because it's very unlikely that whoever comes to rescue them is just going to give up if they can't open the door. If it can't be opened by hand, disassembled, and nothing can be compressed to make room, the next response is to start cutting up the pod with a large saw at which point a mechanism preventing that is very likely to just trip randomly. $\endgroup$
    – OT-64 SKOT
    Jan 14 at 10:59
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To prevent suicide by space psychosis or otherwise panicked and inept civilians from killing themselves and everyone else inside.

Or. to prevent ships from being used by rebels as as drop ships

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Frame challenge:

Since this is near-future, the only place it'd be even reasonable to land on would be Earth. I don't think any other planets or moons that might have human outposts on would be enterable with a heat-shield and parachute. Mars' atmosphere is too thin. Luna has no atmosphere at all. There's no point entering an uninhabited gravity well as there'd be no surviving outside the pod, and even if the pod survived the descent and the conditions on the surface, the gravity well just makes recovery of the pod significantly harder.

So I'm interpreting this as a question about escape pods arriving on the surface of the Earth.

If they're a way of escaping from a problem in Earth orbit, it seems really weird to make escape pods that should survive reentry to Earth, because that's massively more complex than an escape pod that just sits there and awaits a recovery vehicle.

The retrofitting to re-enter requires also having guidance jets on board sufficient to create enough delta-v that it'd reenter: not just "accelerate away from the spaceship to a safe distance", but "accelerate away, then use attitude jets to pivot, then thrust in the correct vector to re-enter".

Similarly, even if you're remaining in orbit, "these manned escape pods will accelerate away from the spaceship ... until the thruster is completely depleted." is just going to make the pod's orbit elliptical, and it will risk collision with the ship they were escaping from, about half an orbit later, and twice every subsequent orbit, when it crosses the line of the ship's orbit. Save fuel for attitude maintenance.

It'd almost always be safer to remain in orbit and await recovery, except where a Kessler event makes any reachable orbit unsafe, or your attitude jets run low on fuel and your orbit degrades to the point where controlled reentry is the only safe option.

For those edge cases only...

Accidental design problems:

  1. Design/test failure: The door was not tested after undergoing the heat, cooling and ablation of re-entry, which effectively welds the door shut.

  2. Pressure differential: The doors are "plugs", designed to open outwards, so they can't accidentally be opened in space (eg the ISS, Apollo 1 fire). But on landing, particularly after heating the air inside during reentry, there is still a sizeable pressure differential between the inside and outside. Say the door is 1 square meter in area. Average bench press strength for men is 100kg, or about 1000 N. You only need a pressure differential of one kPa (1000 N/sq m) to keep that door shut at that pressure. That's the equivalent of a height difference of just 100m, or about 1/3rd of normal daily variance, so is easily doable, but because this is such a well-known effect in escape capsule design, this would seem ridiculous to most educated readers, but it may be acceptable as a design factor when combined with some deliberate design tradeoffs.

Deliberate design decisions:

  1. Design inertia: "Some newer design comes with a heat shield and a parachute which comes in handy during an atmospheric entry" - could be that the door plugs were not upgraded when the heat shield and parachute were added to the design. The edge cases where re-entry needs to be survived are so slim that it's just not worth the extra weight of the mechanism to open the doors from inside, plus the unbalancing effect of all that mass, would mean redesigning the pods completely to allow it. (Seems reasonable, except I doubt reentry could be just a "retrofit" to an existing design).

  2. Water landing: the pod is not designed to safely be opened in ocean, and in this mode, it is intended to be rescued by a recovery ship, just as if it were in space, as that will have higher survivability. If, for safety reasons, they always land on the ocean, then that's what you'll get 100% of the time. Seems the most reasonable and likely, but might not work with your narrative if you need a solid landing.

  3. Unexpected operating mode: Manual opening is possible but unexpected and so not made obvious (eg Tesla Model 3 manual door opening). Tesla-style "hiding the manual override because style is more important than lives" seems unlikely in an escape craft, which are designed for survivability, not style. But it could be that the opening is meant to be automatic, but for some reason that is unavailable, and the users don't know that they have to take the wrench from the front stowage and use it to loosen the door bolts until air pressure equalizes, or whatever.

    Hidden Tesla Model 3 door handle

  4. Overreliance on automation: Related to the Tesla option, but taken further, such that there is no mechanical option. Seems unlikely.

  5. Design tradeoff: While pods with the new features could be fitted into existing pod bays, the pod bays are designed such that people climb up into the pod through its base, which is where the heat shield goes, and what the ship will land on. Without tipping the landed pod over, there's no way out. Changing this would require a massively-expensive in-space retrofit of the space-cruiseliner.

  6. Safety override: the occupants are prevented from opening the door as sensors (correctly or incorrectly) detect a lack of safety outside. Perhaps it's detected as too hot until the re-entry heating has cooled, which would at least temporarily prevent opening.

  7. Legal reasons: There are legal reasons why people shouldn't be allowed to walk out on their own. (suggested in other answers were contamination risk from people fleeing a plague ship, and desire to prevent defecting). If other habitable planets were available, then this might include the desire to prevent people from contaminating virgin planets with bacteria. Perhaps the ship owners are legally responsible for the location of their passengers, and want to ensure passengers can be recovered without wandering off.

  8. Economic reasons: Perhaps so they can charge the customers (or customers' insurance) extra for recovering the craft. Perhaps their insurance charges them less if they guarantee they recover the craft rather than requiring insurance to cover people getting out before the rescue team gets there.

  9. Omnipresent recovery services: If you can assume that the re-entry will be tracked and you'll definitely have a recovery team on site wherever on Earth it lands, there's just no point having ANY manual controls. Not worth the extra risk and weight, and for pod door plugs, that'd be a lot of weight and extra pieces: it's not just a doorhandle. Of course, then you may need to change the narrative to factor in why the pod doesn't have a rescue team on site.

These various reasons, and others, can be combined. A lot of design decisions don't have one clear reason, but rather a preponderance of factors.

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    $\begingroup$ Note the only escape pod seriously considered besides an entire Soyuz (fun history story why the US owns one Soyuz spacecraft) is the MOOSE which was so light that it didn't have its own pressure system, but had enough Delta V to deorbit itself. $\endgroup$
    – Joshua
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The escape pods are designed to kill the occupants, because it's cheaper for the spacelines to pay out wrongful death settlements once than pay for medical bills and trauma for the lifetime of surviving passengers.

This answer is based on real world (false) conspiracy theories that the brace position passengers are instructed to assume during an airliner crash is designed to kill them.

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Do they always have to not be able to be opened from the inside? Because I can think of a case that pretty much does this and makes sense:

Consider Dragongeek's answer. In the vast majority of cases opening the pod is death. And doors into low pressure are always a safety issue--you want plug doors if at all possible, but they're big and require substantial clear interior volume. (Jetliner doors are an example of such. The extra bulk on the bottom is the slide but note how bulky they are and that they give up precious space in the airplane for the swing of the doors. Cargo doors can't give up this space--and off the top of my head I'm aware of two jetliners lost due to the lack of this safety.)

Thus I propose a slight variation on his system that's even more foolproof but permits escape where it might be possible.

First, the "door" is simply a panel that is fitted into the opening when needed. When fitted it approximates airtight but doesn't need to be anything like perfect. Note this means we don't need good space-worthy seals that will in time degrade. Instead, when the pod is subject to vacuum there's now a huge pressure against the panel. This activates a chemical reaction that fuses the joint so it actually is space-worthy. The layer that seals is actually thin, there is a second layer that is the real door, the filling between is oxygen-sensitive other than a thin layer towards the inside. Normally this is sealed, but the heat of fusing the first seal breaks this seal. In the presence of oxygen it rapidly corrodes.

Thus if the pod comes to rest in an oxygen-bearing atmosphere it can be opened, otherwise only the rescue crews can get in.

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The mechanism doesn't allow it

EscapePod v1 used purely mechanical seals. The prototypes worked great, but when mass produced the problems with the design became clear. One weak seal and the person dies faster than if they'd stayed on the exploding ship. Not to mention that debris from a nearby exploding ship or ramming into existing space junk could puncture the pod. The whole thing has way too many points of failure, and after a few high profile, preventable deaths, it became clear that an alternative was needed.

Then some clever cogs invented the auto-welding-gel 3000. Spread this gel on a metal surface, and the material self-welds faster than air can escape. The pod can simply be two halves of a capsule that are held apart, with all the supplies inside, and the gel on the outside. No more maintenance problems - as long as the gel is wet, the pod is set!

Now of course, opening up these pods after the fact is not easy (that is point of the gel after all). You could try using some sort of tool to cut yourself out, but you'd have to fight the gel. Heat causes the gel to become inert (hence the need for heat shields) but a lot of heat is required. Not a problem for an outside helper who can have that heat dissipate, but for someone inside with a blowtorch they'll cook themselves before they manage to get out. In the end, it was better to just leave an escape tool out of the kit. But ultimately, this one small flaw in the self-welding pod was better than an escapable pod with multiple points of failure.

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Oppressive Dictatorship

A variation on profane-tmesis.info's answer -

The people in the ship are citizens of an evil North-Korea style dictatorship which doesn't want people to escape, just to survive a disaster on board. Therefore, escape pods can't be used as a means of defection. Only the authorities who will conduct the subsequent rescue missions will be able to open them and "free" the passengers. It can be spun as a "safety measure", of course

Of course this probably means changing your entire story so it won't work if your story isn't already an oppressive dicatorship!

But if it's only a specific spaceship you need to apply this to, you could also have it so that this ship was bought / captured / inherited from an oppressive regime, and when that was done, no one ever thought to check that escape pods could be opened from the inside, and only now when you need to escape are you discovering it!

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Difficulty making changes legally

Even though space tourism is new, regulations are very restrictive when it comes to the safety equipment. Adding the parachute and heat shield took three years of lobbying and 50 million USD hiring lawyers for a feature no politician would fight. No one is interested in going through that again, especially for the unnecessary (although useful) feature of being able to open the escape pods from the inside. The same machines that open escape pods in space can open them on the ground well enough, after all.

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Why don't police cars allow the rear-seat occupant to open the door from the inside? Because prisoners have a nasty habit of wanting to escape even if it places other people in danger.

Why do passenger vehicles come with the ability to lock-out the ability to open rear-seat windows and doors? Because children, bless their hearts, don't always know what's in their best interest and will try to climb out of the car when it's in motion.

Why are commercial airplane doors unopenable from the inside during flight? Because at the altitudes and velocities those planes travel, it's whomping dangerous to have an open door — and then there's legal liability....

Why are submarine doors unopenable from the inside while underwater? Because the environment outside the submarine when it's underwater is antithetical to the well being of those inside the submarine.

There are reasons right now why we don't allow vehicle doors to open from the inside. And there are some commonalities.

  • Safety.
  • Legal or insurance liability.
  • Competence of the operator to make a sound judgement.
  • Discretion of authority.

On the other hand... a frame challenge

There are reasons to open an escape pod door from the inside.

  1. The conditions inside become more dangerous to the occupants than outside, like fire (see @TheDemonLord's answer). This is necessary to avoid legal liability. Another obvious condition would be a successful planetary landing (unlimited welfare on the outside vs. limited welfare on the inside).

  2. Occupants demonstrate authority (e.g. some form of override like a password).

  3. The escape pod is in its "idle" condition, allowing maintenance. In other words, locking in the person who's trying to oil the hinges when the pod isn't being used as an escape pod is a bad thing.

Finally, engineers are embarrassed to learn lessons like Apollo 11

We engineers are regularly taught the following: your assumptions + the unpredictable = lose your job. While engineers aren't perfect, the idea that an escape pod would be built without the ability to leave it unassisted is a remarkably bad idea that would lead to the loss of employment (if not incarceration for negligent homicide). A good pod design for your story would be a pod that makes sense but has a sensible failure mechanism for the instance or circumstance you need.

No engineer from a competent educational institution would design an escape pod from which the occupant cannot escape. If that doesn't make sense, then there's no reason to have escape pods in the first place.

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The pods are also used for joyrides to the Earth

The tourists can, for a hefty sum, take a ride in a single person pod with excellent views of the re-entry and parachute landing to the ocean.

The space tourism company doesn't want its customers to drown themselves if they happen to panic when the pick-up ship gets delayed a bit. Sure, it is uncomfortable waiting in the pod but that doesn't make the international headlines.

The pods doubling as a rescue mechanism is rarely needed, and the risk of no ship picking the pods up is considered negligible.

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Recall the incident of Liberty Bell 7, America's second human spaceflight. The hatch of Gus Grissom's Mercury capsule opened (by itself, though there was speculation he did it) during rescue operations at sea, and he nearly drowned.

A capsule could land on land, but that takes some kind of thrust at landing to prevent injury, and a lot of capsules avoid that complication. Soyuz does it because land was the only Soviet territory available that was also private so they could cover up any disasters. SpaceX wanted to land with retro thrusters, but found it too complicated and gave up.

So, where can a capsule go? It can remain in space, where opening the hatch would be bad. It can be picked up by a ship, but opening the hatch without external air pressure or proper docking would be bad. It can crash into an airless object (satellite or moon), which would be bad. It might not be designed for a safe landing on land. Or it could land at sea, and now you know why manually opening the hatch there is bad.

So assuming the capsule avoids landing on land, I see no good reason to allow opening the hatch from the inside.

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