# Where on my spaceship can I justify more space for my humans?

Spaceships are a peculiar thing; as are the Humies - the hardy folks working and living inside these hunks of metal for weeks or months at a time. Ironically in space living-space is at a premium. Any places inhabited for amounts of time need to be oxygenated, ventilated and shielded from radiation - even the hardiest meatbags are pushovers when it comes to environmental conditions.

Thus spaceships were forced to become the marvels of spatial use that they are today, reducing down-times wherever possible:

• Sharing bunks between shifts, or using them for storage
• Having the mess serve double duty as meeting-/working-space
• Using the 3-dimensional geometry by moving appliances to ceilings and walls (e.g. have the cooking area of the mess opposite of the seating area)
• Combining an observation room/cupola with hydroponics

While these conditions mean near-optimal space-usage, they also mean less privacy and ways to escape each other during the weeks or months spent aboard ships.

Q: Where on my spaceship can I justify creating & maintaining these expensive living conditions, allowing me to expand available crew-space as a by-product?

Data on ships:

• Travelling between astronomical- as well as man-made-objects in the solar system
• Trips taking anything from a few days, to weeks, to months at a time
• Transporting anything that could possibly be needed to be transported between two, or more, points in space
• Crewed by usually 2 to 6 people, but sometimes more, sometimes less
• Crews rosters are, as with current-day spacecraft, intended to provide a varied set of skills necessary to facilitate spaceflight, as well as facilitate a redundancy of the availability of such skills among the crew

If the given data does not seem sufficient for any part of your answer, please assume a near-future society and extrapolate sensibly. Also consider looking at the linked questions & articles, they're not just there because I like coloured text.

• Obviously we need to go a little futuristic to answer this, we don't build long-range spacecraft, yet, but how far? – Ash Aug 12 '18 at 12:40
• What do you mean by "where on my ship"? It's difficult to answer that without a description of your ship's structure - this isn't as immediately obvious as the structure of a sailing ship or a bus. Both due to the fictional aspect of these ships, but also in the same way that buildings can be vastly different according to function, aesthetics and cost (e.g. the USS Enterprise, the Nostromo from Alien, Firefly's Serenity and FarScape's Moya all have very different structures - so the answer would drastically change for each [no room for links, just Google images of each to get the picture ;)]). – G0BLiN Aug 12 '18 at 12:59
• To the person downvoting: If you could, please take a minute or so to elaborate the reason for your downvotes (and if possible even another minute to maybe bring up some ideas of how to improve the question to prevent further downvotes) - this would help me immensely :) – dot_Sp0T Aug 12 '18 at 14:13
• @dot_Sp0T There are critical details missing: what is the primary function(s) of your spaceships, other than carrying humans on board? Also, what is the expected duration of the trips your ships will be making? – nullpointer Aug 12 '18 at 14:29
• @dot_Sp0T I have to second G0BLiN's comments. Both the purpose of the ship and its duration of travel are required in order to answer your question. The primary purpose of the ship would suggest its size and hence how much it can afford to 'spend' on housing people,also additional constraints like protection from incoming fire. Duration directly affects what measures need to be taken to house humans – nullpointer Aug 12 '18 at 14:57

In space, things that robots can do they will do. Already on Earth robots do things like washing clothes and cooking. These robots do not need to share conditioned meatball space with the humans.

from OP /Using the 3-dimensional geometry by moving appliances to ceilings and walls (e.g. have the cooking area of the mess opposite of the seating area)/

Appliances will be outside the conditioned space. Robots outside the living area will contain interior pressured spaces cook for cooking and cleaning. Storage spaces will likewise not be pressurized and will be minimally shielded. Stored items will be tracked by computer and delivered on request. Washing of nonliving material will definitely be done in non-pressurized areas, which will greatly facilitate the process.

Interior spaces for human habitation will be used for that and only that. Any space a human could occupy will be reserved for that use alone.

It will be tight quarters. In one respect it will make a diesel submarine seem roomy - but because protruding stuff and appurdances do not clutter living space (as they do on a sub) the spaceship living spaces will also seem clean, smooth, well lit and aesthetically pleasing.

• This is a nice spin on the issue! – dot_Sp0T Aug 12 '18 at 15:03
• +1 just for the term ‘meatball space’. – Joe Bloggs Aug 14 '18 at 7:46

Assuming that on a long trip you want pseudo-gravity for the health of your crew, a reasonably large ring section is probably in order. Given that the outer "floor" of said structure is going to be experiencing 1 gee of pseudo-gravity you are going to lose the utility of most of the three dimensional space between that floor and the core of the ship. You can, without serious increases in cost, open that lost space out giving the crew some headroom. You could halve the headroom and have expanded bunk spaces at half-gravity as well.

• Wouldn't a spinning ring produce a massive amount of surface-area that needs to be shielded and maintained? (in comparison to a gravity-less tube for example) – dot_Sp0T Aug 12 '18 at 14:04
• Reading your comment the thought crosses my mind that you assume these ships/trips to be a means to depose people on stellar bodies eventually. This question is not about that. It's really only about people living extended periods of time in spaceships (and maybe habitats between trips, etc.) – dot_Sp0T Aug 12 '18 at 14:12
• @dot_Sp0T I did assume that by space-colonisation you meant interstellar colonisation without you actually saying so, but for any really long term space habitation we'll want something like gravity if we can get it, and we probably can. – Ash Aug 12 '18 at 14:16
• Note that you can also simulate gravity by continuously accelerating (or decelerating) at 1g - this makes sense for journeys where you are in constant burn - accelerating for the first half, than turning about and decelerating for the second half to match velocities with the destination. That type of gravity generation doesn't require a ring section, but rather a multi-floor design (where the engines are at the bottom floor thrusting "upwards") – G0BLiN Aug 12 '18 at 15:01
• You don't need a ring for centrifugal gravity. A small capsule with a tether and counterweight would work just as well and be much cheaper. – Robin Bennett Jun 17 at 14:02

## tl;dr: Justify the space with a moss carpet on the ground and edible plants on walls and ceiling.

The way I see your question is this:

You want to make crew rooms/living space bigger, so you need a justification for it. The problem with bigger crew spaces are that they are more expensive and have more mass, meaning more fuel, meaning more \$.

In order to justify extra space, you need to use all of that space for something.

Presumably, only living things would justify more space.

For example: We could have no O2 tanks on the ship and store all of the oxygen in the living areas at 1 atmosphere, but that would be inefficient- we can save mass by compressing O2 in a tank on the outside of the ship. The O2 doesn't need the extra space, and it doesn't care about radiation or temperature.

Therefore, you need to justify the extra space with something that needs the same things humans need, including ample space, but without being a human, because that wouldn't make the area any less cramped.

For this, you could fill your ship with dogs. Dogs love being in space [citation needed], and they would be great companions. However, dogs have disadvantages.

They wouldn't need too much more space than already exists, so the crew space wouldn't go up much. They eat too, and they are not vital to the ship's operations, so they would drain resources. Dogs also need lots of care.

You need something hardy instead. It has to take up lots of space, need minimal care, and be essential.

My suggestion is a plant. A hydroponic moss or vegetable would be able to feed the crew. It would need lots of space to feed a medium size crew for the duration of the trip. It would require food, water, heat, radiation shielding, and an atmosphere of pressure.

Instead of creating a separate room for the plants, you could build them right into the living space. The floor could be a hardy moss (vegetables might not stand up to being walked on). Goodbye CO2 filtering- the moss would take care of it. The walls and ceiling could be vegetables, like potatoes or carrots. There goes any need for food storage because you can grow food. Taking these components off the ship would make it lighter and save money.

Depending on whether the ship has gravity, you might run into problems. With gravity, the plants on the walls and ceiling would fall. To fix that, you can make the walls vertical planters and plants on the ceiling could be suspended upside down like this, except filling the entire ceiling.

If you fill the crew spaces with plants, you can justify making them larger to accommodate more plants to filter the air and feed your crew. That means the crew will have more space to move around in.

• Hi @JohnLocke, welcome to Worldbuilding.SE! We hope you enjoy your stay, here is the tour and the help-center. – JavaScriptCoder Aug 19 '18 at 21:08
• @dot_Sp0T Is this along the lines of what you are looking for? My understanding is that you want an reason/excuse to give your crew a large living space and as the author you want to make the extra space seem plausible. – John Locke Aug 20 '18 at 16:03
• "The O2 doesn't need the extra space, and it doesn't care about radiation or temperature." Do not exspose O2 to radiation, that's a great way to make O3 which is toxic. – Clay Deitas Aug 22 '18 at 23:06
• @ClayDeitas It's ok. We can just put some Cl gas in the tank to break down the ozone ;) – John Locke Aug 22 '18 at 23:49
• Oh good idea. Lets also store all our water as hydrogen gas and condense it with oxygen when we need it. – Clay Deitas Aug 23 '18 at 0:23

space/volume isn't really an issue in microgravity, just mass. There isn't any air resistance. If the ships are built in microgravity then the only real consideration will be the mass of the additional shielding.

The reason space is limited in current spacecraft is that they had to fit in the shuttle's bay or on a rocket that had to push itself out of our atmosphere.

If you can get a drive tech that produces >= .1 G, you may not have a gravity issue for the humans. A tenth of a G is, theoretically (no one has actually tested it, YMMV), what the body needs to maintain health. A souped up ion drive or NERVA drive would work for this.

As for shielding, one proposal has been to create a "storm shelter" on the ship that has a high degree of shielding that everyone can run to if there is a CME or other event. That would allow the expansion of living space without adding too much of a mass burden.

• Argumenting with the square-cube law - I like it – dot_Sp0T Aug 22 '18 at 17:40
• @dot_Sp0T, Yep. And if you go with the storm shelter method, the cost of extra space is pretty negligible. It would make maneuvering more difficult since you have to get the far ends of the thing turning but that's just another incremental cost. – ShadoCat Aug 23 '18 at 17:00

There are some spaces on a spaceship that are going to be available that would not be on a submarine. In particular:

1. Fuel pods. Early in the trip, you have lots of fuel. This is because you need enough fuel to push not only the payload but the fuel. As you travel, you need less and less fuel. But this opens up more room to use.

If you do a long blast initially, that will use up more than half your fuel. So you can take over all that space for the rest of the voyage.

Perhaps that's where you put the gymnasium. Because if you're in free fall, you'll want some big space to help you move around.

2. Food space. When you launch, you need an awful lot of space for food. As you finish off the frozen, canned, and durable food, you can recover that space and allow other spaces to expand into where it was.

3. Intermix rooms with hydroponics. As you mentioned, hydroponics can be mixed with other space. Rather than having multiple people bunking in the same room as in a submarine, scatter the rooms throughout the hydroponic space. When your off-shift is over, compress the room. Then your neighbor, who is coming off shift, can expand that room into the place where your room was. That way both of you can have some elbow room when in your room. And your window can look out onto the hydroponics.

You might even make the rooms mobile. So you don't always have to look at the same view. Move your bunkroom to the view that you want. Hydroponics. Stars. Lay out and tan under the sun (assuming proper screening). Whatever makes you happy.

4. Trash. All those food wrappers and stuff? On a submarine, they keep those in the sub with you. On a spaceship, you can put them outside.

5. Atmosphere cans. A special case of trash is the atmosphere cans where you carry compressed air. You release that as you use up the fuel and put out the trash. The cans themselves can go outside.

Or maybe you don't use cans but spaces. So you keep the atmosphere compressed by the fuel. But the wall moves. So as you use up the fuel, the pressure in the room with the atmosphere drops to normal levels. Once finished, the hatch opens and people can use the space. If you put the fuel inside a sort of balloon, you don't even have to clean up afterward. The balloon itself becomes trash, which you stow outside in the vacuum.

• There was one book I read - for some reason I want to say it was 2061: Odyssey Three, that used water for reaction mass. The ship's pool was literally one of the fuel tanks. Obviously you could only use it when the ship was under thrust. :) – T.J.L. Aug 20 '18 at 17:38
• I wanted to write the fuel idea too. The Skylab space station was a repurposed second stage of the Saturn V rocket. So if it was possible in the 70s it certainly is now/ in the near future. – CKA Aug 21 '18 at 12:43
• @T.J.L. What happens if the engines stop? Does everyone in the room drown? – John Locke Aug 22 '18 at 23:55
• You can't put trash outside unless it's in some guided, powered canister set to crash into a sun. Space trash already causes headaches now. Hate to think what even a lolly wrapper would do at the speeds needed for interstellar flight – Thorne Aug 23 '18 at 5:03
• @Thorne I didn't say to leave it loose and allow it to float away. I said to stow it outside, where it doesn't take up internal space. – Brythan Aug 23 '18 at 5:15

In the near-future, the development of more comfortable, lightweight and reliable spacesuits could change the definition of what is a living space in a spaceship. If your suit is no more uncomfortable or cumbersome than a diver's wetsuit, then you can spend most of the day using it, even recreation time.

So it's possible the pressurized, oxygenated, shielded rooms on spaceships might not grow much bigger, and will focus on changing rooms, eating and sleeping quarters, and bath/toilet.

More and more rooms would become spaces where you need to wear a spacesuit, but that's okay if it is comfortable and gives you full dexterity in your hands. This would actually simplify some things. Engineering rooms would not longer have to be built so carefully to avoid small sparks setting fires, since they are now in vacuum instead of an oxygen-rich environment. Things can be built with an open plan instead of a cramped design, making maintenance and repairs much easier. If the suits are as comfortable as a wetsuit, then astronauts could spend recreational time wearing them. If they need to get out of the cramped, windowless spaces that are pressurized, they could simply do a tethered EVA and just sit on the outside of the ship (possibly in a lawn-chair zip-tied to the ship, plugging a mimosa capsule into their suit's hydration system). A big un-pressurized, un-shielded box would not be too expensive to assemble in-orbit and pull along, and astronauts in these new suits could take some kind of space ball in there and bounce it around in some zero-g ball game.

These new kinds of living and working spaces, in which people wear space-suits, has basically no requirements other than not letting significant debris get in and not letting the astronauts float away. Thus it would be easy and cheap enough to make that you could justify much more of it.

# Put human bodies into suspended animation caskets (SACs)

This will be the most sustainable option because you do not need a lot of materials to run actual space. Living spaces must at all times be:

• sanitized
• monitored
• air-conditioned
• pressurized
• lighted
• gravitated

These requirements are just for designing a general livable space. Specialized living spaces like bathrooms, bunkbeds, kitchens, living rooms, cockpits, laboratories, viewing windows, etc., require a lot more conditions, meaning a lot more resources.

BUT if you just put everyone to sleep, then you just need highly sophisticated bunk beds that also function as dining rooms, comfort rooms, and all sorts of utility rooms. Your only problem will then be all about running a place where interaction is necessary and/or encouraged, i.e. cockpits, laboratories, and living rooms. My solution is just to

# Put human minds in full-immersion virtual realities (FIVRs)

Everything in an FIVR is limited only by what computational power your ship can allot for such simulations. The only thing you need to ensure is the hierarchy of command within the ship, the accuracy of your simulation compared to real-world physics, and the correlation of the simulation with the control processes of the ship.

Basically, you need to provide an interface for the simulation and the real world such that if the captain in the simulation decides to crank a simulated lever to steer the ship leftward, the ship will steer leftward based on the value of the cranked lever.

It would be like controlling the ship itself from within the simulation.

This simulation-reality correlation can be extended to all the other functions of the ship like

• running the simulation
• regenerating food sources
• navigating through space

Summarizing: The freedom and safety you desire can be efficiently provided by virtual spaces. You can place a sophisticated, self-sustained, single-size bed anywhere on your ship. You only need that bed to be able to read and carry out the thoughts of the person on it. Maybe just add propulsion and the bed itself can become the ship, or link several of these beds together and equip them job-specific extra utility functions.

TL;DR: By making the ship, the humans, and the interfaces between the two to be as integrated as possible, you do not need to know specifically where inside the ship should you put your humans.

• Sounds a little like the Matrix. – John Locke Aug 23 '18 at 14:34
• Yes that's it! Can't believe I didn't think of that. But yes. Basically put the humans in the Matrix and give them just enough power and control. All will be well. – Kyle Zabala Aug 24 '18 at 14:27
• Until they decide they like the matrix with AIs they can interact with more than the cramped spaceship their bodies inhabit, so they create a fantasy land in the computer and live there instead. Then they park their spaceship in orbit around a star so they have solar power for the matrix for the rest of their lives. – John Locke Aug 24 '18 at 15:08
• That's a good option, especially if the ship is actually a Von Neumann probe creating Matrioshka Brains upon reaching star systems. The opposite is also still an option though, when they realize that control over everything in virtual reality is more boring than limited control over an unexplored reality. Definitely your captain's call. – Kyle Zabala Aug 24 '18 at 22:20
• Good point, I hadn't thought of the VR as possibly being less interesting. I was saying that the people might abort whatever mission they were on to just live in VR instead, but if you don't have AI in the simulation, that could make it less interesting than real life. Although keeping them in the VR might have an upside of keeping the crew alive while whatever task (like an M brain developing) happens so they are alive to monitor its progress. – John Locke Aug 25 '18 at 0:47

The rocket would look much like current rockets, with people strapped in for the take-off. Once it had cleared the atmosphere and entered space proper, it would slide extensions out from the side, like certain RV's have. These spaces would provide more living space than the main rocket; as a matter of fact, they could maybe pack more stuff into the vehicle than currently (assuming weight isn't an issue) since there would be no movement space for the people during takeoff and landing while they are strapped into their seats and the extensions retracted.

Inflatable tents

Using an airlock hatch, an inflatable tent (constructed of suitable materials) could be rigged to give space to live on the outer hull of the ship.

Radiation shielding isn't needed at all times, it'll be monitored and the crew can move to safety in time, or specialized clothing could be worn instead.

A crewman uses the same amount of oxygen wherever they are, and if ventilation is actually a problem, a breathing tube could be rigged up.

The easiest way I see to create lots of extra space, is to have your space ship designed in a very particular way. And thats with removable and modular interiors. Basically your spaceship will consist of an outside shell which contains your shielding, ventilation and other necessary living requirements. The shell is designed to open up, so that the interior of it can be replaced very quick. You can throw in giant storage units, living compartments, food production, maintenance bay and so one, just by opening a shell, pulling out the interior and putting a new one in.

The point of this is during space travel, once you have reached your desired speed you can open up the shell and remove the interior and let it float alongside your space ship. Of course you attach it to your ship via some prebuilt struts so it doesn't just float away, and you can keep accelerating. You then reseal the shell and bring out a bunch of collapsible furniture/equipment or move the equipment from your already cramped living quarters into the empty shell(which is now sealed, pressurized, shielded and ventilated because those sections are build into the shell and not the actual interior (the interior will just connect onto those parts in the shell).

Now you might think to yourself, why would anyone sacrifice the extra room for having separate interior and exterior walls. The answer is pretty simple, speed and flexibility. A space ship can be loaded and launched in an incredibly small amount of time using this system. The interior storage units are prepacked and once a spaceship arrives, you pull out their interior, push in a new one and off it goes. Think of Formula 1 racing, where they literally have pit stops down to a few seconds. You'll be doing that but with space ships instead. The nature of the goods your sending will also change and this provides you with the flexibility to carry any goods that can be packaged into your interior. It doesn't matter if its passengers, cargo, sensitive material, or a black hole. As long as it fits into the interior compartment, its going to fit in your spaceship.

The only issues I see with this, is that these spaceships aren't going to actually every land on a planet. That would make it too costly. Instead they could dock at an orbiting station where cargo would be removed and put back in before they continue on their way. This will provide you with more spaceship throughput, and you could attach more exterior shells (everything is modular) to allow you to transport more good if required. Now you might think, why don't they just attach extra goods on the outside? and the reason is because more mass means more energy to accelerate which means more fuel. There is a set limit on how much strain and how fast you can accelerate with externally attached modules, and you have to worry about applying the force offset from the center causing spin.

TL:DR?

What I am envisioning is basically giant train like spaceships with compartments made to fit storage containers. Once you stop accelerating, you remove the storage container and let it float outside your compartment. You are then free to use the compartment however you like, until you start to decelerate.

## Surface-area-to-volume-ratio is (for the first time ever) your friend:

The space humans have to live in is proportional to the volume of the cabin.

The material required to make the cabin is proportional to the surface area of the cabin (yes, air pressure maintenance is proportional to volume, but by mass and cost it's negligible).

The thing is, as volume increases at a linear rate, the surface area increases at a rate proportional to the square of the cube root of the rate of volume increase. Therefore, it's more cost efficient to have a large living space than a small one. If a 100m^3 cabin takes 60m^2 of material to produce, a 200m^3 cabin takes 95m^2 of material to produce.

Volume has little impact on spaceflight, because there's no friction. As long as the cabin is roughly symmetrical, the center of mass is maintained.

You get more value out of a large cabin than a small one, and the larger it is, the more resource efficient. They know that people need space, and it's relatively easy to build a large cabin for the crew.

You can justify any space that's connected to a vital system as critically important to be fully pressurized and oxygenated. Passageways leading to the engine, main computer, generator, moisture catcher, and any other life support/ critical system all need to be pressurized, And the easiest way to do this is to simple make a box around all these systems. Any space within this box would be pressurized in order to give the crew access to anything they might need to work on, but that also means the crew quarters will be as large as the space not used by vital systems, within a cuboid the width and height of the largest system, and the length required to accompany all systems within the ship.

Exterior expansion. Think exterior hull add ons.

Start with a basic pod like option designed to be an additional house with a hallway for maintenance access and connections and whatever else is needed to sync the pod to the ship.

Then in a competitive universe... You'd see cheap models, expensive mansion style models, shed sized ones just for storage, military ones where it adds turret stations, or medical facility additions, maybe even models of different designs based on their home planet, but from there the possibility expands drastically. Especially if at these various stations you mention there are sites which offer the service to add pods on and prep them for space travel.

With that you'd see space crafts of obscure shapes with customized pod additions attached to the hull of the main ship.

Hope that helps. Enjoy.

• This is very creative, but the whole justification part is missing... – dot_Sp0T Aug 19 '18 at 6:54
• @dot-sp0t I'm trying to be charitable here, but you're really not doing a very good job of articulating what you really want. I almost feel like you're trying to hide your intent from us so you can get an answer without anybody actually understanding what the real question is. – Morris The Cat Aug 20 '18 at 1:05
• @MorrisTheCat nobody expects you to be charitable, it's a nice gesture but doesn't get you anything really. I did the best job I could do, if that's not enough - so be it. I cannot change your feelings or experiences leading you to these feelings, if you can't strip them then it's not my problem. The real question is detailed at the top of this thread, and it cannot be that unclear because A) the question got a seizable amount of great answers, and B) there have been not Votes to close this question as unclear as far as I recall. Maybe it's just you..? – dot_Sp0T Aug 24 '18 at 19:51

I guess I'm not really sure I understand the problem you're trying to solve here.

The bottom line, assuming near-future space travel, is nowhere. You would never have large open spaces on a well designed spacecraft unless having that large open space were a SPECIFIC design constraint, in which case the followup question is "What do you need it for"?

Ultimately, if you're talking about any kind of near-future space travel engineering, the primary design constraint is mass. The objective is always to make the spacecraft as light as it possibly can be to fulfil its mission, because the heavier your spacecraft is, the more reaction mass you need to use to move it around, which is also reaction mass that you have to MOVE by expending even MORE reaction mass, etc etc.

So, I'm sort of trying to extrapolate the Real Question here, which I THINK is "Under what conditions would a near-future spacecraft have the large open spaces I want for dramatic purposes", and I think the answer is that you have to rely on a propulsion system that's MASSIVELY more efficient in terms of Specific Impulse than anything we're currently using, and/or construction materials that have a much greater strength-to-mass ratio than anything we're currently using.

You might be able to solve the latter problem by relying on carbon nanotubes/nanofibers for construction, and for the former you might want to start here: https://en.wikipedia.org/wiki/Specific_impulse

• I am not sure where you are getting the 'large & open' requirement from :/ The question, as stated, is about finding out where on a ship we could tease out more space for humans - space that needs to be pressurized, shielded, etc. – dot_Sp0T Aug 19 '18 at 6:37
• Well, in that case I think the answer is "Anywhere you want it.". If we're talking about a near-future spacecraft, then the only real design constraints you have that are even relevant to a "where" question are that you need your reaction drive at the back, and the fuel source right next to it, and then everything else you can arrange almost any way you want to. As you say, pressurized space is EXPENSIVE so any good design isn't going to have a pressurized space that doesn't serve as many purposes as possible. – Morris The Cat Aug 19 '18 at 22:48
• Frame challenge, +1. How can "I justify creating & maintaining these expensive living conditions?" - You don't, because ten thousand people will raise their hand to go to space even if you tell them they'll be in a three foot box for a month. – Mazura Mar 2 at 2:20

Our experience with spaceship design is fairly limited so far - however consistently it is the importance of the mission that often determines it's configuration, size and complexity.

Several factors need to be considered:

• How far your destination for this ship is
• How long it would take to get there
• How many crew are there / passengers would there be
• How much weight you can carry

As an example, the Apollo missions had Command modules no larger than a car cabin, and an attached Lunar module not much bigger again. This was tight, but the three crew were only in there for 8 days, plus they were highly trained and professional, purposely for the mission.

Another, the ISS, is much larger, contained a crew most times of 6, and a volume of 930 cubic m. The modules are quite comfortable, even for extended periods of most of a year, with plenty of 'nooks and crannies' for sleeping areas and private areas. Considering the cost of the station (the most expensive item every made), every surface is optimised and invested with the utmost of utility.

If however, you are aiming for long voyages abroad, then an analysis of current ships on the drawing board may be in order. Have a look at Space X's BFR and Mars mission as an example. This is meant only to be a ferrying ship, and even for 3 months the crew are expected to not need a large amount of space internally as they are on a relatively short voyage, disembarking upon destination.

If you are aiming Interstellar - well, this is much more different. Space is big, really big, and it would take a long time to travel to a distant (or close) system.

There are currently 2 'size' camps:

• Interstellar Small Ships: Go small, as small as you can, to accelerate as fast as you can (and hopefully slow down easier too). A cryogenic ship, seed ship or data ship is very small, but if not then a small single man crew may be desirable, as every kg makes it just that much harder to accelerate. Even then it may take a long time (decades or centuries).

• Interstellar Big Ships: Go big, as big as you can, to make the journey the priority as much as the destination. A Generation Ship is along these lines. Adequate space for a society to survive the millennia it would take for the ship to reach its destination, perhaps km in width and length. You can't beat an asteroid, hollowed out with atmosphere, spun to create gravity, pushed to reach the next star system in a 1000 years or so.

Basically there is no superfluous space on a ship, you don't need more space than you need because of weight penalty, unless you go Generation Ship, which would be massive, and likely more space than you need personally (enough for a society anyway).