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We know traveling in the vastness of space is very boring, as all galaxies and stars appear as dots against the black emptiness of space. It has been established that portholes play an important role for crews to visually inspect and report on the exterior of the spaceship for any abnormality as a standard safety protocol. However, all the portholes on generation ships are rectangular in shape instead of circular.

I was wondering why a state of the art generation ship has such an Achilles heel? Aren't round windows better suited for pressured chambers?

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    $\begingroup$ Portholes of any shape are a terrible idea from a safety viewpoint, any exterior observations - especially of the ship itself - are better done by a rotating camera mounted on a boom or a drone. If you want a justification for windows at all, whether rectangular or round, then much more information is required on the ship and crew, in particular its acceleration, whether it spins for gravity, which surface/s any portholes are mounted in etc. $\endgroup$ Jan 5 at 6:33
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    $\begingroup$ "space is very boring, as all galaxies and stars appear as dots against the black emptiness of space" I'm getting the impression that you've never had the chance to look at the sky on a clear night somewhere with no light pollution. $\endgroup$ Jan 5 at 11:19
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    $\begingroup$ Portholes are not dependent on energy and so are failsafe. Also, they read Orphans of the Sky and want to ensure the generations are aware of the outside. $\endgroup$
    – Mary
    Jan 5 at 13:18
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    $\begingroup$ Rectangular windows, obviously, frame the protagonists much better, as we look in at them from outside. $\endgroup$
    – CCTO
    Jan 5 at 15:21
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    $\begingroup$ "However, all the portholes on generation ships are rectangular in shape instead of circular." It's unclear what you're trying to say here. Are you telling us that you've invented a world where such ships must have rectangular windows and now you're asking for an explanation why? Or, if not, what makes you think that all generation ships have rectangular windows? Where is this constraint coming from? $\endgroup$
    – J...
    Jan 5 at 19:32

12 Answers 12

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They are screens, not windows

window

They are rectangular monitors connected to cameras on the outside. That has advantages to structural integrity, but it also allows the users to cycle through different zoom levels, light sources (infrared, ultraviolet, cosmic background radiation) and also just display passenger information and movies and the like. These would be way more useful than actual windows.

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    $\begingroup$ Better for radiation shielding too - cosmic rays are no joke, so for a window to be safe, you'd have to put so much lead in it that it would no longer be clear. (ISS doesn't have this problem, since the Earth's magnetic field protects it from charged particle radiation) $\endgroup$
    – codeMonkey
    Jan 5 at 15:33
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    $\begingroup$ @J... You cannot tesselate the inside of a circle, and it's useful to have all pixels be of the same shape and size. I buy a species accustomed to hexagonal monitors over round ones. $\endgroup$
    – KeizerHarm
    Jan 5 at 21:44
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    $\begingroup$ @J... My assumptions are not about culture, they are that A) a monitor will be composed of a lot of pixels, B) mass-producing things is more efficient, and C) things are more efficient to mass-produce if they are identical. Sure, people can do non-optimal things for cultural reasons but that argument applies to every written word on this website. $\endgroup$
    – KeizerHarm
    Jan 5 at 22:14
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    $\begingroup$ CRT monitors and TVs did have phosphors in an hexagonal grid more often than not. $\endgroup$
    – Pablo H
    Jan 6 at 12:08
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    $\begingroup$ Why limit yourself to only visible spectrums the humans can see. Especially when you can give them infrared, ultra-violate, and even radio wave vision. Screens, floor to ceiling in the high end quarters and "observation decks? $\endgroup$
    – boatcoder
    Jan 7 at 3:16
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The passengers installed these windows.

This, among many other modifications to the ship en route. The windows were made by removing a panel and replacing it with a clear plastic sheet. The panels were generally rectangular elements between hull struts and so the windows are the same shape.

The removed panels were supposed to be kept next to the window where they were, so they can be replaced. In fact nearly all of these panels have been pressed into service in other ways over the decades since they were removed.

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    $\begingroup$ Never underestimate the ability of the mid-journey generations to go off the mission plan. $\endgroup$ Jan 5 at 15:39
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    $\begingroup$ Just wait until they decide to install the porch! $\endgroup$
    – Joe Bloggs
    Jan 6 at 10:32
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    $\begingroup$ @JoeBloggs So long as that doesn't come with a screen door... $\endgroup$ Jan 7 at 14:38
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Actually - we do have angular windows in space.

Round windows on aircraft are more the result of reducing metal fatigue. The curvature of the window is more for the corners to not be sharp and form weak points when the metal flexes / expands and contracts to suit differing temperature and pressure during multiple flights.

Round windows in shipping are for both practical and aesthetic reasons. Although, if you may notice, most windows on ships are actually rectangular - pressure resistance is more accomplished by the thickness of glass, and the strength of the frame it sits, than it is the shape of the window.

In space, pressure is not too much of an issue. Note the windows on the Apollo Lunar Modules are actually triangular to save space and allow for other instruments which had a higher priority:

enter image description here

In your case, it is possible to have windows of any configuration on a space ship. It is simply an equation of economics, practicality and usability - the glass would likely be designed thick enough anyway to withstand the air pressure difference (only 101 kPa plus live loads), and the frames would simply be designed to suit such a required load.

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  • $\begingroup$ Is that picture from Homeworld? $\endgroup$ Jan 5 at 15:53
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    $\begingroup$ Worth stressing the point - round windows on planes are because the plane is repeatedly going up and down, and the outside pressure changes based on altitude. A spaceship, once in space, has basically constant pressure the whole time, so long as it stays in space. For a ship which repeatedly goes to space and then lands again, you'd go back to rounded windows, e.g. the Space Shuttles. $\endgroup$ Jan 5 at 16:50
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    $\begingroup$ Have to make a correction: watertight ship portholes are all round or oval. If you see a square window, it's almost always in the superstructure, above the watertight main deck. Such windows are only weathertight, i.e. they're designed to withstand splashes, but not immersion in water. $\endgroup$
    – ZOMVID-21
    Jan 5 at 20:51
  • $\begingroup$ The Shuttle uses oblong or other rounded corner shapes rather than round windows, so no, round portholes aren't required or even standard. britannica.com/technology/space-shuttle $\endgroup$ Jan 5 at 22:35
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    $\begingroup$ @computercarguy That's why I said "rounded" and not "round". Comment was long enough, I didn't want to complicate it even more. $\endgroup$ Jan 6 at 14:08
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There are no portholes

The entire hull is made of, instead of metallic matter, some sort of transparent crystalline substance, that seems supernaturally tough compared to other materials. Due to this construction, the hull is entirely solid, without any perforations or portholes

The windows, instead, are simply unpainted sections of the hull. As these windows are a matter of paint, they can be whatever shape the designers want

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    $\begingroup$ Ahh the reference to the Puppeteers.... $\endgroup$
    – boatcoder
    Jan 7 at 3:13
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    $\begingroup$ I see transparent aluminum has a competitor. $\endgroup$ Jan 7 at 19:44
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A true generation ship would likely be so technologically advanced that pressure issues would be negligible; and geometric issues would be based on artistic and culture preferences, throughout the ship.

Pretty much as it is on Earth. Small round portholes here would stand up better to high winds, would be less likely to be broken by debris, easier to clean, etc. But I've seen seaside houses with 8' tall and 30' wide rectangular windows facing square to the sea to take the wind head on. They are just overbuilt to handle a hurricane, in order to create a visually pleasing aesthetic experience.

We do the same thing with houses. Mathematically speaking, a circle encloses the most area with the least material, it is the most efficient shape, and the lack of flat surfaces and corners make it more resilient to wind. That's important for huts and stone where material may be in short supply. But it isn't easy to arrange space inside a circular dwelling. We could go triangular, but that has similar problems, so square gives us the most usable square feet of floor space. Yet for aesthetic reasons, nearly all our buildings and houses are built as connected rectangles, not a big square space. (some skyscrapers have a pretty square footprint though.)

I would imagine any culture capable of building a generation ship would have the technology to make it look like whatever they wanted, and their aesthetics would override any differences in cost or efficiency.

They are building something they intend for people to spend their entire lives in, birth to death in old age. Wouldn't they make it as pleasing and comfortable as possible?

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    $\begingroup$ look at the windows on the ISS for an example, a good view is justification in and of itself. nytimes.com/2020/11/02/science/space-station-cupola.html $\endgroup$
    – John
    Jan 5 at 22:03
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    $\begingroup$ Flat glass must be thick enough to withstand the stress. It's more accurate to say a cirular window that has a convex curved (3D catenary) surface is the the most efficient use of material. $\endgroup$
    – Bohemian
    Jan 5 at 22:23
  • $\begingroup$ @Bohemian Fair enough, +1, but my contention holds: If a culture is technologically advanced enough to build a generation ship, it is technologically advanced enough to build its windows, doors, ports etc in any shape it wants; it doesn't have to worry about minimizing stressors or the most efficient use of materials. Just like we don't really do that on earth. We spend billions to make weird shaped skyscrapers that are works of art. And other monuments, like the Taj Mahal, or Colosseum; we make things both functional and beautiful. $\endgroup$
    – Amadeus
    Jan 6 at 11:13
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It is cheaper The generation ships production has become such a competitive market, that every cent counts. When building a ship with tens of thousands of windows, you want those windows be as cheap as possible because because a 20% discount on a 10 000 USD, window gives you a saving of around 20M$ per 10000 windows.

Due to material inefficiency (the slab of glass can be cut into rectangles with no waste material), the transportation volume (You can store more windows in the same space) and overall streamlining of windows production process (cutting a circle is just more complex/expensive/fault prone), it soon came down to Hexagonal and Rectangular windows, and finally the rectangular won because it was able to cut the production costs by extra 2% on the cutting process while the hexagonal could not match this.

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  • $\begingroup$ Given glass can be melted down and reused to make more windows, I'm not sure the material-efficiency is really an angle that would affect things much. $\endgroup$
    – Ruadhan
    Jan 7 at 12:58
  • $\begingroup$ @Ruadhan while true, this material recycling would again increase the inefficiency somewhere. Per this proof arxiv.org/pdf/1009.4322.pdf densest circle packing is ~0.907, meaning that no matter how well you optimize, there will be at least ~10% material or energy inefficiency in your glass making process. More in some cases, as you need to melt the glass into slabs, cut out the shaper, and then remelt the remainder in the new batch. $\endgroup$
    – Dvorkam
    Jan 7 at 14:10
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Generation ships are generally used when transporting a population to colonize a far-off world. Since they'll be building a civilization from scratch, your ship was designed so that it could be almost completely disassembled and the components re-used for building homes, farm equipment, light industry, etc. The window is square because it's destined to become part of someone's living room. All of your colonists will essentially be unskilled laborers upon arrival, so the ship's various parts and sub-assemblies tend to be simple, easy-to-work-with shapes like rectangles.

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The body of the ship is made from mangalloy

The body of the ship needs to last a long time. In general, alloys that are made tougher by fatigue will survive the constant vibration of your ships engines over the course of centuries of abuse compared to work softened alloys like most aluminum and titanium alloys which would literally shake themselves apart over the long journey. It also resists the brittling effects of cold much better than many other alloys

Mangalloy is a form of steel that contains enough manganese to turn it into a work hardened alloy. This stuff is several times tougher than other kinds of steel and only becomes tougher the more you abuse it. This makes it a very popular choice for things like mining equipment, but it comes with special caveats that make it unpopular in other respects. The biggest thing that makes it unpopular is that it is untoolable. Once you cast it, it is practically impossible to mill or bend into other shapes making it an extremely complicated to create anything other than basic geometric shapes with. However, its toughness also means you can use a lot less steel than you would otherwise allowing you to make vibration proof structures that achieve the same lightness per toughness as aluminum/titanium alloys.

Being mostly made out of iron, mangalloy is also significantly cheaper than many other alloys you could choose. When produced in bulk it only costs ~\$375 per ton as opposed to aluminum which is ~\$2500 per ton or titanium which is ~\$4800 per ton. Since generation ships have to be so big, this is a very important factor to consider.

So the windows, and everything else about the ship is based on straight lines as opposed to curved ones because the advantages of using this one particular alloy (or something similar to it) far outweighed the disadvantages of square portholes.

To get an idea of what making a spaceship out of mangalloy would look like, consider the Tesla Cybertruck. It owes its unique shape to this special steel variant being using it its construction.

enter image description here

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Aircraft windscreens are rectangular or more complex shapes as well.

Older, 737:

737 windscreen

Recent, 787: 787 windscreen

Combat, Su-25: Su-25 canopy

It's very possible to make non-circular pressurized windows. Circular or oval ones are simply lighter.

At very high pressures, or against severe cyclic loads, circular windows win. Watertight ship portholes are generally made round or oval. However, atmospheric pressure within a ship is small enough that a non-circular window is a very tolerable weight penalty.

If you want an explanation, it's because the designers valued crew comfort above weight savings.

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    $\begingroup$ I don't see a single rectangle in those pics $\endgroup$
    – Bergi
    Jan 6 at 16:19
  • $\begingroup$ @Bergi Being trapezoid is no better, but just if someone isn't sure, I'll throw in a 737... $\endgroup$
    – ZOMVID-21
    Jan 6 at 17:41
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Airplanes originally had square windows. It's cheaper and easier to build. Unfortunately, square windows turn out to be a horrible idea on something that undergoes repeated major temperature fluctuations. The corners become the origin point of cracks due to metal fatigue and your plane comes apart in flight.

Pilots need big windows--but when you look closely you'll find the corners are rounded off.

Your generation ship will experience only two temperature fluctuations, one in departing the original star system and one in arriving at the destination system. Thus the reasons against square windows go away and simple engineering says you have square windows if you're going to have windows at all.

(As for the radiation problem--you can't hope to put enough shielding in a window. Your window is therefore outside the radiation shield. The dose you would get is low, and it could be made very low by adding an electromagnetic shield.

Build a big electron gun/accelerator on your ship. Let's say you boost the electrons to 1GeV and eject them behind your ship. Your ship becomes positively charged to the tune of 1GV. Any particle that wanders around reacts to this field--a negatively charged particle falls in, gaining 1GeV in the process, a positively charged particle loses 1GeV. This means electrons slam into your ship very hard indeed--but they're easy to stop. Any positively charged particle with less than 1GeV of energy is deflected, the ones coming in hotter lose that much energy. The dose from positive particles goes way down, the dose from neutral ones is unchanged--but in interstellar space that was pretty close to zero anyway.)

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Because it's better

A round porthole is a compromise of structure vs utility. Round windows are structurally stronger and can withstand more pressure than the same material in a rectangle.

A civilisation which can build a generation ship has no real reason not to build big windows where they can. The material-science obviously isn't an obstacle!

More width means more people can enjoy the view, but a round window is as tall as it is wide, which limits things somewhat if you want a big observation-deck.

But really that's not a compromise a generation-ship needs to make.

So beef up the thickness, brace the window-frame better and have your wide rectangular plate-glass and enjoy it.

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Rapid installation of bulkheads

It's not the window that's square. It's the bulkhead that goes over it.

The windows are for comfort in low risk cruise conditions. But when the ship has taken damage, or is at risk for taking damage, a bulkhead is fitted and locked down over the window opening from the inside. In fact, the bulkhead is sitting right there, behind a concealment.

To install the bulkhead, the gravity is greatly reduced and the bulkhead is simply man-handled into place. This is part of bringing the ship into "general quarters" or other high material condition of readiness.

There are also hoist points where the bulkhead could be hoisted into place in full gravity, though that is not generally done.

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