In Iain M. Banks', fairly rockin' Culture novel, Consider Phlebas a good third of the book takes place on what is called the "Vavatch Orbital". An orbital is apparently a massive artificially created megastructure, similar to the Death Star or the titular Halo.

At one point in the book the Vavatch Orbital is described as a minor orbital, not as big as a ring or a sphere. Then later it is almost directly described as having a ring shape. Still earlier in the story it is described as a bucket being swung in circles, though this description maybe used only to describe how the orbital uses centrifugal force instead of actual gravity.

Whatever the size, the orbital has to have enough sea space for a Megaship (a city sized ocean ship) to travel for more than a century before reaching land again.

Wikipedia tends to suggest that all orbitals are rings, but then why the mention of a sphere, or that Vavatch is not big enough to be a ring?

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    The Vavatch was actually bigger than most orbitals.
    – Solemnity
    Commented Feb 24, 2013 at 23:08
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    "An orbital is apparently any massive artificially created megastructure, similar to the Death Star or the titular Halo" No. An orbital means a ring. Can't recall right off which book that is in, but an orbital is a ring. Commented Feb 25, 2013 at 6:50
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    Also, the Bungie team when originally releasing Halo commented that they'd based the Halo ring design on Iain M. Bank's orbitals. Worth reading: vavatch.co.uk/books/banks/cultnote.htm
    – Alex
    Commented Aug 7, 2014 at 3:08

8 Answers 8


There's an illustration (by Mark Salwowski) of Vavatch on the cover of the 1988 Orbit (UK) paperback edition of the novel:

The flat plane of the orbital, tilted at an angle to the right, fills the foreground with a blue sea under white clouds, with the blue haze of atmosphere fading to the black of space above.  In the distance the orbital curves off to the right, a band of blue-white against the star-flecked black of space.

The first description of the Orbital in the book also gives its dimensions:

Vavatch lay in space like a god’s bracelet. The fourteen-million kilometre hoop glittered and sparkled, blue and gold against the jet-black gulf of space beyond. As the Clear Air Turbulence warped in towards the Orbital, most of the Company watched their goal approach on the main screen in the mess. The aquamarine sea, which covered most of the surface of the artefact’s ultradense base material, was spattered with white puffs of cloud, collected in huge storm systems or vast banks, some of which seemed to stretch right across the full thirty-five-thousand-kilometre breadth of the slowly turning Orbital.

So it's 35,000 km wide and 14,000,000 km in circumference (4,500,000 km in diameter), giving it a surface area of 4.9 × 1011 km2, about 960 times the surface area of Earth. A ship taking an (Earth) century to circumnavigate Vavatch would need to travel at an average speed of about 16 km/hour (8.6 kt).

  • so about 3/4 the diameter of Neptune
    – endolith
    Commented Dec 5, 2015 at 2:52
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    Wait, I read that wrong. It's way huger than Neptune. The breadth of the ring is similar to the diameter of Neptune, and the diameter is 4.5 million km?? It's 3.2 times the diameter of the Sun!
    – endolith
    Commented Dec 5, 2015 at 5:17
  • A very impressive structure indeed!
    – Cupit
    Commented Feb 1, 2019 at 15:12
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    @endolith but much smaller than the Ringworld.
    – Spencer
    Commented May 18, 2022 at 12:07

Here's how Banks describes Orbitals himself, in his essay A Few Notes On The Culture :

Perhaps the easiest way to envisage an Orbital is to compare it to the idea that inspired it (this sounds better than saying; Here's where I stole it from). If you know what a Ringworld is - invented by Larry Niven; a segment of a Dyson Sphere - then just discard the shadow-squares, shrink the whole thing till it's about three million kilometres across, and place in orbit around a suitable star, tilted just off the ecliptic; spin it to produce one gravity and that gives you an automatic 24-hour day-night cycle (roughly; the Culture's day is actually a bit longer). An elliptical orbit provides seasons.

  • This is the most accurate representation, explaining every aspect of the device including its weather, gravity and seasons. My only worry is the size and energy output of the star. I am left to assume there is a means to protect the populace from the high levels of radiation from a star the size of our sun. Commented Nov 11, 2014 at 21:34
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    @Thaddeus The ring is in orbit around a star, it doesn't have a star in the center of the ring. It's in an orbit similar to that of a planet. "One thing almost every Orbital ... does have, is a Hub. ... the Hub sits in the centre of the Orbital, equidistant from all parts of the main circumferential structure (but not physically joined to it, normally). The Hub is where the Orbital's controlling AI (often a Mind) usually exists"
    – endolith
    Commented Dec 5, 2015 at 5:18
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    Don't forget that The Culture have crazy forcefield tech. To the that point that GSVs don't even have physical hulls anymore, it's all forecfields. Solar radiation would be trivial to them.
    – Cupit
    Commented Feb 1, 2019 at 15:23

I think it is clear from the Culture novels that there are various mega-structures that are found in the culture universe, including spheres, rings, orbitals, shellworlds and mega-ships like GSVs that can accommodate billions of people themselves.

It seems clear from their regular appearance in the novels, that orbitals are relatively common. @DanielRoseman's excellent answer quoting Banks describes that pretty well - but from this description and the novels we find that Orbitals are ring shaped structures, in orbit around a star (not surrounding a star). They are sometimes complete and continuous (like Vavatch) and sometimes not complete or finished, and comprise 'plates' that people live on - such as the Chiark Orbital from Player Of Games. Orbitals tend to have a 'hub' comprising a mind located at the point that it revolves around.

I think the description in Consider Phlebas is a little confusing, but it is meant to distinguish orbitals (these relatively small structures in orbit around a star) from a 'true' ring in the sense of a Niven Ringworld, or a sphere, by which I presume is referring to a Dyson Sphere. A Niven Ringworld is a vastly bigger structure than an orbital - a ring at Earth orbital distance around a star would be over 900 million kilometers in circumference - much larger than the 3 million kilometers that Banks describes an orbital. Rings if they are rotated for gravity, unfortunately take the laws of physics to breaking point - Niven had to invent magical new materials for it to be made from. In the Culture however, perhaps (equally magical) force fields can be used in place of unrealistically strong materials.

I think we are meant to presume that rings and spheres are known in the Culture Universe, but perhaps much, much less common than orbitals.

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    Here's an illustration of ring vs orbital: orionsarm.com/eg-article/5151b9b79834e orionsarm.com/eg-article/4845ef5c4ca7c
    – endolith
    Commented Dec 5, 2015 at 3:15
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    Capital-R Rings seem like an artifact of the early series before he had fully worked out the size and scope of the civilization - given what we learn later, they're far too large for the Culture to bother building for itself (it might be able to, but wouldn't justify ruining a solar system to achieve it). The Culture's total population is later revealed to be similar to that of the Ring from Ringworld (which was post-apocalyptic and considered effectively deserted).
    – user36551
    Commented Feb 28, 2017 at 16:22

Look to Windward contains a description of an Orbital in chapter 12

'It is what they call an Orbital; a band of matter in the shape of a very thin bracelet, orbiting around a sun - in this case the star Lacelere - in the same zone one would expect to find an habitable planet.

'Orbitals are on a different scale from our own space habitats; Masaq', like most Culture Orbitals, has a diameter of approximately three million kilometers and therefore a circumference of nearly ten million kilometers. Its width at the foot of its containing walls is about six thousand kilometers. Those walls are about a thousand kilometers high, and open at the top; the atmosphere is held in by the apparent gravity created by the world's spin.

'The size of the structure is not arbitrary; Culture Orbitals are built so that the same speed of revolution which produces one standard gravity also creates a day-night cycle of one of their standard days. Local night is produced when any given part of the Orbital's interior is facing directly away from the sun. They are made from exotic materials and held together principally by force fields.


'Each Orbital is different and each Hub has its own personality. Some Orbitals have only a few components of land; these are usually square parcels of ground and sea called Plates. On an Orbital as broad as Masaq' these are normally synonymous with continents. Before an Orbital is finished, in the sense of forming a closed loop like Masaq', they can be as small as two Plates, still three million kilometers apart but joined only by force fields. Such an Orbital might have a total population of just ten million humans. Masaq' is toward the other end of the scale, with over fifty billion people.


I pictured it as a HUGE ring, but ring in the sense of the thing on your finger, it orbits itself, the slow rotation causes things to fall, but doesn't generate gravity due to having limited mass (compared to a GSV or planet), the "surface" is either the inside "up" or the outside "down", I'm guessing the outside would be unlivable.

The "inside", if you will, is a huge expanse slowly curving upwards, like our planets horizon curves downwards, but as it is so vast the curvature happens outside humans fields of vision, appearing to be a flat ocean etc. Imagine a perfect skateboard ramp circle, with open ends, and possibly the width of a planet, but with nothing Inside but space & air.. (maybe not even air in the middle)..

  • GSVs would not have significant gravity either. Commented Feb 25, 2013 at 1:33
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    They use fields on GSV's for artificial gravity, which is awesome, cause then they can suspend it at will.
    – Grizly
    Commented Feb 25, 2013 at 2:47

There is definitely no air in the middle, since the rotation pushes the air towards the inner surface.

However, you do not need a ceiling; only walls to keep the air in.

See Elysium for a demonstration of the idea.


"Consider Phlebas" calls Vavatch a hoop on page 255:

Vavatch, that fourteen-million-kilometre hoop, was starting to uncoil. A chain, it had been cut


As others have mentioned, it's a large ring which rotates to generate centrifugal force to simulate gravity on the inner wall. The ring is in orbit around a star like a planet orbits a star (with the star far outside the circumference of the ring itself). In this way, the inhabitants inside the ring can watch the sun rise and set as the ring turns (imagine "midnight" as the time when they are closest to the sun, their feet pointed toward the sun, and it is obscured by the floor. And "noon" as when they are furthest from the sun, their feet pointed away from it, and it can be seen roughly overhead).

Other responses have neglected to mention that the surface of the orbital is also sloped toward the edges so that the inner surface looks like a parenthesis in cross-section. (If you were on the inner surface, with both edges equal distances, you would need to "climb" to escape the ring). This is explained as the principle reason the atmosphere stays inside the ring, as there's no solid ceiling. There is also a layer of artificial dust suspended in a magnetic field to shield the inner wall from solar radiation and create different climates.

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    This is flatly wrong. The cross-section of the Orbital plates are flat in the direction normal to its spin direction, and the atmosphere is retained by slanted walls (2000km high) on the edges. There is a clear description in CP about crossing the "underside" of the Orbital and "rising" alongside the Edgewall: "the shuttle climbed in empty space beside the Edgewall. Two kilometres away there was air, even if it was thin air [...] The shuttle crossed that knife-edge, two thousand kilometres up from the base of the Orbital"
    – DavidW
    Commented Nov 12, 2021 at 15:22
  • @DavidW "This is flatly wrong" I see what you did there Commented Nov 15, 2021 at 13:06

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