What is the actual shape of the Vavatch Orbital? A true ring?

Question

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?

Answer 1

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

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).

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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)..

Answer 6

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.

Answer 7

"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

Answer 8

I know this is old but didn’t see the answer so…an orbital is shaped like a ring, at least when complete, but is not a “ring”. Orbitals, like planets and asteroids, orbit around a star. Rings and spheres are Dyson-type structures that completely encircle a star.

Answer 9

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.