The Coalition and Orbital Grids

[Graham Kennedy]

The development of orbital grids of some form is a relatively common step in the life of most galactic powers. Although they vary hugely in the methods, technologies and materials used to implement them, not to mention the environments they support, orbital grids are an obvious way of providing large areas of living space in a convenient location.

Earth's orbital grid is the largest and most populated in the Coalition, and the oldest in the Human membership block. It's origins date back almost a thousand years, to 2055, when construction of the Skyhook was begun. Earth's first orbital tower (aka "Beanstalk") was a simple cable constructed of carbon-based materials which extended from the surface up to a station in geostationary orbit, and then beyond to a distant counterweight. Although expensive at the time, when it was completed in 2068 the Skyhook reduced the launch cost to orbit by a factor of more than a thousand and permitted a massive revolution in space exploration and exploitation.

Further orbital towers followed over the next few centuries, each using more advanced materials and techniques, until Earth's equator was studded with more than a dozen towers. The stations up in synchronous orbit blossomed into large space ports in their own right, eventually rivaling many Earth communities in size and population.

The next step was obvious, and had indeed been predicted by some visionaries centuries earlier. Cross travel between the various space ports remained a difficult and expensive business, often involving going down to Earth, crossing thousands of miles, and then ascending another tower. Connecting the ports with an orbital ring made far more sense. And of course once the first orbital ring was completed, it was only natural that further facilities would spring up along it. Within a century the ring was less a road in space, more a continuous unbroken space city, almost a quarter million kilometres long.

During the Saravan occupation of Earth the ring underwent a fundamental change. Before it was devoted largely to industrial facilities; ports, spacecraft construction facilities, refineries, zero gee manufacturing facilities, etc. The Saravan retained much of this, but added large living areas. Most of this consisted of rotating sections with the ring passing through the axis. During the two centuries of occupation by the Saravan, the permanent population of the ring rose from tens of millions to billions.

Once the occupation was over, Earth faced a unique crisis. In the run up to the Turgran/Human/Saravan war, the Turgrans had deliberately capitalised on the many myths and legends the primitive Human slave population had of an ancient Human home world, covertly fostering a warrior religion amongst the slaves. A major foundation of this religion was that once the Saravan were vanquished Humanity would return to Earth, the Utopian promised land. Once the war was successfully concluded and the Humans freed, they did indeed want to return home. All 90 trillion of them. Worse, the heavily theocratic government now in power was inclined to let them, regardless of the practicalities.

The Turgrans stepped in as a calming influence, but they only convinced Earth to restrict immigration to the maximum practicable. Transports loaded with immigrants arrived at the ring at the rate of ten thousand a day; the surface population soared. And so the planet's orbital grid underwent a transformation.

The geostationary ring expanded, crammed with new manufacturies which were largely focused on one thing - producing more rings. All of the orbital towers were hugely enlarged and renovated, and the first new ring was added. Well above the geosynchronous level, the new ring was nothing like the old. No jumbled amalgamation of a billion factories, this was a single ribbon, fifty kilometres wide and one hundred thousand in diameter. That single structure provided almost as much much area as the whole of Russia - all of it specifically designed as living area. By 2610 the population of Earth's orbital grid passed the one trillion mark.

Another ring followed, and another, and another, and another. The cataclysmic shattering of the Human religion brought a more secular, more rational Imperial government to power, but the urge for Humanity to return home was something that even Emperors hesitated to stand in the way of at a time when politics was a rather fragile affair. And so the grid grew. And grew.

Today Earth's grid consists of twenty three rings; the inner geostationary one is 84,300 km in diameter, ranging out to the outer one 355,000 km in diameter. Widths also increase as the rings go out, the original 50 km width for the second ring was replicated on the third, but the fourth went to 60 km, then 75 km, then 100, and so on. The last few rings to be added have all been 275 km across; greater widths are possible with present day technology, but not really necessary given the recent trend on Earth for a stable population size.

As a result, the habitable rings of Earth's orbital grid total slightly over 3 billion square kilometres in area - six times larger than the surface area of the planet itself, and more than twenty times the land area. Approximately a third of this area is cityscape, with extensive parks and recreation areas around them. The total population of the grid is ten trillion.

Almost all Coalition worlds have at least one orbital tower - completing such by the end of the colony phase is part of the standard government colonisation contract. Most full members have at least an elementary orbital grid, though few approach the size or population of Earth's. Populations in the tens to hundreds of billions are far more common, with barely a thousand grids exceeding the trillion level and only a hundred over five trillion. Although it is common in the Coalition for people to believe that the extensive colonisation effort is needed to "ship out the surplus population", in truth the transport of colonists to new planets, whilst not exactly insignificant, is only a fraction of the answer to support of the Coalition's population. The true answer lies in the grids - and in the grids, the Coalition has taken a large step away from a planetbound existence.

[Tsukiyumi]

Wow. That's pretty extreme, GK. I mean that in a good way, of course.

[Monroe]

I like it

Whats the extreme case of the orbital girds? I take it humans don't have anywhere near the largest.

[Teaos]

So these "towers" arent actually solid but a cable lift? The entire grid is basically free floating in orbit?

So the shadow these things would cast, would that be a big problem for the surface?

[Graham Kennedy]

So these "towers" arent actually solid but a cable lift? The entire grid is basically free floating in orbit?

So the shadow these things would cast, would that be a big problem for the surface?

The original towers were nothing but a few wires which cars would slide up and down, yes. And the original geostationary ring was free floating in orbit. Over time the towers were built and expanded upon; today they are giant high rise buildings in their own right, through only poor people live in the towers.

The way orbits work, anything below Ring 1 wants to orbit in less than 24 hours, anything above wants to orbit in more than 24 hours. Since the whole structure is fixed and radial from the Earth, though, all of it moves with the Earth. For Ring 1 that's fine, it's in orbit. There are no rings below that but if there were, they would feel Earth's gravity pulling them down. That's what you would feel going down a tower, if the cars didn't have artificial gravity - zero gee at Ring 1, rising steadily to 1 g as you reach the surface.

Above Ring 1 it's the other way around; Ring 2 is going faster than orbital speed for its height, so there is an apparent net force upwards, away from the Earth. The further out from Earth you go, the bigger this force gets, though it's actually not all that big at any height.

The math is straightforward. Any object in Earth's gravitational field feels a force equal to GMm/r^2, where G is a constant, M is the mass of the Earth, m the mass of the object, r the radius.

Keeping any object in a circular motion requires a force on it of mv^2/r, where v is the velocity of the object.

If you are going to be in orbit, then those two things have to be equal because it's gravity that keeps the object in circular motion. So GMm/r^2 = mv^2/r

For a fixed 24 hour period, going below geostationary orbit means gravity dominates. Going above means the rotation dominates. That last is actually pretty useful in the early days of towers, because it means that if you ride up to the top of a tower and let go, you go flying off into space. Time when you let go just right and it can throw you off on a course towards other parts of the system. By the Coalition's time such things are unimportant because the sublight drive systems available make such things trivial.

As for blocking the sun... from the surface the widest ring is only about 0.15 degrees across, which is less than a third the angular diameter of the sun from Earth. I've been in an eclipse, and can attest from personal experience that even with 3/4 of the sun covered the difference in light levels is hardly noticeable. Under the grid you might be aware that it's not as bright as it is a couple of hundred kilometres to the north, but nobody is walking around in permanent darkness or anything. You certainly would be able to look at the sun through those funky dark glasses or just squint at it and see the band across it, though.

The night sky is more fun. You can see the grid from anywhere on Earth stretching across the sky. From somewhere like the US you can see all the rings individually, each up to a third the width of the moon, a third of a degree or so apart. They're big enough that you can make out large scale things like lakes, islands and big cities with the naked eye. Through a good telescope you can see all sorts of detail. Kids love it.

[Graham Kennedy]

I like it

Whats the extreme case of the orbital girds? I take it humans don't have anywhere near the largest.

Earth's orbital grid is somewhat limited in size because of the moon. If they go much bigger than they are now, they'll have to move the moon further out, with all sorts of ecological issues for Earth. There are planets in the galaxy without that limitation whose grids extend out many times larger than Earth's.

The extreme case is that you build a Niven style Ringworld around the sun, or a full on Dyson sphere. The Zaketh do both.

[shran]

Would the structure of the rings be something kids learn at schools as well, like we learn the various locations of countries today, would they also learn the maps of those rings?

[Graham Kennedy]

Absolutely, though with a slightly different emphasis than today since there are no "countries" on Earth any more. They'd learn about the different rings in much the same way that American kids learn about different states in the US, or British kids learn about the different counties of the UK.

[Monroe]

That'd be pretty wild going into the far future to take a history course.

A race that coulld build Dryson spheres is pretty bad ass I really like your universe when are we going to start seeing the resemblence of a book structure posted? I really want to read it

[Graham Kennedy]

Lol, as I've said before, the whole book thing is far more theoretical than actual. You may never see it.

[Monroe]

Lol, as I've said before, the whole book thing is far more theoretical than actual. You may never see it.

Lame Get a writer to work something up

[Graham Kennedy]

A cross section through a 275 km wide ring section, showing an orbital tower. The tower is 2,430 m wide; the rim walls rise 11 km above the surface, with a "glass roof" stretched between them. The roof is supported by cables attaching to structures which rise above the rim walls, and to the tower on the other side. Between the orbital towers a series of smaller towers rise up from the ring floor to provide an attachment point for the support cables.

The floor of the ring is covered in 120 metres of rock and soil; underground transportation systems run through this, along with sewage and power lines, etc - all the things you'd expect under the surface of any developed planet. The lakes and seas are carved into this layer - which does mean that no body of water on a ring is more than a few hundred feet deep. The cities you can see are made of buildings up to 3.8 km tall.

The rings enjoy a natural 24 hour day/night cycle; above the equator, they are tilted 23 degrees to the plane of Earth's orbit, which means even the lowest ring is well clear of Earth's shadow during the summer and winter months. During spring and autumn they spend some time within the shadow during each rotation; even for the lowest ring this comes to no more than 70 minutes, dropping to 15 minutes for the upper ring. The rings are designed to have temperate climates.

[Graham Kennedy]

A portion of the cross section at much larger zoom. Note the buildings, which may bear a vague resemblance to modern day constructions!

In order from top to bottom, the layers are :

A soil/rock layer. As mentioned, 130 m deep.

Foundation material : A metal alloy, about as strong as steel but considerably lighter. Buried in it is a layer of forcefield generators. With these active the foundation layer is by far the strongest part of the ring.

Gravity generators. The green things are gravity generator machines, designed to be exceptionally long lasting and reliable (at the cost of considerable bulk). Generators are networked together, and each could cover an area at least twenty five times greater than it actually does. As a result, the great majority of the generators could fail without any real measurable difference to the ring's field. Indeed in excess of twenty five adjacent generators would have to fail before even one area was affected.

Inner ring floor. Made of a low grade exotic material, the base material is strong enough to maintain the integrity of the ring entirely alone, even without the foundation layer and force fields.

Insulating layer. A layer of insulation material.

Outer ring floor. Essentially identical to the inner floor, the outer floor is again capable of maintaining the physical integrity of the ring. The outer layer is also more than strong enough to withstand any likely impact.

[Captain Seafort]

Very cool, and with your customary attention to detail.

Apart from the fact that these ring surround planets, rather than being free-floating, they're somewhat reminiscent of Culture Orbitals. Are they inspired by Orbitals, and does the Coalition-verse have Orbital-like structures (i.e. free-floating)?

[Graham Kennedy]

They were not inspired by Orbitals, no. I don't claim the idea of a grid is mine or anything - Arthur C. Clarke suggested multiple orbital towers joined by a band in geostationary orbit in his novel "The Fountains of Paradise". When I read it I thought "and why not more rings than that, too!" I'm sure the idea has been explored many times before, seems like every megastructure has something dedicated to it somewhere.

I don't like certain things about Culture Orbitals, actually. Once they are finished they're great, but they start building them by having two square plates spinning opposite one another, joined by a forcefield, millions of km apart. Then they add new plates as they need to until the ring is complete. Call me paranoid, but the idea that a forcefield failure could effectively destroy a 90% complete Orbital gives me the heebie jeebies.

The Coalition doesn't make freefloating space structures on the scale of Orbitals. They do make what are basically giant space stations, called habitats. Some are hollowed out asteroids, usually old mining colonies which have endured past the time when the mines are gone (I'll post my notes on what happened to Ceres soon, it's a case just like this). Others are more akin to Rama, habitats designed to operate within the solar system, or occasionally ones modified to wander between systems at sublight speeds. Few habitats are built these days, they've been rendered largely obsolete by the production of orbital grids.