MEGASTRUCTURES
                              --------------

                          Compiled by Ross Smith
                      (alien@acheron.amigans.gen.nz)

SPOILER WARNING:  For obvious reasons, this list must necessarily contain
spoilers for many of the books described.  You have been warned.

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                               Introduction
                               ------------

I've always been fascinated by the science fiction idea of the
"megastructure", a gigantic artificial structure that can serve as the
background for all kinds of interesting stories.  ("Megastructure" is my
own word for the idea; David Gerrold calls it "the Enormous Big Thing".)
I've assembled this list of all the megastructure stories I could remember,
with a brief description of each.  If you have any additions, corrections,
or comments, mail them to the address above, or post them to
rec.arts.sf.written (in particular, I'd like to get dates for all of the
novels mentioned).

The best-known megastructure novel, of course, is Larry Niven's _Ringworld_
(1970).  Niven also wrote an article, "Bigger than Worlds", which can be
found in his collection _A Hole in Space_ (1974); he describes many
different kinds of structure, and goes into interesting details such as how
to build a Ringworld.  (You dismantle the planets, one at a time, and use
the material to make disc-shaped plates, orbiting the sun and linked by
cables, then move the inhabitants of the next planet to the plates while
their planet is being dismantled; eventually you join all the plates into a
ring.  See also _The Player of Games_ by Iain M Banks.)

But the very first author to make use of megastructures (to the best of my
knowledge) was Olaf Stapledon, whose classic novel _Star Maker_ (1937)
describes many of the ideas (in this and other areas) that would later be
rediscovered by other writers and hailed as original (including the
star-girdling sphere that is usually attributed to Freeman Dyson).

My current best attempt at a definition of a megastructure is:  "An
artificial structure (this is intended to include living creatures) which:
(1) Has either a length of at least 1000 kilometres or a surface area of at
least 10,000 square kilometres; (2) Requires materials or construction
techniques beyond the capability of 20th century technology; (3) Is either
a single object, supported by its own strength, or a stable cluster of
objects in space."

Note that clause 2 is intended to exclude such things as solar sails (which
can be large but are theoretically within our reach now, so they don't
"feel" like SF megastructures to me), and clause 3 is intended to exclude
planet-covering cities such as Isaac Asimov's Trantor, which don't really
count as single structures.

The list of books is divided into two sections:  first, books which are
primarily about megastructures, and dominated by one or more particular
structures; and second, books in which megastructures are mentioned, but
are not central to the story.

Thanks to everyone who helped me compile this list, especially Eric Max
Francis and Sinya B Schaeffer.

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                     Classification of Megastructures
                     --------------------------------

This is based to some extent on the classification in Niven's article.  The
types are arranged in approximate order of increasing size.

Hollow World:  An asteroid (or something similar) hollowed out and set
rotating for artificial gravity, with landscaping on the inside.  It may or
may not be fitted with some form of propulsion system as well.  The idea is
an old one in SF, and it's probably impossible to find out who first
thought it up.

Orbital Tower:  In its simplest form, a very strong cable lowered from a
synchronous satellite to the surface of the Earth (or another planet, of
course).  Usually a second cable extends outwards, with an asteroid or
something similar on the end as a counterweight.  There are many variations
on this theme.  The first SF novel to use it was almost certainly Arthur C
Clarke's _The Fountains of Paradise_ (1979), but the idea goes back decades
in astronautical literature.

Artificial Planet:  A planet-sized sphere, artificially constructed but
otherwise similar in size and shape to a natural planet such as Earth.  It
may or may not be recognisable as artificial from the outside.  An old SF
idea, probably first used by Olaf Stapledon in _Star Maker_ (1937).

Discworld:  A flat disc, comparable in surface area to an Earthlike planet.
One side or both may be populated.  The idea was thought up by Terry
Pratchett, probably inspired by the Alderson disc (see below), and as far
as I know his novel _Strata_ (1981) is the only appearance of the idea in
written SF (although one appears in the graphic novel _Starstruck_ (1984)
by Elaine Lee and Michael William Kaluta, and of course Terry has since
written a very successful series of fantasy novels based on a related
concept).

Rosette:  Several planets or planet-sized objects orbiting each other in a
circle; there may or may not be another object at the centre.  The first SF
use of the concept is probably in Larry Niven's _Ringworld_ (1970)
(incidentally, Niven's claim that such a system would be stable is false).
The "order" of a rosette is the number of objects (e.g.  the Puppeteer
rosette in _Ringworld_ is order 5).

Superplanetary Sphere:  An artificial sphere intermediate in size between a
normal planet and a Dyson sphere (see below).  The first appearance of such
an object in SF (and the only one, to my knowledge) is Tony Rothman's _The
World is Round_ (date?).

Topopolis:  A long, cylindrical object, rotating for gravity, and wrapped
around a star in a spaghetti-like mass (or mess).  The concept was invented
by Pat Gunkel and mentioned by Larry Niven in "Bigger than Worlds", but as
far as I know nobody has yet had the audacity to write a story about it
(unless you count Greg Bear's _Eon_ and _Eternity_, which describe a
vaguely related concept).

Ringworld:  A circular ribbon, very strong, rotating for gravity, with a
star at the centre.  The idea was thought up by Larry Niven and first used
in his novel _Ringworld_ (1970).  It was later pointed out to him that the
Ringworld would be unstable and would require some form of active control
system to keep it centred on its sun.

Alderson Disc:  A massive disc the size of a planetary system, with a small
hole in the centre through which a star bobs up and down.  Different
intelligent species, with different temperature requirements, would live at
various distances from the centre.  Thought up by Dan Alderson and
mentioned by Larry Niven in "Bigger than Worlds"; as far as I know it has
never been used in a story (the idea is mentioned, as a hypothetical
possibility that has never been built, in Terry Pratchett's _Strata_
(1981)).

Dyson Sphere:  An artificial sphere the size of a planetary orbit.  There
are two distinct forms.  The original version (which I call "type I")
consisted of a vast number of small structures, travelling in separate
orbits and surrounding the Sun so densely that no light escapes; this is
generally attributed to scientist Freeman Dyson, although Dyson himself
admits to having borrowed the idea from Olaf Stapledon's novel _Star Maker_
(1937).  The second version ("type II"), more common in SF, is a solid,
continuous sphere; people may live on either the inside or the outside (or,
occasionally, both).  The earliest appearance of this version that I know
of was in Robert Silverberg's novel _Across a Billion Years_ (date?).  I'm
told that one appears in a recent episode of _Star Trek -- The Next
Generation_ ("Relics"), but it hasn't reached these shores yet.

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                        Novels About Megastructures
                        ---------------------------

(I've made a token attempt to give specific spoiler warnings by marking
entries that contain major spoilers for the novel in question with "**".
In some cases, of course, the mere presence of a title in this list is a
major spoiler in itself; there's not much I can do about that.)

    Author:  Greg Bear
    Title:  _Eon_ (1985)
            _Eternity_ (1988)
    Type:  Variation involving features of the hollow world and topopolis
    Description:  From the outside it appears to be an asteroid, but on the
inside it's an (apparently) infinitely long cylinder, with occasional
openings leading to various points in space and time.  A city occupies part
of the axis.

    Author:  Greg Bear
    Title:  _Hegira_ (1979) **
    Type:  Dyson sphere (type II)
    Description:  A sphere constructed in the distant future and displaced
into a pocket universe of its own, to ensure the survival of humanity
through the destruction and rebirth of the "real" universe.

    Author:  Terry Bisson
    Title:  _Wyrldmaker_ (1981) **
    Type:  Rosette (order 3)
    Description:  A spaceship on a centuries-long voyage to "seed" other
planets with life; it consists of three artificial worlds, with a control
station at the centre.

    Author:  Jack Chalker
    Title:  _Midnight at the Well of Souls_ (1977)
            _Exiles at the Well of Souls_ (1978)
            _Quest for the Well of Souls_ (1978)
            _The Return of Nathan Brazil_ (1980)
            _Twilight at the Well of Souls_ (1980)
            (two more books whose titles escape me)
    Type:  Artificial planet
    Description:  A planet that is actually a giant computer, used by the
ancient Markovians to create most of the other life forms in the Galaxy
(including humans).  The surface is divided into 1260 hexagonal regions,
each inhabited by a different intelligent species.

    Author:  Arthur C Clarke
    Title:  _The Fountains of Paradise_ (1979)
    Type:  Orbital tower
    Description:  The book describes the construction of the first orbital
tower, made of an artificial fibre based on diamond.  In later centuries,
the original tower and five others are combined with an orbiting ring to
form a structure resembling a gigantic ship's wheel.  (A full description,
with dimensions, is given in the book; unfortunately my copy is currently
AWOL.)

    Author:  Arthur C Clarke (and Gentry Lee in second and following books)
    Title:  _Rendezvous with Rama_ (1973)
            _Rama II_ (1989)
            _The Garden of Rama_ (1991)
            _Rama Revealed_ (1993)
    Type:  Hollow world
    Description:  A huge alien starship enters the Solar System, and is
investigated by the crew of the only ship able to intercept it, with the
occasional help of some back-seat scientists on Earth.  They find all sorts
of strange things inside, but no sign of the aliens who built it.  In later
books more ships are encountered (but I haven't read them and probably
never will).

    Author:  Philip Jose Farmer
    Title:  _Inside Outside_ (date?) **
    Type:  Hollow world
    Description:  A hollow world created by the alien "Ethicals" is used to
test human souls before birth.  (The book is a "prequel" to the Riverworld
series.)

    Author:  Harry Harrison
    Title:  _Captive Universe_ (date?) **
    Type:  Hollow world
    Description:  A hollowed asteroid is sent on an interstellar voyage,
inhabited by a primitive society descended from the Incas; in order to keep
the nature of their world secret, their intelligence is kept artificially
low by genetic engineering.

    Author:  Colin Kapp
    Title:  _Cageworld 1:  Search for the Sun_ (date?)
            _Cageworld 2:  The Lost Worlds of Cronus_ (date?)
            _Cageworld 3:  The Tyrant of Hades_ (date?)
            _Cageworld 4:  Star-Search_ (date?)
    Type:  Dyson sphere (type II)
    Description:  In the distant future, the Solar System has been
transformed into a series of concentric shells (one for each planet, plus
an extra one between Saturn and Uranus, if I remember rightly).  People
live on the outer surface of each sphere, and have forgotten about the
outside universe.  Dimensions of the system (overall):  diameter 12 billion
kilometres; mass 5.2e36 kilograms (2.6 million Suns).

    Author:  John C McLoughlin
    Title:  _Toolmaker Koan_ (1988) **
    Type:  Hollow world
    Description:  A hollow asteroid, built by a long-extinct people and
controlled by an artificial intelligence from another dead world, is found
by humans, themselves the last survivors of nuclear war on Earth.  The
three peoples attempt to cooperate to ensure their survival, against all
the evidence that says that intelligent species inevitably destroy
themselves.  Dimensions:  length 380 kilometres; diameter 30 kilometres;
mass is given as 2.7 billion tonnes but this is much too small for its size
(by perhaps a factor of 1000).

    Author:  Larry Niven
    Title:  _Ringworld_ (1970)
            _The Ringworld Engineers_ (1980)
            (third book in preparation)
    Type:  Ringworld; also mention of a rosette (order 5)
    Description:  The canonical ringworld, as described above.  A set of
"shadow squares" surround the sun, providing a day/night cycle on the
surface.  Dimensions:  diameter 306 million kilometres; width 1.6 million
kilometres; mass 2e27 kilograms (330 Earths); rotation period 9.375 Earth
days; surface gravity 0.94 Earth gravity (the figure given by Niven in the
second book is incorrect).  The ring is made of a very dense material
called "scrith", whose strength must be comparable to the forces that hold
the atomic nucleus together (!).

    Author:  Frederik Pohl & Jack Williamson
    Title:  _Farthest Star_ (1975) **
            _Wall Around a Star_ (1983) **
    Type:  Dyson sphere (type II)
    Description:  Object Lambda, alias Cuckoo, is approaching our Galaxy at
a sixth of lightspeed.  A scientific team is sent on a one-way trip via
matter transmitter/duplicator, and discover it to be a gigantic "lifeboat"
from an exploding galaxy.  Dimensions:  diameter 600 million kilometres;
mass 1.3e32 kilograms (66 Suns); surface gravity 0.01 Earth gravity (the
effect of low gravity on human evolution is an important part of the
story).

    Author:  Terry Pratchett
    Title:  _Strata_ (1981) **
    Type:  Discworld; also mention of an orbital tower
    Description:  A flat disc whose surface is formed into a map of the
Earth, enclosed in a sphere with stars painted on the inside.  Made by the
creators of the universe, as an intentional flaw in their creation.
Dimensions:  diameter 21,000 kilometres; mass 8.1e24 kilograms (1.4
Earths); surface gravity 1.0 Earth gravity.

    Author:  Tony Rothman
    Title:  _The World is Round_ (date?)
    Type:  Superplanetary sphere
    Description:  Patra-Bannk is an artificial world, much larger than a
planet, but orbiting a star in the normal way.  A black hole forms its
core, power source, and high-tech materials factory.

    Author:  Bob Shaw
    Title:  _Orbitsville_ (1975)
            _Orbitsville Departure_ (1983)
            _Orbitsville Judgement_ (1990)
    Type:  Dyson sphere (type II)
    Description:  A solid sphere surrounding a star, built by an ancient
alien species, apparently as a kind of trap for intelligent beings, for
unknown reasons (I haven't read all the books, so I don't know all the
secrets).  A cage-like structure around the sun provides a day/night cycle
for the landscape that covers the inner surface.

    Author:  Charles Sheffield
    Title:  _The Web Between the Worlds_ (1979)
    Type:  Orbital tower
    Description:  Generally similar to the one described by Arthur C Clarke
in _The Fountains of Paradise_.  Sheffield's "beanstalk" is assembled in
space and anchored to the Earth's surface in a complicated and dangerous
orbital manoeuvre; I'm inclined to agree with Clarke that Sheffield's
method would never be allowed.

    Author:  Brian Stableford
    Title:  _Journey to the Centre_ (date?)
            _Invaders from the Centre_ (1990)
            _The Centre Cannot Hold_ (1990)
    Type:  Artificial planet
    Description:  Asgard appears to be an Earth-sized world with a frozen
surface, but is actually a huge artifact, with thousands of internal
levels, some abandoned, some inhabited by various kinds of alien.

    Author:  John Varley
    Title:  _Titan_ (date?)
            _Wizard_ (date?)
            _Demon_ (date?)
    Type:  Hollow world
    Description:  A wheel-shaped object, found orbiting Saturn, turns out
to be a living thing, an intelligent world with various peculiar creatures
living inside.

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                               Other Novels
                               ------------

    Author:  Douglas Adams
    Title:  _The Hitch-Hiker's Guide to the Galaxy_ (date?) **
            _The Restaurant at the End of the Universe_ (date?)
            _Life, the Universe, and Everything_ (date?)
            _So Long and Thanks for All the Fish_ (date?)
            _Mostly Harmless_ (1992)
    Type:  Artificial Planet
    Description:  The Earth is actually a gigantic computer, commissioned
by mice (who are actually hyper-intelligent pan-dimensional beings) and
built by the planetary engineers of Magrathea, in order to figure out the
Question to the Ultimate Answer.

    Author:  Brian Aldiss
    Title:  _Hothouse_ (1962)
    Type:  Orbital tower (variation)
    Description:  Billions of years from now, the Earth and Moon are linked
by immense webs built by huge, spider-like creatures descended from plants.

    Author:  Iain M Banks
    Title:  _Consider Phlebas_ (1987)
            _The Player of Games_ (1988)
    Type:  Ringworld
    Description:  Several "Orbitals" (small ringworlds) appear in these
novels, including one under construction, using the method described by
Niven in "Bigger than Worlds".  The first book describes the spectacular
destruction of a ringworld by "controlled hypergrid intrusion".

    Author:  Steven Barnes and Larry Niven
    Title:  _The Barsoom Project_ (1989)
    Type:  Orbital tower
    Description:  A proposal for building an orbital tower on Mars, to help
with a terraforming project.

    Author:  Gregory Benford
    Title:  _Beyond the Fall of Night_ (date?)
    Type:  Orbital tower (variation)
    Description:  A living creature, tens of thousands of kilometres long,
spins end over end, the ends alternately touching the Earth's surface and
then flinging whatever was picked up into space.  It was created as a kind
of self-repairing orbital elevator.

    Author:  Gregory Benford
    Title:  _Tides of Light_ (date?)
    Type:  Orbital tower (variation)
    Description:  Essentially identical to the creature in _Beyond the Fall
of Night_ (I think this book actually came first).

    Author:  Lloyd Biggle Jr
    Title:  _Watchers of the Dark_ (1966) **
            plus several sequels
    Type:  Artificial planet Description:  The planet Primores, seat of the
galactic government, turns out to be a giant computer, Supreme.

    Author:  David Brin
    Title:  _Sundiver_ (date?)
    Type:  Orbital tower
    Description:  Two "needles" which carry passengers and freight between
earth and orbit are briefly mentioned.

    Author:  Harry Harrison
    Title:  _Star Smashers of the Galaxy Rangers_ (1973)
    Type:  Ringworld
    Description:  A ringworld, apparently similar to Niven's, was built to
provide living space for an expanding civilisation.  When the two edges of
its growth meet on the far side of the ring, thousands of years later, a
vicious war breaks out.

    Author:  John C McLoughlin
    Title:  _The Helix and the Sword_ (1983)
    Type:  Hollow world
    Description:  In the year 7758, humanity is spread across the Solar
System in 74,922 "Islands", engineered life forms resembling huge versions
of O'Neill-style space colonies; the Earth has been abandoned, and
inorganic technology is a near-forgotten legend.

    Author:  Kim Stanley Robinson
    Title:  _Red Mars_ (date?)
    Type:  Orbital tower
    Description:  Phobos is used as a counterweight for one end of an
orbital tower.  [Haven't read this; thanks to David Goldfarb for details.]

    Author:  Robert Silverberg
    Title:  _Across a Billion Years_ (date?) **
    Type:  Dyson sphere (type II)
    Description:  A team of archaeologists, searching for the remains of a
vanished civilisation, finds it in a giant artificial world.

    Author:  Olaf Stapledon
    Title:  _Star Maker_ (1937)
    Type:  Dyson sphere (type I); also mention of artificial planets
    Description:  An epic history of life in the universe, describing many
kinds of artificial world, including what later came to be referred to as
Dyson spheres.

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--
... Ross Smith (Wanganui, New Zealand) ... alien@acheron.amigans.gen.nz ...
... GCS/S d? p c++++ !l u-- e- m---(*) s+/++ n--- h+ f g+ w+ t-/+ r+ y? ...
        "Philosophy is useless.  Reality is worse."  (Dire Straits)