Megastructure refers to structures on a planetary scale.

Examples of megastructures are:

	1. DysonSphere
	1. RingWorld
	1. SpaceElevator/SpaceHook
	1. BlackHoleEngine
	1. CarbonEngine
	1. Bussard ramjet, also known as a electromagnetic ram scoop
	1. FullerRingBridge
	1. PlanckEnergy particle accelerator (for testing/exploiting a TheoryOfEverything)
	1. Gravitational Detector array
	1. Landfill of all AOL disks sent in mail

There are many proposed MegaStructure''''''s that involve a long, strong cable, like the SpaceElevator and SpaceHook. The SpaceHook appears to spin; typically one end comes down to (near) the planet surface, grabs the cargo, then pulls back out ... and releases it somewhere out in space. "rotavators, which are basically rotating shorter spacehooks in lower orbits".

A black hole can be used as an efficient power source. Quasars output > X% (90?) of the gravitational energy of any matter they consume as radiant energy.

An advanced SolidStateCivilization would require a lot of carbon. Unfortunately, the most abundant element around is hydrogen which is singularly useless either as a structural material or for electronics. Such a civilization would find itself hydrogen-rich and carbon-poor and decide that converting one into the other is a good idea. Fusion is the obvious solution but small-scale fusion of the sort involved in fusion reactors would never do. Rather, a giant fusion reactor would need to be constructed.

One possible design might involve using a core of collapsed matter (aka neutronium) onto which is dumped the hydrogen. If the core is sufficiently massive to fuse the hydrogen but not so as to collapse it then the resulting release of energy should free the carbon product from the core of the device.  Chunks of collapsed matter might be harvested by exploding a neutron star using a mass of antineutronium accelerated at near the speed of light. This is essentially shooting a bomb inside of the neutron star. Accelerating the antineutronium is necessary since a mass large enough to disrupt the star would tend to bounce back as soon as it came into contact with it. Intuitively, you want the back of the bomb to go through the explosion produced by the front of the bomb. Accelerating the mass would require a megastructure with incredible length and power requirements.

Producing a sufficient mass of antineutronium may involve some difficulty.

''Almost as difficult as getting a suitable neutron star''

Of course, this may just be a crazy hare-brained scheme.

See also
http://en.wikipedia.org/wiki/Megastructure