Planetary Resource Extraction and Disassembly
Raw materials for the construction of infrastructure in a colony system can be extracted from a number of sources. Asteroid mining and mining in the outer Oort clouds (where present) are important, especially in the earlier portion of the colony's history; also important are scoopship mining from the upper atmosphere and extraction of material from planetary rings. As demand increases, material can be extracted from local gas and dust clouds. and from the star itself by star lifting. Also important is the utilisation and extraction of resources from planetary bodies, from dwarf planets up to gas giants; this article discusses some of the advantages and disadvantages of planetary utilisation.
|This partially disassembled planet is surrounded by nearly-completed suprashell, which will serve to collect material for onward distribution while also serving as a radiator to emit waste heat.|
Due to the proportionally high energy cost of material export compared to asteroids, planetary surfaces are not the most convenient source of raw material. Regardless, planets do possess enormous volumes of mass which can be a sizable contribution to larger construction projects. Other reasons to mine them may be to create a swarm of habitats that more efficiently utilize the bodies' mass, or they may simply want the mass gone.
Terrestrial and rocky worlds can be landed on and built upon; many world support a moderate or even large population. But to extract material from a planet for use elsewhere. the gravitational pull must be overcome, for which there are two main fundamental methods: propel the mass with direct thrust, or launch it with kinetic infrastructure. Propellant rockets are rarely utilized as they can be slow and energy expensive to operate, though they have the advantage of being able to launch from anywhere to any orbit. Kinetic infrastructure such as mass drivers is the preferred method, allowing for a constant flow of packaged material to be rapidly launched into orbit, but with the drawback of having a set launch vector - that being whichever direction into space the driver happens to be facing at the time - and requiring massive static infrastructure.
Gaseous bodies are a common source of resources for any system, their dense upper atmospheres hosting easily accessed resources. It is typical for any system to have arrays of scoopship infrastructure in elliptical orbits around gaseous worlds, bringing the ships through the atmosphere for material extraction which is then released on the aphelion of the orbit. The material can be processed onboard the ships, or sent to a local orbital facility for processing.
For total disassembly, worlds will see stages of disassembly techniques. The mass of the world is a primary concern in the decision to undertake this process, as planets vary considerably in mass and volume, and thus the energy and time needed to disassemble them. The techniques used will accommodate the challenges weighed against what the bodies performing the extraction intend to do with the material and the system at large. One method is to use systems of orbital rings or loops reaching down into the atmosphere, supporting pipes which compress and contain the material and lift it out against gravity. The world may be totally encompassed by a suprashell or similar structure, with arrays of rings or loops extending down from the inside of the shell.
The loop-extraction process may be supplemented or entirely replaced by more energy-hungry methods. Gas worlds can be spun up and rotated fast enough that the effective gravity on the equator is reduced, making extraction easier; at higher speeds material will begin to fly off on its own. The planet can also be targeted with focused heat to excite the atmosphere to the point it begins to "boil" and expand, again leading to easier or inherent extraction. These processes are generally used with a series of suprashells maintained at different temperatures, which gather the extracted material and radiate any waste heat (which can be considerable. Mass drivers attached to the suprashell, or supported by eccentric orbital loops, facilitate delivery of material to distant destinations.
Energy required for total disassembly To totally disassemble a planet and transport its mass out of its own gravity well, it is necessary to overcome the gravitational binding energy of that planet. The amount of energy required to achieve this is very large; such large amounts of energy can be obtained either by collecting the luminosity of the local star (using a Dyson swarm or bubble), and/or by the use of fusion or conversion technology. In many cases a combination of all three sources of power are used.
Assuming relatively efficient use of the total luminosity of a Sun-like star, an Earth-sized planet could be disassembled in approximately 22 standard days, given a gravitational binding energy of 2.18 ×10e32 Joules. A gas giant world the same size and mass as Jupiter could be disassembled in 563 standard years, and this timescale could be reduced if the matter could be utilised in a fusion or conversion reactor. Smaller worlds similar to Mercury could be disassembled in a matter of hours.
In practice, the power available from a Dyson swarm would not be available in the earliest stages of a planet's disassembly (unless the swarm was already in existence), and conversely the speed of disassembly would also be limited towards the end of the process because the disassembling technology would emit a lot of waste heat. Additionally the intrinsic heat of the planet's core would cause severe overheating problems towards the end of the process, a factor which would require the construction of ever larger radiation surfaces to maintain a reasonable operating temperature. For this and related reasons, the last stages of planetary disassembly are generally carried out by devices and operatives which are tolerant of very high temperatures.