Editing Astroengineering

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[[File:Array.png|thumb|300px|The Ark and the 7 Halo rings.]]

'''Astroengineering''' is name given to the construction of megastructures in space by technologically advanced beings. It is a form of megascale engineering, but deals with structures that are "easily observable" from interstellar or even intergalactic distances with 20th century astronomical instruments: i.e. An orbital elevator is an example of megascale engineering, but it is not an example of astroengineering. Typically proposed feats of astroengineering are on the scale to remake an entire stellar system.

Construction of these megastructures seems to be restricted to either [[Forerunner|Tier One]] or [[Covenant|Tier Two]] civilizations. Although listed as a Tier Three civilization, the [[UNSC]] has no known astroengineered structures.

==Forerunners==
The [[Forerunner]]s are renowned for their mimicry of natural environments, but it is their engineering achievements that stand as monuments to their extraordinary prowess, centuries after they have passed on. Their Halo Installations, Shield Worlds, and the [[Installation 00|Ark]] are all artificial habitats on a vastly larger scale than anything that either [[Human|humanity]] or the [[Covenant]] could have accomplished. All known [[Forerunner]] megastructures are a part of the [[Halo Array]].

===Orbital===
{{Main|Halo Array}}
[[Image:Delta Halo.jpg|thumb|200px|[[Delta Halo]], the second Halo discovered by the UNSC and the Covenant.]]
The Halo Installations are planet-sized artificial worlds, shaped like a ring. The interior surface contains a breathable atmosphere and seemingly natural terrain, including oceans, lakes, mountains, forests, and tundras. Underneath this is a support layer, upon which this terrain has been put in place, consisting of a vast grid network of metallic plates that provide the base. Though centripetal forces may provide at least some of a Halo installation's gravity, it also uses artificial gravity generators to generate [[Earth]]-like gravity.<ref>'''[[Halo: The Flood]]''', page 14</ref>

The exact size of a Halo seems to vary. [[Alpha Halo]] has a diameter approximately equal to that of [[Earth]]<ref>'''[[Halo: The Flood]]''', page 13</ref>, but [[Delta Halo]] was described as being only as large as a moon<ref>'''[[Halo: Ghosts of Onyx]]''', page 188</ref>. Because these are the only two known Halo Installations, it remains to be seen whether these are standard sizes or whether each Installation is different in size and structure.

The Halo's were constructed as weapons of mass destruction on a galactic scale, designed to kill all sentient lifeforms in their radius of effect, approximately 25,000 light-years. The exact means by which they do this is unknown.

===Artificial Planets===
{{Main|Shield World}}
[[Image:Onyx.jpg|thumb|200px|Artificial planet [[Onyx]], before its destruction.]]

The Forerunners were also adept at creating artificial planets, such as Onyx. Internally, the structure is maintained by, and even ''composed of,'' trillions of [[Onyx Sentinel|Sentinels]] and at least one immense [[Sentinel Constructor Factory #Onyx|Sentinel Constructor Factory]], while externally the planet can appear like many other terrestrial planets, with a wide variety of terrain.
 
A variation of the concept also exists, built in a more conventional fashion. It's a structure whose surface is composed of an outer shell, with a hollow interior and a habitable inner surface, and a miniaturized artificial star in the center. The interior resembles a [[Dyson Sphere]], though on a far smaller scale.

====Onyx====
The artificial planet [[Onyx]] was used as a cover for the [[Shield World]] in it's core. It was later colonized by the [[UNSC]], oblivious as to its true origins until [[2552]], when its [[Onyx Sentinel|Sentinels]] activated to defend the Shield World. It was later damaged by [[FENRIS Nuclear Warhead]]s, and destroyed as its Sentinels burst free and set up defensive stations around the Shield World portal.<ref>'''[[Halo: Ghosts of Onyx]]''', pages 377-378</ref>

====Flood-Controlled Shield World====
Unlike Onyx, this [[Shield World]] was a hollow spherical shell with a terraformed inner surface and an internal sun. The installation's outer surface was heavily infested by the [[Flood]]. With an approximate diameter of 2900 kilometers<ref>http://www.youtube.com/watch?v=A8lxRH9zqWw</ref>, it's one of the smallest Forerunner megastructures.
It was destroyed by the [[UNSC]] forces in [[2531]] when the overloaded [[Shaw-Fujikawa Translight Engine|Slipspace Drive]] of {{UNSCShip|Spirit of Fire}} sent the internal star to [[Supernova]] state.

===Micro-Dyson Spheres===
{{Main|Micro Dyson Sphere}}
The [[Forerunner]]s also constructed massive Dyson Spheres, with a diameter of 2 astronomical units<ref>'''[[Halo: Ghosts of Onyx]]''', page 380</ref>, encapsulated them in a [[Slipspace]] field to protect them from the Halo Array as it activated. Essentially a sphere, with its habitable surface on its internal surface rather than external, Shield Worlds are also equipped with their own stars<ref>'''[[Halo: Ghosts of Onyx]]''', page 379</ref>, providing warmth, light and energy to the installation. Originally intended as a way to circumvent the Halo effect, the Shield Worlds were not put into use by the Forerunners due to the rampant actions of one of their own [[Mendicant Bias|AI constructs]].<ref>'''[[Halo 3]]''', [[Terminals]]</ref>
The interior of the [[Shield World (Halo Wars)|Flood-Controlled Shield World]] was essentially a variation of this concept, albeit on a far smaller scale and not enveloped in Slipspace.

===Alderson Disks===
{{Main|Installation 00}}
[[Image:ARK.jpg|200px|thumb|[[Installation 00]]]]

The concept of an Alderson Disk includes a massive disk-shaped megastructure with a star residing in a hole in the center. 

The only known structure resembling an Alderson disk constructed by the [[Forerunners]] is [[Installation 00]].  With a diameter of between 90,000 and 100,000 kilometers<ref>[http://carnage.bungie.org/haloforum/halo.forum.pl?read=871617 Carnage Bungie Forum]</ref>, and a larger total surface area than a [[Halo Array|Halo Installation]], it incorporates many similar elements, including [[Earth]]-like gravity and atmosphere and a rich and diverse ecosystem. Located in the center of the Installation is a small planetoid, presumably used for raw materials, and a star orbiting nearby despite its location: 2<sup>18</sup>, or 262,144 light years outside of the [[Milky Way Galaxy]], where stars cannot naturally form. It's possible that this is an artificial sun created by the Forerunners.<ref>'''[[Halo 3]]''', [[The Ark (Level)]]</ref>

Rather than being a superweapon, like the [[Halo Array|Halos]], the [[Installation 00|Ark]] functions as both a control center for the entire array and as a construction facility for Halos, using the planetoid to provide metals, gases, elements and other resources needed for reconstruction. After the construction is complete, the [[Halo Array|Halo]] is transported to the site of its predecessor via a Slipspace portal.

Altough Installation 00 resembles an Alderson Disk, it has several differences to the original concept: It doesn't have a star in the center, it is far smaller than an actual Alderson Disk, and it has curved arms instead of being a flat disk. However, because of the close outward resemblance, it could be considered an Alderson Disk.

===Stars===
[[Image:Artificial sun.jpg|thumb|right|150px|The Ark's Artificial Sun]]
The Forerunners had the ability to either create artificial stars, or move existing stars across distances of thousands of lightyears, either of which would be a tremendous technological feat. Additionally, they seem to be able to extrude whole stars (and probably the surrounding system as well) into Slipspace.  One star was used in the construction of the [[Shield World]], [[Onyx]], while an artificial star, created just for it, orbited [[Installation 00]]. The [[Shield World (Halo Wars)|Flood-Controlled Shield World]] also had a miniaturized artificial star in its center.
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==Covenant==
[[Image:High charity and Alpha Halo.jpg|thumb|High Charity, next to the ruins of [[Alpha Halo]]]]
Though on a far smaller scale, the Covenant have been known to build structures that almost rival those built by the Forerunners that they so revere.

===High Charity===
{{Main|High Charity}}
High Charity was the Covenant capital city prior to 2552. Presumed to be built around a chunk of rock taken from the [[San 'Shyuum]]'s home planet, it was not only an artificial planet, but capable of traveling through slipspace, powered by a surviving [[Forerunner Dreadnought]]. It was the largest known Covenant artificial planetoid, at 348 kilometers in diameter, as well as the home of the majority of the [[San 'Shyuum]] population, and was infested by the Flood, and eventually destroyed by Spartan-117.

===Unyielding Hierophant===
{{Main|Unyielding Hierophant}}
The Unyielding Hierophant was a space station in Tau Ceti, a former UNSC colonized star system. Approximately 10 kilometers long, with two bulbous sections joined by a docking ring at the middle, it was a significant Covenant military base in the region, capable of resupplying up to 500 warships and carried thousands of Covenant personnel internally, including Banshee and Wraith pilots. It too was destroyed by Spartan-117.

==Human==
===Rubble===
The asteroids that made up The Rubble were mined and constructed by a mix of Kig-Yar and Humans. The Humans that lived on The Rubble were either Insurrectionists, sympathizers or surviving colonists from the UNSC world Madrigal. The habitats were made up of many asteroids that were linked together with docking tubes. Each of these asteroids had its own means of propulsion, and they were kept together by the machinations and calculations of the A.I. Juliana. She had been operating far past her normal 7 year life span and was approaching rampancy, but she had to remain in operation because the tasks that she performed were too difficult for humans.

==Construction==
[[Image:1209484737 Halo002lowrb9.jpg|thumb|300px|Scaffolding islands of a Halo installation.]]

[[Image:1209584069 MountainsoftheArk.jpg|thumb|300px|A Mountain Range on the Ark in panorama.]]
{{Quote|A Halo’s construction is executed by armies of Sentinels: some are the size of cities. Viewing the picture of the reconstituted asteroid material, you can see the process of skinning the Halo.  There are four huge terraforming factories moving across the face of the Halo.  They hold in the atmosphere which would leak out across the face, eventually pouring through the super structure, tugged into place by centrifugal force.|[[The Art of Halo 3]]<ref>'''[[Art of Halo 3]]''', page 117</ref>}}
The exact methods used by the [[Forerunners]] to construct these artificial worlds is unknown. Presumably, large numbers of [[Constructors]] and [[Sentinels]] play a role in the construction process, laying down the initial structure. Over this is laid a vast network of scaffolding, over which the artificial environment is placed, including earth, rocks, and significant quantities of water.

[[The Ark]] plays a significant and noteworthy part in construction, and is the location where replacement Halo Installations are built and later transported, should one be destroyed by the [[Flood]] or opposing forces. Although the [[Ark]] constructs smaller installations, it is unknown how the [[Ark]] was initially built or if it is capable of repairing itself.

==Sources==
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[[Category:Astronomy]]
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