Ancient shields refer to the shielding technology developed and utilized by the Ancients as a defensive measure to protect their spaceships and cities.
The Ancients are one of the earliest races in the known universe to have developed shielding technology, having utilized it on spacecraft over 50 million years ago. As such, they are known to have developed various shield systems as they advanced technologically over the millennia. At the height of their civilization, the Ancients developed shields that, even to the current day, are among the most advanced in the known universe, being on par with those developed by the Ori and Asgard.
The oldest shield system known to have been developed by the Ancients is the system aboard the spacecraft Destiny. Despite it's age, it is still immensely powerful; It is one on the only known shield systems able to successfully protect a craft against the tremendous heat and turbulence experienced while flying through even an o-class star 24 times bigger than the Sun. (SGU: "Earth", "Blockade")
The shield itself is yellow in color. Instead of forming a "bubble" around the ship, as most shield systems do, Destiny's shield is contoured to the ship's hull. In addition to enveloping the entire ship, it may also be localized to specific hull-breaches as to retain the atmosphere in sections of the ship exposed to space. Destiny's shields constantly change frequencies in the hope of matching enemy fire; the closer the frequency, the less damage Destiny takes. While this makes the shields less effective against specific types of energy weapons, it provides better general protection overall. (SGU: "Gauntlet")
Shield strength is dependent on the ship's overall power levels and the number of localized shield emitters currently active. As such, if power levels are low, or the ship's weapons systems are simultaneously activated, the shield's effectiveness may be greatly decreased. Though weakened by the time and not enought power, the shield is capable of withstanding the bombardment of 9 Nakai Motherships for more than 45 minutes. (SGU: "Light", "Earth", "Space", "Incursion, Part 2")
The Atlantis Expedition developed a shield for the Gateships modifing the cloaking generator. These shield are capable of withstanding at least one drone weapon of Atlantis itself powered by 3 ZPM´S without failling and the presure of the ocean below 300 meters for about 30 minutes (despite Atlantis shield are capable of withstanding the presure of more depth for about 10000 years powered by 3 ZPM´S, this is an impressive feat, due to the gateship isn´ t a ship constructed for using shield and its energy source is vastly inferior compared to a single ZPM).
Asuran Cruiser Edit
The cruisers are ships developed by the ancients and used by themselves and by the Asurans too.
Little is know about these shields, but are capable of resisting at least a dozen Naquadah-Enhanced missiles from the Apollo.
Like those of the Destiny, the shield of Aurora-class ship ships contour the hull. However, they are dark brown in color. These shields allow Aurora-class battleships to withstand intense weapon fire with minimal bleed-through. They have also been shown able to withstand the intense heat and pressure of an erupting supervolcano. (SGA: "Inferno").
The older versions of these ships used by the Asurans, are capable of withstanding sustanined fire from Wraith Hive Ships and traveler Generational Ships, and 3-4 shots of the Asgard Plasma Beam Weapons. However, the plasma beam weapons are capable of destroying them relatively easily and single ships were unable to adapt to them to the point that the entire Replicator fleet retreated rather than face continuing attacks from the Daedalus and the Apollo. (SGA: "Be All My Sins Remember'd").
The newest version of the ship, the Travelers Aurora-class has been seen along the new BC-304 Daedalus and Apollo beings the ones that survive with not much damage, and, possibly, the strenght of these shield are equal to the BC-304 or superior (SGA: "Be All My Sins Remember'd").
- Main article: Atlantis' shield
The shield of Atlantis is a dome-shaped shield that serves as the main defense for the Ancient City-ship, and is largely considered to be the most powerful shield ever created. The shield requires massive amounts of energy to be activated, which a Zero Point Module usually provides. (SGA: "Rising")
The shield of Atlantis is unique in that almost nothing can penetrate the shield as long as there is enough power to sustain it (unlike starships, which deplete under external forces and slowly lose integrity no matter how much power is available). If there is no pressure on the shield, it can remain active almost indefinitely. However, even mid-level energy weapons (like those on Wraith ships) will rather quickly deplete the power to the city shield under sustained bombardment, when powered with only one ZPM. (SGA: "The Siege, Part 3")
While the shield is typically used to protect only the city and the immediately surrounding area, it can be expanded to cover a significant portion of an average-sized planet or even shrunken to encompass individual objects inside the city itself. (SGA: "Echoes")
In a space battle, the Atlantis shield was quickly depleted by the massively powerful super-hive and nearly collapsed before the super-hive was destroyed. This was while being powered by three fully-charged ZPMs. It also was barely able to hold long enough for planetary reentry and collapsed shortly afterwards. In contrast, while powered by one full ZPM and one slightly charged ZPM, the Atlantis shield was able to hold up well against an entire Wraith fleet of hive ships and cruisers with the shields only briefly dropping below 70% and quickly recharging above it. By the end of the battle, the shields were still holding at around 70%. (SGA: "Enemy at the Gate", "Inheritors")
- Main article: Stargate shield
The Ancients have been known to place shields on Stargates, designed to prevent unwanted travelers from exiting a Stargate, and was possibly first developed to protect Lantean-controlled planets from the Wraith. Nevertheless, the only Stargates known to be protected by a Lantean shield are the ones in Atlantis and in the orbital station of P7L-418.The Stargate shield of Atlantis is placed so close to the event horizon that it prevents the integration of even sub-atomic particles, a flaw in the metal Iris of Earth, thus preventing anything, even the Unstable vortex of an activating wormhole, from penetrating the shield; indeed, it is the primary method of defense from hostile, non space-faring populations who would take Atlantis for themselves. It is unknown if the Ancients also placed shields on the Stargates of other City-ships, but it seems likely. (SGA: "Rising", "Casualties of War")
Personal shield emitterEdit
The Ancients also created a Personal shield emitter that, once activated by someone with the Ancient Technology Activation gene, would generate an advanced dampening field that prevents penetration by objects such as bullets, as well as allowing the user to perfectly withstand a fall of almost any altitude, and even powerful explosions. The one weakness of the Personal shield emitter was that the user needed to breathe, so they were still susceptible to death via methods such as drowning or being buried alive. Also, the user needed to eat, which required a specific mental command to allow food through the shield. This is not obvious to first-time users and so many will have to deactivate the shield altogether. (SGA: "Hide and Seek", "Irresponsible")