Shield



Shields are devices which use energy that prevents matter from passing through them. Shields are used by many races, so they can vary.

Ancients
The Ancients possessed some of the most powerful shields ever created, capable of withstanding multiple hits from both projectile and energy weapons for a lengthy amount of time, and extreme natural phenomena. The most powerful shields ever built by the Ancients were the shields utilized by Ancient city-ships. Powered by ZPMs, they are capable of withstanding Wraith energy weapons for an indefinite amount of time, the weight of the ocean on Lantea for 10,000 years, and even coronal mass ejections. During a storm year, Rodney McKay and Radek Zelenka channeled the energy of the storm's lightning strikes to power the shield of Atlantis, although when the Wraith attacked they were unable to activate the shield until a ZPM arrived. The shield also plays a critical role whenever a city-ship takes off, flies through space, and lands on another planet, since it's the shield which prevents the air from leaving a city-ship and protects the occupants from the vacuum of space and the high temperatures caused by the friction of atmospheric entry, thus acting as an outer hull of sorts. Unlike the shield technology of other space-faring races, the effectiveness of the shield of a city-ship does not deplete under external forces, and will remain impenetrable, preventing any residual energy from passing through, as long as sufficient power exists to sustain it, which means that a city-ship will only suffer damage once the shield fails. The only downside to the shield of a city-ship is that the amount of power used up to sustain the shield is directly proportionate to the amount of stress the shield is under; if there is no pressure on the shield it remain activated for an indefinite amount of time amount of time.

Ancient outposts are known to possess shields; not much is known about them, but it can be assumed that they are almost as effective as those on city-ships. Unfortunately, they use up massive amounts of energy even when under little to no strain, and were never designed to remain active at full strength for extended periods of time.

Aurora-class warships possess shields not seen on any other ship, being contoured around the hull instead of forming a 'bubble' like other shields do. The shields on the Aurora-class are capable of resisting an incredible amount of heat and pressure, which means that they would have been more than capable of resisting the energy weapons of a single hive-ship and/or several Wraith cruisers at full strength.

The Ancients were also 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. The only known Stargate protected by a Lantean shield is the one in Atlantis. The gate 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 unfriendly, 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.

The Ancients also created a personal shield that, once activated by someone with the ATA 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 was that the user needed to breathe, so they were still susceptible to death via methods such as drowning or being buried alive.

Asgard
Asgard shields are as equally impressive as those of the Aurora-class, if not more so: being capable of resisting most hits from the weapons of an entire fleet of Ha'taks, as well as several consecutive hits from the central energy weapon of an Ori mothership, which had never been done before. However, while traveling through, and for a short period of time after exiting, hyperspace, Asgard shields are inactive, leaving ships vulnerable to attack; a weakness Samantha Carter would exploit to develop a viable tactic against a Replicator fleet converging on the Asgard homeworld. Another weakness of Asgard shielding technology is the fact that, not only is the effectiveness of their shields directly proportional to the amount of power regulated to them, they will also gradually weaken under sustained fire, allowing energy from attacks to bleed through, and so they need time to recharge afterwards. Asgard shields are also one of the few known types of shield technology capable of preventing direct penetration from drone weapons, although they are placed under heavy strain resisting them. In gratitude to the Tau'ri for their help against the Replicators, the Asgard gave them access to much of their technology, including their shields. The shields on Tau'ri vessels are not as powerful as those on Asgard ships, but that is only due to power requirements.

Goa'uld
The Goa'uld have shields which, while no doubt impressive, are nowhere near comparable to those of the Ancients, Asgard, and Ori. The shields carried on Ha'tak vessels are capable of resisting naquadah-enhanced nuclear warheads, and can remain in the chromosphere of a star for up to ten hours without the crew feeling any ill-effects. Shields are also used to cover the viewing post on the pel'tak, as the Goa'uld have no transparent substance capable of withstanding the hardships hyperspace. The effectiveness of Goa'uld shields is directly proportional to the amount of kinetic energy used, meaning it will stop energy weapons and high speed projectiles, but not slower moving projectiles like knives or arrows. It is likely that the early version of Prometheus uses reverse engineered Goa'uld shields. Even Goa'uld shields upgraded with ascended knowledge are ineffective against drone weapons.

Ori
Built with ascended knowledge, the Ori possess some of the most powerful shields ever encountered. They are capable of withstanding virtually anything, including a fleet of ha'taks, Asgard energy weapons, and even the Dakara superweapon, although Ancient drone weapons are known to be somewhat effective against them, as stated in an alternate reality. Bra'tac once tried to crash a fully functioning ha'tak into an Ori mothership at full speed, but it merely impacted within the shields. The only thing known to overwhelm the shields of an Ori mothership is the unstable vortex of an activating Supergate, and the most advanced Asgard energy weapons. The Ori also possesses shields which can collapse a planet into a micro-singularity. These shields expand after absorbing enough energy, which can be accelerated by weapons fire, although they require vast amounts of energy to be transferred into them, often through an active Stargate on the planet being collapsed, for the expansion to be noticable.

Tau'ri
The Tau'ri do not possess shields of their own design, instead utilizing shields of Asgard origin, which were donated to them in thanks for the help the Tau'ri had provided the Asgard in their conflict against the Replicators. Asgard shielding was first equipped to the Prometheus and eventually the Daedalus-class, allowing the Tau'ri to better confront the warships of the Goa'uld and, eventually, the Wraith. However, with the invasion of the Ori, the shields of the Prometheus, and even those on the more advanced 304-series of warships, proved virtually ineffective against the powerful weapons of Ori motherships, and so a far more advanced version of Asgard shielding was later installed on the Daedalus-class series of warships after the Asgard donated their entire knowledge bank to the Tau'ri. Due to the easy availability of Asgard shielding technology, the Tau'ri have not yet seen fit to conduct their own research into this area; however when Rodney McKay had his intelligence increased, he passed on an algorithm to Hermiod which increased the effectiveness of the shields equipped on Daedalus-class warships. Whether the algorithm was entirely McKay's design or if he was utilizing Ancient shield technology as a basis is still unknown, but is is likely that the majority of his knowledge on the subject came from the Atlantis database.

Tok'ra
The Tok'ra have one-way shields, usually arranged to completely enclose an area of space, that holds matter inside but allows external objects to enter. They have been used in an attempt to capture a Kull Warrior, and to keep Khalek imprisoned while allowing shots to be fired into the cell. What few ships the Tok'ra do possess almost always use Goa'uld shields for protection, which were typically obtained either through theft or were already integrated into the vessels when they were acquired.

Wraith
Hive-ships and Wraith cruisers do not have any energy shields per se, instead relying on an organic armored hull that has a limited form of regeneration to nullify damage. They do, however, utilize a program that prevents Asgard beaming technology from transporting objects inside a Wraith ship or close to it's exterior. The only form shield technology known to be utilized by the Wraith is in their Darts, which only use shields to serve as canopies for their cockpits. These shields are completely opaque, and send information to the pilot via written Wraith.