 IRISFitting of its name, an iris covers Earth's Stargate during its operation at the S.G.C. Originally constructed of pure titanium, the iris is composed of more than 20 interlocking plates that hide away within the housing of the Stargate's inner track, capable of swiftly ejecting, sliding into place at a single command from the base's computer system. The purpose of the iris is to keep unwanted intruders, be it a person or object, from entering the S.G.C. Once deployed, the iris rests a few micrometers in front of the event horizon, preventing matter from reintegrating as it arrives through the wormhole. Objects are destroyed, and living beings are killed instantly upon "impacting" on the iris. Known substances capable of passing through the gate despite the iris include radio waves and accelerated particle beams (capable of moving at near-light velocities). The iris has only been breached by Tollan technology, capable of passing through any solid matter. During an encounter with the gravity well of a black hole, the original iris was torn from its housing and lost through the Stargate. After the accident, a new trinium-titanium composite replacement was installed. It is capable of withstanding temperatures in excess of 130 degrees Fahrenheit. When an incoming wormhole arrives at the S.G.C., the iris is immediately deployed, and can only been opened when an IDC signal ("iris deactivation code") arrives via radio transmission from an SG team returning to Earth. (Some allies, including Bra'tac and the Tok'ra, have also been given IDC transmitters.) Sometimes automatically, but usually manually, the iris is opened -- retracting to allow admittance to Earth. The base computer is equipped with a palm scanner for opening the iris, so that the command may only be executed by authorized personnel. |