A class of starship launched in the 2360s by the United Federation of Planets
The outermost hull layer is composed of a 1.6 centimetre sheet of AGP ablative ceramic fabric, chemically bonded onto a substrate of tritanium foil, 0.15 centimetres thick. This material is formed into segments of approximately 3.7 metres squared, and is attached to the radiation attenuation layer by a series of duranium fasteners. This allows individual segments to be replaced as necessary. Micrometeoroid erosion is kept to a minimum by the deflector shield system, but is still sufficient to warrant replacement of 30% of leading-edge segments on the average of every 7.2 Standard years. Individual outer hull segments are machined to a tolerance of +0.5 millimetres to allow for minimum drag through the interstellar medium. Joints between segments are manufactured to a tolerance of ± 0.25 millimetres. Also incorporated into the outermost hull layer is a series of superconducting molybdenum-jacketed waveguide conduits. These serve to distribute and disperse the energy of the tactical deflector system. Selected segments of this network also serve as radiators for starship thermal management.
On a Galaxy-class starship, the structural integrity field is produced by five generators working in tandem. Two of these are located on deck 32 in the engineering hull; the remaining three are on deck 11 in the saucer section. There are also two backup generators, one in each hull, which can provide 55 percent of the maximum rated power for as long as 12 hours. Each of the seven is made up of twenty 12-megawatt graviton polarity generators, which feed two subspace field-distortion amplifiers, the latter rated at 250 millicochranes. The generators produce an enormous amount of heat, but this is dissipated by a pair of continuous-duty liquid helium loops, which can disperse 300,000 megajoules an hour. The generators are designed to go 1,500 hours between routine services. They normally operate on a cycle of 36 hours on followed by 24 hours off. When the generators are down they are degaussed and undergo routine maintenance. At least one generator in each hull is active at all times. If the ship is required to perform unusually stressful activities, more generators can be brought online.
During Red and Yellow Alerts, all the generators are on standby, ready for immediate activation. This is important because the SIF is an essential part of the ship's defences, and can compensate for most hull breaches. The damaged area is instantly sealed with a forcefield, equalizing the pressure of the entire vessel. In emergencies, additional power can be diverted to the SIF from other sources, such as the warp engines. If necessary, other systems can draw on the power of the SIF generators, but this is rarely done, because if the SIF fails it almost invariably leads to the disintegration of the ship.
Gravity generators are located throughout the habitable volume of the spacecraft. Because of this, inertial potential can vary from one location within the ship to another, especially during severe turning manoeuvres. In order to allow translation of excess inertial potential from one part of the ship to another, the gravity generators are connected together by a network of small waveguide conduits that allow field bleed for gravitational stability.
During normal refueling, antimatter is passed through the loading port. This circular device, located on Deck 42, is 1.75 metres wide, and equipped with twelve physical hard-dock latches and magnetic irises. Surrounding the antimatter loading port are thirty storage pods, each measuring 4 by 8 meters and constructed of polyduranium, with an inner magnetic field layer of ferric quonium. Each pod contains a maximum volume of 100 metres cubed of antimatter, giving a 30-pod total supply of 3000 metres cubed. This is typically enough for a normal three-year mission period. Each pod is connected by shielded conduits to a series of distribution manifolds, flow controllers, and electro plasma system power feed inputs. In rapid refueling conditions - reserved for emergencies - the entire antimatter storage pod assembly can be drawn down on jackscrews and replaced in less than an hour. In the event of loss of magnetic containment, this same assembly can be ejected by micro-fusion initiators at a velocity of 40 metres a second. This pushes it clear of the ship before the fields decay, and so before the antimatter has a chance to react with the pod walls. While small groups of pods can be replaced under normal conditions, the magnetic pump transfer method is preferred. Antimatter, even contained within storage pods, cannot be moved by transporter without extensive modifications to the pattern buffer, transfer conduits, and transporter emitters, for safety reasons. Specific exceptions apply for small quantities of antimatter stored in approved magnetic containment devices, normally used for specialized engineering and scientific applications. Refueling while in interstellar space is possible through the use of Starfleet tanker craft.
Galaxy-class ships have two independent autodestruct systems. These ensure the vessel can be completely destroyed, even if the saucer has been separated. Autonomous sub-processor nodes located around the vessel ensure that the autodestruct sequence can still be activated and carried out when the main computer has been disabled. The primary autodestruct system is designed to vaporize the ship with an enormous matter-antimatter explosion, which is created by initiating a controlled release of the warp engine reactant materials. This produces a massive mechanical and thermal shock that destroys the ship rapidly and completely.
When the autodestruct sequence enters the final phase, the computer generates a deliberate cascade failure in which all warp engine safety interlocks are compromised. All the antimatter in the storage pods on deck 42, and the matter in the primary deuterium tanks, is released simultaneously. This generates an explosion that is roughly equivalent to the explosive force of a thousand photon torpedoes. The amount of energy released is in the region of 1,015 megajoules. This is significantly greater than the amount of energy normally released as the result of antimatter containment loss, and it ensures that the ship and any valuable technology are completely eliminated. If the computer cannot send the necessary instructions to the engineering system, the ship is equipped with a backup autodestruct system. This secondary system is somewhat more primitive. Ordnance packages are fitted to various locations, including the antimatter storage pods. If necessary, they can be detonated, releasing the antimatter. At the same time, the secondary system can deliberately overload the fusion reaction chamber. This will generate an explosion equivalent to that of 500 photon torpedoes, approximately 109 megajoules. Although this is only half as powerful as the primary autodestruct system, it is more than enough to vaporize the ship. Because the primary autodestruct sequence uses the antimatter storage tanks in the engineering hull, it cannot be used to destroy the saucer section when the ship is in separated flight mode. However, the secondary system is sufficient to destroy the saucer on its own, and this becomes the saucer's primary autodestruct system when the two parts of the ship are not joined.
In combat it is normally only deemed necessary to destroy the ship when all propulsion and weapons systems have been disabled, and there is little or no prospect of assistance from other Federation vessels. Computer models have also shown that it may be necessary to destroy the ship if navigational control has been lost and it is on a collision course with a populated area. Ultimately, the decision to activate the autodestruct systems rests with the ship's commander. The autodestruct sequence requires authorization by at least two command-level officers. If the captain and first-officer are dead or disabled, the computer will automatically look for the next highest ranked officer; however, it will not accept an autodestruct order from an officer below the position of operations manager. To activate the sequence, the two most senior command officers instruct the computer to begin the autodestruct procedure, and then confirm their identities with a dermal imprint or by giving their personal access codes. Once the computer has verified their authority, the senior officers give the command to set the autodestruct sequence. The computer asks the other officer if he or she agrees, and, if they do, the senior officer sets the duration of the countdown until the system is activated. The computer informs the crew of the time remaining until the ship is destroyed by making repeated audio announcements and producing graphics on displays throughout the vessel. The two initiators of the autodestruct procedure can order a silent countdown if so desired. The autodestruct sequence can be aborted at any time before the countdown reaches zero and the ship is actually destroyed. The abort order does require both officers who initiated the autodestruct to be in agreement.