Structural Integrity Field System
This information can be found in Section 2.4 of the Star Trek: The Next Generation Technical Manual.
The mechanical integrity of the physical spaceframe of a starship is augmented by the structural integrity field (SIF) system. This system provides a network of forcefield segments that compensate for propulsive and other structural load factors that otherwise exceed the design limits of the spaceframe. The SIF applies forcefield energy directly to field conductive elements within the spaceframe and increases the load-bearing capacity of the structure.
Field generation for the SIF is provided by a number of field generators. A Galaxy-class vessel has five generators, three on Deck 11 of the Primary Hull, and two on Deck 32 in the Secondary Hull. Each generator consists of a cluster of twenty 12 MW graviton polarity sources feeding a pair of 250 millicochrane subspace field distortion amplifiers. Heat dissipation on each unit is provided by a pair of 300,000 megajoules per hour (MJ/hr) continuous-duty liquid helium coolant loops. (Two backup generators are located on each Hull of the Galaxy-class, providing up to twelve hours of service at 55% of maximum rated power). Normal duty cycle on generators is thirty-six hours online, with nominal twenty-four hours degauss and scheduled maintenance time. Graviton polarity sources are rated for 1,500 operating hours between routine servicing of supercondictive elements.
The output of each SIF generator is directed by means of a network of molybdenum-jacketed triphase waveguides which distributes the field energy throughout the spaceframe. SIF conductivity elements are incorporated into all major structural members. When energized by the SIF, the load-bearing capacity of these structural elements is increased by up to 125,000%. Secondary feeds also provide for reinforcement of the vehicle's external shell.
Cruise Mode operating rules require at least one field generator to be active at all times in each hull, although the Flight Control Officer may call for activation of a second generator when extreme maneuvers are anticipated. During Alert modes, all operational units are brought to hot standby for immediate activation. Reduced Power Mode rules permit a single field generator to feed the entire spaceframe using the field conduit umbilical connect between the primary and engineering sections.