Inertial Damping System
This information can be found in Section 2.5 of the Star Trek: The Next Generation Technical Manual.
Operating in parallel with the structural integrity field (SIF) system is the inertial damping field system (IDF). This system generates a controlled series of variable-symmetry forcefields that serve to absorb the inertial forces of spaceflight which would otherwise cause fatal injury to the crew. The IDF is generated separately from the SIF, but is fed by a parallel series of waveguides that are then conducted through synthetic gravity plates.
The IDF operates by maintaining a low-level forcefield throughout the habitable volume of the spacecraft. This field averages 75 millicochranes with field differential limited to 5.26 nanocochranes/meter, per SFRA-standard 352.12 for crew exposure to subspace fields.
As acceleration effects are anticipated, this field is distorted along a vector diametrically opposed to the velocity change. The IDF thereby absorbs the inertial potential, which would otherwise have acted upon the crew.
There is a characteristic lag time for the shifting of IDF direction and intensity. This lag varies with the net acceleration involved, but averages 295 milliseconds for normal impulse maneuvers. Because IDF control is generally derived from Flight Controller data, normal course corrections can be anticipated so there is rarely any noticeable acceleration to the crew. Exceptions to this sometimes occur when power for IDF operations is restricted or when sudden maneuvers or other externally caused accelerations occur more rapidly than the system can respond.
Flux generation for the IDF is provided by field generators. The Galaxy-class starship has four field generators on Deck 11 in the Primary Hull, and two generators on Deck 33 in the Engineering Hull. Each generator consists of a cluster of twelve 500 kW graviton polarity sources feeding a pair of 150 millicochrane subspace field distortion amplifiers. Heat dissipation on each unit is provided by a pair of 100,000 megaJoules/hour (MJ/hr) continuous-duty liquid helium coolant loops. (Three backup generators are located on each Hull of the Galaxy-class, providing up to twelve hours of service at 65% of maximum rated power). Normal duty cycle on generators is fourty-eight hours online, with nominal twelve hours degauss and scheduled maintenance time. Graviton polarity sources are rated for 2,500 operating hours between routine servicing of supercondictive elements.
Cruise Mode operating rules require at least two field generators to be active at all times in each hull, although the Flight Control Officer may call for activation of additional units 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.