Star Trek Starship Operations Systems

Operations Systems
The largest category of systems on a starship fall under the heading of operations systems. They include sensors, computers, and many other systems related to the daily command and operation of the ship.

Sensor Systems
Tractor Beams
Cloaking Devices

Operating Modes
Based on the conditions and circumstances existing at any given moment, a starship will assume one of several operating modes which dictate which systems become (or remain) active, the preparations made by the ship's personnel, and so forth. The following brief descriptions indicate what each mode involves.
Cruise Mode
The standard operating mode during non-crisis situations. Level 4 diagnostics run on all primary and tactical systems at each shift change. One major system operational; at least one maintained on standby. Long-range sensors and main deflector in use if ship is moving. A minimum of 40% of phaser bank elements are one torpedo launcher on cold standby status (available for full activation in two minutes). One shuttlebay maintained at five minutes launcher readiness.
Yellow Alert
This mode indicates that the ship is prepared for a potential crisis situation. Level 4 diagnostics run on all primary and tactical systems, power and propulsion systems brought to full operating condition. At least one auxiliary power source brought to hot standby. Phasers, torpedo launchers, and battle bridge (if any) brought to partial standby.
Red Alert
This mode indicates an actual state of emergency; it's established in, for example, any combat situation. Level 4 diagnostics run on all primary and tactical systems every five minutes. All sensors brought to fully operational status. Shields are brought to tactical configuration and weapons and battle bridge to full standby. All shuttlebays are brought to 30 seconds' launch readiness. Isolation doors and force fields are automatically activated as a proactive measure to contain any potential damage.
Blue Alert
Ships with planetfall capability must declare a Blue Alert before starting the descent. This alerts all crewmembers to assume their Blue condition stations and prepare for the landing. Level 4 diagnostics run on all primary and tactical systems. Power and propulsion systems brought to full operating condition. At least one auxiliary power source brought to hot standby.
Reduced Power
This mode is designed for maximum power conservation in the event of fuel shortages, failure in the power generation systems, or tactical situations which require that most power be diverted to tactical systems. The crew performs a cold shutdown of the warp engine unless the ship's traveling at warp speeds or it's the only remaining source of power (or soon likely to be). Hourly energy budgets and consumption reports are made to the appropriate persons. Weapon systems are brought to cold shutdown unless deemed necessary. Some systems (IDF, SIF, main deflector, environmental systems) are operated at minimum levels; others (transporters, replicators) may not be used without special permission.
Silent Running
Invoked for "stealth" missions, Silent Running mode is designed to minimize a ship's profile to enemy sensors. All active sweeps and communications outside the ship are forbidden. All non-essential systems, such as lighting, replicators, and holodecks, run at half power or may be used only with permission (as appropriate). Any shipboard activity which might alert an enemy to the ship's presence is curtailed.
Separated Flight
On ships which have saucer separation or multivector attack capability, this mode applies when the vessel is separated. For the most part it resembles Cruise Mode, unless Red Alert conditions apply. The IDF and SIF of the two "parts" of the vessel are usually set to high output.
External Support
This mode applies when a ship is docked at a starbase or similar support facility. It signifies a state of reduced activity, where many systems are completely powered down and many personnel are on shore leave.



Source
Spacedock - Starship and Construction Manual (pages 42-65)