Grey mode is an alert status used aboard Federation starships. When in grey mode, the starship runs on reserve power, cutting power to non-essential decks and ship systems. It allows for maximum power conservation, budgeting a starship's energy resources during a time of crisis, while still maintaining an operating status. Grey mode can be invoked during a massive fuel shortage, or when the tactical situation requires a reduction in discretionary energy usage.
A number of ship systems are either reduced to a lower operating status, or shutdown completely, including:
- the warp core, which is brought to a cold-shutdown
- inertial damping and structural integrity systems, which are operated at minimum output
- tactical and lateral sensors, which are only used for primary ship functions
- deflector systems, which are either shutdown, or reduced to minimum levels for non-flight operation
- weapons systems, phasers and photon torpedo launchers, are brought off-line
- shuttlebay operations are suspended, as the shuttlecraft can provide energy support if necessary
- life support systems are brought to minimum levels, and shutdown on non-essential decks
- transporter usage is terminated
- turbolift usage may be suspended at the commanding officer's discretion
- food replicator are not used, and emergency rations are distributed
- holodeck or holosuite usage is terminated
The recycling of non-essential items, which can be broken down into raw matter patterns by the replicator, is commonly practiced. Preserving the replicator for usage only during critical situations (such as replicating repair tools, medicine, etc.) can help extend the energy resources of the ship.
Starships are often forced into this condition, due to tactical situations or spatial phenomena, which can also coincide with a red alert. During the year-long temporal conflict with the Krenim Imperium, the USS Voyager entered a reduced power mode. (VOY: "Year of Hell", "Year of Hell, Part II")
Grey mode was used aboard the USS Voyager in 2374 when its supply of deuterium was almost depleted, allowing the ship to conserve its reserves for as long as possible. (VOY: "Demon")
The following year, Voyager entered grey mode in an attempt to sneak past a Devore sensor array near the Tehara system. (VOY: "Counterpoint")