The Grav Deck, short for Gravity Deck is the one of two ways to create "artificial" gravity for spacecraft in the BattleTech universe.
With the BattleTech universe lacking any advanced "science-fiction" means of creating gravity aboard spacecraft, the two options are the real world options of reaction gravity and centrifugal gravity.
Reaction gravity is the primary form of gravity generation used by DropShips, with gravity emulated in the opposite direction to the direction of thrust. Save for the flip-over at the half-way point, generally a DropShip in flight will always be under thrust and thus generate some degree of gravity for the health of the crew.
For larger vessels such as JumpShips and WarShips which have to spend time effectively motionless so as to charge their Jump Drives, and relatively stationary objects such as Space Stations which lack engines large enough to generate reaction gravity, a Grav Deck is carried. A ring-shaped section that produces gravity by rotating around the axis of the ship or station and so acts like an enormous centrifuge, as the grav deck spins, the centrifugal force pushes objects outward from the deck's center and the deck's wall becomes the "floor".
In general, only the largest WarShips or Space Stations have single or even multiple grav decks of suitable size to allow limited crew or guest quarters, most JumpShips and smaller vessels generally devote their limited space to recreation and exercise areas for the crew and passengers, and for medical bays for patients with conditions worsened by prolonged exposure to zero-gravity. Even aboard larger vessels, the size of the crew will be many times the available space on the Grav Deck, so rosters are generally used to ensure access to the grav decks is evenly split, which can become a sore-point on prolonged voyages.
Grav decks are available in many sizes, but for convenience they are typically divided into one of three classes. Small grav decks are less than 100 meters in diameter and cost 5,000,000 C-bills. A medium grav deck's diameter is between 100 and 250 meters and cost twice as much as a small grav deck. A large grav deck is any grav deck with a diameter over 250 meters. These mammoth constructions cost 40,000,000 C-bills and are usually included only in the largest space stations.
- Strategic Operations, p. 159, "Advanced Aerospace Unit Costs Tables"
- Tactical Operations, pp. 314-315, "Grav Deck"