Most vessels have several areas in addition to personnel airlocks which must be capable of communion with the environment exterior to the ship. These areas typically are used for the storage of auxiliary craft or cargo.
Hangers are large compartments dedicated to the storage of vehicles. Hangers on unstreamlined craft, which seldom land on planetary surfaces, typically have powered door mechanisms which allow carried vehicles to leave the hanger. Hangers designed for ships that land often will have ramps or other devices as well, to allow vehicles to exit the compartment and reach the planetary surface.
A vehicle bay is a hanger designed to fit a specific vehicle. Bays are significantly smaller than hangers and do not include access space. Some vehicle bays, especially those used for auxiliary vessels, do not have gravity or environmental systems. Like hangers a vehicle bay may include a ramp or other device to allow its vehicle to exit.
Cargo holds are usually designed with full gravity and environmental control. A cargo hold can be anything from an empty space where items are set on shelves to warehouse sized spaces where transport containers are stacked. Almost all cargo spaces on commercial vessels will have a system installed to allow cargo to be tied down to prevent shifting in transit. Large ships may have installed handling equipment to facilitate the movement of the cargo. Ships optimized for carrying bulk cargo will almost always have such a system.
Doors and Hatches
There are a variety of door and hatch types that are used in the design of hangers, bays and cargo holds. Doors are multipart constructs which use technology similar to iris valves. Such doors are made of many separate panels and roll or slide open to allow the compartment to be opened to the exterior environment. Hatches are designed in one piece and usually swing on motorized pivots. Hatches are often designed to move down so as to double as ramps, or move up as as to provide protection from weather when the ship is on the ground. A split hatch can do both.
All doors and hatched are vacuum tight and provide a barrier to the hostile environment outside the vessel. They are always motorized and require that ship's power be online or that an emergency power system be installed. Personnel doors are sometimes installed as well. These are sometimes iris valves, but are most often hatches to give access even when power is offline.
Bay and hanger doors and hatches are typically controlled from aboard the vessel or are designed to respond to a remote encrypted radio signal. Since most are more complicated to operated than a personnel lock they do not have emergency manual override systems.
Cargo Bay Doors
While some cargo holds will have their own cargo transport airlocks, many are designed to never be exposed to space or external environment except in a hanger or other area where there is a standard atmosphere. There is a cargo door version of the passage tube, which allows cargo to be transferred in a shirt sleeve environment. A cargo bay containing nothing but sealed containers could be evacuated to allow direct transfer of cargo to a vacuum world, but this is unusual, and would require careful preparation, as not all ship's systems are resistant to vacuum damage.
A standard cargo bay door will typically have several control stations. One will be inside in the cargo bay, one in a central control station dedicated to cargo handling, and one at a remote station elsewhere on the vessel, typically on the bridge.
All stations will tyically require a special access code to operated the doors. Some door controls will also have an interlock system to prevent the door from being opened to vacuum or a hostile atmosphere. An override system usually will require another set of access codes to allow the doors to be opened in an emergency, even if external environmental conditions are not suitable.
Vehicle Bays & Hanger Doors
Bays and hangers are almost always designed to act as their own airlock and possess the same systems as do personnel airlocks: A gas control system, an environmental monitoring system, and a control station. Bays and hangers will sometimes have an internal airlock to allow entry to the bay even when it has been evacuated or full of an exotic or toxic atmosphere.
A system sometimes seen on large vessels is the elevator platform. To recover a vehicle the elevator is raised flush with the outer hull. The vehicle lands on the elevator and is lowered into its vehicle bay. A door then slides into place isolating the bay from the outside. This system can also be used with a hanger, in which case when lowered to the hanger deck level, the vehicle usually clears the elevator so that it can be used by other vehicles.
Many cargo bays, hangers and vehicle bays will have a number of remote indicators, to allow bridge or security personnel to monitor the status of the doors and hatches, as well as the internal environment. Like other ship compartments, these spaces will often have fire protection and security devices that are centrally monitored from the bridge or another security station. These sometimes include include visual and audio pickup devices.
The simplest, and most common piece of handling equipment is the overhead crane. Many cargo holds, even on small trader vessels, are equipped with an overhead crane to allow large, heavy objects to be moved within the hold. Overhead cranes can be of simple or very complex design. The simplest consist of the static hoist. A more complicated design is the monorail which consists of a trolley that runs on a single track. A working line or rig is lowered from the trolley, and used to lift the load. A more common design, even on small vessels, is the bridge crane.
- Fixed Hoist. Fixed Hoists can be located anywhere in the hanger or cargo bay. A Fixed Hoist is used for a static lifting situation. Such a hoist can be located over any deck iris valve or hatch, including those in an airlock. A motor lifts the load.
- Monorails. Monorails can be located anywhere in the ship. Monorails can be run throughout the cargo bay and into adjoining spaces or, if run on an overhanging hatch or suspended rail, even outside.
- Single Girder Overhead. Single girder overhead cranes can typically carry a heavier load than a simple monorail. The girder is typically attached to the ship's frame and the trolley can only move up and down the girder.
- Single Girder Underslung. Single girder underslung cranes have an even greater load capacity. The girder is installed with cross members at each end to allow limited movement in all four directions.
- Double Girder Overhead or Bridge Overhead. Double girder overhead crane for maximum loads. The bridge and cross griders allow a single crane to cover the entire hold or hanger.
Cranes can be outfitted with standard hooks or specialized rigs. Ships which specialize in containerized cargo have cranes which can lift standard containers without time consuming rigging. This is done by special carriers, which attach to the hardpoints of Series 4 (Interstellar) Standardized Cargo Containers.
Ships which have large hangers containing modular cutter modules often have installed systems to handle modules. These can consists of special crane carriers which attach to the module couplings or independent vehicles which can move modules within the hanger.
Bulk Cargo Systems
Bulk Cargo can be divided into several categories. Liquids and gases are stored in tanks and moved with pumps through pipes. Ships which carry such cargos are equipped with exterior pumping stations. Solid bulk cargos, like seeds, sawdust, and ores, are stored in bunkers and can be moved with augers or sometimes blown through pipes. Tanks and bunkers are not usually grav compensated. They are usually pressurize with inert gases or not at all, depending on the cargo. Pumping stations are usually centrally controlled. Some ships have auxiliary pumping stations outside to facilitate the off loading of bulk cargo. Freighters which carry bulk cargo are almost always specialized for the task, be they gas tankers or ore carriers.
Several methods of contrAgrav or gravity assisted cargo movement systems are in use in known space.
The most dangerous method of gravity assisted cargo handling is to simply reduce the environmental gravity of the cargo bay using the installed grav plating. This is generally dangerous because even though a 25 ston cargo container might be made to weigh only 50 lbs, it still will have the inertia of a 25 ston load. Attempting to move such a load by hand is almost certain to result in an accident.
The common method used to move heavy loads using grav technology is the contragrav module, also called the "sky hook." Each module, which uses the same combination of contragrav device and reactionless thrusters as the grav belt, are remotely controlled and can lift up to 1 ton. Multiple units can be used together to lift larger loads.
Larger ships will have grav cargo robots, grav trucks and other vehicles to facilitate the movement of cargo.