DropShip



In the BattleTech universe a DropShip is defined as a type of spaceship massing between 200 and 100,000 tons that is itself incapable of faster-than-light (FTL) travel. They essentially conduct all other aspects of space travel, including transit between planets and Jump Points and planetary landings. For FTL interstellar movement, they dock with JumpShips by means of a Docking collar.

DropShips are the workhorse of interplanetary space travel. It is the DropShips (and occasionally their smaller cousins, the Small Craft) that move cargo and passengers between planetary surfaces, orbits, space stations and jump points. While transport is their primary role, some have been built for special purposes and act as tugs, rescue ships, fighter carriers or even designated combat DropShips. Accordingly, a wide and diverse variety of DropShip types exist.

Even though many DropShips serve as military spaceships, naval terms such as "Corvette", "Destroyer", "Cruiser" etc. are never applied to them; these are exclusively used for true WarShips, i.e. the huge Combat JumpShips that outclass DropShips by an order of magnitude (typically massing several hundred thousands or even millions of tons).

History
The term "DropShip" was first used in the 22nd century to describe the cargo-carrying shuttles then in use to ferry cargo and passengers between the JumpShips of that era. It was not until the 25th century when "DropShip" became the official designation for a type of ship more sophisticated than the earlier shuttles. Instead of being carried within the hull of a JumpShip, these vessels were now attached on the outside and would "drop" away once it had arrived. By the 31st century, there were over 250 DropShip designs on record, though only approximately 100 were still in service, with twenty of those constituting the majority of DropShips in existence.

Construction
While DropShips come in a variety of shapes and sizes, the heart of every DropShip is its engineering section, which is comprised of two systems: a power plant and an engine. The fusion engine works by expelling plasma through shielded exhaust nozzles to create thrust. All DropShips have a main exhaust nozzle to propel the ship forward at a steady acceleration. The most advanced also have numerous plasma exhaust nozzles dotting their hulls to control steering, but such devices are fragile and expensive, leaving many DropShips equipped with hardier but less efficient chemical rockets to fulfill this role. The plasma exhaust is created as a by-product of nuclear fusion and requires a constant supply of fuel in the form of liquid H2, which is carried aboard in large storage tanks and fed to the drive by one of two systems. The one found on all DropShips is a heat-expansion system where the H2 is fed into a heated chamber; here the high temperature causes it to expand, with the resulting pressure forcing it into the engine core. Military DropShips will also have a series of high-speed pumps which can supply a constant stream of fuel for the engine, allowing for rapid changes in thrust. Unlike the engine core, the fusion plant which provides power for the DropShip is a closed system, reprocessing its own by-products and requiring little additional fuel. It can however tap into the same H2 storage tanks used by the engines when needed.

Each DropShip also has a control room, typically known as the bridge, which vary in size in accordance with each design. At minimum there will be stations for a pilot, navigator, communications officer, and weapons/computer officer. Larger vessels will have more than one station for each position or additional stations for specialists such as docking officer, security officer and ship captain. Their primary task is to monitor the main computer as it performs each task and provide manual backup in case the main computer fails; backup computers can allow each station to operate most of the ship's systems if necessary. This includes controlling life support and hatch access in other areas of the ship, a necessary function in the event of accidental hull breach or enemy borders. As such the bridge is designed to be isolated from the rest of the vessel, and both military and even some civilian DropShips will take the extra precaution of positioning marines to guard the bridge and other sensitive areas of the DropShip.

Most DropShips are equipped with weapons organized into weapon bays. Each bay will any combination of missile, energy or projectile weaponry, along with the necessary ammunition feeds, cooling systems, and radar/laser targeting systems. Aiming and firing each weapon bay is determined by the ship's fire-control computer, which is linked to the main computer and radar array, allowing the DropShip to engage targets hundreds of kilometers away while traveling at thousands of kilometers per hour. In the event the main fire-control computer shuts down, each weapon bay is on a local circuit control with an adjacent gunnery station where human gunners can take control.

The primary function for nearly all DropShips is to carry cargo of one sort or other. These Cargo Bays can occupy up to three-fourths of a DropShip's interior, and a DropShip may contain multiple different types of bays depending on its mission.

DropShip Category
DropShips are based around two basic hullforms, aerodyne and spheroid. Depending on their intended role, DropShips can be constructed following either of these two alternative approaches.

Although all DropShips are either of the spheroid or the aerodyne subtype, there is arguably a third one: ships which are limited to operating in deep space for one reason or another and would be destroyed when attempting to enter an atmosphere or land on a planet, rendering the differences between aerodyne and spheroid designs irrelevant to them. Examples include the super-large Behemoth class cargo hauler, which is a spheroid design but has insufficient acceleration for planetary operations and is too large and fragile to operate in gravity, and the nominally aerodyne Achilles and Vengeance class military DropShips which were never designed for atmospheric operations.

Aerodyne DropShips
Aerodyne DropShips are shaped roughly similar to conventional aircraft, using their aerodynamic hull shape to generate lift within an atmosphere. This makes these DropShips ideally suited for atmospheric operations, at the expense of being more expensive and harder to produce than sphereoid ships and with more restrictive size requirements. Many aerodynes also require runways to land and take off, limiting where they can operate. To facilitate atmospheric and deep space travel, most aerodynes are equipped with two sets of exhaust nozzles, one on the bottom and one on the rear. Aerodynes will use their bottom thrusters and transit drive during space operations, then switch over to after thrusters and maneuver drive when in an atmosphere. While taking up additional space, this alleviates the issue of internal orientation by allowing the vessel's nose and rear to remain "forward" and "aft" at all times.

Spheroid DropShips
Spheroid DropShips are so named for their rounded hulls, making them easier and cheaper to construct. Their simple design also makes them more sturdier and allows them to be built much larger than aerodyne DropShips, with the largest spheroid outmassing the largest aerodyne many times over. Spheroid DropShips have a single engine drive positioned on the ship's bottom which is used to vertically descend onto a planetary surface and take off in the same way. This allows spheroid DropShips to operate independent from runways or even spaceports, making them ideal for exploring unknown planets and giving them a tactical advantage in military operations. However, their simple and versatile landing and take-off pattern requires more fuel and can cause significant damage to the ground. They also cannot travel through the atmosphere as quickly as aerodyne vessels and their method of flight is more unstable, making them less practical for atmospheric combat. A complex system of thrusters positioned around the hull and controlled by the main computer helps make atmospheric flight and landing possible, but if these systems are damaged a spheriod DropShip can easily lose control and crash.

Classification of DropShips
In addition to their type, the majority of DropShips can be classified into six main classifications based around the mission profiles for which they were originally designed: assault ships, BattleMech carriers, cargo carriers, fighter carriers, troop carriers, and passenger liners.


 * Assault - This primary military DropShip is designed for maximum firepower. Typically used for anti-aerospace fighter and anti-DropShip operations, they can be used ground assault purposes but this is rare. Some models of assault ships which carry anti-WarShip weaponry are referred to as Pocket WarShips. This type of DropShip is also known to carry limited quantities of BattleMechs, Battle Armor, Marines, and aerospace fighters; Usually just enough to provide "point-blank" defense.
 * Pocket WarShip - A military DropShip type based on the Assault DropShips. These ships are designed to carry Capital Missiles and sometimes Sub-Capital Weaponry. Most are typically heavily armed with standard BattleMech scale weaponry. Early versions of this ship type were known as Q-Ships. Following the Jihad, with so many nations' shipyards damaged or destroyed, many factions turned to these as the backbone of their navies.
 * Fighter Carrier or Aerospace Carrier - Designed for carrying/supporting aerospace fighter craft operations. Though other DropShips are referred to as 'Mech Carrier, Troop Carriers, etc., a ship described as a "carrier" is understood to be a fighter carrier. These ships typically have CV (for Carrier Vessel) appended to their name, as in Leopard CV.
 * Cargo Ship - Typically civilian model of ship, used for hauling bulk cargo. Some ships are fitted to transport liquids and are usually referred to as Liquid Carriers.
 * 'Mech Carriers - Military type of DropShip, principally designed to carry BattleMechs into combat. They are generally modestly armed.
 * Troop Transport - Typical infantry carrying DropShip, which may have capacities of moving various size vehicles. They are normally modestly armed craft.
 * Q-Ship - Military conversion of a civilian vessel, typically cargo ships. First introduced by the Star League Defense Forces prior to the Star League Civil War.
 * Passenger Liner - Civilian DropShip design for passenger service. Normally, these ships are lightly or never armed. Rarely these ships are used as Troop Transport for infantry.

DropShip Operations
Once a DropShip has arrived at a system's jump point and detached from its JumpShip, it can begin the long journey to its destination point within the system. This depends on the star system in question, where the DropShip is trying to travel to, and how fast the ship accelerates during the course of its journey. Thanks to their powerful fusion engines and fuel reserves, DropShips can travel interplanetary distances by constanting accelerating towards their destination then, at the midway point, flipping around and using their engines to decelerate at the same rate. Assuming the distance between the start and end point are known, this can be calculated with T = 2√(D/A), where T equals time in hours, D is distance in kilometers from the starting point to midway point, and A is acceleration in kilometers per hour per hour. In most cases it would take several days or more for a DropShip to travel between a jump point and a planet in-system. During this time the DropShip will be burning fuel to maintain its constant acceleration and deceleration and any maneuvering it must undertake. The most common way of expressing this is by burn-day, which is the amount of fuel burned by accelerating at 1 G for one day.

When landing or lifting off from a planet, DropShips can do so vertically if sphereoid or horizontally if aerodyne; aerodynes may also land horizontally if the planet lacks an atmosphere. Verticle landings and takeoffs are more versatile as they require only as much space as to fit the DropShip, but are more difficult as a DropShip at low velocity is more unstable, burns more fuel and causes ground damage. Horizontal landings and takeoffs require a runway of at least 600 meters, though experience pilots can land on shorter stretches using their bottom thrusters. Once grounded, cargo is typically offloaded or loaded by DropShip crew members, usually wearing Exoskeletons to make the job go quicker, though some military units will use their 'Mechs to help speed up the process.

During combat operations, military DropShips that land to disembark their cargo will typically do so well away from the front lines as a means of preserving them, both for their incredible expense and for their ability to withdraw troops from a losing engagement. In instances where troops must be landed closer to an enemy force, or where a DropShip cannot land due to hazardous terrain, it may instead carry out a Combat Drop. In a combat drop, BattleMechs and Battle Armored troopers will exit the DropShip while at high altitude or in orbit. These units use their integral jump jets or disposable jet packs to control their descent and safely land, but even among well-trained forces a combat drop is a hazardous endeavor. For orbital combat drops, a special Drop Cocoon is used which protects the unit during atmospheric re-entry then falls away. A variation on this tactic is known as the Hover-Drop Maneuver.

Maintaining a DropShip is a constant endeavor, not least because many will be decades if not centuries old. Reducing wear and tear by avoiding atmospheric operations or active maneuvering can help, but nothing short of mothballing it will help preserve a DropShip that doesn't have a well-trained crew to look after it. Even for the smaller DropShips, the weekly maintenance needed to keep the vessel running can cost hundreds of C-Bills, nevermind repairing and replacing components or armor due to battle damage. Having a well-oiled crew is also important for a DropShip, though on most civilian vessles only the senior crew will sign on with a permanent contract, with the rest signing on for a limited time span. For security reasons, a military DropShip's crew will all be permanent members who have gone through extensive screening. Crew wages vary by vessel and era, but in the middle of the 31st century the average DropShip pilot earned 550 C-bills a month at minimum, while an engineer earned 450 C-bills.

Manufacturing
The smallest known spaceship to meet the DropShip criteria is arguably the 200-ton K-1 DropShuttle, although it is generally classified as a Small Craft instead. The largest DropShip ever constructed is the 100,000-ton Behemoth, which due to its sheer size is incapable of leaving gravity wells stronger than .6 g. The biggest DropShip that can actually leave atmosphere in standard gravity is the 52,000-ton Mammoth.

The most common military BattleMech transport classes are the Leopard (one Lance: 4 'Mechs, 2 Fighters), the Union (one Company: 12 'Mechs, 2 Fighters) and the much rarer Overlord (one Battalion: 36 'Mechs, 6 Fighters); the most common Aerospace Fighter carrier is the Leopard CV class (one Squadron: 6 Fighters).

Known DropShip classes include (sorted alphabetically):