Vehicle

A vehicle is a type of machine used for transportation. Tetrian vehicles are classified as groundcraft, aircraft, spacecraft, or watercraft, based on their primary method of locomotion. Some vehicles blur the lines between these categories, however, such as aircraft and groundcraft that are capable of moving across the surface of water.

Groundcraft

 * See Main Article: Groundcraft

Groundcraft are vehicles that are built to travel over flat surfaces, usually on wheels or treads, although some make use of ground-effect thrusters to levitate just above the ground. Most use hydrogen as a fuel source and have a complicated power train that converts energy between electrical, chemical, and mechanical forms. Final drive may be electric or mechanical from a turbine or internal-combustion engine that burns hydrogen directly.

Aircraft

 * See Main Article: Aircraft

Aircraft are vehicles that move through air and are the most widely used category of vehicle on Tetro. They are generally powered by hydrogen turbine engines and stay aloft via a combination of aerodynamic lift and vertical thrust. While traveling at full speed, most aircraft can stay aloft from aerodynamic lift alone, and rely on vertical thrust only for takeoff, landing, and low-speed maneuvering. Various methods of thrust vectoring are used to transition between these modes of flight.

Spacecraft

 * See Main Article: Spacecraft

Spacecraft are vehicles designed for transportation in the vacuum of space. In addition to hydrogen turbines for atmospheric propulsion, they are usually equipped with a gravity drive for travel through vacuum. They often carry a supply of liquid oxygen so that the turbines can be used in vacuum.

Watercraft

 * See Main Article: Watercraft

Watercraft are an uncommon category of vehicle that is built primarily for movement across the surface of water. Many use hydrogen as a fuel source, with electric or mechanical final drive, although some are propelled directly by the wind or waves.

Scale
Due to the wide range of sizes among the intelligent species on Tetro, vehicles that are a perfect fit for one species may be too small or too large for others. To remedy this, Tetrians have developed a set of standardized scales used when building vehicles. These are described below, listed from smallest to largest.

Frelian Scale
Vehicles built to Frelian scale are able to perfectly accommodate Frelians while being spacious for Magnetates. Humans can sometimes fit, but find the space cramped.

Human Scale
Human scale is a comfortable fit for Humans and quite spacious for Frelians, but still impossibly small for Vithians, Q-Crawlers, and Pyronate Avians.

Standard Scale
This scale is generally the best compromise for craft carrying many different species. It is spacious for Humans and Avians, and enormous for Frelians and Magnetates. It is a tight fit for Vithians and Q-Crawlers, but still feasible.

Grand Scale
Grand scale is also commonly used as a compromise for many different species, and functions to make everyone on board feel small. It is spacious for all species but Hydroleans.

Mixed Scale
Mixed-scale vehicles are divided into multiple interior spaces built to different scales. This allows every species on board to have something just their size. Often scales are arranged from smallest to largest along the length of the craft. These vehicles may include multiple control decks for pilots of different species.

Specialties
Vehicles are also classified by the role they fulfill in Tetrian society. Most fall into one of the following categories.

Commuter
Commuter craft are only equipped for short journeys. They tend to be filled with seats that are close together to fit the maximum number of passengers into the available interior space.

Touring
For a trip lasting multiple days, touring vehicles are the preferred mode of transport. They provide private quarters for every passenger, a complete life-support system, copious storage space, and dining facilities.

Off-Road
Off-roaders are a specialization of groundcraft ideal for tackling rugged terrain far from civilization. Like touring craft, they include accomodations for long journeys. Additionally, they may be equipped with retractable spikes in the tires, grappling hooks, and winches.

Freighter
The interior of a freighter is mostly storage space for cargo. Many freighters are specifically built to accomodate standardized types of shipping containers.

Utility
Utility vehicles are built to perform a specific type of work, such as planting crops, assembling modular structures, or tunneling.

Military
Military vehicles are specialized for offensive or defensive use in combat. They are designed for maximum comfort and safety of the occupants.

Methods of Propulsion
Throughout Tetrian history, many different technologies have been applied to Vehicle propulsion. Many vehicles make use of multiple power sources, intended to be used in conjunction or with one as a backup for the other.

Manual Power
The earliest vehicles were built before any type of engine had been invented, and relied on the occupants to turn a crank or move levers to propel the vehicle. The first groundcraft and aircraft were manually powered and used geartrains to adjust speed or vary the amount of torque applied to the wheels or propellers.

Gas Turbojet
The turbojet engine was invented 528 million Earth-years ago. A turbojet consists of a cylindrical enclosure containing an intake fan, compressor, and turbine mounted to a central driveshaft. The blades of the intake fan have a relatively low pitch angle in order to pull in large volumes of air from in front of the engine at a low pressure. This air is fed into a compressor, a rotor with high-pitch blades that increases the pressure by forcing the air at high speed into a small combustion chamber, where it is mixed with natural gas and ignited. The burning gas passes through a turbine which turns the driveshaft powering the intake fan and compressor. It then flows out through an exhaust nozzle, providing forward thrust. Gas turbojets fell out of use quickly once hydrogen fuel was developed, due to hydrogen's higher energy density.

Electric Motor
Electric motors were invented 376 million Earth-years ago shortly after the discovery of electricity. They consist of a solid enclosure containing a driveshaft attached to several ferrite cores wrapped in coiled wire. The driveshaft is surrounded by magnets with alternating polarity that are affixed to the enclosure. Electrical contacts on the driveshaft are connected to the ends of the coiled wire. A set of complementary outer contacts are mounted to the enclosure, such that the flow of current through the coils is reversed repeatedly as the driveshaft rotates. When a voltage is applied to the outer contacts, magnetic fields are induced in the ferrite cores, with a polarity that attracts them toward the magnet ahead and repels them from the magnet behind, causing the driveshaft to rotate. As the driveshaft turns to the point where the magnetic forces are in equilibrium, it breaks the connection between one set of contacts and connects the next pair, reversing the direction of current through the coils and thus the polarity of the cores. Although more energy efficient propulsion methods have since been invented, electric motors have several advantages over chemical propulision: they do not produce exhaust that needs to be vented away, and the conductive wire that supplies their electricity has a higher rate of energy transfer per unit of cross-sectional area than all known methods of transferring chemical energy. As a result, they are still prevalent in many modern vehicles and devices.

Hydrogen Turbojet
As hydrogen became the preferred fuel source 375 million Earth-years ago, the design of the gas turbojet was adapted to combust hydrogen. The basic principles remained the same, but the blade pitches were adjusted to handle hydrogen's significantly lower density.

Metallic Hydrogen Turbojet
The creation of metallic hydrogen 203 million Earth-years ago necessitated a new form of turbojet engine that could harness all of the stored energy within hydrogen pellets. These new engines added a component called the vaporizer. To produce mechanical energy, the pellets are heated in the vaporizer, causing the atoms on the surface to recombine into molecular hydrogen. The energy of recombination pressurizes the released gas, which is then piped through hoses to a turbine where the flow of gas over the blades causes them to turn. In many vehicles the hydrogen is ignited as it enters the turbine to provide slightly more energy. Rotation of the turbine shaft is harnessed by converting it into electricity with a generator, or simply used to move other mechanical parts. The flow of exhaust out of the turbine is used in some aircraft and spacecraft to provide propulsion for the vehicle.

Vehicle Manufacturing

 * See Main Article: Vehicle manufacturing industry

Most vehicles are manufactured by small companies that design and build each vehicle to an individual buyer's specifications. As a result, almost all vehicles on Tetro are unique. Engines and other parts are often shared by multiple vehicles from the same company, but there is an expectation among customers that the exterior and interior styling will be individualized to their vehicle. The idea of mass-producing a single design was not explored until Earth-year 1998, when Verockla Vehicular Industries introduced the V line of groundcraft and aircraft.