A spacecraft is a vessel, manned or unmanned, which is designed to function in the vacuum of space. Spacecraft can be suborbital, orbital, interplanetary, or interstellar, depending on their design, main function, and mission objectives. The technological clade spacecraft can be broken down into two main subclades based on propulsion systems: subluminal and superluminal.
Subluminal spacecraft can only reach velocities arbitrarily less than the speed of light c. They generally operate within a planetary system, where sub-c velocities can be used within reasonable timeframes; however, in the earlier stages of a civilization's spacefaring endeavors they may equip exploratory interstellar spacecraft with high-yield subluminal propulsion. Common forms of subluminal propulsion include: chemical reaction rocketry, nuclear reaction rocketry, antimatter reaction rocketry, electrically-induced directed ion discharge, solar wind pressure systems, electromagnetic imbalanced pressure drives, quantum vacuum drives, and pseudogravity systems. Warp drives, by their nature, also have the ability to move objects at speeds less than c, though this is a rather inefficient use of warp technology.
Superluminal spacecraft are characterized by their ability to cross arbitrary distances in less time than an unobstructed photon. The common umbrella term for such methods of transit is FTL, an acronym that stands for Faster Than Light. This term can be used as a noun (as in referring to a faster-than-light drive) or adjective (as in referring to the state of moving faster than the speed of light; synonymous with the adjective form of superluminal). In fact, most methods of FTL do not actually supersede the speed of light; they merely circumvent its limitations. There are at least four major forms of superluminal travel.
Spacetime Distortion Amplified Acceleration
Generally called warping or hyperspace, SDAA is by far the most common method of superluminal transportation in the galaxy. As the name suggests, warp drives utilize negative mass and antimatter technologies that distort spacetime in a way that amplifies motion through realspace. Vessels using warp drives are enclosed in a "bubble" of distorted spacetime that effectively multiplies their apparent velocity due to the "bunching up" of spacetime around them.
The physical stipulation to warp travel, however, is that it increases velocity in any direction, so operators must ensure their velocity is absolutely aligned to their desired vector before engaging the warp device. This factor and its associated process are loosely termed "hyperspace relative velocity"; once HRV is within acceptable parameters it is safe to enter hyperspeed.
Artificial Transspatial Portal Induction
Often simply termed portaling or wormholing, ATPI is a rather basic and –by modern standards– cumbersome mode of FTL transit that involves setting up a three-dimensional hole in spacetime (i.e. a wormhole or portal) to pass through from one point in spacetime to another point. This can be done either by provoking the collapse of an entangled singularity or the penetration of the u-fabric by a graviton entanglement beam. Portals condense the space between points to hyperspatial pathways linked by open singularities, allowing mass and energy to pass through to the other side in a very short amount of time (in many cases, almost instantaneously).
Additionally, subatomic-sized wormholes (which are significantly easier to create and maintain) play a key role in the FTL communications network called the Etherlink. In essence, they allow photons to pass between distant points to facilitate entanglement decryption on either side, thus transmitting information much faster than light ordinarily travels.
It should be noted that engaging a warp drive while traversing a portal shortens the distance traveled in said portal by a factor of the warp velocity. This is often labeled as a separate FTL method, commonly called "short-bridging" or "crunching". This is not recommended, as it can and in many cases does lead to the creation of black holes and/or isolated pocket universes.
Spacetime Ripple Transversal
Also known colloquially as "ripple jumping" or i-travel, SRT utilizes the natural ripples in spacetime to traverse vast distances in less time than ordinarily required by the mandates of relativity. In essence, a craft using SRT "hops" through nonreal-space (or imaginary (i) space; different from nullspace) directly from the crest of one ripple to the crest of the next, rather than traveling through realspace down into the trough and up the next ripple. Functionally, the process is similar to portaling, though it is based on different mathematics and does not inherently require the use of an exterior gateway.
However, while portals connect any two points in space, i-travel only allows the user to jump between specific points. Additionally, since the distance is only shortened to a limited degree, SRT is the most inefficient of FTL travel methods.
Aether Gateway Transversal
AEGT, more commonly called a nullspace circuit, is an incredibly advanced and highly dangerous method of superluminal travel that involves exiting realspace and traveling through the physics-less Aether (nullspace) "between" universes to reenter real-space at a destination. AEGT is dangerous not only because of the infrequent unpredictability of reentry location, but also due to the devastating effects of nullspace exposure to sophont minds.