This guide divides all spacecraft into distinct classes, not by mass or carried weapons and tools, but by their function in the fleet. The differences are fluid and decided by comparison with other ships, both yours and those of other people. Designs by different authors may vary considerably and it is only understandable that some will work better than others. If a ship intended to be a battleship loses a firefight with a cruiser, it needs to be rethought and either have its armor and firepower increased or be reclassified and, for example equipped with more powerful drives to run away from its tormentor.

Small craft are one- or two-seated vessels built with specific purpose in mind, intended to dock within other vessels and carried aboard into combat. Small craft may or may not be prepared for atmospheric flight.
Scouts are small and nimble craft, whose purpose is discovering targets, identifying them and retreating before the enemy engages in combat. The game doesn’t provide much in terms of stealth and detection, but it can be assumed, that a proper scout will have excellent sensors or optics, low heat signature and camouflage, allowing it to detect enemy ships without being detected itself. If stealth is unfeasible, it will at least be furnished with a light frame and powerful engines, to allow it to evade pursuing enemy fighters.
Superiority fighters are intended to fight other small craft and achieve space superiority, which is a situation in which friendly craft can operate freely and the enemy cannot. It may be presumed that the main opponents with be other fighters. Constructing a good superiority fighter is one of the most difficult tasks a space engineer may approach and a true test of his abilities, requiring finding a compromise between maneuverability, armor and firepower.
Interceptors are fighters with a singular purpose of catching up with enemy bombers and destroying them before they are able to reach their target. They have a very high forward thrust, low armor and only forward-facing weapons; they operate under assumption that the enemy will not engage in dogfight.
Multirole fighters are prepared to perform two or more roles that are available to small craft, from dogfighting, through fire support, to bombing. Mind you, they may not necessarily be good at all of them. They need to be moderately fast, armed and armored. Merge blocks in strategic positions will enable them to customize the loadout for a specific mission.
Bombers are craft that carry heavy anti-capital ship weapons, be it inertial bombs, missiles or torpedoes. Since their targets are much bigger and meaner than themselves, piloting a bomber is one of the most dangerous tasks in a space fleet and mortality is high. However, if a bomber wing manages to ambush an enemy capital ship without escorts, the damage they can do far outweighs the cost of a few small craft that will inevitably be lost.
Gunships accompany other fighters and provide them with heavy firepower. They are not intended to engage in dogfighting, merely provide fire support.

Corvettes are the smallest class capable of operating independently and not expected to dock inside other ships. As such, they should be equipped with crew quarters (medical room is a minimum). Too fragile to participate in the battle, they are used in patrolling and law-enforcement. Their expected opponents are small craft and perhaps other corvettes. Some may be equipped with jump drives, but on most patrol craft this feature is unnecessary.

Frigates are ships intended to take specific roles in the battlespace. Anti-fighter frigates excel at destroying small craft, but are helpless when other, more heavily armed frigates come to chew on them. In turn, anti-capital ship frigates may find themselves outclassed by heavy gunboats, not being able to hit them with their slow-firing cannons. Frigate-class vessels are usually expected to operate in bigger groups to circumvent that weakness. Frigates and larger vessels will be equipped with jump drives.
The surface of anti-fighter or flak frigates (from German Flugabwehrkanone – anti-air cannon) is riddled with Gatling turrets, whose purpose is to blast any fighters or bombers that attack them or the ship they escort.
Assault frigates are frigates that hunt other frigates. The idea is that they should be armored enough to withstand the fire of flak frigates and maneuverable enough to dodge the fire of gravcannon frigates.
Gravcannon frigates (sometimes called incorrectly railgun frigates) are armed with a spinal-mounted gun that uses a battery of gravity generators to propel solid projectiles at enemy capital ships.
Minelayer frigates construct and deploy mines around key installations.

Capital ships (not “capitol”) are the backbone of the space fleet. Well armored and armed with diverse weapons, they have no glaring weak points and are capable of taking on any target. Their size allows them to carry some small craft in hangar bays.
Destroyers are hybrid vessels comparable with frigates, but having more balanced weaponry. They can be used protecting larger vessels from smaller craft, like bombers and frigates, but are well able to successfully ambush and damage heavier vessels. This versatility is the main difference between a destroyer and just another type of frigate. They are outgunned by cruisers and battleships, but their nimbleness allows them to escape and strike at a more favorable time.
Cruisers are jack-of-all-trades ships, combining high maneuverability and solid firepower. They can operate independently or in wolf packs, using teamwork to tire out and destroy much bigger prey, without taking any significant damage.
Battlecruisers are cruisers with firepower similar to that of battleships, albeit not as well protected. They can serve as a less costly support for proper battleships. Their higher maneuverability will allow them to outflank the enemy more easily, which is good, since they don’t feel well being at the front of enemy battleship guns. They can also lead cruiser groups – when the enemy is weakened by their escorts, the battlecruisers move in for the kill.
Battleships are the main workhorse of the navy. They’re at the front of every attack, sport multiple batteries of heavy artillery raining fire on the enemy and enough armor to survive being subjected to the same treatment. They don’t need to be very fast; in fact, if your battleship is able to catch up with cruisers, you probably need thicker armor.
Spacecraft carriers may be equipped with point-defense guns, but their main armament are the small craft they carry in their huge hangar bays. Since their hangar entrances are obvious weak points, putting carriers in the front of the fleet is probably not the best of ideas. They feel better in the center or back, where they can launch waves of bombers at exposed targets.

Shuttles carry personnel and materiel for short distances between two big ships or between the ship and the nearest station or outpost. They are not expected to participate in combat. Shuttles may or may not be prepared for atmospheric flight.
Cargo ships are used to resupply and reinforce the fleet, typically covering large distances in each cruise. They are sometimes heavily armed to discourage pirates from attacking them for their bountiful cargo.
Planetary landing ships are among the heaviest vessels able to land on a planet. When a beachhead has been captured by the marines, they land and unload reinforcements (infantry, combat vehicles, aircraft etc.) to secure the area and push the advance. Heavy load may prevent them from performing evading maneuvers and force to stay away from combat if possible.
Boarding ships have a specific purpose to dock within larger vessels and unload a team of commandoes to capture it or at least cause critical damage. They may be lightly armed, but weapon systems occupy precious space that could be taken by infantry.
Dropships are troop transports intended to deliver soldiers from orbit to the battle waged on the surface of the planet and, once they disembark, provide them close air support.
Drop pods are small capsules that descend upon the world and unload troops. Unlike dropships, they cannot fly away and need to be recovered after each mission. Some orbital drops may start by sending pods equipped with turrets to soften the enemy before the marines disembark.
Rescue ships are ships whose purpose is to reach stranded spacemen and give them medical treatment. They’re equipped with a medical bay connected to the oxygen system. May also serve as a mobile respawn point. Rescue ships should be able to operate in atmosphere.
Escape pods are small capsules designed to save the crew of a heavily damaged ship from sharing its fate. They are supposed to get them away from the enemy who downed their ship and support them long enough to be rescued by allied forces.

Combat often leaves a lot of wreckage. The purpose of recovery ships is to find wrecks and either tow them back to base, where they are repaired, or grind them down to salvage useful components.
Tugs are ships whose purpose is towing ships with damaged or unfinished drives, ships whose drives are too sensitive for precise movement or equipment that lacks drive systems (like cargo containers). They may double as recovery ships.
Auxiliary drives are either ships or just free thrusters with a merge block, whose purpose is to attach themselves to bigger ships and provide them more acceleration. Unlike tugs, these ships let themselves be controlled by the master vessel.

The main purpose of tenders is resupplying and repairing friendly vessels in or near the battlespace. They consist mostly of cargo space filled with spare parts, ammo, uranium and/or hydrogen fuel. Some may be assigned to a specific battlegroup; some may patrol randomly looking for someone in need of help.
All ships may be remote controlled (though it makes most sense in fighters), but the antenna range is limited, making it necessary for the drone pilots to be near the battle. A drone controller is a ship equipped with multiple stations for drone pilots, which stays in the antenna range of friendly drones and allows them to leave the close neighborhood of their base of operations.
Decoy ships are sturdy ships equipped with one or more decoys, perhaps with a welder to repair them. Their purpose is to draw the fire of enemy turrets and allow more expensive ships to avoid taking unnecessary damage. Finding madmen to pilot these ships may be difficult, so they will probably be remote controlled.
Any ship can serve as a flagship for the fleet admiral, but occasionally a dedicated command ship may be built specifically to fill that role. The most important features are a command and control center that can be used to coordinate fleet operations and a meeting room where the ship captains may discuss tactics.
Regular ships need a base of operations, where they can be repaired and resupplied. A mothership, however, is its own base of operations. It is equipped with mining equipment, refining and component manufacturing, as well as shipyards, which allow it to create a new fleet practically from scratch and transport it in hangars to where it is needed. They may be armed, but will probably rely on the accompanying fleet to protect it.

The “mother” in the name refers to giving birth to other ships.

Cargo ships or freighters are ships transporting goods across space. The word “freight” means payment for the goods, but is often used synonymously with “cargo”. Freighters are commercial cargo ships, as distinct from transport ships in military service. “Merchant ships” is another synonym.
Cargo container ships carry goods inside standard cargo containers connected to the conveyor system.
Tankers transport hydrogen fuel or oxygen inside pressurized tanks.
Haulers are ships that, rather than transporting cargo inside their holds, connect to external containers and push them or haul them behind. After achieving its destination, instead of unloading the goods by conveyor, they disconnect and leave the entire container there, waiting to be picked up by another ship.

Mining cars (also miners, resource collectors) are ships with drills that bore into asteroids and retrieve useful ores. The need somewhat strong thrusters to be able to move around with full cargo hold. Miners may vary considerably in size; from small ships with one drill to behemoths that hollow out the entire asteroid.
Gravity funnels use a shaped gravity field to prevent ores from floating into space. It may be a spherical gravity generator surrounded by collectors or just a normal gravgen that pushes rocks against the asteroid’s surface, allowing them to be picked by hand.
Mobile refineries have resource drop-off points that allow miners to dock and unload their cargo. The ores are directed to arc furnaces and refineries to be processed.

Yachts are small ships used for personal transport and recreation. They usually don’t move away from secure areas, but may be lightly armed in case of a pirate attack.
The purpose of liners is to comfortably transport a big number of people. If the destination is near, their entire furnishing may be just rows of seats; if it’s days of travel ahead or more, they may need passenger cabins.
When the length of the journey is intolerably long, a passenger ship may opt to put its passengers to cryogenic sleep. This may be a controversial decision, as even with cryo chambers you cannot freeze time and the passengers may not like having a good chunk of their lives stolen.
Generation ship is a theoretical concept. If the journey is expected to take centuries, the ship will in practice become the passengers’ new home. They will work aboard, marry, have children and die while in transit. The line between a passenger and crew blurs if not outright disappears, since everyone has a role to fill, if not tending to the ship, then to other people. The generation ship will probably be the size of a whole city and the necessity of being prepared for absolutely everything, with no hope for support or rescue, may force the ship to double as a mothership.

Builder ships are ships used in construction of other vessels and deconstruction of those which have been retired. They are equipped with modest cargo containers, welders and, optionally, grinders.
Exploration ships visit unknown regions of space and mark them down for future expansion. They must be prepared to operate away from base for an extended period of time, so they are frequently equipped with mining gear, refinery and an assembler. Solar panels and oxygen farms allow it to be independent from found ores. Explorers need to carry some weapons in case of hostile encounter.
Space is big. Like, really, really big. Law enforcement cannot be everywhere and there will always be individuals who choose to profit by preying on others. Pirate vessels are converted civilian ships or decommissioned military craft. They carry light weapons; enough to disable the victim without outright destroying it. They often operate in dens hidden in hollow asteroids and on the surface of small moons.