Continuing the discussion from HD 33866 V: "Arcolais":
Well, let’s see.
Ground to Orbit
Vehicles built for orbital launch and re-entry are shuttles if they have wings and ram-rockets, or lighters if they don’t. Lighters use water as a cheap propellant with high thrust at given operating temperature, shuttles have an air-breathing mode.
• Assault shuttles carry marines from orbit to ground for landings in combat zones. They are armoured to withstand infantry weapons and armed for point defence. Small assault shuttles are built for a commando section (eight marines plus their robots) equipped for battle, and the large ones are made for a platoon (32 marines plus their robots).
The Imperial Navy has three tasks in orbital space.
• Cutters are for inspecting orbital facilities and spaceships between the Kármán line and synchronous orbit, where colonials are allowed to operate spacecraft for peaceful purposes. They are true spacecraft, not designed to land on planets, need weapons only to disable torpedoes and unarmoured ships out to a thousand kilometres or so, and don’t need to withstand heavy hits from true warships. But they have to carry boarding parties, including Imperial marines. They need modest thrust, medium drive endurance, and accommodations fit for sorties of several days.
• Monitors are for defending planets from incoming vessels or missiles from other planets or interstellar space, for “support of counter-terrorism operations” within the atmosphere, and (say it quietly) for destroying vessels and missiles launched from the surface. They are built around honking great lasers with enormous objective mirrors. They have some drive capacity for station-keeping, occasional changes of orbit, and random evasion during laser duels, but they are pretty nearly battle stations. I’m not sure whether they all use versatile 500-nm lasers, or whether in each system there are some with UVC lasers specialised for ranges out to about a million kilometres and some with visible-light lasers for dealing with targets in the atmosphere (and still useful in space out to lakhs of kilometres).
• Tenders are for delivering supplies to and rotating crews through monitors and other space stations.
• Corvettes are small armed interplanetary vessels for inspecting asteroid mining operations and sometimes intercepting vessels in transfer orbits. They need modest drive performance, considerable drive endurance, the same armour as a cutter but bigger UV lasers, plus maybe some torpedoes, and accommodations for a marines team or section for months. Depending on what asteroids and moons the locals are exploiting, they may need microgravity landing and takeoff ability, or to carry shuttles.
• Frigates are larger armed interplanetary vessels for inspecting asteroid settlements, deep-space habitats, and larger space facilities etc. They have same drive spec as corvettes, but tend to have better armour and bigger lasers, and more definitely carry torpedoes. A frigate carries accommodations for a platoon of marines. Depending on what asteroids and moons the locals are exploiting, they may need microgravity landing and takeoff ability, or to carry shuttles.
• Assault carriers are for delivering marines and other intervention forces from Sector HQ and other mustering points to the places that they are needed and accommodating and marshalling them in orbit pending landing. Assault carriers need interstellar engines, drive specs similar to a passenger liner, and light armour. They have to carry assault shuttles, and need short-range visible-light lasers to give ortillery support to their landings. The smallest probably carries a commando company with spare space for a platoon of the staff and support troops if needed. The largest practical size is probably a regimental assault carrier with accommodations for a commando regiment with its hospital, engineering, recovery, and HQ companies and their full battle rattle. Any larger intervention would use multiple carriers.
• Cruisers are armed interstellar vessels for reinforcing systems where trouble in orbit is not expected. They have interstellar engines, drive spec like a passenger liner, light armour, visible-light lasers intended for use through atmosphere, few torpedoes if any, and usually carry a commando platoon of marines and several small assault shuttles.
• Battlecruisers are armed interstellar vessels for reinforcing systems where trouble in orbit is feared. They have interstellar engines, drive spec like a passenger liner, significant armour, UV lasers intended for use at range through vacuum, and torpedoes, and usually carry a commando platoon of marines and several small assault shuttles.
• Dominators are armed interstellar vessels built to “retake” systems in which “pirates” have established control of planetary orbit. They have interstellar engines, minimal drives, and UV lasers with truly vast objectives, with which they can destroy satellites, battle stations, monitors, orbital facilities, etc. from astronomical ranges. Each dominator is escorted by decoys, pickets, sensor drones etc., which are usually not manned.