Military spacecraft types

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).

Planetary Orbit

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.

Interplanetary space

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.

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I realise that this is intended as background detail rather than as the focus of a campaign. That said, how often are these forces called on to do their thing? Part of the justification for putting forces in orbit of friendly world A is that unfriendly world B might attack it; but B is also under Imperial control, so wouldn’t that problem usually be solved in B’s orbital space?

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I wonder whether important planets also need super-monitors, armed like dominators but lacking the interstellar drives, in quasi-satellite orbits.

Oh, absolutely. That’s why I doubt that monitors would find UV lasers as useful as 500-nm lasers: the first and most effective layer of defence for any planet is in the atmosphere of the planet that would attack it. The Imperial Navy is telling the truth albeit not being very frank when it says that its monitors are built and operated to defend colonies from each other, as well as offering a missile defence to Balkanised planets and being used to support anti-terrorism operations on planets.

Now, supposing that some pirate uprising overpowered the Imperial defences of a planet and launched raids against another planet, or that terrorists evaded inspections in some outer system and assembled an illicit spaceship, or hijacked some civilian interplanetary operation, and attacked a planet. Then the monitors would fire outwards, and would wish that they had UV lasers. But far the more common thing is for them to provide orbital fire support for marines operations including counterterrorism ops but also landings in prosecution of an intervention act, strategical orbital laser bombardment ditto, or evaporating orbital spaceships that deviate from their approved flight plans.

Likewise, the super-monitors in quasi-orbits around the Suite worlds, SHQ worlds, and worlds with naval dockyards in orbit — if they exist — would be ostensibly there to defend those strategic targets against attacks in force by enemies with dominators (such as aliens, maybe), but in fact to say to potential rebels “Don’t get twitchy about it, but we have in effect four dominators in your system and are not going to do the Formation Wars again. Stay frosty.”

What problem does the super-monitor solve that a bunch of normal monitors doesn’t solve better? I mean, do they have significantly thicker armour, or more capable weapons? (Bigger laser mirrors, I guess.) Clearly they are more intimidating, which is not nothing.

I.e. is the space warfare assumption WWI “only a battleship gun can damage a battleship” or Cold War “a tiny ship can have a one-shot punch that will smash a big one”, or something else?

I do understand the realpolitik argument; I’m just wondering how much of the Navy’s time is spent drilling compared with actual fighting, giving rise to the potential for bureaucratic drift and officers being promoted for their report-writing more than their ship-fighting skills. (And thus the quality of officers you have in place when things do kick off.)

I’m not sure about the super-monitors: I just thought of them then. I think they are out of range of ground lasers and surprise attacks by swarms of missiles, such as might be launched either from the ground or from colonies’ orbital facilities and reach or overwhelm monitors in planetary orbit. But I haven’t inked up the backs of any envelopes yet.

(I am pondering super-monitors that consist of a 100,000-ton SM+12 upper stage for an SM+13 ship that otherwise consists entirely of hardened rock armour and just enough drives to keep its arse pointed at the planet.)

I mean, do they have significantly thicker armour, or more capable weapons? (Bigger laser mirrors, I guess.) Clearly they are more intimidating, which is not nothing.

Super-monitors are larger, and have thicker armour, more powerful lasers that will burn through more defences, and wider objectives that give them longer range, which lets them light things up without taking effective return fire and gives them more defensive depth against torpedoes. Their defining characteristic is being in quasi-satellite orbits and therefore at a safer distance. They need the wide objective to be effective from way our there. Size follows.

What super-monitors can do that a bunch of simple monitors can’t is to fight at longer range.

I.e. is the space warfare assumption WWI “only a battleship gun can damage a battleship” or Cold War “a tiny ship can have a one-shot punch that will smash a big one”, or something else?

I’m running mostly on “the one with the wider objective mirrors is the one who survives the fight”. It looks as though no defences can be tough enough to let any ship close range with a ship with a much-longer-range spinal or primary laser. Fighting in low orbit is a bag of wet cats, but you can stand off in quasi orbit and scrub low orbit clean without ever getting in danger from fire from the ground.

I do understand the realpolitik argument; I’m just wondering how much of the Navy’s time is spent drilling compared with actual fighting, giving rise to the potential for bureaucratic drift and officers being promoted for their report-writing more than their ship-fighting skills. (And thus the quality of officers you have in place when things do kick off.)

There is a lot in what you say. It is further complicated by the fact that the ship’s brains are genius-savant orbital tacticians, and the human officers are there primarily to make moral decisions. Realistic training, such as perhaps sparring against rival officers in a simulator, might keep ship-fighting skills sharp. But no drill or simulation with test whether naval officers have the nerve to torpedo a liner full of civilians that has been hijacked by terrorists, without orders.

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Once upon a time in, a land far, far away, the back of an envelope told me that the Empire carries out about 21 interventions (i.e. invasions of planets contrary to the will of the colony’s government) per year. Not all of those would involve space combat, but approximately all would involve orbital laser bombardment and landings of assault shuttles.

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Standard GURPS Spaceships rules don’t let weapons on an upper stage (or a front section, in general) fire at targets “behind” the ship. Though you could have five systems of armour and one system of spinal-mount weapon in the aft section of the ship.

So what the cunning insurgent wants to do is come up with a plan that looks like a standard thing that the Navy will respond to in the standard way, then make the real plan something that works round that. (“You ask me for a miracle, Theo, I give you the Imperial Marines.”)

Which immediately says that the way to attack a large warship is via another ship which has an entirely legitimate need to approach the target, but unknown to everyone, also has an powerful, but non-catalytic, thermonuclear bomb on board.

I’d expect that in any system where the locals could build an H-bomb there are always several Imperial ships around, and that there’s a traffic control convention that only one of them can be approached by a local vessel at a time.

The Imperial Navy will also have vessels with catalytic thermonuclear weapons, but nobody likes to talk about that.

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I was thinking of separating the upper stage in the event of combat. The asteroid shield is in case of surprise attacks by a beam weapon,

The first line of defence is Naval Intelligence AIs monitoring publicly-available information, and Naval Intelligence officers on every planet employing secret agents and offering rewards to dobbers

  1. tracking the personnel and resources that would be needed to build a WMD, orbital launch vehicle, or beam weapon capable of damaging a ship in orbit, in hope of detecting any clandestine weapons program
  2. scanning for the formation of any intent to use such a thing.

The problem is that at high development levels the material that such terrorists would need and the technical ability to adapt it to purpose are widely disseminated and not much different from regular civilian capabilities. Which means that some colonial governments have secret arsenals of anti-spacecraft weapons and that there is a regular trickle of attempts by crackpot terrorists to nuke or flash something, including Imperial vessels in orbit.

Yes, and I’d expect that Imperial warships flashlamp anything that deviates from its flightplan in a way that is at all threatening to anything with people on it, and will do so without warning if it is pressed for time. That might include aircraft, I suppose. 9/11-type threats on a world where you can’t be sure that terrorists don’t have an H-bomb are pretty desperate circumstances.

Getting back to the counter-force threat: as the population and DL of a colony rise low orbit becomes heavily exploited, and improvised weapons get larger radiuses of threat. That makes it get ever harder to keep everything at an innocuous distance from a monitor in low orbit. Besides, the threat from the ground becomes more plausible. Where the DL is 4.5 or lower (so that a nuclear program would be highly conspicuous) and the colony doesn’t have its own space program, small unarmoured monitors in low orbit might be practical, but where the colony is using low orbit intensely and building spacecraft and fusion generators the practical necessity might be to put the monitors in wider orbits and give them better point defence and lasers with larger objective mirrors. You end up at a place like Tau Ceti that has a tower facility, orbital habitats, orbital industry etc. where civilian firms manufacture the very drives and weapons that the Navy instals in its warcraft, where only a quasi-satellite orbit is far enough out to be safe and out of the way.

“We can neither confirm nor deny the obvious point that there could be catalytic thermonuclear warheads deployed in some Imperial warships, downport facilities, and residences. The existence of such deployments, or even of the warheads, would shake the dedication of some loyal Imperial servants, so it would be classified as NAKED, and even the existence of NAKED classification would be classified NAKED, if we had a NAKED classification, which I can neither confirm nor deny. Don’t fiddle with anything marked “don’t fiddle with this” or you will be shot without warning, and don’t ask questions about the locations and movements of Eichberger drive components, because that’s all classified and no-one is allowed to talk about it. Next question, please.”

And what the Imperial Marines want is to shoot the cunning insurgent twice in the back of the head while he or she is buying cheese. Certain subtle indications suggest that the Empire is packing about 12,000 clandestine operators whose existence is secret even from the great bulk of the Imperial military.

Sometimes the cat wins. Sometimes the mouse wins.

You know, it’s awfully refreshing to deal with a worldbuilder whose default state isn’t “side X always wins”. Uncertainties make for interest.

It’s very easy to tell a 747 from an ASAT first stage in plenty of time. Rather harder if it’s a Heinleinian sub-orbital.

Right. But ASATs aren’t the only things that the Empire wants to shoot down. It has a bee in its bonnet about mass murder, and it desperately wants to be able to shoot down hijacked 747s before some fanatic flies them into an occupied building.

Ah OK. I’d got the impression that as long as it didn’t have any effects outside atmosphere they didn’t really care much. (On an official policy level, I mean.)

No. The demarcation of Imperial jurisdiction at the Kármán line is a keystone of the Treaty of Luna (i.e. the constitution of the Empire) but was very much forced on the Eichberger Foundation by its enemies. The League of Repressive Autocracies may be a mob of scoundrels, but they aren’t paranoid. The Empire would indeed depose the lot of them in a week if it were allowed. And it spends more money and employs more people in humanitarian assistance than in everything else put together. The Empire’s obsession is with mass death, not with space. Space is what it is allowed to use as a means to its end.

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They do. They also leave room for the possibility that there be something that PCs have to do and cannot leave to the God-mode Sue.

I designed Flat Black partly as an abreaction from Tonio Loewald’s ForeScene, in which the Federation was a moral exemplar of the designer/GM’s ideals, infallible, and had people involved in even quite small events (while PCs in his adventures tended to be involved in rather large ones). As a player, I got sick of being patronised by recurring-NPC members of DJCW (the unofficial assassination-and-sabotage branch of the Department of Justice). Having found Tonio’s Federation boring and frustrating, I very deliberately made the Empire in Flat Black so feeble that it had to ignore many tasks that were still important enough to excite PCs, so monomaniacal that it would ignore many issues that would excite PCs, and fallible enough that PCs might get to cover for its failings.

I’m not happy with (nor even really clear about) the ranges for laser weapons given in GURPS Spaceships, so I have been grubbying up the backs of some envelopes. I took the diameter of a spherical ship as half the listed length of an unstreamlined hull, and the maximum possible diameter of the objective of a laser weapon as the diameter of a sphere with volume equal to the volume of the system. And I took it that the effective range of a laser weapon was the range at which the beam intensity on the target was one thousand times the beam intensity at the objective. The results are as follows:

Effective range of Major Battery lasers

SM hull
(1.5 µm)
(500 nm)
(250 nm)
far UV
(160 nm)
extreme UV
(65 nm)
(yards) (metres) (km) (km) (km) (km) (km)
+5 15 2.5 110 331 661 1 030 2 540
+6 20 3.4 196 588 1 180 1 840 4 520
+7 30 5.1 441 1 320 2 640 4 130 10 200
+8 50 8.4 1 220 3 670 7 350 11 500 28 300
+9 70 12 2 400 7 200 14 400 22 500 55 400
+10 100 17 4 900 14 700 29 400 45 900 113 000
+11 150 25 11 000 33 100 66 100 103 000 254 000
+12 200 34 19 600 58 800 118 000 184 000 452 000
+13 300 51 44 100 132 000 264 000 413 000 1 020 000
+14 500 84 122 000 367 000 735 000 1 150 000 2 830 000
+15 700 118 240 000 720 000 1 440 000 2 250 000 5 540 000

Note well that these are the effective ranges of major battery lasers. The range of a spinal mount will be that of a system one SM larger, that of a medium battery, one smaller, of a secondary, two smaller, of a tertiary, three smaller.

The wavelengths that we are most interested in are 500 nm (cyan) for monitors and cruisers (which are meant to engage targets on planets’ surfaces) and 160 nm (far UV being what GURPS Spaceships describes for the TL10 “UV laser”, and seeming reasonable for an FEL weapon).

  • Cutters engage targets in orbit, and need weapon ranges of at least about 1 000 kilometres, so an SM+5 UV laser has enough intrinsic range. Accommodations for the crew and marines will dictate that the ship be larger than that, and required damage output might dictate a larger weapon. SM+7 might be a good size for a cutter.

  • Monitors use cyan lasers for engaging through atmosphere, and need an effective range comparable with the diameter of a planet for a small squadron to give near-continuous cover. But they don’t need accommodations for marines, so a spinal mount is plausible. That suggests that they might be built around an SM+9 spinal improved laser.

  • Corvettes are probably good with an SM+7 spinal UV laser or SM+8 UV laser major battery, depending on how much space they need for shuttle bays and marines quarters.

  • Frigates look like about SM+8 with a UV laser major battery, a missile launcher, a tertiary battery of rapid-fire UV lasers for missile defence, etc.

  • Cruisers aren’t meant to deal with targets in orbit. They need a weapon like a monitor’s, and I’m not clear how things pan out on the balance between not needing armour on one hand, but needing shuttle bays and marines’ quarters on the other. They are either SM+9 with a spinal improved laser or SM+10 with a major improved laser battery.

  • Battlecruisers look like being about SM+10, with two major batteries (improved laser for dealing with trouble on the ground, UV laser for targets in space to about 46 000 km).

  • Quasi-orbital monitors are at least SM+10 with a spinal battery UV laser and probably bigger. To be actual quasi-satellites and not just distant slow satellites they would have to be outside the planet’s Hill sphere, and so would need either weapons with an effective range of over about 1.5 million kilometres or to close in to fire. Extreme-UV wavelengths or soft-xray lasers might be needed.

  • Dominators are maybe SM+12 with a spinal battery, and they might have something like bleeding-edge extreme-UV lasers.

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