Tactical Doctrine for Near-Future Orbital Combat

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I analyse the tactical situation of combat in relatively low planetary orbit, with near-future techlevel, and attempt to determine plausible tactical doctrine, weapon & vehicle design criteria, and strategic implications.

Surprisingly, a number of naval concepts (most notably that of "crossing the T") re-appear, albeit in modified form, suggesting that the popular "Space Is An Ocean" trope is not as far-fetched as generally believed by hard-SF writers. Indeed, some of the conclusions raise the prospect of a Battle of Space Jutland, a perennial favourite of lazy space-operas.

This is not an absolute claim being staked of "how space combat must necessarily play out"; the results are not nearly resilient enough for that. It is merely, shall we say, an account (hopefully coherent and consistent) of one possible future.

Background Assumptions

I assume that spacecraft still use reaction drives with specific impulses not much more than chemical rockets. A thousand-second Isp might be achievable with nuclear propulsion, but torchships are out of the question — total delta-V expenditure is still a major limiting constraint.

An anti-assumption I make is that not all forces will have access to sensors with global coverage, and perhaps none will; I consider this justified on the grounds that sensor satellites can be tracked in peacetime and neutralised at the outbreak of war by a sufficiently sophisticated ASAT system, while warships positioned for overwatch will, by foregoing the defensive cover of low orbit, be highly vulnerable even to adversaries who lack global sensor coverage. However, this assumption is not essential for my basic conclusions; it merely informs some of the more detailed projections.

Finally, I assume that warships will have a high degree of compartmentalisation and redundancy, meaning that (besides a few vital spots like the main engine and the crew compartment) a weapon hit does not immediately produce a kill. This is justified in the following section.


Most of a spaceship's volume will probably be things like remass, reactors, radiators, and maybe trusses to hold NTRs at arm's length. Assuming the ship design is well compartmentalised, hits to these regions won't be killer, merely causing some loss of capability (e.g. causing one tankfull of remass to vent, losing the delta-V it would have supplied; or slagging a reactor, reducing the ship's available power draw).

Criticality-1 items like the bridge will probably be wrapped in remass tanks, but that's not so easy to do with the engine; besides, a sufficiently energetic weapon strike could penetrate through to the bridge anyway.

The upshot is that the 'kill cross-section' of a ship will be rather small; any shot that doesn't hit one of a few pretty narrow target areas will merely do some attritional damage, and without the targeting ability to focus the attrition on one system (e.g. the port-side redundant truss array), turning this into a kill will take a lot of hits.

What this ultimately means is that dodging incoming projectile weapons will be sufficiently practical to be an important tactic: you may not be able to get your whole ship out of the way of the incoming missiles, but you can drastically reduce the probability of them hitting your vitals.

Evasive Action

If your opponent doesn't have LOS, he can't use lasers, particle-beam weapons &c to attack you; he must rely on projectile weapons. If these are guided, the delta-V required to deflect them onto the target scales roughly with the product of the target displacement and the closing velocity, while the target displacement scales with the acceleration of the target and the square of the flight time; thus the delta-V requirement scales as the reciprocal of the closing velocity but the square of the range. This does assume the projectile is autonomously homing, and can't "see" the target until it gets close enough (e.g. comes over the horizon); if it is guided in with help from a sensor platform / overwatch, the situation gets somewhat better for the attacker. But relying on guidance commands opens up a vulnerability to jamming, spoofing &c which is probably more severe than the corresponding possibility of fooling the homing head.

My conclusion, then, is that, if an incoming missile can be detected at launch time, the target can jink sufficiently to prevent a killer hit, though probably not an attritional 'ding'. (Without the detection ability, you have to random-walk, aka 'drunk', which is prohibitively expensive in delta-V.)

However, this all depends on being able to manoeuvre transversely to the approach direction of the missile. A spacecraft can typically only accelerate (significantly) in the direction it's pointing, while weapons don't need ranging aim (whether a laser, particle beam or missile, it'll just keep going until it hits something. For low orbit and massive projectiles, inertia is circular (pace Galileo!) but the principle still applies). These combine to make dodging enfilade fire impossible: accelerating towards the inbound missile won't make it miss you. So you will always want to ensure you are broadside-on to the enemy as long as he can see you and shoot you (these may not be the same due to aforementioned circular (ok, elliptical, pace Kepler) inertia; 'indirect fire' shooting over the horizon is a possibility, and changes the direction the munition will approach you, so 'broadside' does not mean the enemy is at relative bearing 090).

However, you will probably sometimes need to accelerate in other directions for tactical manoeuvres (orbit changes are usually best done with pro/retrograde burns), which means opening yourself up to potential attack.

Given all this, "crossing the T" is a natural goal in any engagement, as it allows you to dodge while denying your opponent the same. A further result of this is that weapons will be designed to fire broadside, unless there is some reason (e.g. spinal mount) to do otherwise.


Ships will typically be long and thin, because that makes coping with acceleration loads easier (as Atomic Rockets puts it, spaceships will be built like skyscrapers), and this in turn means they can roll much more quickly than they can yaw. So, they will have 'broadside'-like weapon mounts, with a reasonable field of fire in the fore/aft sense but probably incapable of shooting close to prograde or retrograde (you weren't pointing straight at the enemy anyway, remember...) and relying on rolling the whole ship to aim them in the other ('azimuthal'?) sense.

Consequently, laying out your weapons like a naval battleship (turrets along the length of the vessel, pivoting around an axis perpendicular to the vessel) makes a lot of sense. One difference is that you will probably want the guns on the long axis rather than above or below it, so that any recoil does not produce a roll moment. It will of course still tend to produce a yaw moment unless the armament is suitably balanced fore-and-aft.

Missiles do not, of course, produce recoil, but as they require remass, they are far less mass-efficient than (for instance) railguns, coilguns, or (closed barrel) ram accelerators, which would probably be preferred for that reason.

Battle Line

Given the foregoing, how do you arrange your order of battle? You want all your battleships to be able to target the enemy, without blocking each others' field of fire, but also without getting in the way of dodging (if you have a classic naval 'line astern' formation, your acceleration is constrained by the ship in front of you, and if the enemy aims at the front of the line, he'll probably hit something).

Fortunately, this is space, so you have a third dimension to play with. Your battle line consists of ships side-by-side, forming a plane whose normal points at the enemy; each ship can move up (or down) the plane to dodge.

How best to orient this plane? (I assume that the missile approach direction — the 'side' of the broadside — is roughly pro- or retrograde.) If 'up' is (orbital) normal, then your ships are stacked radially and thus have different orbital periods, disrupting your neat formation and basically ruining everything. If 'up' is radial, however, your ships are stacked by inclination; they will thus drift along the battle line sinusoidally, meaning they have to keep (radial) separation from ships they're crossing, but that's not too difficult to arrange (bellringing… in… space!). Whereas dodging (making radial burns) just changes the eccentricity of the orbit, not (to first order) its period, meaning that your "battle plane" will 'ripple' but not completely disintegrate.


To dodge a projectile, you must first see it coming. (Drunking / Random-walking is expensive in delta-V!) If you see it launch (or make course-corrections), you can pick it up by thermal, but once it's ballistic, that gets a lot harder. (It's not impossible, because it probably still has some electronics on board generating heat, and it may be slamming into micrometeoroids pretty fast, but a ballistic, unmanned, unguided vehicle is perhaps the only exception to There Ain't No Stealth In Space.)

So if you have eyes on your enemy but not vice-versa (which of course requires that there's a planetary horizon in the way to block LOS), you can indirect-fire kinetic-kill vehicles that your enemy can't dodge.

In other words, if you know where your opponent is, hide behind a hill and throw rocks at him!

There are of course several different ways you might locate your opponent, but (assuming he's not doing anything daft like broadcasting his location with active radar pings) they all boil down to some kind of artillery spotter.


The easy answer to spotting is sensor satellites. But these have predictable orbits and are thus vulnerable to enemy action; popping your enemy's overwatch birds from your warship is as easy as shooting down observation balloons from an S.E.5a. (Aha! Not all my analogies are naval!)

Instead, you need something that can manoeuvre and jink — which to me makes it a warship. (It doesn't have to be manned, but then technically nor do any of these warships I'm talking about — although a crew might be useful for damage control. I won't examine this question further.)

A warship specialised for reconnaissance will be highly manoeuvrable, and probably carry no weapons (except possibly point-defence weapons, for which see below). This kind of artillery-spotting scoutship (if you want a land-army analogy for a change, it's somewhat like late cavalry) will probably be parasitical on the capital ship or battle group it supports, rather than carrying remass and supplies for long-term independent operation.

The reaction to this is that you will also be looking for ways to neutralise the enemy's scoutships. As they will probably be cheap and numerous, it's not really worth the capital ship's time swatting them, at least not when those guns could be lobbing shots at enemy capital ships. So now you have a use for Destroyers: smaller, nimbler warships that escort the capital ship and pop the enemy scoutships with their comparatively small guns.

Point Defences

Sometimes, you fail to dodge a projectile, and it's headed straight for your warship's squishy gonads. What do you do now? You can't meaningfully deflect it, the closing speed is way too high for that. How do you destroy it?

Lasers are a popular answer: the short range keeps the beam dispersion small. However, a laser can't do much about a kinetic-kill vehicle, and even warhead deliveries are difficult to pop quickly with lasers that aren't seriously high-powered, at which point aiming and cooling both become chrome-plated pains in the posterior. My opinion is that laser point defences would be impractical.

Railguns and coilguns are a much better choice. Not only will they do much better at taking out an incoming warhead, they are also an effective defence against kinetic-kill vehicles, working on the same principle as micrometeoroid shields: give the projectile something to hit, converting a concentrated slug into an expanding cloud of debris which can then be blocked by comparatively light armour. The answer to a KKV is… another KKV.

Ship Metrics

What are the figures of merit for a space warship design? Knowing this will help to project what classes of warship might exist.

Firepower is an obvious one: can you throw enough ordnance to either take out an opponent through cumulative damage, or overwhelm the point defences of its vital areas? The figure of merit here is something like number of projectiles per unit time multiplied by damage done or probability of kill for each one that gets through; clearly the latter factor depends on the opponent.

On the receiving end, vulnerability matters: how big is your 'kill cross-section', how effective are your point defences, how many hits can you take to remass tanks before you're crippled?

Acceleration determines how effectively you can dodge; how much you need depends on both sides' recon — yours for detecting launches, the enemy's for guiding missiles.

The total amount of delta-V you have available is also important; all through a fight you're using it up to dodge, and if you run out you're a sitting duck. It's also important for any beyond-low-orbit excursions you might make (e.g. sending an expeditionary force to fight a battle around Mars), but those are out of scope for this article.

Easily overlooked is atmosphere capability: if your ship was assembled in orbit and can never land, repairs are likely to get expensive. Meanwhile, a heat-resistant, aerodynamic scoutship can dip into the upper atmosphere for a quick (and propellant-efficient) inclination change. The usefulness of such a capability has yet to be determined. (But it'll get built anyway, because USAF gonna USAF.)

Ship Classes

An entire category of ships will get ignored here, namely "long-range" ships that can operate independently on expeditionary missions. So there will be no "Cruiser" class in this article. That's not to say that there won't be cruisers in this possible-future, just that the conclusions of this article won't necessarily apply to them as they may have to fight in free space rather than low planetary orbits. (Unless, that is, intercepting enemy warships in deep space is impractical, in which case battles would still be fought around planets even though some of the ships were built for interplanetary travel.)

That leaves "main battle fleet" ships. The 'queen of the orbits' will be the battleship equivalent (aka man-o-war or ship-of-the-line); in this setting there is no reason for it to be displaced by a carrier-like ship because there is no analogue of air power. There are no submarines either (No Stealth In Space); the only thing that can kill a Battlespaceship is another Battlespaceship. This may lead to an arms race like the 1900s naval expansion. ("My gun is bigger than your gun.")

As previously mentioned, spotting will necessitate scoutships, which will in turn lead to destroyers to interdict the enemy's scoutships. To run interference on the destroyers, there may be a use for a (corvette? E-boat?) class of fast, armed ship, analogous to a lancer or shock cavalry: make a high-relative-speed pass on the enemy formation, jumble the destroyers, and get out of range before the battleships can get a kill shot on you.

There may be a need for tankers and/or tenders; although they would seem more relevant to an expeditionary force, non-atmosphere-capable capital ships would surely need repair, refuel and resupply between engagements.


Written by Edward Cree on 15th September 2016.

This is the first draft.

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